Hybrid Electric VehiclesAn alternative for the Swedish market?

Karl-Erik EgebäckSören Bucksch

KFB-Report 2000:53

TITEL/TITLEHybrid Electric Vehicle. An alternative for theSwedish market?FÖRFATTARE/AUTHORKarl-Erik Egebäck, Autoemission K-E EConsultant, Sören Bucksch, KFBSERIE/SERIESKFB-Report 2000:53

ISBN 91-89511-08-5ISSN 1104-2621PUBLICERINGSDATUM/DATE PUBLISHEDOctober, 2000UTGIVARE/PUBLISHERKFB – Swedish Transport andCommunications Research Board, StockholmKFBs DNR 2000-388

SUMMARY

See page 8

KFB Reports are sold through Fritzes’, S-106 47 Stockholm.Other KFB publications are ordered directly from KFB

Hybrid Electric VehiclesAn alternative for the Swedish market?

Karl-Erik EgebäckSören Bucksch

This report was originally written in Swedishand it has now been updated and translated into English

during July – September year 2000by

Karl-Erik Egebäckand

Liz Egebäck Foxbrook

KFB Report 2000:53

CONTENTSTABLES.............................................................................................................................................................. 5FIGURES ............................................................................................................................................................ 6

1 SUMMARY.................................................................................................................................................... 8

2 INTRODUCTION ....................................................................................................................................... 11

3 THE COMPLEXITY OF THE DEVELOPMENT OF FUELS AND VEHICLES.............................. 14

4 HYBRID SYSTEMS ................................................................................................................................... 17

4.1 Series hybrid systems ............................................................................................................................ 174.2 Parallel hybrid systems.......................................................................................................................... 184.3 Further developed hybrid systems ......................................................................................................... 19

5 FUELS .......................................................................................................................................................... 21

5.1 Fossil fuels............................................................................................................................................. 225.1.1 Standardization of gasoline, diesel oil and some other fuels......................................................... 225.1.2 Gasoline......................................................................................................................................... 235.1.3 Diesel oil........................................................................................................................................ 255.1.4 Liquefied Petroleum Gas (LPG).................................................................................................... 265.1.5 Natural Gas ................................................................................................................................... 27

5.2 Flexible fuels ......................................................................................................................................... 285.2.1 Methanol........................................................................................................................................ 295.2.2 Dimethyl ether (DME) ................................................................................................................... 305.2.3 Synthetic gasoline and diesel oil.................................................................................................... 305.2.4 Hydrogen ....................................................................................................................................... 31

5.3 Not fossil fuels....................................................................................................................................... 325.3.1 Biogas............................................................................................................................................ 325.3.2 Ethanol and methanol.................................................................................................................... 33

5.4 Summary of automotive fuels................................................................................................................ 34

6 ENGINES – POWER UNIT ....................................................................................................................... 36

6.1 Otto engines........................................................................................................................................... 366.2 Diesel engines........................................................................................................................................ 406.3 Alternative engines ................................................................................................................................ 456.4 Fuel cells................................................................................................................................................ 48

7 DEVELOPMENT OF BATTERIES.......................................................................................................... 58

7.1 Present day batteries .............................................................................................................................. 587.2 Choice of batteries for hybrid vehicles .................................................................................................. 63

8 HYBRID VEHICLES ................................................................................................................................. 66

8.1 Potential for improved energy use in hybrid systems with different types of internal combustion engine66

8..1.1 Theoretic background for the potential in improved energy use ................................................... 678.1.2 The interaction between the control unit, the energy transmitters and the mechanical powertransmitters in a hybrid system...................................................................................................................... 698.1.3 Result of the PNGV program......................................................................................................... 728.1.4 The influence of hybrid systems on conventional engines ............................................................. 758.1.5 Series hybrid or parallel hybrid? .................................................................................................. 77

8.2 Examples of developed and demonstrated hybrid vehicles ................................................................... 788.2.1 Mercedes series hybrid .................................................................................................................. 788.2.2 DaimlerChrysler’s Necar fuel cell series ...................................................................................... 798.2.3 Toyota Prius, parallel hybrid ........................................................................................................ 808.2.4 Ford’s parallel hybrid vehicles ..................................................................................................... 828.2.5 Nissan’s parallel hybrid ............................................................................................................... 848.2.6 Some other light hybrid vehicles.................................................................................................... 86

8.3 Some examples of heavy-duty hybrid vehicles ..................................................................................... 87

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8.4 Comparison between different fuels/drive trains................................................................................... 95

9 EFFICIENCY – FUEL ECONOMY ....................................................................................................... 100

9.1 The efficiency of hybrid systems......................................................................................................... 1009.2 The use of energy and efficiency at different driving patterns. ........................................................... 102

9.2.1 Studies of hybrid systems for BMW ............................................................................................. 1039.2.2 Energy use and efficiency of Mitsubishi hybrid trucks ................................................................ 104

10 FUEL AND DISTRIBUTION .............................................................................................................. 106

10.1 Conventional fuel ............................................................................................................................... 10610.2 Alternative fuels ................................................................................................................................. 10610.3 Electric energy.................................................................................................................................... 108

11 TEST METHODS ................................................................................................................................. 110

12 IMPACT ON THE EMISSIONS ......................................................................................................... 114

12.1 Theoretical background for a emission potential................................................................................. 11412.2 Emissions related to the hybrid system................................................................................................ 116

12.2.1 The series hybrid from Mercedes-Benz ....................................................................................... 11612.2.2 The parallel hybrid vehicle Prius from Toyota............................................................................ 117

12.3 The relationship between the driving pattern and the emissions ......................................................... 118

13 SUMMARY OF COSTS ....................................................................................................................... 120

13.1 Cost of the System............................................................................................................................... 12113.2 Cost of the Batteries ............................................................................................................................ 12113.3 Total costs............................................................................................................................................ 122

14 EFFECTS ON HEALTH ...................................................................................................................... 124

15 PROBLEMS - BALANCING ............................................................................................................... 130

16 SHORT TERM DEVELOPMENT...................................................................................................... 132

17 DEVELOPMENT IN THE LONG TERM ......................................................................................... 135

REFERENCES .................................................................................................................................................. 137

TABLESTable 1. Environmentally classified parameters and components in gasoline in Sweden (MK1). ...........................23Table 2. Environmentally classified parameters and components in diesel oil in Sweden ......................................25Table 3. Composition of the Danish natural gas from the North See.......................................................................28Table 4. Natural gas in the world – resources, production and ventilated/flared, year 1997..................................28Table. 5. The composition of purified biogas according to an analysis. ..................................................................33Table 6. Summary of physical and chemical characteristics of various engine fuels. .............................................34Table 7. Emission Standards for light duty vehicles EU. Source: Auto/Oil II. ........................................................37Table 8. EU-Standards for passenger cars and other light-duty vehicles................................................................40Table 9. EU-standards for heavy-duty diesel fueled engines. Source: EU Directive 1999/96/EC...........................40Table 10. EU-standards for heavy-duty diesel fuelled and gaseous fueled engines................................................41Table 11. Comparison between different types of fuel cells. ....................................................................................51Table 12. Anode and cathode reactions of SOFC ....................................................................................................52Table 13. Anode and cathode reactions in a fuel cell with PEM. ............................................................................53Table 14. The mass of the fuel cell and an estimation of how the mass can be reduced. .........................................55Table 15. Development of lead acid batteries EU. Source: Cooper and Moseley, 1998. ........................................63Table 16. Vehicle manufacturers and their choice of battery. .................................................................................64Table 17. Comparison between a series hybrid and a conventional drive system. (Source: Mercedes (Abthoff et

al., 1998). .........................................................................................................................................................79Table 18. Fuel consumption (as gasoline) for Toyota Prius and some other vehicles with low fuel consumption. .82Table 19. Some particulars for a number of hybrid buses and some trucks with hybrid systems. ...........................88Table 20. Comparison between a series and a parallel hybrid vehicle respectively with a conventional vehicle.104

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Table 21. The effect of charging strength on the working efficiency of charging and on the durability................109Table 22. Japanese 10–15 mode emission standards and emissions for Toyota Prius. .........................................117Table 23. Result from emission tests according to the US EPA FTP-75 test procedure. .......................................118Table 24. Result from emission tests according to the US EPA HFET test procedure. .........................................118Table 25. Estimation of the cost levels for various details in the hybrid system/vehicle........................................121Table 26. Evaluation of various batteries. .............................................................................................................122Table 27. Estimate of risks for yearly incidence of cancer associated with air pollution.. ....................................124Table 28. Unit risk factors. Cancer mortality risks from life-long exposure to 1 µg/m3*.......................................128

FIGURESFigure 1. Series hybrid system. (Source: DOE, USA)..............................................................................................18Figure 2. Parallel hybrid system. (Source: DOE, USA). .........................................................................................19Figure 3. Specific energy used in a gasoline fuelled car and a series hybrid when driven on road (Iwai, 1998). ..20Figure 4. Estimation concerning the use of various fuels in a fuel cell. Source: Sasaki, 1999................................35Figure 5. The relationship between the displacement of the engine and its efficiency. ...........................................38Figure 6. The specification (left) of the engine shown in the figure (right). ............................................................39Figure 7. Diagram for control of engine, DIATA. Source: Breida 1998. ................................................................43Figure 8. The HPCR fuel system with its components. Source: Breida 1998. .........................................................44Figure 9. Typical torque curve and power curve respectively for a Stirling engine................................................46Figure 10. Stirling engine. Source: USCAR, 1999. ................................................................................................47Figure 11. GM’s gas turbine. Source: USCAR, 1999. .............................................................................................48Figure 12. Basic principals of fuel cells. Source: US Department of Defence. ......................................................51Figure 13. The three sections of a fuel cell: fuel processor, stack of fuel cell and DC/AC transformer. Source:

US Department of Defence. ..............................................................................................................................52Figure 14. Fuel cell with solid oxides (ceramic). Source. US Department of Defense............................................53Figure 15. Components of a fuel cell system. ..........................................................................................................54Figure 16. Organization for the development of batteries. Source: Sutula et al., 1998...........................................59Figure 17. Specific effect respective to specific energy for various batteries. .........................................................65Figure 18. Mussel diagram over fuel consumption for a 1.25 liter gasoline engine, modified by Ecotraffic

(Sweden). Source: (Menne et al., 1996). ..........................................................................................................67Figure 19. The Japanese 10-15 mode cycle. ...........................................................................................................71Figure 20. Different cases for calculation of the braking energy recovery (0-0.15g). ............................................71Figure 21. Improvement of fuel consumption for a series hybrid when tested according to the ............................72Figure 22. Potential for different automotive system. Source: NRC, 98..................................................................73Figure 23. Mercedes hybrid car Necar 3, equipped with fuel cells. ........................................................................79Figure 24. Mercedes hybrid car Necar 3, equipped with fuel cells. ........................................................................80Figure 25. Schematic configuration of the hybrid system from Toyota. ..................................................................81Figure 26. Schematic picture of Ford’s hybrid car(”LSR”). Source: Automotive Engineering

International/February 1999). Reference: (Buchholz, 1999) ...........................................................................83Figure 27. Ford’s hybrid system PTH with gasoline engine. Source: Buschhaus et al, 1998. ................................84Figure 28. Scematic configuration of the hybrid system from Nissan. Kitada et al., 1998. .....................................85Figure 29. Nova Transit Bus. Source: Whartman, 1998.........................................................................................90Figure 30. Volvo hybrid delivery truck. ...................................................................................................................91Figure 31. Power unit (APU) for hybrid vehicle.....................................................................................................93Figure 32. Control systems, internal combustion engine and the emission control system. Source: Monrad och

van der Weijer, 1998. .......................................................................................................................................94Figure 33. Mitsubishi aerial working truck. Source: (Horii et al., 1998)................................................................95Figure 34. Efficiency improvement by hybrid strategy. (Source Takaoka et al., 1998). .......................................101Figure 35. Comparison of fuel consumption at different driving modes................................................................102Figure 36. Mitsubishi service truck. Comparison of energy used between a hybrid truck and a diesel truck.

Source: Horii et al., 1998. ..............................................................................................................................104Figure 37. Mitsubishi working truck. Comparison of energy used between a hybrid truck and a diesel truck.

Source: Horii et al., 1998. ..............................................................................................................................105Figure 38. Energy efficiency of same important component of a HEV. Source: Horii et al., 1998. ......................105Figure 39. Tests with parallel hybrid vehicle developed at the University of California Davis. Source: Duoba,

M. and Larsen R., 1998 ..................................................................................................................................111Figure 40. Tests with series hybrid vehicle developed at the West Virginia University. Source: Duoba ,M. and

Larsen R., 1998 ..............................................................................................................................................112Figure 41. Engine operational area and exhaust temperature. Source: Hirose et al., 1998. ................................115

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Figure 42. Emissions for Mercedes series hybrid vehicle (prototype)...................................................................117Figure 43. Cost of various driving systems. Source Mercedes Benz. .....................................................................120Figure 44. Exemple of relevant aldehyds. Source: Egebäck and Westerholm, 1997.............................................126Figure 45. Examples of relevant alkenes. Source: Egebäck and Westerholm, 1997. ............................................126Figure 46. Examples of relevant alkyl nitrites. Source: Egebäck and Westerholm, 1997. ....................................127Figure 47. Examples of relevant Monoaromatic compounds. ...............................................................................127Figure 48. Examples of relevant PAC. Source: Egebäck and Westerholm, 1997..................................................128

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1 SUMMARYAccording to the Swedish National Encyclopaedia the word hybrid comes from the Latinword (h)i’brida, hy’brida which means “cross” or “bastard” and its origin is the Greek word“bastard”. If one continues to the phrase hybrid vehicle the encyclopaedia describes thisas “a vehicle which is fitted with more than one type of energy transformer and energy storagesystem for its propulsion, and where the drive or the regulating system of the vehicledetermines which type shall be used. The energy converter can, for example, be a heat engine,a hydraulic engine, an electric engine or a fuel cell. Energy storage can be carried out bymeans of a chemical, kinetic, electric or hydrostatic energy storage system or by means ofheat storage. In the future the development of hybrid electric vehicles will be of specialinterest since they provide an intermittent freedom of exhaust gases”.

The object of this report, which has been produced within The Swedish Transport andCommunications Research Board’s (KFB’s) Electric and Hybrid Vehicle Program, is toassemble information on and describe the situation for the development of hybrid vehicles andvarious alternatives within this field of development. In the report the description isconcentrated mainly on the combination of combustion engine and electric battery, which isthe most common combination in present day hybrid vehicles. In order to take a glimpse intothe future even the combination of fuel cells and electric battery is described.

Among the important factors for vehicle owners are the cost of the vehicle, the fuel and theuse of the vehicle. For alternative vehicles the cost of the vehicle is usually higher than for an“ordinary” vehicle, quite simply because the alternatives are manufactured in smaller series.For the vehicle manufacturer and even for the buyer of the vehicle it can therefore be of greatimportance that as large a market as possible is obtained for the alternative vehicle, forexample electric vehicle or hybrid vehicle. One way for the vehicle manufacturer to quicklycreate a large market can be to sell the cars at a lower than usual price, for a period of time.Examples of this are electric vehicles, which are manufactured by Ford and GM and thehybrid car Prius, which is manufactured by Toyota. One can ask the question as to whetherthe environmental advantages would be a sufficient reason for paying the higher price, if thevehicles were not subsidized or if the running costs had not been decreased by alterations intaxation.

In present day hybrid systems one of the energy converters consists of electric batteries. Acontinued, comprehensive development of batteries is required in order to improve thetechnique and to reduce the costs. One important reason for introducing hybrid vehicles is toimprove fuel economy, so that a considerable part of the report is devoted to this. Thedistribution of fuel and electricity is described briefly. The costs are also described briefly dueto the fact that techniques of hybrid vehicles are so new that there is not yet sufficientinformation on which to base a clear picture of the costs. This can also be said of the testingmethods for the hybrid vehicles in question, since no standardized testing methods have yetbeen determined. The effect on emissions is not completely clear, but present daydevelopment certainly seems to be leading in the right direction.

It is obviously not especially difficult to find problems in a technique development which hasnot yet been tested on the open market other than on a small scale. The report suggests whichare judged to require further technical development. The real barrier to a speedy introductionof the hybrid system is probably the cost.

There are several questions, concerning vehicles, which have been in the limelight for the last30 to 40 years, namely emissions, fuel consumption and safety. When we discuss running

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hybrid vehicles and the possible advantages of them, it is chiefly the following points whichgive rise to a problem of greater or lesser magnitude.

Vehicle emissionsEnergy conversion and fuel savingsBattery developmentCosts

The assessment which has been carried out and is presented in this report has provided a basisfor the evaluation of some different lines of development for hybrid systems. In the short term(0-5 years) the picture is relatively clear since it takes time and money to develop and presentnew ideas. It seems clear that in the case of light-duty vehicles a continued effort will be putinto developing the hybrid system, to some extent. In the case of heavy-duty vehicles there isa certain degree of uncertainty as far as the development of hybrid busses is concerned, due tothe fact that it is generally private bus companies who carry out the development. Certainlythis development generally takes place in conjunction with the manufacturers, but thequestion is how strongly the manufacturers are engaged in the development work. Under thesecircumstances strong support from the authorities is required in order for the developmentwork to be carried out, since such activities are generally expensive.

The light-duty hybrid electric vehicles that have hitherto been developed are mainly parallelhybrids. If the development of hybrid systems takes place it will most certainly concern light-duty vehicles, and these will be parallel hybrids equipped with an otto or a diesel engine,depending on which of these the manufacturers wish to back.

The requirement for energy efficiency is easier to meet with a diesel engine in the hybridsystem. Of all the hybrid systems which have been studied for this report, it is Ford’s parallelhybrid with a diesel engine which takes top place as far as energy is concerned. Generallyspeaking diesel engines have experienced a period of positive development, especially duringthe last decade. This is due, to a great extent, to the fact that diesel oil has been successivelyimproved, and this is particularly true for Sweden. It now remains to be shown that the currentdevelopment of purification techniques for the reduction of nitrogen oxides and particulateemissions will provide a system with such a good durability that it can be accepted for useduring a long period. If such a development can be demonstrated and the development ofdiesel oil continues to give good results then the diesel engine can prove to be a suitablealternative for, amongst others, vehicles with hybrid systems (both light-duty and heavy-duty).

The efficiency of the otto engine will not reach the efficiency level of the diesel engine.However, continuous development of the otto engine is taking place in order to improve thefuel efficiency. The fuel consumption of an advanced otto engine with direct fuel injection issomewhere between that of the diesel engine and of the conventional otto engine.

Where the emission of exhaust gases and noise are concerned one can reverse the argument.In the short term it can be difficult to achieve the same emission requirements for dieseldriven vehicles as for petrol driven ones. Unfortunately the direct injected otto enginesdeveloped up to the present day have shown a higher level of the emissions of oxides ofnitrogen and particles than their conventional counterparts. Vehicles with direct injected ottoengines will also probably achieve the same emission performance as the vehicles fitted withconventional otto engines in the not too distant future.

When determining the development of hybrid driven heavy-duty vehicles it should beremembered that there are clear differences between light-duty and heavy-duty vehicles. Onedifference is that the heavy-duty vehicles have, as a rule, more space available for additionaland heavier equipment than have passenger cars. However there is no absolute solution,

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especially for busses in city centers, which have a limited space unless some passenger spaceis sacrificed. The general opinion is, however, that heavy-duty vehicles can carry a relativelyheavier packet of batteries than a passenger car. Providing that one can charge the batteriesfrom the mains, this could mean that a system with series hybrids is advantageous. But it isnot completely certain that this is a correct conclusion for all types of heavy-duty vehicles. Ifone considers the whole scale of heavy-duty vehicles, from light trucks to busses, there can bemany cases where a parallel hybrid is a better alternative than a series hybrid. Therecommendation is therefore that each type of vehicle and each possible use of the vehicleshould be considered when choosing a hybrid system.

In the long term it is not easy to foresee the development but in the case of hybrid electricvehicles some possible scenarios are already in sight, and these could be achieved during thecoming 5 to 15 years:

1. Parallel hybrids will come to be the dominant system for light-duty vehicles and possiblyeven for certain other groups of vehicles.

2. Series hybrids will come to be used solely for heavy-duty vehicles.

3. The present day development of fuel cells will lead to more manufacturers paying greaterattention to electric or hybrid vehicles with fuel cells.

The development of fuel cells will most probably continue, at least at the present day level.Technical speaking it is likely that vehicles fitted with fuel cells will function satisfactorilyuntil mass production is begun. A hinder for the development of a larger market is howeverthe cost. Will the average vehicle owner be able to afford such a vehicle?

A vehicle powered by a fuel cell can be considered to be an electric vehicle. If the fuel cellcontinues to be developed at the same pace as at present, so that a reasonable price level willbe achieved on the market, the market for electric vehicles will also be favored.

In the report the use of series hybrid vehicles is estimated to be limited to heavy-duty hybridvehicles. Hybrids will not be likely to be relevant for heavy-duty vehicles, with the exceptionof those trucks which operate in city centers, i.e. trucks which are used for the distribution ofgoods to shops, as garbage vehicles and as certain types of working vehicle for servicepurposes. Continued development of the hybrid system for busses seems uncertain for variousreasons. It is chiefly local bus companies and private contractors who develop hybrid busses,leading to uncertainty in the continuance of the development.

If there is a technical breakthrough in the manufacture of batteries and simultaneously themanufacturers increase their efforts to develop hybrid vehicles, the situation can be changedso that there is a speedier introduction of hybrid systems for heavy-duty vehicles.

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2 INTRODUCTIONAccording to the Swedish National Encyclopaedia the word hybrid comes from the Latinword (h)i’brida, hy’brida which means “cross” or “bastard” and its origin is the Greek word“bastard”. If one continues to the phrase hybrid vehicle the encyclopaedia describes this as “avehicle which is fitted with more than one type of energy transformer and energy storagesystem for its propulsion, and where the drive or the regulating system of the vehicledetermines which type shall be used. The energy converter can, for example, be a heat engine,a hydraulic engine, an electric motor or a fuel cell. Energy storage can be carried out bymeans of a chemical, kinetic, electric or hydrostatic energy storage system or by means ofheat storage. In the future the development of hybrid electric vehicles will be of specialinterest since they provide an intermittent freedom of exhaust gases”. The hybrid vehiclesdescribed in this report are hybrid electric vehicles (HEVs) – a commonly used definition of ahybrid electric propulsion system vehicle equipped with an internal combustion engine as onepower source and electric traction motor as the other power source.

Today there are in principal two types of hybrid system the “series hybrid” and “parallelhybrid”, see section 4 for a detailed description of these two systems. In this report thepresentation about hybrid systems will primarily be concentrated to the combination internalcombustion engine and electric motor which is today the most common combination forhybrid vehicles. However, when looking into the future, even the combination fuel cells andelectric batteries will be described. A question that seems to be difficult to answer is whattype of hybrid system will be the dominant one on the market for light-duty hybrid vehicles.Today it is likely that the development of hybrid systems for light-duty vehicles will beconcentrated to the parallel system. However, this does not necessarily mean that serieshybrid systems will be an uninteresting alternative in the long run. For heavy-duty vehicles itis likely that the series hybrid system will be the commonly used system. There are also othersystems of types which can be seen to lie somewhere between series and parallel hybrids.

Since the number of hybrid vehicles is limited and since some of them are only prototypes –except, possibly, in the case of Japan – the car owners are generally not familiar with this typeof vehicles. It can also be said that long term testing of hybrid vehicles is so far rather limited.

The fuel to be used in hybrid vehicles (and also in fuel cell vehicles) is a question of highimportance since one strong motive for the use of the hybrid technology (and electricvehicles) is to reduce the emissions and to improve the fuel economy. In one section of thisreport dealing with the fuel cycle it is shown that the technology used for reforming the fuel inthe vehicle will have a significant influence on the fuel economy. However, in this case, thepractical possibility of storing fuel in the vehicle may be seen to be more important thanenergy efficiency. The classical example concerning the storage, distribution and use ofgaseous fuels as fossil gases (natural gas and others) contra storage, distribution and use ofliquid fuels is valid even in the case of fuel cells.

Some of the key questions for the car owner are of course the cost of the vehicle whenpurchased, the fuel and the use of the vehicle. For alternative vehicles the of purchasing thevehicle is generally higher than for the commonly used commercial vehicles since thealternative vehicles are mostly produced in low quantities. For the car manufacturer but evenfor the purchaser of the vehicle it will be an advantageous to create a large market for analternative such as the electric vehicle or the hybrid. One possibility for the manufacturer tocreate a larger market may be to sell the vehicles at a lower price during the introduction ofthe actual vehicle, resulting in a reduced profit. Examples which can be mentioned are the

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electric vehicles manufactured and sold in the USA and the hybrid vehicle Prius manufacturedby Toyota, Japan. It can also be asked whether the desire of the buyers of alternative vehiclesto keep the pollution as low as possible would be strong enough for them to buy such vehiclesif the costs of the purchasing and using these vehicles were to be subsidized. These andrelated questions are discussed in some papers which are referred to in this report.

Since many of the articles and some reports of investigations in papers give somewhat similarinformation, a selection of the information has been carried out done (not systematic,however) in order to reduce the number of references. The fact that some of the information inthe papers may old or not relevant for hybrid vehicles and therefore not valid for this reporthas been considered when selecting the literature references. The development of batteries isone of the subjects which are not easy to describe since there is a great number of report andother information to take notice of and that there may be a difference between the requirementfor batteries for hybrid vehicles compared with requirements for batteries to be used inelectric vehicles. In hybrid vehicles charging and discharging of the battery occurs incontinuously repeated cycles during driving in traffic. This is true to some extent even forelectric vehicles using regenerative braking (the energy released during decelerations –“braking”- is recycled to the battery) and this recharging must certainly be taken into accountwhen developing batteries for hybrid vehicles and also for electric vehicles using a system forregenerative braking. One difference between a electric vehicle and a hybrid vehicle is thateven the capacity for depth-of-discharge (DOD) may have to be larger for a battery used in anelectric vehicle than for a battery used in a hybrid vehicle. A drawback for hybrid vehicles(and to a higher extent for electric vehicles) is that the cost of the battery is high. This isespecially so for light batteries with high energy density; (in one case the cost of the batterypack was higher than purchase price of the vehicle). It seems therefore to be necessary toreduce the cost of the battery in order to use it in a vehicle produced in a large quantity. Thisshould be made possible by an improvement in the production of the batteries.

The USA constitutes a large part of the global market for vehicles and during the last decadethe development of alternative vehicles has to a large extent been influenced by the programPartnership for a New Generation of Vehicles (PNGV) started 1994. The program is based onan agreement between the US Government (including 12 Departments) and Chrysler, Fordand General Motors. The program is directed towards passenger cars and the goal of theproject is to improve the fuel economy of these vehicles to 80 MPG (approximately 3 liters/100 km). Further aims are as follows:

The first goal is to: ”Significantly improve national competitiveness in manufacturing”. Thismeans an improvement of the productivity of the US base for manufacturing by an significantupgrading of the US manufacturing technology, including adoption of agile and flexiblemanufacturing and reduction of costs and lead times, while reducing environmental impactand/or improving quality.

The second goal is to: ”Implement commercially viable innovation from ongoing research onconventional vehicles”, which among other things means to pursue advances in vehiclesleading to improvements in fuel efficiency and emissions while pursuing safety advances tomaintain safety performance. The car industry will commit itself to applying thosecommercially viable technologies that are expected to significantly increase vehicle fuelefficiency and improve emissions.

The third goal is to: ”Develop a vehicle to achieve up to 3 times the fuel efficiency of today’scomparable vehicle”. This is a “fuel efficiency improvement of up to three times the averageof Concorde/Taurus/Lumina, with equivalent customer purchase price of today’s comparablesedans type of vehicles adjusted economics”. The requirement for fuel economy is 80 MPG

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(approx. 3 l/100 km). Other requirements include emission standards as Tier II, which are;0.125 for HC, 1.7 for CO and 0.2 for NOx, in g/mile at the odometer reading of 100 000 miles,which is equal to HC: 0.078, CO: 1.06 and NOx: 0.124 in g/km at the odometer reading of 160000 km. According to PNGV at least 80 % of the vehicle has to be recyclable or to quote”Achieve recyclability of at least 80 %”.

This report is prepared for The Swedish Transport and Communications Research Board(KFB) and is based on the results and experiences which have been presented in theinternational literature. The impression is that there is a great optimism, especially about thedevelopment of fuel cells. Unfortunately this optimism may be misplaced since the barriersare described as fewer than those which will have to be solved in reality. This optimism maylead to the time frame for the remaining development of fuel cells being shortenedunrealistically. Fuel cells are certainly not a new invention, but the application to ourcommonly used passenger cars requires that they be produced at a reasonable cost and thatthey can be proven to be efficient energy transformers without having negative effects on theenvironment or causing other problems.

The aim of this report, which has been prepared within KFBs program for electric and hybridvehicles, was to combine and describe the situation concerning the development of hybridvehicles and the different alternative for this development. This report will constitute one ofthe reports on which the final report for the electric and hybrid vehicle will be based.

The disposition of this report is as follows: firstly there will be a discussion of the complexityof the development and introduction of reformed or new automotive fuels and newtechnologies for propelling motor vehicles. After this there will be an introductory descriptionof two different hybrid systems according to the terminology used for such systems. Sinceboth gasoline and diesel oil and even alternative fuels may be used for the actual energytransformers, the internal combustion engine or fuel cells, a rather extensive description of thedifferent fuels is given. In the case of the above mentioned two types of energy transformers,it is expected that a considerable development will occur in addition to that which has alreadyoccurred. Since this will also have an impact on the development of the vehicles, the expectedchanges will be discussed in two of the sections. In present day hybrid systems one of theenergy transformers is the battery and in order to increase their life cycle, and thereby eventhe costs, further extensive research and development has to be carried out. An important aimof the introduction of hybrid vehicles is to improve the fuel economy and this will bediscussed rather extensively in this report. The distribution of fuels and electricity will bebriefly described, as will the costs, since the technology of hybrid vehicles is quite new andthere is, so far, no clear information concerning costs. This also applies to testing methods forrelevant hybrids, since no standardized methods have been determined. The effect of theemissions has not been thoroughly mapped out, but the trend seems to be decidedly positive.

It must be mentioned that Peter Ahlvik, Ecotraffic, has supplied valuable contributions to thereport and has also checked the report in its final stages, which is highly appreciated.

The authors of the report, Karl-Erik Egebäck, Autoemission K-E E Consultant AB, tel. +46(0)155 28 24 44 and Sören Bucksch, Sören Bucksch AB, tel. +46 (0)8 580 33 330 would liketo thank Liz Egebäck Foxbrook for the help with the translation from Swedish to English andthe languish check. A thanks is directed also to KFB, who has financed this work.

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3 THE COMPLEXITY OF THE DEVELOPMENT OF FUELSAND VEHICLES

During recent years there has been much activity in the development of both conventionalvehicles, engines such as direct injected otto engines (GDI) and alternative vehicles such aselectric vehicles, hybrid vehicles in which the electricity has been generated by fuel cells.Even concerning fuels much development has taken place. The conventional fuels, gasolineand diesel oil, are reformed in different ways. For example in the case of gasoline, in order touse more environmentally friendly components there has been a reduction in the content ofbenzene, an addition of an alcohol to the gasoline, a reduction in the vapor pressure etc. Theimprovements of diesel oil mean primary that the content of both sulfur and aromatics arereduced and that the cetane number is increased to the level of 48 to 50 or higher. Despitethese changes of gasoline and diesel oil the fuels must of course still be of such quality thatthey can be used in existing vehicles on the market. The owners of the vehicles must as far aspossible be kept indemnified and therefore it is important that no changes in the fuels arerealized that will create a problem for the car owner.

The gasoline must have a sufficiently high octane number in order to not cause knocking inthe engine. After the introduction of lead-free gasoline, during the second part of 1980s, therehas been a requirement that a gasoline with a lubricating additive should be available for theolder cars in order to protect the valves in their engines. On the other hand it has been of greatimportance that the “lead-free” gasoline should not contain lead of such amount that there isdeterioration of the emission control system.

For the diesel oil it is important that its density is kept within specified limits so as not to havean undue influence on the engine power set by the engine manufacturer. It is also importantthat the diesel oil has such a lubricating quality that the wear of the engine and especially thefuel injection system does not increase.

The introduction of a new technology not only requires certain changes in society, forexample a new infrastructure if a new alternative fuel is to be introduced, but it will also havean impact on the user of the new technology. This is true not least in the area of automotivevehicles and the reason may be that the ownership and use of a motor vehicle is costly bothfor the private person and society, but also because of the fact that new technologies arelinked to feelings of uncertainty when they are introduced. If we keep to area of automobilesthe experiences are that even small problems in the introduction of a new technology canchange a positive attitude within the car owners to a negative attitude. Of course the cost ofthe new technology is an important factor in this case. The above discussion indicates that thecomplexity of even small and positive changes will have an effect on the car owner and use ofhis or her vehicle. The improvement of the environmentally related quality of the fuel or theintroduction of renewable fuels will probably be accepted as something positive for most of usincluding the car owner. In the case of the introduction of lead-free gasoline, which was asuccess in Sweden without causing any great problems, it was important that there was a gooddegree of co-operation between the authorities and the oil and car industry.

Usually the car owner does not suffer if there are changes in the style or function of the car orif there are changes in the fuel composition unless there is an increase in the cost ofpurchasing the car and in running it. The latter may, however, be a problem for many carowners. Fortunately some changes can be advantageous even if they lead to higher costs forthe car owner. One such advantage can be that a vehicle with high environmental qualitiesmay be accepted for use in areas where the use of cars is restricted.

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There may be advantages with some types of vehicles despite their being “odd”, providedthey function well and especially if they are more fuel efficient than other vehicles. Thereduction in the cost of using these cars may balance the higher cost for the purchase of thecar. However, it is not easy to find such cases though progress in this direction can beexpected to occur in the long term. If the interest in hybrid vehicles remains as keen as it hasbeen, they may be interesting objects for purchasers of new cars. However, success for hybridvehicles depends in the end on whether the car manufacturers make an effort to develop suchreliable, well performing and not too costly hybrid concepts as will be attractive for thepurchasers. During a transitional period it seems necessary for governments or governmentalauthorities in the progressive countries to financially or by other means support at least somepart of the development and introduction of the hybrid vehicles. Such support was given forexample in Sweden at the end of the 1980’s, on the introduction of the present-day efficientemission control system for light duty vehicles. One problem concerning hybrid vehicles isthat the costs of developing these vehicles and the batteries to be used in them will be on amuch higher level than for the above mentioned emission control system.

The competition for customers and the increasing requirements concerning the emissions andfuel economy has led to the use of large resources among the car manufacturers and enginemanufacturers in the search of new solutions for new types of engines and vehicles. Suchtrials may on the other hand lead to a shortness of resources, which require different prioritieswithin the actual industry. For the car industry there may also be a dilemma that there aremany alternatives to study in order to take the right decision and to maintain sound priorities.

The shortness of resources and today’s focusing on fuel cells and the development of fuel cellvehicles may lead to a shortage in resources for the development of electric- and hybridvehicles as compared to the case without this focusing on fuel cells. This focusing on fuelcells may also obstruct the development of alternative fuels for internal combustion enginessince a successful development and introduction of alternative fuels is more closely related toa lower cost of these fuels, and especially biobased fuels, than it is to their having a potentialfor lowering the emissions of harmful substances. In the case of hybrid vehicles there is apossibility that the car manufacturers see these vehicles as transfer technology up to fuel cellvehicles, and that the only main change to be carried out is to use a stack of fuel cells insteadof the internal combustion engine.

Returning to the subject of hybrid vehicles, there is a question as to whether renewable fuelswill be one of the possible alternatives, especially as improvements of gasoline and diesel oilshave resulted in a higher potential for these fuels to meet the requirements concerning healthand environment, except in the case of the so-called greenhouse gases carbon dioxide,methane, nitrous oxide etc. However there do not seem to be any technical obstacles to the useof renewable fuels for hybrid vehicles and, as has already been underlined, there is an obviousadvantage in the reduction of greenhouse gases when using renewable fuels and even, in somerespects, in the form of a reduction in the emission of NOx and particles. The latter is true alsofor other alternative fuels such as natural gas.

Since the development of hybrid vehicles is taking place in the car manufacturers’ plants allover the world, the description of the hybrid vehicles is based on information found in theinternational literature and obtained through communication with different persons working inthe field of development of hybrid systems. One problem is that the information from the carmanufacturers is restricted and it is difficult to obtain information about the status of thedevelopment. In the meantime, from the start of a report like this many new inventions havebeen presented by the car manufacturers but not officially published and some new prototypesor other types of hybrid vehicles have been presented on the market. Unfortunately some ofthis information, which may be important, has not been included in this report.

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So far most of the development of hybrid vehicles has occurred chiefly in Japan but even inthe USA. So far there are only one or two prototypes of hybrid vehicles which have beenpresented by the European car manufacturers to the knowledge of the authors of this report.One of these is a Renault Kangoon and this vehicle will be available on the market year 2001..

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4 HYBRID SYSTEMSAs has been described above the conception “hybrid”, related to motor vehicles, is a vehicleequipped with more than one energy transformer. By this definition it is not stated which typeof energy transformers are used in the hybrid system. However, this does not mean that thenumber and types of energy transformers are unlimited when looking at practical, technicaland economical possibilities. Fuel cells may, for example, be used in hybrid vehicles and suchvehicles are already presented as prototypes, but are not today either so technically welldeveloped or economically feasible as to be introduced on the market. The aim here is todescribe the main alternatives of hybrid systems in greater detail, in order to provideinformation for those readers who are familiar with the hybrid technology for motor vehicles.

It is usual today to have an internal combustion engine connected to an electric generator usedas one of the (or the main) energy transformer system and a battery in combination with anelectric motor as the other energy transformer system. The engine can most commonly be anotto engine or a diesel engine but other alternatives are possible such as sterling engines, gasturbines etc. The different types of engine are presented in Section 6.

There are many different types of battery available such as special lead (acid) batteries, avalve regulated lead accumulator (VRLA), nickel metal hydride batteries (NiMH), natrium(sodium)-nickel chlorine batteries (named ZEBRA), zinc air batteries, lithium-ion andlithium-polymer batteries respective and some others. The use of capacitors and especiallyultra-capacitors constitutes an important possibility of storing electric energy. The ongoingdevelopment of batteries is discussed in Section 7.

The combination fuel cell and battery is a possible and attractive long-term alternativecombination in hybrid vehicles. However, an even more attractive alternative would be avehicle where the fuel cell is directly connected to the electric motor as the fuel cell can itselfbe regarded as a battery. The problem associated with such a system seems to be that electricenergy is commonly not stored in a fuel cell system, such as the one mentioned, and thereforethe fuel cells must rapidly convert the chemical energy in the fuel to electric energy, since thefuel cells has to produce a variably flow of electricity. The question is whether such a vehicleshould be called a hybrid or an electric vehicle and one such vehicle is presented in Section8.2.2. However, the energy efficiency of such a vehicle can exceed quite considerably that ofa vehicle having both a fuel cell and a battery. The fuel cells are presented in Section 6.

As already described there are two main types of hybrid systems, classified as series hybridsand parallel hybrids. There seems also to exist systems which could be classified as being of atype somewhere between series hybrids and parallel hybrids. However, in this report we areconcentrating our description to the two main systems.

4.1 Series hybrid systems

By definition one can classify a series hybrid as a vehicle where an internal combustionengine (or some other type energy transformer) is placed in series with an electric motor (ormore than one electric motor) for the traction of the vehicle. This implies in practice that themain function of the internal combustion engine is to generate electricity for the battery whichin turn feeds the traction motor (or electric motor) either directly or by the battery, via agenerator. In this manner there is no direct mechanical connection between the internalcombustion engine and the driving wheels.

Simply expressed one can also say that a series hybrid vehicle is basically powered by twosources. A common layout for a series hybrid system is shown in Figure 1.

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The internal combustion engines used in a series hybrid system are usually rather small(compared with conventional traction system) and rarely deliver more than 50 % of themaximum power needed for propelling the vehicle*. Since there is no direct mechanicalconnection between the engine and the driving wheels, the engine in the most extreme casecan be run more or less at constant load and speed. The condition - that the engine does nothave to follow a certain dynamic driving cycle – means that the chances of obtaining lowemission levels are good if for example an otto engine with a three-way catalyst system isused in the series hybrid system.

Figure 1. Series hybrid system. (Source: DOE, USA).

In series hybrid vehicles an electric motor (or more than one motor) is used for the traction ofthe vehicle. Series hybrid systems are usually designed to be used in heavy-duty vehicles. Inthe case of buses where more than one electric motor is used these motors may be placedclose to the driving wheels. One drawback of the series hybrid vehicle is that it has to beequipped with a rather powerful battery with a high energy density since all or at least 50% ofthe power may in extreme cases have to be delivered from the battery for the traction of thevehicle. The large batteries are heavy and add a considerable weight to the vehicle and arealso considered to be costly.

4.2 Parallel hybrid systems

The traction equipment of the parallel hybrid type of system is powered by two energytransformers, which work parallel with each other. In this case the internal engine ismechanically connected to the driving wheels via a gearbox and the electric motor supportsthe engine when more power is needed than can be delivered by the engine. Commonly theengine is larger and more powerful than in the series hybrid system while the electric motor issmaller and consequently less powerful. The internal combustion engine has to follow thetype of dynamic driving conditions of the vehicle because of the mechanical connection to thedriving wheels and this will somewhat reduce the potential for low emission levels. However,the impact of heavy transients can be a little less if a certain leveling by “peak shaving” isused in the hybrid system. One advantage with the parallel hybrid system is that the batteryused is smaller and consequently lighter and less costly compared with the battery for serieshybrids.

A layout for a parallel hybrid system is shown in Figure 2.

* The most extreme variant of a series hybrid is an electric vehicle equipped with an auxiliary engine in order to

increase the driving range of the vehicle.

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Figure 2. Parallel hybrid system. (Source: DOE, USA).

4.3 Further developed hybrid systems

Today the development of hybrid vehicles seems to be towards the use of series hybridsystems, especially in heavy-duty vehicles and primarily in buses, while parallel hybridsystems are being developed for light duty vehicles. As has been pointed out earlier, thecontrol of the internal combustion engine of a series hybrid vehicle involves a less varied loadcycle than that is used for the engine of a parallel hybrid vehicle. Due to the less varied loadof the engine a higher efficiency is achieved for an engine used in a series hybrid vehicle thanfor an engine in a parallel hybrid vehicle. This is discussed in more detail in section 6 and 8.

Naturally it would be an advantageous in terms of fuel economy if the internal combustionengine in a parallel hybrid vehicle could be run in an area of the load cycle where theefficiency if the engine is highest. Areas with low loads should be avoided especially for ottoengines since the efficiency of this type of engines drastically drops as the specific fuelconsumption increases at low loads of the engine, which can be seen in Figure 3. In the figuredifferent lines are shown for cases where the efficiency of the electric drive system (generator,charging/ discharging of the battery and the converter) is 77 % and 60 % resp. and where themaximum efficiency of the engine is as high as 35 %.

In order to reduce the fuel consumption as far as possible the parallel hybrid system can, firstof all, be designed according to the following characteristics:

The internal combustion engine is switch off at the limit of low power needed for the tractionof the vehicle. The battery is then used as the only energy source.

The internal combustion engine switches off when the vehicle is stopped.

The energy released during braking is fed back to the battery.

The size of the internal combustion engine is adjusted to a lower requirement of power, asnecessary. For acceleration and some other driving conditions, when the power of theinternal combustion engine not is sufficient there will be support from the electric motor.

Matching of the internal combustion engine with regard to the most fuel economic drivingconditions by the use of a continuous variable transmission (CVT).

Figure 3 shows the specific fuel consumption for a minivan and a series hybrid vehicle(SHEV*) system equipped with an internal combustion engine with an efficiency of 35 % and * Series-Hybrid-Electric-Vehicle

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a generator. The specific fuel consumption was measured when driving on an even horizontalroad. The SHEV exceeded the gasoline-fueled vehicle without hybrid system in fueleconomy, i.e. in used energy under the following provisions;

• when the efficiency of electric generation/charging/discharging of the battery is at least60 %;

• when the speed of the vehicle is less than 50 km/h;• when the efficiency of the electric generation/charging/discharging of the battery is at

least 77%** and the speed of the vehicle is below 80 km/h.The performance of the SHEV was significantly better, concerning the use of energy, whenthe vehicle speed was less than 20 km/h.

