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Bleed air in aerospace engineering is compressed air taken from the compressor stage of a gas turbine, upstream of its fuel-burning sections.Automatic air supply and cabin pressure controller (ASCPC) valves bleed air from low or high stage engine compressor sections; low stage air is used during high power setting operation, and high stage air is used during descent and other low power setting ...
Low pressure (40–70 psi or 280–480 kPa), high volume air from the compressor section of the APU is bled off through a system of pipes to the engines where it is directed into the starting system. This bleed air is directed into a mechanism to start the engine turning and begin pulling in air. The starter is usually an air turbine type ...
The compressed air can be supplied from an on-board auxiliary power unit (APU), a portable gas generator used by ground crew or by cross feeding bleed air from a running engine in the case of multi-engined aircraft. [19] The Turbomeca Palouste gas generator was used to start the Spey engines of the Blackburn Buccaneer.
In some aircraft, the shut-off function is a different valve located after the fuel selector valve. Typically, after the selector valve—situated at a low point in the fuel run—there is a gascolator — a fuel filter that can be opened on the ground and drained of fuel impurities denser than petroleum, mainly water and sediment. Other ...
Air bled from the engine fan is blown across the pre-cooler, located in the engine strut, and absorbs excess heat from the service bleed air. A fan air modulating valve (FAMV) varies the cooling airflow to control the final air temperature of the service bleed air. Notably, the Boeing 787 does not use bleed air to pressurize the cabin.
An air start system has three main components along with various safety components, namely the air start injector, the distributor and the air receivers. When the system is initiated, starting air from the receivers is distributed by the distributor unit to each respective air start valve according to the firing order of the engine’s cylinders.
The first German jet engines built during the Second World War used a mechanical APU starting system designed by the German engineer Norbert Riedel.It consisted of a 10 horsepower (7.5 kW) two-stroke flat engine, which for the Junkers Jumo 004 design was hidden in the intake diverter, essentially functioning as a pioneering example of an auxiliary power unit for starting a jet engine.
It was initially developed by Garrett AiResearch, for use as an APU for McDonnell Douglas DC-10. [1] Garrett was merged into AlliedSignal in 1985, then into Honeywell in 1999. Honeywell still provide support for the TSCP700's in circulation. Besides the DC-10, it is also used as APU on the MD-11 and Airbus A300/A310. [2]