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Effects of butanol–diesel fuel blends on the performance and emissionsof a high-speed DI diesel engine

D.C. Rakopoulos a, C.D. Rakopoulos a,*, E.G. Giakoumis a, A.M. Dimaratos a, D.C. Kyritsis b

a Internal Combustion Engines Laboratory, Department of Thermal Engineering, School of Mechanical Engineering, National Technical University of Athens,Zografou Campus, 9 Heroon Polytechniou St., 15780 Athens, Greeceb University of Illinois at Urbana Champaign, Department of Mechanical Science and Engineering, 1206 West Green Street, Urbana, IL 61801, USA

a r t i c l e i n f o

Article history:Received 8 July 2009Accepted 18 February 2010Available online 19 March 2010

Keywords:Butanol–diesel fuel blendsHigh-speed diesel enginePerformanceEmissions

a b s t r a c t

An experimental investigation is conducted to evaluate the effects of using blends of n-butanol (normalbutanol) with conventional diesel fuel, with 8%, 16% and 24% (by volume) n-butanol, on the performanceand exhaust emissions of a standard, fully instrumented, four-stroke, high-speed, direct injection (DI),Ricardo/Cussons ‘Hydra’ diesel engine located at the authors’ laboratory. The tests are conducted usingeach of the above fuel blends or neat diesel fuel, with the engine working at a speed of 2000 rpm andat three different loads. In each test, fuel consumption, exhaust smokiness and exhaust regulated gasemissions such as nitrogen oxides, carbon monoxide and total unburned hydrocarbons are measured.The differences in the measured performance and exhaust emission parameters of the three butanol–die-sel fuel blends from the baseline operation of the diesel engine, i.e., when working with neat diesel fuel,are determined and compared. It is revealed that this fuel, which can be produced from biomass (bio-butanol), forms a challenging and promising bio-fuel for diesel engines. The differing physical and chem-ical properties of butanol against those for the diesel fuel are used to aid the correct interpretation of theobserved engine behavior.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Engine manufacturers worldwide have achieved to develop die-sel engines with high thermal efficiency and specific power output,always trying to keep inside the limits of the imposed emissionregulations that every day becomes more stringent. Significantachievements for the development of cleaner diesel engines havebeen made, over the last decades, by following various engine-re-lated techniques, e.g. the use of common-rail systems, fuel injec-tion control strategies, exhaust gas recirculation, exhaust gasafter-treatment, etc. [1,2].

Furthermore, especially for the reduction of pollutant emis-sions, researchers have focused their interest on the domain offuel-related techniques, such as for example the use of alternativegaseous fuels of renewable nature, which are friendly to the envi-ronment or oxygenated fuels, which are able to reduce particulateemissions [3–8]. Sometimes, for obtaining the desirable results, re-sort is being made to the simultaneous use of engine- and fuel-re-lated techniques [9].

Dwindling crude oil reserves and their increasing prices haveplaced increasingly sensitive loads on the trade balances of the

non-oil producing countries and, meanwhile, have come to repre-sent a threat to the existence of the developing and industrializedcountries. Thus, considerable attention has been paid on the devel-opment of alternative fuel sources in various countries, with par-ticular emphasis on the bio-fuels that possess the addedadvantage of being renewable fuels that can be replenishedthrough the growth of plants or production of livestock, showingan ad hoc advantage in reducing the emitted carbon dioxide[10,11]. There is a commitment by the USA government to increas-ing bio-energy threefold in 10 years, which has added impetus tothe search for viable bio-fuels [12].

Given the depleting supply of fossil-based fuel sources and thelikely need for logistics managers to increasingly consider alterna-tive fuel sources, in Ref. [13] fossil-based fuels with their mostcommonly discussed potential alternatives are contrasted. Specifi-cally, these authors evaluated six fuel types using analytical hierar-chy process (AHP) as a method to compare their total productviability in a formalized manner; they examined the viability ofpetroleum gasoline (the current source fossil fuel for the vastmajority of energy requirements of today’s logistics systems)versus five potential alternatives, viz. hybrid electric vehicles,hydrogen fuel cells, bio-diesel, bio-ethanol and bio-butanol, stress-ing the importance of the latter new bio-fuel.

Concerning the environmental aspect, rational and effi-cient end-use technologies are identified as key options for the

0196-8904/$ - see front matter � 2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.enconman.2010.02.032

* Corresponding author. Tel.: +30 210 7723529; fax: +30 210 7723531.E-mail addresses: [email protected] (C.D. Rakopoulos), [email protected]

(D.C. Kyritsis).

