Aircraft fuel

(materials) The material used as a source of energy by an aircraft engine to provide propulsion.

The source of energy required for the propulsion of airborne vehicles. Aircraft fuel is burned with ambient air and is thereby distinct from rocket propellants, which carry both fuel and oxidant. An important criterion for aircraft fuel is that its energy density, or heat of combustion per unit of weight, be high. This allows reasonable expenditures of fuel during takeoff, efficient performance in flight, and long range of flight duration.

There are two general types of aircraft fuels in conventional use: gasolines for reciprocating (piston) engines, and kerosene-like fuels (called jet fuels) for turbine engines. Because of anticipated limitations in the supply of these crude-oil derived fuels, alternative fuels are being considered for future aircraft.

Piston engine fuels, or aviation gasolines, are special blends of gasoline stocks and additives that produce a high-performance fuel that is graded by its antiknock quality. The gasoline blending stocks are virgin (uncracked) naphtha, alkylate, and catalytically cracked gasoline. In general, the chemical composition of aviation gasoline can be approximated as C_xH_1.9x where the number of carbon atoms x is between 4 and approximately 10. Tetraethyllead (Tel) is a common additive used in concentrations of up to 4 ml/gal (1.057 ml/liter) of fuel to increase the antiknock quality of the fuel. See also Gasoline; Naphtha.

Turbine engine fuels are distillate hydrocarbon fuels, like kerosenes, used to operate turbojet, turbofan, and turboshaft engines. While all piston engine fuels have the same volatility but differ in combustion characteristics, jet fuels differ primarily in volatility; differences in their combustion qualities are minor. Turbine fuel contains aromatic hydrocarbons; limits are placed on this content owing to concerns about smoke and coke formation. An increasingly important requirement is to provide a fuel that is stable at relatively high temperatures.

Many forecasts of world crude production indicate a peak or plateau in the oil production rate before 2010; hence, the availability of crude-based fuels for aircraft is not certain. Alternative fuels made from coal, oil shale, or solar or nuclear energy plus a suitable raw material are being considered.