Iwai (Iwai, 1998) point out that a vehicle equipped with a parallel hybrid system (SPHV)***

has the best fuel economy i.e. energy efficiency at both low load and high load by driving thesystem as a SHEV at low load and as an internal combustion engine alternative at high load.According to Iwai it requires that the engine in a SHEV be propelled with high efficiency andan efficiency of at least 77 % and 60 % respectively for the electric drive system, for theSHEV to be able to surpass a gasoline fueled vehicle without hybrid system in the question ofefficiency.

Figure 3. Specific energy used in a gasoline fuelled car and a series hybrid when driven onroad (Iwai, 1998).

The car manufacturers, for example Ford and Toyota, use the possibilities described by Iwaifor the control of their hybrid systems. To be more specific, Ford uses them partly and Toyotauses them nearly full out. There are naturally further technical possibilities for improving theenergy efficiency in the hybrid systems. Different hybrid vehicles are presented in Chapter 8.

The above described study of the possibilities for further development and the two mentionedhybrid electric vehicles Toyota and Ford have shown that there is a potential for furtherimprovements of hybrid systems.

** Iwai has then calculated that the efficiency of the generation of electricity of 90 %, 95 % for the rectifier.*** Series-Parallel-Hybrid-Vehicle.

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5 FUELSWhen developing the internal combustion engine for a hybrid vehicle the choice of fuel is animportant question, because this is decisive for the type of engine to be used. The choice offuel is also decisive for the efficiency of the engine as an energy transformer and itsperformance concerning the emissions of exhaust gases and noise. The question is thenwhether the hybrid vehicle should be optimized for high efficiency or low emissionperformance. This is decided, among other things, by the choice of fuel and the type ofinternal combustion engine to be used, but also by other components in the hybrid system andthe interaction between these as directed by a control system. The authors of this report do nottake any position concerning the choice of strategy regarding the best efficiency and the bestemission performance by the hybrid system but have given some views about the role of fueland engines in the coming sections. Hopefully the selection of the “right” fuel may contributeto achieving the goal of both an excellent efficiency and a good emission performance.

The fuels which are actual for hybrid vehicles are the conventional fuels, gasoline and dieseloil, and those which are called alternative fuels. Of the latter the following may be used:

Fossil fuels/fossil-based fuels (also called alternative fuels) such as natural gas (for exampleCNG or LNG), liquefied petroleum gas (LPG), dimethyl-ether (DME) synthetic gasolineand diesel oil and methanol based on natural gas.

Bio-based fuels such as alcohols (ethanol and methanol), bio-gas and fatty oil esters(commonly called FAME).

Hydrogen.

It is technically possible to use different fuels, and therefore it is firstly a question as towhether a sufficient amount of fuel can be supplied, whether the fuel can be efficientlydistributed and if the fuel is reasonable priced. However, the critical question is whether thereis sufficient interest in investing in an alternative fuel. Which fuel will be elected to be usedfor fuel cells in the long run is, so far, an open question even if it from the point of energyshould turn out that a gaseous fuel would be more efficient than methanol, which is a popularfuel for one of the popular fuel cells (PEM), see section 6.4. For hybrid vehicles gasoline ordiesel oil commonly is used but for heavier vehicles, such as buses, gaseous fuels or analcohol is used in some cases instead of diesel oil, see section 8.

Fuels produced from either fossil-based material or bio-based materials are called flexiblefuels in this report. In order to show one advantages of such a fuel, methanol can be taken asan example. In order to reduce the emission of the greenhouse gas CO2, it can be argued thatmethanol can be used in the long run, since it can be produced from natural gas to start withand later on from a bio-based material if an efficient and reliable method has been developed.However, there are various disadvantages of this, amongst others the risk that the introductionof bio-based methanol will be delayed many years if the cost of this fuel is regarded as beingtoo high.

In the following the discussion will be concentrated on gasoline, diesel oil, LPG, natural gas,bio-gas, ethanol, methanol, DME and two other synthetic fuels. Hydrogen will be mentionedas one alternative and then as a fuel for fuel cells but also as an energy carrier for otherpurposes. It can be of interest to mention that the government of Island has signed anagreement with the DaimlerChrysler-Ballard group, which may result in the production ofhydrogen in Island, if the agreement is realized.

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5.1 Fossil fuels

As has already been pointed out, there are many fuels within the fossil fuel group. However,in this context, it is of interest to primarily discuss gasoline and diesel oil, since these twofuels are commercially available in different countries all over the world. It seems also thatthey will be the primary fuels on the market for the transport sector, for a long time in thefuture. Natural gas and methanol based on natural gas are alternatives on an internationalmarket and they are therefore clearly objects of interest in this discussion.

The development of automotive fuels in Sweden and even internationally has resulted in thepresent day situation where it is difficult to clearly define the over-all availability of thedifferent gasoline blends and the different types of diesel oil. As a consequent, thespecifications of these fuels changes from time to time since the increasingly severe emissionstandards not only affect the development of new vehicles but also of better fuels. In additionthe specifications allow that the composition of fuels may show a variation not only from onecountry or group of countries to another group of countries – for example between the USAand Europe – but of course also between different classes of gasoline and diesel oil. InSweden for example there is so far no requirement that all gasoline must contain a certainpercentage of oxygenates, but on the other hand it not been explicitly declared that it isforbidden to blend gasoline with a certain amount of an alcohol or for instance MTBE orsome other ether.

Concerning MTBE the use of this oxygenate in gasoline is forbidden in California since thereare evidence that the groundwater has been contaminated with MTBE in certain areas. Also inthe federal USA a discussion has started as to whether MTBE should be fazed out fromgasoline or whether the use of MTBE should be limited. These actions can result in the use ofother ethers being questioned in the USA and California. It can be added that no similaractions have been taken in Europe on the EU level but a discussion has started which mayalso influence the use of MTBE in Sweden. However, to sum up the results of thedevelopment of gasoline and diesel oil, it is clear that both of these fuels have been improvedduring the last decade both in the USA and Europe and further improvements will be seen.

5.1.1 Standardization of gasoline, diesel oil and some other fuels

Neither gasoline nor diesel oil is a uniform mixture. Gasoline is produced by blendingdifferent hydrocarbons in order to meet the required specification primarily arrived at in co-operation between the car manufacturers and the oil industry. In Sweden this co-operation isorganized by the Standards Institute (SIS-STG), which is also administratively responsible forthe work, for the organization of meetings, for setting up the protocols and to printing andpublishing the agreed standards. Authorities in Sweden such as the Environmental ProtectionAgency propose requirement for certain components in the fuel, especially if the fuel is goingto be environmentally classified. In this case representatives for the agency or fuel expertsusually participate in the work of preparation of standards.

For a long time an extensive co-operation for international standardization of fuels forautomobiles has been in existence. In Europe this work is organized within an organizationcalled CEN (European Committee for Standardization). Experience has shown that there is anadvantage in a co-operation within CEN, even if the requirements concerning some of thecomponents or parameters in the fuel can differ from country to country. In areas withvariable climatic conditions, such as the south of Europe and the Nordic countries, it is naturalthat the requirements for the automotive fuel differ. The connection between the compositionof the fuel and health effects is briefly discussed in section 14.

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5.1.2 Gasoline

In Sweden gasoline is classified environmentally. Some years ago there was no highest classMK1, i.e. a gasoline specified so as to have the best environmental quality, but today suchgasoline exists on the Swedish market. The different classified parameters can be seen in thefollowing summary, see Table 1.

Gasoline has since long been regarded as a cleaner fuel than diesel oil. This judgment iscertainly linked to the exhaust emissions from diesel-fueled vehicles. These have been seen asmore dangerous from the health point of view than the exhaust emissions from gasoline fueledvehicles. The diesel vehicle exhaust has been shown to contain a greater mass of polycyclicaromatic hydrocarbons (PAH) than the gasoline vehicles. The greater mass of PAH is alsolinked to a higher mutagenic activity caused by the diesel vehicle exhaust when comparedwith gasoline vehicle exhaust. The diesel vehicle exhaust also contains a larger mass ofparticles which leads to a higher health risk when compared with gasoline vehicle exhaust. Tothis should be added that the smell of diesel vehicle exhaust is experienced as moreunpleasant than the exhaust from gasoline fuelled vehicles.

It is likely that many of these results and experiences can be referred to the difference incombustion process between the spark ignition engine (otto engine) and the compressionignition engine (diesel engine). On the other hand there are, or at least were, emissions whichcould be linked to components in the fuel. Not many years ago there were compounds withlead in gasoline in Sweden and additives are still used in gasoline in many other countries. Itcan also been underlined that gasoline contains benzene and other harmful hydrocarbons ofwhich benzene is regarded as a carcinogen. Therefore it is wise to handle gasoline as a poisonand also to be careful so as not to let gasoline touch the skin or to breathe gasoline vapor.

Table 1. Environmentally classified parameters and components in gasoline in Sweden(MK1).

Parameter Unit MK 1 ”temporaryblend of gasoline”1998 - 2000

MK 1 from year 2000(the date when EU spec.2000 was implemented)

Benzene Max. vol.-% 2.0 1.0

Aromatic index Max. 5.5 -

Aromatic content Max. vol.-% - 42

Sulfur Max ppm (mass.) 100 50

Olefins Max. vol.-% 15 13

Evaporated at150 °C1 Min. vol-% 75.0 75.0

Additives Not ash forming Not ash forming

Source: STATOIL, Sweden.

The organic lead components belong to a group of additives which are regarded as the mostpoisonous components in gasoline. The existence of these organic lead pollutants in theenvironment was the main reason in Sweden for reducing lead additives in gasoline from 0.80to 0.85 g/liter before 1970 to 0.70 from 1970, 0.40 from 1973, 0.15 g/liter 1980/81. “Green”(i.e. unleaded) regular gasoline was introduced year 1986 and 1995 the use of lead in gasolinewas forbidden. Similar actions has been taken also in many other countries around the world.Later on the lead was faced out completely in the so called lead-free gasoline because leadwas proven to be a poison for catalysts. Up to around the middle of the 1990’s there were one

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or two blends of “green” gasoline in Sweden containing approximately 0.07 g/liter of leadadditives. After that time another additive not containing lead (as used of lead was forbidden)has been used (see the second paragraph after this).

Concerning the lead-free gasoline it can be of interest to know that even this gasoline maycontain small amount of lead as long as leaded gasoline is distributed, due to the a risk forcontamination during distribution of the fuel. The distribution lines for unleaded gasoline maynot have been completely separated from those used for leaded gasoline. Therefore theconcept “lead-free” is not relevant - a more adequate concept should be “unleaded gasoline”.Commonly the requirement for the non-leaded gasoline was that it should not contain morethan 0.013 g lead per liter gasoline. Since no leaded gasoline exists in Sweden the blend ofunleaded gasoline of today may be completely lead-free.

There were two reasons for using lead-additives in gasoline of which one was that the octanenumber was increased and the second was that the valves in the engine were lubricated bylead. When the oil companies in Sweden decided to not use lead-additives in gasoline thisadditive was replaced with other additives – containing sodium or potassium - of whichpotassium was preferred since sodium gave high-temperature corrosion in the engine’s turboaggregate. The opinion in the oil industry is that most of the cars in Sweden do not need anyspecial lubrication for the valves and therefore they have decided to stop the blending oflubricating additive in gasoline. The replacement this time will be bottles containing apotassium additive, available at gas stations, which the owners of old cars can use whenfilling up gasoline.

As already mentioned gasoline consists of a mixture of different hydrocarbons as can be seenin Table 1. One of the requirements for a good function of gasoline is that the motor octanenumber and the research octane number are high. For the Swedish unleaded (green) gasolinethe research octane number has to be at least 95. For some years the oil companies in Swedenhave provided the market with a premium gasoline with a research octane number of 98.Since the use of octane-increasing lead-components in the gasoline for catalyst carsintroduced at the end of the 1980s was not allowed, oil companies had to use high octanecomponents, such as isomerized hydrocarbons, at a higher rate than earlier. Aromatichydrocarbons such as benzene and others also have a high octane number. The content ofthese hydrocarbons tended to increase and especially when 98 octane unleaded gasoline wasintroduced. This was also a consequence of a higher rate of the cracking of larger and heavierhydrocarbon molecules in order to have access to lighter hydrocarbon components for theproduction of gasoline. As can be seen in Table 1 the content of benzene is limited to 1% byvolume according to EU specifications for gasoline which is an advantage.

Since a high content of aromatics in gasoline is not desirable, when striving towards a blendof environmentally friendly automotive fuels, the content of aromatics and especially benzene(in gasoline) should be kept as low as possible. However, it is obvious that there is acorrelation between certain hydrocarbons and the physical performance of the fuel such asbetween aromatics and the octane number of gasoline. Therefore other hydrocarbons, whichdo not expected to give negative health effects, should be used even if alternative productionmethods have to be used. In the case of aromatics the technology for production of otherhydrocarbons such as alkylates is available but certainly more expensive and alkylates do notincrease the octane number as aromatics do. According to information (Lindberg, 2000) thecontent of aromatics in the EU gasoline have to be reduced to 35% from year 2005.

In Table 1 the difference can be seen between MK1 as “the transition quality” and gasolineaccording to the EU specification (the present day MK1 gasoline in Sweden) which has amaximum content of 42 % by volume (a rather high value). As noted above, benzene is a

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component which favors the octane number but despite this has been decreased. Since thecontent of aromatics in gasoline will be limited to 35% within EU from year 2005 it may bedifficult to produce since high octane the reformat used in the today’s 98 octane gasolinecontains a high amount of aromatics.

The environmental authorities in Sweden and others interested in the environment have seen itas important to keep the vapor pressure of gasoline as low as possible in order to limit theemission of evaporated fuel. However, the petroleum and car industry maintain that the vaporpressure must be kept at a high enough level enough to avoid cold start problems of especiallyold cars and this has resulted in the vapor pressure being considerably higher in the Swedishgasoline than in gasoline in, for example, USA.

5.1.3 Diesel oil

There is also an environmental classification for diesel Sweden. Diesel oil is divided intothree classes, MK1, MK2 and MK3 of which MK1 is defined as the most environmentalfriendly diesel oil. The environmental classification was implemented many years ago inSweden and this has resulted in the stability of the system today. Preceding the classification,extensive investigations took place of more than ten different blends of diesel oils. Theinvestigations clearly showed that there was a considerable potential in a new moreenvironmentally directed specification of a diesel fuel. A decision could therefore be takenand the environmental classification was implemented without any delaying discussions. Thisled also to MK1 taking a large part of the market after only a few years. It should bementioned that a part of the success of MK1 was that the introduction was supported by a taxincentive. The following requirements are valid for the different classes of diesel oil, seeTable 2.

Table 2. Environmentally classified parameters and components in diesel oil in Sweden(MK1, MK2 and MK3).Parameter/component MK 1 MK 2 MK 3Density at 15 °C, kg/m3 800-820 800-820 All ofCetane index !50 !47 other

Distillation, IBP, °C 180 180 standardized

Destination, 95 %, °C 285 295 dieselAromatics, vol.-% "5 "20 fuelsPAC in aromatics, vol.-% 0.02 0.1 on theSulfur, mass-% "0.001 "0.005 market

Source: The Swedish Environmental Protection Agency

Even within EU there has been a development of diesel fuels during recent years and newstandards have been worked out and implemented even if these not as far reaching as theSwedish standards concerning the environmental improvement of diesel oil. The parameterswhich EU have given highest priority to, i.e. have seen to be most important to change, are thecetane number and the content of sulfur. According to the today’s standard the maximumcontent of sulfur in the fuel is 350 ppm (0.035 %) by weight, but a decision has been taken inorder to limit the content of sulfur to 50 ppm (0.005 %) by weight from year 2005. Because ofthe negative effect of sulfur on catalysts (especially DeNOx catalysts), there is a demand fromthe car industry that the content of sulfur should be reduced to 30-35 ppm (0.0030-0.0035 %)by weight or as low as 5 ppm (0.0005 %) by weight.

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Diesel oil has also been improved in many other countries. This started in California manyyears ago, but according to received information the environmental authorities in someeastern countries in the Far East and at least in Hong Kong have taken or will take actionswhich will lead to a reduction in sulfur content. A driving force for the reduction of sulfur isthe need to reduce the emission of particles from diesel fueled engines. The Europeanemission standards for diesel fueled heavy-duty engines are such that emissions have to bereduced to a level not regarded as possible some years ago. By this it seems necessary thatnew and very much improved diesel fuel will be introduced on the market.

In this context it should be mentioned that in the early 1990’s a trial of synthetic diesel oil wascarried out in order to prepare for the introduction of that fuel on the Swedish market.However, this attempt failed for at least two reasons. Firstly this synthetic diesel oil, whichcould in fact have reduced the particulate emissions and certain other emissions such aspolycyclic aromatic hydrocarbons if used properly, required an adjustment of the fuelinjection pump in order to increase the fuel flow and thereby achieving the same power outputas when using commercial diesel fuel. On the other hand this should have resulted in a smokyengine when commercial fuel was used, which could happen quite often since the syntheticdiesel oil was not distributed over the whole market in Sweden. The other reason for thefailure of the introduction was that the synthetic fuel did not fulfil the requirements set forMK1 diesel fuel which meant that this fuel could not benefit from tax incentives from theGovernment.

5.1.4 Liquefied Petroleum Gas (LPG)

LPG as Liquefied Petroleum Gas is commonly called is one of the standardized automotivefuels and it must therefore meet the requirements concerning, among other things, the amountof the different of gaseous hydrocarbons – mostly propane and butane - specified in thestandards. In Sweden the Standards Institute (SIS-STG) has adopted the standard for LPGcalled SSEN 589, which is also a European standard. According to the earlier standard forLPG, SS 115 54 20 the content of propane should be at least 70 %, the content of olefins notmore than 10 % and the content of certain heavier hydrocarbons (C5 and heavier) should be amaximum of 15 % or a little more. In addition the old standard required a maximum and aminimum value of the vapor pressure. In the today’s standard (SSEN 589) the maximumvalue for vapor is 1550 kPa. The minimum value for vapor pressure is 250 kPA has beendefined for four limit temperatures: Class A: -10 °C, Class B: -5 °C, Class C: 0 °C and ClassD +10 °C and in Sweden Class A has been applied.

There are two particular reasons for having certain requirement concerning the vapor pressure.First of all it is important to keep the vapor pressure as low as possible in order to restrict theevaporative emissions and secondly there must be a sufficiently high pressure in the gaseousfuels so that the fuel will flow into the engine as long as the fuel (liquefied LPG) is notpumped into the intake manifold of the engine. The composition of the gas must be such thatthe engine can be started and that the vehicle can be driven even at low temperatures. Themain reason for the limiting of olefins in the gas is that olefins form deposits in the fuelsystem and the engine. During the 1970’s it was popular to use LPG in Sweden, especially intaxi cabs, as a consequence of there being a lower tax for LPG than for gasoline. However therate of the tax was changed later on and this resulted in LPG was not being used to a sufficientextent to keep filling stations open and today LPG seems not to be a popular fuel in Sweden.

There are many reasons for a very limited use of LPG in Sweden. There is no existinginfrastructure for the distribution of LPG and it is not clear whether there are any economicadvantages in the use of LPG. The vehicle has to be equipped with a special fuel system and it

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is likely that many car owners would prefer to have one fuel system for LPG and one forgasoline if LPG was going to be used. In cases where the car is converted so as to add a LPGfuel system the gas tank may be placed in the luggage compartment. It is also uncertainwhether the use of LPG will be favorable in terms of emissions especially in cases where“green” gasoline is available. In Sweden there have been incidences where a LPG fueledindustrial truck has been used in halls for ice-hockey resulting in people, especially theplayers being poisoned from the emission of NO2. However, industrial trucks used for loadingand unloading ships are often LPG-fuelled even if many of these trucks have now beenreplaced with electric powered industrial trucks.

In order to sum up the discussion concerning the use of LPG it should be underlined that thereis a good potential for achieving low emission levels if a proper technology is used for theadaptation of the vehicles to LPG. First of all the equipment used for LPG and also the enginemust be dedicated for LPG and secondly the emission control system, including the catalyst,must be developed so as to be able to be used for LPG fueled vehicles. During recent yearsfuel systems have been developed with a function similar to fuel systems for today’s gasolinefueled vehicles.

5.1.5 Natural Gas

Natural gas has a clear potential for being a more friendly automotive fuel than both gasolineand diesel oil, despite the fact that its use contributes to problems caused by greenhouse gases.These greenhouse gases are mostly carbon dioxide, emitted also by other fossil fuels and, inthe case of natural gas, even methane. Up to now, however, the development has shown thatthere are certain technical difficulties in using gaseous fuels compared to the use of liquidfuels. This leads to the conclusion that there is a need for basic research and development ofengines and the emission control system for the use of natural gas. However, the use ofnatural gas for engines in series hybrids can be estimated to be easier than its use in non-hybrid vehicles because it is no pronounced need for transient operation of the engine in aseries hybrid.

In Sweden it is a clear disadvantage in the use of vehicles fueled with natural gas, since thereis no existing infrastructure for the distribution of natural gas in the main part of the country.The future for natural gas in Sweden is uncertain because no decision has been taken in orderto build up a distribution system. It is true that natural gas is available for automobile use inthe Southwest of Sweden but this distribution can only be maintained due to the fact that themain part of the gas is distributed to the industries in the area. It can also been said that nofirm price of the natural gas used in vehicles has so far been decided. The price to be paid bydriver of the car seems not to reflect the cost of the gas but is more or less linked to the priceof the commercial fuels, especially gasoline. It is therefore not possible today to judge whatthe price of natural gas will be for the motorist, when more commonly used.

Natural gas is estimated to be mainly a result of the decomposition of organic material butsome events have indicated that natural gas also exists deep down under of the earth’s crustand that this gas is not a result of decomposition of organic material. If this is true, then thereexists a huge quantity of natural gas in different parts of the world. However, even without theabove mention natural gas under the earth’s crust, a great amount of natural gas can be found.

Natural gas contains mostly methane but, depending on the well of the gas, it may contain upto 10 % or more of other saturated hydrocarbons such as butane, propane and ethane and evenother combustible gases. Unfortunately natural gas also contains components which are to beregarded as pollutants, i.e. such a an amount of sulfur compounds that the gas has to becleaned if used in for example fuel cell vehicles. Helium, which after hydrogen is the most

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common element in the universe, is extracted from natural gas by lowering the temperature ofthe gas under high pressure.

As already has been mentioned, the composition of natural gas varies from source to source.The Danish gas found in the North Sea has the following composition, especially of thefollowing hydrocarbons and carbon dioxide and nitrogen see Table 3.

Table 3. Composition of the Danish natural gas from the North See.COMPONENT CONTENT %Methane, CH4 91.6Ethane, C2H6 4.7Propane, C3H8 1.8Higher hydrocarbons 1.1Carbon dioxide, CO2 0.5Nitrogen, N2 0.3

Source: The Swedish National Encyclopedia.Most of the huge quantity of natural gas can be found in the areas shown in Table 4. Thegreatest quantities can be found in Qatar (a peninsula in the Persian Gulf) and in Russia butalso in the Far East, Africa and North America there are large amounts, as can be seen in thetable. The production of natural gas was, according to BP 1 785.8 million tons in oilequivalence per year under the period 1988 – 1992, which is equal to approximately 50 % ofthe production of oil.

Table 4. Natural gas in the world – resources, production and ventilated/flared, year 1997.Region Access*

Billion m3ProductionBillion m3

Ventilated/flaredBillion m3

North America 8 442 734 15 (~1.6 %)Central and South America 6 272 83 16 (~12.2 %)Western Europe 4 525 280 4 (~1.3 %)Eastern Europe and previousUSSR

53 903 701 No amount declared

Middle East 48 727 171 26 (>9.3 %)Africa 10 059 102 47 (~21.3 %)Far East and Oceania 12 355 243 Incomplete

declarationTotal in the world 144 284 2 314 ----

Source: US Department of Energy. *Amer. billion = 109 (1 000 000 000).

The proportion of natural gas in the total energy consumption varies considerably fromcountry to country. In the Nordic Countries about the same amount of natural gas is consumedin Finland (gas from Russia) as in Denmark while Sweden consumes only a small part.Norway has a proportionally large production of the natural gas in Europe but it scarcely usesany of the gas itself at least up to now.

5.2 Flexible fuels

Flexibly produced automotive fuels are in this report characterized in that their production canbe based either on a fossil stock, primarily natural gas, or renewable raw material. The fuelsdiscussed in this report are methanol, DME, synthetic gasoline, synthetic diesel oil and

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hydrogen. According to the definition used here even ethanol should be discussed here.However, the production of ethanol for use as automotive fuel is almost entirely based onrenewable raw material and it will be discuss under the heading “Non fossil fuels”.

The Fischer-Tropsch process is used for the production of synthetic gas from different rawmaterials or fossil stocks. These can be coal, natural gas but also bio-based material such aswood (wood products), rubbish, waste, refuse manufacturing losses or other materials built ofmolecules containing coal. These material are suitable for the production of other liquid fuels,other than methanol which today commonly is produced from coal and and/or natural gas.Gaseous fuels such as DME, which is a gas at normal pressure and temperature, and also othergases, can be produced, in addition to liquid fuels.

The synthetic gas produced by the Fischer-Tropsch process can be used for the manufactureof different chemical products of which automotive fuels are one group. One advantage ofthese fuels is that they contain almost no impurities and have a well-defined compositionsince the production process essentially can be tailored with regards to which product is to beproduced.

5.2.1 Methanol

Methanol (CH3OH) is, as in the case of ethanol (C2H5OH), well defined, independent ofwhether it is produced from, for example, natural gas or is based on renewable raw material.Therefore there is no reason in this context to differentiate between the function of the fuelswith respect to the base material used for their production. To be correct, methanol producedfrom renewable material should be discussed under the heading “Non-fossil fuels”. However,there is an important difference, depending on the material used for production, in thatmethanol produced from a fossil material contributes to a larger extent to the greenhouse gasCO2 than methanol produced from renewable materials.

The Fischer-Tropsch process is used for the production of methanol and it is usually based onnatural gas. Franz Fischer and Hans Tropsch developed the Fischer-Tropsch process inGermany 1925. The original use of the process was to produce gasoline from coke or lignite.According to received information, the last Fisher-Tropsch plant in Germany closed in 1992.

In South Africa where there is a huge supply of coal the company Sasol has used the Fischer-Tropsch process for many years and today both gasoline and diesel fuel are produced there.It was the long lasting embargo against South Africa which resulted in the starting up of theproduction of automotive fuels, and Sasol has been known worldwide for their use of theFischer-Tropsch process. A byproduct of the production of gasoline and diesel oil accordingto the Fischer-Tropsch process is alcohols, for example ethanol. Some time earlier ethanolwas mixed into gasoline and during a period when Brazil was short of ethanol this alcoholwas exported to Brazil. According to received information (Ahlvik, 1999) Sasol has decidedto return to the routine of blending ethanol in gasoline. It is well known that the Fischer-Tropsch process is used also for the production of methanol. Today the Fisher-Tropschprocess is used for production of automotive fuels, for example synthetic gasoline and dieseloil also from bio-based raw material. It should also been mentioned that two modifiedFischer-Tropsch processes for the use of natural gas have been developed and studied(Borgwardt, 1998). These studies have shown that the production of methanol can be moreefficient in the future.

The use of methanol is briefly discussed under section 6.3.2. A comparison of different fuelsis shown in Table 6.

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5.2.2 Dimethyl ether (DME)

The process for production of DME was developed by Haldor Topsoe A/S (Denmark) andaimed at a production of DME as a propellant gas instead of CFC, which is not commonlyused today as it is regarded as a strong greenhouse gas. By a co-incidence it was discoveredthat DME could be advantageously used as a fuel for compression ignition engines. DME hasa high cetane number and the use of DME has been demonstrated to result in low levels ofespecially oxides of nitrogen and particles. Despite DME having such physical qualities that itcan be compared with LPG (is a liquid at a moderate pressure) and despite its having created amanifested interest within the car industry, DME has not yet succeeded in being used as anautomotive fuel. During the development of engines to be used for DME unexpected problemwith fuel injection system occurred and this is certainly one reason for engines fueled withDME not having been introduced. However, according to the Volvo Bus Company, there is agood chance that engines adapted to the use of DME will be a success if governmentalauthorities support the development of such engines.

5.2.3 Synthetic gasoline and diesel oil

It is well known that synthetic gas can be used for the production of high-octane alkylgasoline (not described here) for otto engines and a high cetane diesel fuel containing almostonly paraffins, to be used in compression ignition engines. A clear advantage of this fuel isthat it does not contain sulfur and therefore the emission control technology with catalysts caneasily be used. Also this fuel does not lead to the formation of such as high rate of particles ascommercial diesel oil.

Because the above mentioned fuel commonly has a low density, present day diesel enginesmay have to be adapted to the fuel in order to maintain the power output from the engine. Thisproblem does not need to be permanent if the diesel engines are developed so as to tolerate avariation of the fuel and thereby also the density of the fuel.

The question is open as to whether there will be a place on the market for fuels produced fromnatural gas according to a method, which a Consultant within the oil industry has developed,based on the Fischer-Tropsch process (Syntroleum 1, 1999). In a press release from the 5th ofJanuary 1999 (Syntroleum 2, 1999) it is declared that Syntroleum’s fuel is produced by usingthe company’s process for converting natural gas to synthetic liquid hydrocarbons which donot contain sulfur and aromatics. These components commonly exist in petroleum-based fuelsand both sulfur and aromatics cause emissions of unwanted pollutants. In addition sulfur iscreates problems in the emission control system. According to Syntroleum their fuel also hasthe advantage that it can be used in present day engines without modifications and that it canbe distributed by the existing distribution system.

According to Newsletters from both US Department of Energy (DOE) and US EnvironmentalProtection Agency (EPA) it can be seen that both of these authorities are interested insynthetic fuels, among others synthetic diesel fuels. It can also be said that a Swedishcompany Oroboros AB has plans for producing synthetic automotive fuels (bio-alkyl-fuels, agasoline fuel, and a bio-paraffin, a diesel fuel) from wood. However, it seems not to be clearwhether there will be a market for such fuels if the cost of the fuel is considerably higher thanthe cost of the commercial fuels available today.

For hybrid electric vehicles of the future equipped with fuel cells it is estimated that the accessto synthetic fuels may be important if these are hydrogen rich. As mentioned above there is anincreasing interest in the USA in the possibility of producing synthetic fuels since the need forimporting oil and petroleum fuels been growing (approximately 60 % today). From reportsand notices in the literature the conclusion can be drawn that there are plans within DOE to

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study the economic and environmental aspects of producing liquid synthetic fuels fromnatural gas and coal. As can be seen from Table 4 the access to natural gas is huge and,according to received information, the amount of natural gas in energy terms is larger than theaccess to crude oil. One disadvantage of the production of synthetic fuels from natural gas andcoal is that it is likely that this will contribute to an increasing pollution by greenhouse gasesand other pollutants.

In the USA as in some other countries it is a large access to coal but also in Alaska there arelarge resources in natural gas. These resources are of course of vital importance today but thegas is not easy to transport as a gas from Alaska to the central of the USA. Therefore DOE hassaid that “Advances in Chemical conversion of natural gas suggest an add option for ANS(Alaska’s North Slope) to market. Using chemical GTL (Gas-to-Liquids) technology, the gascould be converted into a petroleum-like liquid that is more easily transported via oil pipelineand tanker to market”. According to received information the reserve of natural gas in theUSA is about 4 680 billion cubic meter. Not yet discovered reserves of natural gas aresupposed to be larger than the reserves of crude oil.

5.2.4 Hydrogen

The use of hydrogen as an automotive fuel is not yet common but is likely to increase in thefuture. Primarily the intention is to use hydrogen for fuel cells but there is also an intention touse hydrogen in internal combustion engines. The use of hydrogen in internal combustionengines (otto engines) has a potential of drastically decreasing the emission of all pollutantsexcept for oxides of nitrogen, as long as air is used as the oxygen supply for the combustion(air contains a high proportion of nitrogen). The high combustion temperature when usinghydrogen will contribute to the formation of nitrogen oxide and therefore the oxide ofnitrogen can be even larger compared to the emission when using gasoline. Provided that theengine is fed with hydrogen and oxygen the emissions will be close to zero but then it must berealized that there is a higher risk for explosion when hydrogen is mixed with oxygen (limitsfor explosion 4.7-94 % hydrogen in oxygen) compared with air (5-75 % hydrogen in air).

The produced of hydrogen can either be petroleum based or based on renewable material.Therefore hydrogen can be classified as flexible fuel. Today it is most likely that it is mosteconomic to produce hydrogen from natural gas in stationary establishments. Among thosewho are interested in the use of hydrogen as an automotive fuel there are expectations thathydrogen will be produced at current market prices. It is possibly that energy from the sunwill at that time be more directly used for the production of hydrogen, and it will then beproduced by electrolytic decomposition of water. If the production of hydrogen could bebased on by electrolytic decomposition or some similar technology it is likely that there willnot be any shortage of energy.

For fuel cells there is a discussion going on as to whether hydrogen will be produced byreforming, for example, methanol from natural gas on board the vehicle or in stationaryestablishments. There are many problems to be solved before an efficient production,distribution and storage of hydrogen can be realized and on board the vehicle there are alsoproblems to be studied in order to solve problems concerning the technology, economy andsafety. It is certainly more efficient to produce hydrogen in stationary establishments than onboard of the vehicle but if producing hydrogen in stationary establishments the problem withdistribution has to be solved. According to a report from the Swedish Technical Attachés(KFB, 1999:30) trials with hydrogen are going on in some parts of the world – among othersat BMW in Germany in internal combustion engines.

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In Germany Shell has established a station for hydrogen in Hamburg and also started researchon reformers for the production of hydrogen from gasoline in co-operation with, amongothers, DaimlerChrysler. At Munich airport Aral has assisted in the establishment of a stationfor hydrogen to be used in buses and cars.

In the USA a station for hydrogen has been opened in Chicago and Illinois. These stations areused in a trial aimed at a study of tanking hydrogen in buses equipped with fuel cells. Fordhas opened a station for hydrogen in Dearborn, Michigan. The station is linked to theirresearch and development of fuel cells and internal combustion engines and it is equippedwith two pumps for liquefied hydrogen and one pump for gaseous hydrogen. The aim is,among other things, to study in which form hydrogen should be filled up in the car (liquefiedor gaseous). An addition plan, according to Ford, is to study which type of nozzle should beused and also the most suitable pressure in the fuel line during filling up. The cost of theestablishment was $1.5 million inclusive of the construction, erecting, renting of equipmentand supply of hydrogen under five years.

In an article in (The Hydrogen & Fuel Cell Letter, 1998a) the plans for a co-operationbetween the Government of Island, DaimlerChrysler and Ballard Power Systems is describedand the aim for the co-operation is to establish a hydrogen economy in Island within 15 to 20years. One of the first steps is to carry out tests by using one of the hydrogen fueled busesdeveloped by Daimler-Benz within one or two years. At the same time both sides of thepartnership have to begin studies in order to investigate the impact on Island’s economy of thetransformation of the country to a hydrogen-economy. According to the plans the aim of theconcept is to convert Island’s very large fishing fleet – Island’s most important industry – forthe use of fuel cells and to produce hydrogen locally. In addition the intention is that thecountry’s cars and buses gradually will be converted so as to be able to be fueled withhydrogen or methanol. The possibilities of producing hydrogen or methanol in Island forexport to other countries are also to be investigated.

5.3 Not fossil fuelsFuels based on bio-based material produced in Sweden today are ethanol, biogas and to a notcertain degree some Rapeseed Methyl Ester (RME). The potential for future production ofrapeseed oil in Sweden is strongly limited. The question whether methanol should beproduced from wood instead of ethanol has been discussed and is still open even if thereseems not be any great interest in starting a production of bio-methanol. On the other handsome new ideas have been presented in that as already has been mentioned the company,Oroboros AB has announced their intention to establish a production of bio-alkenes. There isalso an investigation presented by KFB regarding production of bio-DME. Both of these twofuels can be produced by gasification of wood or some other biomass and the sametechnology can be used also for production of bio-methanol. Technology for production ofvarious bio-fuels is available and therefore it is more or less a question of economy, access tonatural resources and a market for the above bio-fuels whether a production should beestablished or not. Sweden is a proportionately small country and therefore there is no marketfor many of such fuels which are not established on an international market.

5.3.1 Biogas

One advantage of the production of biogas is that the production is based on sludge fromwaste water purifying plants, slaughterhouse waste, waste from food industries andrestaurants, waste from households and even farmyard manure. Almost all that is used for theproduction of biogas is such that society regards as waste, to be got rid of. It can, however, beused for the production of biogas to be used in industries and as an automotive fuel. Even

33

crops such as grass and clover can be used, but in this case the gas will be more expensivecompared with the use of waste. Another advantage of biogas is that methane, the main part ofthe gas, which is a result of putrefaction, can be used instead of being emitted to theatmosphere, which would otherwise add to the greenhouse effect. Before using biogas as anautomotive fuel it has to be cleaned from carbon dioxide and other unwanted components.Table 5 shows the result from an analysis of cleaned biogas. Table. 5. The composition of purified biogas according to an analysis.

Component Unit ConcentrationOxygen Vol-% <0.5Nitrogen Vol-% 0.5Methane Vol-% 97.5Carbon dioxide Vol-% 2.0Hydrogen sulfide ppm <25

The use of biogas is in principle equal to the use of natural gas since the engine does not needto be recalibrate and the function of the engine is the same as for natural gas as long as thebiogas meets the specifications. One drawback of the use of biogas is that the availability islimited. This means that the number of vehicles adapted to the use of methane must bematched to the availability of gas, as long as no natural gas is available or an alternative fuelcan be used in the vehicle. In Stockholm where biogas is mostly used in light duty vehicles(passenger cars and vans) the vehicles are adapted to the use of a bi-fuel which in this case isgasoline. Another drawback is that the use of biogas is usually limited to a certain area such asa town or some other populated area. As in the case of natural gas biogas is not easy todistribute over larger area and in Sweden its cost is somewhat unclear. Today the price of thebiogas seems to be somewhat lower than gasoline in terms of energy equivalence.

5.3.2 Ethanol and methanol

At the present time ethanol is commonly produced by using a long-known fermentationprocess by which wheat, corn, cane sugar, grapes and cellulose are the basic raw materials. Anew method is under development where enzymes are going to be used in the process for rawmaterials cellulose containing. Work towards developing the process is underway at theUniversity of Lund in Sweden and a large amount of development work is also taking place atthe National Renewable Energy Laboratory (NREL) in Colorado, USA. If this ongoingresearch is successful it is expected that the production of ethanol will become much moreefficient thereby reducing the production costs which, at the present time, are regarded asbeing too high.

It has already been mentioned above that gasification of wood is the first step in the processfor the bio-based production of methanol, the next step being the production of synthetic gas.The synthetic gas is then further processed by using the same technology as for production ofmethanol natural gas via synthetic gas.

The alcohols, ethanol and methanol, have since long been used on both a smaller scale(Sweden and in some other countries) or on a larger scale (Brazil and the US) - in Brazil onlyethanol, but in the US methanol but mostly ethanol. They have been used both as neat fuelsand mixed into gasoline (or in diesel oil for some test fleets). In an international overview itcan be seen that ethanol is far ahead of methanol in its amount of use. However, both thesealcohols can be used as automotive fuels without too many intricate problems. On the otherhand there are some differences between ethanol and methanol, which may have to be takennotice of when adapting vehicles and the distribution systems for the use of an alcohol fuel.To take a few examples – the use of neat ethanol in Sweden requires that it be denatured while

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this is not necessary when using neat methanol. Whereas denaturalization is specificallyrequired for ethanol the distribution of methanol also requires special precautions because ofits poisonousness. The authorities in California have thus worked out special instructions andrecommendations for the handling of methanol (Egebäck et al., 1998).

It should also be added that representatives from Ford in the USA and also from the buscompany Metropolitan Transit Authorities (MTA) think the problems of corrosion of theengine is more severe when using methanol than when using ethanol (Ford, 1995; Karbowskiand Davis, 1995). However the problem of corrosion can certainly be solved.

When considering the international situation of today there appears to be a difference in theview about methanol contra ethanol. For different reasons (agricultural-political) there seemsto be a preference for ethanol among the authorities in some countries and even among manyof the more or less independent actors. On the other hand there are, in an international view,some strong spokesmen voting for the use of methanol instead of ethanol and it is thereforenot easy to see what will happen in the future. It must also be taken in account that methanolcosts less to manufactured today, since its production is based on natural gas and in thiscontext it also should be considered that there seems to be a preference for methanol amongthose involved in the development of fuel cells. However, in Sweden there is a strongmovement towards the use of renewable fuels, both among politicians and other authoritiesand it therefore seems unlikely that the production of methanol from natural gas will bepromoted. A decision may be taken in the future concerning the production of ethanol ormethanol on a larger scale, based on renewable raw material.

Technically there are no special obstacles in using an alcohol as a fuel for a hybrid vehicleequipped with an internal combustion engine. On the contrary, the potential is better from thepollution point of view, for using a renewable fuel such as ethanol, methanol or biogas forhybrid vehicles. This is especially true when replacing a diesel fueled engine, since this wouldlead to a reduction in the emissions of particles, oxides of nitrogen and carbon dioxide, if arenewable fuel were used. In Sweden it may be advantageous to use ethanol since there arevaluable experiences in the use of ethanol and there is also an initial infrastructure fordistribution of ethanol. However, since it is still unsure whether ethanol or methanol is goingto be used it could be wise to adapt the fuel distribution system to the use of either methanolor ethanol.

Both ethanol and methanol have been used as fuels even in compression ignition engines andtoday there are many buses in Sweden equipped with compression ignition engines which useneat ethanol. In order to use neat ethanol in a compression ignition engine which is notequipped with an ignition aid, such as glowplugs or sparkplugs, it is necessary to use anignition improver in the fuel since the cetane number of ethanol is as low as 9. The ignitionimprover used in Sweden is a Polyethylene Glycol (PEG) also called Beraid! and the contentof this ignition improver is 7 vol-% and in addition 3 vol-% of a denaturating agent is blendedinto the fuel.

5.4 Summary of automotive fuels

A summary of certain fuel parameters for methanol, ethanol, gasoline, diesel oil, natural gasand DME (dimethyl ether) is shown in Table 6. An estimate of the use of different fuels forfuels cells is illustrated in Figure 4.

Table 6. Summary of physical and chemical characteristics of various engine fuels.Type of characteristic Methanol Ethanol Gasoline Diesel CNG 2DMEChemical Structure CH3-OH CH3-CH2-OH - - CH4 CH3O-CH3

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Molecule mass [g/mole] 32.04 46.07 ~100 - 16.04 46.07Elementary composition (mass)% oxygen% carbon% hydrogen

50 %37.5 %12.5 %

34.752.213.1

(mix of C4to C14

hydrocarb.)

(mix of C6to C14

hydrocarb.)

074.925.1

34.852.113.1

1Density, (kg/l) vid 15 °C, (kg/m3) at 0 °C 0.793 0.791 ~0.72-0.75 ~0.80-0.85 0.7171) 0.6772)

Octane number (Research)* 1113) 1083) 95-98 - 130 -Cetane number 5 8 - 47-50 - >>55Stoicheiometric A/F** 6.5 9.0 14.8 14.6 17.2 9.0Dissolvable in water [mg/L] soluble soluble Somewhat

solubleSomewhat

soluble- ?

Vapor pressure (kPa), at 38°C 32 ? 45-95Lower Calorific Value [MJ/kg] 19.5 27.1 ~43-44 ~43 50 27.6Boiling Point [°C] 65 78 ~25-225 ~180-300 -161 -20Vaporizing temp. (kJ/kg) at 20 °C 1110 904 ~180 ~250 - 410Auto-ignition Temperature, (°C) 450 420 ~ ? ~250 650 235Flash Point (°C) 12 ? 6 ~70-75 ? ?3Explosion Limits (% Gas in Air) 5.5-26 3.5-15 ~6.0-36.5 ~0.6-6.5 5-15 3.4-18

1kg/m3 (0 °C), 2) kg/l (15 °C) Observe that DME pass over in vapor phase at ca -20°), 3)Differentvalues exist.In Figure 4 an estimation of disadvantages and advantages are shown concerning fuels such asnatural gas, methanol and gasoline for when they are intended to be used in fuel cells.

