James Turner, Andy Lewis and Darren MillwoodUniversity of Bath, UK

With acknowledgement toSebastian Verhelst

Ghent University

Alternative Low Carbon Fuels – Pathways and Opportunities for the Spark-Ignition Internal Combustion Engine

TRYING TO REPLACE THE INCUMBENT TECHNOLOGY

The Incumbent Technology…

The internal combustion engine has become the dominant prime mover for transport because:

It is made from abundant materials

Using simple processes

And it uses a cheap energy storage system

3

The Incumbent Technology…

Furthermore:

The energy supply and distribution system is efficient in terms of energy density and energy transfer rates and it suffers minimal losses

4

Customers have to be able to afford transportation since they are the only financial input to the system

All the other stakeholders take the money out

– Governments – Fuel Supply Companies – Consumers

Trying to move away from any of these factors will incur significant risk to the economic model Which is mature and which is known to work for all stakeholders OEMs

An Ideal Scenario

A form of panacea would be to be one where evolution of liquid fuels could be undertaken towards a zero-carbon end gameThese fuels should be symbiotic with existing and future internal combustion engine technologies so that the overall energetic efficiency of the system can increase as they are introduced This will minimize the necessary upstream investment in low-carbon energy

Factors for consideration should include: The solution should be scalable to full amounts It needs to provide stability in the taxation system (with minimal inducements in

the short term which will not stop the process when they are phased out) The ability to evolve the distribution system should be simultaneous The ability to unlock new and more abundant renewable energy supplies

around the planet to address energy security would be really beneficial Ideally the overall technology level should be similar to what we have now, or

use previously-proven solutions5

RENEWABLE SPARK-IGNITION ENGINE FUELS

Renewable Fuels for SI Engines

The principal renewable fuels for SI engines are the alcoholsThey can be made from biological sources (principally ethanol and butanol) or via thermochemical routes from biomass or renewable carbon (methanol)They are fully miscible in gasoline Although care must be taken to avoid phase separation in the presence of water

Advantages include very high octane numbers, high latent heats of vaporization, high laminar burning velocities and lower adiabatic flame temperatures compared to pure hydrocarbons All of these factors are complementary to the major directions that the SI engine is

following• Downsizing with DI, application of cooled EGR and lean combustion systems

Disadvantages include lower energy density, varying levels of toxicity, low vapour pressures (high in mixtures with hydrocarbons) and aggressivity These factors are understood and countermeasures are in place or exist

7

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Net gravimetric energy density / [MJ/kg]

Net

vol

umet

ric e

nerg

y de

nsity

/ [M

J/l]

Gasoline

Diesel

E85

EthanolM85

Methanol

L H2

700 bar H2

200 bar Methane

Batteries

8

On-Board Energy Density

Liquids

Gases

Solids

These can also be made from

biomass and as ‘Carbon-Neutral

Liquid Fuels’

Courtesy Lotus Engineering

Scalability

Ethanol penetration has traditionally been restricted due to issues of scalabilityIts ‘biomass limit’ varies from region to region, but the full transport energy requirement cannot be met by bioethanol The biomass limit includes factors such as food chain disruption and ILUC

Butanol is similarly effected

This has led to these alcohols being discounted as a viable energy vector

Methanol can be made from any carbonaceous feed stock, including: Coal (widely done in China) Natural gas (5% lower carbon intensity than gasoline) Biomass (via a thermochemical route) Waste CO2 (in combination with hydrogen)

As a consequence, there is no practical limit to the feed stock available9

Fuel Pathways Using Alcohols

Primary Energy

Renewable /Nuclear

Fossil Oil

Biomass

Pure Fuel

BlendedFuel

HydrocarbonFuel

Atmospheric /Waste CO2

H2 from Water

BiologicalProcesses

Methanol

Ethanol

Butanol

Refining

HydrocarbonSynthesis

Process / Feed Stock Alcohol Fuel Type

Long-termLimited

MostLimited

LeastLimited

Chemical Liquefaction of

Hydrogen

ThermochemicalProcesses(Syngas)

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Breaking the Biomass Limit…

electrolysis of water

222 O21

HOH +

Energy in Hydrogen from

Carbon outSynthetic

and productshydrocarbons

Carbon in2CO from fossil

fuel burningpower plants

Methanol synthesisOHOHHC3HCO 2322 ++

CO2 consumption

Atmospheric 2CO

CO2 emission

Fuel use

23 O23OHCH +

OH2CO 22 +

Adapted from Olah et al., The Methanol Economy

capture2CO

From Lackner, K.,‘Options for Capturing Carbon Dioxide from the Air, May 2008’

Gasoline, diesel and kerosenecan also be synthesized from these feed stocks – with an energy penalty (c. 8% point)

Sustainable Methanol

Adapted from Olah et al., ‘The Methanol Economy’

