Following are the sub-topics discussed herein under the general heading of "Fuel" (all links except the Introduction).
Gasoline (petrol) 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, gasoline used as fuel in motor vehicles contained an additive, Tetra Ethyl Lead (TEL) (4.2 grams per gallon) - to improve fuel performance by preventing pre-ignition in the cylinders of the engine. Pre-ignition results in power-reducing knocking, and thus reduced efficiency -- and it can ultimately cause damage to the engine. (See our article on Octane Rating and VW Engines for a more complete discussion of knocking and octane rating.)
In 1984 the allowable level of TEL utilized in gasoline in the U.S. was reduced from 4.2 to 0.1 grams per gallon. To compensate, the concentrations of benzene and other aromatic hydrocarbons (e.g., toluene and xylene) in gasoline was increased to raise the octane rating. However, 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%.
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