page_title: Afterburner
section_title: Thrust augmentation by heating bypass air
hierarchical_section_title: Afterburner / Thrust augmentation by heating bypass air
caption_attribution_description: English: Bristol Siddeley BS100 turbofan engine on display at the Fleet Air Arm Museum, RNAS Yeovilton.
context_page_description: An afterburner is an additional combustion component used on some jet engines, mostly those on military supersonic aircraft. Its purpose is to increase thrust, usually for supersonic flight, takeoff, and combat. Afterburning injects additional fuel into a combustor in the jet pipe behind the turbine, "reheating" the exhaust gas. Afterburning significantly increases thrust as an alternative to using a bigger engine with its attendant weight penalty, but at the cost of very high fuel consumption which limits its use to short periods. This aircraft application of reheat contrasts with the meaning and implementation of reheat applicable to gas turbines driving electrical generators and which reduces fuel consumption.
  Jet engines are referred to as operating wet when afterburning is being used and dry when not. An engine producing maximum thrust wet is at maximum power, while an engine producing maximum thrust dry is at military power.
context_section_description: Thrust may be increased by burning fuel in a turbofan's cold bypass air, instead of the mixed cold and hot flows as in most afterburning turbofans. 
  An early augmented turbofan, the Pratt & Whitney TF30, used separate burning zones for the bypass and core flows with three of seven concentric spray rings in the bypass flow. In comparison, the afterburning Rolls-Royce Spey used a twenty chute mixer before the fuel manifolds.
  Plenum chamber burning (PCB), was developed for the vectored thrust Bristol Siddeley BS100 engine for the Hawker Siddeley P.1154. The cold bypass and hot core airflows were split between two pairs of nozzles, front and rear, in the same manner as the Rolls-Royce Pegasus, and additional fuel and afterburning was applied to the front nozzles only. It would have given greater thrust for take-off and supersonic performance in an aircraft similar to, but bigger, than the Hawker Siddeley Harrier.
  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. 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.
caption: The plenum chamber burning Bristol Siddeley BS100. In this vectored thrust engine reheat was applied to the front two nozzles only
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