1) HOW AN ENGINE WORKS : ( very briefly ! )
A turbofan engine is made of 4 main components :
This is what we can see in a more acurate manner on this cross section of the PW6000 engine :
document : Pratt & Whitney Commercial Engines
A modern turbofan , the CFM56 ( see the fan propeller on the fore front ) :
2) MAIN BLEED AIR SYSTEM FUNCTIONS
On the compressor different ports are arranged on different compressor stages providing high pressure air to be tapped according to the aircraft flight phases.
For example during the descent phase when the engine is running at low power, air is bled from the high pressure port HP. During the cruise phase where the engine is providing a high power, air is bled from the intermediate pressure IP port which has a lower pressure but this is more efficient for the engine and its fuel consumption. This is carried out with two components :
The first role of the bleed air system is to select the right bleed port.
The second role of the bleed air system is to decrease pressure and temperature to levels acceptable for the downstream pipes and the air cooling system.
This is carried out with 2 main components :
Accordingly at the precooler outlet the air temperature is lowered.
3) THE ENGINE BLEED AIR SYSTEM ARCHITECTURE is often as follows and one can find the hot air flow cooled down by the cold air flow inside the precooler:
MAIN SITE NAVIGATION :
bleed air system / air cooling system / zone temperature control system / cabin pressure control system