Figure 4. Estimation concerning the use of various fuels in a fuel cell. Source: Sasaki, 1999.

* The octane number which is stated on the gasoline pump at the gas station.** ”Air/Fuel ratio in the fuel mixture to the engine (kg air per kg fuel).

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6 ENGINES – POWER UNITThe hybrid systems described in chapter 4 are mainly equipped with conventional internalcombustion engines as one of their power units. Radical changes of these engines have notbeen discussed. In the case of hybrid electric vehicles alternative engines are discussed as areplacement of conventional engines. Fuel cells are also an alternative in the long run and thedevelopment of fuel cells will be discussed in Section 6.4. Since the alternative internalcombustion engines have not yet been fully developed and they cannot be regarded ascommercial, their potential for improved fuel economy is still somewhat unsure. However,certain indications concerning the magnitude of improvements can be seen for some of thehybrid systems. Since it will take a long time (approximately 10-20 years or more) beforeother alternatives than internal combustion engines (such as fuel cells) can competeeconomically as power units, all the alternatives should be compared with a further-improvedinternal combustion engine for use in a hybrid vehicle.

Most types of internal combustion engines can also be fueled with alternative fuels. Thechoice of power unit influences the potential for alternative fuels and the influence isconsequently not the same for alternative power units as for conventional power units. Thepower unit and the fuel to be used must therefore be considered as a whole. In existing hybridsystems an otto engine or a diesel engine is used as an energy transformer for liquid orgaseous fuels. Since these engines are commonly used in hybrids, an otto engine will besomewhat closer described in Section 6.1 and a diesel engine in Section 6.2. In Section 6.3some alternative engines will be described and in Section 6.4 the most common types of fuelcells will be described.

In addition to the rather short descriptions of otto engines and diesel engines two alternativeengines, the Stirling engine and the gas turbine will be discussed. However, the estimation isthat neither of these two engines will be used to any great extent in hybrid vehicles. Since fuelcells are being widely discussed with great interest a rather extensive description is givenbased on available literature. Despite there being some prototype vehicles equipped with fuelcells, it is estimated that hybrid vehicles with fuel cells will not be common in the streetsduring the coming 10 to 20 years, even if an introduction of such hybrid vehicles will be seenearlier.

6.1 Otto enginesThe otto engine has gone through many transformations during time it has existed. HenryFord, who started mass production of the engine, was of the opinion, at least during oneperiod, that the engine should be fueled with ethanol. However, gasoline replaced ethanol andfor the last 70 years gasoline has in reality been the dominant and almost only fuel for ottoengines except for in some countries during the Second World War when the shortage ofgasoline made it necessary to use other fuels.

A new era for the development of otto engine began at the end of the 1950s when it becameobvious, especially in California, that the use of internal combustion engines created bothhealth effects and environmental problems due to their emissions. An intensive developmentof the otto engine has been carried out during the last 30 to 35 years in order to limit thepollution from the vehicles. The largest of the many steps was taken when the three-waycatalyst system was introduced in the late 1970s. The three most important parts of the three-way catalyst system are the unit controlling, among others, the fuel flow, the oxygen sensorand the catalyst both of the last two being placed in the exhaust system. Before this systemwas introduced different equipment for emission control was used mainly in order to oxidize

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CO and HC in the exhaust and among these there was even an oxidation catalyst. The three-way catalyst system is unique in that it also reduces oxides of nitrogen (in chemical terms) atthe same time as CO and HC are oxidized.

Today the otto engine is regarded as an engine with low emission levels at least when theengine is working well and is warmed up (by driving). However at low temperatures, at startand driving during the warming up phase of the engine and the catalyst, considerableemissions are released. In order to minimize these emissions, investigations and developmentsare in progress and some improvements have been achieved.

One problem of the otto engine, compared with its competitor the diesel engine, is that theefficiency is low especially at low loads and idling. This is discussed in more detail in Section8. That the low efficiency of the otto engine resulted in high fuel consumption was not seen asa serious problem, at least up to the first oil crisis year 1973. This was because the price paidfor gasoline by the car owner was low and access to gasoline not considered to be restricted.Some years later a new oil crisis appeared and the price of gasoline increased somewhat more,in addition to the increase which followed the shortage of gasoline in 1973. The price ofgasoline is now nearly 10 SKR (Swedish kronor which is between $1.10 and $1.15 at thepresent exchange rate) per liter. This has led to that fuel consumption of gasoline fueled carsis being regarded as one of the most important parameters for car owners, at least in Europeincluding the Nordic countries. However, it should be stressed that this does not mean that carmanufacturers have previously not worked on the improvement of the fuel economy but it hasnow become more important than ever. The improvement of the fuel economy is in reality thedriving force for the development of new types of power units for vehicles such as hybridsystems and fuel cells. This development is further described in the coming sections and forhybrid vehicles in Section 8.

In the previous sections and even later on, the emissions from motor vehicles are described asone of the most important disadvantages for the people’s health and for the environment. Thisconclusion can also be drawn when studying the actions taken by the authorities and oneexample for light duty vehicles is shown in Table 7, where the present day (“Euro” 3) andcoming Euro Standards are presented.

Table 7. Emission Standards for light duty vehicles EU. Source: Auto/Oil II.

GASOLINE

Designation (Year andmonth for implementation)

CO THC NOx HC+NOx PM

Euro 2* (1996-10) 2.2 (3.2) (0.341) (0.252) 0.5 -Euro 3 (2000-10) 2.3 0.20 0.15 - -Euro 4 (2005-10) 1.0 0.10 0.08 - -

EEV(option 1) 0.6 0.04** 0.04 - 0.01***EEV(option 2) 0.6 - 0.04 - 0.01***

* Test cycle with idle period of 40s before measurements ( ) Modified Dir 94/12.** Up until Euro 4 (2005) this value is derogated to 0.05 g/km.*** Note: review of the measuring procedure for particulate emissions is necessary.

One example of an otto engine, which is adapted for use in a hybrid vehicle, is the engine thatToyota has developed to be used in their hybrid vehicle, Prius. There are several reportsdescribing Prius and its engine and two of these are referred to here in this context (Takaokaet al., 1998; Hirose et al. 1998).

During the process of investigating and evaluating the different alternative of engines whichcould be used in their hybrid vehicle, Toyota carried out extensive studies of the advantagesand disadvantages of the different alternatives choices for their study. Finally the companydecided that the best alternative was a gasoline-fueled engine with fuel injection into the

38

intake ports of the cylinders of the engine. Furthermore the engine should be optimized for ahybrid system having high expansion and low friction. The opinion of Toyota was, in fact,that the gasoline fueled engine has a lower energy efficiency than some other power units, thatthis could be overcome by the design of a new engine and the hybrid system. The engineswhich was regarded to be closest to the chosen engine alternative was a diesel fueled engine adirect injected gasoline fueled engine with stratified charge.

Iwai (Iwai et al., 1998) has, in an educationally manner, described the matching between theinternal combustion engine and the hybrid system. Schematic he shows how the matchingbetween the drive train of the internal combustion engine and the hybrid system, see Figure 3(SHEV means series hybrid) should be for two different efficiencies, 77 % and 60 %, of thebattery, see also Figure 5. This comparison can also be used for a parallel hybrid system.Concerning the parallel hybrid, the opinion of Iwai is that it can be operated most efficientlyas a series hybrid at both low and high loads. This is true for the second case (60%efficiency) if the efficiency is lower than the total efficiency, i.e. when the efficiency of theengine is multiplied by the efficiency of the battery system. In connection with thisdescription, Iwai does discuss whether the battery should be loaded from the mains or by theinternal combustion engine via a generator. This question will be discussed in a later section(Section 9).

The responsible technicians at Toyota have certainly analyzed the questions and problemswhich have been discussed by Iwai. A presentation of the Toyota hybrid vehicle can be foundin Section 8 among other hybrid vehicles. Here the presentation is limited to that which hasbeen discussed about the Toyota engine for Prius and in this context only a few points will bementioned which are regarded as being the most important. There are certainly other enginesof interest to be informed about, since new inventions can now and then be found in theliterature.

Figure 5. The relationship between the displacement of the engine and its efficiency.Source: Hirose et al., 1998.

In order to reach the goal of high thermal efficiency the technicians at Toyota based theirdecisions on the following three points:

1. The only restriction for the choice of the displacement of the engine was that it shouldmeet the requirement of power and the restrictions for instability. This make itpossible to use a high-expansion-ratio cycle with delayed intake valve closing, as wellas to reduce friction loss by lowering the engine speed.

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2. In order to achieve the highest reduction of the emissions the engine had to be run at#=1 over its whole working area and a three-way catalyst system had to be used.

3. Active steps had to be taken during the development in order to reduce the weight andto increase the efficiency of the engine.

The relationship between the displacement of an engine and its efficiency is shown in Figure5. As can be seen the efficiency increases with the increase of the displacement but the fueleconomy of the vehicle decreases from approximately 1500 cc and up. However, according toHirose et al. the efficiency is higher for a small engines at low load than for larger engines.

The decision taken by the technicians at Toyota was that the engine should meet therequirement set up for power output and for installation of the hybrid vehicle. This decisionmade it possible to keep to the intention of using a high-expansion-ratio cycle with delayedintake valve closing, as well as to reducing friction loss by lowering the engine speed. Oneproblem was the vibrations during start and stop of the engine. These were efficiently reducedby the use of a special arrangement of the valve in the cylinders named VVT-i (“intelligentvariable valve timing”). The engine and its specification are shown in Figure 6.

Figure 6. The specification (left) of the engine shown in the figure (right). Yaegashi et al., 1998.

Atkinson’s cycleThe internal combustion engine in the Toyota hybrid vehicle is design for the use of the so-called Atkinson’s cycle, named after its inventor James Atkinson at the end of 19th century i.e.more than 100 years ago. In a conventional otto engine cycle the compressions ratio and theexpansions ratio are nearly equal. In the original engine constructed by Atkinson a crankmechanism was used which gave a shorter crank motion for the compression than the crankmotion for the expansion, i.e. lower compression ratio than the expansion ratio. This willtheoretically result in a higher efficiency compared with a common otto engine having anequal expansion ratio. The expansion ratio for the engine in Toyota Prius is 13.5:1 while theeffective compression ratio can be regarded as being approximately the same as for aconventional engine (i.e. about 10:1)

Unfortunately it was shown that the crank mechanism used by Atkinson was too complicatedto be practical. A variant of the theme is the so-called Miller system, invented by R. Miller inthe 1940s. In this system a restriction of the compression ratio is caused by a control of theclosing of the intake valves (earlier or later). This cycle is often named the “Miller cycle”,which is not completely correct since the cycle is related to the Atkinson cycle. However theMiller system implies a simplification of the apparatus compared with Atkinson’s originalidea. Strictly speaking, it should be said the Toyota engine uses a cycle with a functionaccording to the Atkinson cycle and that the Miller system is used in order to achieve apractical use of the cycle. The Miller system is often combined with the use of a super charger

40

for the intake air in order to reduce the losses of power and torque which are a result of thereduction of the efficient compression ratio. In the case of Toyota the displacement of theengine has been increased instead of using a turbo charger.

6.2 Diesel enginesIn Section 5.1.3 in which diesel fuel is discussed it is underlined that there is an interest in theUS to use reformulated diesel fuels in order to reduce the emissions from diesel-fueledvehicles. A similar increasing interest can be found also in Europe. A great part of theincreased interest is linked to an improved fuel economy where the diesel fueled compressionignition engine is superior to a gasoline fueled otto engine. The Achilles heel of the dieselengine is the emissions. In this respect the diesel engine is far from being able to competewith the otto engine. It is true that intensive investigations and research/development aregoing on which have considerably lowered the emission levels of the diesel engines but thequestion is whether this type of engines will ever be broadly accepted even with theseimprovements. According to emission standards agreed within EU, there now seems to be afinal agreement within the EU-Commission also about the EURO 5 Standards including theEEV-Standards. As can be seen of Table 8, diesel engine are still being considerablyimproved, especially in order to meet the standards decided in California and Federal USA,meaning that the emission levels of diesel fueled vehicles will be quite low in the future.

1. EU Emission standards for passenger cars and light-duty trucks (g/km).Table 8. EU-Standards for passenger cars and other light-duty vehicles.

Source: Auto oil, 2000.DIESEL FUELLEDDesignation (Year andmonth for implementation)

COg/km

HC+Noxg/km

NOxg/km

PMg/km

Euro 2 (1997-10) 1.0 0.7 (0.9) - 0.08 (0.1)Euro 3 (2001-10) 0.64 0.56 0.50 0.05Euro 4 (2006-10) 0.50 0.3 0.25 0.025( ) DI diesel engines.

2. EU Emission standards for heavy-duty vehicles and buses. Diesel fuelled vehicles.Source: EU Directive 1999/96/EC.

Limit values – ESC and ELR testsThe specific mass of the carbon monoxide, of the total hydrocarbons, of the oxides of nitrogenand of the particulates, as determined on the ESC test, and of the smoke opacity, asdetermined on the ELR test, shall not exceed the amounts shown in Table 9.

Table 9. EU-standards for heavy-duty diesel fueled engines. Source: EU Directive 1999/96/EC.

Row

Mass ofcarbon monoxide

(CO)g/kWh

Mass ofhydrocarbons

(HC)g/kWh

Mass ofnitrogen oxides

(NOx)g/kWh

Mass ofparticulates

(PT)g/kWh

Smoke

m-1

A (2000) 2.1 0.66 5.0 0.10 0.13 (a) 0.8B 1 (2005) 1.5 0.46 3.5 0.02 0.5B 2 (2008) 1.5 0.46 2.0 0.02 0.5C (EEV) 1.5 0.25 2.0 0.02 0.15(a)For engines having a swept volume of less than 0.75 dm3 per cylinder and a rated power speed of morethan 3000 min-1."EEV" means Enhanced Environmentally Friendly Vehicle which is a type of vehicle propelled by an enginecomplying with the permissive emission limit values given in row C of the Tables 9 and 10.

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2. Specifications Concerning the Emission of Gaseous and Particulate Pollutants andSmoke. Source: EU Directive 1999/96/EC.

For type approval to row A of the Table 9 the emissions shall be determined on the ESC test(a new 13 mode steady state test procedure for diesel engines) and a ELR tests (a smoke testprocedure for diesel engines) with conventional diesel engines including those fitted withelectronic fuel injection equipment, exhaust gas recirculation (EGR), and/or oxidationcatalysts. Diesel engines fitted with advanced exhaust aftertreatment systems includingdeNOx catalysts and/or particulate traps, shall additionally be tested on the ETC test (atransient test procedure for heavy-duty engines).

For type approval testing to either row B1 or B2 or row C of the Table 9 the emissions shallbe determined on the ESC, ELR and ETC tests.

For gas engines, the gaseous emissions shall be determined on the ETC test Table 10.

The ESC and ELR test procedures are described in Annex III, Appendix 1 and the ETC testprocedure in Annex III, Appendices 2 and 3 of the EU Directive 1999/96/EC.

3. EU Emission standards for heavy-duty vehicles and buses. Diesel fuelled andgaseous fuelled vehicles. Source: EU Directive 1999/96/EC

Limit values – ETC tests (b)

For diesel engines that are additionally tested on the ETC test, and specifically for gasengines, the specific masses of the carbon monoxide, of the non-methane hydrocarbons, of themethane (where applicable), of the oxides of nitrogen and of the particulates (whereapplicable) shall not exceed the amounts shown in Table 10.

Table 10. EU-standards for heavy-duty diesel fuelled and gaseous fueled engines. Source: EU Directive 1999/96/EC.

Row

Mass ofcarbon monoxide

(CO)g/kWh

Mass of non-methanehydrocarbons

(NMHC)g/kWh

Mass ofmethane(CH4)

(c)

g/kWh

Mass ofnitrogen oxides

(NOx)g/kWh

Mass ofparticulates

(PT) (d)

g/kWh)A (2000) 5.45 0.78 1.6 5.0 0.16 0.21 (a)

B1 (2005) 4.0 0.55 1.1 3.5 0.03B2 (2008) 4.0 0.55 1.1 2.0 0.03C (EEV) 3.0 0.40 0.65 2.0 0.02

(a) For engines having a swept volume of less than 0.75 dm3 per cylinder and a rated power speed of morethan 3000 min-1.

(b) The conditions for verifying the acceptability of the ETC tests (see Annex III, Appendix 2, section 3.9)when measuring the emissions of gas fuelled engines against the limit values applicable in row A shallbe re-examined and, where necessary, modified in accordance with the procedure laid down inArticle 13 of Directive 70/156/EEC.

(c) For NG engines only.(d) Not applicable for gas fuelled engines at stage A and stages B1 and B2.

The emission standards for heavy-duty vehicles are presented in two tables, Table 9 and Table10, since there is one set of standards referring to the ESC test cycle and the ELR test cyclefor diesel fueled engines (Table 9) and second set of standards referring to the ETC test cyclefor diesel fueled and gaseous fueled engines. The decision taken by the EU-Commission issomewhat complicated and therefore it cannot be described here except concerning a fewdetails. One example is that gaseous fueled engines and diesel engines fitted with advancedemission control systems including deNOx catalysts and/or particulate traps, shalladditionally be tested on the ETC test (a transient test procedure for heavy-duty engines).

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The requirements for meeting the above presented emission standards have also resulted in adiscussion about the quality of the fuel to be used in the future. Among other requirements forthe fuels there is a strong demand, expressed by the engine and car manufacturers, that thecontent of sulfur in the fuel must be reduced to a level far under the level which is commontoday. The real cause of the demand to reduce the content of sulfur in the fuel is the emissioncontrol technology to be used in order to meet the future emission standards. The systems ofcatalysts for reduction of especially oxides of nitrogen do not tolerate sulfur, which result in afast deterioration of the system. Sulfur in the fuel will also cause problems in the control ofparticulate emissions.

Of the literature presented in the US, etc it seems to be clear that the content of sulfur in thefuel has to be reduced. Going back in history it can be said that California was first in seeingthe impact of sulfur and aromatics on the particulate emissions which lead to a requirement toreduce aromatics and sulfur in the diesel fuel. It should be underlined that reducing thecontent of aromatics will result in an increase of the cetane number which is also anadvantage. Despite the improvements of the diesel fuel and the fact that the diesel engine ismore energy efficient than the otto engine there seems to be opposition against diesel fuelvehicles in California, which has the most rigid emission standards in the world. Even in theFederal USA the interest for diesel fueled vehicles has been low among the authorities andothers caring about the environment and people’s health. However, as in other countries in theworld most of the heavy-duty vehicles are diesel fueled.

In order to reduce the emissions from these types of vehicles the possibilities of improvingdiesel fuel is under investigation in many parts of the world and especially in the US andEurope, so as to be able to use more efficient emission control technology. Extensive researchand investigations of the exhaust gas recirculation (EGR) technology in combination withother systems of filters have shown that it is possible to reduce the particle emissions to alevel of 0.01 g/bhp-hr* (ca 0.014 g/kWh). Even the emissions of NOx + HC can be reduced toapproximately 2.5 g/bhp-hr (ca 3.38 g/kWh) (Manufacturers, 1999a). Furthermore,investigations have also shown that the use of low sulfur containing diesel oil results in alarger reduction of emissions than diesel oils with higher sulfur levels. Diesel oil with 54 ppmsulfur was compared with diesel oil with 338 ppm sulfur.

Intensive research is going on especially concerning the use of catalysts for the reduction ofNOx-emissions. The different technologies of current interest are; the DeNOx technology,(”Lean-NOx”), ”NOx Adsorbers” i.e. (NOx ”Traps”) and the (SCR) technology. In addition tothese the DeNOx and SCR (selective catalyst reduction) are well known at least in Sweden bythe research carried out at the University of Lund (Sweden) whereas the technologies with”NOx Adsorbers” and non-thermal plasma are less known. Combinations between these twotechnologies also exist. In short the meaning of the NOx Adsorber technology is to oxidizeNO to NO2 and to store NO2 in order to use this component for the reduction of NOx. NOx canalso be reduced by the non-thermal plasma technology but in this case the most interestingmay be that it can be combined with DeNOX or the Adsorber variants.

Because different nitrogen-oxygen components, for example N2O (a strong greenhouse gas)can be formed and that there is a risk for an increased emission of NO2 when using thetechnology with NOx Adsorbers and the technology with plasma, it could be of interest foramong others the environmental protection authorities to follow the up the development anduse of the here mentioned technologies.

The ongoing research and investigations carried out have shown that there now exist aninterest for using strong measures in order to reduce the emissions from diesel fueled vehicles. * grams/brake horsepower hour

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If the difficulties with the diesel engines related emissions could be solved an increased use ofdiesel engines even in light-duty vehicles could be of interest for both car owners and carmanufacturers because of the fact that diesel engines are the most energy efficient vehicles oftoday. The fact that the compression ignition engine is more efficient than the spark ignitionengine could be the reason why Ford choose a diesel engine for their hybrid vehicle instead ofan otto engine (see next page and Section 8.2.4).

Some time in the future the use of a technology with compression ignition of a premixed fuel-air mixture may be developed. In principle this can be regarded as a diesel engine with lowemission levels and high fuel efficiency. The system is called Homogenous ChargeCompression Ignition (HCCI) presented in (Ahlvik and Brandberg, 1999).

In order to get an idea about the possibilities of developing a diesel engine for a parallelhybrid studied a report (Jaura et al., 1998) has been studied which deals with the developmentof the diesel engine for Ford’s hybrid vehicle. There is a strong opinion that both theemissions and the energy use are extremely good for a hybrid vehicle.

According to the report the responsible representative at Ford decided to develop a CIDI(Compression Ignition Direct Injected) engine denoted DIATA (Direct Injected AluminiumThrough Bolt Assembly), which according to Ford is compact, has low weight, has a highpower/weight ratio and is ”environmentally friendly”. The displacement of the engine is 1200cc and it is equipped with four valves per cylinder (a 4 cylinder engine). It gives 55 kW at4500 rpm and is also equipped with a turbo with variable geometry (VGT), an EGR systemand has a fuel system with ”High Pressure Common Rail” (HPCR). In addition the engine isequipped with a series of electronic control units. Since the engine can be regarded as aprimary concept for a future diesel engine some of the most important features of the enginewill be described in somewhat closer detail. This description will be based on Figure 7.

Figure 7. Diagram for control of engine, DIATA. Source: Breida 1998.

In Ford’s hybrid vehicle individual units or modules control the electric motor, ASM, and theinternal combustion engine (DIATA). In order to operate the different devices in combinationaccording to a control program which optimize the fuel economy. Emissions and engineperformance, a control system (VSC) for the whole vehicle was developed.

The accelerator and certain other functions of the engine are controlled by VSC. When thedriver of the vehicle presses the accelerator, the VSC indicates the rate of charging of thebattery, the speed of the vehicle and the engine temperature and decides on the strategy for thetorque delivered by the engine and electric motor. VSC also indicates the stops of the vehicleand decides whether the engine has to be shut off.

The exhaust manifold: In order to give space for the lean NOx catalyst, for reduction of theemissions, the design of the exhaust is such that the exhaust system fits in according to theWCR standards and so that the engine does not cause any turbulence and unnecessary back- pressure.

44

Water inlets and outlets need sensors to govern the fans and these have been designedespecially for the hybrid vehicle.

The turbo charger (VGT) has an electric accelerator for fast response and low inertia. Theaccelerator has a linear control signal which controls the position of the vans by means of aturbo module in the control loop.

”High Pressure Common Rail” (HPCR) has been developed by Bosch (Figure 8). It is used inthe engine for the hybrid vehicle. The injection pressure is independent of the engine speedand the power output. Using the pilot injection, which implies the injection of a small amountof fuel, it is possible to reduce the noise emissions and there is also an advantage when usingEGR. HPCR includes a high-pressure radial jet fuel pump which is operated by the camshaft.

The actual pump has three pumping elements placed radially. It has a high volumetricefficiency, requires only low torque for operation, is lubricated with the fuel and requires nosynchronization between the pump and the engine shafts. The fuel is pumped using highpressure to the injectors and the volume has been optimized for fast response. The system isdesigned so that the oscillations caused by the pump and the injectors are damped. The high-pressure injectors have an electromagnetic 2/2-valve actuator and the injection profile isadjusted by shaping the orifice. The time for opening and closing is 250 microseconds and theinjectors fit into the injector bores of a conventional engine with four cylinders.

The system for emission control is based on a lean NOx catalyst i.e. a catalyst which reducesNOx in the exhaust even when there is an excess of oxygen (for a three-way catalyst systemthere must not be any excess of oxygen in the exhaust). In the exhaust from a diesel enginethere is always an excess of oxygen and a catalyst for such an engine must also be such that itreduces the emissions over a broad temperature range. In the case of the Ford CIDI engine anEGR system is used which reduces the NOx formation during the combustion to a certainextent. In a lean NOx catalyst a type of reductant such as urea, ammonia or hydrocarbons (canbe diesel fuel in the case of a diesel engine) is used in order to support the catalytic reaction.

The description of the Ford CIDI engine is presented as one example of the complexity of adiesel engine which has been designed for low emissions levels and high fuel efficiency. Inthis case, it is a diesel engine designed for a hybrid vehicle but many of the units, modules andother details can certainly be found even in other engines. It should be underlined that theengine presented here has many more important details than those presented in this section.

Figure 8. The HPCR fuel system with its components. Source: Breida 1998.

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6.3 Alternative engines

The engines described above are all engines with a reciprocating piston and where thecombustion occurs within the cylinder of the engine, using conventional fuels. Neither haveany thorough changes of these engines been discussed except the use of more electronicequipment in order to control the engine and auxiliary systems. For hybrid vehicles alternativeengines (or energy transformers) are often discussed for used instead of the conventionalinternal combustion engines. A fuel cell package is also an alternative to be used in hybridvehicles but it will be discussed separately in Section 6.4 since fuel cell engines are neitherinternal combustion engines or heat engines. Since the alternative engines, generally speaking,are not completely developed and are not regarded as commercial in this context, theirpotential for improved fuel economy and lowering emission levels is still unsure. Certainindications can, however, be seen for an estimation of the potential of some alternativesystem. There are for example such physical limitations in some of the alternative engines ofenergy transformers, which have to be taken into account when estimating whether theirapplicability is better than that of commercial engines. Seeing that it will take long timebefore alternatives to the present day commercial engines can economically compete, thealternative must be compared with further developed internal combustion engines.

The present day so-called alternative fuels can without any great difficulties be used in almostany type of internal combustion engines provided the engine is adapted to the fuel. Since thepotential of the fuel is affected by the engine used, the engine and the fuel must, as alreadyhas been underlined, be regarded as an entirety. A new emission control technology for NOxemissions when using an alcohol in a compression ignition engine can be mentioned as anexample. In this case it has been shown that the function of the catalyst is most efficientwithin a limited temperature interval, when considering both regulated and non regulated (notlimited by law) emissions. One possibility of avoiding or evening out a fluctuation of theexhaust temperature would be to use the engine in a hybrid system where the engine can becontrolled so as to achieve the best conditions for the reduction of NOx. For the fuel economyit can generally be said that the fuel consumption, in terms of energy, for the same type andsize of engine does not differ very much when either a commercial or alternative fuel is used.

The types of engines discussed in this section are the Stirling engine and the gas turbine. Ofthese engines the Stirling engine can be of interest for use in series hybrids for both light-dutyand heavy-duty vehicles while the gas turbine or turbo generator may be used in serieshybrids for heavier vehicles (buses and trucks). During the literature studies no hybrid vehiclewith a Stirling engine have been found except for a hybrid system presented in a laterparagraph in this section (Rajashekara et al., 1998). In the case of the gas turbine only tworeports have been found and in one of these a hybrid system with a gas turbine developed fora bus was reported (Malmquist et al., 1998). In the other report the use of a hybrid systemwith a turbo generator was presented (Brown et al., 1999). For reasons of costs and/oreffectiveness or other reason it is unsure whether a Stirling engine or gas turbine (or turbogenerator) in a hybrid system will be able to compete with the future otto engine or dieselengine in a hybrid system.

Stirling engines are used today at least in one well-known application namely in submarines.In the 1970’s and somewhat later a Swedish company, United Stirling, introduced the Stirlingengine as a power unit for passenger cars. Later on the engine was tested in differentapplications in the US and plans have been discussed concerning the use of the engine forelectric generation and in this case by using solar energy as a direct energy source.

The Stirling engine, which is a heat engine, differs basically from an internal combustionengine such as the otto engine and diesel engine in that it uses heated air or some other gas for

46

example helium as a working media. Since the working media is heated in a separate part ofthe engine any source producing heat can be used but in reality a liquid or a gaseous fuel isused. Trials have been carried out using solar energy as already mentioned. Nearly 200 yearsago (1816) the Scottish priest and engineer Robert Stirling received a patent for his inventionthe heat engine named the Stirling engine. For reason of costs and also technical reasons theStirling engine has not been accepted, so that it has not obtained a share of the market whichits advantageous emission qualities in fact deserve.

The authors of the report ”Control System for a Stirling Engine Driven Induction Generator”(Rajashekara et al., 1998) are of the opinion that the Stirling engine can be characterized by itshigh efficiency, low emission levels, that different fuels can be used and in passenger carsinstead of otto engines.

The authors of the report also mean that Stirling engine which is coupled to an electricgenerator can be used as a power unit in a hybrid vehicle as an Auxiliary Power Unit (APU).An APU is used in a series hybrid in order to load the batteries and to divide the power outputfrom the engine and the batteries. The authors underline the fact that there is a difference incontrolling the power from a Stirling engine compared to controlling the power from aninternal combustion engine. In an Stirling engine the fuel flow does not have an impact on themass of the working media (the gas) in the engine and therefore the flow of fuel cannot beused for controlling the power output. Another difference between a Stirling engine and anotto engine is that torque curve is rather flat in Stirling engine (see Figure 9) which can beseen as a special advantage.

0

20

40

60

80

100

120

10 20 30 40 50 60 70

TorquePower

x100Speed

Figure 9. Typical torque curve and power curve respectively for a Stirling engine.Source: Rajashekara et al., 1998. .

In order to control the power output from a Stirling engine different methods have beendeveloped. These control methods usually control different parameters of the engine, such astemperature, piston stroke (swash plate* control), pressure, phase angle, speed, load or deadvolume. Each scheme has its advantages and disadvantages; however, the temperature controland swash plate control methods are most commonly used. These affect the fuel flow and itseffect on the temperature of the engine. Another method of power control is by changing thedepth of the piston stroke at constant gas mass. This method is less complex more reliable andfaster than the control method using the working gas mass.

* The expression ”swash plate” is used for a rotating disc mounted with a certain angle and is attached with the

piston (see Figure 10).

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In the developed system the Stirling engine drives an inductive generator and the electriccurrent from the generator is converted to a variable direct current by the use of a specialtransistor. The control variables for the generator are easy to manipulate and by this thecontrol of the piston stroke, as a method for varying the power output from the generator, doesnot need to be used. The control method which has been developed uses a field orientedtechnique in order to control the generator system and vary the power output from the Stirlingengine. By this the system for control of the power output is designed so as to control thegenerator instead of the Stirling engine.

The Stirling engine – induction-generator-system was extensively tested in the laboratory andat present is running in a mini-van. For the operating power range of 8 – 40 kW and speedrange of 3000 –12,000 rpm, the system efficiencies ranged from 85% to 92%. While theStirling engine runs at approximately 40% efficiency, the predicted system efficiency wasabout 34% at most operating points. At low speeds, below 3000 rpm, the total APU efficiencywas below 34% due to the nature of the operation of an induction machine.

General Motors (GM) in the US has also been looking at the possibility of using a Stirlingengine in a hybrid vehicle. Information from USCAR Media Center says that GM has beeninterested in using a Stirling engine in a series hybrid (USCAR, 1999). According to laterinformation from other sources the conclusion can be drawn that this interest has not lead toany action concerning the use of Stirling engines.

A model of the Stirling engine is shown in Figure 10.

Figure 10. Stirling engine*. Source: USCAR, 1999.

Gas turbines are commonly used in airplanes but also in certain types of ships and for thegeneration of electricity. The gas turbine has also been of interest for passenger cars at, amongothers, Volvo. In its most simple execution the gas turbine system consists of turbine and oneof the turbine-operated compressors and a combustion chamber. A simple small type ofturbine is a part of a super charger primarily for diesel engines but during recent years also forpassenger cars equipped with otto engines.

In the report (Malmquist et al., 1998) a new generation of a gas turbine for a hybrid bus isdescribed and this has been developed in co-operation between Volvo and ABB (Asea BrownBoweri). The development of the new hybrid bus is based on an earlier development of ahybrid bus with a gas turbine. The hybrid system in the bus is briefly presented in Section 8. * A "swash plate* is shown in the figure.

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In this section the Volvo hybrid system is briefly discussed, based on the report referred toabove about the system for control of the power flow.

Three different algorithms were determined for the generation of the power reference for thepower module controller. The three algorithms were for line related control, energy balancecontrol and average power control and they were all implemented for evaluation purposes.The sum of the three signal paths forms a reference signal which is then directed to the powermodule controller. The structure of the signal paths is chosen for the purpose of easy systemevaluation and optimization.

In another project for the evaluation of a hybrid bus, presented by NASA’s John H. GlennResearch Center a type of gas turbine fueled with natural gas is used but in this case it isnamed ”Turbogenerator”, see Figure 11. The reason for this may be that it was originally a jetengine from an airplane. The project is carried out in co-operation between the government,industry and scientists (Brown et al., 1999).

The goal for the project is to improve the fuel consumption by 50 % (“double the fueleconomy”) for buses in city traffic and to reduce the emissions by a tenth of the EPA (USA)emission standards. What is unique about the hybrid system for this bus is its system forstorage of energy. For a buss with a maximum weight it may be advantageous to use ultra-capacitors for energy storage since capacitors seem to be superior to batteries concerningaccelerating for regenerative braking and low-temperature characteristics.

Figure 11. GM’s gas turbine. Source: USCAR, 1999.

The car industry seems to have lost its interest in gas turbines for use in hybrid systems.However, according to an early information from USCAR Media Center, GM has expressedits interest in a gas turbine to be used in a hybrid vehicle. GM points out that a gas turbine iseasy to fuel, “just burns anything that burns”, and that an increase in the energy efficiency ofup to 50 % can be expected. The gas turbine is a strong candidate for use in order to meet thegoal for the PNGV program. With regard to there being no great interest in gas turbineswithin the car industry this efficiency seems to be somewhat optimistic. The conclusion to bedrawn here is that there must be a lack of clear information about the advantages anddisadvantages of the gas turbine. A gas turbine is shown in Figure 11.

6.4 Fuel cells

The technology of fuel cells is not new but there has been no cause to use it in the vehicleindustry until recent years. The opinion is that it will not be ready for mass production before10-20 years or more. There are both technical and economic problems to solve and bothconventional and alternative engines, which have been described above will be used for a long

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time in the future. If the introduction of fuel cells is successful it will mean that a new era ofpower unit for automobiles will arrive. This will happen when there is a transition from the100 year old internal combustion engine to a quieter system with fewer moving parts and. Onecan also say that two important steps have been taken in that direction by the introduction ofelectric and hybrid vehicles.

There is much interest in using the technology of fuel cells for developing new methods ofpropulsion for motor vehicles. One can see this from all the journals, articles and reports tobe read. Take for example a recent article in Automotive Engineer where Allied BusinessIntelligence of New York State states that “a fuel cell will power four out of every 100vehicles on US roads by the end of the decade, and proton exchange membrane (PEM) cellsare set to take an 80 % share of the market”. (July/Aug 2000 edition). Information is alsoavailable on fuel cells on the Internet and in daily newspapers. A large part of the availableinformation has been examined in order to provide a background to our evaluation of futurehybrid systems. One problem with the information which is published in reports and othersources is that the development in the field of fuels cells appears to proceed faster that thedevelopment of other important systems in vehicles. There is a great risk that the informationone receives one month is not quite “up to date” by the next month. Besides this, one readsoptimistic statements about the development of fuel cells and the time for the introduction ofsystems ready to be put into production – statements which are difficult to evaluate. All thiscontributes to the uncertainty which is reflected in the descriptions of fuel cells and the fuelwhich can come to be used in them.

All vehicle manufacturers are, however, not certain that resources should be used for thedevelopment and introduction of fuel cells. BMW can be taken as an example of theseexceptions, since the company has stated that it will not use any resources for developing fuelcells but will use their resources for the development of hybrid vehicles, which is a moreinteresting alternative for vehicle manufacturers, at least in the short term (Maruo, K., 1998).

Maruo has, on behalf of KFB, carried our a systematic evaluation of the technology for fuelcells and on-going development of fuel cells in various parts of the world. He states that onecan describe three different scenarios – one optimistic, one realistic and one pessimistic(Maruo, K., 1998).

For his description of an optimistic scenario Mauro takes DaimlerChrysler/Ballard as anexample. The alliance seems to be using a great deal of resources and keeps on makingpresentations of versions of Necar. This puts a great deal of pressure on the other vehiclemanufacturers.In his description of a realistic scenario Maruo says that vehicles with fuel cells will havereached the same state of development by 2004/2005 as electric vehicles were in 1997/1998.

He also estimates that by 2004/2005 several hundred fuel cell vehicles will be produced peryear at a cost of 40 000 dollars or more.

For the pessimistic scenario Maruo points to a number of events which can occur and amongstother things that a decision that fuel cells cannot meet the expected demands in the case ofemissions and good efficiency. Another difficulty is that the price if gasoline and diesel oilmay remain at the present low level and the cost of using fuel cells will prove to be too high.

Maruo also estimates that the greatest barrier to a successful introduction of fuel cells is thequestion of how the delivery of the fuel should be managed. The reason for this is thatsubstantial investments, of tens and hundreds of billion dollars will be required in order toestablish a production and distribution system of the new fuel, which could be methanol,natural gas or hydrogen.

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Maruo also presents other alliances which have been built up in the vehicle industry for thedevelopment of vehicles using fuel cells.

There is a general opinion that fuel cell techniques will eventual replace present daytechniques using internal combustion engines (Stobart, R., 1999a). Fuel cells have thepotential for being clean and quiet energy converters, which can be used in fields other than invehicles. We have pointed to the American Energy Authority, (DOE), and the large amountof money they have invested in the development of fuel cells for stationary establishments forthe production of electric energy (see further on in the text). The hope is that it will bepossible to use the technique even as an energy converter in small establishments for exampleplaces where it is estimated to be too expensive to draw electric cables.

In the case the fuel cells, hopefully at least within the coming 15-20 year period, will be morewidespread in their use, there is a need for them to be more practical to use, and above otherthings, for them to cost less than at present. According to Stobert, (Stobert, R.K. 1999), thecosts at the present time are in the region of 5 000 dollars/kW which means that a 50 kWstack of fuel cells would cost more than 250 000 dollars. According to the same source thegoal of the Californian Air Resources Board (CARB) is that the costs can be cut to 60 dollarsper kW, which even than would lead to a high cost in comparison with an internal combustionengine which is between 15-20 dollars per kW. Fuel cells must also be compact and not weightoo much in order to be attractive for various applications. Stobart has given, in one of hisreports, (Stobart, 1999a) a short description of the technology for fuel cells under theheadings:

Fuel cell technology

What more is required in order fore fuel cells to be a power system

Where are the applications

Future challenges and when can fuel cells come to be used more generally.

Expressed simply, fuel cells convert a flow of fuel to electric energy. This can be compared toa battery where the production of electricity continues all the time. In the separate fuel cell thefuel takes part in the electrochemical process, where it is combined with oxygen, and does notonly produce heat but primarily produces electric energy.

In one type of fuel cell with PEM (Proton Exchange Membrane) every cell has beenconnected together to a membrane of a material which is both electrical isolating andconductive for protons (Stobart, R., 199a), (see also Figure 12). The figure shows that in fuelcells with PEM the membrane is pressed between two electrodes and the resultingmembrane/proton aggregate is mounted between two bipolar plates. The fuel cell packet isassembled from a large number of separate fuel cells, and each contributes with ca 0.7-1 volt.In order to arrive at the required voltage a large number of cells are required probably severalhundred, depending on the power one requires.

In a brief document from the US Department of Defense (DoD) “Fuel Cell Descriptions” adescription can be found of a system which can generate electric energy without consumingfuel and this is therefore the most attractive system from the point of view of the environment(DoD, 1999a). The attractive characteristics of the fuel cell are:

high efficiency for energy conversion

consists of modules

very low level of chemical and acoustic pollution

fuel flexibility

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ability to work together

fast load response

All fuel cells work according to the same principle – applied fuel is subject to catalyticreaction (electrons move from the fuel elements) in the fuel cell in order to generate anelectric current. The fuel cells consist of electrolytic material which is placed in a stackbetween two thin electrodes (porous anode and cathode) like a sandwich, (see Figure 12).

The applied fuel passes over the anode (and oxygen over the cathode) where it catalyticallysplits into ions and electrons. The electrons pass through the external circuit in order to servean electric load while the ions move through the electrolyte toward the oppositely chargedelectrode. At the electrode, ions combine to create by-products, primarily water and CO2.Depending on the input fuel and electrolyte, different chemical reactions will occur. (DoD,1999a).

Figure 12. Basic principals of fuel cells. Source: US Department of Defence.

According to the US Department of Defence there are basically four types of fuel cell, basedon the electrolyte which is used, as follows:

Fuel cell with phosphorus

Fuel cell with carbonate (melted)

Fuel cell with solid oxide (ceramic)

Fuel cell with proton exchange membrane, PEM

In the following table (Table 11) the four types of fuel cell are compared.Table 11. Comparison between different types of fuel cells. US Department of Defence.

PAFC1 MCFC2 SOFC3 PEMFC4

ELECTROLYTE Phosphoric acid Molten carbonatesalt

Ceramic Polymer

OPERAT. TEMPERATURE 375 ºF (190°C) 1200°F (650°C) 1830°F (1000°C) 175°F(80°C) FUELS (H2) Reformat H2/CO/ Reformat H2/CO2/CH4 Reformat H2 Reformat REFORMING External External/Internal External/Internal

External OXIDANT O2/Air CO2/O2/Air O2/Air O2/Air EFFICIENCY 40-50 % 50-60 % 45-55 % 40-50 %1Fuel cells with phosphoric acid. 2Fuel cells with carbonate (melted). 3Fuel cells with solid oxide. 4Fuelcellswith proton exchange membrane fuel cell, PEM (Proton Exchange Membrane).

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Figure 13. The three sections of a fuel cell: fuel processor, stack of fuel cell and DC/ACtransformer. Source: US Department of Defence.

Fuel cells are divided into three sections, (see Figure 13).

1. Fuel processors.2. Section for production of electric energy (stack of fuel cell).3, Transformer direct to alternating current.

Hydrogen gas is produced from natural gas in the fuel processor. (Also the fuel is cleaned inthe fuel processor, sulfur and CO being removed. These would otherwise decrease theworking efficiency of the fuel cell. Fuel cells with PEM are especially sensitive to CO). Thehydrogen-rich fuel is mixed with air and fed into the stack (the power section) where DC isgenerated, together with heat (which can be used for heating purposes). The DC is thentransformed to AC in the transformer (power conditioner) and the “spikes” in the current areevened out.

In the literature about fuel cells, the cells with PEM are especially mentioned as a strongalternative to fuel cell for vehicles. This is partly due to the fact that they are lighter in weightand faster to start up than other fuel cells (DoD, 1999b). This fuel cell comes from adevelopment from a later period than SOFC, for example, which is another promisingtechnology using ceramic electrodes, and which produces oxide ions (rather than protons)which meet the fuel at the cathode. The construction of SOFC is simple (see Figure 14) andhas the advantage that it works with several different fuels. The disadvantage is that if it is tobe used in vehicles the working temperature is up to 1000 degrees C and it takes a certainlength of time to start up. The reaction in the fuel cell can be seen in Table 12.

Table 12. Anode and cathode reactions of SOFC

Source: US Department of Defence

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Figure 14. Fuel cell with solid oxides (ceramic). Source. US Department of Defense.

