Aviation Gasoline

Avgas (aviation gasoline) is a high-octane fuel used for airplane using piston or Wankel engines.   Gas turbines can operate on avgas, but typically do not.   Turbine and diesel engines are designed to use kerosene-based jet fuel.   Avgas has a lower volatility, i.e., does not evaporate as quickly, than mogas (motor gasoline=automobile gasoline), which is important for high-altitude use and higher temperatures.   The particular mixtures in use today are the same as when they were first developed in the 1950s and 1960s, and therefore the high-octane ratings are achieved by the addition of tetra-ethyl lead (TEL), a highly toxic substance that was phased out for automobile use in most countries in the 1980s.   The main petroleum component used in blending avgas is alkylate, which is a mixture of high-octane isoctanes formed by an alkylation process, and some refineries add reformate, complex hydrocarbons made from simpler hydrocarbons by catalytic reforming. ^{Wiki n.p.}

Avgas is available in several grades with differing maximum lead concentrations.   Since TEL is an expensive additive, a minimum amount of it is typically added to the fuel to bring it up to the required octane rating so actual concentrations are often lower than the maximum.   To avoid the carcinogenic and polluting gasoline, some airplane engines are fitted with highly fuel-efficient diesel engines running on jet fuel.   Civilian aircraft use Jet-A, Jet-A1 or in severely cold climates, Jet-B.   There are other classification systems for military turbine and diesel fuel. ^{Wiki n.p.}

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