15.12 Flashcards
What is the acceptable temperature range inside the engine?
800 to 1150 degrees
How do we keep engines to the correct temperature?
By cooling them with air
What is the hottest section of the engines?
Around the turbine
What does the secondary air do?
Cools the engine
Where do we get secondary air from?
Bleed air in the early stages of the compressor
What 4 things is secondary air used to cool?
Turbine disc
Vanes
Blades
Exhaust bearings
What does secondary air passing through the engine cool?
The combustion chamber liners
What is the most critical lubricating point due to the high temperatures?
Exhaust turbine bearing
As well as air cooling what method is also used to cool the bearings?
Oil cooling
Where are cooling inlets located?
The exterior of the engine
What cools the engine exterior and the nacelle?§
Passing fan air
What are the 3 zones?
Fan case compartment
Intermediate compressor case compartment
Core engine compartment
What are the 3 zones separated by?
A fireproof bulkhead or seal
What prevents the build-up of any harmful vapours?
Airflow
What is zone 1?
Area around the fan case that contains the accessory case and the ECC
What is 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
What is zone 3?
Area around high-pressure compressor to the turbine cases (also contains fuel and oil lines and other accessories)
In the majority of engines what 3 things utilise cooling air?
Compressor
Combustion
Turbine sections
What are the problems ice can cause?
Disruption of airflow
Ice can break off and damage the engine
What prevents formation of ice on the engine inlet cowls?
An anti-ice system
What temperature can ice form at and why?
5 degrees and below due to the chilling effect of high inlet velocities
What are anti-icing systems controlled by?
Automatically by a switch on the flight deck
After heating the lip where does air exit through?
A grill on the nose cowl
Can the flight crew select a manually select anti-ice if required?
Yes
Where can an indication that the anti-icing valve is open be viewed?
On the engine parameters page
What are the 5 internal subsystmes?
Compressor cooling
Combustion chamber coolings
Turbine disc cooling
Turbine Nozzle Guide Vanes (NGV) and blade cooling
Accessory section
What is the temperature range at the rear stages of the compressor?
350 to 400 degrees
What minimises the effect of heat on the compressor?
The compressor rotor cavity is provided with cooling air from an intermediate compressor stage
What does the combustion chamber consist of?
An outer casing with a perforated inner liner
That is the air in the combustion chamber divided into?
Primary and Secondary paths
How much of the air is primary air?
20% - 30%
How much of the air is secondary air?
70% - 80%
Where does secondary air go?
To the combusts periphery at several hundred m/s
What does secondary air form?
A cooling air blanket on both sides of the inner liner
What does secondary air ensure about the flame?
It doesn’t contact the liner
What are the 2 ways cooling takes place in the combustion chamber?
Cooling air removes heat from the combustion liner
Colling air creates a film which acts as a thermal barrier between the hot gases and the combustion line
What temperature do the turbine blades and vane operate at?
300 to 400 degrees
What is the most common method to cool the turbine components?
Engine bleed air
What is done to limit the effects of temperature variations of the turbine dic?
Cooling sir is directed over each side of the disc
What is done to increase the life expectancy of the turbine NGV and blades?
They are cooled by compressor air (guide vanes are cooling by compressor discharge air)
What air cools engine accessories and electrical generators?
Air from intakes in the fan cowlings or from the compressor
How is oil cooled?
By an air-cooled oil cooler where fan air is used
What air is used for the sealing of the engine bearing chambers?
LP compressor bleed air
What stops oil from escaping out of the bearing chamber?
Pressurised air acting on the air and oil seals
Where is air that enters the bearing compartment vented?
Overboard through the hollow N1 rotor shaft
What is a secondary function of the compressor?
To supply air to the various systems on the aircraft
What stages of the compressor can bled air be taken off?
Any
What are 4 examples of where bleed air is used?
Cabin pressurisation, heating and cooling
De-icing and anti-icing equipment
Pneumatic starting of engines
Auxiliary Drive Units (ADU)
Where does the external cooling system cool?
External areas between the cowling and the engine case
What are the 2 sections that the areas below the engine cowling are divided into?
The fan compartment
The core compartment
What doe the external cooling system ensure?
That the engine case and all fan components and core compartments are sufficiently cooled
What does the external cooling system also prevent?
Flammable vapours from collecting in the engine compartments
What are the fan and cor compartments separated by and what does this mean in terms of cooling?
Bulkheads and fir seals meaning they are cooled and vented separately