Energy Conversion and Management 51 (2010) 1989–1997

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achievement of the Kyoto targets of greenhouse gas emissionsreduction. For the transport sector of the European Union (EU), en-ergy savings of 5–10% in the medium term and an aggregated of25% in the long term (2020) are aimed at, with an expected cutof carbon dioxide (CO2) emissions by 8% by the year 2010. TheEuropean Union has issued a directive on the use of bio-fuelsaccounting to at least 5.75% of the market for gasoline and dieselfuel sold as transport fuels by the end of 2010 [14,15].

Bio-fuels made from agricultural products (oxygenated by nat-ure), may not only offer benefits in terms of exhaust emissions, butalso reduce the world’s dependence on oil imports. Furthermore,local agricultural industries can be supported and farming incomesenhanced, besides providing a better energy security for manydeveloping countries. Among those, bio-alcohols and vegetable oilsor their derived bio-diesels (methyl or ethyl esters) are consideredas very promising fuels. Works on the use of vegetable oils and bio-diesels in diesel engines have been reported for example in Refs.[15–20].

Because of its high octane number, ethanol is a good spark–igni-tion engine fuel, while vegetable oils and bio-diesels are good die-sel engine fuels owing to their reasonably high cetane number. It istrue that alcohols, mainly ethanol and to a much lesser extentmethanol, have been considered as alternative fuels for diesel en-gines too [12,21,22]. Methanol can be produced from coal or petrolbased fuels with low cost production, but it has a restrictive solu-bility in the diesel fuel. On the other hand, ethanol is a biomassbased renewable fuel, which can be produced by alcoholic fermen-tation of sugar from vegetable materials, such as corn, sugar cane,sugar beets, barley, sweet sorghum, cassava, molasses and the like,and agricultural residues, such as straw, feedstock and wastewoods by using already improved and demonstrated technologies[10,23].

Therefore, ethanol has the advantage over methanol of highermiscibility with the diesel fuel and of being of renewable nature(bio-ethanol). Works on the use of ethanol in diesel engines, withthe main purpose of smoke reduction, have been reported forexample in Refs. [24–33].

Nonetheless, there are several critical issues to consider withthe use of ethanol in the diesel fuel. While anhydrous ethanol issoluble in gasoline, additives must be used in order to ensure sol-ubility of anhydrous ethanol (that is highly hygroscopic and thuspractically impossible to stay as such) in the diesel fuel under awide range of conditions, especially at lower temperatures. Fur-thermore, ethanol possesses lower viscosity and adding ethanolto diesel fuel can reduce lubricity and create potential wear prob-lems in sensitive fuel pump designs. Ethanol, apart from having alower calorific value than diesel fuel, possesses a very low cetanenumber that reduces the cetane level of the diesel–ethanol blend,requiring normally the use of cetane enhancing additives forimproving ignition delay and mitigating cyclic irregularity [34–37]. Ethanol has much lower flash point than the diesel fuel andhigher vapor formation potential in confined spaces, thus requiringextra precautions to ensure safe handling and use of these blends[12].

Thus, various techniques involving ethanol–diesel dual fueloperation have been developed, to make diesel engine technologycompatible with the properties of ethanol-based fuels. They can bedivided into the following three categories: (i) ethanol fumigationto the intake air charge by using carburetion or manifold injection[24–26,28], (ii) dual injection system [24], and (iii) blends (emul-sions) of ethanol and diesel fuel by using an emulsifier to mixthe two fuels [24,27,29–33].

Bio-fuel production is a rapidly growing industry in many partsof the world. Ethanol and bio-diesel are the primary alternatives atpresent to gasoline for spark–ignition engines or diesel fuel forcompression–ignition (diesel) engines, respectively. However,

other bio-fuels such as bio-butanol, biomass-derived hydrocarbonfuels and hydrogen in the longer term are being researched at pres-ent and may be regarded as the next generation fuels [10].

A very challenging alcohol competitor for use in diesel enginesis butanol, which, nonetheless, has not been experimented with ondiesel engines. Butanol is of particular interest as a renewable bio-fuel, as it is less hydrophilic and it possesses higher heating value,higher cetane number, lower vapor pressure, and higher miscibilitythan ethanol, making butanol preferable to ethanol for blendingwith conventional diesel fuel. Therefore, all the disadvantagesmentioned in the previous section of ethanol as a diesel fuel arehighly mitigated when using butanol, which has properties closerto diesel fuel than ethanol and more so than methanol [10,38]. Ta-ble 1 provides the base properties of ethanol and n-butanol (nor-mal butanol) as well as of the Greek automotive, low sulphur(0.035%) diesel fuel (gas oil), which was used as the baseline fuelfor the present experiments.

