Fuel ethanol is a denatured alcohol that meets the standard specification use as a fuel in spark-ignition engines.
Ethanol is Made From Biomass
Most of the fuel ethanol produced around the world is made by fermenting the sugar in the starches of grains such as corn, sorghum, and barley, and the sugar in sugar cane and sugar beets. In the United States, nearly all fuel ethanol is produced from corn kernel starch, which is considered a traditional biofuel in the United States. Brazil—the world's second-largest consumer of fuel ethanol after United States—uses sugar cane to produce ethanol.
Other potential sources of ethanol come from fermented feedstocks including corn and rice stalks, fast-growing poplar and willow trees, grasses such as switchgrass and bamboo, algae, and biomass in municipal solid waste. Trees and grasses require less fuel, fertilizers, and water to grow than grains do, and they can be grown on lands that are not suitable for growing food crops. Ethanol made from these sources is called cellulosic ethanol and is considered an advanced biofuel. However, despite the technical potential for cellulosic ethanol production from those sources, economical production has been difficult to achieve. As of the end of 2020, there was no commercial cellulosic ethanol production in the United States.
Ethanol As a Transportation Fuel
The History of Ethanol Use
Ethanol was one of the first automotive fuels in the United States. With the exception of the two world wars, only small amounts of fuel ethanol were used until the 1970s. The oil embargo against the United States by major oil producers in the Middle East in 1973 and increases in oil prices in the late 1970s and early 1980s spurred interest in fuel ethanol as a way to reduce U.S. oil imports for making gasoline. Various state and federal government policies and programs dating as far back as the mid-1970s have led to increased ethanol use in gasoline. About two million gallons of fuel ethanol were consumed in 1981, and about 13.9 billion gallons were consumed in 2021.
Fuel ethanol use increased significantly in 2002 as states began to ban the use of the gasoline additive known as methyl tertiary butyl ether (MTBE) because of concerns that it contaminated groundwater. Ethanol quickly replaced MTBE across the country. Ethanol use also increased after Congress passed the Renewable Fuel Standard (RFS) requirements under the Energy Policy Act of 2005 and then expanded and extended the RFS under the Energy Independence and Security Act of 2007. The U.S. Renewable Fuel Standard (RFS) Program ensures that transportation fuel sold in the United States contains a minimum volume of renewable fuel.
Ethanol is Blended With Gasoline - Understanding E10, E15, and E85
The most common use of ethanol as a fuel is in mixtures of finished motor gasoline. Most of the gasoline sold in the United States contains some ethanol. Gasoline fueling pumps that dispense motor gasoline containing fuel ethanol in the United States identify or label the gasoline according to its ethanol content. There are three basic labelling categories according to the maximum level of the ethanol blend: E10, E15, and E85.The exact amount may vary by region and season of the year. but nearly all of the motor gasoline sold in the United States is about 10% ethanol by volume, and gasoline that is 10% ethanol by volume is called E10. Any gasoline-powered vehicle in the United States can use E10. Cars, light trucks, and medium-duty vehicles of model year 2001 and newer can also use E15, which is about 10% ethanol by volume. Only flexible-fuel vehicles can use gasoline with ethanol content greater than 15%. Flex-fuel vehicles can run on any mixture of ethanol and gasoline up to E85. Flex-fuel vehicles may be identified by a badge or plaque on the body of the vehicle with terms such as E85, Flex Fuel, or FFV.
E85 is a gasoline-ethanol blend containing 51% to 83% ethanol, depending on geography and season, is mainly sold in the Midwest and can only be used in a flexible-fuel vehicle. E85 is defined as an alternative fuel. Although most E85 use in the United States occurs in the Midwest, there are about 4,180 public E85 fueling stations located around the country.
Gasoline that does not contain ethanol - E0 (or ethanol-free gasoline) - may be available in some locations around the country for use in gasoline-powered tools, landscaping equipment, boats, and other equipment with gasoline engines for which E0 is recommended.
Because ethanol contains about 67% of the energy content of gasoline per gallon, use of ethanol blends results in lower vehicle fuel economy (miles traveled per gallon) relative to gasoline that does not contain ethanol. For example, vehicle fuel economy may decrease by about 3% when using E10.
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