The following is an excerpt from Sustainable Ethanol: Biofuels, Biorefineries, Cellulosic Biomass, Flex-Fuel Vehicles, and Sustainable Farming for Energy Independence
E10, E85, and Flex-Fuel Vehicles
You might already be using ethanol in your car. E10 (10% ethanol) is widely available and approved by automobile makers. You might even be driving a vehicle that can burn up to 85% ethanol (E85). E85 is formulated for flex-fuel vehicles. These vehicles look the same as other cars, trucks, and vans, but run perfectly on anywhere from 0% to 85% ethanol.
Ethanol, also known as ethyl alcohol or fuel alcohol, is a potent version of drinking alcohol with the molecular formula CH3CH2OH. The federal government requires fuel alcohol to be denatured by adding up to 5% gasoline or other denaturant, “poisoning” the brew to prevent human consumption.[i]
The “E” in E10 and E85 stands for ethanol, while the numbers indicate ethanol percentage. E10 is 10% denatured ethanol and 90% gasoline. E85 is 85% denatured ethanol and 15% gasoline. Because the ethanol is denatured, E85 and E10 actually have slightly less than 85% or 10% ethanol content. Ethanol percentage also varies on a seasonal basis. E85 can contain as little as 75% denatured ethanol during the winter to help with cold weather starting.[ii]
E10 Price and Fuel Economy
Due to tax breaks and sometimes lower production costs, ethanol is usually less expensive than gasoline. Not only is ethanol less expensive, but it also adds 2.5–3 octane points (a measure of engine knock resistance[xi]) to E10 gasoline.[xii] Ethanol can be an ingredient in low octane gasoline by using a low octane blendstock (base gasoline). More often, though, ethanol is used in higher-octane gasolines (mid-grade or premium).
During 2005, 2–4 cents was the normal discount for E10 according to Ron Lamberty of the American Coalition for Ethanol.[xiii] In Missouri during 2007, E10 could be had for as much as 10 cents less per gallon than the least expensive ethanol-free gasoline. Since E10 causes little or no loss in fuel economy in many vehicles, a lower price can mean actual savings. At the 10% level, the favorable combustion properties of ethanol more or less compensate for its lower energy density. A 1998 Study by the U.S. EPA showed an average 1.64% gain in miles per gallon for E10 as compared to ethanol-free gasoline. Tests were performed at 0°F and 75°F on 11 vehicles, model years 1977 to 1994.[xiv] The American Coalition for Ethanol conducted a fuel economy study of three passenger cars, model year 2005. They detected an average 1.47% lower fuel economy for E10 as compared to unleaded gasoline without ethanol.[xv] This translates to an average 0.41 fewer miles per gallon—less reduction than you would expect based on energy density alone.
See chapter 5 of Sustainable Ethanol for these additional topics:
Running on E10
Running on E85
Purchasing a Flex-Fuel Vehicle
E85 Cost and Fuel Economy
Figure 5-1. Same location U.S. National Average Retail Gasoline and E85 Prices, 2006-2007
Figure 5-2. Break-even Prices for Gasoline Alternatives Based on FuelEconomy Reduction
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[i]. U.S. DOE National Renewable Energy Laboratory & National Ethanol Vehicle Coalition, Handbook for Handling, Storing, and Dispensing E85, 2002, 2.
[ii]. Keith Reid, “Alcohol at the Pump,” National Petroleum News, (August 2005): 40.
[xi]. John D. Heywood, Internal Combustion Engine Fundamentals (New York: McGraw-Hill, 1988), 852.
[xii]. Reynolds, Gasoline Ethanol Blends, 3.
[xiii]. Nate Jenkins, “Buying E10 May Not Always Save Money,” Lincoln Star Journal, October 14, 2005.
[xiv]. Based on tests reported by KT Knapp, FD Stump, & SB Tejada, “The Effect of Fuel on the Emissions of Vehicles over a Wide Range of Temperatures,” Journal of the Air & Waste Management Association 43 (July 1998).
[xv]. Based on tests by the American Coalition for Ethanol, Fuel Economy Study, 2005, http://www.ethanol.org/documents/ACEFuelEconomyStudy.pdf.