Fuel cells with PEM have, as stated above, been recently developed and are judged to befavorable due to their low weight, which means that they can more easily be moved around in,for example, a vehicle. According to Maruo (Maruo 1998) they are going to be developed byvarious vehicle manufacturers such as Chrysler, GM/Opel, Ford, Honda, Mazda, Mitsubushi,Nissan, Peugeot/Citroen, Renault, Toyota, VW/Volvo and Zevco. Maruo states, as already hasbeen referred to, that BMW is not one of the manufacturers which are now developing fuelcells, because they think the working efficiency is too low and do not believe that fuel cellswill be able to compete economically within the newt 20 years. According to informationfrom another sources, BMW is using its resources for developing hybrid vehicles and is alsoworking with a hydrogen fueled internal combustion engine.

Fuel cells with PEM use hydrogen gas as fuel (DoD, 1999a). The stream of hydrogen meetsthe electrode (anode) where it is ionized. This results in the protons being led through themembrane. The electrons flow through the electrode and into the bipolar plate. Theseelectrons continue through the cell and pas through the output circuit.

Table 13. Anode and cathode reactions in a fuel cell with PEM.

Source; US Department of Defence

Tables 12 and 13 and Figures 11 and 13 illustrate which reactions take place in a fuel cell withPEM (Proton Exchange Membrane), and a Solid Oxide Fuel Cell; (see also Table 11).

In document recently presented by Stobart, (Stobart, R.K., 1999b) Arthur D. Little,Cambridge, UK describes the fuel cell as the most promising alternative technology forvehicles. It has been named as the successor of the internal combustion engine, otto enginesand diesel engines. Despite a great deal of investment and much interest among vehicle andengine manufacturers to get the fuel cell vehicles on the market, there remains a great manyquestions about their concept. Some of the questions concern the technology – can a fuel cellmeet the demands for working efficiency and performance? Are vehicle owners prepared topay the higher price for an environmentally superior alternative? A great many of the

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advantages of this alternative are still thought, by the consumer, to be impossible to achieve,but there are other more valid, for example;

“Clean” – the vehicle will probably be able to meet the SULEV* demands in California andseveral projects have demonstrated “non-measurable” emission of NOx.

“Silent! – such as en electric vehicle: vehicles using fuel cells do not have high pressure or asignificant source of noise, even if there are pumps and a need for cooling.

“Available” – vehicles which use fuel cells, classed as EZEV (efficient zero emission vehicle)can make it possible for the owner to drive in a so-called environment zone in towns, whichwould otherwise not be allowed.

Figure 15. Components of a fuel cell system.In the above figure, Figure 15, can be seen the key components in a fuel cell system for avehicle. Their function is briefly;

A fuel processor which provides a stream of a hydrogen-rich gas mixture to the fuel cells.Generally the fuel processor supplies a mixture which has far too high a content of CO,which must be reduced to a low content (typically 10 – 30 ppm).

A stack of fuel cells (in the case of Necar 4 the stack consists of 400 fuel cells) which aresupplied with two streams of gas, fuel and oxygen (in the form of air). There are severaltypes of fuel cell, but the demands seem to indicate that it will be PEM (fuel cell with protonexchange membrane) which will come to be used, or a type with solid polymers, which useshydrogen gas as fuel and tolerates air as the source of oxygen.

A compressor-expander unit, which supplies air under pressure to the fuel processor and tothe use cells, which use the energy from the exhaust, gases.

A water collection system which consists of condenser and water container.

The weight of the fuel cell is a critical factor and the levels, which are involved, can be seen inTable 14.

* SULEV has been suggested as a set of demands for the State of California for light-duty vehicles and they are

0.01 g/mi (0.0062 g/km) for organic gases excluding methane (NMOG), 1 g/mi (0.62 g/km) for CO and 0.02g/mi (0.0124 g/km) for NOx.

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Table 14. The mass of the fuel cell and an estimation of how the mass can be reduced.Power density ofthe power stack,kW/l

Specific powerdensity of thepower stack, kW/kg

Power density of the fuelprocessor, kW/l

Specific power of fuelprocessor, kW/kg

År 2000: 0.35År 2004: 0.50

0.350.50

0.600.75

0.600.75

Source: The Hydrogen & Fuel Cell Letter, 1998b.

In a news letter it states that the DeNora S.p.A company in Milano has developed PEM fuelcells for a small truck, which supplies a private company called Coval H2 Partners inCalifornia, USA (The Hydrogen & Fuel Cell Letter, 1998b). The fuel cell stack contains 1000separate fuel cells, which are operated by using hydrogen gas. It is stated that methanol willbe used as fuel for the cells, and that this has a working efficiency of ca 21% at the present,but that there is a good potential for radically increasing this efficiency.

The question is whether vehicles with fuel cells will come to replace battery driven electricvehicles and hybrid vehicles (Electric Vehicle Progress, June 1998). Certain vehiclemanufacturers believe that they will have commercially available fuel cell vehicles inproduction by 2004, others see fuel cells in vehicles as a technology of the future. Since onecan consider the fuel cell vehicle as being an electric vehicle, there is some thought that thedevelopment of fuel cells which is now taking place will be advantageous for the electricvehicle market.

United Technologies Corporation (UTC) has stated that they plan to use PEM fuel cells forvehicles and busses (Electric Vehicle Progress, September 1998). UTC’s fuel cell technologyhas been used in NASA’s space project. The company’s newest fuel cell is 100 kW and isdesigned for busses. The fuel cell is a PAFC (phosphoric acid) cell, which will be drivenusing methanol as fuel. This is the first fuel cell for busses which uses a liquid fuel.

Zevco is a company which aims to produce zero emission vehicles and they have nowannounced their plans for developing taxi vehicles for London. These vehicles will beequipped with fuel cells and have been christened “Millenium Taxis” (Electric VehicleProgress, November 1998). These will be hybrid fuel cell/battery vehicles, and the fuel cellwill be AFC (alkaline fuel cell) driven by hydrogen gas. The company thinks that this isfavorable from the power/weight point of view when compared with PEM fuel cells. The fuelcell charges the battery of the taxi, which then drives an electric engine.

A new organization has been started which consists of the foremost actors within the fuel cellindustry. The active members are 3M, Daimler Benz, Ford MotorCorp, Energy ResearchCorp., Ballard Power Generation and the American Methanol Institute (Electric VehicleProgress, Dec 1998). The members represent a cross-section of fuel cell technology and workwith SOFC (solid oxide) fuel cells and a ceramic, MCFC (molten carbonate) fuel cell withmolten carbonate PAFC (phosphoric acid) fuel cells and PEM (Proton Exchange Membrane)fuel cells.

The Energy Department (DOE) has chosen 16 companies and educational institutions in ninestates who will receive roughly 70 million dollars towards the cost of new research inadvanced fuel cells and combustion engines with high working efficiency (Walsh, M., 1999).

This reward supports the goal of a “Partnership for a New Generation of Vehicles” betweenindustry and the government. The new project will also provide support for developingsimilar technology for fuel cells for use in related applications for the production of heat, forcooling and electricity, (see DOE, 199b). The project is being prepared and the aim is that itwill be run for 2-3 years.

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Research workers at Humboldt State University’s Schatz Research Center have developed amore effective fuel cell (probably a PEM fuel cell) which can be driven with high pressureinput air, which reduces the demands for high effect for the compressor and thereby increasesthe working efficiency of the fuel cell. The process has been tested by an independentlaboratory and found to better than two commercially developed fuel cells.

Daimler/Chrysler, which has previously presented a new vehicle, Necar 3, driven with fuelcells has now presented its Necar 4 (Crosse, J., 1999). Necar 4 has PEM fuel cells and isfueled with liquid hydrogen gas. The system produces 55 kW and gives Necar 4 a top speedof 145 km/h and an operating distance of 450 km. Fuel consumption is stated to be 3.2 l/100km in gasoline equivalent. The vehicle weighs 1 5880 kg against 1 170 kg for a correspondinggasoline driven vehicle. GM, which has already developed two electric vehicles – a passengervehicle (EV1) and a truck (S10), states that they will be able to present a fuel cell drivenvehicle in 2004 (Engine, 1/1999). GM carries out development work in co-operation withExxon and at present they are evaluating how gasoline and natural gas can be used for theproduction of hydrogen gas.

Renault, which is engaged in the FEVER project for the development of fuel cells, states thatthey use their Lagunda combi-vehicle for the development of fuel cells together with –deNora, Ansaldo, VolvoTD, Ecole de Mines and Air Liquide (Engine, 1/1999). A transformer,which can reach a working efficiency of 92% for the greater part of its working range,transforms the voltage to 250V. The power will be transferred to a synchron engine through afixed gear to a stack of batteries (Ni-MH). The specification states that Lagunda will have aworking distance of 400 km.

For the future there is great hope that the technology of fuel cells will be able to be combinedwith good environmental characteristics and an energy efficiency which is comparable withthe that of the best diesel engines (Stobat, R and Linna, J R, 1/1999). A limited demonstrationof fuel cells under constant use has been found to have a working efficiency of 30% and apotential for over 40%. It will not be easy to realize this potential for transient drivingconditions and cold starts where one must compromise the effectivity. One also has toremember that research and development is under way on new concepts for combustionengines, in order to reach low levels of emission and high working efficiency. Some examplesof these studies to be pointed out are the ultra-lean compression engines with homogenousfuel-air mixture and engines with throttle and spark plug ignition.

According to an article by Crosse (Crosse, J., 1999) GM Opel has confirmed plans tocommercial manufacture usable electric vehicles by 2004. GM is not the only manufacturerto use fuel cells as a source of electricity for there are plans at DaimlerChrisler, Honda,Toyota, Nissan and Ford to produce FCEV vehicles, but these have not spoken of theirstrategy and time scale as clearly as GM.

GM’s efforts are connected with their GAPC (“Global Alternative Propulsion Center”) inMainz-Kastel, Germany, which also has research resources at Warren, Michigan andRochester, New York (Crosse, J., 1999). GM has a great deal of research underway on fuelcells. The chiefs of the research center are DR Byron McCormic and Dr Erhard Schubert. Animportant factor here is the co-operation with the oil company Exxon/Esso in order to haveaccess to expert knowledge within the field of fuel technology and the infrastructure.

A critical question of which fuel should be used. GM is, according to the information, neutralin this question, while DaimlerChrysler has already decided to use methanol (see howeverunder “hybrid vehicles” in Chapter 2). DaimlerChrysler states that, at the present, do noexclude the use of gasoline for the production of hydrogen. In the question of the choice offuel for fuel cells, there was lively discussion at a conference at Ypsilanti in the US during the

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summer of 1999, without any conclusion being reached. The conclusion that one could drawfrom the discussion was that the vehicle industry still has an open mind in the question, andthat that includes even DaimlerChrysler. Another open question is whether hydrogen shouldbe produced on board the vehicle of whether it should be produced at stationaryestablishments.

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7 DEVELOPMENT OF BATTERIESElectric propelled vehicles, industrial machines and especially industrial trucks have existedfor a long time. With the increasing interest in electric fueled vehicles there has also been agreat deal of attention paid to improving batteries and producing new types of batteries withhigher energy density (Wh/kg) other than lead acid batteries. With the lead acid batteries thedriving distance is limited to 70 to 80 km if an acceptable battery mass is used. The estimationtoday is that the driving distance will be considerably increased with the new types ofbatteries.

The introduction of new batteries with higher energy density has, however, led to unexpecteddifficulties being encountered, which take time to solve. First of all it was necessary to adjustthe development of the batteries for use in vehicles, so that the car owner does not have tospend too long recharging the batteries. This phase of development is not at all finished andtherefore it is today not possible to determine, with any degree of certainty, whether the goalsfor the development will ever be reached. A capacity for the production of the new batteriesmust also be established. In order to reduce the cost of the batteries already in production andestablish an acceptable level for the cost of new types of batteries the production efficiencymust be increased.

The present day cost of the more efficient batteries is regarded as being too high to beacceptable. A hindrance to cost reduction is that many of the material used in batteries (forexample lithium) are expensive. The use of other, cheaper material may have to be restrictedfor environmental reasons, unless satisfactory routines for the use of these materials areestablished; cadmium for example is regarded as being one of the most dangerous poisons. Agreat deal of attention has to be paid to this fact when using cadmium. In the case of theproduction of batteries there may be some hindrance, such as a shortage of material ordifficulties in acquiring certain materials. Later on in this section some more information willbe presented concerning the development and production of batteries.

The aim of this section was primarily to discover which types of batteries were most suitablefor hybrid vehicles. One of the difficulties is to get access to the information about the latestand newly invented batteries and the state of the art especially about the development ofbatteries for hybrid vehicles. One special difficulty has been to find out what differentbatteries will cost in the future. It must be taken into account that the basis for a successfuldevelopment, introduction and production of batteries is that the manufacturers can see aninterested market. In this case no such market can be seen at present.

7.1 Present day batteries

With regard to the current state of the art the most prominent systems for hybrids are serieshybrids and parallel hybrids. In these systems it is otto engines or diesel engines which aremost commonly used in combination with a generator/electric motor or electric motors and abattery or batteries. Series hybrids usually have a larger package of batteries than parallelhybrids since they often serve larger vehicles and the internal combustion engine is notdirectly connected to the driving wheels. The power from the engine is used to load thebatteries via the generator and during some part of the driving of the vehicle the batteries arethe only energy source i.e. when the engine is shut off. This can be the case in heavilypopulated areas such as down town areas.

The different types of hybrid systems have been presented in Section 4. From the descriptionof the parallel hybrid system it can be seen that in this system there is an interaction betweenthe two energy sources in that the battery supports the internal combustion engine via the

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electric motor when more power is needed. The engine then “pays back” that energy whenless power for propelling the vehicle is needed.

In many cases such as in the case of the Toyota Prius, there is another difference between aparallel hybrid system and a series hybrid system concerning the charging of the battery orbatteries. It is only the internal combustion engine which charges the battery in Prius. For thebattery in a series hybrid it is common that this battery can also be charged from the mains.However, it is not certain that this difference exists in every case since the arrangement for thebattery in a parallel hybrid can be such that it can be charged from the mains in addition tobeing charging from the engine via a generator.

The question about the type of battery to be used in light-duty vehicles and heavy-dutyvehicles, or whether the same type of battery can be used, seems not to have beensatisfactorily answered. The mass of the battery in relation to its capacity for the storage ofenergy seems to be an important factor as does the cost of the battery. In Vol. 20 No. 22 ofElectric Vehicle Progress (Nov. 1998) it is underlined that the cost of the batteries must bedramatically reduced for electric vehicles to be able to compete with vehicles powered with aninternal combustion engine. It is also pointed out that the cost of the batteries can be such thatthe car manufacturers, at least in beginning of the period of introduction, lose money sellingelectric vehicles. Such a situation is however not uncommon when introducing a new product.The situation should not last too long, however, or the interest for the product may be lost.

In the US the Department of Energy (DOE) is involved in a program called ”AdvancedAutomotive Technologies” (ATT) and the aim of this program is to bring together a broadspectrum of research activities to an integrated activity to develop advanced energy storage.The participators in PNGV (”Partnership of a New Generation of Vehicles”) are the leaders ofthis program and it is also served by, among others, Chrysler, Ford and GM throughrepresentatives for ”United States Council for Automotive Research” (USCAR). One task ofthe program is the development of batteries for electric vehicles and hybrid vehicles. High-power batteries are developed for hybrid vehicles and high energy density batteries for electricvehicles. The structure of program can be seen in Figure 16 (Sutala et al., 1998).

Figure 16. Organization for the development of batteries. Source: Sutula et al., 1998.

The aim of the U.S. Advanced Battery Consortium (USABC) is to develop high-energybatteries to meet the requirements of the emerging electric vehicle market in California. The

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U.S. Department of Energy (DOE) supports an active program of long-range R&D to developadvanced energy storage and related systems technologies that will be necessary for thecommercial viability of competitive hybrid electric vehicles. USABC is organized so as tosupport the PNGV program. By focusing on the hybrid electric vehicles the target of thePNGV program may be reached. The contributions within USABC and DOC are aimed atsupporting the development of high-storage batteries such as nickel-metal hybrid and lithium-ion batteries (Sutula et al., 1998).

According to DOE one of the most important requirements for batteries in a hybrid system isa high-power to energy ratio. Batteries with power-to-energy ratios greater than 20kW/kWh,which use the USABC method of rating battery power and energy and with long cycle life arenot available for high-power energy storage. The goal for energy storage is a 10-secondpower/energy ratio of 25 W/Wh already year 2000. The lifetime is not known but 10-yearcalendar life is required in order to achieve the goal for the overall system costs.

R&D on ultra-capacitor and flywheel technologies for high-power storage devices has alsobeen of interest. Within these activities for the development of batteries two interestingalternative were investigated, one of which was an ultra-capacitor and the other was aflywheel battery. Both of them have a rather high specific power (<1000 W/kg). Despite someimportant progress having been reached, support within this area has low priority since thecriticism is that the goal for the PVG program cannot be reached.

Considerable progress has, however, been reached for the chemical batteries. In the past aspecific power of 100 W/kg was seen as a good value for a lead acid battery. Now it seems tobe fully possible to reach over 500 W/kg and as high as 1000 W/kg is thought to be possible.If the later could be realized a battery with a power of 50 kW would weigh only 50 kg. Thisweight is considerably less than the large batteries in a series hybrid vehicle, weighing as theydo up to 300 kg, which was the case some years ago.

For the so-called “mild” hybrid vehicles, according to DaimlerChrysler’s definition, the lowweight of the battery indicated above may possibly be reduced by half (25 kg). By this themass of the power unit (battery, electric motor, engine etc) could be approximately the sameas the mass of the internal combustion engine in a conventional vehicle.

Some 25 reports were studied in order to acquire background information about the state ofthe art concerning the development of batteries. Of these reports 20 were presented during1998, which can be regarded recent and were used for the evaluation of the batteries. Themain activities concerning the development of batteries are taking place in the US, Japan andEurope and according to the reported projects, Japan can be seen as the leader. However manynew invention may have been presented since year 1998 and therefore the state of the arttoday may be more optimistic both concerning the function of the battery and the costs. Adrawback for the development could be that no real large market for electric vehicles yet canbe seen. The situation seems to be more positive for hybrid vehicle but today it is not clearwhether this type of vehicle will be attractive for the average car owner.

Those involved in the studies, research and development of batteries in the USA are first ofall: Advanced Lead Acid Battery Consortium, Electrosource Inc., General Motors, OvonicBattery Company, Saft Advanced Technology Division, Saft America Inc., SouthernCalifornia Edison Company, United Chemi-Con, United States Advanced BatteryConsortium/Ford Motor Company, University of Wisconsin-Madison, US Nanocorp Inc. andChrysler.

In Japan Toyota, Nissan, Honda and two battery companies, Lithium Battery Energy StorageTechnology Research Association (Libes) and Panasonic EV Energy Co., Ltd, have presentedthe reports which have been used for this literature survey about the research and development

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of batteries in Japan. Since the requirements on batteries to be used in hybrid electric vehiclesdiffer somewhat from the requirements for batteries in electric vehicles the preference for thechoice of battery changes depending on the actual type of vehicle (see the discussion aboutthe choice of battery further down). To mention an example Honda has presented aninteresting solution for the deterioration of the battery caused by the memory effect in anickel-metal hydride battery (Sato Noboru et al., 1998). The authors found that the use of acertain relationship between the battery power and the motor power is an effective way toimprove the life of the battery. Another phenomena, which should be taken into account whilefurther developing the battery, is heat generation during the charging process of the type ofbattery, mention here. Because of this heat generation the cooling system must be properlyconstructed and the battery sub-reaction must be suppressed.

Both Honda and Toyota use nickel-metal hydride batteries while Nissan uses lithium-ionbatteries. It is of course important that the car manufacturer takes full responsibility for whichbattery should be used in the vehicle so that the requirement for the integration and testing ofthe battery in the vehicle will be met. It is certain that the car manufacturers are involved inthe development of batteries in Japan as in other car manufacturing countries. It will of coursebe necessary that the car owner follow the car manufacturer’s instructions for the maintenanceof the battery and the type of battery to be used in case of replacement.

In Europe a development of light-duty hybrid vehicles and hybrid buses is also in progress.Most of the studies and development of batteries in France are taking place at EcoleSupérieure d’Ingénieurs de Marseille, EIGSI – CERAVE, Oldham France S.A., PSA PeugeotCitroën, Renault and SAFT. In Germany it is the two well-known companies AEG (AEGAnglo Batteries) and Varta Batterie GmbH and the University of Kaiserslauten who arecarrying out this work. When studying the different reports the impression is that the carmanufacturers in Europe are less involved in the development of batteries than in Japan andthe US. In the US there are, in addition to the car manufacturers, different companies andorganizations including universities which are involved in the evaluation of batteries.

The impression is that the plans are somewhat different in Europe compared to the plans inthe US and Japan. In the US the three dominant car manufacturers have signed an agreementwith the government which aims at approximately a threefold improvement in fuel efficiencyand in addition very low levels of emissions for at least a prototype car (PNGV agreement).The US is a very important market for the Japanese car manufacturers. This will have animpact on the plans for the development of low emission vehicles. Even if the European carmanufacturers are dependent on the market in the US, they can first of all work towardsmeeting the emission standards on the European market and then make an effort to meet theemission requirement in the US for models sold on that market. The requirement for fueleconomy according to the CAFE Standards is not such that it will, generally speaking, causeany real problem for the European car manufacturers. The conclusion is that in recent yearsthe European car manufacturers have been in a phase of evaluations and system analysis aboutwhich way to go concerning the development of vehicles offered both on the European marketand the US market. The aim is to achieve extremely low emission levels and good fuelefficiency but not necessarily meeting the PNGV requirements.

The following manufacturers in Europe have presented their development of batteries:

• In Belgium, Union Minière is the leading deliverer of raw material for production ofbatteries. The company is an established, internationally prominent company whichsupplies non-ferrous metals suitable for production of different types of batteries such asnickel-metal-hydride and lithium based batteries (Meeus och Gravenstein, 1998).

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• In England Beta Research and Development Ltd is a manufacturer of a sodium-nickel-chloride (ZEBRA) batteries. The battery cell in the ZEBRA battery has a centralelectrode which mainly contains nickel-chloride and sodium-chloride in addition tosodium-aluminum-chlorine (NaAlCl4) – a liquid electrolyte which is contained in a tubeof beta-aluminum – a solid electrolyte. Testing a second generation of the battery hasshown a stability over more than 1500 cycles (charging/discharging) during the first 18month (Bull et al., 1998).

• One of the companies in France, Saft Advanced Technology Division, is among othersconcentrated on the improvement nickel-metal-hydride batteries and lithium-ion batteries.The company points out that there is a considerable difference between the battery’stheoretical specific energy and that which can be achieved in reality – only 16%-28% ofthe theoretical specific energy can be achieved for lead acid batteries, nickel-cadmiumbatteries, nickel-metal-hydride batteries, ZEBRA batteries and lithium-ion batteries. Eventhe maximum driving distance has been studied and the following results were found(Cornu, 1998):

Driving distance, km Battery 70 lead acid battery 100 nickel-cadmium 130 nickel-metal-hydride 170 ZEBRA

300 lithium-ion

• Also Saft in France has developed a lithium-ion battery for electric vehicle and haspresented a report in co-operation with Saft in the US (Cuesta, et al., 1998). The authorspoints out that at that time of the presentation of the report it was planned that Saft, aftertesting the lithium-ion battery, should go over to the phase of production and field testsbefore year 2000. From Figure 17 it can be seen that lithium-ion battery has a relativelyhigh specific power and even a high specific energy.

• In 1993 another company in France, Bolloré Technologies and Electricité de France,started the development of batteries based on metallic lithium and a dry polymerelectrolyte. A first phase of the development was reached in 1997 with positive resultsand the plan at the time of the presentation of the report was that the second phase shouldbe finished in year 2000. The goal was that the development should result in cells with aspecific energy of 150 Wh/kg and 120 Wh/kg for modules at C/2 and more than 500cycles at 100 % DoD (Depth of Discharge, i.e. 100 % discharge), (Marginedes et al.,1998).

• In Italy the EXIDE Company is interested in semi-bipolar lead acid batteries. Some yearsago EXIDE started a program for the development of a semi-bipolar gas-recombinantlead-acid battery for, among other things, the increasing market for electric vehicles.According to EXIDE the technology for the new lead acid battery is characterized by thatthey can be used in both electric vehicles and hybrid vehicles. The battery is of typeVRLA (”valve regulated battery” i.e. which is regulated with valves), (Bassini et al.,1998).

• In Germany the development of batteries is carried out by VARTA BATTERIEAG. The company thinks that there is an advantage in nickel-metal-hydride batteriesand calls attention to the fact that batteries must be tailored for use in both electricvehicles and hybrid vehicles. Of the nickel-metal-hybrid batteries there is one type withhigh power (specific power up to 300 W/kg) and one type with ultra-high power (aspecific pulse power of >850 W/kg). However, VARTA is also developing batteries witha specific energy of 80Wh/kg. For these batteries the specific power is approximately 200W/kg (Köhler and Niggermann, 1998).

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• By a special adapted program for research and development carried out during the lastyears VARTA BATTERIE AG has been working with an upgrading of lithium-iontechnology. By the use of lithium manganese spinel (MgAl2O4) and coal as activematerial, lithium-ion cells of 110 Wh and 250 Wh could be developed. The aim for futuredevelopment is to increase the energy density of the battery cells and to reduce therelatively high weight and volume of the battery. By these means it is expected that thespecific energy can be increased to 100 Wh/kg at the battery level (Brohm och Meissner,1998).

• The authors of the “Brite Euram Program” (Cooper and Mosely, 1998), funded by theEuropean Commission points out that the ongoing discussion has been focused on thedriving distance between chargings of the battery and by this the specific energy of thebattery. The opinion of the authors is that range per charge is less important than the costof the battery provided that the battery can be recharged within a short time. The fact thatthe energy density has been doubled since 1990 has shown that there has been aconsiderable development of lead acid batteries. The studies and trials which have beengoing on have also shown that it is essential that the recharging of a lead acid batteriesfirmly follows a correct procedure and also that a fast-charging of the battery can bebeneficial for the lifetime of the battery. It has been shown that the battery can withstandup to 900 cycles of charging/discharging instead of the 250 cycles when usingconventional charging/discharging. Table 15 shows the different steps of thedevelopment.

Table 15. Development of lead acid batteries EU. Source: Cooper and Moseley, 1998.

7.2 Choice of batteries for hybrid vehicles

There are many reasons for the difficulties in choosing the “right” battery for a hybrid vehicle.First of all there are many alternative battery systems of which some are still underdevelopment. By further development even the cost can be reduced. In addition to otherquestions, it may be wise to ask whether efficient production has been developed for the typeof battery of interest.

A decisive factors which has an impact on the choice of the type of battery is its specificenergy contra it specific power. With a hybrid vehicle - and especially a parallel hybrid whereinternal combustion engine or the alternative to that energy transformer has a relative lowpower – it is important that the battery via the electric motor can assist the engine drivingwhen higher power is needed than the engine can deliver. In this case a battery with high

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power is needed. For a pure electric vehicle a battery, high energy is needed in order to fulfillthe requirement for along enough range between the chargings. If the use of energy in thevehicle has to be kept at a low level the mass of the battery must be kept as low as possible.Köhler and Niggermann discuss this matter (Köhler and Niggermann, 1998) and they havealso underlined that the batteries have to be tailored with respect to the requirements. Theypoint out, for example, that nickel-metal-hybrid batteries can be tailored with respect to therequirement of specific energy or specific power - high energy (HE), high power (HP) andultra high power (UHP) respectively. UHP batteries have been under development and aretoday possibly in production.

For batteries in a hybrid vehicle there is also a requirement that they must tolerate many (evensmall) chargings/dischargings – usually a higher number than for an electric vehicle even inthe case where the electric vehicle is equipped with a system for regenerative charging. Thedevelopment of batteries for especially hybrid vehicles must be directed towards a robustproduct which can withstand cycles of discharging/charging which typically can be as low as3-5 % discharging/charging. The lifetime of batteries depends strongly on a positivedevelopment in this direction. Table 16 shows which batteries are used by some of thedifferent car manufacturer and also shows the suppliers of the actual batteries.

One of the goals for the development and use of hybrid vehicles is that use of energy isexpected to be less than for a vehicle without hybrid system. It is not yet completely clear howfar in this direction it is possible to go with a hybrid system since there are not many types ofhybrid light-duty vehicles and hybrid heavy-duty vehicles in existence at the present time.Hybrid vehicles of today are either a few types on the market or they are presented asprototypes. Existing hybrid passenger cars are relatively small and are produced from light-weight material, which is a reason for the difficulties in comparing hybrid passenger cars withcommercial passenger cars. A closer comparison between some different hybrid systems ispresented in Section 8. The reason for pointing out this matter here is that the mass of thebattery has a great impact on the mass of the vehicle. Whether or not lightweight material isuse in the body of the vehicle it will still be heavier than the same vehicle without hybridsystem. For hybrid vehicles it is therefore an advantage to choose a battery with respect toweight and specific power in order to reduce the weight of the car. However, this requires acareful analysis from one case to another.

Table 16. Vehicle manufacturers and their choice of battery.Car Battery Battery manufacturerHonda Ni-MH Panasonic EV EnergyToyota Ni-MH Panasonic EV EnergyNissan Li-jon SonyGM Ni-MH GM-OvonicFord Ni-MH Panasonic EV EnergyChrysler Ni-MH SAFTMercedes Benz Na-NiCl2 AEGBMW Na-NiCl2 AEGNone Li-polymer LIBES

Source: Sato, 1998.From the point of view of costs, it is most likely more advantageous in Sweden to charge thebattery from the mains than to load the battery with electricity produced when using aninternal combustion engine. In terms of energy the cost is much lower for electricity than forfossil fuel. On the other hand the cost may be lower when charging the battery with electricityproduced by an engine than taken from the mains, if that electricity is produced in an electricgenerating plant fueled with a fossil fuel. However, in the latter case, the higher cost is not

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paid by the user of electric in Sweden since the price of electricity is mainly the same and isindependent who produces the electricity. (Only a very small fraction of electricity isproduced from fossil fuel in Sweden).

The fact that series hybrid vehicles are designed so as to have their batteries charged from themains is of course, a matter for the car manufacturer. On the other hand it is not yet commonpractice that a parallel hybrid is designed in that way. The parallel hybrid is often equippedwith a small battery since power from the battery is used only when supporting the internalcombustion engine during accelerations or other driving conditions when an access of poweris needed.

W/kg

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Specifika energy for different batteries

Figure 17. Specific effect respective to specific energy for various batteries.Source: Meeus och Gravenstein, 1998.

In Figure 17 the specific power and the specific energy for seven different batteries are showngraphically. In the case of specific power the nickel-metal-hydride battery is in a top positionand in the case of specific energy, the lithium polymer battery is best. One problem in thiscontext is that there is not yet any clear picture concerning the future cost of batteries withhigher specific power and specific energy. According to one source of information the cost ofa lead acid battery can be up to $100/kWh. The costs for both nickel-metal-hybrid batteriesand lithium-ion batteries are higher than for lead acid batteries but the first mentionedbatteries have a longer life cycle and they may therefore be less expensive to use in the longrun.

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8 HYBRID VEHICLESIn Section 4 the two main alternatives of hybrid vehicles, series hybrids and parallel hybridshave been presented. Despite the fact that the first hybrid passenger car was presented on themarket as late as year 1997, as a hybrid vehicle in production and also as some prototypessomewhat later (mostly passenger cars and buses), different alternative of hybrid vehicles canalready be seen. The presentations have covered fuels to be used, internal combustion enginesfor hybrids, fuel cells, batteries, system and units to be used for the control of the hybridvehicles and it can be said that a great interest has been shown in these types of vehicle.

Electricity is produced for charging the battery by the APU (defined as the internalcombustion engine and the generator). For a series hybrid there could be an advantage indesigning the vehicle to be charged from the mains, an alternative which is not common for aparallel hybrid vehicles. Because in many cases that the battery pack represent a rather heavymass, the parallel hybrid system is, in reality, the dominant system for light-duty vehicles.However, even for parallel vehicles the mass of the battery can be a problem and this is one ofthe driving forces for the development of improved or new types of batteries with higherspecific power.

For heavy-duty vehicles and especially buses operated in densely populated areas like cityareas pure electric operation is an advantage for the environment and therefore these types ofhybrids commonly are series hybrids with a rather heavy battery pack. For these types ofvehicles there is a need for batteries with a high specific energy despite a heavy battery packmay not being the same burden for a heavy-duty vehicle as for a light-duty vehicle.

In the following section the potential improved energy use (or improved fuel consumption)for hybrid vehicles is discussed and some of the engine technology and hybrid systems arealso discussed. In addition a rather large number of prototypes of hybrid vehicles arepresented, especially buses. A comparison between different fuel/hybrid system combinationsis also presented.

8.1 Potential for improved energy use in hybrid systems withdifferent types of internal combustion engine

Many different interactive possibilities exist for the improvement of fuel consumption orenergy use* when considering every element in a vehicle or every factors having an impact onthe use of motor vehicles. This fact has been clear to the car manufacturers for a long time andat the present time the improvement in the use of energy when driving the car is one of themain issues within the automotive industry even if it is not always seen in reality. However,the co-operation between the industry and the government expressed in the PNGV program(discussed in for example Section 8.1.3) has certainly had a great impact on the developmentof new ideas within the automotive industry and others involved. It has influenced not onlythe car industry in the USA but even in Japan and Europe and is one of the driving forces forimprovement of vehicles in this respect even if the PNGV agreement with the US governmentonly apply to Chrysler, Ford and GM. Unfortunately the use of less energy when driving thecar has so far not had the required effect on the user of the car.

Some of the factors having a great impact on the use of energy in the motor vehicles are thesize of the body of the vehicle its weight and the size and power of the engine. It is a question * In this context the expression ”energy use” is preferred since physically energy can only be used not consumed.

When discussing the use of alternative (different fuels) it may be an advantage to use energy units.

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as to whether the electric and hybrid vehicles which have so far been presented constitute anew trend regarding, among other things, the size of the passenger cars. Today there is acommon opinion that the size of the car has to be reduced if the goal is to be reached,expressed in for example the PNGV program, of fuel economy of 80 miles per gallon. This iscomparable to approximately 0.3 liter per 10 kilometer gasoline equivalent. The fuelconsumption for some of the hybrid vehicles is presented in some of the following sections.

8..1.1 Theoretic background for the potential in improved energy use

Hybrid operation opens the possibility of improve the working efficiency of the of the internalcombustion engine since the engine can be run in an advantageous areas from the point ofview of fuel-efficiency. A three-dimensional diagram can illustrate this over the specific fuelconsumption (in g/kWh) for a certain fuel engine combination. Such a diagram is called amussel-diagram since the iso-lines (in this case for equal fuel consumption) together form apattern which looks like a mussel-shell. Figure 18 is an example of a mussel-diagram. It isdiagram for a 1.25 liters engine to be used in a passenger car from Ford (Menne et al., 1996).The diagram was primarily amended by Ecotraffic (Sweden) in order to show iso-lines forconstant power.

Figure 18. Mussel diagram over fuel consumption for a 1.25 liter gasoline engine, modifiedby Ecotraffic (Sweden). Source: (Menne et al., 1996).

When following the iso-line for constant power (the dashed lines going from the upper left tothe bottom right) it can be clearly seen that the consumption of fuel varies for the differentspeeds. In the figure there is also a line (the dashed line going from zero torque and upwardsto the right) showing the most favorable consumption of fuel. Certain considerations havebeen taken to the risk for vibrations and loss of comfort caused by engine speeds at high loadsat such a low engine speed as 1200 r/min. For comfort reasons (vibrations and noise) it maynot be tolerable to follow the dashed line to an engine speed as low 1200 r/min. and lower.However, in order to keep to as low fuel consumption as possible it would be favorable to

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always follow the dashed line shown in the figure. Since normal driving in traffic rarelyrequires high power, the above-described driving conditions means that it should be necessaryto always run the engine at speed in the range of 1200 to 2500 r/min. For practical reasons it isnot possible to use such an extreme gear ratio of the gearbox (a gearbox with 6 to 7 gears) anda completely changed gear ratio for a car with such a small engine as 1.25 liter, is notreasonable.

For such a gear ratio, as said above, the reserve of power should be close to zero and a verysmall slope of the road should force the driver to change the gear*. In practice the fullpotential of maximum energy efficiency of the internal combustion engine can be reachedwhen using a common mechanical gearbox. A car driver would not accept such frequent gearchanging that such an extreme gearbox would require**. In heavy-duty vehicles the situation isdifferent (higher mass/power ratio) and in this cases up to 16 different gear ratios are used. Anautomatic gearbox makes use of somewhat lower gear ratios*** in the cardan transmission.However an automatic gearbox is less energy-efficient than a mechanical gear box andtherefore the fuel consumption is usually higher for a given car with an automatic gearbox oris at best the same when compared with the same type of car with a mechanical gearbox.

For an electric drive system for transmitting power from the electric motor to the wheels thesame possibilities exist - or better ones - as for a car with an automatic gearbox, to run theinternal combustion engine in a range with high efficiency. In addition it also has a bettercontrollability (is faster). Therefore this type of system gives the basic possibilities to quicklymove the operation of the engine to a more favorable area than that in which it has beenrunning.

A gear box with Continuously Variable Transmission (CVT,) or a series hybrid system willtheoretically be able to follow the curve for best energy efficiency (or fuel consumption)shown in Figure 18.A parallel hybrid system combined with a CVT can also be operated similarly to the above-mentioned combined system while the same possibility does not exist for a conventionalmechanical gearbox (because the restricted number of gears).

If the mechanical gearbox is equipped with a similar gear changing automatic system as in,for example, a Formula 1 car, the difference is less when compared with the CVT gearbox.The same comfort will not be obtained as with a CVT because the gear changing is notcontinuous. However, the automatic gear changing system for this type in passenger cars isnow being introduced on a large scale. One example of this introduction is a new type ofpassenger car introduced by Volkswagen (VW Lupo 3L).Besides the fact that it is not possible to use an extreme final gear in combination with amechanical gearbox there is another problem in that the internal combustion engine is over-dimensioned for most of the driving conditions. As an example it can be said that power outfrom the engine must be 20 to 25 kW in order to achieve the highest efficiency according toFigure 18, which would mean that the driver would have to keep to a much higher speed thanis allowed in Sweden. In a hybrid system on the other hand the size of the engine can be muchsmaller and, by these means, come closer to the most efficient area for operation of the * In this context it should be reminded that at the end of the 1970’s and at the beginning of the 1980’s some of

the car manufacturers had a very extreme gear ratio in their cars in order to reduce the fuel consumption butthis also rendered in many complains from their customers.

** A frequent changing of the gear also results in certain energy losses.*** In this context ”lower gear ratio” is used to characterize a gear ratio which result in lower engine speed for a

given speed of the vehicle. In terms of mathematics this is correct. In some popular literature thereunfortunately is an misunderstanding of the concept when the wording “high gear ratio” is used as a synonymfor a higher speed of the vehicle for a given engine speed.

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engine. Even if the energy efficiency is somewhat lower than for a full-scale engine, it iscompensated for by the more favorable operation of a smaller engine in a hybrid system.

Both types of hybrid systems are usually designed so as to use the energy released duringbraking by the so called regenerative braking and this means that the system includes anotherpossibility for improved energy use by the car, especially when driving in city areas. Despitethere usually being less braking when driving on the road the system with regenerativebraking make the hybrid system superior over a vehicle without a hybrid system.Unfortunately the losses during charging and discharging of the battery are relatively large(see a coming section), and this considerably reduces the potential of regenerative braking.The losses the rest of the electric system (excluding the battery) are also rather large sincethey occur both at charging (braking) and discharging (acceleration) affect the whole system.

Despite that an electric controlled system for transmitting power from the electric motor to thewheels has about the same energy efficiency as an automatic gearbox it is clear that it has aconsiderable lower efficiency than the energy transmission by a conventional mechanicalgearbox. Transmission of power via two gear wheels (grasping of teeth) in a gear reductionset result for example with efficiency of 98 % which can not be achieved for such an electriccontrolled system for transmission of energy. Even if the maximum efficiency for a wellfunctioning electric motor of suitable size can have an efficiency as high as 90-95 %, it cannot compete with a mechanical gearbox in this respect. In an electric drive system fortransmission of energy also the losses in other components (generator inverter, battery and soon) must be accounted for. The weakest chain in this system is the batteries which have anefficiency of maximum 70 % for charging/discharging as a best and often much less (50 – 60%) under the variety of driving conditions. For a situation where the battery is used a longtime during the driving (as in a series hybrid) these losses will be considerable high. It is notsurprising that the battery pack must be equipped with a cooler in order to avoid overheatingduring such driving conditions and to thereby reduce the deterioration of the batteries.

It can be seen that there is a considerable potential to increase the energy efficiency providedthat the efficiency of all components in the drive train are high. Even in this case theexpression is valid that no chain is better than its weakest link, which leads to the strategy thatimprovements of the batteries is a good way to reduce losses of efficiency.

8.1.2 The interaction between the control unit, the energy transmitters andthe mechanical power transmitters in a hybrid system

In the previous section the theoretical possibilities for a reduction of energy use in anautomobile have been discussed but there are limitations for energy reductions in a hybridsystem of chemical and physical reasons. In this section the interaction between the differentunit in the system will be discussed and some example about factors influencing the energyefficiency will be given.

The control unit in a hybrid system can be seen as its brain. With present day technology forelectronic control there are many possibilities for the control of different functions and thistechnology can also be used for the control of many functions in a hybrid vehicle. The controlunit can be “taught” to “feel” what the gear ratio should be, in for example a transmission likethe CVT, so as to run a given electric motor or an internal combustion engine as efficiently aspossible. The control unit can decide at what load the internal combustion engine shall be shutoff and the vehicle be propelled only with the electric motor and also when to quickly start theengine so as to support the electric motor during such accelerations when more power isneeded. In a parallel hybrid system the control unit can be programmed so as to propel thevehicle with only the internal combustion engine and to assist the engine with the electric

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motor at higher load modes. For both of the systems the control unit has to facilitate thefunction of regenerative braking if that function is included in the hybrid system.

In connection with the discussion about the control unit it should be said that there could be aproblem to program the control unit for a hybrid vehicle so as to achieve reliability inoperation of the vehicle and a comfortable ride. That means that no vibrations in the vehicleshould occur and that there should be no sudden hesitations during driving caused by falseinformation to the control unit resulting in that the control unit overestimating thephysical/mechanic possibilities of the hybrid system. All mechanic systems or units for powertransmission have their limitations but if they are operated within their area for good functionthey are mostly run reliably and are reliable during continuos operation. Since hybrid vehiclesare a new type of vehicle with many new functions, the constructors have many new functionsto design. In their work they must be especially careful that the interaction between thedifferent functions is secured and that the different systems including the internal combustionengine and the electric motor are operated with high efficiency.

In a report from Japan, certain factors influencing the energy efficiency in a hybrid system,are discussed (Iwai, 1998). A part of this was discussed in Section 4.3 and here the report willbe discussed in somewhat more detail, especially some important factors in a hybrid system,which the author of the report has pointed out. The opinion of Iwai is that the thermalefficiency of a conventional engine is only about 15 % when the car is run according to theJapanese 10-15 mode cycle – a typical low load low speed cycle (Figure 19) and especiallythe part of the cycle which contain the 10 modes. He calls attention to the fact that the carsshould run with an efficiency of 30-40 % provided that the following conditions are fulfilled;

(1) the elimination of idling and operation of the internal combustion engine in areaswhere the thermal efficiency is low, so that the engine is operated only in areas withhigh thermal efficiency;

(2) accumulation of the energy released during braking of the vehicle;(3) installation of a system for power transmission, which can be operated with high

energy efficiency independent of area for operation;(4) the use of a bottoming cycle (Stirling cycle or steam cycle) which generates electric

energy by driving a generator with the exhaust energy at low engine load.

The studies that Iwai carried out, are based on experiments and vehicle tests. He has alsocarried out calculations based on certain assumptions and in one case he has calculated howmuch of the energy used during acceleration can be recovered during deceleration. What heshows, in Figure 20, is the percentage of the braking energy which can theoretically berecovered using an electric system with varying efficiency for the recovery, when the rate ofdeceleration equals the rate of acceleration. The figure is based on accelerations up to 40km/h. The vehicle was free rolling during the decelerations i.e. the gear was not engaged. Thedifferent curves in Figure 20 are as follows;

• the “EFF100%” curve shows the maximum theoretical recovery;• the “EFF 77%” curve shows the maximum theoretical recovery with a power generation

efficiency of 90% and the inverter efficiency of 95%;• the “EFF 60%” curve shows the maximum theoretical recovery with a power generation

efficiency of 90%, the inverter efficiency of 95% and a charging/ discharging efficiencyof 70% for the battery.

