There's A Special Chemistry To Gasoline

March 01, 1998|By Bob Weber. Special to the Tribune.

There's more to gasoline than you might imagine

And there is no such thing as pure gasoline. The stuff you pump in your car is a mixture of more than 200 hydrocarbons including paraffins, olefins, naphthenes and other aromatics.

To this base, many additives are added.

One of the first additives was lead (tetraethyl lead), which raised the octane. About the same time, gum-fighting and antioxidant compounds were added. Because of its toxicity, lead was gradually eliminated beginning in the 1970s.

After World War II, pipelines through which the gas is shipped added corrosion inhibitors to keep rust out of the gas.

In the '50s, detergents were introduced to keep carburetors clean.

They also kept fuel injectors clean in the 1980s, but caused deposits to build up on the backs of the intake valves, which created driveability problems-- especially on cold engines.

To combat this, polyether amines were added, which not only keep the valves clean, but also tend to keep combustion chamber deposits from forming. By law, all gasolines were required to add these beginning in 1995.

Anti-icing compounds are often blended into the fuel in the colder parts of the nation.

To reduce carbon monoxide emissions, the Environmental Protection Agency requires polluted parts of the country, including Chicago, to blend oxygenates into the fuel.

The two most common are MTBE (methyl tertiary butyl ether) and ethanol. In the Midwest, ethanol from corn is more common. Both reduce fuel economy slightly.

Additive ingredient packages, protected more closely than the recipe for Frango Mints, are what separate one company's gasoline from another's.