Like ethanol, butanol is a biomass based renewable fuel that canbe produced by alcoholic fermentation of the biomass feed-stocksreferred to above (bio-butanol). It is very coincidental that new andinnovative processes for managing and utilizing the crude glycerolco-product from the bio-diesel production processes have beendeveloped [39], which convert, for example, by anaerobic fermen-tation [40] the crude glycerol to significant yields of the valueadded products of mainly butanol, and 1,3-propanediol (PDO)and ethanol. This is very fortunate, since the increasing demandof bio-diesel production causes great problems with the disposalof the by-produced crude glycerol (10% by weight of the total) bythe bio-diesel producers, given that its conversion to pure glycerolis no longer financially feasible due to the falling prices of the highquantities available then for its market uses.

A primary factor that distinguishes fuel alcohols and bio-dieselfrom petroleum-based fuels is the presence of oxygen bound in themolecular structure. Alcohols are defined by the presence of a hy-droxyl group (–OH) attached to one of the carbon atoms. For exam-ple, the molecular structure of methanol is CH3OH, of ethanolC2H5OH and that of butanol C4H9OH. Butanol has a 4-carbon struc-ture and is a more complex alcohol (higher-chain) than ethanol asthe carbon atoms can either form a straight-chain or a branchedstructure, thus resulting in different properties. It exists as differ-ent isomers, based on the location of the hydroxyl group (–OH)and carbon chain structure. It is mentioned that butanol produc-tion from biomass tends to yield mainly straight chain molecules.The molecular structure of butanol isomers are shown in Fig. 1[10]. 1-Butanol, also better known as n-butanol (normal butanol),has a straight-chain structure with the hydroxyl group (–OH) atthe terminal carbon. This is the isomer used in the present exper-imental study.

The present research group has already reported the effects ofusing various blends of ethanol with conventional diesel fuel onthe performance and exhaust emissions for the engine used inthe present study, at various loads [32]. An emulsifying agentwas used to satisfy ethanol–diesel fuel mixture homogeneity andprevent phase separation, while no ignition-improving additiveswere used. The differences in the performance and exhaust emis-sion parameters, from the baseline operation of the diesel engine(working with diesel fuel), were determined and compared.

At this point it is stated that there seems to be an obvious scar-city of theoretical models scrutinizing the formation mechanismsof combustion-generated emissions when using liquid bio-fuels,unlike the advanced models existing for the study of diesel engineswhen using conventional diesel fuel [1,41–44]. Recently, a detailedmulti-zone combustion modeling with ethanol–diesel blends hasbeen reported [45] by this research group, along the lines of a sim-ilar paper [46] applied for the engine in hand when using vegetableoils or their derived bio-diesels, which has in turn expanded on a

1990 D.C. Rakopoulos et al. / Energy Conversion and Management 51 (2010) 1989–1997


similar multi-zone one that has dealt only with the related physicalprocesses [47]. As a ‘bridging’ agent for correctly interpreting theprevious ethanol–diesel blends results and with a view to assistthe related multi-zone combustion modeling, a heat release analy-sis for the relevant combustion mechanism, combined with thewidely differing physical and chemical properties of the ethanolagainst those for the diesel fuel, were used by the authors in Ref.[48] for the same engine, ethanol–diesel fuel blends and operatingconditions. Also, a work has appeared recently [49] for this sameengine with the above ethanol–diesel fuel blends and operatingconditions, evaluating its combustion characteristics using experi-mental–stochastic techniques [50] and its propensity for combus-tion cyclic variability given the low cetane number of ethanol [51].

The open literature concerning the use of butanol–diesel fuelblends in diesel engines and its effects on their performance andexhaust emissions is nearly absent. To the authors’ knowledge,only one such work exists [52], with drive cycle analysis of n-buta-nol/diesel blends in a light-duty turbo-diesel vehicle. Two moreworks by another group [53,54] deal with the performance and ex-haust emission characteristics of diesel engine fuelled with vegeta-ble oils blended with oxygenated organic compounds, includingethanol and n-butanol. Also, in Ref. [55] a very small quantity ofn-butanol was used only for the purpose of improving the solubil-ity of the ethanol–diesel fuel blends used.