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Figure 19. The Japanese 10-15 mode cycle.

The acceleration/deceleration that the calculations are based on are heavier (0.15 g) than theaccelerations/decelerations of the ECE driving cycle (the low speed part of the complete ECEcycle of today) but they certainly occur in real traffic on the road. On the other hand a speedof 40 km/h must be seen as somewhat low and in the calculations carried out by Iwai this isthe only case of acceleration/deceleration which is dealt with. Therefore the abovecalculations should be seen as an example presented in order to demonstrate some factorsinfluencing the braking energy recovery and the impact of some parts in the hybrid system onthe efficiency on the system. Iwai points out that when a lower acceleration/deceleration rate(0.08 g) is used as a base for the calculation of the braking energy recovery, the result will beonly approximately 50 % recovery. Iwai indicates that the efficiency of charging/dischargingof a battery for an electric car is 55% and that an efficiency of 70% is at the upper limit for abattery. A question not answered by the above calculations concerns the level of energyrecovery in reality and the real efficiency of charging/discharging of batteries (see also Figure20).

Figure 20. Different cases for calculation of the braking energy recovery (0-0.15g). Source: Iwai, 1998.

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The tests, computer simulations and calculations carried out according to the aboveparagraphs have also resulted in a presentation of a figure showing the energy improvementsfor different driving conditions (see Figure 21). The figure represents improvements in km/lgasoline when the mass of the car as a hybrid has been normalized to the same car as agasoline-fueled car. If the mass of the car is not normalized the comparisons would not becorrect (according to Iwai) since the mass of the car is higher when the hybrid system isinstalled.

Figure 21. Improvement of fuel consumption for a series hybrid when tested according to theJapanese 10-15 mode cycle (1.8 ton ”minivan”). Source: Iwai, 1998.

The designation SHEV” stands for series hybrid electric vehicle. Since the hybrid system hasnot been presented in detail it is not possible to determine how well the different alternativesdepicted in Figure 21 are representative of an average series hybrid systems. However, theimpression is that much work has been carried out for the above presented studies andcalculations. Different hybrid systems can certainly show different efficiency depending onthe design of the system, resulting in the energy transformations in one hybrid systemdiffering from the energy transformations in another (see also Section 8.1.1).

8.1.3 Result of the PNGV program

Within the PNGV program the potential of hybrid systems has been evaluated with respect toreduced fuel consumption. The goal for the PNGV program is to improve the fuel economyfor passenger cars from the present day level up to 80 miles per US gallon (3.785 liter. 80miles/gallon=0.301 liter/10 km). This applies to a vehicle the size of a middle sized US

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passenger car (type Ford Taurus) according to the PNGV requirement for fuel economy. Thesize of Ford Taurus is considerable larger than the size of European cars with the same fuelconsumption, such as a car recently presented on the marketm the VW Lupo, 3 liter. WithinPNGV there are also stringent requirements for emissions, safety, performance, costs etc. Theprogram started 1994 and is a 10 year program.

For the time schedule to be followed, prototypes of the specified cars, ready for productionand meeting the stringent requirements, are to be presented in 2004. An evaluation of thePNGV has been presented in a report published in 1998 (NRC, 98) and thereby gives anestimation of the potential for reduced fuel consumption in different system combination. Theresults of a summary presented by Ecotraffic (Sweden) are shown in Figure 22. Each of thehorizontal bars shown in the figure represents an interval of the uncertainty in the estimatedfuel consumption (energy used). The vertical thicker line approximately represents the 80miles/gallon goal for fuel economy – here in liter per 100 kilometer gasoline equivalents.

Figure 22. Potential for different automotive system. Source: NRC, 98.

Of Figure 22 it can be seen that the ongoing development of the chassis and the body of thecar with the goal to minimize the air drag and friction coefficient has the largest impact on thefuel consumption. The goal for the development of the chassis/body is far reaching. In thefigure it can be seen that none of the conventional systems for propelling the vehicle (i.e. non-hybrid systems) are expected to have the potential to reach the goal for fuel consumption, noteven the new advanced vehicles. A diesel hybrid (of parallel type) and the two variants ofhybrid vehicles equipped with fuel cells are the only vehicles which are estimated to fulfil thePNGV requirement for fuel economy. It can be noticed that a stack of fuel cells includingequipment for the production of hydrogen can be regarded as a hybrid system since both thefuel cells and the batteries are the energy sources for propelling the vehicle. The only hybridalternative for such a vehicle is a series hybrid since the fuel cells generate electricity but notmechanical work.

It can be seen as somewhat surprising that the potential for fuel cells is not estimated to behigher than shown in the figure, despite their high status as efficient energy transformers. Fuel

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cell efficiencies of up to 70% are often reported which would be a remarkable improvementon the 30-40% for an internal combustion engine. The truth about the fuel cells is that a stackof fuel cells may have high efficiency in transforming the energy from hydrogen to electricenergy but there are considerable energy losses in producing hydrogen in a fuel transformerand in other auxiliary equipment needed to run the fuel cells. It would be an advantage if theefficiency of the total system could be reported since it is that efficiency which is of interestwhen comparing systems for propelling the vehicle.

In cases where reformers is used for the production of hydrogen on board a vehicle, fuelswhich are easier to handle than hydrogen (such as ethanol or methanol) can be used but evenhere the energy losses are large. There is an ongoing development of technology in order touse fuels such as natural gas, gasoline (Shell is engaged), even light diesel oil (jet fuel) andpossibly even common diesel oil in fuel cells. However many vehicle manufacturers, regardthe problems, including the infrastructure (for natural gas), as being larger for these fuels thanfor methanol, which is estimated to be the easiest fuel of all to be used for production ofhydrogen on board of the vehicle. Regarding the energy losses for this production, it shouldbe stated that high temperatures are needed for the production of hydrogen and there is alsosome emissions released. It cannot therefore be said that the vehicle is a zero emissionvehicle. Concerning the emissions a study has been carried out on the request of KFB(Westerholm and Pettersson, 1999).

When the PNGV program started in 1994 considerable resources were also used for thedevelopment of alternative engines such as the Stirling engine and gas turbines. The amountof resources spent on such engines seems to have been drastically cut, for two reasons. Firstlythere are considerable technical problems with the engines (exotic materials such as ceramicshave to be used) which leads to a risk for a delay in the time schedule. Secondly it is estimatedthat the use of these engines will result in less impact on fuel efficiency than that obtained bythe use of fuel cells and diesel engines.

The use of advanced otto engines (Parallel hybrid + Advanced otto” in the figure) has beenone of the alternatives evaluated within the PNGV program. The expression “advanced”means in this context an engine designed with direct injection of gasoline – similar to thetechnology for the Mitsubishi GDI engine. At the beginning it was stated that even anadvanced otto engine could not meet the requirements stated for fuel consumption within thePNGV program. It was therefore decided to only carry out observations of the developmentin the area and to spend only a small amount of resources for studies within the program.However, the positive progress and the resolution shown by Mitsubishi have resulted in moreresources now being spent on this technology. Such engines may be of interest in aconventional vehicle and in the case of the required fuel efficiency not being met, the DI ottoengine may fulfil some new somewhat leaner requirement for the fuel efficiency. A problem,which has not yet been solved, concerning the use of the DI otto technology is that the fuelmust be nearly free from sulfur in order to meet the emission requirements, since theefficiency of the deNOx catalyst deteriorates very fast if the fuel contains sulfur.

The most concrete form of prototype vehicles demonstrated today within the PNGV programare the prototypes of parallel hybrid vehicles presented by “the three big” (Chrysler, Ford andGM) and these vehicles have been demonstrated as test vehicles in traffic. The developmentof vehicles equipped with fuel cells is naturally somewhat less advanced. However, even inthis case a few prototypes have been demonstrated, but not within the PNGV program as faras is known. For diesel engines the real problem is to meet the very stringent emissionrequirements. For example the standards for particulate emissions have been set at 0.01grams/mile (0.0062 g/km) which must be regarded as a extremely low level for this type ofengine. In this context the emission requirements stated by the PNGV program could be

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compared with the EU particulate mission standards of 2000 and later, for passenger cars,which was 0.05 g/km. This is equal to 0.08 grams/mile respectively (see Section 6 for moreinformation about the today and future EU European emission standards). The particulatestandards in Europe for light-duty diesel vehicles are 0.025 g/km from year 2005 which is0.04 grams/mile respectively. The comparison between the PNGV requirements and EUstandards for year 2000 shows that the PNGV requirements are set at approximately a tenthsof the current EU standards which means that the PNGV requirements are set at the level of anew three-way catalyst car. This level have been regarded as so low that no particulatestandards have been set for gasoline catalyst cars in Europe.

There is also a practical problem with the PNGV program in that the car manufacturer in theUS have not developed and manufactured a small diesel engine since the middle of the 1980s.This means that they must again acquire the basic technology for developing a small dieselengine before they can start a production. Since the diesel engine is the only commercialengine having the potential for meeting the fuel efficiency requirements, that type of enginestill may be a candidate for the PNGV program, together with the otto type of engine,provided it can meet the stringent emission requirements. If both diesel fuel and gasoline areconsiderable improved there may be a possibility for both types of engines if they are used ina hybrid system. For both fuels it is of great importance that the sulfur content is reduced tothe level required for the use of efficient emission control and to reduce both NOx and theparticulate emissions. The already initiated co-operation between the car manufacturers andthe oil industry for improvement of the fuels must continue. In addition to the commercialfuels even alternative fuels including DME have been mentioned.

8.1.4 The influence of hybrid systems on conventional engines

In this section the potential for reducing the fuel consumption for the today and futuredifferent variants of reciprocating engines will shortly be discussed. Since the efficiency ofthe different engines varies as a function of engine speed and load (see Figure 18) thepotential will not be the same for all systems. The four points below represent a ranking of therelative improvement of the engines, which will be discussed. It should be observed that itthese are not absolute differences but only relative improvements. We do not take a firmposition on the question of which hybrid system is the best for each type of engine (series orparallel) but the ranking is solely based on the prerequisite for the actual type of engine.

1. Conventional otto engine with three-way catalyst.2. Diesel engine (direct injected).3. Advanced direct injected otto engine (stoichiometric, EGR and TWC).4. Advanced direct injected otto engine (lean burn, EGR and deNOX).

The Achilles heel for the otto engine is that it is regulated by quantity, i.e. the engine is fedwith the air-fuel mixture via a throttle*. Thereby the pumping losses are considerable at lowloads. At full load these losses are smallest since the throttle then is fully open. A comparisonbetween an otto engine and a DI** diesel engine will prove that the relative difference in

*The air/fuel ratio is stoichiometric or close to stoichiometric.** Here the comparison is carried out between a direct injected diesel engine equipped with turbo since thistechnology has today approximately 50% of the market and is estimated to take over the diesel engine market. Acomparison between the worst diesel alternative and an IDI engine without turbo would be considerably moreadvantageous for a gasoline engine.

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energy use is approximately 17% less for the DI engine at full load (calculated as the ratiobetween the efficiencies at best of 41% for the diesel engine and 34% for the otto engine,based on Figure 18 for both cases). Because the pumping losses increase at low loads it is notsurprising that the difference between the diesel engine and the otto engine increases by afactor 2 or more at low loads. In a certain driving cycle with typical mean values for theefficiencies of 14% and 18% respectively the relative difference will be approximately 20%.Based on the above discussion it can be clearly shown that the improvement in the efficiencyby a transition from a conventional drive system to a hybrid system will be larger for an ottoengine than for a diesel engine. There will still exist an absolute difference between an ottoengine and a diesel engine which is less than 20% but larger than 17% - if the comparison iscarried out for a hybrid system without regenerative braking. In the case of hybrid systems(with otto and diesel engines) where regenerative braking is used, which seems to be commonand is accounted for, the absolute use of energy will be reduced by approximately the sameamount for both types of engines. However the relative difference in energy efficiency willincrease (mathematically) compared with a case without regenerative braking.

For the advanced otto engines the goal for the development has been to decrease the fuelconsumption at partial load by reducing or eliminating the pumping losses (avoid throttlingi.e. the use of throttle) at part load. Thanks to the fact that direct injected otto engines areoperated at stoichiometric air-fuel mixture (#=1) at full load, exactly like conventional ottoengine, the energy efficiency at full load will be the same for both types of engines or at bestshow a small improvement for the direct injected engine.

Two main types of combustion systems for the direct injection engine seem to have beendefined. One type, which has been commercialized by Mitsubishi and Toyota, uses acombination of excess of air (#>1) and EGR. Through this method the pumping losses can benearly eliminated at low loads. The other variant uses only EGR in order to achieve the sameresult. Despite the fact that the direct injection essentially increases the engine acceptance ofEGR compared with a conventional otto engine, the pumping losses cannot be completelyeliminated since the engine does not tolerate that high EGR rate that is required in order tocompletely eliminate the use of a throttle.

In comparison with a diesel engine it is possible, within a small area of mussel diagram (seeFigure 18) at low load, to nearly achieve the same efficiency as for a diesel engine when usingthe second variant of combustion system (see engine type 4 above). With the first variant ofcombustion system (see engine type 3 above) the same low fuel consumption cannot quite beachieved as for the second variant.

Since the reason for using a hybrid system is to increase the average engine load (where theefficiency is higher) the engine will be operated relatively more in the area where thedifference between a conventional otto engine and the direct injection engine is less than atlow load or at medium load (Figure 18). Therefore the potential for a relative improvement offuel consumption will consequently be less for the direct injection otto engine than for theconventional engine and probably also less than for a diesel engine. Another consideration tobear in mind is that a direct injection otto engine is likely to suit a parallel hybrid systembetter than a series hybrid system since the internal combustion engine is not operated at thesame higher load in a parallel hybrid as in a series hybrid.

If the comparisons for the four different types of engines are based on differences in fuelconsumption the result for ranking of absolute fuel consumption will the following:

1. Diesel engine (direct injected).2. Advanced direct injected otto engine (lean burn, EGR and deNOX).3. Advanced direct injected otto engine (stoichiometric, EGR and TWC).

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4. Conventional otto engine with three-way catalyst.

8.1.5 Series hybrid or parallel hybrid?

During the literature studies it has been noticed that the focus was more on series hybridswhen the PNGV program started in 1994, but that later on it shifted over towards parallelhybrids. Higher costs and a lower potential for reduced fuel consumption for series hybridsthan was first estimated may be the reason for this change of strategy. The hybrid systemswhich are now commercialized (Toyota, Honda, Audi and some other Japanese manufacturer)are all parallel hybrids despite the fact that the systems are somewhat different in theircharacteristics and construction. In some cases the classification “parallel hybrid” can bequestioned since the systems may be seen as something between the two main hybrid systems,but which have chosen to be called parallel hybrids. Furthermore, the three types of hybridsystems presented within the PNGV program are all parallel hybrid types (more like parallelhybrids than the Toyota system). Signals from the European car manufacturers can be seen asan indication that the Toyota system will be the most popular in the short run.

It should also be underlined that that hybrid systems present considerable more possibilities inthe construction of the drive system than was earlier given by the commercial systems. Insome cases the type of system cannot clearly be characterized. It is likely that many differentsystems will be used during the reasonably near future before the most efficient system (in theform of a compromise from different criteria) is determined.

The factors which give a preference for parallel hybrid systems are the higher efficiency, thepossibility of achieving good performance and a well-developed battery. For heavy-dutyvehicles which are produced in limited numbers, there is also an advantage with the parallelhybrid system in that standard components can be used in many models, which supports thecosts of the development.

In order to sum up it can be said that there is a considerable potential, in using a hybridsystem, for improved fuel economy (less energy use). Also the transition to the use of fuelcells is facilitated by the use of an electric drive system in hybrid vehicles. One idea to realizecould be to use hydrogen in the vehicle for the fuel cells (to improve the fuel cell system) inorder to eliminate the use of the battery as back up for the fuel cell (see Section 8.2.2). This isprovided that the battery is not required for compensation of the power drop during start of thevehicle.

The structural problem of handling hydrogen requires a development of the technology for thestorage of hydrogen and improved methods for the production of hydrogen before a broaderintroduction will occur. For local fleets the situation may be somewhat more favorable but inthis case hydrogen will be used only within for example a city area. Since fuel cells (like gasturbines) are used only in series hybrids, the parallel systems will be replaced when fuel cellstake over the market for hybrid vehicles.

BMW in co-operation with Dresden Technical University has evaluated and compared theseries hybrid system with the parallel hybrid system (Friedmann et al., 1998) and found thatthere is an advantage with parallel systems in terms of “use of energy”. In the first place theypoint out that there are advantages with all hybrids in that they have a potential for “exhaustfree” driving in environmental sensitive areas. They also have an additional power source andthe hybrid can recover energy during braking. The authors also point out the advantage of andpossibility to control the internal combustion engine in a way that is not possible with theengine in conventional vehicle. In Sections 9.1 and 9.2 more detailed presentations of thework, carried out by the authors of the above-referred report, can be found.

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The sensational conclusion the authors of the report came to, concerning the fuel economy, isthat the series hybrid with present day technology has a poorer energy use than a vehicle witha conventional engine despite the hybrid vehicle being equipped with regenerative braking -“Braking Energy Recovery” (BERG). With the parallel hybrid (with BERG) the energy usecan be improved, even in the case of electric driving, up to 40 km/h when driving according tothe European driving cycle and up to 30 km/h when driving according to the European urbandriving cycle (EUDC). Both of the systems (series and the parallel) are advantageous in termsof emissions compared with a conventional car, but even here the parallel hybrid is in front ofthe series hybrid.

Iwai (Iwai, 1998) is also of the opinion that the parallel hybrid is superior to the series hybridconcerning the energy use, but this is valid under certain conditions. If the internalcombustion engine can be operated in the area with highest efficiency there is a potential forthe series hybrid to surpass the parallel hybrid in terms of energy use. However, the problemis that this operating condition is extremely difficult to maintain in reality.

8.2 Examples of developed and demonstrated hybrid vehicles

The hybrid passenger cars presented today are in most cases smaller than their counterpartswithout and the greater part of them are manufactured from lighter material than the materialused in ordinary commercial vehicles. Despite the fact that the parallel hybrids are equippedwith a smaller internal combustion engine and a lighter battery than the series hybrids, all theextra equipment including the electric motor to be used in a hybrid vehicle contribute to thefact that the parallel hybrid vehicle will be heavier than a vehicle of the same size withouthybrid system.

8.2.1 Mercedes series hybrid

In a SAE report Mercedes presents results from measurements of emissions and fuelconsumption (energy use) for a prototype car with a series hybrid system (Abthoff, J.O. et al.,1998). Data is presented only for the US EPA FTP-75 cycle, i.e. the same cycle as that used inSweden from the middle of the 1970’s up to 1997, representing urban driving (see Table 17.).It should be added that Mercedes-Benz later on presented a series of vehicles equipped withfuel cells which according to the definition used here can be regarded as series hybrid vehicles(see below).

As was earlier indicated, the reduction in the fuel consumption (or used energy) is small. Forthe hybrid vehicle it was 8.8 l/100 km when the system was optimized for low emission levelsand 8.0 l/100 km when it was optimized for low energy use, which should be compared with9.0 l/100 km for the commercial version of the same car. The reason for the small reduction ofused energy is regarded as being related to the relatively high mass, 1 758 kg, of the hybridvehicle which is an increase from 1 350 for the vehicle without hybrid system. Despite anincrease in the men value of the efficiency of the hybrid system this improvement is eaten upby the higher mass of the vehicle. However, it should be taken into account that the presentedcar was a not finally developed prototype and is not representative of a series hybrid with afully developed system. In the presented vehicle only minor changes have been introducedcompared to the original vehicle and therefore it is quite clear that even changes of the bodyin the car would have improved the above-presented results. One advantage with this hybridsystem from Mercedes, which is worth pointing out, is the battery pack which has an energydensity of 1 000 W/kg and a total power of 55 kW. Despite these advantageous batteries theconclusion is that the increased mass of the vehicle is considerable.

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Table 17. Comparison between a series hybrid and a conventional drive system. (Source:Mercedes (Abthoff et al., 1998).

Fuel consumption in FTP-75Characteristic 1.8 l class

productionSeries hybrid opt.

for emissionsSeries hybrid, opt.for fuel consumpt.

Acceleration 0-100 km/h (s) 12.0 14 14Max. speed (km/h) 193 >150 >150Emission levels (FTP-75) TLEV1 EZEV2 -Used energy (gasoline l/100 km) 9.0 8.8 8.0Vehicle weight (kg) 1 350 1 758 1 758Notes:1The TLEV level exists in a commercial vehicle with a 2.3 liters engine but may also be possible to meeteven with a 1.8 liters engine.2EZEV emissions, without the additional emissions required for distribution of the fuel, which has to becalculated for by the car manufacturer according to EZEV.(”TLEV” and ”EZEV” represent emissions requirements in California).

8.2.2 DaimlerChrysler’s Necar fuel cell series

The first car of the Necar series – an A-class car - was presented in 1994 and the third car,Necar 3, in 1997. Today a forth generation in the series, Necar 4, is now presented (see nextparagraph), which may mean that first three in the series of hybrids are replaced by the newcar. It should also be said that a new company has been formed by the joining of MercedesBenz and Chrysler in 1998 into one company named DaimlerChrysler. (see Figure 23) andaccording to information from DaimlerChrysler that was the first car operated with fuel cellsas the main power source. Necar 3 was equipped with a reformer used to produce hydrogenfrom methanol on board of vehicle.

Figure 23. Mercedes hybrid car Necar 3, equipped with fuel cells.Source: DaimlerChrysler home page.

The latest version vehicle of the Necar series is, as far as known, Necar 4 equipped with a fuelcell stack. Necar 4 is equipped as to be fueled with hydrogen and to be correct Necar 4 shouldnot be regarded as a hybrid vehicle since it has no battery and is operated with a electric motorpowered with electricity direct from the fuel cell. Consequently Necar 4 is an electric vehicle

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by definition. The top speed of the car is 90 miles per hour (245 km/h) and the operationrange is 450 km between refueling. As Necar 4 uses hydrogen as a fuel, which result in zeroemissions according to DaimlerChrysler. Of figure 24 it can be seen that Necar 4 rathersimilar in shape to its forerunner Necar 3, Figure 23.

According to information in the home page of DaimlerChrysler Necar 4 will be used for thetransfer of “VIPs and pilots from the airport in Munich”.

Figure 24. Mercedes hybrid car Necar 4, equipped with fuel cells.Source: DaimlerChrysler home page

A representative for DaimlerChrysler said that they have decided to improve the cars, whichmay be interpreted as that the company is planning for new cars in the Necar series or somenew car model equipped with fuel cells. DaimlerChrysler has declared that they are firmlydetermined to continue the development of fuel cell vehicles and points out that they aregoing to commercialize a fuel cell car in 2004. Furthermore they underline that at the presenttime the company has spent 1.4 billion dollars on this project which is at the same level as thesum of money spent on such high sellers as Chrysler 300 M, Chrysler Concorde, ChryslerLHS and Dodge Intrepid.

At a seminar in November 1999 Dr Ferdinand Panik said that the question of an infrastructurefor fuel cells must be seriously discussed as soon as possible “if a competitive advantage is tobe secured in the U.S. and Germany”. Panik also said that the work carried out by hiscompany DaimlerChrysler has proved that there is a technical feasibility in the use of fuelcells. More than 60 companies around the world are working in the field of fuel cells and areintending to launch vehicles with fuel cells within the next five years. Four of the largestJapanese automobile companies will have invested more than 546 million US dollars at theend of 1999 in the development of fuel cells.

8.2.3 Toyota Prius, parallel hybrid

Another interesting example to study is the Toyota hybrid Prius. According to earlyinformation Toyota started the introduction of Prius in December 1997 and has this year (year2000) started introduction in Europe. A few cars used for demonstration have been seen bothin Europe inclusive of Sweden and in the US since 1998. It has also been announced that the

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production of Prius should be 1 000 cars per month to start with (it is assumed that the numberof cars will be raised after the introduction of Prius on a broader market).

Contrary to the example of Mercedes series hybrid demonstration, Toyota Prius is already ahybrid car ready for the market. The total mass of Prius is 1 240 kg which may be 100-150 kgmore than a commercial car of the same type and size. The difference in mass is, however,much less than for the above-presented hybrid from Mercedes.

According to data published by Toyota (Toyota, 1998; Takaoka et al., 1998) the fuelconsumption of Prius is 3.6 l/100 km (67 mpg) gasoline when driving the vehicle according tothe Japanese 10-15 mode cycle (see Figure 25). This level of fuel consumption must beregarded as a low for a low-speed driving cycle like the Japanese driving cycle. However,when a hybrid vehicle is compared with a conventional vehicle the difference in use of energyis generally largest at low load and speed, which favors the hybrid vehicles, since the internalcombustion engine commonly is shut off at low loads and at idling and this is also the casewith Prius. In addition the braking energy is mainly recovered in a hybrid vehicle. Whendriving on roads outside of cities etc. the difference between a hybrid vehicle and acommercial vehicle is less but Toyota has not presented any data for tests according to theEuropean driving cycle. In the case of Toyota, where the battery is charged only by theengine, the energy delivered by the battery should not be accounted for when calculating theaverage energy used.

Figure 25. Schematic configuration of the hybrid system from Toyota. Source: Takaoka et al., 1998.

An investigation of the Toyota Prius has been carried out and published by US EPA (Hellmanet al., 1998) and in this case energy use in terms of gasoline fuel economy was 49.8miles/gallon (approximately 4.72 l/100 km) when the EPA test cycle was reported. The speedof the two parts of the test cycle is 45 and 55 miles/h (72 and 88 km/h) respectively. In thefollowing table a recalculation from miles per gallon to liter per 100 kilometer for somedifferent vehicles has been carried out (see Table 18). The differences between the results forfuel economy given above and the results for Toyota Prius presented in the table are related tovarying data and a result of rounding off.

As can be seen in Table 18 the used energy is at a considerable lower level for Toyota Priusthan for Toyota Corolla. However, it should be noted that Toyota Prius is a rather smallvehicle (a sub compact) compare with Toyota Corolla and it is of the same size class asSuzuki Metro but heavier than Suzuki which used energy at the lowest level of all of thevehicles in the table. The energy used for the diesel-fueled vehicles (Passat and Jetta) is alsoat a slightly lower level than for the Toyota Prius despite that they are both larger and heavier.The fuel economy* of 67.4 miles/gallon (28 km/l or 3.57 l/100 km) which is reported by * In the USA the expression fuel economy commonly is used while in Europe the expression fuel consumption

always is used. Here both these expressions are used in order to satisfy the presumptive readers.

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Toyota is much lower than the figure for fuel consumption shown in Table 18. It is probablethat this figure for fuel consumption been understood in Europe as the fuel consumption whenmeasured according to the European test cycle and in the US as the fuel consumptionmeasured according to the EPA FTP-75 test cycle. Even if the figure for gasoline fuel usedper driving distance is remarkable good it is not as good as is stated in newspapers andmagazines. An important aspect to take notice of when comparing different vehicles is stillthat the Toyota Prius hybrid system presents the same comfort as an automatic gearbox andtherefore the comparisons should be carried out with conventional vehicles equipped with anautomatic gearbox. Such a comparison would result in a more favorable position for ToyotaPrius.

Table 18. Fuel consumption (as gasoline) for Toyota Prius and some other vehicles with lowfuel consumption.

Vehicle Size of vehicle Inertiaweight,

[kg]

Fuel Fuel consumption[l/100 km] [MJ/100 km]

Gear box

Suzuki Metro Sub-compact 964 Gasoline 4.32 ca 141 M5VW New Beetle Sub-compact 1 418 Diesel oil 4.56 ca 163 M5VW Passat Mid-size 1 531 Diesel oil 4.58 ca 163 M5VW Jetta Compact 1 418 Diesel oil 4.62 ca 165 M5Toyota Corolla Compact 1 247 Gasoline 6.44 ca 210 M5Toyota Prius Sub-compact 1 361 Gasoline 4.84 156 AT (THS)a

Notes: Energy content: gasoline=44 MJ7kg, diesel=43 MJ/kg. Density: gasoline=0.74 kg/l, diesel=0.83 kg/l.a Automatic gearbox does not exist in reality but the function in the hybrid system (THS, Toyota Hybrid System)can be compared with an automatic gearbox.

8.2.4 Ford’s parallel hybrid vehicles

The new hybrid systems presented by the American car manufacturer Ford are the result of,among others things, computer simulations and work with models by which Ford identifiedtwo parallel hybrid systems. These are expected to meet the requirements for gooddriveability and good fuel economy at the same time as good emission performance isachieved. Ford has named one of the systems ”Post-Transmission Hybrid” (PTH) where theelectric motor is direct connected to the driving wheels after the gearbox in the driveline. The”PTH” hybrid vehicle is equipped with a 1.8 liter, 4-cylinder gasoline fueled engine and a 5-speed transmission. .

In the other hybrid system denoted ”Low Storage Requirement” (LSR) a small electric motoris used in combination with a nickel-metal-hybrid battery (which can be seen as a type ofauxiliary unit) for storage of energy and also in order to support the internal combustionengine when more power is needed. In order to avoid a misunderstanding it should be pointedout that there are two alternative hybrid systems of which one, the LSR, is equipped with aCIDI diesel engine (see Section 6.2) denoted DIATA (”Direct Injected Aluminium ThroughBolt Assembly”).

The LSR hybrid system (see Figure 26) is mounted on a platform (a Contour/Mystique/-Mondeo chassis), which is manufactured from low weight material. The CIDI diesel enginefor the LSR has a displacement of 1.2 liters and a max. power of 55 kW at 4 500 rpm. The caris denoted P 2000 and it is equipped with comprehensive electronic control system. The totalweight of the P 2000 is 2 000 lbs. (908 kg) which is 40% lower weight than Ford Taurus’1997 year’s model of 3318 lbs. (1506 kg). The comparison is valid for P 2000 without hybridsystem, which in its present version will add approximately 990 lbs. (450 kg), but the goal fora well-adapted hybrid system is an additional weight of a little more than 600 lbs. (275 kg).

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According to Ford (Buschhaus et al., 1998) energy use in terms of diesel oil of 3.5 l/100 km(68 miles/gallon fuel economy) has been achieved for the LSR vehicle with the CIDI dieselengine DIATA. Energy use of 3.4 l/100km (69 miles/gallon fuel economy) has been achievedfor the LSR vehicle, when it is equipped with the same engine. It is noted in the report thatboth vehicles meet the Tier II emission standards.

So far no information, in addition to that from Ford, has been available for this report andtherefore all information used here is that from them. People at Ford dealing with research,investigations and development call attention to the fact that there are three predominantcharacteristics for hybrid vehicles. These are 1) that the internal combustion engine is shut offwhen the vehicle is stopped and that it is easy to start again; 2) the size of the engine isreduced and 3) that regenerative braking is included in the system. They also point out thatthere are other functions of importance, for example that the battery can be recharged fasterthan the existing 400 V belt driven inverter manages to do under operation. Furthermore theelectric motor (”Starter/alternator”) can assist the internal combustion engine duringaccelerations (see also Figure 26).

Figure 26. Schematic picture of Ford’s hybrid car(”LSR”). Source: Automotive EngineeringInternational/February 1999). Reference: (Buchholz, 1999)

Ford’s “LSR” hybrid vehicle has been equipped with a special ”Starter Alternator” which isnot a new invention. It has not however been presented as an individual unit in for exampleToyota’s and Nissan’s hybrid systems (see Nissan’s hybrid system below).

In 1993 Ford received a contract from US Department of Energy (DOE), which stated thatFord had agreed to develop a hybrid system. It also stated that Ford should investigate anddevelop a synergistic combination of the technology for combustion and the technology forpower drive. This was in order to increase the internal combustion engine technology, at thesame time as the performance and the comfort of the vehicle had to meet the demands fromthe car owner.

The plan for development of the above presented hybrid system, “PTH”, which meant that thevehicle should be equipped with an CIDI diesel engine, did not satisfy the requirements statedby DOE. Therefore in 1997 it was agreed between DOE and Ford that Ford should not use theDIATA engine in its PTH hybrid vehicle. Instead it was decided that a Mondeo based car,

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which was already under development, should be used in the hybrid system to be delivered toDOE at the end of the time for the original contract. The hybrid system to be used in the car isschematically shown in Figure 27 and contains a PTH drive and an otto engine. As far as hasbeen understood of the report (Buschhaus et al., 1998) the actual version of PTH in a Mondeotest bed (Figure 27) is equipped so that the battery can be charged from the mains.

The construction of the “LSR” hybrid system in a P 2000 test bed (see Figure 26) is, however,such that alternative charging from the mains is not of any great use. Therefore this abilitydoes not exist, even if this fact cannot clearly be seen in the figure or by the presentation ofthe system. The car cannot be run on only the battery since only a small battery is used.

Figure 27. Ford’s hybrid system PTH with gasoline engine. Source: Buschhaus et al, 1998.

8.2.5 Nissan’s parallel hybrid

Some of the fundamental parts of Nissan’s hybrid system are as follows.

Internal combustion engine integrated with a CVT (”Continuously Variable Transmission”).

Equipped with a lithium-ion battery.

Fuel economy: + 100 % compared with conventional car.

Acceleration: Equivalent to conventional car model.

Planned introduction in Japan early year 2000.

The basic construction of Nissan’s parallel hybrid vehicle is that the system (see Figure 28) iscomposed of a highly efficient otto type engine, a generator mounted on the front of theengine, a belt-drive continuously variable transmission (CVT), an electric motor and a lithiumion battery (Kitada et al., 1998). The system also includes a clutch with the basic function totransmit engine torque during the engine-powered mode and to isolate engine friction duringthe motor-powered mode (including regenerative braking). The use of a CVT has resulted inthe electric motor and the internal combustion engine being able to be operated in areas withthe highest efficiency (see Figure 18 mussel diagram). When driven the hybrid system iscontrolled according to the following six points:

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(1) The internal combustion engine is shut off when the car is stopped; a creeptorque is generated by the electric motor (traction motor) with the clutchactivated.

(2) Since the car is initially run by the traction motor a gear ratio is chosen(automatically) which allows the traction motor to operate with a high torque.When the speed of the car increases the generator is activated and it starts theinternal combustion engine and activates the clutch. In cases with fast start theengine is started and the clutch is smoothly engaged, which result in the carbeing accelerated by both the motor and the engine in the same manner asduring the cruising speed.

(3) During cruising speed a gear ratio is chosen which allow the internalcombustion engine to operate in its most efficient area. During this mode thetraction motor/generator (one feature of the traction motor is that it can alsooperate as a generator) charges the batteries after the discharge during the start-phase of the car. Nissan points out that the use of energy (expressed as fuelconsumption) is reduced since the engine can be efficiently operated. Anotherreason is that operation at a smaller gear ratio is possible because of the largesupplementary torque that can be expected from the traction motor.

(4) During acceleration the traction motor assists the internal combustion engineand the batteries supply the energy needed.

(5) During decelerations the function of the traction motor is to be a generator forcharging the batteries. During this sequence the clutch is engaged in order torecover maximum energy to the batteries.

(6) When moving the vehicle backward (reversing) the traction motor operates inreverse. Normally the batteries provide the traction motor with energy, but ifthe batteries are not fully charged the engine starts in order to charge thebatteries.

Figure 28. Scematic configuration of the hybrid system from Nissan. Kitada et al., 1998.

The reason for this detailed description of hybrid system from Nissan is that, in many details,it is different to the systems from for example Toyota and Ford. Probably there are noremarkable differences between the Nissan system and the other two systems but in the hybridfrom Nissan the traction motor propels the car during the start phase and also when reversingthe car which may decrease both the emissions and the fuel consumption. Whether the hybridsystems from Toyota and Ford have these two functions is not clear. In the hybrid systemfrom Ford the diesel engine is not shut off during low loads, which is the case in the Nissan

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system. The reason for not shutting off the engine in the Ford system may be that the fuelconsumption is very low when a diesel engine is idling.

With the control of the hybrid system used by Nissan it is clear that the fuel consumption (useof energy) is especially effected at low loads and idling. Unfortunately no data for either thefuel consumption or the emissions was available for this report. However in a report fromNissan (Kitada et al., 1998) it is said that the fuel economy is increased by 100%. This meansthat the fuel consumption is reduced by 50% when driving according to the Japanese 10-15mode cycle while it is unchanged during accelerations from 0-100 km/h and at top speed, allcompared with a conventional car. One problem concerning such information is that there isno information about whether the conventional car was a low or a high consumer.

8.2.6 Some other light hybrid vehicles

The focus on the use of hybrid vehicles as a possibility to reduce the use of energy (or fuelconsumption) and emissions has attracted many car manufacturer, consulting companiesworking in the area of motor vehicles and institutions connected to universities. They havestudied, analyzed and, in relevant cases, developed hybrid systems and vehicles with hybridsystems.

At a conference ”EnV’99, Alternative Fuels and Advanced Technology Vehicles”, whichdealt with alternative fuel technology and alternative vehicle technology, the presentationsabout hybrid systems were of special interest. In addition to the hybrid systems presented hereit was shown that, among others, Honda and Southwest Research Institute (SwRI) havestudied and developed hybrid systems. Representatives for both of these have presentedplans/ideas for development and presumably also prototype hybrids. Honda announced thatthe company was planning an introduction of hybrid systems for the Japanese market.

Honda: At the time for the preparation of this report no report was available which describedin any detail the hybrid system from Honda. However, in the home page from Honda therewas some brief information about a hybrid system named “Insight” which was underdevelopment. From this information it can be seen that the body of the car will be constructedfrom aluminum and that a 3-cylinder 1.0 liter internal combustion (gasoline fueled) lean burnengine (compression ratio 10.8:1 and 67 hp/5 700 rpm), will be used. The electric motor wasan “ultra-thin” and carefully designed ”for outstanding performance and efficiency” motor –probably having that shape in order to fit the space at one end of the engine where it wasgoing to be mounted. According to the plan the system would not be designed to permitcharging the battery from the mains. The fuel economy was expected to be 61 miles/gallon(3.9 l/100 km) for city driving and 70 miles/gallon for highway driving. No fixed time forintroduction was given and the intention of Honda may be, according to the giveninformation, to be like Toyota and Nissan, in that the introduction be limited to the Japanesemarket. However the information says that: “The Honda Insight is the first gasoline- hybridelectric vehicle to be sold in the United States”. And further “Plus, it meets California’sstringent Ultra-Low Emission Vehicle (ULEV) standard, making it one of the world’scleanest, most fuel-efficient gasoline-powered automobiles”.Southwest Research Institute (SwRI): The engineers at SwRI have developed ”A ParallelHybrid Train” (SwRI, 1999). Since they not have mounted their system in a vehicle theyhave instead constructed a test bed and equipment for testing the hybrid system. This testinghas been carried out in order to verify that the results meet what was expected during theplanning of the system. The investigations carried out are, to a great extent, computersimulations but there have also been tests of different components of the system. Thecomputer simulations of fuel consumption and emissions have been based on that the hybrid

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system was mounted in a Ford Taurus – a rather large vehicle for Europe (1360 kg) andespecially when compared with other hybrid vehicles. This has resulted in fuel consumptionnot being at the same level as for Toyota Prius – one of the hybrid vehicles which has metmost interest to date.

One features of special interest, despite not being new – is the ”Continuously VariableTransmission” (CVT) developed by Van Doorne in Holland. By the use of a CVT the hybridsystem can be driven in four different modes (”Powertrain Power Flow”):

Charging mode: The internal combustion engine (otto) is operated at full load at its mostefficient area. The excess power (the power not required to propel the vehicle) is transferredby the planetary gear system to the electric motor in order to charge the battery.

“Assist” mode: In this mode both the engine and the electric motor are used for traction. Thiscombination delivers the maximum power to the drive wheels. It is the least fuel-efficientmode since the electric motor cannot deliver any excess power and the engine is notnecessarily operated in its most efficient area.

Electric mode: The electric motor supplies power to the drive wheels, exploiting itssuperiority to the otto engine.

Regeneration mode: The deceleration (and braking) energy is recovered (i.e. delivered to thebattery) via the electric motor.

According to a representative from SwRI the function of the CVT is such that the internalcombustion engine can be operated in its most efficient area and also that this parallel hybridsystem can be controlled in a similar way as the engine for a series hybrid. Since data is onlyavailable from computer simulations in a laboratory there are some difficulties in estimatingthe performance of the system concerning energy efficiency and emission performance.

According to the above summary different hybrid vehicles and hybrid systems for light dutyvehicles are being developed and constructed and most of this work is being carried out inJapan and the US. Similar development work does not seem to be occurring in Europe, or atleast to a much less extent. One exception presented above is Mercedes Benz or its successorDaimlerChrysler. According to the latest information found in their home page it seems likethat DaimlerChrysler is most interested in fuel cells and their more recently presentedpassenger car is not a hybrid vehicle but is electric vehicle powered with a fuel cell. For therest of Europe there is some activity in the area of hybrid light duty vehicles, at least at someof the car manufacturers’ plants, for example BWW (Friedmann et al., 1998), PSA(Peugeot/Citroen) (Beretta, 1998; Badin et al., 1998) and Audi (Hanauer, 1998). According tonewly received information Renault will introduce a hybrid vehicle in year 2001.

8.3 Some examples of heavy-duty hybrid vehicles

Development of hybrid systems for heavy-duty vehicles has been in progress for many yearsbut has been especially focused on buses. Most of the vehicles involved in this activity arestill under development, which has recently included both heavy-duty trucks and light-dutytrucks. The difference between buses and especially light-duty trucks is that some of the latterare parallel hybrids while all the buses so far known are series hybrids. The development ofhybrid systems for trucks is still in an early phase and therefore it is not possible to estimatethe future for the development of hybrid systems for this category of vehicles.

Since the different hybrid systems have been described in detailed above only an overview ofthe different systems activities and vehicles will be presented in this section. There are manyvehicles under development, or such vehicles that have been involved in the development of

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hybrid systems. Most of these vehicles are different to each other. As far as is known only afew car manufacturers, but many bus operating companies, have been involved in the workwith buses and there the hybrid systems are more or less tailored according to specificationsprovided by local bus authorities. In addition there are only a few cases where this activity hasbeen found as presented in a proper report.

The hybrid systems for buses are almost without exception series hybrids. Only one case ofparallel hybrid system for a bus has been found and that bus was equipped with a lead acidbattery, which seems to be a common battery used in buses presented in this section. Since nofirm information was available in many cases, there is an uncertainty in the statementconcerning the batteries. However, according to reports and other information at least one busof these presented in Table 19 is equipped with a nickel-cadmium battery and a few buses areequipped with a high efficiency ultra-capacitor/battery. According to William West, SouthernCalifornia Edison, new types of battery have been developed but they are estimated to be tooexpensive for the users. Now the situation is that many buses are equipped with a stack ofbatteries weighing as much as 4600 pounds (ca 2088 kg). The weight of another bus was 50000 pounds (ca 22 700 kg) – a common weight of a bus without passengers is 26 400-28 600pounds (ca 12 000-13 000 kg). However, it should be noted, that in these cases, as in manyothers, these are prototypes or the first generation of this kind of buses. In the case of the veryheavy bus the company responsible for the conversion has promised that the weight of the buscould be close to 30 000 pounds (ca 13 620 kg) when further developed which seems to be amore appropriate weight. According to Table 19 different fuels, different APUs and somedifferent units for energy storage (mostly lead acid batteries) are used (see Table 19).

Table 19. Some particulars for a number of hybrid buses and some trucks with hybrid systems.Operator Deliverer of

hybrid systemFuel Int. combust. eng.

or other unitBatterypack

Comments

B u s e sBus company inGothenburg, Swed.

Volvo/ABB Ethanol Gas turbine + battery190 kW*

Lead acidbattery

Volvo co-operatewith ABB

Not declared Mercedes-Benz Hydrogen Fuel cell 190 kW fordrive etc.

Non Tanks with45 000 l hydrogen

Chicago TransitAuthority

Ballard forFuel cells

Hydrogen Fuel cell 275 hkca 200 kW

Non? Large progr. for fuelcells accord. to B

Not declared TNO Hollandconsult inst.

