15.12 Air Systems Flashcards
Where is the hottest section of an engine?
Around the turbines
What is the cooling purpose of secondary air ?
Cools the combustion chamber liners
What does the construction of the combustion chamber liners force the formation of ?
A fast moving film of air moving over both inner and outer surfaces of the liner
Other than oil, what else do some engines use to cool bearings ?
Air
Where is secondary cooling air tapped from and where is this air provided to ?
Tapped from Early stages of the compressor and is used to cool turbine disks, vanes, combustion chamber lining and exhaust bearings
How is circulated cooling air removed from the engine?
Air is vented into the exhaust stream
How is the exterior of the engines and the nacelles cooled ?
By passing fan air around them
What are the three primary zones that are isolated by fireproof bulkheads ?
- fan case compartment
-the intermediate compressor case compartment
The core engine compartment
Where is fireproof zone 1 ?
Around the fan case that contains the accessory case and the EEC
Where is fireproof zone 2 ?
Cooled by fan air from the upper part of the fan duct, and is exhausted at the lower end back into the fan air stream
Where is fireproof zone 3?
The area around the high pressure compressor to the turbine cases. This zone also contains fuel lines, oil lines and other accessories
Where is fireproof zone 3?
The area around the high pressure compressor to the turbine cases. This zone also contains fuel lines, oil lines and other accessories
What are the disadvantages of ice formation on the engines?
-Reduces efficiency,
- possibility for chunks of Ice to break off and break or damage the compressor blades
What abnormal condition can cause ice to form when it’s not supposed to ?
Ice can form on the inlet when there is fast air speeds at temperatures up to 5°C
How are anti ice systems controlled ?
Automatically via a switch or flight crew can manually select functions if it is required
Where can an indication that anti ice valves are open be seen ?
On the engine parameters page
What are the five internal cooling systems ?
-compressor cooling
-combustion chamber cooling
-turbine disc cooling
-turbine nozzle guide vanes and blade cooling
-accessory section
What is the temperature range at the rear stages of the compressor ?
350-400 °C
Where is compressor drawn cooling air supplied to ?
Compressor’s rotors
What is special about the lining of the combustion chamber and what is their purpose ?
It is perforated to cool combustion gasses. Air is supplied via primary and secondary airflow
What percentage of primary and secondary air is used to cool the combustion chamber ?
20-30% primary airflow is sent into the perforated liner
70-80% secondary airflow is sent around the combustor’s periphery
What are the two ways the perforated lining provides cooling?
-Cool air removes heat from the combustion liner
- cooling creates a film which acts as a thermal barrier between hot gasses and the combustion liner
How much more effectiveness does cooling give on turbine blades and vanes ?
They can operate up to 300-400°C higher than the materials operating range
What is the major limiting range of gas turbine engines?
Temperature
What is the most common method of cooling the turbine ?
By utilising bleed air
How does the turbine disc heat up ?
By conduction of the heat on the blades
What is the hottest part of the turbine disc ?
The disc rim
How is the turbine disc cooled ?
By directing cooled air over each side of the disk
Why are turbine nozzle guide vanes cooled ?
To increase life expectancy due to high temperatures
Where does the air come from to flow out of the NGV and turbine blade cavaliers ?
Compressor discharge air
Where is air drawn from to cool accessories and computers?
From intakes in the fan cowlings or a stage from the compressors
What is used to cool oil for oil cooled generators or lubrication oil cooling ?
Air cooled oil cooler when fan air is used as the cooling medium
What is used for sealing of the engine bearing chambers?
The low pressure compressor bleed air
What does pressurised air acts as?
Acts on the air seals and oil seals and has an additional sealing effect that prevents oil from escaping out of the bearing chamber
Where does air go from the bearing compartments?
Vents overboard through the hollow N1 rotor shaft
What do engine bleed air external surfaces include?
Cabin pressurisation heating and cooling, De-icing and anti-icing, pneumatic starting of engines, auxiliary drive units (ADU)
What are bleed ports?
Small openings in the compressor case adjacent to the stage from which the air is bled from
Where does the external cooling system cool
External area between the cowlings and the engine casings
What are the two areas below the engine cowlings?
The fan compartment and the core apartment
