Vehicle Emissions Reduction

Ethanol

Ethanol has attracted considerable attention as a motor fuel due to the success of the Brazilian Prooalcool program. Despite the technical success of this program, however, the high cost of producing ethanol (compared to hydrocarbon fuels) means that it continues to require heavy subsidies.

As the next higher of the alcohols in molecular weight, ethanol resembles methanol in most combustion and physical properties. The major difference is in the higher volumetric energy content of ethanol. Fuel grade ethanol, as produced in Brazil, is produced by distillation, and contains several volume percent of water. In addition, pure (anhydrous) ethanol is used as a blend stock for gasoline both in Brazil and in the US By blending 22% anhydrous ethanol with gasoline to produce gasohol, Brazil was able to quickly eliminate completely the requirement for lead as an octane enhancer.

Emissions from ethanol-fueled engines are not well characterized, but are believed to be high in unburned ethanol, acetaldehyde, and other aldehydes. These can be controlled with a catalytic converter. Uncontrolled NOx emissions should be somewhat higher than for methanol, but still lower than for gasoline engines. Cold starting of ethanol engines is not a serious problem in the warm Brazilian climate, but could be a concern in countries with cold winters.

Ethanol is produced primarily by fermentation of starch from grains or sugar from sugar cane. As a result, the production of ethanol for fuel is in direct competition with food production in most countries. The resulting high price of ethanol has effectively ruled out its use as a motor fuel except where (as in Brazil and the US) it is heavily subsidized. The Brazilian Prooalcool program to promote the use of fuel ethanol in motor vehicles in that country has attracted worldwide attention as the most successful example of an alternative fuel implementation program extant. Despite the availability of a large and inexpensive biomass resource, however, this program still depends on massive government subsidies for its viability.

• Alternative fuels - Ethanol