15.12 Air Systems Flashcards
A large vloume of air cools the hot sections of the engine, to what acceptable temperature range?
800 - 1150 degrees C
What ‘type’ of air is used to cool the combustion chamber liners?
Secondary air.
What are considered the primary zones of the engine? (3)
- Fan case compartment.
- Intermediate compressor case compartment.
- Core engine compartment.
What is included in the Zone 1 area?
The area around the fan case, containing the accessory case and EEC.
How is the zone 1 area vented and cooled?
Ram air enters through and inlet tube in the nose cowl. It exits through a vented panel in the RHS engine fan cowling.
What does the Zone 1 area have to protect against overpressure?
Pressure relief door.
What is included in the Zone 2 area?
Fuel and oil lines.
How is the zone 2 area cooled?
Cooled by fan air from upper fan duct, and exhausted out at the lower end to rejoin the fan-air stream.
What does the zone 3 area cover?
The area around the HP compressor to turbine cases. Also contains fuel/oil lines and other accessories.
How is the Zone 3 area cooled?
Air enters the from the outlet of the pre-cooler, and exits through the aft edge of the thrust reverser inner wall and turbine exhaust sleeve.
At what temperature can ice form on the inlet?
Any temperature up to 5 degrees C.
Is the anti-icing system normally controlled automatically or manually?
Normally controlled automatically.
How does the anti-ice system operate automatically?
The system activates when icing condtions are detected.
The system opens a bleed valve, that bleeds hot air from the compressor.
What areas of the engine are fed with hot bleed air for anti-icing? (3)
- The inlet leading edge.
- Nose dome.
- Inlet guide vanes.
Where does the bleed air that’s used to heat the inlet, exit the aircraft?
Via grills in the nose cowling.
What is the approximate temperature of the aft section of the compressor?
350-450 degrees C.
How is the aft stage of the compressor cooled?
Rotor cavity is provided with air from the intermediate compressor stage, which is a bit cooler.
What type of airflow cools the combustion chamber inner liner?
The secondary airflow.
What 2 things does the secondary airflow do to help keep the inner liner cool?
- Forms a cooling air blanket on both sides of the liner, acting as a thermal barrier.
- Removes heat directly.
What feature of the combustion chamber’s outer-casing inner liner, also assists with cooling?
The inner liner is perforated.
How does the secondary airflow assist with flame propagation?
It keeps the flame straight, preventing it from contacting the inner liner
What is the main benefit of using cooling systems on turbines?
It allows the turbine to operate at 300-400 degrees C above the limits of their metal alloys.
What’s the most common method used to cool the turbine section?
Bleed air.
What is usually at a higher temperature on the turbine disc, the rim of the disk or the centre of the disk?
The rim of the disc.
How is the turbine disc cooled, generally?
Cooling air is directed over each side of the disc.
How is the HP turbine disc cooled?
By compressor discharge air (P3).
How is the LP turbine disc cooled?
By intermediate compressor stage air.
What are the two methods of turbine blade cooling?
- The disc acts as a heat-sink to cool the blades.
- The disc has holes drilled into the front face, that receive cooling airflow that flows up into the blades through holes in the blade roots.
How are Nozzle Guide Vanes cooled?
By compressor discharge air (P3).
What cools accessory units in-flight?
Atmospheric air.
How are accessory units cooled on the ground?
Compressor air passes through nozzles in cooling air outlet duct at high velocity, reducing the pressure in this area that draws-in atmospheric air.
What air is used as the cooling medium in air-cooled oil coolers?
Fan-air.
What air is used for sealing engine bearing chambers?
LP compressor bleed air.
What creates an additional sealing effect on air seals and oil seals?
Pressurised air.
How is the air, that enters bearing compartments, eventually vented overboard?
Through the hollow N1 shaft.
What systems is bleed air used for? (4)
-Cabin pressurisation, heating, and cooling.
- De-icing and Anti-icing.
- Pneumatic engine starting.
- Auxillary drive units.
Where can bleed air be ‘tapped off’ from in the compressor section?
Any compressor stage, dependent on the pressure and temperature of the bleed air required by the receiving system.
What gives the highest pressure and temperature of bleed air?
HP compressor.
Underneath the fan cowls, what two compartments is the engine divided into?
- Fan compartment.
- Core compartment.
As each compartment is seperated by bulkheads and fireseals, how is each compartment cooled and vented?
Seperately.
What specifically-named type of inlets scoop-up ram air for cooling?
NACA ducts/inlets.
What is a Bowed-rotor condition?
Engine bending due to different thermal expansion rates between the upper and lower zones.
What are the effects of a Bowed-rotor condition?
- Distortion can cause rotors to contact the stator cases.
- High vibration on engine start.
- Hung-up engine start.
How is Bowed-rotor condition prevented?
By waiting a specified minimum time between engine shutdown and successive start.
What’s can cause a critical Bowed-rotor condition?
The lower part of the engine becomes colder than the upper part of the engine.
