Oxygenated Fuels

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% methanol 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.

ADDITIVES
Additives are blended with gasoline for better performance. Gasoline typically contains several of the following:

Antiknock Agents
MTBE and ethanol (oxygenated fuels) are the two most common antiknock agents. Toluene (aromatic hydrocarbon) is another common antiknock additive.

Detergent/Deposit Control Agents
Detergents and deposit control agents are found in most fuels to help prevent and, in some cases, remove deposits from the throttle body, [1][2]intake manifold, ports, fuel injectors, and valves.

Anti-oxidants
Anti-oxidant additives stabilize fuel during storage and shipment, which helps reduce gum formation.

Metal Deactivators
A metal deactivator inhibits the oxidation of the fuel which is catalyzed by trace metals such as copper.

Corrosion Inhibitors
Corrosion inhibitors prevent the corrosion of iron.

Dyes
Dyes are used to identify different fuel grades and brands (by color).

Anti-icing Agents
Anti-icing agents help prevent ice formation that may cause restrictions and possible stalls. In cold weather, as humid air passes over a throttle plate, moisture can condense and freeze on the throttle plate.