afterburner
Second combustion chamber in a turbojet or turbofan engine, immediately in front of the engine's exhaust nozzle. The injection and combustion of extra fuel in this chamber provide additional thrust for takeoff or supersonic flight; in most cases, the afterburner can nearly double the thrust of a turbojet engine. The jet nozzle must be larger when using the afterburner, so an automatic, adjustable nozzle is an essential component of the afterburner system. Because the afterburner sharply increases fuel consumption and is generally less effective at subsonic speeds, its use is usually restricted to supersonic military aircraft.
afterburner [′af·tər‚bər·nər]
Afterburner
a secondary combustion chamber in certain turbojet engines that is used to augment the engine thrust for a short time (see). An engine equipped with an afterburner is called an afterburning engine.
An afterburner is situated between the turbine and the jet nozzle of a turbojet engine or a dual-cycle engine. The gas that leaves the turbine still contains much oxygen; in a turbojet engine, this gas alone enters the diffuser of the afterburner. In a dual-cycle engine, a mixture of the gas that leaves the turbine and air from a bypass duct enters the diffuser. The speed of the gas flow is reduced in the diffuser, and fuel—usually aviation kerosene—is then injected into the flow. When the fuel is burned in the afterburner, the temperature rises and the exhaust jet velocity increases.
Flameholders are used so that the combustion process occurs over the shortest possible distance. A liner is employed to shield the walls of the afterburner. The afterburner is started by a flame from a precombustion chamber (see Figure 1).
Afterburners may also be used to boost the power of free-piston engines.
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