NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Impact of Policy on Fuels 

RD&D

Chris Gearhart

Center for Automotive Research 

December Briefing

Farmington Hills, Michigan

December 5, 2013 

NREL/PR-5400-60974
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Today’s Discussion

• Fuel Policy and Regulation

• Low-Carbon and Energy-Efficient Solutions

• Current Fuel and Engine Efficiency RD&D

• Challenges

Cover photos by Dennis Schroeder, NREL
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Greenhouse Gas Reduction – Fuels Pathway

Source: Transitions to Alternative Vehicles and Fuels (National Academy of Sciences)
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Greenhouse Gas Emissions and Fuel Economy Limits

• EPA and NHTSA set standards to reduce greenhouse gases (GHG) and 

improve fuel economy for model years 2017–2025 cars and light trucks

• Average industry fleetwide level of 163 grams/mile of carbon dioxide 

(CO2) in model year 2025 – equivalent to average fleet fuel economy of 

54.5 mpg

• GHG emission limit will be met mainly by increasing vehicle fuel economy

Source: EPA and NHTSA Set Standards to Reduce Greenhouse Gases and Improve Fuel Economy for Model Years 2017-2025 Cars and Light 

Trucks. (U.S. Environmental Protection Agency, 2012) http://epa.gov/otaq/climate/documents/420f12051.pdf
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Renewable Fuels Standard

Source: Alternative Fuels Data Center. http://www.afdc.energy.gov/laws/RFS
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Advanced & Cellulosic Diesel Biofuels

•Biomass-Based Diesel and Advanced Biofuel

– 50% reduction in GHG emissions, EPA approved

 Production process path + feedstock path

– Biomass-based diesel—EPA approved

 Biodiesel: from soy, canola, animal fat, waste grease, and 

other

 Hydrotreated Renewable Diesel: from same feedstocks

– Other future processes approved by EPA

– Other fuel derived from cellulosic biomass

• Cellulosic Biofuel

– 60% reduction in GHG emissions

– Derived from cellulose, hemicellulose, or lignin

Photos by Warren Gretz , NREL
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2011 Transportation 

Fuel Use

A Market Dominated by Petroleum

Source: Melaina, M.W.; Heath, G.; Sandor, D.; Steward, D.; Vimmerstedt, L.; Warner, E.; Webster, K.W. (2013). 

Alternative Fuel Infrastructure Expansion: Costs, Resources, Production Capacity, and Retail Availability for LowCarbon Scenarios. Transportation Energy Futures Series.

Source: Melaina, M.W.; Heath, G.; Sandor, D.; Steward, D.; Vimmerstedt, L.; Warner, E.; Webster, K.W. (2013). 

Alternative Fuel Infrastructure Expansion: Costs, Resources, Production Capacity, and Retail Availability for LowCarbon Scenarios. Transportation Energy Futures Series.

GHG Projections by 

Transportation Fuel Type
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Solution Part 1: Advanced Biofuels

• Cellulosic ethanol

• Renewable diesel

• Advanced biofuels

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Photos by Dennis Schroeder, NREL
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Displacement Potential

Source: Ruth, M.; Mai, T.; Newes, E.; Aden, A.; Warner, E.; Uriarte, C; Inman, D.; Simpkins, T.; Argo, A. (2013). 

Projected Biomass Utilization for Fuels and Power in a Mature Market. Transportation Energy Futures Series..
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Potential of Ethanol for Meeting RFS Targets

•Ethanol is currently limited to a 10% blend

– 15% in 2001 and newer cars

•Options

– Dramatic expansion of availability and use of “flex 

fuel” (E85)

 Requires rapid increase in number of flex fuel vehicles 

(FFVs) and refueling pumps

– High-level ethanol blends for high compression ratio, 

high-efficiency engines

 State and federal regulatory hurdles

 ASTM standards

 Not backward compatible (new class of vehicles)
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Potential of Biomass-Based Diesel

