Oxygenated Fuels

Beginning Nov. 1, 1992, oxygenated fuels are required in 39 carbon monoxide non-attainment areas of the U.S. during the winter months. By slightly increasing the oxygen in the air/fuel mix, combustion can be improved and carbon monoxide emissions reduced.

Oxygenated fuels contain oxygen in their chemical makeup. Common oxygenated fuels are methyl tertiary-butyl ether (MTBE) and ethanol. When blended with gasoline, oxygenated fuels increase the octane rating and lower carbon monoxide emissions.

Methyl Tertiary-Butyl Ether (MTBE)  - MTBE is an ether manufactured by reacting methanol and isobutylene. Present laws permit fuel to contain a maximum of 15% MTBE. Fuel with 15% MTBE will raise the pump octane by about 2.5 octane numbers, will not increase RVP, is not sensitive to water, will reduce tailpipe CO emissions, and is not harmful to the engine.

Ethanol  - Ethanol (grain alcohol) is a renewable resource produced from corn or sugar cane. Present laws permit gasoline to contain a maximum of 10% ethanol. Ten percent ethanol boosts the gasoline's octane by 2.5 to 3 octane numbers, raises RVP by 1 psi, and lowers tailpipe CO emission levels. Ethanol has the ability to absorb water and thus prevent fuel line freeze-up. However, excessive water causes the ethanol to separate from the gasoline.

Methanol  - Methanol (wood alcohol) is produced from natural gas or coal. Methanol contains about 50% oxygen. Fuel that is more than 5% methane is bad for the engine and should not be used. It can corrode metal parts in the fuel system and damage plastic and rubber. To avoid these problems, cosolvents and corrosion preventers must be added to the fuel. Five percent methanol boosts the gasoline's octane by 2.5 to 3 octane numbers but raises RVP by 3 psi. This higher RVP results in more fuel evaporating into the atmosphere.