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Ethanol Fuel Basics

July 30, 2013 - 12:00pm


biomass in beekers

Ethanol is a renewable fuel that can be made from various plant materials, collectively known as "biomass." Studies have estimated that ethanol and other biofuels could replace 30% or more of U.S. gasoline demand by 2030.

More than 95% of U.S. gasoline contains ethanol in a low-level blend to oxygenate the fuel and reduce air pollution. Ethanol is also increasingly available in a high-level blend called E85, an alternative fuel that can be used in flexible fuel vehicles.

Several steps are required to make ethanol available as a vehicle fuel. First, biomass feedstocks are grown and transported to ethanol production facilities. There, biomass is broken down into its component sugars and converted into ethanol. Afterwards, a distribution network supplies it to fuel blenders, who then ship ethanol-gasoline blends to fueling stations for use by drivers.

What Is Ethanol?

Ethanol (also known as ethyl alcohol, grain alcohol, and EtOH) is a colorless, flammable liquid. It is composed of the same chemical compound (CH3CH2OH) whether it is produced from starch- and sugar-based feedstocks such as corn grain, or from agricultural residues and dedicated energy crops.  

Making ethanol from cellulosic feedstocks—such as agricultural residues, woody plants, and dedicated energy crops—is more challenging than using starch or sugars. These materials must first be broken down into their component sugars for subsequent conversion to ethanol in a process called biochemical conversion. Cellulosic feedstocks can also be converted into ethanol using heat and chemicals in a process called thermochemical conversion.

Ethanol works well in internal combustion engines. In fact, Henry Ford and other early automakers thought ethanol would be the world's primary fuel before gasoline became so readily available. One consideration of ethanol, though, is that a gallon of pure ethanol contains about 30% less energy than a gallon of gasoline.

Ethanol is a high-octane fuel. Octane helps prevent engine knocking and is extremely important in engines designed to operate at high compression ratios, which generate more power. More than 95% of the gasoline in the United States contains up to 10% ethanol to boost its octane level.

Ethanol Blends

Ethanol is blended with gasoline in various amounts for use in vehicles. Low-level blends, up to E10 (10% ethanol, 90% gasoline), are classified as "substantially similar" to gasoline by the U.S. Environmental Protection Agency, meaning they can be used legally in any gasoline-powered vehicle.

E85 (a gasoline-ethanol blend containing 51% to 83% ethanol, depending on geography and season) can be used in flexible fuel vehicles, which are designed to tolerate the fuel's high ethanol content. E85 cannot be used legally in conventional gasoline-powered vehicles.

The gasoline content in E85 enables flexible fuel vehicles to operate normally under cold conditions; fueling a vehicle with pure ethanol (E100) creates problems during cold-weather operation.

Other than lower gas mileage, motorists will see little difference when using E85 versus gasoline. E85 has about 30% less energy per gallon than gasoline. However, E85 is sometimes priced lower than gasoline, so that cost per mile can be comparable.

More Information

Visit the Alternative Fuels Data Center to learn more about ethanol.