Gasoline is the most widely-used automotive fuel. Gasoline is a mixture of mostly saturated (fully hydrogenated) hydrocarbons of between four and twelve carbon atoms; ordinary commercial grades also contain paraffins, olefins, naphthenes, and aromatics in substantial concentration. Gasoline is obtained by fractional distillation of hydrocarbons.
From the mid 1920's until the mid 1980's motor gasoline fuel contained an additive, tetraethyllead (less than 3 ml per gallon), that improved fuel performance by preventing preignition in the cylinders of the engine. Preignition resulted in damaging and efficiency and power reducing knocking. (See Octane Rating and VW Engines for a more complete discussion of knocking and octane rating.)
In 1984 the allowable level of lead utilized in gasoline in the U.S. was reduced from 4.2 to 0.1 grams per gallon. Increasing the concentrations of benzene and other aromatic hydrocarbons (e.g., toluene and xylene) in gasoline is one way to increase the gasoline's octane rating. Benzene is a carcinogen, and the content of benzene and other aromatics must be considered when choosing a manufacturing process for unleaded gasoline. In the United States, the benzene content of gasoline is limited to 1%; in the European Community and Australia, it is limited to 5%.
Following are the sub-topics discussed herein under the general heading of "Fuel."
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Last revised 5 May 2004.