From the above, it is made obvious that a major gap exists forthe performance and environmental behavior of this challengingnext generation fuel, especially concerning its use in diesel en-gines. Filling or rather starting to fill this gap, the present work re-ports the results of such an experimental investigation conductedat the authors’ laboratory on a standard experimental, Ricardo/Cussons ‘Hydra’, high-speed, direct injection (DI), naturally aspi-rated diesel engine of automotive type (with no modification onit), which possesses a high versatility and control over the variation

of its operating parameters. The work evaluates the effects of usingvarious blends of n-butanol (99.9% purity) with normal diesel fuel,with 8%, 16% and 24% (by volume) n-butanol, on the performanceand exhaust emissions at various loads. The differences in the per-formance and exhaust emission parameters from the baselineoperation of the diesel engine (working with diesel fuel) weredetermined and compared. Consideration of theoretical aspectsof diesel engine combustion and of the differing physical andchemical properties of the butanol against those for the diesel fuelwere used to aid, in a qualitative way, the interpretation of the ob-served engine behavior with these blends.

2. Experimental facilities and fuels tested

2.1. Engine description

Facilities to monitor and control engine variables such as enginespeed, load, water and lube-oil temperatures, fuel and air flows,etc., are installed on a fully automated test bed, single-cylinder,four-stroke, water cooled, Ricardo–Cussons, ‘‘Hydra”, high-speed,experimental standard engine located at the authors’ laboratory.This engine has the ability to operate on the Otto (spark–ignition)or direct injection (DI) diesel or indirect injection (IDI) diesel, four-stroke principle, by changing various parts of the crank gear mech-anism, cylinder and head.

For the present investigation it is used as a naturally aspirated,DI diesel engine having a re-entrant bowl-in-piston combustionchamber. The engine and injection system basic data are given inTable 2. Fig. 2 gives a full schematic arrangement of the engine testbed, instrumentation and data logging system.

2.2. Test installation description

The engine is mounted on a fully automated test bed and cou-pled to a ‘‘McClure” DC motoring dynamometer, having loadabsorbing and motoring capabilities, which is equipped with a loadcell for the engine torque measurements. There is one electric sen-sor for speed and one for load (torque), with these signals fed toindicators on the control panel and to the controller via knobs onthe control panel, the operator can set the dynamometer to controlspeed or load. There is also a capability of setting automatically thestatic injection timing from a switch on the control panel.

Electrically driven pumps assure the coolant (water) and lube-oil circulation, with the temperature controlled by water-fed heatexchangers. The secondary water-cooling system for these heatexchangers was shop made, comprising a big water tank and a cor-

Table 1Properties of diesel fuel, n-butanol and ethanol.

Fuel properties Dieselfuel

n-ButanolC4H9OH

EthanolC2H5OH

Density at 20 �C, kg/m3 837 810 788Cetane number 50 �25 �8Lower calorific value, MJ/kg 43 33.1 26.8Kinematic viscosity at 40 �C, mm2/s 2.6 3.6a 1.2Boiling point 180–360 118 78Latent heat of evaporation, kJ/kg 250 585 840Oxygen, %wt. 0 21.6 34.8Stoichiometric air–fuel ratio 15.0 11.2 9.0Molecular weight 170 74 46

a Measured at 20 �C.

Fig. 1. Molecular structure of butanol isomers.

Table 2Engine and injection system basic data.

Engine modeland type

Ricardo/Cussons ‘Hydra’Single-cylinder, compression–ignition, directinjection, naturally aspirated, four-stroke, watercooled, high-speed

Speed range 1000–4500 rpmBore/stroke 80.26 mm/88.90 mmCompression ratio 19.8:1Inlet valve It opens at 8� CA before TDC

It closes at 42� CA after BDCExhaust valve It opens at 60� CA before BDC

It closes at 12� CA after TDCFuel pump ‘Bosch’ with 11 mm diameter plungerInjector body and nozzle ‘Bosch’ with four injector nozzle holes

Nozzle hole diameter: 0.25 mmOpening pressure: 250 barAdvance (at pump spill): 0–40� CA

CA means crank angle. TDC means top dead center. BDC means bottom dead center.

D.C. Rakopoulos et al. / Energy Conversion and Management 51 (2010) 1989–1997 1991


responding (secondary) heat exchanger. Heaters are used to main-tain oil and coolant temperatures during warm up and light loadconditions. Thermocouples are located at strategic points in the en-gine, with their indications shown on a multi-point electronic tem-perature indicator. The engine exhaust system is connected to ashop made silencer system. A viscous type, ‘Alcock’ laminar flow-meter is used for measuring the air-flow aspirated by the engine.

