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Some engine maintenance manuals refer to such systems as "customer bleed air". [3] [4] [5] Bleed air is valuable in an aircraft for two properties: high temperature and high pressure (typical values are 200–250 °C (400–500 °F) and 275 kPa (40 psi), for regulated bleed air exiting the engine pylon for use throughout the aircraft).
The bleed air comes from the engines but is bled from the engine upstream of the combustor. Air cannot flow backwards through the engine except during a compressor stall (essentially a jet engine backfire), thus the bleed air should be free of combustion contaminants from the normal running of the aircraft's own engines.
An interesting feature of all three German jet engine designs that saw production of any kind before May 1945 (the German BMW 003, Junkers Jumo 004 and Heinkel HeS 011 axial-flow turbojet engine designs) was the starter system, which consisted of a Riedel 10 hp (7.5 kW) flat twin two-stroke air-cooled engine hidden in the intake, and ...
When the rotating speed of the engine is sufficient to pull in enough air to support combustion, fuel is introduced and ignited. Once the engine ignites and reaches idle speed, the bleed air and ignition systems are shut off. The APUs on aircraft such as the Boeing 737 and Airbus A320 can be seen at the
Bleed air from the engines, an auxiliary power unit, or a ground source, which can be in excess of 150 °C and at a pressure of perhaps 32 psi (220 kPa), [1] is directed into a primary heat exchanger. Outside air at ambient temperature and pressure is used as the coolant in this air-to-air heat exchanger.
By the time the cold outside air has reached the bleed air valves, it has been heated to around 200 °C (392 °F). The control and selection of high or low bleed sources is fully automatic and is governed by the needs of various pneumatic systems at various stages of flight. Piston-engine aircraft require an additional compressor, see diagram ...
Bleed air systems are used by most large aircraft with jet engines or turboprops. Hot air is "bled" off one or more engines' compressor sections into tubes routed through wings, tail surfaces, and engine inlets. Spent air is exhausted through holes in the wings' undersides. A disadvantage of these systems is that supplying an adequate amount of ...
] A first is the elimination of bleed air systems using high temperature/high pressure air from the propulsion engines to power aircraft systems such as the starting, air-conditioning and anti-ice systems. Both engines enable the move towards the More Electric Aircraft, that is, the concept of replacing previously hydraulic and pneumatic ...