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, typically E10 (10% ethanol, 90% gasoline), to oxygenate the fuel and reduce air pollution.
Ethanol is also available as E85, or high-level ethanol blends. This fuel can be used in flexible fuel vehicles, which can run on high-level ethanol blends, gasoline, or any blend of these. Another blend, E15, has been approved for use in newer vehicles, and is slowing 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
- Ethanol is produced from feedstocks at a production facility and then transported to a blender/fuel supplier
- Ethanol is mixed with gasoline by the blender/fuel supplier to make E10, E15 or E85, 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. 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 is the main component in high-level ethanol blends. (See E85 Specification to learn more.)
Ethanol contains less energy per gallon than gasoline, to varying degrees, depending on the volume percentage of ethanol in the high-level blend. Per gallon, ethanol contains about 30% less energy than gasoline. E85 contains about 25% less energy than gasoline.
Ethanol Energy Balance
In the United States, ethanol is primarily produced from the starch in corn grain. Recent studies using updated data about corn production methods demonstrate a positive energy balance for corn ethanol, meaning that fuel production does not require more energy than the amount of energy contained in the fuel.
Cellulosic ethanol, which is produced from cellulosic feedstocks, is expected to improve 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 is also expected to reduce the amount of fossil fuel energy used in production. Another potential 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, see the U.S. Department of Energy's Bioenergy Technologies Office'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)