gasoline

—gasolineless, adj. —gasolinic /gas'euh lee"nik, -lin"ik/, adj.

/gas'euh leen", gas"euh leen'/, n.

a volatile, flammable liquid mixture of hydrocarbons, obtained from petroleum, and used as fuel for internal-combustion engines, as a solvent, etc.

[1860-65, Amer.; GAS + -OL² + -INE²]

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British petrol

Mixture of volatile, flammable hydrocarbons derived from petroleum, used as fuel for internal-combustion engines and as a solvent for oils and fats.

Gasoline became the preferred automobile fuel because it releases a great deal of energy when burned, it mixed readily with air in a carburetor, and it initially was cheap due to a large supply. Costs have now increased greatly except where subsidized. Gasoline was first produced by distillation. Later processes increased the yield from crude oil by splitting large molecules into smaller ones. Still other methods, such as conversion of straight-chain hydrocarbons into their branched-chain isomers, followed. The resulting gasoline is a complex mixture of hundreds of hydrocarbons. A gasoline's octane number indicates its ability to resist knocking (premature combustion) and can be altered by changing the proportions of certain components. The compound tetraethyl lead, once used to reduce knocking, has been banned as toxic. Other additives include detergents, antifreezes, and antioxidants. Since the mid-20th century gasoline fumes have been recognized as a major component of urban air pollution. Efforts to reduce dependence on gasoline, which is a nonrenewable resource, include use of gasohol, a 9:1 mix of gasoline and ethanol, and the development of electric automobiles.

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▪ chemistry

also spelled  Gasolene,  also called  Gas, or Petrol,  

      mixture of volatile, flammable liquid hydrocarbons derived from petroleum and used as fuel for internal-combustion engines. It is also used as a solvent for oils and fats. Originally a by-product of the petroleum industry (kerosene being the principal product), gasoline became the preferred automobile fuel because of its high energy of combustion and capacity to mix readily with air in a carburetor.

      Gasoline was at first produced by distillation, simply separating the volatile, more valuable fractions of crude petroleum. Later processes, designed to raise the yield of gasoline from crude oil, split large molecules into smaller ones by processes known as cracking. Thermal cracking, employing heat and high pressures, was introduced in 1913 but was replaced after 1937 by catalytic cracking, the application of catalysts that facilitate chemical reactions producing more gasoline. Other methods used to improve the quality of gasoline and increase its supply include polymerization, converting gaseous olefins, such as propylene and butylene, into larger molecules in the gasoline range; alkylation, a process combining an olefin and a paraffin such as isobutane; isomerization, the conversion of straight-chain hydrocarbons to branched-chain hydrocarbons; and reforming, using either heat or a catalyst to rearrange the molecular structure.

      Gasoline is a complex mixture of hundreds of different hydrocarbons. Most are saturated and contain 4 to 12 carbon atoms per molecule. Gasoline used in automobiles boils mainly between 30° and 200° C (85° and 390° F), the blend being adjusted to altitude and season. Aviation gasoline contains smaller proportions of both the less-volatile and more-volatile components than automobile gasoline.

      The antiknock characteristics of a gasoline—its ability to resist knocking, which indicates that the combustion of fuel vapour in the cylinder is taking place too rapidly for efficiency—is expressed in octane number. The addition of tetraethyllead to (tetraethyl lead) retard the combustion was initiated in the 1930s but was discontinued in the 1980s because of the toxicity of the lead compounds discharged in the combustion products. Other additives to gasoline often include detergents to reduce the buildup of engine deposits, anti-icing agents to prevent stalling caused by carburetor icing, and antioxidants (oxidation inhibitors) used to reduce “gum” formation.

      In the late 20th century the rising price of petroleum (and hence of gasoline) in many countries led to the increasing use of gasohol, which is a mixture of 90 percent unleaded gasoline and 10 percent ethanol (ethyl alcohol). Gasohol burns well in gasoline engines and is a desirable alternative fuel for certain applications because of the renewability of ethanol, which can be produced from grains, potatoes, and certain other plant matter. See also petroleum.

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