A shop made tank and flow-metering system is used for fuelconsumption measurements of the various blend samples as fol-lows. A glass burette of known volume was placed in parallel tothe 3.5-l tank, and the time taken for its complete evacuation ofthe fuel sample feeding the engine was measured. A system ofpipes and valves was constructed in order to achieve a quick drainof a fuel sample, including the return-fuel from the pump andinjector, and the refill of metering system with the new fuelsample.

2.3. Exhaust gas analyzers system

The exhaust gas analysis system consists of a group of analyzersfor measuring soot (smoke), nitrogen oxides (NOx), carbon monox-ide and total unburned hydrocarbons (HC). The smoke level in theexhaust gas was measured with a ‘Bosch’ RTT-100 opacimeter, thereadings of which are directly provided as Hartridge units (% opac-ity) or equivalent smoke (soot) density (milligrams of soot per cu-bic meter of exhaust gases).

The carbon monoxide concentration in ppm (parts per million,by volume) in the exhaust was measured with a ‘Signal’ Series-

7200 non-dispersive infrared analyzer (NDIR). The nitrogen oxidesconcentration in ppm in the exhaust were measured with a ‘Signal’Series-4000 chemiluminescent analyzer (CLA). The total unburnedhydrocarbons concentration (in ppm) in the exhaust were mea-sured with a ‘Ratfisch-Instruments’ flame-ionization detector(FID). The last two analyzers were fitted with thermostatically con-trolled heated lines.

2.4. Properties of fuels

The conventional diesel fuel, which forms the baseline fuel ofthis study, was supplied by Aspropyrgos Refineries of the ‘HellenicPetroleum SA’, representing the typical, Greek automotive, low sul-phur (0.035%) diesel fuel (gas oil).

The isomer of butanol (C4H9OH) n-butanol (otherwise called1-butanol), having a straight-chain structure and the hydroxylgroup (–OH) at the terminal carbon, was used in the presentstudy. It was of 99.9% purity (analytical grade). It was blendedwith the normal diesel fuel at blending ratios of 8/92, 16/84and 24/76 (by volume). Preliminary evaluation tests on the solu-bility of n-butanol in the diesel fuel with blending ratios up to40/60 proved, actually, that the mixing was excellent with nophase separation at all for a period of many days. Then, no emul-sifying agent was necessary.

The properties of the diesel fuel and the n-butanol are summa-rized in Table 1, together with the corresponding properties ofits lower-chain alcohol counterpart ethanol, for comparativepurposes.

RicardoHydraDieselEngine

CONVERTERCABINET

COOLING MODULE

Shaft

Control Control

Control

Oil Water

Oil andwater

pumpsWater supply

return

1ph. mains

ACU

Thro

ttle

posi

tion

Inje

ctio

n tim

ing

Fuel

qua

ntity

Load

3ph. mains

AmplifierCyl. presure

Inj. presure

TDC pick up

NOx COHC

Filter

Smok

eFuel Measure-

mentAirMeasure-

ment

Exhaust

Console

ElectricDynamometer

Data AcquisitionCard

PC

Fig. 2. Schematic arrangement of the engine test bed, instrumentation and data logging system.



3. Parameters tested and experimental procedure

The experiments were performed without any modification onthe engine. The series of tests are conducted using each of theabove fuel blends, with the engine working at a speed of2000 rpm, at a static (pump spill) injection timing of 29� crank an-gle before top dead center (TDC), and at a low, medium and highload corresponding to brake mean effective pressures (b.m.e.p.) of1.40, 2.57 and 5.37 bar, respectively. Owing to the differencesamong the lower calorific values H and oxygen contents of thefuels tested, the comparison must be effected at the same enginebrake mean effective pressure, i.e. load, and not at the same in-jected fuel mass or air/fuel ratio.

In each test, volumetric fuel consumption rate Vfc (in m3/s), ex-haust gas temperature, exhaust smokiness and exhaust regulatedgas emissions such as nitrogen oxides, carbon monoxide and totalunburned hydrocarbons are measured. From the first measure-ment, specific fuel consumption and thermal efficiency are com-puted using the fuel sample density and lower calorific value.

By knowing the engine brake torque Mt (in N m), i.e. the load,which is set for each experiment and kept constant by the enginecontrollers, the following engine performance quantities werecomputed, with N the (constant) engine speed (in rpm):

– The brake mean effective pressure, b.m.e.p. (in bar)

b:m:e:p: ¼ ð4pMt=VhÞ � 10�5: ð1Þ

with Vh = (p/4)D2s the (single-cylinder) engine displacementvolume

– The brake power, P (in W)

P ¼ Mtð2pN=60Þ: ð2Þ

– The brake specific fuel consumption, b.s.f.c. (in g/kW h)

b:s:f :c: ¼ ðVfcqf =PÞ3:6� 109: ð3Þ

– The brake thermal efficiency, b.t.e.

b:t:e: ¼ P=ðVfcqf HÞ: ð4Þ

Table 3 shows the accuracy of the measurements and the uncer-tainty of the computed results of the various parameters.