Courtesy Lotus Engineering

Also provides a buffer for

renewable energy

Synthesis of Higher Hydrocarbons

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Taken from “The Indirect and Direct Conversion of CO2 into Higher Carbon Fuels”, France et al., 2015

Methanol can be converted into gasoline e.g. the ExxonMobil ‘MTG’ process,

which has been commercially proven at industrial scale

Although there is a reduction in fuel energy of 8% points

CO2 itself can be directly converted into higher hydrocarbons using Fischer-Tropsch chemistry Again, with lower energetic efficiency

These pathways open up the possibility of decarbonizing all forms of transport –including aviation For which there is no practical alternative

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Compatible Fuels, Engines and Vehicles…

Fuels Engines Vehicles

Fossil kerosene Gas Turbine Ships/Aircraft

Fossil diesel CI Cars/Vans/Buses/Trucks/Trains/Ships

Fossil gasoline SI Cars/Vans

C-N kerosene Gas Turbine Ships/Aircraft

C-N diesel CI Trucks/Trains/Ships

CI Vans/Buses/TucksC-N alcohol

C-N alcohol SI Cars/Vans/Buses/Trucks

Carbon-Neutral Fuels Carbon-Neutral Vehicles

Courtesy Lotus Engineering

ALCOHOL BLENDING OPPORTUNITIES

Alcohol Blending

There are various blending opportunities which make alcohol introduction easierBlending for constant stoichiometry has been found to produce ternary blends of gasoline, ethanol and methanol (GEM) identical to equivalent-stoichiometry binary gasoline-ethanol blendsThis was a result of some initial calculations at Lotus which showed that for equal AFR, all ‘iso-stoichiometric’ GEM blends have the same volumetric lower heating value, to 0.25%It was postulated that this approach could enable ‘drop-in’ fuels to be formulated for existing E85/gasoline flex-fuel vehicles, which could then be used to extend the biomass limit of ethanol Which has been shown to be the case in vehicle and engine tests conducted by

several researchers Distillation curves and Reid vapour pressures have also been investigated

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GEM Blend Concentrations at 9.7:1 AFR

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85

Ethanol fraction / [%]

Frac

tion

of g

asol

ine/

met

hano

l in

blen

d

Blend A – ‘Straight’ E85

Gasoline

Methanol Ethanol

Blend CBlend D Blend B

There is therefore the potential for a true ‘drop-in’ solution

The volumetric LHV is constant

The octane numbers are constant

The latent heat varies by 2% across all such blends

Straight E85 is ‘dry’ and has a stoichiometric AFR of 9.7:1

Courtesy Lotus Engineering

Courtesy Lotus Engineering

72.0 72.0 72.0

15

37 37 37 37

85

21 21 21 21

42 42 42 42

0

10

20

30

40

50

60

70

80

90

100

Gasoline Gasoline Gasoline A C C C CBlend Designation

Volu

mes

for E

qual

Ene

rgy

/ [Vo

lum

e U

nits

]

Gasoline Ethanol Methanol

Gasoline Displacement: Blend C versus A

Equivalent Energy on Each Side

=

72x3+15 = 231 37x4 = 148

36% less gasoline

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25 30 35 40 45 50 55 60

Methanol Fraction in Ternary Blend with 9.7:1 Stoichiometric AFR / [%]

Add

ition

al G

asol

ine

Dis

plac

ed /

[%]

Blend C

Blend A

Blend DBlend B

Gasoline Displacement Curve

Blend C: 36% less gasoline

than Blend A

On a Per-Unit-Energy-Supplied Basis

Courtesy Lotus Engineering

ALCOHOLS IN SI ENGINE COMBUSTION SYSTEMS

Dual Injection Strategies

Alcohols can increase the performance and efficiency of SI engines in their own right In straight admixture with

gasoline in single fuel systemsOr in dual injection strategies, with (for example) gasoline PFI plus DI of high-blend alcohol Permits the maximum gearing on

alcohol availability, albeit with an increase in engine complexity

Proposed by EBS, investigated by Ford/AVL, Birmingham/JLR and others

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Taken from Daniel et al., “Dual-Injection as a Knock Mitigation Strategy Using Pure Ethanol and Methanol”, SAE 2012-01-1152

‘Ultraboost’ Engine Alcohol Fuel Tests at Bath

Several alcohol blends were tested in the Ultraboost extreme downsizing demonstrator engine at the University of Bath 2.0 l capable of delivering the performance of a 5.0 l V8 – 60% downsized A TSB-funded programme with eight partners, led by JLR

One build used external boosting and EGR rigs to closely control manifold conditions Ideal for detailed fuel testing

Blends included two mid-level and two high-level alcohol blends The mid-level blends were E20 and M15

• Stoichiometry was matched to 0.4% and volumetric LHV to 0.9% The high-level blends were E85 and a near-equivalent GEM

• Stoichiometry was matched to -1.0% and volumetric LHV to 0.3%These fuels were each tested at four different speed and load points, with and without cooled EGR, and compared to a baseline 95 RON E5 pump gasoline