Diesel oil Diesel engine High powerbattery

CRT-filterDeNOx catalyst

Not declared ALSTOM/Renault, France

Diesel oil Diesel engine The mains Trolley bus

Atesina, Italy** Not declared CNG isproposed

Otto engine /CNG Notdeclared

Passengers: 10 seats30 standing

Not declared Probably IVECO Diesel oil Diesel engine Notdeclared

Altra has tested onebus***

Not declared VITO, Belgien Diesel oil Diesel engine Lead acidbattery

Problem with theengine control

Different buscompanies

SwRI in co-operate. with GM

CNG 2.2 lit. VW- engine(otto engine)

Notdeclared

Emissionsmeasurements***

Teansp. EnergySyst. Australia

Not declared Gasoline 1. Otto engine 2.2 lit.2. Otto engine 5 lit.

Notdeclared

+70 lit. pressure tank+ flywheel etc.

* Emiss. (City operation in Gothenb.): NOx=1,0, HC=0.1, CO=1,5 and PM=0.05, all in g/kWh. (Malmquist et al., 1998).** Atesina, which operates electric mini buses in the center of Trento intents to introduce hybrid mini buses and hasanalyzed the costs etc. for operation with series hybrids.*** Emission measurements have been carried out and these have been discussed below.

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Alameda/ContraCosta Transit

APS System Propane Rotary (Wankel-)engine, generator

Nickel-cadmium

Two electric motors

Augusta-Rich.County Transit

USDOE particip.in the project

Hydrogen(140 m3)

Standard otto engine Notdeclared

Hydrogen is storedin metal hydride

ChattanoogaArea RTA

Advanced VehicleSystem

CNG,gasoline

Capstone turbine Lead acidbattery

Larger turbines areunder construction

Cleveland RTAMfl (Consort.)

NASA LewisRTA

Naturalgas

Gas turbine Ultracapacitor

900 000 dollarsproject

DUETS A project withmany participants

Notdeclared

Not declared Notdeclared

1.3 million dollarsproject

Indianapolis In-ternat. Airport

General Motors CNG Probably otto engine Notdeclared

Two buses exist - athird is ordered

MTA Los Angeles Advanced Tech.Transit Bus

CNG Diff. engines andalternative (fuel-cell)

Ultracapacitor

51 million dollars6 prototype busses

Different buscompanies

B la New Hamp-shire Techn. Inst.

The sun Sun cell Notdeclared

Co-operation withmany car manufact.

New York MTA Orion BusIndustries

Diesel oil Diesel engine Notdeclared

A very heavy buswill be lighter

Oahu TransitAuthorities

El Dorado Diesel oil Diesel engineParallel hybrid

Lead batt.”Plug in”

Also an alternat. buswith NiCd-batt.

Orange CountyTransp. Autorit.

New FlyerIndustr. Ltd.

Notdeclared

Not declared Notdeclared

One order has beenwritten

Pittsburg Intern.Airport

El Dorado Propane Probably otto engine Lead acidbattery

Problem with the bus

Vandenburg AirForce Base/APS

Carlstadt CNG Probably gas turbine Notdeclared

Many are engaged inthe project

Different buscompanies

Toyota Motor Corp Gasoline Probably otto engine Notdeclared

One smaller bus

Different buscompanies

AMC and KoreaNational Univ.

Diesel oil Diesel engine Notdeclared

The project started in1992

Stockholm Bus Lund tekn. Univ.Industry Electron.

Ethanol Saab otto engine Nickel-me-tal hydride

See KFB: Dnr1997-0344

Malmö, UppsalaBus comp. Sweden

Lund tekn. Univ.Industry Electron.

Naturalgas

Cummins gas engine(otto principle)

Nickel-me-tal hydride

See KFB: Dnr1997-0344

Various servi-ce companies

Trucks

Service vehicle inJapan

Mitsubishi MotorsInc.

LPG,gasoline

Otto engine t Lead acidbattery

Light truck, fuelcons. (see below)

ASAB AB, ABSvelast, AB

Mercedes Benz Diesel oil Diesel engine Lead/gelbattery

6 trucks type Atego1217

(Swed.) ASG AB,Västberga Deliver

Mercedes Benz Diesel oil Diesel engine Lead acidbattery

Truck type Vario814 D

TGM inGothenburgSweden

Volvo TruckComp.

Diesel oil Diesel engine Nickel-cadmium

2 trucks type FL 615

Many of the above hybrid vehicle projects have an interesting profile and are therefore worthfollowing up in order to generate more knowledge and experiences of hybrid operations withheavy-duty vehicles. For at least two reasons it is not possible to describe the project in thisreport. First of all there is a lack of required information and it seems not to be possible tocollect this information. Secondly many of the project have been estimated to be in a phasewhen they still are either under development of the hybrid systems or under evaluation byoperation in real traffic situations. Within a few years there may be interesting and valuablydata and experiences available.

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According to the collected information, those who operate the vehicles seem, in some cases,to have met rather intricate problems, which is no surprise since the hybrid technology formotor vehicles is rather new. The intention of using one or more hybrid vehicles in regulartraffic is an important phase during the development. This will give the operator of the vehiclesuch information which is not possible to obtain during tests in a laboratory, even if the basicinformation about the system has been generated by such tests. Based on all informationwhich has been collected for the preparation of this report the estimation is that the technicalproblems so far met are not such that they cannot be solved. Unfortunately there seem to beother problems (such as the energy efficiency) which may be a more serious barrier. These,together with costs, will be discussed in Section 13.

Of the above-presented projects there are some which are of special interest to discuss insomewhat more detail, despite the fact that they may not be successful in reality or canalready be used as example of failures. The projects to be discussed are as follows;

hybrid busses developed by Volvo (Malmquist, et al., 1998);a truck developed by Volvo (KFB Rapport 2000:8);a bus from Mercedes-Benz (Merdedes-Benz home page, 1999);and a hybrid system from TNO Road-Vehicles Research Institute (Mourad och Weijer);two trucks from Mitsubishi (Hori et al., 1998);a bus from Allison Transmission (division within GM) in co-operation with SouthwestResearch Institute (SwRI) (Bass et al., 1999).

Figure 29. Nova Transit Bus. Source: Whartman, 1998.

Volvo’s hybrid bus is, as are many other hybrid buses, equipped with a series hybrid (Malm-quist et al., 1998). Unlike other buses this bus uses a gas turbine for generating the electricityfor the battery. The use of a gas turbine can be seen as an example of the continuing interest atVolvo in the use of gas turbines since Volvo has already had some experience in the use of agas turbine in a passenger car. Within the concern extensive experience exists since VolvoAero Turbins is the manufacturer of jet turbines for aeroplanes. Consequently, the gas turbinefor the bus was developed by Volvo Aero Turbins. The hybrid system for the bus wasdeveloped by ABB Hybrid Systems AB and the project was sponsored by KFB and NUTEK(Swedish National Board for Industrial and Technical Development). As one contributionfrom Volvo to KFB it was agreed that ethanol should be used for the gas turbine.

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The aim of the project was to;

(1) gain some experiences from a hybrid system by field tests(2) test new control algorithms(3) evaluate a different combination of the dynamic for gas turbine and battery

The max power for the gas turbine is 110 kW and 130 kW for the asynchronous motor whichpropels the bus. The max energy content in the battery is 57 kWh and the maximum tractionpower of the system is 190 kW. According to reported information one of the purposes of theproject was to operate the bus on a regular bus line in Gothenburg. According to non-officialinformation, Volvo, for some reason was not going to continue after this bus was developedand tested.

Hybrid electric truck from Volvo

Volvo Truck Company has, with financial support from KFB, developed two hybrid electrictrucks. After the development the trucks were rented to TGM in Gothenburg (Fast, 2000).

The aim of the project was to construct the trucks for demonstration and to use themcommercially. The trucks are of series hybrid type and are, in their construction, based on thetruck model FL6-15 (see Figure 30). The original drive train of this truck is kept for the clutchand the gearbox. In the drive train a generator and an electric motor is installed for the tractionof the vehicle via the ordinary rear axle. The vehicle is equipped with a diesel engine of typeD6-200hk (EURO2) and a diesel filter of type CRT is installed in the exhaust system. Thepower of the generator is 110 kW and 130 kW of the electric motor (and a brief duration of370 kW). A nickel-cadmium (200 Ah, 43 kWh and 216 V) is used for storage of energyproduced by the engine via the generator. The capacity of the battery is sufficient for two tripsper day in the electric mode. The loading capacity of the truck is 4 600 kg (approximately 5700 lbs.) and a top speed of 90 km/h.

Figure 30. Volvo hybrid delivery truck.

.Mercedes-Benz (DaimlerChrysler) has developed a fuel cell bus named Nebus, which canbe seen as an electric bus, if the information is correctly understood, since the electric motorsare directly powered with electricity from the fuel cells. The fuel cell unit consists of ten fuelcell stacks of 25 kW each which result in power of totally 250 kW. Since the fuel cells

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themselves need some power to be operated the total power output is 190 kW to the wheelsand to the auxiliaries such as the on board electrical and air condition system (this means thatthe energy losses for the operation of the fuel cell is 60 kW and that efficiency of the fuel cellsthemselves is 76%).

According to released information from Mercedes-Benz (Mercedes-Benz, 1999; Dircks,1998) the fuel cells are fueled with hydrogen and oxygen and that the only emissions from thefuel cells is water vapor with a temperature of 55 °C. In the information available for thereport there is no indication about the number of fuel cells in each stack, but it is estimatedthat the number of individual fuel cells in each stack 35 to 40 resulting in the total number offuel cells being 350 to 400. The power electronics includes an AC-converter and a pulse-width modulated inverter of which both are installed on the roof of the bus as control units forthe wheel hub electric motors.

As already indicated the fuel cells provide direct power to the two electric motors which havea capacity of 75 kW each, i.e. total 150 kW. The space for passengers can be increased sinceno internal combustion engine is needed and no axles, cardan shafts, alternators and fuel tankeither. The fuel for the bus – 4 500-liter hydrogen is stored in seven 150 liters tanks on theroof of the bus at a pressure of 300 bars. In the above configuration the bus has an operatingrange of 250 km between refills. Since there is no internal combustion engine in the bus it isvery quiet and according to Mercedes-Benz this is an important feature since the number ofvehicles around the world is estimated to double by the year 2030, which requires fuel-efficient vehicles which are quiet and low polluting.

As a successor to Nebus another bus named Citaro was presented in April this year. Thefollowing information is quoted from the homepage of DaimlerChrysler:

“The Citaro’s fuel cell unit delivers more than 250 kilowatts of power. It was developed andmanufactured by the DaimlerChrysler subsidiary Xcellsis. The gas pressure bottles containingcompressed hydrogen are mounted on the roof of the bus. The environmentally friendly buscan travel up to 300 kilometers at a top speed of 80 km/h and carry around 70 passengers.

The electric motor, transmission, drive shaft and mechanical rear axle are all located at therear of the bus. This ensures smooth low-floor design and easy access during maintenance.The bus also includes three doors for optimal passenger flow”.

“EvoBus GmbH, a wholly-owned subsidiary of DaimlerChrysler, will supply the Mercedes-Benz Citaro low-floor urban buses with fuel cells at a price of 1.25 million euros each. Theprice includes comprehensive technical consulting and on-the-spot maintenance by EvoBusfor a period of two years. While the infrastructure is being set up, DaimlerChrysler willprovide the transport operators with guidance, knowledge and expertise”.

“DaimlerChrysler is the first automaker worldwide to offer fuel cell vehicles on the market.The company plans to build some 20 to 30 urban buses with fuel cell drives during the nextthree years, and then offer them for sale to transport operating companies in Europe andabroad”.

TNO-Road-Vehicles Research Institute has developed an APU (”Auxiliary Power Unit”)which in this case include a diesel engine and a generator (see Figure 31).

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Figure 31. Power unit (APU) for hybrid vehicle.

The reason for the presentation of this case is that the development of especially the internalcombustion engine – a diesel engine – represents an example of how a diesel engine can bedeveloped and adapted to be used in a hybrid system for heavy-duty vehicles. The clue in thiscase is a message saying that it, with regard to local or other conditions, must be decided fromone case to another whether the actual engine is the best choice for the hybrid system to beused. If the local condition has created serious problem by exhaust emissions and noise suchan APU must be used which will meet the special environmental requirements. In a casewhere the efficiency of the hybrid system is the most important parameter the most energy-efficient APU can be used. The following is quoted from a report from TNO (Mourad och vande Weijer, 1998).

”The determination of the general specifications of the APU is based on a Program ofDemands of the vehicle, e.g. performance requirements. Parallel to this the specific hybridlayout is taken into account as well as the preferred Energy Management Strategy (e.g.charge-sustaining). The resulting specifications include required power, efficiency, emissionlevel, and acoustic behavior. The translation from Program of Demands into a TechnicalSpecification is done using a simulation program. This simulation program also enablesevaluation of the consequences of the design choices made. For instance, although the enginecan be downsized when compared to a conventional vehicle (with all its efficiency andpackaging advantages), the continuous maximum speed is somewhat reduced. Theintermittent performance, however, may be equal or even better than that of a conventionallypowered vehicle”.

The hybrid technology offers a potential of clean vehicles but also energy efficient vehiclesbut with the present state of technology the requirement of good emission performance interms of low noise and minimal exhaust emissions of a hybrid vehicle is somewhatcontradictory to the requirement of an optimum energy economy. The different fuels such asgasoline, diesel, LPG, or CNG require different engine specifications and in this respect also adecision of what the demands for the vehicle are.

In order keep to an alternative with high efficiency TNO chose the alternative diesel enginesince this engine offers a higher efficiency than a otto engine despite the emissions of NOxand particles being worse from diesel engine than its counterpart (Mourad och van de Weijer,1998). The diesel engine in TNO’s hybrid system is especially adapted (dedicated) for ahybrid system and equipped with both catalysts and a special particle filter (”CRT particulatetrap”), which in connection to the hybrid system is schematically shown in Figure 32.

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Figure 32. Control systems, internal combustion engine and the emission control system.Source: Monrad och van der Weijer, 1998.

The hybrid system constructed by TNO, which as far as known not was realized in practice atthe time of the presentation of their report, contains a control unit for the torque of thegenerator aiming at a reduction of rapid engine transients. The representatives for TNO pointout that a generator-controlled torque is a special feature. The system also contains a batterynot shown in the figure.

Mitsubishi Motor Corporation (MMC) has developed one hybrid light-duty truck to beused as a delivery truck (presented 1995) and another truck equipped with special workequipment presented (see Figure 33) in a report (Horii et al., 1998). MMC’s goal for thedevelopment of the truck equipped with a hybrid system was, to quote;

(1) “To provide dynamic performance equivalent to that of the basic diesel vehicle so thatthe work vehicle can keep up with the urban traffic flow, when traveling.

(2) To assure a driving range of 200 km or more to allow for operation of the vehicle notonly within the city but to also permit a round trip to a suburban area,

(3) To introduce improvements for lighter weight and higher efficiency in order to reducefuel consumption and emission,

(4) To simplify operational controls for easier driving by taking advantage of motor drive,(5) To enable the vehicle to operate on battery power only in residential areas at night,(6) To provide the capability to drive the hydraulic pump from the electric power

accumulated in the battery without having to use engine generated power so thatemission can be eliminated and noise minimized to permit operation indoors, in tunnels,etc. as well as in residential areas”.

After having studied and investigated different alternative and in the first place parallel hybridsystems contra series hybrid systems they decided to choose the latter type of system and thiswas for two main reasons:

1. Since the internal combustion engine is used only for the purpose of generating electricenergy for the battery it can be operated in power load area where the efficiency is high.MCC believes that the total efficiency and the emission performance of a series hybridis better than a parallel hybrid during city driving, which mostly consists ofaccelerations, decelerations and low speed modes.

2. Since the internal combustion engine is not directly connected to the driving wheels theseries hybrid system has a simpler and freer drive train and will offers betterpossibilities for the mounting of hydraulic equipment etc.

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The hybrid system developed and constructed by Mitsubishi does not differ very much, fromwhat can be seen, from the “usual” system. Seeing that the hybrid vehicle is to be used as aworking machine (see Figure 33) it has been fitted with a piece of equipment named”Transmission with PTO”. This equipment serves the hydraulic pump which has atransmission ratio of 3.476.

Figure 33. Mitsubishi aerial working truck. Source: (Horii et al., 1998).

The delivery truck presented by Mitsubishi in 1995 is fueled with an LPG fuelled otto enginesand based on a truck called canter one of the mass production trucks. MMC has in detailstudied the fuel consumption for a hybrid vehicle with the fuel consumption for a diesel fueltruck of the same type and the results of this study are presented in Section 9. MMC alsopoints out that the emissions of NOx and black smoke have been considerable reduced fromthis vehicle when using the hybrid system.

The intention of Mitsubishi to manufacture and sell their hybrid trucks can be seen from thefact that two hybrid trucks were presented in Beijing according to the following quotedinformation.

“….this second Beijing PSE of the year focused on Electric Vehicles & Substitutional FuelVehicle Technology. Long engaged in developing alternative fuel vehicles, Mitsubishi Motorsbrought two hybrid electric vehicles (HEVs) to the event, the Mitsubishi Space Wagon HEVand the Mitsubishi Canter HEV. The Space Wagon HEV is equipped with an ultra-lowemission CNG (Compressed Natural Gas) generator engine, high energy density lithium-ionbatteries, and high-efficiency twin motors. In place of a diesel engine, the Canter HEV’sgenerator employs an LPG engine backed by organic electrolyte batteries”.

In addition to the reports above, about the different hybrid heavy-duty vehicles presented inTable 19, the following reports (Jeanneret, et al., 1998), (Debal et al., 1999), (Dowell ochReddy, 1998), (Bullock och Hollis, 1998) have been used as a part of the information neededfor this report – the authors and the title of all of the reports can be found in the reference listbelow.

8.4 Comparison between different fuels/drive trains

Several factors influence the choice of the combination fuel-power units for the hybridsystem. There are especially two factors which are most important - the emissions and theenergy efficiency of the system. The choice of the combination type of fuel contra type of

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power unit for a hybrid system is also influenced by international agreements betweendifferent countries, or agreements within the different countries. This is especially true withinareas or countries where the main production of automobiles occurs such as in the US, Japanand Europe.

During recent years the question of fuel economy has grown very strong and in some cases itseems to be more important reducing fuel consumption than reducing the emissions of NOx,particles and other emission components in the exhaust. The many actors being more or lessinvolved in the decision taking or in discussions about the importance of reducing the fuelconsumption in vehicles contra reducing emissions and costs may contribute to an uncertaintyabout which way to go. When estimating the future development of hybrids the above factorshave been taken notice of in addition to the technical possibilities for the two main hybridsystems to meet the two main requirements emissions performance and energy economy.

If the development of the hybrid system is to be based only on the requirement of fuel (orenergy) economy the fuel/power unit combination should certainly be based on thecombination diesel oil/diesel engine today. It is true that the diesel engine is somewhat moreexpensive to produce and also heavier than the otto engine, but the difference in purchaseprice for the car manufacturer and the customer will soon be “paid back” by the higherefficiency of the diesel engine unless some unexpected requirement considerably increases thecost of using the combination diesel oil/diesel engine. This is especially valid for heavy-dutyvehicles. It is true that there exist some alternative to the diesel engine (see Sections 7 and 8)but the problem is that “the state of the art” of these alternatives is so far not on the same levelas the diesel engine and does not have the same market as the diesel engine. Therefore theonly real candidate for meeting the fuel economy requirement (or use of energy) seems to be adiesel engine fueled with diesel oil.

If the development of the hybrid system should be based only on the requirement of goodemission performance the answer is not quite clear especially in an international perspective.From a study of the situation in Japan and in the US as a neutral observer, or from listening tothe discussion in Europe including Sweden, it is quite clear that there are different opinionsabout the necessity of using a certain fuel engine combination for environmental reasons. Inthe USA the car manufacturer Ford presented in 1997 or 1998 a newly developed dieselengine for a hybrid vehicle meeting the Tier II requirements according to presentedinformation – an emission level which, some years ago, not many experts in the field thoughtit was possible to reach. A study of the presented future emission standards also calls forrather remarkable emission reductions.Ford, who is one of the “big three” who has signed an agreement with the Government in theUSA to do research and development within the PNGV program (see Section 8.1.3) has alsosigned an agreement with US Department of Energy (DOE) for the development of a hybridvehicle. From a report (Buschhaus et al., 1998) presented by Ford (see Section 8.2.4) oneconclusion could be that DOE was not satisfied with the presented plan to use a diesel enginein the new hybrid vehicle developed by Ford, since, at the time for the presentation of theabove mentioned hybrid vehicle, it was agreed that Ford should develop a hybrid vehicleequipped with an otto engine. It is well known that the environmental authorities in the USAand especially in California have some doubt whether the combination diesel fuel/dieselengine of environmental reasons should be allowed to be used in at least light-duty vehicles.Similar reactions have also been heard in Sweden and up to some years ago only a smallnumber of light-duty vehicles were diesel fueled vehicles.

The opposition against the diesel oil/diesel engine is based on fact that a mass produced dieselengine has far from reached the same low emission levels as a mass produced otto engine. If

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looking at the emission standards in Europe for example it can be seen that there is a cleardifference between otto and diesel vehicles – vehicles with otto engines being at the lowerlevel. The emissions from diesel engines are still expected to cause a higher health risk thanthe emissions from otto engines. In Section 8.1.4 a description of emission control systems forboth diesel engines and otto engines can be found also for hybrid vehicles. However, thediscussion in the previous paragraph about the diesel engine and the opposition within theenvironmental authorities may have had a decisive impact on the choice of the fuel/enginecombination also for hybrid vehicles. The opinion expressed in many countries concerning thediesel engine have certainly resulted in that many companies have used the combinationgasoline, ethanol or CNG/otto engine instead of diesel oil/diesel engine in their hybrid system.

In cases when the alternative internal combustion engine is an otto engine there are at leasttwo reasons for using gasoline as fuel. First of all an infrastructure has long existed for thedistribution of gasoline and secondly the technology for the combination gasoline/otto enginescan easily be copied when producing smaller engines for hybrid vehicles. The fuels whichcome closest for replacing gasoline are ethanol or methanol. In the question of the gaseousfuels, LPG and CNG, there may be different provisions in different countries but the situationin Sweden is such that natural gas, such as CNG, is certainly preferred to LPG sincecompressed biogas (which contains mostly methane like CNG) is already used in some citiesin Sweden. Both biogas and CNG have are physically two of the “cleanest” fuels for ottoengines and they have a good potential of contributing to lowest emissions of harmfulpollutants when used in engines dedicated for the use of methane-containing gaseous fuels.However, experiences from the use of CNG and compressed biogas have shown that thetechnology for the use of gaseous fuels must be considerably improved in order to fullyexploit the emission potential of these fuels.

The conclusion from the above discussions is that within the nearest 5 years the primarycombination will be the use of gasoline/otto engines for hybrid vehicles. The positiveimprovements of both gasoline and the otto engine will continue. There is still no clearindication that the direct injection otto engine will replace the conventional otto engine within5 years as the gasoline fuelled alternative for hybrid systems. This is especially true if therewill be a positive development of the control system for the hybrid vehicles in line with thepresentation in for example Sections 8.1.1 and 8.1.4. Only Mitsubishi has announced that thecombination direct injection gasoline engine and hybrid system with an electric motor will beused in order to “deliver super-efficient power generation and performance”.

The development of diesel engine is estimated to have a remarkable impact on the emissionsand therefore it will start to make a more positive contribution in the discussion aboutfuel/engine alternative but this positive movement towards a cleaner engine depends stronglyon the cleaning up of the diesel oil. Since it is uncertain whether the diesel engine will havethat advantage, attention in a shorter perspective should be called to the fact that there arealternatives available which may take some part of the market from gasoline and diesel oil.The alternative, in the first place for light-duty hybrid vehicles, is expected to be theethanol/otto engine and for a heavy-duty hybrid vehicle the CNG/otto engine or theBiogas/otto engine could be a strong candidate.

In Section 5.2 the huge resources of natural gas have been discussed. For a country likeSweden the cost for an infrastructure for natural gas over the whole country would beextremely high and in addition it is uncertain whether there is a common interest among theowners of vehicles in using natural gas as an automotive fuel. However, looking at thesituation in Sweden there may exist an interest in using natural gas in certain cities or areas.One possibility which has been discussed is to convert natural gas to methanol and to produceethanol from wood as a biofuel.

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By the development of intelligent control units and better batteries for the hybrid systems, theinternal combustion engine will be operated without rapid transients, which will result in morefreedom for the car manufacturer to improve the interaction between the two power systemsin the hybrid vehicle. The average energy efficiency of the system will increase, especiallyduring driving in city traffic. In addition to the possibilities discussed in Section 8.2 andSection 12 the model for development presented by TNO may give many positive results.These improvements of the energy efficiency etceteras may also result in that the car ownermore easily will tolerate the higher cost of using alternative fuels.

In a Swedish perspective, building up an infrastructure for natural gas and biogas to be used invehicles would result in both natural gas and biogas being more attractive as automotive fuels.The technology for the use of these gaseous fuels in engines would certainly also be affected.Whether there will be a development in that direction is not certain, as the organizing of asuch infrastructure must be based on a political decision. If a decision is taken in Sweden inthis direction the use of CNG in hybrid vehicles is estimated to be limited to heavy-dutyvehicles.

Since there are also some negative factors connected with hybrid systems, especially in thatthe vehicle contains more parts and units than a conventional vehicle, the extra weight and thecost of the vehicle is an extra burden for the car owner. The hybrid system may also result inan increasing need for maintenance. There is an urgent need for batteries with higher powerand energy densities and the question is when such batteries are to be seen. Thesedisadvantages and especially the cost of the hybrid vehicle certainly have a negative effect onthe market, and for a further positive development of the hybrid systems there is a need forlarge market. The fact that fuel cell technology may have a more positive development and bean attractive alternative sooner than expected may be an obstacle to the development of hybridtechnology and especially the drive trains with an internal combustion engine.

In a longer perspective (10 to 20 years) many different ways for the development can be seenand therefore it is not possible to point out a certain direction. The PNGV program and thestrong requirement to use “cleaner” vehicles using less energy will have a strong impact onthe development of fuel, engines and the body of the vehicle. The development of hybridvehicle which has been seen has positively influenced the required improvements of thevehicle. There is good possibility, through the use of hybrid technology, to use the internalcombustion engine and especially the otto engine more efficiently. Since the hybrid systemgives extra weight to the vehicle a lighter body vehicle has been developed and newproduction technology has been exploited in order to compensate for this extra weight. Inaddition many units for the control of the different systems of the vehicle have beendeveloped and all of this in a positive way.

In order to sum up the above discussion and the expected development in the time frame of 5to 10 years it should be underlined that;

- a well pronounced interest in the hybrid technology has been shown among carmanufacturers and these who are responsible for the development of hybrid electricvehicles;

- it has been shown that many actors have been involved in the development of hybridsystems for city buses. Unfortunately only a few car manufacturers have been involvedin that work. Therefore it is unsure whether the development of hybrid systems for citybuses will continue;

- many well functioning hybrid systems for light-duty vehicles have been developed bythe car manufacturers especially in Japan and in the USA. This well organizeddevelopment seems to continue at least in the short time frame;

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- the PNGV agreement between the US Government and the three car manufacturersChrysler, Ford and GM and also other agreements have positively affected the decisionstaken among car manufacturers not only in the USA and Japan but also in othercountries in order to develop fuel efficient vehicles and among these hybrid vehicles.

In order to sum up the above discussion and the expected development in the time frame of 10to 20 years it should be underlined that;

- it is not possible make a firm estimation about the development of hybrid vehicles after2010 to 2015 since there is a considerable uncertainty in some factors affecting a suchdevelopment;

- two scenarios can be seen concerning the development of energy efficient motorvehicles, namely:

(a) a positive continuation of the development of hybrid electric vehicles parallel toresearch and development of fuel cells;

(b) a brake through for the development of fuel cells resulting in (1) the use in fuelcells in hybrid electric vehicles with a battery used for storage of electricity and (2)the use of fuel cells as the only source for the delivery of electric power to thetraction motor in a vehicle without battery for the storage of electricity use for thetraction motor.

- Today it seems most likely that the development of highly fuel efficient vehicle willfollow scenario (a) since it is estimated that the fuel cell technology will be to expensiveto be used in mass produced vehicles within the time frame of 20 years.

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9 EFFICIENCY – FUEL ECONOMYIwai, who was presented in Section 8.1.2 (Iwai et al., 1998), has been studying the efficiencyof different parts in a hybrid system and also discussing the importance of controlling theinteraction between the internal combustion engine and the electric drive train. According toIwai the efficiency, and by this the fuel economy for a vehicle with internal combustionengine, be improved by;

1) eliminating of engine idling and running the engine at low loads where the thermalefficiency is low and by operating the engine only in points of the engine operationalarea with high efficiency;

2) accumulating the braking energy at deceleration;3) installing a power system that can operate with a high degree of efficiency, regardless

of the driving cycle;4) using a bottoming cycle that creates electric energy by driving the power generator

with exhaust energy, making it possible to achieve higher efficiency of the system.

9.1 The efficiency of hybrid systems

BMW has, as was mentioned in Section 8.1.5, engaged Dresden Technical University to studyand evaluate the efficiency of hybrid systems by comparisons with an conventional vehicle(Friedmann et al., 1998). The comparisons were based on tests using a BMW and on resultswhich had been generated by EUCAR on a series hybrid and a parallel hybrid and in additionto some other studies. The researchers who carried out the comparisons at the university, haveanalyzed how the different hybrid systems will be controlled in order to achieve the highestefficiency and they have then also considered how the internal combustion engine has to becontrolled for the purpose of achieving high efficiency. In line with what was said in Section8.1.1 the scientists at the university point out that the efficiency in a drive train of hybridvehicle, which incorporates a generator and an electric motor is considerably less than that ofa mechanical drive train. This is in cases where the engine is direct connected to the drivingwheels via a mechanical drive train.

The above statement is especially valid for series hybrids where the mechanical energy has tobe transformed to electric energy and then again to mechanical energy for the traction of thevehicle. In the case of a parallel hybrid, the branch of the drive train the electric motoretceteras can be directly compared with drive train of a series hybrid. There is, however, animportant difference between the two systems in that one branch of the drive train of a parallelhybrid is directly coupled to the driving wheels. Consequently the conclusion of theevaluation is that a control strategy must be used where the internal combustion engine is asoften as possible operated in its most efficient zones of the engines working area, in order toachieve the maximum efficiency of the hybrid system. In other words the control of the hybridsystem must be such that the average efficiency of, in the first place, the internal combustionengine is increased by the engine “taking back” the losses in the part of the drive trainequipped with an electric motor which is fed by the engine and the battery. In the best casesthe losses are eliminated.

An interesting scenario discussed by the authors in their report (Friedmann et al., 1998) andwhich also have been discussed by others, is that computer simulations and the use ofdifferent control units will be important tools during the phases in the further development ofhybrid vehicles. In the present phase of the development and when some hybrid systems havebeen demonstrated, it is important to evaluate the result achieved so far. However, andimportant question is to what extent the gained experiences will be used as a base for the

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optimization of the future hybrid system. This seems to be most important in the case ofhybrid systems for heavy-duty vehicles. This is because the development systems forespecially buses, in many cases, seem to be suffering from the same type of analyses whichhave been the basis for the development of light duty hybrid vehicles. Testing prototypesunder the phase of development is important in order to learn about the function of thedifferent units in the system but many costly experiments can be replaced by a design basedon computer simulation. This seems to be the message from those who have been analyzingthe efficiency and optimization of hybrid systems.

In this report the importance of using an optimized control algorithm for the hybrid system inorder to achieve a high average efficiency has been repeatedly underlined. It has also beenshown that a direct connection from the internal combustion engine via a mechanical drivetrain causes less losses of efficiency than an electric drive train. On the other hand the averageefficiency of the engine depends on how the engine is operated. The impact of this and otherpossibilities to be used in the hybrid systems can be seen in Figure 34. Matching the differentunits in the system is important for a good performance of the vehicle, low emission levelsand good fuel economy. In the case of the possibilities of improving the hybrid system thepotential for improvements is probable higher for the electric system and especially thebattery than for the internal combustion engine.

Figure 34. Efficiency improvement by hybrid strategy. (Source Takaoka et al., 1998).

A certain modification of the hybrid system seems to be necessary. This has been pointed outby some of those who have studied the hybrid system in detail, such as Iwai and the scientistsat Dresden Technical University. A question to be answered within the next few years iswhether diesel engines will be acceptable for use in some hybrid applications, for example inseries hybrids for heavy-duty vehicles, in order to compensate the lower efficiency of theelectric drive train compared to the mechanical drive train. If the expected considerableimprovements of the diesel engine are realized the acceptance of the diesel engine mayincrease. A possible alternative would be to use an alternative fuel such as ethanol in the newgeneration of diesel engines in order to improve the exhaust emission compared with the

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exhaust from diesel engines. In addition this alternative would improve the energy equivalentfuel economy. An engine in a well-designed series hybrid can be operated with less rapidtransients than the engine in a conventional vehicle. Therefore there is a better possibility foradapting the diesel engine in a hybrid vehicle for the use of an alcohol than to adapt a dieselengine in a conventional vehicle for the use of an alcohol.

The Toyota hybrid vehicle Prius was one of the first hybrid vehicles to be presented andcertainly the first hybrid vehicle to be ready for the market. It can therefore be expected thatsome important improvements of the hybrid system would improve the fuel economy. Despitethis early introduction on the market it should be recognized that Toyota has shown that agood matching between the different units in the hybrid system and the use of a newcomponent in the drive train the, the planetary gear, resulted in a fuel-efficient system. FromFigure 34 it can be seen that the efficiency curve is much higher for the hybrid vehicle whencompared to a conventional vehicle and that low speeds and idling of the engine are cut off.Rapid accelerations of the engine are avoided by the assistance of the electric motor.

According to Figure 34 the average efficiency of Toyota Prius has been increased by 80%from the average efficiency of a conventional vehicle and that there is an additional increaseof 20% from the regenerative braking. However no clear indication has been given about thedriving condition. It is estimated that the comparison was carried out for the Japanese 10-15mode cycle. In Section 8.2.3 it has been shown that the difference between the hybrid vehicleand the conventional vehicle decreases with the increase of the average speed. However whenkeeping to the Japanese 10-15 mode cycle the information from Toyota says that the fueleconomy for Prius compared with a Toyota Carina is 28 km/l contra 14 km/l. Thedisplacement of the engine is the same for both vehicles but the Carina was an automatic. InFigure 35 the comparison of the two vehicles is shown for some different speeds.

Figure 35. Comparison of fuel consumption at different driving modes.Source Takaoka et al., 1998

9.2 The use of energy and efficiency at different drivingpatterns.

In section 9.1 the need for computer simulations were discussed and also their practical use.To use only a test matrix and tests in a laboratory as a basis for taking decisions as to whethera series hybrid or a parallel hybrid is the best alternative is both time consuming and costlyand therefore hardly any car manufacturer will do so. Today the planning of for example anew model is based on an investigation of many factors and not only on the design of thevehicle but also on a study of the market, cost factors and so on. In the case of systems such ashybrid vehicles the situation may be somewhat different. Here some irrelevant factors maygive a need to present new ideas and expectations to achieve such result of the development

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which are unrealistic in reality. On the other hand many new ideas have been realized by trialand errors and in the case of hybrid vehicles there still is a lack of hardware with as goodperformance as it is possible to achieve. One example is the batteries, which with today’sknowledge could be much better.

Careful planning of the different factors, not only the hardware but also the use of the vehicle,can result in more sound and realistic expectations. This will go a long way to achieving acertain result. As a basis for the decision to be taken as to whether a series hybrid or parallelhybrid is the best system for the fulfillment of the expected goal, computer simulations can becarried out. These should use factors such as the driving pattern for the area, where the vehiclewill be operated and the basic parameters for different hybrid systems. One such computersimulation in connection with laboratory measurements is presented and discussed in thefollowing paragraph.

9.2.1 Studies of hybrid systems for BMW

In order to get an idea of how an evaluation of hybrid systems can be carried out the modelused by Dresden Technical University during their investigations and studies carried out forBMW presented is Section 8.1.5 and Section 9.1 respectively. The studies were especiallyconcentrated to the evaluation of the energy efficiency of series hybrids and parallel hybridsand were, for the computer simulations, based on calculations, in one phase, of the differencebetween a series hybrid vehicle and a conventional vehicle. A similar calculation andcomparison was carried out for the evaluation of a parallel hybrid system. Then a serieshybrid vehicle was compared with a parallel hybrid vehicle. The authors of the report(Friedman et al, 1998) point out that there is a loss of efficiency in the electric drive train.They say that, in the case of a parallel hybrid, the electric drive (which transmits force parallelto the mechanical drive train) works like the drive train in a series hybrid.

The result of the evaluation is presented in Table 20. From the table it can be seen that theregenerative braking has a considerable influence on the fuel economy of both the serieshybrid and the parallel hybrid. However, the authors claim that regenerative braking (which isengaged during decelerations) shortens the “exhaust emission free driving” achieved by freerolling of the vehicle during decelerations. According to the authors of the report (Friedman etal, 1998) regenerative braking does therefore not favor the reduction of exhaust emissions(here it should be added that this problem could be handled by the hybrid control unit). Fromthe table it can also be seen that for the series hybrid, according to the calculations there is adecrease in fuel consumption (or energy used) for only one combination, namely “0” forelectric operation range, 0.92 for Degree of coupling and “Yes” for BERG (braking energygeneration). For all other combinations there are increases in fuel consumption from +8% upto 50% when compared with a conventional vehicle.

In the case of the parallel hybrid the picture is somewhat different concerning the savings andlosses in fuel consumption where savings are from 0% up to 15% and the losses from 0% upto 10% according to the calculations.

It should be noted that these results are based on computer simulations using data orexperiences from their own experiments or data from the literature. The example is interestingin that some of the important parameters of the hybrid vehicles are defined and used in amathematical model. In this case it has been shown that a parallel hybrid vehicle is moreefficient than a series hybrid vehicle for a driving pattern such as the driving cycle used in thisexample. This is in line with what that others have pointed out, as for example Iwai (Iwai,1998) who underlines that it is more difficult achieve high efficiency for a series hybridvehicle than for a parallel hybrid vehicle. However, it should be noted that the figures

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presented by the authors of the report (Friedman et al, 1998) will certainly be different tothose from other driving cycles and other efficiency estimations.

Table 20. Comparison between a series and a parallel hybrid vehicle with a conventionalvehicle.

Driving cycle Electricdriving [km]

Regenerativebraking

Degree ofenginedriving

Fc* forconven-tional car

Fc for hybridvehicle

Changes in fuelconsumption

Series Parallel Se-ries

Paral-lel

Series Paral-lel

Series Parallel

l/100km

Series Parallel Series Parallel

CityCity

CityCity

”0””0”

”0””0”

YesNo

YesNo

0.920.94

0.830.85

10.210.2

10.011.0

8.6610.3

-2+8

-15+1

On road.On road

On road.On road

”0””0”

”0””0”

YesNo

YesNo

0.980.98

0.950.95

6.66.6

7.17.3

6.36.6

+8+11

-6±0

CityCity

CityCity

1515

2020

YesNo

YesNo

0.380.42

0.780.79

10.210.2

11.513.0

9.211.0

+13+27

-10+8

On roadOn road

On roadOn road

1515

2020

YesNo

YesNo

0.450.52

0.900.90

6.66.6

8.78.8

6.56.9

+32+34

-2+5

CityCity

CityCity

3030

4040

YesNo

YesNo

0.360.37

0.760.76

10.210.2

12.612.6

9.311.1

+24+44

-9+9

On roadOn road

On roadOn road

3030

4040

YesNo

YesNo

0.420.44

0.900.82

6.66.6

9.79.9

6.77.3

+47+50

+2+10

*Fc: Fuel consumption (Use of energy). Minus sign: Reduced Fc. Plus sign: Increased Fc.

9.2.2 Energy use and efficiency of Mitsubishi hybrid trucks

In Section 8.3 two hybrid trucks – one delivery truck and one aerial working truck -developed by Mitsubishi were presented. In the report (Horii et al., 1998) two figures showingthe fuel consumption and energy efficiency were also presented. The values presented byMitsubishi have been slightly rearranged and are shown here in Figure 36 and Figure 37.

Figure 36. Mitsubishi service truck. Comparison of energy used between a hybrid truck and adiesel truck. Source: Horii et al., 1998.

Three different driving conditions have been compared – idling, 40 km/h and 80 km/h and inthe figures even the efficiency, $, has been filled in for the two trucks and the differentconditions. The values for the energy used was calculated in the way quoted from the report(Horii, 1998). The energy consumption of the HEV was calculated by the use of simulatedvalues. “The actually measured efficiency values of the various parts of the delivery truck

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HEV were partially modified to match the work truck HEV, and the efficiency values of allthe components were multiplied together to work out vehicle efficiency. In addition,theoretical running energy was divided by vehicle efficiency to calculate energyconsumption”. The energy used was presented in kWh/km and “Theor” and “Act” in thefigures below means “Theoretical” and “Actual” respectively.

Figure 37. Mitsubishi working truck. Comparison of energy used between a hybrid truck anda diesel truck. Source: Horii et al., 1998.

Figure 38. Energy efficiency of same important component of a HEV. Source: Horii et al., 1998.

Figure 38 shows the power/energy flow and the efficiency of the individual components usedby Mitsubishi as a basis for the calculation of vehicle efficiency. Since the details ofregenerated power and generated power that are used (that portion of the energy which is usedwithout passing though the batteries and that which is used for recharging the batteries) varyaccording to the operation mode, the regeneration efficiency and battery efficiency werechanged according to the mode of operation.

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10 FUEL AND DISTRIBUTIONIt is only in the case of electricity that distribution differs from that for conventional vehicles,as long as conventional and common alternative engines are used. New alternative fuels cancome into existence if other types of internal combustion engine and sources of power (e.g.fuel cells) come to be used. This will most likely not occur for a long time (10-20 years ormore). One question which needs to be thought about is how will electric energy for hybridvehicles be distributed, so that this will be as effective as possible and is going to meet thedemands which must be placed on it.

10.1 Conventional fuel

The conventional fuels are gasoline and diesel oil. The distribution of these is generally securefor whole Sweden as in other countries countries by the stations, which have been given thenot completely adequate name of “gasoline stations”.

There are at the present time (year 2000) three different qualities of gasoline in Sweden – 95octane unleaded (usually called lead free) gasoline, 98 octane unleaded gasoline and a blendbetween 95 octane and 98 octane in order to achieve a 96 octane quality. The latter will bephased out very soon, unless this has already taken place.

When unleaded gasoline was introduced a discussion took place as to how it would bedistributed, since there were already three different blends of gasoline. It was found to be veryexpensive to fit all the gasoline stations over the whole country with new tanks and pumps forthe distribution of unleaded gasoline. This problem was solved by that the middle variety, 96octane, no longer being distributed through its own pumps but by means of mixture-pumps.Since unleaded gasoline was introduced other important changes have been made (i.e. theintroduction of 98 octane unleaded gasoline), and the question is what the future distributionof gasoline will be like. New demands are being made for gasoline from both the carmanufacturers and the authorities. The truth of the matter is that there is a risk it will be nospace for further alternatives unless an expensive extension of the distribution net takes place.

Three qualities of diesel oil have been defined, MK1, MK2 and a third blend of diesel oildesignated MK3 (see Table 2). Since MK1 took the greatst part of the market within a fewyears of being introduced and completely dominates the market at the present time, it is noteasy to sort out how the other part of the distribution looks. According to received information(Lindberg, 2000) MK2 is no longer distributed but a small amount of MK3.

During recent years a “European Diesel Oil” has been specified after a great deal ofdiscussions and deliberations but so far not any blend of “European diesel oil” is distributedon the Swedish market. The future will show how much of the market diesel oil will have inthe future. There can also be discussions about which sort of diesel oil, with the addition ofRME, water emulsion etc., will be available on the market and if this fuel should be treated asdiesel fuel or as an alternative fuel.

