(Bleed Air)

Bleed Air)

Bleed air produced by gas turbine engines is compressed air that is taken from the compressor stage of those engines, which is upstream of the fuel-burning sections.

In modern airliner engines, two regulator valves (high stage and low stage) turn on and off automatically and are controlled by at least “…two air supply and cabin pressure controllers (ASCPCs) which open and close appropriate valves. Engine Bleed Air comes from the high stage or low stage engine compressor section.

Low stage air is used during high power setting operation and high stage air is used during descent and other low power setting operations.” Bleed air from that system can be used for internal cooling of the engine, cross-starting another engine, engine and airframe anti-icing, cabin pressurization, pneumatic actuators, air-driven motors, pressurizing the hydraulic reservoir, waste and water storage tanks. Some engine maintenance manuals refer to such systems as “Customer Bleed Air.”

Engines take in air from atmosphere and pressurize it through blades. Lot of this air is by-passed in most modern engines and some of this air is used to burn the fuel which in turn rotates the shaft and makes the engine blades rotate.

The pressurized air which is bypassed is at very high temperature and this is the fresh air which has been picked from atmosphere. Part of This air is used to heat the aircraft (at flying altitude the outside temperature is close to -35degree celcius. Also this same air is used in airconditioning system through mixure units to resupply fresh air to the cabin.

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).

No automatic alt text available.

Bleed air is essesntially loss of engine thrust as some air is being taken out it and cannot provide thrust.

This has led to current technological shift of developement of bleed less aircraft (or low bleed use). Boeing 787 is one such example where aircraft heating functions are electric. But this is a trade off as electric functions also add weight to aircraft an need higher electricity generation from engine.

Sources: https://www.faa.gov/…/med_humanfacs/…/2010s/media/201520.pdf

Prepared by: Air.Net Team