Ethanol Fuel Basics
Ethanol is a renewable fuel made from various plant materials collectively known as "biomass." 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 available as E85—a high-level ethanol blend. This alternative fuel can be used in flexible fuel vehicles—a vehicle type that has an internal combustion engine and runs on either E85 or gasoline.
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 made into ethanol at a production facility and transported to a blender/fuel supplier
- Ethanol is mixed with gasoline by the blender/fuel supplier and distributed to fueling stations.
Ethanol as a vehicle fuel is not a new concept. Henry Ford and other early automakers suspected it would be the world's primary fuel before gasoline became so readily available. Today, researchers agree ethanol could substantially offset our nation's petroleum use. In fact, studies have estimated that ethanol and other biofuels could replace 30% or more of U.S. gasoline demand by 2030.
The use of ethanol is required by the federal Renewable Fuel Standard (RFS).
Ethanol (CH3CH2OH) is a clear, colorless liquid. Also known as ethyl alcohol, grain alcohol, and EtOH, the molecules in this fuel contain a hydroxyl group (-OH) bonded to a carbon atom. (See Fuel Properties search.) Ethanol is made of the same chemical compound 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 (which are dedicated energy crops, 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-level ethanol blends generally have a higher octane rating than unleaded gasoline. Low-octane gasoline is blended with 10% ethanol to attain the standard 87 octane requirement. Ethanol is also the main component in E85. (See E85 Specifications to learn more.)
A gallon of ethanol contains less energy than a gallon of pure gasoline. The amount of energy difference varies depending on the blend. For example, a gallon of pure ethanol (E100) contains 34% less energy than a gallon of gasoline.
Ethanol Energy Balance
Ethanol is primarily produced from the starch in corn grain in the United States. Some studies suggest that corn-based ethanol has a negative energy balance, meaning it takes more energy to produce the fuel than the amount of energy the fuel provides. However, recent studies using updated data about corn production methods demonstrate a positive energy balance for corn ethanol.
Cellulosic ethanol, which is produced from non-food based feedstocks, is expected to improve the energy balance of ethanol, because non-food-based 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 is also expected to reduce the amount of fossil fuel energy used in production. Another potential benefit of cellulosic ethanol is that it produces lower levels of greenhouse gas emissions. (See how Ethanol's life cycle energy balance relates to emissions.)
For more information on the energy balance of ethanol, see the U.S. Department of Energy's Biomass Program's Ethanol Myths and Facts, and download the following documents.
- Ethanol - The Complete Energy Lifecycle Picture
- 2008 Energy Balance for the Corn-Ethanol Industry
- Argonne National Laboratory's GREET Model
- DOE response to article, Use of U.S. Croplands for Biofuels Increases Greenhouse Gases through Emissions from Land Use Change
- Life-Cycle Energy Use and Greenhouse Gas Emission Implications of Brazilian Sugarcane Ethanol Simulated with the GREET Model(Abstract)