The experimental work started with a preliminary investigationof the engine running on neat diesel fuel, in order to determine theengine operating characteristics and exhaust emission levels, con-stituting the ‘baseline’ that is compared with the correspondingcases when using the butanol–diesel fuel blends. The same proce-dure was repeated for each fuel blend by keeping the same operat-ing conditions. For every fuel change, the fuel lines were cleaned

and the engine was left to run for about 30 min to stabilize at itsnew condition.

Owing to the high flexibility of this versatile ‘standard’ experi-mental engine, it was possible to keep constant (automatically)sensitive operating parameters of the engine circuits, such as forexample the oil and cooling water temperatures, which can influ-ence mainly the exhaust emission levels, thus increasing the cred-ibility for comparing the measured values. The differences in themeasured performance and exhaust emission parameters fromthe baseline operation of the engine, i.e., when working with neatdiesel fuel, were determined and compared.

4. Discussion of the experimental performance and emissionsresults and their interpretation

All figures to follow provide, in a bar chart arrangement, eachemission or performance parameter for the neat diesel fuel andits blends with 8%, 16% and 24% (by volume) n-butanol, at the threeloads (low, medium and high) with corresponding brake meaneffective pressures of 1.40, 2.57 and 5.37 bar.

It is pointed out from the outset that fundamental studies con-cerning physical (e.g. spray behavior) or chemical aspects of buta-nol in engines are absent. Thus, to aid the correct interpretation ofthe observed engine behavior, the differing physical and chemicalproperties of butanol against those for the diesel fuel will be used,taking also into account, where appropriate, the diesel enginebehavior with corresponding ethanol–diesel fuel blends. It is ex-pected that the relatively high cetane number and solubility inthe diesel fuel does not lead easily to cyclic irregularity as it hap-pens with the corresponding ethanol blends. This was actually ob-served here, where the investigation was extended withoutproblems up to high butanol–diesel fuel blending ratios.

Fig. 3 shows the exhaust smoke (soot) density for the neat die-sel fuel and the various percentages of butanol in its blends withdiesel fuel. One can observe that the soot emitted by the buta-nol–diesel fuel blends is significantly lower than that for the corre-sponding neat diesel fuel case, with the reduction being higher thehigher the percentage of butanol in the blend. This may be attrib-uted to the engine running effectively overall ‘leaner’, since theaspirated air mass remains the same [48], with the combustionbeing now assisted by the presence of the fuel-bound oxygen of

Table 3Accuracy of measurements and uncertainty of computed results.

Measurements Accuracy

Soot density ±1 mg/m3

NOx ±5 ppmCO ±3 ppmHC ±1 ppmTime ±0.5%Speed ±2 rpmTorque ±0.1 N m

Computed results Uncertainty (%)

Fuel volumetric flow rate ±1Power ±1Specific fuel consumption ±1.5Efficiency ±1.5

0

40

80

120

160

Soot

Den

sity

(mg/

m3 )

Diesel

8% Butanol

16% Butanol

24% Butanol

b.m.e.p. : 1.40 bar 2.57 bar 5.37 bar

Fig. 3. Emitted soot (smoke) density, at the three loads, for the neat diesel fuel andthe 8%, 16% and 24% butanol blends.



the butanol even in locally rich zones, which seems to have thedominant influence [7]. It was reported in Refs. [30,31], that in-cyl-inder combustion photography showed indeed lower luminosityflames for the ethanol blends, revealing the lower net soot pro-duced, and this may be applicable for butanol too.

Fig. 4 shows the nitrogen oxides (NOx) exhaust emissions for theneat diesel fuel and the various percentages of the butanol in itsblends with diesel fuel. One can observe that the NOx emitted bythe butanol blends are slightly lower than those for the corre-sponding neat diesel fuel case, with the reduction being higherthe higher the percentage of butanol in the blend. This may beattributed to the engine running overall ‘leaner’ and the tempera-ture lowering effect of the butanol (due to its lower calorific valueand its higher heat of evaporation) having the dominant influence,against the opposing effect of the lower cetane number (and thuslonger ignition delay) of the butanol leading possibly to highertemperatures during the premixed part of combustion. This is adelicate balance weighting more on the one or the other side,depending on the specific engine and its operating conditions[22], which for example may be disclosed by the details of a suc-cessful multi-zone model [45–47].

