Alternative Low Carbon Fuels – Pathways and Opportunities for the Spark-Ignition Internal Combustion Engine James Turner, Andy Lewis and Darren Millwood University of Bath, UK With acknowledgement to Sebastian Verhelst Ghent University
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 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 – Governments – Fuel Supply Companies – Consumers 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 4
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 game These 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 solutions 5
RENEWABLE SPARK-IGNITION ENGINE FUELS
Renewable Fuels for SI Engines The principal renewable fuels for SI engines are the alcohols They 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
On-Board Energy Density 30 Net volumetric energy density / [MJ/l] Diesel Liquids 25 Gasoline E85 20 M85 Ethanol 15 These can also be made from Methanol biomass and as 10 Gases ‘Carbon-Neutral L H2 Liquid Fuels’ 5 700 bar H2 200 bar Methane 0 Solids Batteries 0 5 10 15 20 25 30 35 40 Net gravimetric energy density / [MJ/kg] Courtesy Lotus Engineering 8
Scalability Ethanol penetration has traditionally been restricted due to issues of scalability Its ‘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 CO 2 (in combination with hydrogen) As a consequence, there is no practical limit to the feed stock available 9
Fuel Pathways Using Alcohols Primary Energy Process / Feed Stock Alcohol Fuel Type Pure Fuel Atmospheric / Chemical Renewable / Waste CO 2 Liquefaction of Methanol Nuclear Hydrogen H 2 from Water Least Limited Hydrocarbon Synthesis Thermochemical Processes (Syngas) Biomass Most Biological Ethanol Limited Processes Butanol Blended Fuel Refining Fossil Oil Long-term Hydrocarbon Limited Fuel
Breaking the Biomass Limit… Sustainable Methanol Energy in Hydrogen from electrolysis of water 1 + H O H O 2 2 2 2 Also provides a buffer for renewable energy Carbon out Methanol synthesis S ynthetic + + CO 3H C H OH H O hydrocarbons 2 2 3 2 and products From Lackner, K.,‘Options for CO 2 consumption Capturing Carbon Dioxide from the Air, May 2008’ Fuel use 3 + CH OH O 3 2 2 capture CO 2 2 + CO 2 H O 2 Carbon in CO from fossil 2 Atmospheric CO fuel burning 2 power plants Gasoline, diesel and kerosene CO 2 emission can also be synthesized from these feed stocks – with an Adapted from Olah et al., The Methanol Economy Adapted from Olah et al., energy penalty (c. 8% point) ‘The Methanol Economy’ Courtesy Lotus Engineering 11
Synthesis of Higher Hydrocarbons 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 CO 2 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 – Taken from “The Indirect including aviation and Direct Conversion of CO 2 into Higher Carbon For which there is no practical alternative Fuels”, France et al. , 2015 12
Compatible Fuels, Engines and Vehicles… Fuels Engines Vehicles Fossil kerosene Gas Turbine Ships/Aircraft CI Fossil diesel Cars/Vans/Buses/Trucks/Trains/Ships SI Cars/Vans Fossil gasoline Carbon-Neutral Fuels Carbon-Neutral Vehicles C-N kerosene Gas Turbine Ships/Aircraft C-N diesel CI Trucks/Trains/Ships C-N alcohol CI Vans/Buses/Tucks C-N alcohol SI Cars/Vans/Buses/Trucks Courtesy Lotus Engineering 13
ALCOHOL BLENDING OPPORTUNITIES
Alcohol Blending There are various blending opportunities which make alcohol introduction easier Blending for constant stoichiometry has been found to produce ternary blends of gasoline, ethanol and methanol (GEM) identical to equivalent- stoichiometry binary gasoline-ethanol blends This 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 15
GEM Blend Concentrations at 9.7:1 AFR Straight E85 is ‘dry’ and has a stoichiometric AFR of 9.7:1 Blend D Blend C Blend B Blend A – ‘Straight’ E85 100% Fraction of gasoline/methanol in 90% Gasoline 80% The volumetric LHV is constant 70% 60% The octane numbers are constant blend 50% The latent heat varies by 2% across all such blends 40% Methanol Ethanol 30% 20% There is therefore the potential for a true ‘drop-in’ solution 10% 0% 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 Ethanol fraction / [%] Courtesy Lotus Engineering
Gasoline Displacement: Blend C versus A 36% less gasoline 100 90 Volumes for Equal Energy / [Volume Units] 80 42 42 42 42 70 = 60 85 50 21 21 21 21 40 72.0 72.0 72.0 30 20 37 37 37 37 10 15 0 Gasoline Gasoline Gasoline A C C C C Blend Designation Gasoline Ethanol Methanol 72x3+15 = 231 Equivalent Energy on Each Side 37x4 = 148 Courtesy Lotus Engineering
Gasoline Displacement Curve On a Per-Unit-Energy-Supplied Basis 45 Blend B Blend C Blend D 40 Additional Gasoline Displaced / [%] 35 Blend C: 30 36% less gasoline 25 than Blend A 20 15 10 Blend A 5 0 0 5 10 15 20 25 30 35 40 45 50 55 60 Methanol Fraction in Ternary Blend with 9.7:1 Stoichiometric AFR / [%] 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 systems Or 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 Taken from Daniel et al. , “Dual-Injection as a Knock Mitigation Strategy Using Pure Ethanol and Methanol”, SAE 2012-01-1152 20
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