• Current production from fats, oils, greases – resource 

limited to roughly 2.5 billion gallons

• Future production from biomass by pyrolysis, sugar 

dehydration/oligomerization, and fermentation is not 

yet economical at large scale

Photos by Warren Gretz , NREL (left & right); Dennis Schroeder, NREL (center)
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Biomass-Based Diesel Options

At commercial scale 

Biodiesel

Production

Hydrotreating

Oils and

Greases

(Algae)

Biodiesel

Renewable Diesel

Sugar: 

corn, cane, 

or biomass 

Lignocellulosic 

Biomass

Biochemical

Conversion

Catalytic

Reforming

Fast PyrolysisHydrotreating

GasificationFT Synthesis

Renewable Diesel

Renewable Diesel

Renewable Diesel

FT-Diesel/ 

Renewable Diesel

Pilot scale 

– Demonstrated 

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Biodiesel
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Solution Part 2: More Efficient Engines

• SI and CI engine efficiency

• Emissions control technologies

• Advanced fuels

• Blending components

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Top photo by Dennis Schroeder, NREL

Bottom photo courtesy of Cummins

Illustration and figure: NREL
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Internal Combustion Engine (ICE) Vehicles Have Room for Improvement

A large fraction of energy is lost to friction, 

unrecoverable heat losses, and vehicle inefficiencies:

• 63.4% engine losses

• 17.2% standby-idle losses

• 3.5% driveline losses

• 2.9% accessories losses
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Approaches to Increasing SI Engine Efficiency

• Engine downsizing

– Smaller engines operating at low speed and higher load are 

more efficient

– Optimized with 6- to 9-speed transmission

• Turbocharging 

– Recovering energy from the engine exhaust

– Required for engine downsizing

•Direct injection

– Fuel evaporates in the combustion cylinder, cooling the airfuel mixture

– Also required for engine downsizing

•Increased compression ratio

– Greater thermodynamic efficiency
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Limiting Factor: Engine Knock

• All of the approaches to increasing engine efficiency 

require a fuel with higher knock resistance

• Knock occurs when unburned gas auto-ignites ahead of 

the flame front

• The unburned gas temperature and pressure become 

too high for the knock resistance of the fuel
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Ethanol Has High RON and Heat of Vaporization

• Ethanol research octane number (RON) is higher than that of 

today’s hydrocarbon gasoline

• For direct injection engines, fuel evaporation occurs in the cylinder 

– cooling the charge and reducing knock tendency

• Alcohols have significantly higher heat of vaporization (HoV) 

leading to a higher “effective RON”
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Challenges in Introducing New Fuels

• Many steps and years to introduce a 

new fuel

– Higher ethanol level like E30

– New oxygenate

• Impact on

– Vehicle performance and durability

– Emissions and emission control system 

durability 

– Infrastructure compatibility

– Fuel quality standards

– Fire codes and safety regulations

– Consumer protection laws

– RFS pathway

– Federal, state, and local regulations/laws
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Conclusions

•Current government policies are driving R&D on 

more efficient vehicles and low carbon fuels 

– Cellulosic ethanol: limited by blend wall

– Drop-in hydrocarbon biofuels

•Unique knock-resistant properties of ethanol 

may enable higher efficiency

– Combined high RON and high heat of vaporization

– High GHG emission reduction of cellulosic ethanol (>60% 

relative to petroleum) 

•Challenges to introduction of ≈E30 blend

– Regulatory compliance under Clean Air Act

– Infrastructure compatibility

– Introduction of a new vehicle class
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National Renewable Energy 

Laboratory 

Innovation for Our Energy Future

Learn more at 

www.nrel.gov/vehiclesandfuels 

NREL is a national laboratory of the U.S. Department of Energy, 

Office of Energy Efficiency and Renewable Energy, operated by 

the Alliance for Sustainable Energy, LLC. 

NREL/PR-5400-60974 December 2013