Bleed air in gas turbine engines is compressed air taken from within the engine, after the compressor stage(s) and before the fuel is injected in the burners. While in theory bleed air could be drawn in any gas turbine engine, its usage is generally restricted to jet engines used in aircraft. Bleed air is valuable in an aircraft for two properties: high temperature and high pressure (typical values are 200-250°C and 275 kPa (40 PSI), for regulated bleed air exiting the engine pylon for use throughout the aircraft). This compressed air can be used within the aircraft in many different ways, from de-icing, to pressurizing the cabin, to pneumatic actuators. However, bleed air is quite hot and when being used in the cabin or other low temperature areas, it must first be cooled or even refrigerated by the aircraft's environmental control system (ECS). Newer aircraft rely more on electricity, reducing the need for compressed air. Since most gas turbine engines use multiple compressor stages, some newer engines have the bleed air inlet between compressor stages to reduce the temperature of the compressed air.
Famous quotes containing the words bleed and/or air:
“You may have a wen or a cancer upon your person and not be able to cut it out lest you bleed to death; but surely it is no way to cure it, to engraft it and spread it over your whole body.”
—Abraham Lincoln (18091865)
“What is lawful is not binding only on some and not binding on others. Lawfulness extends everywhere, through the wide-ruling air and the boundless light of the sky.”
—Empedocles 484424 B.C., Greek philosopher. The Presocratics, p. 142, ed. Philip Wheelwright, The Bobbs-Merrill Co., Inc. (1960)