Bleed Air
the air bled from the compressor which is used to cool the internal components of the engine is also utilized to pressure seals, which will increase the efficiency of both the compressor and the turbine. Its also used in air-conditioning, pressurization, fuel tank, thrust reverser,engine/anti-icing. This is shown in the diagram below where the effect of engine of using bleed air.
For use outside the engine itself, air bled from two sources.
the air bled from the compressor which is used to cool the internal components of the engine is also utilized to pressure seals, which will increase the efficiency of both the compressor and the turbine. Its also used in air-conditioning, pressurization, fuel tank, thrust reverser,engine/anti-icing. This is shown in the diagram below where the effect of engine of using bleed air.
For use outside the engine itself, air bled from two sources.
- When air is bled from the compressor it reduces the thrust of the engine. This will be indicated on Engine pressure ratio gauge.
- Reducing the mass flow through the engine will reduce the amount of air cooling the combustion chamber. This will effect of the increasing exhaust gas temperature.
- Bleeding air from the compressor reduces the load on the turbine, this will have the effect of increasing engine R.P.M. for a given fuel flow
- The specific fuel consumption will increase whenever an engine bleed is opened.
Air For Internal use in the Engine
air bled from the compressor is used to cool the turbine blades to seal both the bearing chambers and areas either side of the turbine discs. air has considerable work done on it to raise its pressure as it passes through the engine. To ensure maximum engine efficiency, the air is extracted from as early a stage in the compressor as possible, commensurate with it being able to perform its function. Air used for Engine Cooling
The main parts of the engine that require cooling are the combustion chamber and the turbine section. (early gas turbine engines) The use of single pass internal cooling retained the temperature of the turbine blade below the critical level at which creep would occur. Nozzle Guide Vanes and Turbine Disc cooling
only high pressure air is used. Heat conduction from the turbine blade to the turbine disc requires that the turbine discs are cooled and prevented from suffering thermal fatigue from uncontrolled expansion and contraction. The front and rear of each of the turbine discs is cooled by high pressure compressor air, the actual pressure in each disc cavity being controlled by inter-stage seals. |