Fig. 5 shows the carbon monoxide (CO) exhaust emissions forthe neat diesel fuel and the various percentages of the butanol inits blends with diesel fuel. One can observe that the CO emittedby the butanol–diesel fuel blends is generally lower than that forthe corresponding neat diesel fuel case, with the reduction beinghigher the higher the percentage of butanol in the blend. Conclu-sively, the emitted CO follows the same behavior as the emittedsoot by the engine, a fact collectively attributed to the same phys-ical and chemical mechanisms affecting almost in the same way, atleast qualitatively, the net formation of these emissions.

Fig. 6 shows the total unburned hydrocarbons (HC) exhaustemissions for the neat diesel fuel and the various percentages ofthe butanol in its blends with diesel fuel. One can observe thatthe HC emitted by the butanol–diesel fuel blends are higher thanthose for the corresponding neat diesel fuel case, with the increasebeing higher the higher the percentage of butanol in the blend. Thisis the behavior reported by almost all investigators on varioustypes of engines and conditions with ethanol–diesel fuel blends[22]. As known, the formation of unburned hydrocarbons origi-nates from various sources in the engine cylinder and their theo-

retical study is still at its infancy. The arguments given, forexample, in Refs. [2,32,33,48] for the observed increase of HC emis-sions with ethanol–diesel fuel blends may be well applicable forthe butanol–diesel fuel blends too. These may include, slowerevaporation and so slower and poorer fuel–air mixing due to thehigher heat of evaporation of the butanol blends, increased spraypenetration causing unwanted fuel impingement on the chamberwalls (and so flame quenching) and cushioning in the ring landareas, and increase with butanol of the so called ‘lean outer flamezone’ where flame is unable to exist.

Fig. 7 shows the brake specific fuel consumption (b.s.f.c.) for theneat diesel fuel and the various percentages of the butanol in itsblends with diesel fuel. The fuel blend mass flow rate is calculatedfrom the respective measured volume flow rate value and the

0

200

400

600

800

1000

1200

1400

NO

X (p

pm)

Diesel

8% Butanol

16% Butanol

24% Butanol

b.m.e.p. : 1.40 bar 2.57 bar 5.37 bar

Fig. 4. Emitted nitrogen oxides (NOx), at the three loads, for the neat diesel fuel andthe 8%, 16% and 24% butanol blends.

0

80

160

240

320

400

CO (p

pm)

Diesel

8% Butanol

16% Butanol

24% Butanol

b.m.e.p. : 1.40 bar 2.57 bar 5.37 bar

Fig. 5. Emitted carbon monoxide (CO), at the three loads, for the neat diesel fueland the 8%, 16% and 24% butanol blends.

0

20

40

60

80

100

120

HC (p

pm)

b.m.e.p. : 1.40 bar 2.57 bar 5.37 bar

Diesel

8% Butanol

16% Butanol

24% Butanol

Fig. 6. Emitted total unburned hydrocarbons (HC), at the three loads, for the neatdiesel fuel and the 8%, 16% and 24% butanol blends.



blend density. Since the comparison is effected at the same load(b.m.e.p.) and speed, which is translated into the same enginepower (cf. Eqs. (1) and (2)), the brake specific fuel consumptionvalues are then effectively directly proportional to the fuel massflow rate values (cf. Eq. (3)). It is observed that for all the buta-nol–diesel fuel blends, the specific fuel consumption is a little high-er than the corresponding diesel fuel case, with the increase beinghigher the higher the percentage of butanol in the blend. This is theexpected behavior due to the lower calorific value of the butanolcompared to that for the neat diesel fuel, given that the comparisonis effected at the same load.

Fig. 8 shows the brake thermal efficiency (b.t.e.) for the neat die-sel fuel and the various percentages of the butanol in its blendswith diesel fuel. It is to be noted that the brake thermal efficiencyis simply the inverse of the product of the specific fuel consump-

tion and the lower calorific value of the fuel (cf. Eqs. (3) and (4)).Given the above-mentioned close interrelation between brakethermal efficiency and specific fuel consumption, the results of thisfigure can be explained. It is observed that for all the butanol–die-sel fuel blends, the brake thermal efficiency is slightly higher thanthat for the corresponding neat diesel fuel case, with the increasebeing higher the higher the percentage of butanol in the blend. Thismeans that the increase of brake specific fuel consumption for thebutanol–diesel fuel blends is lower than the corresponding de-crease of the lower calorific value of the blends. This can be attrib-uted to the higher premixed combustion part possessed by thebutanol blends because of the lower cetane number of butanol,leading to higher percentage of ‘constant volume’ combustion,and to the lower heat losses (due to the lower average cylindergas temperatures) and to ‘leaner’ combustion [48].

