15.5 Combustion Section Flashcards
What is the purpose of the combustion section?
To raise the temp of the air passing through the engine, providing energy required at turbine to drive the compressor.
What are the requirements of the combustion chamber?
Safe ignition.
Stable combustion.
Complete combustion.
Equal temperature distribution.
Minimum pressure loss.
The combustion chamber must what?
Be small and light.
Have a dependable cooling system.
High a high operating lifetime.
What is the air to fuel ratio?
15:1
What percentage is primary airflow?
20-30%
What percentage is secondary airflow?
70-80%
What are the main components of the combustion chamber?
Flame tube and casing.
What is the purpose of the casing?
It takes air pressure loads and protects internal and external engine parts from gases.
What is the purpose of the housing ?
Gives support to the flame tube.
What is the purpose of the flame tube?
Controls and guides the flame which is cooled by the secondary airflow.
Where is the flame tube ?
Inside the casing.
Describe the process of the combustion section?
Compressed air enters.
Fuel nozzles/ injectors spray fuel into airflow centre.
Fuel vapourises and mixes with the airflow.
Then the mixture is electrically ignited by the igniter plug.
What are the conditions necessary for safe and correct combustion?
Correct air to fuel ratio.
Air velocity must be slow enough for complete combustion.
Which zone of the combustion chamber does the flame stabilise?
The primary zone.
What is the combustion chamber split into?
Primary and secondary zones.
What are the 3 types of combustion chambers?
Can type.
Can annular .
Annular.
Where is the can type combustion chamber used?
On old gas turbine engines with centrifugal compressors.
What are the types of can type combustion chambers?
Single can or multiple can.
What are the advantages of the can type combustion chamber?
Simple design.
Good structural strength.
Chambers can be removed and replaced individually.
What are the disadvantages of the can type combustion chamber?
Heavy.
Needs lots of space.
Complicated air supply ducts necessary.
Difficult ignition.
Describe a can annular combustion chamber?
A set of flame tubes installed around the combustion section.
Describe the casing of the flame tubes?
The flame tubes have a common outer and inner casing.
What is the advantage of the can annular combustion chamber?
Smaller and lighter.
What are the disadvantages of the can annular combustion chamber?
High aerodynamic losses.
Difficult ignition from 1 flame tube to another.
What type of combustion chamber is most common?
Annular type.
What are the 3 major parts of the annular combustion chamber?
Dome
Inner liner.
Outer liner.
How many flame tubes does the annular combustion chamber have?
1
What is the special deign for small gas turbine engines and APUs?
A reverse flow combustion chamber.
What were the advantages of the annular combustion chamber?
Smaller and lighter.
Large combustion area= efficient
Combustion is complete and smokeless.
What are the disadvantages of an annular combustion chamber?
Expensive to make.
Difficult and time consuming removal.
What are the sections of the annular combustion chamber?
Combustion case.
Flame tube.
External components fitted to the outer wall.
What makes up the combustion case?
Inner and outer wall.
Diffuser.
What is the purpose of the rear flange in the combustion case?
Attaches nozzle guide vanes to HP turbine.
What is in front of the sealing surface in the combustion case?
Compressor Discharge Pressure seal.
What are the stator vanes of the last stage of the HP compressor called?
Exit guide vanes.
What is the integral part of the combustion case called?
The diffuser.
What can be found on the outer wall of the combustion case?
Fuel nozzle pads and igniter bosses.
What is located in the lower half of the combustion case?
2 igniter plugs.
What are the main components of the flame tube?
Inner and outer liner.
Inner and outer cowl.
Dome.
What is the purpose the dome in the flame tube?
To connect the inner and outer liner.
What is outer liner attached to?
The dome.
What is the inner liner attached to?
Bolted to the inner flange of HP turbine nozzle guide vanes.
Describe flame tube film cooling ?
Secondary air passes cowl and enters flame tube through liners forming a cooling film on inner line surface.
How does transpiration cooling differ from film cooling?
Uses less air.
The flame tube inner surface of liners is covered with detachable tiles.
Describe transpiration cooling?
Secondary air enters the flame tube through radial holes.
Then flows through gaps between the liner segments and liners.
What is a rich mixture in the combustion chamber?
Too much fuel for primary air.
What is a lean mixture in the combustion chamber?
insufficient fuel is available in the chamber.
How does a dual dome combustion chamber differ from a standard combustion chamber?
It’s much shorter.
Why is a dual dome combustion chamber used?
It reduces the time that the exhaust gas is in the hot area, reducing the build up of nitrogen oxides.
