Ethanol fuel is ordinary drinkable alcohol used as a fuel source. It is a renewable resource derived from plants, unlike gasoline, to which it is often blended. Ethanol is used extensively as a fuel in the United States and Brasil.
Ethanol has significant differences in chemistry vs. gasoline, and an internal combustion engine tuned well for one is not tuned for the other. However, blended fuels are a mixture of both, and flexible fuel vehicles can change their parameters to handle either.
Among the significant differences between fuels, ethanol contains 2/3 the energy of gasoline. This would mean that 1.5 gallons of ethanol are required to substitute for 1 gallon of gasoline. However, ethanol has a higher octane rating and therefore can tolerate a higher engine compression ratio. This increases fuel efficiency so that the expected 2/3 fuel economy becomes rather 3/4.
Ethanol has a reputation for corroding engines. Ethanol can contain dissolved ions such as chloride that react with the engine metal, and dissolved metal ions cause further problems. Second, contaminants increase the conductivity of the alcohol which generates galvanic corrosion. Ethanol also tends to absorb water from the air. Water interferes with the fuel operation, being non-explosive. It can separate out of solution and clog fuel lines.
Most gasoline in the United States is a blend with 10% ethanol. In Brazil, the fraction is 25%, and flex fuel vehicles can accept any fraction.
Ethanol is commonly produced by fermenting sugar or starch (broken into sugars). In the United States, corn starch is a favorite input, and in Brazil, sugar cane. Conceivably, cellulose could be an input. It, like starch, is composed of a chain of sugar molecules. Use of cellulose is not yet economical, however. Fuel ethanol must be distilled to separate it from other fermantation products and to remove water. Optionally, it may be denatured so that it cannot be used as drinking alcohol.
In 2014, 25 billion gallons of ethanol fuel were produced, mainly by the US and Brasil.