Afterburner
An afterburner (or reheat in British English) is an additional combustion component used on some jet engines, mostly those on military supersonic aircraft.
The afterburning process injects additional fuel into a combustor ("burner") in the jet pipe behind (i.e., "after") the turbine, "reheating" the exhaust gas.
Burning all the oxygen delivered by the compressor stages would create temperatures (3,700 °F (2,040 °C)) high enough to significantly weaken the internal structure of the engine, but by mixing the combustion products with unburned air from the compressor at (600 °F (316 °C)) a substantial amount of oxygen (fuel/air ratio 0.014 compared to a no-oxygen-remaining value 0.0687) is still available for burning large quantities of fuel (25,000 lb/h (11,000 kg/h)) in an afterburner.
[12] Duct heating was used by Pratt & Whitney for their JTF17 turbofan proposal for the U.S. Supersonic Transport Program in 1964 and a demonstrator engine was run.
[13] The duct heater used an annular combustor and would be used for takeoff, climb and cruise at Mach 2.7 with different amounts of augmentation depending on aircraft weight.
Otherwise, if pressure is not released, the gas can flow upstream and re-ignite, possibly causing a compressor stall (or fan surge in a turbofan application).
[15] Modern designs incorporate not only variable-geometry (VG) nozzles but multiple stages of augmentation via separate spray bars.
A notable exception is the Pratt & Whitney J58 engine used in the SR-71 Blackbird which used its afterburner for prolonged periods and was refueled in-flight as part of every reconnaissance mission.
Afterburner efficiency also declines significantly if, as is usually the case, the inlet and tailpipe pressure decreases with increasing altitude.
In a military turbofan combat engine, the bypass air is added into the exhaust, thereby increasing the core and afterburner efficiency.
[21] Early American research on the concept was done by NACA, in Cleveland, Ohio, leading to the publication of the paper "Theoretical Investigation of Thrust Augmentation of Turbojet Engines by Tail-pipe Burning" in January 1947.
[22] American work on afterburners in 1948 resulted in installations on early straight-wing jets such as the Pirate, Starfire and Scorpion.
[23] The new Pratt & Whitney J48 turbojet, at 8,000 lbf (36 kN) thrust with afterburners, would power the Grumman swept-wing fighter F9F-6, which was about to go into production.
Other new Navy fighters with afterburners included the Chance Vought F7U-3 Cutlass, powered by two 6,000 lbf (27 kN) thrust Westinghouse J46 engines.
In the 1950s, several large afterburning engines were developed, such as the Orenda Iroquois and the British de Havilland Gyron and Rolls-Royce Avon RB.146 variants.
The Avon and its variants powered the English Electric Lightning, the first supersonic aircraft in RAF service.
The handful of civilian planes that have used them include some NASA research aircraft, the Tupolev Tu-144, Concorde and the White Knight of Scaled Composites.
[citation needed] A "dump-and-burn" is an airshow display feature where fuel is jettisoned, then intentionally ignited using the afterburner.
