Ethanol Fuel Basics
Ethanol is a renewable fuel made from various plant materials collectively known as "biomass". Nearly 97% of U.S. gasoline contains ethanol, typically E10 (10% ethanol, 90% gasoline), to oxygenate the fuel and reduce air pollution.
Ethanol is also available as E85 (or flex fuel), which can be used in flexible fuel vehicles, designed to operate on any blend of gasoline and ethanol up to 83%. Another blend, E15, has been approved for use in newer vehicles, and is slowly becoming available.
There are several steps involved in making ethanol available as a vehicle fuel:
- Biomass feedstocks are grown, collected and transported to an ethanol production facility.
- Feedstocks are converted to ethanol at a production facility and then transported to a fuel terminal or end-user by rail, truck, or barge.
- Ethanol is mixed with gasoline at the fuel terminal to make E10, E15, or E85, and then distributed by truck to fueling stations.
Ethanol (CH3CH2OH) is a clear, colorless liquid. It is also known as ethyl alcohol, grain alcohol, and EtOH (see Fuel Properties search.) Ethanol has the same chemical formula regardless of whether it is produced from starch- and sugar-based feedstocks, such as corn grain (as it primarily is in the United States), sugar cane (as it primarily is in Brazil), or from cellulosic feedstocks (such as wood chips or crop residues).
Ethanol has a higher octane number than gasoline, providing premium blending properties. Minimum octane number requirements prevent engine knocking and ensure drivability. Low-octane gasoline is blended with 10% ethanol to attain the standard 87 octane requirement. Ethanol contains less energy per gallon than gasoline, to varying degrees, depending on the volume percentage of ethanol in the blend. Denatured ethanol (98% ethanol) contains about 30% less energy than gasoline per gallon. Ethanol’s impact on fuel economy is dependent on the ethanol content in the fuel.
Ethanol Energy Balance
In the United States, ethanol is primarily produced from the starch in corn grain. Ethanol produced from corn demonstrates a positive energy balance, meaning that the feedstock and fuel production does not require more energy than the amount of energy contained in the fuel.
Cellulosic ethanol improves the energy balance of ethanol, because cellulosic feedstocks are anticipated to require less fossil fuel energy to produce ethanol. Biomass used to power the process of converting non-food-based feedstocks into cellulosic ethanol also reduces the amount of fossil fuel energy used in production. Another benefit of cellulosic ethanol is that it results in lower levels of life cycle greenhouse gas emissions. (Find out more about emissions related to ethanol.)
For more information on the energy balance of ethanol, visit the U.S. Department of Energy's Bioenergy Technologies Office and download the following documents:
- Ethanol - The Complete Energy Lifecycle Picture (pdf)
- 2008 Energy Balance for the Corn-Ethanol Industry (pdf)
- Argonne National Laboratory's GREET Model (Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation Model)
- DOE response to article, Use of U.S. Croplands for Biofuels Increases
- Greenhouse Gases through Emissions from Land Use Change