Hello,
I would like to know where does the bleed air come from at an CFM-56 engine.
Normally the bleed air is extracted from the low pressure compressor and if necessary (due to temperature) you can also take bleed air from the high pressure compressor (or mix them). But in an A320 you have on the bleed-page not the indication of LPC, there you have the indication of “intermediate pressure stage (IP)” as bleed source.
Can someone explain what kind of stage an “intermediate pressure stage (IP)” is?
Is it now a low pressure compressor part or not? And why does airbus use IP and not LPC indication on the bleed page?
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Re: Source of bleed air (CFM engine)?
FLASH102 wrote:
Normally the bleed air is extracted from the low pressure compressor
No. Bleed air is almost always taken from the high pressure compressor, but from an early stage…5th on the CFM, as I recall. This is low pressure air. It is supplemented, at idle or under heavy demands, by high stage air…maybe 9th on the CFM.
The CFM is a twin spool engine, which means it doesn’t really have an IP compressor, like an RB211, which is a 3 spool engine. As I recall, the fan and the first 3 stages make up the fan and booster section (N1) and the rest are part of the high pressure compressor (N2, HPC). The IP air is just the air from the low end of the HPC.
By the way, temperature is usually used as a parameter to moderate HPC air. HPC air can easily over-temp the pneumatic system. The HP Controller and/or PRSOV, or equivalent, will choke down the air to keep the temperature within acceptable limits.
Re: Source of bleed air (CFM engine)?
fr8mech wrote:By the way, temperature is usually used as a parameter to moderate HPC air. HPC air can easily over-temp the pneumatic system. The HP Controller and/or PRSOV, or equivalent, will choke down the air to keep the temperature within acceptable limits.
I guess I should elaborate, in the interest of clarity, the restricting of air to control temperature is the last step. Bleed air temperature is primarily controlled by passing fan or booster air over a heat exchanger as, or right before, the bleed air enters the airframe pneumatic system. This fan air is regulated by a fan air valve.
Re: Source of bleed air (CFM engine)?
The "intermediate" probably refers to the pneumatic system. Usually three pressure values are important for pressure regulation. PE (Engine Pressure), PI (Intermediate Pressure) and PM (Manifold Pressure). The engine pressure sensor sits upstream of the high stage valve, so it's the HPC air pressure. PI sits between the high stage valve and the pressure regulating valve, so its the modulated HPC pressure or LPC pressure if the HSV is closed. Manifold pressure is downstream of the pressure regulating valve, so basically the pressure the engine outputs into the pneumatic system.
Note that the terminology can change between engines. On some engines it's called High Stage Valve on others it's called High Pressure Shut Off Valve for example. Some call it PI, others might call it IP. I'm not familiar with the CFM, only with the CF6-80 and the GE90. But the basic principle should be the same.
Note that the terminology can change between engines. On some engines it's called High Stage Valve on others it's called High Pressure Shut Off Valve for example. Some call it PI, others might call it IP. I'm not familiar with the CFM, only with the CF6-80 and the GE90. But the basic principle should be the same.
Re: Source of bleed air (CFM engine)?
CFM56 has two bleed ports both located on hp compresor, IP is on 5th stage and HP pn 9th. IP ports is equipped with flapper check valve which prohibits passage of air coming from 9th stage back to engine, which can cause compresor stall...so air from 5th stage and 9th stage is never mixed. Both ducts are joined together upstream of pressure regulating valve which regulates pressure and via sense line controls HP valve. Both valves have solenoid which controls muscle pressure for regulating circuit. PRV solenoid is controled either manualy by BLEED p/b in cockpit or automatically. HP valve iscontrolled just automatically.
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