Alternative Fuels Characterization

NREL alternative fuels projects help overcome technical barriers and expand markets for renewable, biodegradable vehicle fuels.

These liquid fuels include higher-level ethanol blends, butanol, biodiesel, renewable diesel, other biomass-derived fuels, and natural gas. By studying the fuel chemistry as well as combustion and emissions impacts of alternative fuels, NREL helps improve engine efficiency, reduce polluting emissions, and improve U.S. energy security by reducing petroleum dependency.

Biofuels for Diesel Engines

NREL's diesel biofuels research and development focuses on developing fuel quality standards and demonstrating compatibility with engines and emission control systems. Highly efficient heavy-duty diesel truck engines are the primary power source for global transportation of freight. Light-duty diesel-fueled passenger vehicles have much higher fuel economy than comparable gasoline-powered cars.


Biodiesel use in the United States surpassed 1 billion gallons in 2011. This renewable fuel can be produced from vegetable oil, algal oil, animal fats, and waste grease by a process called transesterification. NREL's biodiesel research includes fuel quality evaluation methods, fuel quality surveys, oxidation stability, cold weather operability, air pollutant emissions effects, and impact on emission control catalysts and filters. Research is focused on demonstrating vehicle and infrastructure compatibility for blends well beyond the current 5 volume percent, up to 20 volume percent.

Fischer-Tropsch Diesel

Fischer-Tropsch (FT) diesel is made from carbon monoxide and hydrogen produced from carbon-containing sources such as natural gas, biomass, or coal. NREL's FT diesel research examines fuel properties and demonstrates the use of this fuel in vehicle fleets.

Hydroisomerized Fats and Oils

Also known as hydrocarbon renewable diesel, this fuel is produced by hydrogenation and isomerization of the same feedstocks used to make biodiesel. NREL investigates chemical composition and properties of this fuel in detail, as well as combustion and emissions impacts.

Biomass Pyrolysis-Derived Diesel

Fast pyrolysis of biomass produces a high-oxygen-content liquid that can be upgraded to distillate fuels by hydrogenation. Research at NREL focuses on the basic properties of these fuels and what levels of oxygen can be tolerated in drop-in fuels.

Cellulose-Derived Oxygenates

A variety of oxygenated molecules might be chemically derived from lignocellulosic biomass, which includes sustainable forest and agricultural waste, as well as perennial crops. NREL is evaluating some of these materials for performance as diesel fuels.

Biofuels for Spark-Ignited Engines

NREL researches and develops biofuels for spark-ignited or gasoline engines, which are currently the predominant power source for personal vehicles.


Each year, the United States produces approximately 14 billion gallons of ethanol, and almost all gasoline sold in this country contains 10% of this corn-derived biofuel. NREL research focuses on developing 15% ethanol blends for conventional cars and on understanding the performance of flex-fuel vehicles that can operate on ethanol levels as high as 83%. The lab also is examining how higher level ethanol blends can be used to enable the development of very efficient, high compression ratio, direct injection, turbocharged engines.

Butanol and Long-Chain Alcohols

These fuel blendstocks can be produced from biomass via several processes. NREL research focuses on how blending butanol and long-chain alcohols into gasoline affects fuel properties such as octane number, vapor pressure, and distillation curve. The lab also characterizes impurities and tailpipe emissions.

Biomass Pyrolysis-Derived Gasoline

Fast pyrolysis of biomass produces a high oxygen content liquid that can be upgraded to distillate fuels by hydrogenation. Research at NREL focuses on the basic properties of these fuels, as well as determining what levels of oxygen can be tolerated in drop-in fuels.

Cellulose-Derived Oxygenates

NREL is evaluating several oxygenates that can be derived by chemical reactions from lignocellulosic biomass. Current research is examining oxygenated properties, fuel blend properties, and combustion.

Natural Gas

NREL is investigating compressed natural gas, liquefied natural gas, and natural-gas-derived gas-to-liquids as additional pathways to transportation sustainability. NREL also leads the Natural Gas Vehicle Technology Forum in partnership with the U.S. Department of Energy and the California Energy Commission.