10.2 Alternative fuels

For hybrid vehicles there are a range of fuels available due to there are various alternativeengines – Stirling and gas turbines – and even fuel cell that are being considered for use inhybrid vehicles. In reality it is quite uncertain that the two named engine alternatives will atall be used to any great extent. Even in the case of fuel cells not much indicates that these willbe used as alternatives to otto or diesel engines other than to a very restricted extent, within

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the coming 10-year period. In fleet trials and in single test vehicle prototype fuel cells can beused for various tests. Since one of the object of the hybrid vehicle is to reduce pollution it isestimated that they will be adapted for the use for environmentally suitable fuels. Thisespecially since newer types of catalyst require ”cleaner” fuel than the gasoline availabletoday and in an international view this applies even the diesel oil. Some form of both gasolineand diesel oil can be relevant as alternatives also for fuel cells. Concerning the distribution offuels that are considered to belong to the group of alternative fuels, the following asalternatives can be of interest.

Natural gas/biogas: Both these fuels can be relevant to be used in hybrid vehicles even inSweden. however, in the short term, their use will be limited to fleets of heavy-duty hybridvehicles used locally in built-up areas. One condition for a widespread use of natural gas inSweden is that distribution pipes are drawn to strategic places in the whole country. Thepossibility of distributing biogas and natural gas in the same pipes should be discussed.Natural gas can be an attractive alternative fuel even for fuel-cell vehicles in built-up areas,chiefly for the production of hydrogen in special establishments. Today tanking of naturalgas/biogas takes place at tanking stations according to a network which has been developed inLinköping, Stockholm, Trollhättan, Uppsala (for biogas) and for certain towns in the countyof Skåne and on the west coast (for natural gas from Denmark).

Methanol/ethanol: No certain conclusion has been drawn in Sweden about whether it is moreadvantageous to distribute both of these fuels, or whether only one should be distributed andin this case, which of them. If and when the distribution network is built up, with tanks andtanking stations, it is important that they are constructed so that either methanol or ethanol canbe distributed without there being any problems with the material used for the stations. Thegreatest demands concerning the material, from the corrosion point of view, apply especiallywhen methanol is to be used. It is also important that routines are established and instructionsgiven for the prevention of accidents, for the protection of the personnel and others whohandle the distribution or otherwise come into contact with alcohol fuels.

LPG/DME: Even if LPG is best used in otto engines and DME in diesel engines, they can beconsidered similar from the point of view of the techniques of distribution. No negativecharacteristics are known about these fuels except those which also apply to gasoline anddiesel oil. LPG consists to a large extent of propane (a gaseous fuel which is uses for heatingand cooking in caravans). One should, however, be aware that both LPG and DME areheavier than air and can therefore collect in depressions or near the floor in the case of leakagein closed areas and that they can be easily ignited by sparks from, for example, an electricswitch. It is for this reason that smelling substance, mercaptan, is added to LPG (this shouldalso be the case for DME). To the knowledge of the authors DME has not been usedcommercially in internal combustion engines. Both LPG and DME can be stored in tanks, inliquid form under low pressure. Both fuels must be tanked in a closed system but they do notrequire as high a pressure as natural gas or biogas. LPG has not had any great success on themarket in Sweden but it is used in large quantities in Holland, Italy and certain other countriesin Europe. It is not expect that LPG will be used to any great extent, as a vehicle fuel, inSweden. In the case of DME it is not easy to speculate.

Hydrogen: At the present time hydrogen is not used commercially as a vehicle fuel. Thissituation can change if hydrogen comes to be used in fuel cells. However, there are someengine manufacturers who are developing internal combustion engines for hydrogen (BMWfor example). Fuel cells are run on hydrogen but the question is whether the hydrogen is to beproduced inside or outside the vehicle. Mercedes-Benz has considerable experience in thisfield and has one time developed a hydrogen driven vehicle using an internal combustionengine. Today prototypes of both passenger cars and buses equipped with fuel cells have been

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developed to be tanked with hydrogen (see Section 8). The future will show whether M-B(now DaimlerChrysler) will continue to use hydrogen as a direct fuel or whether there will bea development so that busses will be tanked with hydrogen but that a liquid fuel, such asmethanol, will be used for passenger vehicles (see previous discussion on this). It is expectedthat there will be a development in this direction since both patience and a certain amount ofcare are required when tanking hydrogen, and it is not all vehicle owners who have thesequalities. In the case of distribution and tanking of hydrogen there are techniques forminimizing the risks which are otherwise associated with hydrogen. Air mixtures with 5-75%hydrogen are explosive.

Hydrogen can be stored and transported as both gas and liquid. Because of hydrogen’s abilityto combine with other substances, a technique has been developed where hydrogen is allowedto bind to metal hydrides for storage and transport. The disadvantage of this is that thetransported fuel will be heavy and there is thus an ongoing development of lighter metalhydrides which is expected to reduce the problem. The question is whether this is the solutionsince there is no certain indication that this technique will be used in motor vehicles. TodayDaimlerChrysler store hydrogen in pressure tanks for their busses with fuel cells. Research isunder way, however, and other more efficient storage methods may be found which can alterthe picture radically.

Despite hydrogen being used in test vehicles with fuel cells it is still uncertain whether the gaswill be able to compete with the liquid fuels. The question can come to be settled within thecoming years by the “California Fuel Cell Partnership” – a co-operation has been establishedbetween the fuel cell manufacturers Ballard, and American, German and Japanese vehiclemanufacturers and also a number of oil companies. Its object is to demonstrate the use of fuelcell vehicles in real traffic. The project seems still to be in the development stage butDaimlerChrysler and Ford have promised to each of them contribute with 5 vehicles equippedwith hydrogen tanks. Each of them will also if possible contribute with 10 vehicles equippedwith methanol tanks. However, the intention within the mentioned partnership is that the trialswill take place from 2000 to 2003.

10.3 Electric energy

In Sweden electric energy is widely available and it has the advantage of not being produced,at present, by the use of fossil fuels. For the private person the cost of electricity isapproximately 40% or more lower than the cost of gasoline, calculated in terms of energy.This is mainly due to the lower tax on electricity. This comparison applies if vehicle ownerscharge their batteries in their own garages or from their flats. The comparison is, however, notcompletely adequate in the case of a hybrid vehicle equipped for charging the battery from themains. This can give an indication of the economic advantage, in the case of a private person,of using electricity as compared with using gasoline. The difference will not be as great whencomparing electricity with diesel oil. It has previously been mentioned that the energytransmission efficiency is better when generating electricity using an internal combustionengine than when using a fossil fuel driven generator for electricity in a stationaryestablishment. In this context it should be noted that the use of electric energy generated inFinland, Norway and Sweden does not generally contribute to the emission of pollutants,except in exceptional cases, since most of the electricity in Sweden or at least 50% isproduced in hydraulic (water) power stations and the rest in nuclear power plants.

Questions on the use of electricity in KFB’s “Electric and hybrid program” are mainlyfocused on the purely electric vehicle. Information concerning the distribution of electricityfor hybrid vehicles can generally speaking be obtained from investigations concerning the

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distribution of electricity to electric vehicles. We shall therefore only briefly mention thatthere is not a great deal decided about how batteries should be charged. Since the cost of thebatteries is an important part of the running costs, for a series hybrid especially, it is importantto charge and maintain the batteries in a way which does not cause the batteries to deteriorate.A great deal of research is being carried out on this subject and a control function has evenbeen developed for the battery, so that charging and discharging take place in the best possibleway. In Japan such a control function has been developed for a nickel-metal hybrid (Noboruet al., 1998; Tojima et al., 1998). This control function protects the battery against beingoverheated, which would not only reduce the working efficiency if the battery but would alsohave a negative effect on its lifetime. In a report (Noboru et al., 1998) it has been pointed outthat the mechanism behind the gradual deterioration of the charging capacity throughundercharging (which is here interpreted that one does not carry out the charging processusing a sufficiently large capacity) has not been established. It is stated that there is adifference between different types of battery, so that certain batteries can be charged in ashorter period of time than others do.

In an investigation of the charging time of a valve regulated lead battery (Cooper and Mosely,1998) it was found that fast charging dramatically increased the lifetime of the battery, whichcan be seen in Table 21.

Table 21. The effect of charging strength on the working efficiency of charging and on thedurability

Parameter Slow Charge Fast ChargeCharge RegimeDischarge Regime

5 hour rateAt 2 hour rate to 11.6V 80%

12 minute rateAt 2 hour rate to 11.6V 80%

Capacity Check afterevery 50 Cycles

Discharge to 10.5V and fullycharged for 3 cycles

Discharge to 10.5V and fullycharged for 3 cycles

Charge EfficiencyCyclesLifetime Discharge

87 %25010 000 Ah

97 %900+30 000 Ah

Status Failed Still Healthy

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11 TEST METHODSA whole new situation has arisen concerning the methods for evaluation of the effects of thefuel consumption (or the use of energy) and of exhaust gas emissions when using hybridsystems, compared with such evaluations when using present day, conventional vehicles.Firstly the energy used during the test of a hybrid vehicle cannot always be related solely tothe use of the specific fuel and not either the emissions released from the vehicle to be correct,since the status of the energy storage battery must be exactly known both before and after thetest. Instead the energy used during the test has to be calculated for both the internalcombustion engine and for the electric motor (motors). Nor can one expect that the two basicsystems, series and parallel, will be able to be tested according to the same method, withoutthe measurements becoming unnecessarily comprehensive. Such differences between the twobasic systems can be found that it can be more rational to test them according to somewhatdifferent methods.

The Society of Automotive Engineers (SAE) has produced a preliminary standard for themeasurement of energy consumption and emissions of hybrid vehicles. The standard is called“Draft SAE J1711”. It is not officially available so we have not been able to study thepreliminary standard. In a SAE report, SAE-paper 981080 (Duoba, M. And Larsen, R., 1998)it is stated that the preliminary standard SAE J1711 has been changed a number of times sinceit first appeared in 1992. It is thought that a key problem with measurement methods forhybrid vehicles is that there are too few hybrid vehicles on the market for the concept of thetest method to be able to be verified.

Technicians at the Argonne National Laboratory (ANL) also have some comments on thepreliminary SAE standard. They think that the SAE J1711 measurement method is too longfor their purposes, and that the suggested standard means that one will be dependent on thevehicle manufacturers to specify how the vehicle reacts for the various tests. They also thinkthat the initial installation of the system in the vehicle must be adjusted in order for thedriving cycles and measurement to be able to be carried out.

After their first draft of the measurement method the committee who was involved with itdecided that hybrid vehicles must be classified in various categories and be tested accordingto different methods suited to the function of the relevant hybrid. According to them this isnot in line with the wishes of either the authorities or the vehicles manufacturers with manyvehicle models. For technical reasons these want a comprehensive measurement methodwhich is suited to all types of hybrid vehicle. Technicians at Argonne think, on the other hand,that the function of the hybrid is too complex for it to be possible to characterize all types ofhybrid vehicle using only one measurement method.

The following steps for characterization of and measurements on hybrid vehicles have beenspecified in a report (Duoba, M. and Larsen R., 1998):

CHARACTERIZATION OF VARIOUS FUNCTIONS OF HYBRID VEHICLES – is acomplete characterization of each discrete way that the hybrid vehicle works. It includes boththe various function steps that are connected in automatically and those which the driver ofthe vehicle can connect in by switching etc.

“ZEV MODE” – if the vehicle is to driven by electricity for a whole driving cycle, this will beregarded as a zero emission stretch or as having “ZEV” possibilities.

“HEV MODES”– HEV functions is defined in the report (Duoba, M. and Larsen, R., 1998) asa single energy-supply strategy – a strategy during which the electric motor and the internalcombustion engine work together to supply the vehicle with sufficient power for driving it.

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“ON BOARD CHARGING” – a HEV function, which means that the vehicle’s batteries arecharged by a special generator while driving.

”CHARGE-DEPLETING* HEV MODES” – results collected from this stage of the testcannot be corrected so that the electric energy, which is used is eliminated – electric energywill always be depleted for this test. For this reason the characterization of this step mustinclude the results of the emissions from the internal combustion engine and also the fuelconsumption. The relationship between these and the amount of electric energy used from thebattery during the test shall be calculated.

“CHARGE-SUSTAINING HEV MODES” – is either the steps in the test where there isinsufficient capacity in the battery for the internal combustion engine to be able to beswitched off, or when the internal combustion engine is sometimes switched on and sometimenot. Because the engine an electric drivetrain are working together during HEV mode thisusually means that the battery is continuously storing and releasing energy throughout theoperation. This leads to unpredictable behavior that requires more test time to characterize aparticular mode accurately

“SOC-CORRECTIONS” – this is an important aid which has been developed to solve theproblem of cycle to cycle variations for transient HEV driving. Measurement of the charginglevel of the batteries, “state of the charge” (“SOC”), is a method of combining the results fromthe various cycles in order to balance out the charging and discharging of the battery during atest. This process produced data concerning the fuel economy (energy consumption) andemissions, which corresponds to the zero net change in SOC.

“LINEAR REGRESSION SOC METHOD” - occurs in the first draft of the preliminary SAEstandard which then comprised a method with linear regression for correcting the battery’scharging level. This method is most useful for vehicles which do not have zero net chargewith a significant stretch using electricity.

The functions or steps in the measurement method which are described above are those whichwe think should be included when measuring energy consumption and emissions from hybridvehicles. Variations in the design of the various steps can obviously occur and the idea withsuiting the method to the type of hybrid system and function of the hybrid system shouldcertainly be considered when finalizing design of a standard method for measurements onhybrid vehicles.

Figure 39. Tests with parallel hybrid vehicle developed at the University of California

Davis. Source: Duoba, M. and Larsen R., 1998

A parallel hybrid system developed at the University of California Davis and a series hybriddeveloped at West Virginia University were tested in one of the US EPA laboratories and thecomplexity in the tests is reflected in Figures 39 and Figure 40. The abbreviations in thefigures are as follows:

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ZEV: A step in the driving cycle where the vehicle is driven as an electric vehicle, i.e. onlyusing energy from the battery.

UDDS: Urban Dynamometer Driving Schedule.

HWF(E)DS: Highway Fuel Economy Dynamometer Schedule

HWY prep*: Warming up cycle before HWFEDS (The same driving cycle as fordetermination of fuel consumption, HWFEDS, is driven once in order to warm up the vehicleimmediately before the HWFEDS test is carried out).

A-h; Ampere hourkWh: Kilowatt-hourAC: Alternating CurrentMPG: Miles per gallon (1 mile = 1.609 km, 1 gallon = 3.785 l).Cold-start: The starting temperature of the test is usually ca 22 degrees C.Hot-start: The vehicle is usually run so that the internal combustion engine reaches drivingtemperature.

SOC Corrected: Corrected State of Charge (level for charging the battery, see above).

Comments to Figure 39: The energy consumption for tests with cold-start and warm-startcan be seen in the right part of the figure. For each pair of squares in the figure the first squaregives the energy consumption in l/100 km (and MPG, i.e. number of miles per 3.785 l fuel,exclusive of the use of electricity). The other square gives the amount of electricity used inAh and kWh and this energy consumption has to be added to the consumption of fuel. Thereis a corresponding situation for reporting the results at warm start and even for tests accordingto HWFEDS.HWY stands for warming up the vehicle before the actual HWFEDS test is carried out.

Figure 40. Tests with series hybrid vehicle developed at the West Virginia University.

Source: Duoba ,M. and Larsen R., 1998

Comments to Figure 40: The results are given here in a somewhat more complicated form.This is because one test (the first square in the left part of the figure) is carried out with thevehicle run only in the electric vehicle position. This gives the possibility of comparing theenergy consumption for two test cases - running as electric vehicle and running with theinternal combustion engine via the electric system. The other square on the left side of thefigure gives the energy consumption in the internal combustion engine of 11.46 l/100 km(25.52 MPG). Since the battery is charged with 1.8 Ah by running the internal combustionengine the real energy consumption during the test must be corrected to 9.14 l/100 km (25.52

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MPG). Compare the values in square 3 and square 4 in the right part of the figure. There is acorresponding situation for test with warm start. However the calculations for the twoHWFEDS tests which were carried out resulted in a minus value for the charging level of thebattery in the first test and a positive value for the charging level of the battery in the secondtest.

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12 IMPACT ON THE EMISSIONSThe studies carried out have shown that there is a realistic potential for a reduction of theemissions by replacing conventional vehicles with hybrid vehicles. However, there are many“ifs” which have to be fulfilled in order to surpass the light duty conventional mass producedgasoline fueled vehicle of the future. Therefore when making comparisons with a such vehiclethere is a higher potential for improved fuel economy than for improved emissions especiallywhen comparing data generated according to standard test procedures. When looking at thereal traffic situations and the use of the vehicle during different meteorological conditions thesituation for the hybrid system seems much more positive. The main reason for this is thatthere are more alternatives and a higher freedom for the parameters and conditions whichhave a significant impact on the emissions. These conditions and/or parameters are, forexample, the cold start situations (which are a problem in the Nordic countries) during whichthe hybrid technology offers some realistic opportunities to minimize the impact on theemissions. The hybrid vehicle can be designed so as to start the trip in the electric mode. Thismay require that the battery is charged from the mains and that the compartment of the vehicleis warmed up by an electric fan. There are also many other possibilities in a hybrid system totake care of the emissions at periods with low temperatures. More of the technology to beused will be discussed in Section 12.1

With a well designed and efficient electric drive train and an optimal matching between theelectric drive train and the internal combustion engine the engine can be operated so as toavoid rapid accelerations which is a risk, especially in a parallel hybrid system. For both typesof hybrid systems and especially for series hybrids there is an urgent requirement to haveaccess to highly efficient batteries, in order to improve the weak link in the electric drive train.In Section 12.2 the emission performance is presented for some of the systems discussedearlier in the report. Unfortunately there are only two systems for which emission data areavailable for this report and it is also a drawback that no emission data for a second generationof hybrid vehicles has been available.

12.1 Theoretical background for a emission potential

Since the hybrid systems have not been commercially available, except in Japan until thisyear, a closer evaluation of their potential for low emission levels has not been possible. InSection 8.2 some result found in the literature have been presented and discussed and theseresults indicate a rather positive emission potential for hybrid light-duty vehicles. For heavy-duty vehicles there is a lack of reliable data for a realistic estimation of the potential. Whendealing with this matter it must be kept in mind that the hybrid systems for which emissiondata have been available are the first generation of these types of vehicles.

When trying to find the right level for an estimation of the emission potential a question israised as to whether there are any fundamental factors that have a negative or a positiveimpact on the emissions from the hybrids.

Both with series hybrids and parallel hybrids there is a possibility to operate the internalcombustion engine in a different regime than the regime it would be operated in if the drivingcycle should be completely followed by the engine. Since the emission control system (TWC)for otto engines rather is sensitive to transients (regardless of fuel) it can be estimated thatclose-to-constant driving favors the emission reduction. It has been shown by experimentsthat rapid accelerations cause higher emission levels. New systems for reduction of NOx fromdiesel engines (fueled with diesel oil or an alternative for diesel oil) the so-called deNOxcatalysts, may also benefit from reduced transients. This is also valid for other emission

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control systems for example EGR (exhaust gas recirculation), where the governing (for bothotto engines and diesel engines) is considerable simplified at steady-state operation of theengine. The greatest impact of reduced transients would be achieved for an engine with acompletely steady state operation. One such example is the so called “Range Extender”which is basically an electric car equipped with a very small internal combustion engine, usedin order to maintain the electric capacity of the battery. Unfortunately there are indicationswhich show that the engine in a present day hybrid system is operated with the same numberof transients as an engine in a conventional vehicle. Whether this is true or not is a matter forcloser studies of the hybrid systems on the market. The number of transients may be the samebut not the shape since the engine in for example the Toyota Prius according to Toyota(Hirose et al., 1998) is operated within a close area of the conventional engine working area(see Figure 41).

Figure 41. Engine operational area and exhaust temperature. Source: Hirose et al., 1998.

Since the size of the engine in a hybrid system is reduced the average load of the engine isincreased with the result that the average temperature would increase. This will result in a riskfor higher strain of the catalyst unless it is designed for a higher degree of conversion.However, the authors of the report (Hirose et al., 1998) claim that the exhaust temperaturedistribution of their THS engine for Prius is lower than for a conventional engine. The greatestadvantage with the reduced size of an engine controlled with a three-way catalyst system(TWC) is most likely that the heating of the system is faster which result in lower level ofemissions during the warming up phase. For a diesel engine, however, a higher exhaust gastemperature is a great advantage since the temperature in the exhaust of a diesel engine isusually too low to achieve a reaction in the catalyst during lengthy periods. One example topoint out is that during driving according to the low speed part of the European driving cycle(4 km of totally 11 km) the conversion in the catalyst for light-duty vehicles is very poor. Thisresults in the average conversion ratio for the whole driving cycle being lower than 50%. Witha hybrid system there is a great possibility to increase the conversion ratio in the catalyst.

One disadvantage with a higher average load of an internal combustion engine is that thesecommonly result in an increased NOx emission from the engine (before the catalyst) whichoccurs in both otto and diesel engines. For otto engines the increase is caused by a higher rateof NOx formation* (increased temperature) and by the fact that EGR is not usually used athigher loads (in the case where the engine is equipped with this type of system). In the case ofdiesel engines the increased ratio of NOx formation is caused by the lower EGR rate (if an * In the case above the increase of NOx emission before the catalyst can be in the order of a factor 4. Typical

values are from 5 g/kWh to 20 g/kWh.

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EGR system is used). For both engines there is a need to rate EGR at higher loads in order todecrease the ratio of NOx formation. This applies when these types of engines are to be usedin hybrid systems or in vehicles equipped with continuously variable transmission (CVT)where the systems, in both cases, are optimized for a minimum of fuel consumption. Theproblem with the increased NOx emissions has also been observed by for example Ossis et al.(Ossis et al., 1996).

Electric preheated catalysts have been developed in order to reduce the emissions from ottoengines during cold start conditions. Even if the commercialization of these types of catalystsis not yet been carried out on a broad bases (BMWs V12 engine is, however, one example) itis quite clear that hybrid electric systems are advantageous in this respect. The situation is thateven if the requirement of electricity has been drastically reduced (one tenth of what wasoriginally needed in 6 to 7 years), more electric energy is needed than a commonly usedbattery can deliver in order to heat the catalyst. This is especially true for cold starts at lowtemperatures. Unfortunately there is an indication that the control strategies used today shutoff the electric heating at considerable low temperatures in order to be able to meet the needfor electricity to the start the engine. In the case of hybrid vehicles with their larger size of thebattery there is no problem for the battery to deliver the electricity needed to heat the catalysteven at low temperatures (see also Section 8.2.5 about Nissan hybrid system).

To summarize this section is can be underlined that a considerable potential exists for thereduction of emissions by the use of the hybrid technology. Moreover, for the hybrid systemwhere the batteries can be charged with electricity from the mains the emissions can bereduced by the fuel consumption being reduced. This is of course valid under the assumptionthat the electricity is generated with low emission levels.

12.2 Emissions related to the hybrid system

In this section the emission-related abilities of two of the above presented hybrid systems willbe analyzed and discussed in somewhat more detail. It should be kept in mind that Mercedes –Benz by their new organization DaimlerChrysler has most likely replaced the use of aninternal combustion engine with fuel cells. However there is certainly some interest instudying the result achieved with the M-B series hybrid vehicle equipped with an internalcombustion engine.

12.2.1 The series hybrid from Mercedes-Benz

It is well known fact that the potential to achieve low emission levels is highest for serieshybrids. In the SAE report (Abthoff, J.O. et al., 1998) from Mercedes-Benz the result fromemission tests on their series hybrid have been presented. In Figure 42 the result from theseemission tests are shown and also the emission standards for ULEV and EZEV. From thefigure it can be clearly seen that significant emission reductions have been achieved with theseries hybrid vehicle. Compared with the European emission standards of today the CaliforniaULEV standards are considerable more stringent. The standards which are valid for year 2000are somewhat less stringent than the ULEV standards and close to the California standards forLEV. The ULEV standards are, in comparison with the first generation of the first catalyst(TWC) cars in Sweden (model 1987-1989), considerable more stringent in that the levels ofthe standards are 5-10 times lower. In comparison with the ULEV standards the proposals forEZEV standards even more stringent in that the emission levels proposed are only 10% of theULEV standards. From Figure 42 it can be seen that the emission levels of the tested M-Bseries hybrid vehicle are lower than the EZEV standards.

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Figure 42. Emissions for Mercedes series hybrid vehicle (prototype).Source: Abthoff et. Al.

12.2.2 The parallel hybrid vehicle Prius from Toyota

Emission data for the parallel hybrid vehicle Prius have been presented by Toyota (testsaccording to the Japanese 10-15 mode cycle) and by US EPA (UA EPA FTP-75 tests).Unfortunately no results from emission test according to the European test cycle have beenavailable for this report. The results presented by Toyota can be seen in Table 22.Table 22. Japanese 10–15 mode emission standards and emissions for Toyota Prius.

Emissions (g/km)

Emissiondemand/vehicle

CO HC NOX

Japan 10 –15 2.1 0.25 0.25

Toyota Prius 0.21 0.025 0.025

If the above presented emission data was also valid for tests according to the European testprocedure (and with the European specification of the vehicle), the emission performancewould be much better than that of the vehicles which meet the current European emissionstandards and rather closer to the ULEV standards. Unfortunately there are too few hybridvehicles available for carrying out the investigations which are required in order to establish areliable emission level for hybrid vehicles based on the present day technology. In order toimprove this short emission evaluation, data generated by US EPA (Hellman et al., 1998) hasbeen summarized in a table in Section 12.3 where the relationship between the driving patternof the vehicle and the emissions is discussed.

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12.3 The relationship between the driving pattern and theemissions

In the different sections above it has been underlined that the fuel consumption “savings” in ahybrid vehicle compared to a conventional vehicle are largest at low speeds and loads of thevehicle. A question was raised as to whether this is also true for the emissions. In order to getan indication, despite the lack of specific data needed, the emission data generated at US EPAwas used for this purpose, in addition to that it was of interest to present emission values fromtests according to the FTP-75 driving cycle. Results from the tests carried out by US EPA aresummarized in Table 23 and Table 24. It should be observed that the values presented here areconverted to SI units.

Table 23. Result from emission tests according to the US EPA FTP-75 test procedure.Test date FID HC NMHCE CO NOx CO2 Fc Net charg. *

g/km g/km g/km g/km g/km l/100 km Amp-h.980403 0.037 0.037 0.249 0.031 112.5 4.95 -0.285980417 0.031 0.025 0.249 0.031 110.0 4.84 -0.252980423 0.037 0.031 0.249 0.044 113.1 4.98 -0.132980424 0.037 0.031 0.249 0.031 108.1 4.77 -0.038

*Negative values are related to the net charges of the battery during the driving cycle.Source: Hellman et al., 1998.

Table 24. Result from emission tests according to the US EPA HFET test procedure.Test date* FID HC NMHCE CO NOx CO2 Fc Net charg.**.

g/km g/km g/km g/km g/km l/100 km Amp-h.980403 0.025 0.025 0.186 0.031 110.0 4.835 -0.488980403 0.025 0.025 0.186 0.037 101.9 4.472 -0.08980417 No analysis No analysis No analysis No analysis No analysis No analysis -0.444980417 0.006 0.006 0.124 0.025 103.2 4.534 -0.052980423 0.006 0.006 0.124 0.037 111.97 4.905 -0.37980423 0.006 0.006 0.124 0.031 103.8 4.572 -0.014980424 0.012 0.012 0.124 0.025 110.0 4.838 -0.338980424 0.012 0.012 0.062 0.031 102.6 4.520 -0.097*The first value in each column of HFET (Highway Fuel Economy Test – a test for measurement of fuel

consumption) refers to the first test of FTP-75, the second value to the second FTP-75 test and so on (comparethe test dates in the tables). In this case measurement of emissions and fuel consumption have also been carriedout for the preparatory driving according to the HFET cycle, which is not a common procedure.

** Negative values are related to the net charges of the battery during the driving cycle. Source: Hellman et al.,1998.

The result of the tests carried out by EPA show that the emissions of HC at FTP-75 are, onaverage, more than 40% larger than the values presented by Toyota (Table 23) but as anaverage approximately 50% less than the Toyota values when driving according to the HFETcycle. It should be kept in mind that the data presented by Toyota were generated according tothe Japanese 10-15 mode cycle (see Section 8.1.2).

The emission of CO does not vary for the FTP-75 tests and is at the same level as the COemission values reported by Toyota. For the HFET cycle the average values are nearly 50%less than the values reported by Toyota (compare Table 23 with table 24).

On average, the emission of NOx is 0.034 g/km for the FTP-75 tests and 0.031 g/km for theHFET tests i.e. 37% and 24% respectively higher levels than the Toyota NOx values.

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Comparing the results from FTP-75 (which represent a lower average speed than the HFETcycle) with the results from the HFET cycle there is an indication of a negative correlationbetween the average speed and the emissions i.e. the emission levels are higher at a loweraverage speed than at a higher speed.

According to the tests carried out by US EPA the fuel consumption is considerable higherthan data reported by Toyota (see also Section 8.2.3)

Since there is a good potential for obtaining low emission levels and high fuel efficiency, thehybrid vehicle alternative can be seen as a more attractive alternative today than an electricvehicle. However, the development of the future may give the answer as to which of thealternative hybrid or electric vehicle is more attractive. If there will be a successfuldevelopment and reasonable cost of fuel cell vehicles which work like a electric vehicle, theanswer may be definitely “electric vehicle”.

In line with the ranking for best fuel economy (see Section 8.1.4) the ranking can be carriedout for the emission performance for conventional vehicles. To keep it simple, the ranking iscarried out only for the emissions of NOx and particles. The result of such a ranking will be asfollows:

Conventional otto engine with TWC emission control.Advanced otto engine with direct injection (stoichiometric, EGR and TWC)Advanced otto engine with direct injection (lean-burn, EGR and deNOX)Diesel engine (direct injection)

Comments: It is possible to carry out a similar ranking even for other emission componentsthan for NOx and particles but then the picture will be more complicated depending on thetechnology used for emission control etceteras and it has been excluded for reasons of space.

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13 SUMMARY OF COSTSA more thoroughly costs estimates was not really included in the enquiry for the preparationthis report since there is no on-going production of hybrid electric vehicles and that the extracosts involved for the hybrid vehicles therefore are difficult to estimate. One cannot, however,ignore the fact that this type of vehicle involves the cost of a double driving system. Sincethere must also be batteries in the system the cost are further increased in the case of thebatteries having to be very large. A cautious estimation is that, if a conventional vehicle, withthe size of the Toyota Prius, now costs 150,000 Swedish crowns a cost up to 100,000 Sw.cr.would have to be added for a hybrid vehicle, even if there was a relatively large-scaleproduction (10 000 units per year). Chrysler has estimated that their prototype (PNGV) wouldcost 15,000 dollars more (approximately 140,000 Sw.cr. in year 2000 exchange rate). This ishowever a considerable improvement on the previous prognosis from the same manufacturerof +60,000 dollars. To this it can be added that the difference in the actual cost for a FordFocus flexible fuel vehicle and a Toyota Prius (both of them are to be sold in Sweden) isapproximately 80 000 Swedish crowns (approximately $8 400 in the today’s exchange rate).A calculation of cost given by Mercedes for their previously mentioned hybrid system (seesection 8.2.1) is shown in Figure 43.

Figure 43. Cost of various driving systems. Source Mercedes Benz.Comparison of production costs for various types of driving system (basis for calculations: 10,000 units)Conventional driving system 100%, Convention driving system with EZEV emission level 124% , Serieshybrid (EZEV) 204%, Electric vehicle (ZEV) 226%, Source Mercedes Benz

As can be seen in Figure 43 the cost of a driving system for both a hybrid vehicle and a purelyelectric vehicle exceed the cost of a conventional driving system. In the future and whenlarger series are involved, the extra cost could probably be reduced to ca 25,000 Sw.cr., buteven this extra cost can be too high to be able to motivate a large-scale use of the technique.It can be seen from the figure that a conventional driving system developed to meet the EZEVlimits would be considerably less expensive. Since the parallel hybrid system has the potential

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of being considerably cheaper than the series hybrid system, this would be a strong reason forit being more successful in the short and relatively long-term.

The opinion of the authors concerning the hybrid system for passenger vehicles is that theextra cost of series hybrids will be far too high, within the foreseeable future (to 2010) for it tobe able to compete with a conventional driving system. Even if a parallel hybrid system canbe somewhat cheaper, it seems that the extra cost even for that system is also a considerablehinder. A number of technical break-throughs must thus take place for the hybrid system to beable to compete with a conventional system for passenger vehicles. The great potential forreduced fuel consumption will however probably lead to a great deal of interest for thesedriving systems in the future.

13.1 Cost of the System

The above paragraph deals with a vehicle manufacturer’s calculated extra cost for a hybridvehicle. A comparison of costs between a conventional driving system, a conventional drivingsystem with very low emissions levels, a series hybrid with very low emission levels and anelectric vehicle were discussed and shown in Figure 43. The discussion and the percentagesshown in the figure clearly show that there will be a difference in costs between the variousdriving systems. In the table below, Table 25, an attempt has been made to give a roughestimation of the costs of certain vital parts of the hybrid system. These are stated as “high”,“medium” and “comp conv” (comparable with conventional vehicle).

Table 25. Estimation of the cost levels for various details in the hybrid system/vehicle.Equipment or detail in thehybrid system/vehicle

High Medium * Compareconvent.**

Comments

Body + chassis X Use of light materialInt. combustion engine X Smaller but specialElectric motor/generator X Alternator unitBattery X Depends on type of batteryControl electronics X Large function requirementsCont. variable transmission X Vital part of the systemProduction method X Several mom. at production.

*One has to calculate a larger or smaller extra cost, due to there being differences compared with aconventional vehicle

**There can be certain differences from the cost of a conventional internal combustion engine the chassis/bodyrespectively. Similar material will commonly be used in the conventional vehicles

These estimations are based on small series of vehicles.

13.2 Cost of the Batteries

There is a great degree of uncertainty concerning what the batteries will cost, and this makesit very difficult to make a prognosis. As in most cases the costs depend on the amount of unitswhich the manufacturer can sell. In the case of batteries there seems to be three things whichaffect the basic costs;

the cost for a development and production unit;development costs;costs of materials.

The cost for the development and production building and for the development of batteriescan be greatly influenced by the number of items sold. However, the costs of materials will

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not be affected in a positive direction other than in special cases. On the contrary, the cost ofmaterials will increase if the number of items sold is large and there is a limited availability ofmaterial (see Table 26).Table 26. Evaluation of various batteries.Parameter Unit Lead

AcidNickel-cadmium

Nickel-me-tal hydride

Zebra Litium-ion

Specificenergy

Wh/kg 30 55 65 90 150

Specificpower

kW/kg 0.080 0.175 0.175 0.100 0.300

Life cycles No. of cycles at80 %

500 1500 1500 1000 1000

”OEM” price Euro/kWh 110 380 380 460 150Factor of“Merit”

Wh x kW xNo. of Cycles/“OEM” price

11 30 45 20 300

In a report (Cornu, 1998) “Factor of Merit” characteristics have been developed for a numberof batteries and these factors have served as the basis for the determination of interest in thesebatteries. The interest among vehicle manufacturers in lead batteries was found to be lowestand for lithium-ion batteries it was found to be highest. (See Table 26).

13.3 Total costs

Certain total costs can easily be calculated, such as the fuel costs and the cost of electricity ifthe batteries are to be charged from the mains. There are however three costs which areespecially uncertain, namely;

Depreciation cost for the vehicle;Costs for exchanging batteries;Service and maintenance costs.

Since these three costs are so uncertain, at this stage of the development of hybrid vehicles,there is of no value for the reader of this report in the authors making any speculations aboutthe costs. Hopefully certain experiences will be generated as soon as Toyota’s hybrid vehiclecomes on the market in Sweden, among other places. In the case of series hybrids, whichusually have a built-in possibility of being charged from the mains, this charging is expectedto lead to lower running costs than if the batteries were to be charged from an internalcombustion engine while being driven. This must however be weighed against the fact that, inthis case, a greater battery capacity is required than in the case of a parallel hybrid, which isusually not equipped for charging from the net.

Running costs can be affected in a way, which is related to the hybrid system/vehiclecompared with running cost for a conventional vehicle, and in any case for the present dayhybrid vehicles such as Toyota Prius, Ford’s hybrid vehicles, Nissan’s hybrid vehicles andcertain others which have been developed recently. The investigation of the hybrid system,which has been presented in this report shows that there is a potential for a reduction in fuelconsumption (or use of energy) when driving hybrid vehicle compared to drivingconventional vehicles and especially for parallel hybrids in light-duty vehicles. Several of thehybrid vehicles have lighter weight material and other improvements have been made, whichare positive for running costs. In the future we do not expect that the use of light weightmaterial in vehicles and the fact that hybrid vehicles are smaller in size than the conventional

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“average vehicle” will be unique. The driving system of a hybrid vehicle represents a greatermass than the driving system of a conventional vehicle. The question is whether and by howmuch the mass of the driving system of a hybrid vehicle can be reduced compared to aconventional vehicle.

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14 EFFECTS ON HEALTHHealth risk estimations have long been used as an aid in investigating the need for limitingemissions from traffic. Some major studies of health risks have been carried out in Sweden, aswell as some of lesser magnitude. To name just two of the major studies, one investigationwas conducted by a parliamentary committee, “The Swedish Government Committee onAutomotive Air Pollution” (Motor Vehicle and Cleaner Air, 1983), and comprised a medicalassessment of various exhaust gas pollutants under the leadership of Professor Lars Friberg.The other large-scale study, “The Swedish Ambient Air Project” (Environmental HealthPerspectives, 1994), led by Professor Jan-Åke Gustafsson, which in reality took 12 years tocarry out, dealt with cancer risks associated with exposure to air pollutants in built-up areas.The Swedish Environmental Protection Agency initiated and financed the latter researchproject in the different fields of automotive emissions, characterization of pollutants in theexhaust, biological testing and health risk assessments.

When studying the final reports from the project, it should be kept in mind that the material onwhich the final report is based was developed during the 1980s and 1990s as well as duringthe late 1970s. Many important steps have been taken since then, including positive changesin the fuel matrix and in vehicle emission performance, in order to improve the air quality inpopulated areas. Consequently, it is of no benefit in this presentation concerning health effectsto go too deeply into the results from these studies. However, it should also be mentioned thatthe substances found in the exhaust and also in the air (in 1983) are more or less the same atthe present time but at a lower level. In addition, it can be noted that since 1983, one pollutantin the exhaust gas from vehicles has been nearly completely eliminated in Sweden, namelyemissions related to lead in gasoline.

With respect to the above discussion concerning the substances, it can be of value to quote apassage from the Vehicle Exhaust Gas Committee’s report where it was pointed out that, “Thevarious substances causing air pollution can produce different types of effects on humanhealth. They may have effects of either an acute or chronic nature on lungs and respiratorypassages”. “Moreover, different substances can enter the bloodstream, where they can have anadverse effect on virtually any bodily organ (toxaemia)”

It can also be of some value to refer to a table presented in the final report from the SwedishAmbient Air Project, which provides a comparison of estimated cases of cancer per millioninhabitants in the USA and in Sweden (see Table 25). For scientists in Sweden doing researchin the field of heath risks related to exhaust from automobiles, it has been of advantage torefer to experiences and data generated in the USA, since many important health effectstudies have been carried out in both the federal USA and in California.

Evaluations of health risks caused by various substances in the environment are based firstlyon results of experiments in which human, animal or biological test systems were exposed tothe substances of concern, but also on epidemiological studies by which the health of differentsectors of the country’s population is studied. While not going more deeply into these studies,it can nevertheless be said that both have considerable shortcomings and it is thereforedifficult to draw accurate conclusions from them.

One problem in experimenting on animals and humans is that only a limited number ofindividuals can be examined. Experiments on humans can be performed only for short periodsand at moderate levels of exposure. This makes it difficult to clearly establish the effectthresholds for various substances on the basis of experimentation.

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Since animals experiments are time consuming and costly to perform, methods for short-termbioassay tests have been developed and extensively used in order to compare the totalmutagenic activity of samples taken in the motor vehicle exhaust and in ambient air. InSweden, for example, two types of short-term biological tests have been used of which one isthe well known Ames test in Salmonella typhimurium, which has been shown to be a usefultool. The other test method used involves the dioxin receptor affinity tests, a less knownbiological test which, however, can be seen as a complement to the Ames salmonella test.Studies have shown that extracts of particulate matter and samples taken in the semi-volatilephase in motor vehicle exhaust and in ambient air contain components with high affinity forthe receptor in rat liver which specifically binds 2,3,7,8-tetra chloro dibenzo-p-dioxin(TCDD). Both of these biological test methods are described in a report (Westerholm andEgebäck, 1991), as well as elsewhere.

Concerning epidemiological studies, there are two main approaches. In one, a section of thepopulation suffering from a specific effect is compared with a reference group that isunaffected, and an attempt is also made to try to determine the various factors, such asexposure to air pollution, that explain the difference. The second approach is to comparepopulation groups exposed, for example, to different levels of air pollution in order to find outwhether the state of health of the two groups differs and, if so, to determine whetherdifferences in exposure can provide an explanation.Table 27. Estimate of risks for yearly incidence of cancer associated with air pollution..

Source: Möller et al., 1994). Cancer cases/year/millioninhabitants

Pollution in the air USAa Swedenb

Particulate phasePOM, PAH [as B(a)P]POM .[and different equivalents], all cancer cases

1.0--

11.634.9

Gas phase1-3 ButadieneBenzene, leukemia All cancer casesFormaldehydeAcetaldehydeEthene, all cancer casesGasoline

0.9-1.00.4-0.60.4-0.60.1-0.2

<0.1--

0.07-0.3

5.80.61.22.9

<0.13.5--

Abbreviations: POM, polycyclic organic material; PAH, polycyclic aromatic hydrocarbons.adata from US EPA (US EPA, 1990). bdata from Törnqvist and Ehrenberg (Törnqvist and Ehrenberg, 1994);based on the present (1994) average Swedish level of exposures according to (Boström et al., 1994).

When referring to the different studies on health effects expected to be caused by pollution inthe ambient air, it must be emphasized that the results from such studies suffer from anunknown factor of uncertainty. Although the aim of this presentation is not to deliberate uponthe results from different health effect studies, as a complement to the above commentsreference can be made to Table 25, which shows great differences between the USA andSweden. Some of these differences can certainly be explained by differences in the samples –whether they represent all sources of the pollutant or whether they represent exclusivelypollutants caused by motor vehicle emissions. One example is the high Swedish value of 34.9for POM, which is not clearly defined, thereby constituting a drawback regardless of whetherthe results from such studies represent the situation in the 1980s or the situation today. This isespecially important since even if health effect studies suffer from shortcomings, they arenevertheless important tools for those making decisions concerning emission requirementsand measures concerning air quality.

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As has previously been pointed out, engine exhaust gases contain a very complex mixture ofvarious chemical compounds which consist of unburned fuel components and chemicalpollutants which have been formed during the combustion process in the engine. The enginelubricating oil also contributes with unburned and pyro-synthesized components. Thecontribution from engine lubricating oil is greatly dependent on whether oil leaks past theengine pistons. Relevant non-regulated exhaust gas components, which can be related toenvironmental effects and health risks, can be seen in the list below. Important exhaust gascomponents in a global perspective are greenhouse gasses such as carbon dioxide, laughinggas and methane. Since there are a large number of pollutants in vehicle emissions, there willalso be unknown pollutants in various amounts which can be expected to give rise to healthrisks, especially for sensitive humans. With this reservation in mind, important non-regulatedexhaust gas components are presented below with respect to their health risks. This list is notcomplete and it is expected to be up-dated when future research results are taken into account.Carrying out a complete characterization (identification and measurement of all thepollutants) of the pollutants which exist in emission samples from internal combustionengines is not possible.

AldehydesAldehydes, Figure 44, are known to be irritants and can initiate allergic reactions in sensitivehuman beings. Formaldehyde is judged to be carcinogenic (CARB, 1989). In Stockholm therehave been complaints about a bad odor from ethanol buses, which can partially be explainedby the production of aldehydes and acetic acid during unfavorable circumstances, and thesehave a disagreeable smell. This problem has been solved, to a large extent, in the newgeneration of ethanol fueled busses.

Figure 44. Exemple of relevant aldehyds. Source: Egebäck and Westerholm, 1997.

