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Ethanol Fuel Basics

July 30, 2013 - 12:00pm

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Ethanol is a renewable fuel made from various plant materials, which collectively are called "biomass." Ethanol contains the same chemical compound (C2H5OH) found in alcoholic beverages. Studies have estimated that ethanol and other biofuels could replace 30% or more of U.S. gasoline demand by 2030.

Nearly half 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 E85, an alternative fuel that can be used in flexible fuel vehicles.

Several steps are required to make ethanol available as a vehicle fuel. Biomass feedstocks are grown and transported to ethanol production facilities. After ethanol is produced at the facilities, a distribution network supplies 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 clear, colorless liquid. Its molecules contain a hydroxyl group (-OH) bonded to a carbon atom.

Ethanol is made of the same chemical compound—and it is the same renewable biofuel—whether it is produced from starch- and sugar-based feedstocks such as corn grain (as it primarily is in the United States) and sugar cane (as it primarily is in Brazil) or from cellulosic feedstocks.

Making ethanol from cellulosic feedstocks—such as grass, wood, crop residues, or old newspapers—is more challenging than using starch or sugars. These materials must first be broken down into their component sugars for subsequent fermentation to ethanol in a process called biochemical conversion. Cellulosic feedstocks also can 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. A gallon of pure ethanol (E100) contains 34% 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 a higher compression ratio, so they generate more power. These engines tend to be found in high-performance vehicles. Low-level blends of ethanol, such as E10 (10% ethanol, 90% gasoline), generally have a higher octane rating than unleaded gasoline. Low-octane gasoline can be blended with 10% ethanol to attain the standard 87 octane requirement.

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 (85% ethanol, 15% gasoline) can be used in flexible fuel vehicles, which are designed to tolerate the fuel's high ethanol content. E85 cannot be used legally in standard gasoline-powered vehicles.

The 15% 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 27% less energy per gallon than gasoline. However, E85 is typically priced lower than gasoline, so that cost per mile is comparable.

More Information

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

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