Clean Cities Technical Response Service Question of the Month.

Question of the Month: What emerging alternative fuels are under development or are already developed and available in the United States?

Answer: Clean Cities coordinators and stakeholders are familiar with the most commonly used alternative fuels, which have been covered over the last several months in the Question of the Month “key terms” series. However, there are also several emerging fuels that are currently under development or already in use in the United States. Like other alternatives, these fuels can increase energy security, reduce emissions, improve vehicle performance, and stimulate the U.S. economy. In addition, some are considered alternative fuels under the Energy Policy Act of 1992 ( and may qualify for federal and state incentives.

Below we have listed a few emerging alternative fuels, their characteristics, and their benefits:

  • Biobutanol (butyl alcohol):
    • Composition and production: Biobutanol is a 4-carbon alcohol that can be produced from the same feedstocks as ethanol, including corn, sugar beets, and other biomass wastes.
    • Use as a transportation fuel: Biobutanol can be blended with other fuels for use in conventional gasoline vehicles.
    • Benefits: Domestically produced from various feedstocks, Produces fewer emissions than gasoline, High energy content, Blends well with gasoline and ethanol, Can be produced using existing ethanol production facilities with some modifications, Less soluble in water than ethanol, thus less likely to cause a sludge build-up in fuel tanks.
  •  Drop-In Biofuels:
    • Composition and production: Drop-in biofuels are hydrocarbon fuels that are substantially similar to petroleum-based gasoline, diesel, or jet fuels. They can be produced from various biomass feedstocks, such as crop residues, woody biomass, dedicated energy crops, vegetable oils, fats, greases or algae.
    • Use as a transportation fuel: Drop-in biofuels are in an early stage of development, with several commercial plants in the United States and abroad. The focus is aimed at eventually replacing gasoline, diesel, and jet fuel.
    • Benefits: Domestically produced from biomass feedstocks, Produces fewer emissions than conventional fuels, Compatible with existing engines and infrastructure, Can be used as replacement fuel for diesel, jet fuel, and gasoline can be produced from various feedstocks and production technologies at stand-alone plants or those located alongside petroleum refineries where drop-in fuels can be inserted into the refinery process
  •  Methanol:
    • Composition and production: Methanol, or wood alcohol, has similar chemical and physical fuel properties to ethanol. Methanol can be produced using various feedstocks, including carbon-based feedstocks, such as coal. However, natural gas is currently the most economical feedstock.
    • Use as a transportation fuel: In the 1990s, 100% methanol and 85% methanol/15% gasoline blends (M85) were used in compatible vehicles, similar to ethanol flexible fuel vehicles (FFVs) on the market today. The National Renewable Energy Laboratory is currently researching ways to use methanol for fuel cell vehicles.
    • Benefits: Domestically produced, Produces fewer emissions than conventional fuels, Low production costs, Improves safety compared to gasoline due to lower risk of flammability.
  •  Renewable Natural Gas (Biomethane):
    • Composition and production: Renewable natural gas (RNG), also known as biomethane, is pipeline-quality gas that is fully interchangeable with fossil natural gas. RNG is essentially biogas (also known as swamp gas, landfill gas, or digester gas) that has been processed to purity standards. Biogas is typically composed of 50-80% methane, 20-50% carbon dioxide, and trace gases such as hydrogen, carbon monoxide, and nitrogen. It is produced by decomposing organic matter, such as sewage, animal byproducts, and agricultural, industrial, and municipal solid wastes.
    • Use as a transportation fuel: Renewable natural gas can be used in existing natural gas vehicles without modification.
    • Benefits: Can be produced domestically at facilities alongside landfills, sewage treatment plants, or livestock operations. This allows for the systems to use the biogas as a renewable power source to run their operations.  Reduces emissions by capturing methane, a potent greenhouse gas, and keeping it from being released into the atmosphere. Reduces the cost to landfills to comply with U.S. Environmental Protection Agency combustion requirements.  Reduces landfill, sewage, and livestock wastes and odors, produces nutrient-rich fertilizer, and requires less land than aerobic composting
  •  xTL Fuels (Fischer-Tropsch):
    • Composition and production: Synthetic liquid transportation fuels, otherwise known as xTL fuels, are produced through various conversion processes. These processes convert fuels from carbon-based feedstocks to yield various fuels, such as gasoline, diesel, ethanol, and methanol. In particular, the Fischer-Tropsch process produces liquid fuels from coal and natural gas. Coal can also be converted into liquids through liquefaction.
    • Use as a transportation fuel: Much like drop-in biofuels, xTL fuels can replace conventional petroleum diesel for use in vehicles without modifications to the engine or fueling infrastructure.
    • Benefits: Can be produced domestically using the United States’ vast coal reserves and natural gas, Reduces greenhouse gas emissions, Fischer-Tropsch diesel emits little or no particulate emissions due to its low sulfur and aromatic content, as well as its reduced hydrocarbon and carbon monoxide emissions, Compatible with current diesel and gasoline powered vehicles and fueling infrastructure, Provides similar or better vehicle performance than conventional fuels, Converts relatively inflexible energy sources, such as coal or biomass, into useful transportation fuels
  •  Dimethyl ether (DME):
    • Composition and production: DME is a non-toxic, colorless gas that can be easily liquefied to a biodegradable synthetic liquid fuel. It is produced from various feedstocks, such as natural gas, coal, biomass, or even carbon dioxide.
    • Use as a transportation fuel: DME can be used in conventional diesel engines and stored in similar vehicle storage tanks to those used for propane fuel.
    • Benefits: Domestically produced, Emits no particulate matter, no sulfur oxides, and very low levels of nitrous oxides and carbon dioxide, Provides similar or better vehicle performance than conventional fuels due to the high cetane number, Easy to store and transport, and liquefies at low pressure, removing the need for costly, high-pressure storage containers

More information on emerging alternative fuels can be found on the AFDC Emerging Alternative Fuels page 

For more information on DME, please see SAE International’s presentation DME from Natural Gas or Biomass: A Better Fuel Alternative