AlkenesCertain alkenes, Figure 45, such as ethene, propene and 1,3 butadien have a potential to beconverted by the enzymes of the body into reactive metabolites which can initiate cancer.Ethene metabolizes to the reactive metabolite ethylene oxide in both animals (Törnqvist et al.,1988) and human beings (Törnqvist et al., 1991).

Figure 45. Examples of relevant alkenes. Source: Egebäck and Westerholm, 1997.

Alkyl nitritesAlkyl nitrites, Figure 46, are mutagenic (Törnqvist et al., 1983) and can therefore bepotentially carcinogenic. Alkyl nitrites are formed from unburned alcohols and oxides of

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nitrogen in the exhaust gas from a vehicle which is driven on methanol/gasoline and onmethanol/diesel mixtures (Jonsson and Bertilsson, 1982).

Figure 46. Examples of relevant alkyl nitrites. Source: Egebäck and Westerholm, 1997.

Aromatic compoundsMonoaromatic compounds, Figure 47, of special interest are benzene, toluene, creosol andphenols. Occupational exposure to benzene can give rise to an increased risk of leukemia.(Törnqvist and Ehrenberg, 1994).

Figure 47. Examples of relevant Monoaromatic compounds. Source: Egebäck and Westerholm, 1997.

Polycyclic aromatic compoundsWithin the group of substances called Polycyclic Aromatic Compounds, PAC, Figure 48,some substances have been shown to cause cancer in animals (IARC, 1983). Due to this, thesecompounds must be seen as potentially carcinogenic even for humans. Polycyclic* AromaticHydrocarbons, PAH, are formed during incomplete combustion of organic material in air andtherefore exist in the exhaust gases from motor vehicles. There are several factors whichaffect the emissions of PAH, such as cold-start, driving pattern, engine concept, concept forafter treatment of exhaust gases, choice of fuel, etc. In the Swedish standard for theenvironmentally classified diesel fuel, MK1, the amount of PAH is specified as a fuelparameter. The emissions of PAH in vehicle exhausts are partly a result of the pyro-synthesized fuel and the engine lubricating (lub) oil (formed during the combustion process),and partly unburned PAH which comes from the fuel and lubricating oil (Westerholm and Li,1994). This means that PAH emissions in the motor vehicle exhaust can be minimized if thefuel PAH content is as low as in MK 1 diesel fuel. PAH samples are divided between PAHadsorbed on particulates and PAH which are in the gaseous form (Westerholm et al., 1991).When measuring PAH emissions from vehicles, both particulate associated and semi-volatilecompound samples must be taken in order to obtain a total value for PAH emitted by motorvehicles. It is especially important that samples are also obtained in the gas phase when lowparticulate emissions are expected (as in gaseous fuels), i.e. in cases when it is expected thatPAH are mainly associated with gaseous pollution.

* In Europe it is thought that polycyclic aromatic hydrocarbons consist of di-(two) and several ringed benzene

rings which is not semantically correct. The correct form is polycyclic, tri- (three) and several condensedbenzene rings.

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Figure 48. Examples of relevant PAC. Source: Egebäck and Westerholm, 1997.

Oxides of nitrogenWhen nitrogen dioxide (NO2) is inhaled, the gas penetrates far down into the lungs. Thisprimarily affects the air passages and the alveoles. The health effects of short-term and long-term exposure to NO2 have been observed in epidemiological studies. The studies of theacute effects have shown that they are associated with NO2 in the surrounding air. Reports ofthe effects include symptoms in the respiratory organs. A study of children who lived near aninstallation where tri-nitro toluene was manufactured and who were exposed on average toconcentrations of 20-90 µg/m3, and two other studies of 30 micrograms/cubic meter, showedincreased incidences of ill health due to symptoms from the lower air passages. There are alsoother cases which demonstrate health effects from NO2 in the surrounding air (Bylin, 1991;Boström et al., 1996).

Scientific estimations of the risk of mortality caused by pollutants in motor vehicle exhausthave been carried out by both the EPA in the USA and, among others, the Swedish researchteam of Ehrenberg and Törnqvist. As can be seen in Table 26, there are certain differences inthe estimations of the risks of mortality due to exposure to formaldehyde and PAH, whereEhrenberg/Törnqvist state that there is a higher risk than that indicated by the EPA in theUSA.

Table 28. Unit risk factors. Cancer mortality risks from life-long exposure to 1 µg/m3*

Emissionskomponent Ehrenberg/Törnqvist US EPAFormaldehyde 10*10-5 1*10-5

Acetaldehyde 0.2*10-5 0.2*10-5

Benzene 0.8*10-5 0.8*10-5

• Ethene 5*10-5 0.5*10-5

• Propene 1*10-5 0.1*10-5

• 1.3 butadiene 30*10-5 30*10-5

• PAH 2800*10-5 400*10-5

• Particles 7*10-5 7*10-5

*Note. It should be observed that the values in the table give the relative cancer risk for life-long exposure to1µg/m3 of the substance in the ambient air (i.e. not to be regarded as the content in the exhaust).

It should also be mentioned that the choice of fuel for the internal combustion engine has aconsiderable effect on the emissions, including those shown in Table 26. The importance ofthe composition of the fuel applies not only to the conventional vehicles but even, to a greatextent, to light-duty vehicles and heavier vehicles (all trucks and buses) which are equippedwith a hybrid system.

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As an example it can be mentioned that normal European diesel fuel (and the reference fuelwhich is used at certification, after control, etc,) contains up to 100 times more PAH thangasoline. The Swedish MK1 diesel oil has, however, a content of PAH in the exhaust gaswhich roughly corresponds to MK2 gasoline. Mutagenicity has been shown to correspond tothe content of PAH. It is thus not only the type of engine (diesel or otto) which has an effecthere, but rather one can be justified in saying that gasoline is (or at least has been) “cleaner”in this case. Recent research has shown, for example, that it is especially the very smallparticles, less than 2.5 micrometers, which can give rise to problems, due to the fact that theypenetrate down into the alveoles of the lungs.

Many comparisons have been made through the years between gasoline and diesel fuel. Thedifference between running on gasoline or diesel oil, with respect to the health effects, hasbeen considerably reduced during recent years and will most likely be further reduced by theadvances which are now taking place in the development of diesel engines (for example, bythe use of particulate filters and catalysts based on low sulfur fuel) and in diesel fuel.

The development of alternative fuel which has taken place is also very positive, and it hasbeen seen that the potential for the reduction of emissions is very high for most of these fuels.One aspect which has not been considered in this report concerns which renewable fuels havean effect on humans health. However, it is well known that some of the alternative fuels,including the renewable fuels such as alcohols and methane containing fuels, have aconsiderable advantage over the fossil fuels. They emit less harmful substances (especiallyCNG and biogas) and only a small amount of greenhouse gases if the “correct” technique isused for the whole of their life cycle (alcohols).

The increasing requirements for emission reductions which, among others, can be seen whenstudying the new emission standards in the USA and Europe, will result in the developmentof new and more efficient exhaust gas control systems. This will contribute to a considerablereduction in the amounts of the various air pollutants. One example can be given regarding thecontent of carbon monoxide, which was at such a high level up to the beginning of the 1990sthat it was regarded as a danger to health. The situation has now changed so that the emissionof CO by vehicle traffic can no longer be classified as a health risk, with a few possibleexceptions. Vehicle exhaust gases contain a very complex mixture of substances and some ofthese can give rise to health risks at very low doses. There are substances in vehicle exhausts(see Table 25) for which there are no threshold values, i.e. a level under which there is no riskthat the substance would be a health risk, i.e. cancer.

It is well known that the degree of health effects can be altered by various measures,especially in populated areas such as cities. The advantage of a new and more efficientemission control technology has been emphasized. It can also be pointed out that the positivedevelopment of hybrid vehicles can certainly have a good effect on the health of thepopulation in built-up areas due to the possibility of driving a series hybrid vehicle, such as anelectric vehicle, in these areas. When driven in built-up areas, even the use of the parallelhybrid can lead to a considerable positive effect on the emissions. This is clearly shown by theemission measurements on Toyota Prius carried out in both Japan and the US (see especiallySection 8 in this report).

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15 PROBLEMS - BALANCINGThe development of hybrid driven vehicles is no new activity, but has in fact been takingplace, including testing of the vehicles, from the end of the 1960s.

At the time when the discussions taking place about the reduction of emissions were becameintense, several ideas for systems and pollution control were being investigated, even thoughmost of these were in fact shelved. The intention here is not to concentrate too long on thisstage of development but only to point out that even hybrid operation was one of the ideaswhich was temporarily shelved, and then brought out into the light again. General Motorsdeveloped both an electric vehicle – Electovair II with silver/zinc batteries – and a hybridvehicle with a Stirling engine and electric power - STIR –LEC a hybrid system whichcontained roughly the same components as can be seen in present day systems.

It is obviously not especially difficult to find problems in a technique which has not yet beentested on a larger scale in a real market situation. In this report some fields which seems torequire further attention have pointed out. In the first place, however, it is the cost which isreal barrier to a speedy introduction of a hybrid system.

There are several topics concerning vehicles which have received a lot of attention during thelatest 30 to 40 years, first of all emissions, fuel consumption, and safety. When discussing theuse of hybrid technology and the possible advantages of this, it is chiefly the emissions(exhaust gases and noise) and fuel consumption which have received the most attention. Apartfrom these questions there are a further two questions which have a decisive effect on thecontinued development of hybrid systems. Consequently the following questions should bepointed to, since they can be defined as problem areas to a larger or smaller extent:

EmissionsThe use of energyBattery developmentCosts

In the case of emissions it is not the possibility of reaching new low emission levels that willaffect the development but rather the question as to whether hybrid vehicles will eventuallyhave a better emission performance than commercial vehicles.

The use of energy is a question which will have an important role to play, at least in the shortterm (before the introduction of the fuel cell). Will the vehicle manufacturers in the US beable to develop a hybrid system which meets the demands of the PNGV program? Today it ishard to see this as a real possibility, in the short term but the PNGV program has already had aconsiderable impact on the fuel economy at least for light-duty vehicles..

There is probably a good potential for developing more effective batteries but here again it isa question of costs. Is a further developed lead battery the answer to the problem? It is worthpointing out that there has been a positive development in the field of lead acid batterieswhich is shown in two tables in this report, Table 15 and Table 21. However, the preferencefor lead batteries does not seem to be very large, especially among the larger vehiclemanufacturers, (see Table 26) which will certainly have a strong influence on the choice ofbattery. The calculated cost of the further developed lead batteries is, however, relatively low- $0.05/mile or 0.25-0.30 Sw. Cr. per km.

The greatest hinder to the introduction of hybrid vehicles is naturally the cost. No figureshave been presented by the vehicle manufacturers which have been reliable for calculation ofthe future costs of a hybrid system. Some manufacturer has discussed the extra cost of such a

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system but no possibility has been given for looking into the future in the question of costs. Atthis stage it is understandable that most of the vehicle manufactures do not have a detailedinformation on prices. As far as known it is only Toyota which so far sells hybrid vehiclescommercially outside of Japan, and they probably do this without the need to show a normalprofit on the deals. The question is whether this price can be additional reduced by furtherdevelopment. Some information is also available concerning the cost of batteries, but it is stillhard to estimate the cost and the performance of batteries in real use in traffic.

However, to sum up, there seems to be a great interest among car manufacturers in hybridelectric vehicles and this may also result in a development of less costly reliable batteries andalso of other parts in the hybrid system - consequently a lower cost for the hybrid vehiclethan today.

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16 SHORT TERM DEVELOPMENTThe review which has been carried out and presented in this report has provided a basis forthe determination of various lines of development for hybrid systems. In the short term (0-5years) the picture is quite clear since it takes time and resources to develop and present newideas. However it is estimated that the development will continue on hybrid systems, andespecially on light-duty vehicles. For the heavy-duty vehicles there is a certain degree ofuncertainty, especially due to the fact that it is usually a private bus company which carriesout the development. It may true that there is often a degree of co-operation with a vehiclemanufacturer, but the question is how deeply the manufacturer is engaged in the development.Under these conditions a strong support from the authorities (government) is required, if theneeded development will be carried out, since such work is usually expensive.

If development work on hybrid vehicles does continue, it is most likely that the light-dutyvehicles will be parallel hybrids equipped with either an otto or a diesel engine depending onthe preference of the manufacturer. Just now it looks unlikely that the demands of the PNGVprogram for improvement of fuel economy and reduction of emissions will be met within thestipulated time frame. However, by means of further development work and by making themost of experiences which have been gained, the hybrid systems can be made more efficienct.This may be more difficult than it seems, especially in the light of the fact that there aredifficult problems to be solved in increasing the efficiency of hybrid systems by the amountrequired to meet the PNGV demands. Some important steps have, however, been taken in theright direction. In the weighting between fuel economy (or use of energy) and emissions it isestimated that the goal for emissions will be easier to meet than the goal for fuel economy.

The three major car manufacturers in the USA work within the PNGV program by developingtechniques and prototypes which meet the stricter demands. The vehicles which first reach themarkets of Europe, Asia and the US will most likely not meet these demands. Limiting factorssuch as price and availability of fuel will steer the development of commercial hybridvehicles. The PNGV program and the high emission requirements, especially in Californiawill have a strong influence on this development work even in Japan and Europe. In the nearfuture the vehicle manufacturers in both Japan and Europe will lie well to the fore.Development work on hybrid vehicles, which has taken place within the vehicle industryduring the most recent years, has, to some extent, been concentrated on the energy efficiencyof the vehicles. Hybrid techniques will probably play an important roll here. However, it isnot only the hybrid techniques which have contributed to the reduced use of energy whenrunning the vehicles, but also the fact that lighter weight materials have been used to constructthe vehicle body. Besides this there is a tendency for vehicles to be smaller and smaller. Sucha development would have a positive effect on use of energy, as long as the production of thematerials used in the manufacture of the vehicles does not require a large expenditure ofenergy.

The demand for energy efficiency is more easily met for diesel engines and hybrid systems.Ford’s parallel hybrid system with a diesel engine is the best hybrid system which has beenstudied. It now remains for car manufacturers and their co-partners to show that the ongoingdevelopment of the emission control technology, for the reduction of NO2 and particleemissions in diesel engines, will lead to a system with such good emission performance andsuch a good durability, that it can be accepted for use during a longer period of time. If such adevelopment can be demonstrated, and that the improvement of diesel oil continues to givegood results the diesel engine can be an alternative for, amongst others, both light-duty andheavy-duty hybrid vehicles. Toyota Prius is equipped with a well-developed otto engine and it

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remains to se how well the commonly used gasoline engine is being developed in the future.Special attention should be paid to increase the efficiency without increasing the emissions soas to eliminate the negative correlation between fuel consumption and emissions.

In the case of emission of exhaust gases and noise it can, in the short term, be difficult toachieve the same emission levels for diesel vehicles as for gasoline vehicles. Table 7 showsthe future EU emission standards for light-duty gasoline fueled vehicles and Table 8 for dieselfueled vehicles. When comparing the standards in the tables it can be seen the emission levelof NOx for the diesel fueled vehicles are considerably higher than the emission level forgasoline fueled vehicles. Apart from this there is a general opinion that the level of particulateemissions are much higher for diesel fueled vehicles than for gasoline fuel vehicles despitethat considerable improvements are to be seen for the diesel engines. No mandatoryparticulate emission standards are set in Europe for gasoline fueled vehicles. Therefore itremains to see to what extent the expected difference agrees with the real situation whencomparing direct injected gasoline fueled with a future diesel fueled vehicle. Consequently itis important that this will be studied within the coming years.

Beside the emissions of NOx and particles one of the most obvious disadvantages of a dieselfueled vehicle is the noise emission and the question is what will the noise emission from ahybrid vehicle be like. It is true that a diesel engine does not have to be driven with such alarge load as a gasoline engine, to obtain good efficiency. On the other hand it does require arelatively high temperature of the exhaust gases, i.e. a relatively high load, in order achieve anoptimal performance of the emission control system including a catalyst.

In the short term the choice of fuel for hybrid vehicles will be determined by the availabilityon the market. This will presumably lead to only diesel and gasoline being available forhybrid vehicles during the coming 5-year period. In the USA there is no infrastructure fordiesel fuel for passenger vehicles, and in addition the vehicle manufacturers have difficulty ingetting the authorities to accepting the use of diesel engines in passenger cars. This will resultin diesel being an unlikely choice in the USA. Since most of the vehicle manufacturersdevelop their vehicles for introduction on the markets of the US, hybrid vehicles will probablybe equipped with gasoline engines, in the near future, despite the better efficiency of thediesel engine.

When evaluating the development of hybrid heavy-duty vehicles it should be borne in mindthat there are clear differences between light-duty and heavy-duty vehicles. One difference isthat the heavy-duty vehicles generally have the possibility to provide space for more andheavier equipment than the light vehicles. This does not actually apply to all heavy-dutyvehicles, for example busses in city traffic often have a limited amount of space to “sacrifice”.The general opinion is, however, that a heavy-duty vehicle can carry a relatively larger batterypacket than a passenger car. This could lead to series hybrids being chosen in that type ofvehicles. However, this may not be a correct conclusion for all types of heavy-duty vehicles.If one considers the whole scale of heavy-duty vehicles, from light-duty vans to busses, manyinstances where a parallel system would be preferable to a series system can be found. Therecommendation is therefore that each type of vehicle and area of use for the vehicle shouldbe taken into consideration when choosing a hybrid system.

In the case of hybrid systems for heavy-duty vehicles it is not certain that the energy use willbe lower than when using a diesel engine in a conventional vehicle. On the other hand thereare two factors which can be decisive. Firstly, if the batteries are charged with electricity fromthe mains, lower running cost can be obtained than if the batteries are charged from agenerator which produces electricity by a combustion engine. Secondly, a well designed andoptimal hybrid system can considerably reduce the emissions from the vehicle. The question

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that should be asked is whether a well designed diesel engine, using an alternative fuel such asalcohol, would meet the same emission requirements as these which have been set as the goalfor hybrid systems. The noise level is certainly one hinder to the use of a diesel combustioncycle, but even in this field progress is being made.

The estimation presented as a summary of Section 8 is repeted here in order to underline theexpected development in the time frame of 5 to 10 years;

- a well pronounced interest in the hybrid technology has been shown among carmanufacturers and these who are responsible for the development of hybrid electricvehicles;

- it has been shown that many actors have been involved in the development of hybridsystems for city buses. Unfortunately only a few car manufacturers have been involvedin that work. Therefore it is unsure whether the development of hybrid systems for citybuses will continue;

- many well functioning hybrid systems for light-duty vehicles have been developed bythe car manufacturers especially in Japan and in the USA. This well organizeddevelopment seems to continue at least in the short time frame;

- the PNGV agreement between the US Government and the three car manufacturersChrysler, Ford and GM and also other agreements have positively affected the decisionstaken among car manufacturers not only in the USA and Japan but also in othercountries in order to develop fuel efficient vehicles and among these hybrid vehicles.

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17 DEVELOPMENT IN THE LONG TERMIn the case of the long term it is difficult to foresee the development, which will take place,but where hybrid vehicles are concerned there are several possible scenarios which can takeplace within the next 5 to 15 years.

1. The further development of fuel cells will lead to several vehicle manufacturers placinggreater weight on electric vehicles and than hybrid vehicles with fuel cells.

2. Parallel hybrids will come to be the dominant system for light-duty vehicles and possiblyeven for other types of vehicle.

3. Series hybrids will mostly only be used for heavy-duty vehicles.4. Of heavy-duty vehicles a hybrid system will preferably be used in vehicles to be used in

city areas.

These scenarios will be described below. It should be pointed out that the validity of thescenarios depends on the costs being reduced to an acceptable level, in order that buyers oflight-duty vehicles and users of heavy-duty vehicles will come to accept the hybrid system.

The development of fuel cells will most likely continue, at least at the level which applies atthe present time. Support for this statement comes from the Department of Energy in the US,in its support for research and development of fuel cells for fixed installation for the supply ofelectricity. The development of fuel cells for vehicles is chiefly carried out by a group havingDaimlerChrysler and Ballard as its leader. The development of vehicles equipped with fuelcells, at Mercedes Benz, began at the beginning of the 1990s, and in 1994 MB presented thefirst vehicle in the Necar series. The 4th vehicle model in this series was recently presented. In1997 the first bus driven by means a fuel cells was presented. The above mentionedpartnership gives DaimlerChriysler and Ballard an advantage in their efforts to lead thedevelopment of fuel cells within the vehicle industry. In this short review the influence of apossible successful introduction of the fuel cell buses from DaimlerChrysler should not betaken as a guarantee for a successful future for fuel cells, since such buses are estimated to bevery expensive also in the view of 10 to 15 years.

A question is how the majority of vehicle owners will react to vehicles with fuel cells.Technically speaking, vehicles using fuel cells will function satisfactorily before the advent ofmass production, but a hindrance for a larger market being developed is costs and a questionis - will the average man be able to afford such a vehicle?

Even within the field of heavy-duty vehicles, development is not especially easy to foresee. Itis not at all certain that the vehicle industry will be willing to develop busses powered by fuelcells. Certainly there is a degree of interest among the bus companies for the development ofsuch busses but the question is whether the busses will be economically attractive. A large buscompany in San Paulo in Brazil has, for example, declared their interest in changing their fleet, which comprises a large number of busses, to vehicles using fuel cells. Will this in fact cometo pass? Brazil has certainly one of the worlds most developed industries for the manufactureof busses, and it also has valuable natural resources such as hydro-produced electricity, butthe question is whether there is an economic possibility for such an action. However, it makessense to to use these resources in order to improve air quality in large cities.

It is estimated that the development of hybrid vehicles will continue with a development oflight-duty vehicles. There are two reasons for this estimation. Firstly the vehicle industry inthe US has taken upon itself the development of vehicles with considerably better fueleconomy than that of present day vehicles, without affecting the emission standards. Duringthe studies for the preparation of this report it has been shown, that an important progress has

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already been made but also that the most difficult part remains to be solved in order to reachthe PNGV goal and then especially for the reduction of the costs. The PNGV program isdirected to passenger vehicles, and has the goal of achieving a fuel economy of 80-MPG (ca3-l/100 km) within a few years from now.

In order to avoid a misunderstanding we stress that the PNGV program consists of anagreement between the government in the US, including 12 departments (including theDepartment of Energy, DOE) and Chrysler, Ford and General Motors. By these studies it hasbeen shown that the PNGV program also affects the vehicle industry in Europe, andespecially the industry in Japan. This is clearly revealed by what has happened at Volkswagenand at the large vehicle manufacturers in Japan, led by Toyota. We estimate that the Japanesemotor vehicle industry will use its resources try to reach the PNGV goals even if they are notbound to any agreement like the “big three” in the USA.

The other reason is that we believe in a continued development of hybrid vehicles is that itprovides the vehicle industry with valuable experiences for future progressive development inthis field. However, this kind of interest may end up to that the car manufacturers will besatisfied with developing a few models of hybrid vehicles and that the manufacture of thesemodels will be limited. At present the Japanese car industry to start with will limits theselling of hybrid vehicles on the Japanese market. As has already been pointed out such astrategy can favor the vehicle manufacturers, since they do not then need to take the wholeresponsibility for the field tests, nor for a large fleet of vehicles.

Summarizing, the opinion is that;

• the use of series hybrid vehicles will be limited to heavy-duty hybrid vehicles possiblybuses. Hybrids will probably not be used for heavy-duty trucks, except for those truckswhich run in cities.

• If there is a technical breakthrough in the development of batteries and if, at the sametime, the vehicle manufacturers increase their efforts in developing hybrid vehicles, theresult can be that there is a faster introduction of hybrids even for heavy-duty vehicles.

• the use of parallel hybrid system will chiefly be used for light-duty vehicles.• the use of fuel cells is a possible development, but at present it is unclear as to how long

it can be before a more wide scope introduction of fuel cell vehicles takes place.• the demand for more environmentally friendly and energy effective transport will provide

an incentive for the development of both hybrid system and fuel cells.

Despite the uncertainty concerning the future for development of hybrid vehicles within atimeframe of 10 to 20 years the following estimation has been presented (see Section 8.4).

- two scenarios can be seen concerning the development of energy efficient motorvehicles, namely:

(a) a positive continuation of the development of hybrid electric vehicles parallel toresearch and development of fuel cells;

(b) a brake through for the development of fuel cells resulting in (1) the use in fuelcells in hybrid electric vehicles with a battery used for storage of electricity and (2)the use of fuel cells as the only source for the delivery of electric power to thetraction motor in a vehicle without battery for the storage of electricity use for thetraction motor.

Today it seems most likely that the development of highly fuel efficient vehicle will followscenario (a) since it is estimated that the fuel cell technology will be to expensive to be used inmass produced vehicles within the time frame of 20 years.

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REFERENCESAbthoff J. O., Antony P., Krämer M., and Seiler J.: ”The Mercedes-Benz C-Class Series Hybrid.”, SAE Paper981123, 1998.

Ahlvik, P. (1999). Personal discussion about synthetic fuels, August 1999.

Ahlvik, P. and Brandberg, Å. (1999). Exhaust emissions from light-duty fueled with different alternative fuels.Effects on health, environment and the use of energy. KFB-report, 1999:38. (In Swedish).

AUTO/OIL (2000). Evaluation of alternative fuels.

Badin, F., Jeanneret, B.Harel.F., Combes, E., Personnaz. J. Och Cottard, C. (1998). 1998 FISITA WorldAutomotive Congress. The Second Century of the Automobile. Paris, September 27 - October 1, 1998.

Bass, E., Wildemann, P. And Fritz, S. Emisssions and Economy of a Series Hybrid Shuttle Bus. The 15th

International Electric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Bassini, M., Fossati, G. Och Iemmi, G. (1998). 1998 FISITA World Automotive Congress. The Second Centuryof the Automobile. Paris, September 27 - October 1, 1998.

Beretta, J. (1998). New Classification on Electric Termal Hybrid Vehicles. The 15th International ElectricVehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Bernhardt, W., (1998). Methanol Fuel Cell the Powerplant of the Future-12th International Symposium onAlcohol Fuels” in China 21 – 24 Sept, 1998.

Bohm, T. Och Meissner, M.M. (1998) Advanced Litium-Ion Batteries for Electric Vehicles. The 15th

International Electric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Borgwardt, R.H., (1998). Methanol Production from Biomasses and natural Gas as Transportation Fuel. Ind.Eng. Chem. Res. 1998, 37. 3760-3767.

Boström, C-E. Almén J., Steen, B. Och Westerholm, R. (19994) Human exposure to urban air pollution.Environmental Health Perspect 1and 2 (Suppl. 4): 39-47, 1994.

Boström, C-E., Camner, P., Egebäck, K-E., Ewetz, L., Ljungquist, S., Omstedt, G., Pettersson, L. Törnqvist, M.and Westerholm, R. (1996) Health risk assessmeent of ethanol as a bus fuel. KFB-Report 1996:19.

Brawn, J.C., Eichenberg, D.J. och Tompson, W.K. (1999). Baseline Testing of the Hybrid Electric Transit Bus.EnV’99, Alternative Fuels and Advanced Technology Vehicles14 – 16 June 1999.

Brawn, J.C., Eichenberg, D.J. och Tompson, W.K. (1999). A Hybrid Electric Transit Bus (HETB) Design,Development and Test Result. EnV’99, Alternativa Fuels and Advanced Technology Vehicles14 – 16 June 1999.

Buchholtz, K., (1999). In search of earth-favoring vehicles. Automotive Enineering International/February 1999.

Bull, K.N., Bugden, W.G., Brooker, S.D., Galloway, R.C. och Holmes, W.A. (1998). Sodium/Nickel ChlorideZebra Batteries: Lifetime and Performance Characteristics. The 15th International Electric Vehicle Symposiumand Exhibition, Sept. 29 – Oct. 3, 1998.

Bullock, K.J. och Hollis, P.G. (1998). Energy Storage Elements In Hybrid Bus Applications. The 15th

International Electric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Bucholz, K. (1999). In search of earth-favoring vehicles. Automotive Engineering International, February, 1999.

Bylin, G. (1991). Air pollution and asthma caused by pollen. Report 4409:Risk estimation –Health andenvironment. The Environmental protection Agency (Sweden) UISBN 91-66620-4409-5, ISSN 0282-7298. (InSwedish)

CARB California Air Resourses Board (1989) USA. IARC (1983), Monographs on the evaluation ofcarcinogenic risks of chemicals to humans: Polynuclear Aromatic Compounds, part 1, Chemical, environmentaland experimental data, Volume 32, Lyon, France.

Cooper, A. And Moseley, P.T. (1998). Lead Acid Electric Vehicle Battries – Improved Performance of theAffordable Option. The 15th International Electric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Cornu, U>J-P. (1998). 150, 250 km, … the Evs range doped by Nickel-Metal Hydride and Lithium-Ion batteries.1998 FISITA World Automotive Congress. The Second Century of the Automobile. Paris, September 27 -October 1, 1998.

138

Crosse, J., (1999). Fuel Cell Technology – Sold on Cells. Automotive engineer, May 1999, page 34.

Crosse, J., (1999). Cells pitch. Automotive engineer, The Magazine for the Industry, March 1999, page 61.

Cuesta, R., Hadjadj, S. Och Flament, P. (1998). Saft Li Ion EV Battery Performance. The 15th InternationalElectric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Dircks, K. (1998). Recent Advances in Fuel Cells for Transportation Applications. The 15th International ElectricVehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

DoD, (1999a). Fuel cell description. Overview of Fuel Cells.

DoD, (1999b). Fuel cell description. Solid Oxide Fuel Cells.

DOE, (1999a). Schatz Center Develops More-Efficient Fuel Cell.

DOE, (1999b). Fuel cell/Turbine ”Hybrids”. Five U.S. Companies Working to Explore 21st Century PowerTechnologies.

Debal. P., De Keukeleere, D. Och Pelkmans, L. (1999). Development of Hybrid Buses in Belgium. EnV’99,Alternativa Fuels and Advanced Technology Vehicles14 – 16 June 1999.

Duoba, M. and Larsen, R. (1998). Investibgation of Practical HEV Test Procedures with Prototypes from the1997 FutureCar Challange. SAE paper 981080.

Egebäck, K-E., Larsson, E. och Laveskog, A. (1998). Metanol - hantering säkerhet och arbetsmiljö, KFBMeddelande 1998:7.

Ekdunge, P. and Råberg, M. (1998). The fuel cell vehicle analysis of energy use, emissions and costs, Int. J.Hydrogen Energy. Vol 23. No 5.pp 381-385. 1998.

Electric Vehicle Progress, (1998). Commercializing fuel cell electric vehicles: Is it happening. Electric VehicleProgress, Management news and technical developments in the electric and hybrid vehicle industry, June, 1998.

Electric Vehicle Progress, (1998). Zevco applies fuel power to London taxi. Electric Vehicle Progress,Management news and technical developments in the electric and hybrid vehicle industry, September, 1998.

Electric Vehicle Progress, (1998). Zevco applies fuel power to London taxi. Electric Vehicle Progress,Management news and technical developments in the electric and hybrid vehicle industry, November, 1998.

Electric Vehicle Progress, (1998). Zevco applies fuel power to London taxi. Electric Vehicle Progress,Management news and technical developments in the electric and hybrid vehicle industry, December, 1998.

engine, (1/1999). Fuel cell development, Engine technology INTERNATIONAL, March 1999, page 4.

Fast, R. (2000). Concept vehicle of type hybrid. A following up. KFB-report 2000:8. (In Swedish)

Friedmann. S., Gerbig, F., Brunner, H. and Winger, A. (1998). Potential of Series and Parallell Hybrid Vehiclesto Improve Individual Mobility. FISITA World Automotive Congress. The Second Century of the Automobile.Paris, September 27 - October 1, 1998.

Ford (1995). Personal discussion with representatives for Ford.

Hanauer, D. (1998). Dryfit technology for electric & hybrid vehicles – system solllution. A future for the city.The 15th International Electric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Hellman, K.H. Peralta, M.R. and Piotrowski, G.K. Evaluation of a Toyota Prius Hybrid System (THS).EPA4420-R-98-006, Technical Report.

Hirose, K., Ueda, T., Takaoka, T. and Kobayashi, Y. (1998) The high-expension-ratio gasoline engine for thehybrid passenger car. JSAE Review 20 (1999) page 13-21.

Horii, Y. Takeda. N. and Imai, S. (1998). Development of a Hybrid Electric Truck. FISITA World AutomotiveCongress. The Second Century of the Automobile. Paris, September 27 - October 1, 1998.

IARC (1989), Monographs on the evaluation of carcinogenic risks of chemicals to humans: Diesel and gasolineengine exhausts and some Nitro-PAH, Volume 46, Lyon, France.

Iwai, N. (1998). Analysis on fuel economy and advanced systems of hybrid vehicles. JSAE Review 20 (1999)page 3-11.

Jaura, A.K., Breida, M.T. and Gomes, E.D. (1998). Interfasing a CIDI Engine in a Hybrid Vehicle. The 15th

International Electric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

139

Jeanneret, B., Badin, F., Trigui, R, Nguyen, T and Periot, R. (1998). Drive train evaluation using simulationApplication to the V2G/VEG vehicle developed by ALSTOM and Renault VI. The 15th International ElectricVehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Jonsson A. and Bertilsson B-M. (1982) Formation of methyl nitrite in engines fuelled with gasoline/methanoland methanol/diesel. Environmental Science & Technology Vol. 16, 106-110.

Karbowski G. and Davies R. (1995) The bus company MTA (The Los Angeles County MetropolitanTransportation Authority), Los Angeles. Personal discussion.

Kitada, s., Aoyama, S., Hattori, N., Maeda, H. and Matsou, I. (1998). Development of a Parallell HEV SystemIncorporating a CVT. The 15th International Electric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3,1998.

Kodama, T. (1996). R&D of Litium Batteries in Japan –Dispersed Battery Energy Storage Technology-. EVS-13. The 13th International Electric Vehicle Symposium, 1996.

Köhler, U. and Niggemann, E. (1998). High Performance Nickel-Metal Hydride Batteries for Electric andHybrid Vehicles. The 15th International Electric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Lee, J., Lee, S. and NamGoong, E. (1998). Dynamic State Battery Model with Self-Adaptive Aging Factor forEV and HEV Applications. A future for the city. The 15th International Electric Vehicle Symposium andExhibition, Sept. 29 – Oct. 3, 1998.

Lindberg, B., Statoil, Sweden (2000). Personal communication.

Malmquist, A., Rosendahl, L., Berb, N. and Aglén, O. (1998). 2nd Generation Gas Turbine Driven Hybrid CityBus. The 15th International Electric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Manufacturers (1999a). Demonstration of Advanced Emission Control Technologies Enabling Diesel-PoveredHeavy-Duty Engines to Achieve Low Emission Levels: Interim Report Number 2. Diesel Particulate FilterTechnology. Manufacturers of Emission Controls Association, Washington.

Manufacturers (1999b).The impact of Sulfur in Diesel Fuel on Catalust Emission Control Technology.Manufacturers of Emission Controls Association, Washington.

Maruo, K., (1998). Strategisk Alliances for the Development of Fuel Cell Vehicles. KFB-Rapport 1998:37.

Menne R. J., Heuser G., and Morris G., D. (Ford): ”Potential of the new Ford Zetec-SE engine to meet futureemission standards.”, IMechE Paper C517/038/96, 1996.

Marginedes, D, Huglo, F and Lascaud, S. (1998). Achievment of the French Program on Litium PolymerBattery. The 15th International Electric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Meeus, M. and Gravenstein, Y. (1998). Non-Ferros Metals Make Electric Vehicles Move. The 15th InternationalElectric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Mercedes-Benz (1999). Homepage, Internet.

Mercedes-Benz (2000). Homepage, Internet.

McDowell, J. and Reddy, D. (1998). Bridging Expectations to Hybrid Bus Operation. The 15th InternationalElectric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Mourad, S. (1998). Dedicated Auxiliary Power Units for Hybrid Vehicles. The 15th International ElectricVehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Möller, L., Shuetzle, D. and Autrup, H. (1994). Future Resarch Needs Associated with the Assessment ofPotential Human Health Risks from Exposure to Toxic Ambient Air Pollutants. Environmental HealthPerspectives Supplements, Volume 102, Supplement 4, October 1994, pp193-210.

National Institutes of Health (1994). Risk Assessment of Urban Air: Emissions, Exposure, Risk identification,and Risk Quantitation. Environmental Health Perspectives Supplements, Volume 102, Supplement 4, October1994.

Noboru, S. Yagi, K. and Sakurai, T (1998). Control Technology of Ni-MH Batteries for Electric Vehicles. The15th International Electric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

NRC, (98). ”Review of the Partnership for a New Generation of Vehicles (PNGV) – Fourth Report.”, NationalAcademy Press, Washington D.C., 1998.

140

Osses M., Clarke P., Andrews G (1996). (Univ. of Leeds), Ounzain A., and Robertson G.: ”Enhanced exhaustgas recirculation using exhaust throttling for NOX reduction at WOT.”, IMechE Paper C517/011/96, 1996.

Peugeot (1999). PSA Peugeot Citroën presents the first Particle Filter System to be fitted as a standardequipment in a vehicle at the start of the year 2000. Press releases.

Putois, F. (1996). ”Long-Term Batteries. EVS-13. The 13th International Electric Vehicle Symposium, 1996.

Rajashekara, K., Shah, R.J. and McMullen, S. (1998). Control System for a Stirling Engine Driven InductionGenerator. The 15th International Electric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Sasaki, M. (1999). Development of the Nissan Fuel Cell Vehicle. EnV’99, Alternativa Fuels and AdvancedTechnology Vehicles14 – 16 juni 1999.

Sato, S. (1998). Electric Vehicles in Earth Environment and Advanced Battery Technology. 1998 FISITA WorldAutomotive Congress. The Second Century of the Automobile. Paris, September 27 - October 1, 1998.

Seiler, J. and Schröder, D. (1998). Hybrid Vehicle Operating Strategies. The 15th International Electric VehicleSymposium and Exhibition, Sept. 29 – Oct. 3, 1998.

Sheehan, J. (1999) National Renewable Energy Laboratory (NREL). ”Bioethanol Roadmap: A TechnologyDevelopment Framework”. Muntlig presentation vid konferensen ”EnV’99, Alternativa Fuels and AdvancedTechnology Vehicles” 14 – 16 June 1999.

Stobart, R and Linna, J-R., (1/1999). Fuel economics of scale. engine technology INTERNATIONAL, March1999, page 36.

Stobart, R., (1999a). Fuel Cell Power – Now or in the distant future? – and for my car or my computer.

Stobart, R.K., (1999b). Fuel Cell for Passenger Cars – What Barriers Remain?

Stodolsky, F., Gaines, L., Marschall, C.L., F. and Eberhart, J.J. (1999). Total Fuel Cycle Impactsd of AdvancedVehicles, SAE paper 1999-01-0322.

Sutula. R.A., Heitner, K.L., Rodgers, S.A., Duong, T.Q., Patil, P.G. and Venkateswaran, S.R., (1998). The 15th

International Electric Vehicle Symposium and Exhibition, Sept. 29 – Oct. 3, 1998.

SWRI (1999). Electric & Hybrid Vehicles. EnV’99, Alternativa Fuels and Advanced Technology Vehicles. 14 –16 June 1999.

Syntroleum 1, (1999) Creating the Fuels of the Future. Syntroleum Gas-to-Liqids Tecjnology. SyntroleumCorporation information 1999.

Syntroleum 2, (1999). Syntroleum Synthetic Fuels Showcased At North American International Auto Show.Syntroleum Corporation, January 5, 1999.

Takaaki, A. Nakagawa, T., Horie, H. and Tanjyou, Y., (1998). Development of a High-Power Battery BatteryCooling System for Series HEVs. A future for the city. The 15th International Electric Vehicle Symposium andExhibition, Sept. 29 – Oct. 3, 1998.

Takaoka, T. Hiroshi, H., Hirose, K., Nouno, Y., Sasaki, N., Ueda, T., (1998). Super High Efficient GasolineEngine for the Toyota Hybrid System. 1998 FISITA World Automotive Congress. The Second Century of theAutomobile. Paris, September 27 - October 1, 1998.

The Hydrogen & Fuel Cell Letter, (1998a). Island and Daimler-Benz/Ballard Start Plans for Hydrogen Economy.The Hydrogen & Fuel Cell Letter, June 1998 Vol. XIII/No. 6, ISSN 1080-8090.

The Hydrogen & Fuel Cell Letter, (1998b), The Fuel Alternative – Renewable Fuels. U.S. Mini-Fuel cell Truckwith an Italiah PEM System Debutes in Venice, The Hydrogen & Fuel Cell Letter, June 1998 Vol. XIII/No. 6,ISSN 1080-8090.

Tojima. K., Sekimori, T., Asakawa, F., Etho, T. and Nakayama, Y. (1998). Development of Battery system forHybrid Vehicle. A future for the city. The 15th International Electric Vehicle Symposium and Exhibition.

Toyota, (1998). In Search for the Ultimate Eco-Car. Various Approaches to Various Issues. Toyota information.

Törnqvist M., Rannug U., Jonsson A. and Ehrenberg L. (1983) Mutagenicity of methyl nitrite in Salmonellatyphimurium. Mutation Research Vol. 117, 47

Törnqvist M., Kautiainen A., Gatz R. and Ehrenberg L. (1988) Haemoglobin adducts in animals exposed togasoline and diesel exhaust. 1. Alkenes. Journal of Applied Toxicology, Vol. 8, 159-170

141

Törnqvist M., Segerbäck D. and Ehrenberg (1991) The "rad-equivalence approach" for assessment andevaluation of cancer risks, exemplified by studies of ethylene oxide and ethene. In: Human carcinogen exposure,biomonitoring and risk assessment, Edit: R. Garner, P. Farmer, G. Steel and A. Wright. Oxford IRL Press, 141-155.

Törnqvist M. and Ehrenberg L. (1994) On Cancer Risk Estimation of Urban Air. Environ. Healt Perspec. Vol.102, 173-182.

USCAR (1999) GM Considering Stirling Engines for Hybrids of 21st Century. United States Coouncil forAutomotive Research. About Specific Technologies,

US EPA (1990). Cancer Risk from Outdoor Exposure to Air Toxics, Vol. 1 and 2. EPA-450/1-90-004a.

Walsh, M., (1999). Energy Department Awards Funds for Fuel Cell and Engine Research. Car Lines, March1999.

Wartman, J. (1998). Zink Air Battery-Battery Hybrid for Powering Electric Scooters and Electric Buses. The15th International Electric Vehicle Symposium and Exhibition.

Westerholm R. and Egebäck K-E. (1991) Impact of fuels on exhaust emissions: A chemical and biologicalcharacterization. Swedish Environmental Protection Agency (SwEPA) Report 3968, Solna.

Westerholm, R., Almén, J, Li, H., Rannug, U., Egebäck, K-E. and Grägg, K. (1991). Chemical and BiologicalCharacterization of Particulate, Semi Volatile and Gas Phase Associated Compounds in Diluted Heavy-DutyDiesel Exhausts: A comparison of three different semi volatile phase samplers. Environmental Health andPerspectives, Vol. 25, pp 332-338 (1991)

Westerholm R. and Li H. (1994) A Multivariate Statistical Analysis of Fuel Related Polycyclic AromaticHydrocarbon (PAH) Emissions from Heavy Duty Diesel Vehicles. Environmental Science & Technology, Vol.28, No.5, pp 965-992.

Westerholm R. and Egebäck K-E. (1994). Exhaust Emissions from Light and Heavy Duty Vehicles: ChemicalComposition, Impact of Exhaust Aftertreatment and Fuel Parameters. Environmental Health and Perspectives,Vol. 102, pp13-23 (1994)

Westerholm R. and Li H. (1994) A Multivariate Statistical Analysis of Fuel Related Polycyclic AromaticHydrocarbon (PAH) Emissions from Heavy Duty Diesel Vehicles. Environmental Science & Technology, Vol.28, No.5, pp 965-992.

Westerholm, R. and Pettersson, L. (1999). State of the art. Multi-Fuel Reformers for Automotive Fuel CellApplications. Problem identification and research needs. KFB-Information 1999:29.

Yoshihara, Y., Ando, K., Hirao, A Hiramatsu, A and Hoshihara, N. (1998). Development of Long Life TypeVRLA Battery for EVs and HEVs. A future for the city. The 15th International Electric Vehicle Symposium andExhibition, Sept. 29 – Oct. 3, 1998.

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