What is ethanol, and how is it used?

Ethanol is a form of alcohol (think whiskey) that is combustible and can power engines easily. In the United States, it is made in the primarily from corn, but also from a small amount of sugarcane in Louisiana. New types of biorefineries are also being built to create ethanol from non-food material such as wood chips, switch grass and even municipal waste, although these technologies are not yet yielding fuel on a large scale. Overseas, ethanol is more often produced from sugar and wood chips.

The idea of running cars on ethanol is not new. Henry Ford designed the first Model T to run on ethanol so that farmers could produce their own fuel.

Ethanol alcohol for cars is denatured, blended with about 1 percent gasoline to make it non-potable.

In the Unites States, ethanol is sold primarily in two forms. Today, 70 percent of gasoline is blended with ethanol as in a 10/90 ethanol/gasoline mixture called E10, according to the Energy Information Agency. Ethanol in E10 serves as an oxygenate, which helps gasoline burn cleaner to reduce smog. E10 can be used in any new car.

Alternative fuel advocates have promoted a higher blend of ethanol, E85 (85 percent ethanol and 15 percent gasoline) for use in flex-fuel vehicles—models that can operate on gasoline or E85, or any blend in between. In E85, gasoline is used to provide enough starting power for cars in cold weather. (A list of FFVs is available from Growth Energy, a group promoting ethanol use.)

More recently, ethanol advocates have been promoting intermediate blends dispensed with special "blender pumps." Auto engineers say these intermediate blends can still be used only in FFVs, and that expanding their use will require all cars to be made flex-fuel compatible. Using intermediate blends in non-FFVs can cause increased emissions and catalytic converter wear, as well as premature deterioration of fuel-system components, because ethanol is corrosive. FFVs use special fuel tanks, lines, and pumps designed to be more corrosion resistant. Their emissions systems are also specially designed to recognize and compensate for higher blends of ethanol. Making cars E85-compatible costs automakers about $200 per car, according to some estimates. Therefore, engineering a car to run on E85 costs much less than building it to operate on other alternative fuels, such as diesel.

Conventional vehicles could technically be converted to run on E85, but it would be prohibitively expensive once the car leaves the factory, and it may violate emissions-control laws in some states.

Ethanol's lower fuel economy results from its lower energy content compared to gasoline. For example, E85 contains 75,670 British thermal units of energy per gallon instead of 115,400 for regular unleaded gasoline, according to the National Highway Traffic Safety Administration. So you have to burn more fuel to generate the same amount of energy. In addition, FFV engines are designed to run most efficiently on gasoline. Some engineers we interviewed say E85 fuel economy could approach that of gasoline if manufacturers optimized engines for that fuel, however.