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Ultraboost Engine Alcohol Fuel Tests at the University of Bath

Test points were: Point A: 2000 rpm, high load, no EGR Point B: 2000 rpm, high load, 10% EGR, compensated boost pressure Point C: 3000 rpm, high mid load, 10% EGR Point D: 3000 rpm, high mid load, 10% EGR, higher EBP

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Point A Point D

Comparison of E20 and M15:Matched stoichiometry

Boosting system work is not included, but engine had representative boundary conditions and also high friction

Ultraboost Engine Alcohol Fuel Tests – Torque

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E5 G

asol

ines

E5 Gasolines

Mid

Ble

nds

Mid Blends

Hig

h B

lend

s

High Blends

Ultraboost Engine Alcohol Fuel Tests – Thermal Efficiency

E5 Gasolines Mid Blends High Blends

Ultraboost Engine Alcohol Fuel Tests – BSFC

E5 Gasolines Mid Blends High Blends

PFI Engine Measurements on GEM Fuels by Ghent

4 cylinder PFI production engine, fuelled with four different GEM blends Corresponding to the blends discussed aboveSteady state operating conditions at various engine speeds Stoichiometric operation (λ = 1) and MBT timing

Effect of different GEM blends on performance and emissions was investigated to check the ‘drop-in’ potential of GEM fuels

Confirmation of similar BTE, volumetric efficiency, BSFC and knock behaviour was reported for all the tested operating points Fuel Vol. 117, pp. 286-93, 2014

DI Engine Measurements on GEM Fuels by Ghent

4-cylinder DI production engine fuelled with 2 different GEM blends E85 (Blend A) and M56 (Blend D)Steady-state operating conditions at various engine speeds Stoichiometric operation (λ = 1) and MBT timing

Measurements were done for E85 at fixed loads of 50, 75 and 150 Nm for a range of engine speedsAll parameters regarding injection (start of injection and injection pressure) and ignition were kept the same for the measurements on M56 to investigate the effect on injection and burn duration Only very small adjustments of the throttle valve were necessary to maintain the

same torque outputThis work again reinforced that GEM fuels configured for the same stoichiometry can indeed function as drop-in alternatives in direct-injection engines

SAE 2015-01-0768

Ultimate Potential of Alcohols

Given the extremely favourable characteristics of alcohols, it would be possible to move towards engines much more optimized towards them Production flex-fuel engines to date have been hamstrung by a desire to maintain

broadly-equivalent performance on pump gasoline to that on alcoholIt would be possible to optimize to the alcohol and offer reduced performance on gasoline to offset range anxietyOptimization towards alcohols has been shown to yield higher thermal efficiencies than diesel enginesGiven parity of unit energy costs, this form of optimization would: Reduce the absolute amount of renewable fuel that would have to be provided Lead to customer behaviour where gasoline was only used in extremis

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More Efficient than Diesel…

The scale of the possibilities has been shown by US EPA Converted at VW 1.9 TDI to SI and operated it on

ethanol and methanol at higher BTE than it recorded as a diesel

Used 19:1 CR and diesel ports, with cooled EGRThe methanol test was repeated by Ghent and vehicle modelling was then conducted Showed significant energetic improvements on

drive cycles Lean operation was also investigated with further

significant energetic gains and very low NOx due to the characteristics of methanol

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Brusstar et al.,SAE 2002-01-2743

CONCLUSIONS AND OBSERVATIONS

Conclusions and Observations

Alcohols can be used in existing, proven and cost-effective IC engines because they are liquid fuels which can be stored and distributed easily They can be made in full amounts and as a result could provide a low-carbon

successor to gasolineThey have highly favourable combustion characteristics entirely synergistic with the major technology trends in SI engines Higher thermal efficiencies with alcohols are possible than diesel engines can

provideThey can be blended into gasoline in a variety of ways and therefore provide an evolutionary path to the full decarbonization of transportPathways to synthesize higher hydrocarbons exist, which will enable the decarbonization of aviation Practically speaking, there is no other way to achieve this

Dual injection strategies may provide a stepping stone to greater gasoline displacement than could be provided by simple blending

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Conclusions and Observations

In order to facilitate this, a taxation system is required with two levers which Tax energy (not volume) [Lever 1] Account for the fossil CO2 footprint of each unit of energy [Lever 2]

By doing this, adjustment of the two levers would permit transport fuel tax revenues to be held constant while penalizing fossil fuel usageAs such alcohols provide a path of least resistance for all stakeholders: Governments (lower immediate investment in renewable energy) Fuel companies (no quantum change from a liquid fuel infrastructure) Vehicle manufacturers (since the technology is similar to current products) Vehicle customers (who will still be able to afford motoring)

We cannot lose sight of this – they provide all of the money into the systemAny technology which is not perceived as near-cost-equivalent by the general public (not early adopters) will failThis has been shown by the EV experience in the market place to date

Thank You for Listening