Lastly, Fig. 9 shows the exhaust gas temperature for the neatdiesel fuel and the various percentages of the butanol in its blendswith diesel fuel. It is observed that for all the butanol–diesel fuelblends, the temperature is slightly lower than that for the corre-sponding neat diesel fuel case, with this decrease being higherthe higher the percentage of butanol in the blend. This is in accor-dance with the corresponding trend of slightly higher thermal effi-ciency, as justified above, by denoting a better expansion process;to this side may also be corroborating the lower calorific value andthe higher latent heat of evaporation (and so lower produced tem-peratures) of the butanol blends against those for the diesel fuel.

5. Conclusions

An extended experimental investigation was conducted toevaluate and compare the use of n-butanol as supplement to theconventional diesel fuel at blending ratios of 8/92, 16/84 and 24/76 (by volume) in a high-speed, direct injection, naturally aspi-rated diesel engine located at the authors’ laboratory. The seriesof tests were conducted using each of the above fuel blends, withthe engine working at a speed of 2000 rpm and at three loads(low, medium and high).

In each test, exhaust smokiness and exhaust regulated gasemissions such as nitrogen oxides, carbon monoxide and totalunburned hydrocarbons were measured. Brake specific fuel

0

100

200

300

400

500

600

Brak

e Sp

ecifi

c Fu

el C

onsu

mpt

ion

(g/k

Wh)

Diesel

8% Butanol

16% Butanol

24% Butanol

b.m.e.p. : 1.40 bar 2.57 bar 5.37 bar

Fig. 7. Brake specific fuel consumption, at the three loads, for the neat diesel fueland the 8%, 16% and 24% butanol blends.

0

0.1

0.2

0.3

0.4

Brak

e Th

erm

al E

ffici

ency

(-)

Diesel

8% Butanol

16% Butanol

24% Butanol

b.m.e.p. : 1.40 bar 2.57 bar 5.37 bar

Fig. 8. Brake thermal efficiency, at the three loads, for the neat diesel fuel and the8%, 16% and 24% butanol blends.

0

100

200

300

400

Exha

ust G

as T

empe

ratu

re (0 C

)

Diesel

8% Butanol

16% Butanol

24% Butanol

b.m.e.p. : 1.40 bar 2.57 bar 5.37 bar

Fig. 9. Exhaust gas temperature, at the three loads, for the neat diesel fuel and the8%, 16% and 24% butanol blends.



consumption and thermal efficiency are computed from the mea-sured fuel volumetric flow rate, and densities and calorific values.The differences in the measured performance and exhaust emis-sion parameters from the baseline operation of the engine, i.e.when working with neat diesel fuel, were determined and com-pared. The differing physical and chemical properties of the buta-nol against those for the diesel fuel are used to aid the correctinterpretation of the observed engine behavior.

The smoke density was significantly reduced with the use of thebutanol–diesel fuel blends with respect to those of the neat dieselfuel, with this reduction being higher the higher the percentage ofbutanol in the blend.

The NOx emissions were slightly reduced with the use of thebutanol–diesel fuel blends with respect to those of the neat dieselfuel, with this reduction being higher the higher the percentage ofbutanol in the blend.

The CO emissions were reduced with the use of the butanol–diesel fuel blends with respect to those of the neat diesel fuel, withthis reduction being higher the higher the percentage of butanol inthe blend.

On the contrary, the unburned hydrocarbons (HC) emissionswere increased with the use of the butanol–diesel fuel blends withrespect to those of the neat diesel fuel, with this increase beinghigher the higher the percentage of butanol in the blend.

Concerning the engine performance with the butanol–dieselfuel blends against the neat diesel fuel case, with increasing per-centage of butanol in the blends, a little higher specific fuel con-sumption was observed with corresponding slight increase ofbrake thermal efficiency and little lower exhaust gas temperatures.

A general practical conclusion is that this next generation chal-lenging fuel, n-butanol, can be used safely and advantageously upto high blending ratios with the diesel fuel in the diesel engine,both from the viewpoints of thermal efficiency and exhaust emis-sions, given also its relatively high cetane number and high solubil-ity in the diesel fuel requiring no cetane enhancing additive orsolubilizer as it happens normally with the corresponding etha-nol–diesel fuel blends. Research is ongoing by the present authorswith butanol–diesel fuel blends on other types of diesel engines tofurther prove its merits, with the results to be reported in a futurecommunication.

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