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M15 > 15.5 Combustion Section > Flashcards

15.5 Combustion Section Flashcards

1
Q

What is the purpose of the combustion section?

A

To raise the temp of the air passing through the engine, providing energy required at turbine to drive the compressor.

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2
Q

What are the requirements of the combustion chamber?

A

Safe ignition.
Stable combustion.
Complete combustion.
Equal temperature distribution.

Minimum pressure loss.

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3
Q

The combustion chamber must what?

A

Be small and light.
Have a dependable cooling system.
High a high operating lifetime.

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4
Q

What is the air to fuel ratio?

A

15:1

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5
Q

What percentage is primary airflow?

A

20-30%

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6
Q

What percentage is secondary airflow?

A

70-80%

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7
Q

What are the main components of the combustion chamber?

A

Flame tube and casing.

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8
Q

What is the purpose of the casing?

A

It takes air pressure loads and protects internal and external engine parts from gases.

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9
Q

What is the purpose of the housing ?

A

Gives support to the flame tube.

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10
Q

What is the purpose of the flame tube?

A

Controls and guides the flame which is cooled by the secondary airflow.

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11
Q

Where is the flame tube ?

A

Inside the casing.

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12
Q

Describe the process of the combustion section?

A

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.

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13
Q

What are the conditions necessary for safe and correct combustion?

A

Correct air to fuel ratio.
Air velocity must be slow enough for complete combustion.

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14
Q

Which zone of the combustion chamber does the flame stabilise?

A

The primary zone.

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15
Q

What is the combustion chamber split into?

A

Primary and secondary zones.

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16
Q

What are the 3 types of combustion chambers?

A

Can type.
Can annular .
Annular.

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17
Q

Where is the can type combustion chamber used?

A

On old gas turbine engines with centrifugal compressors.

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18
Q

What are the types of can type combustion chambers?

A

Single can or multiple can.

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19
Q

What are the advantages of the can type combustion chamber?

A

Simple design.
Good structural strength.
Chambers can be removed and replaced individually.

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20
Q

What are the disadvantages of the can type combustion chamber?

A

Heavy.
Needs lots of space.
Complicated air supply ducts necessary.
Difficult ignition.

21
Q

Describe a can annular combustion chamber?

A

A set of flame tubes installed around the combustion section.

22
Q

Describe the casing of the flame tubes?

A

The flame tubes have a common outer and inner casing.

23
Q

What is the advantage of the can annular combustion chamber?

A

Smaller and lighter.

24
Q

What are the disadvantages of the can annular combustion chamber?

A

High aerodynamic losses.
Difficult ignition from 1 flame tube to another.

25
Q

What type of combustion chamber is most common?

A

Annular type.

26
Q

What are the 3 major parts of the annular combustion chamber?

A

Dome
Inner liner.
Outer liner.

27
Q

How many flame tubes does the annular combustion chamber have?

A

1

28
Q

What is the special deign for small gas turbine engines and APUs?

A

A reverse flow combustion chamber.

29
Q

What were the advantages of the annular combustion chamber?

A

Smaller and lighter.
Large combustion area= efficient
Combustion is complete and smokeless.

30
Q

What are the disadvantages of an annular combustion chamber?

A

Expensive to make.
Difficult and time consuming removal.

31
Q

What are the sections of the annular combustion chamber?

A

Combustion case.
Flame tube.
External components fitted to the outer wall.

32
Q

What makes up the combustion case?

A

Inner and outer wall.
Diffuser.

33
Q

What is the purpose of the rear flange in the combustion case?

A

Attaches nozzle guide vanes to HP turbine.

34
Q

What is in front of the sealing surface in the combustion case?

A

Compressor Discharge Pressure seal.

35
Q

What are the stator vanes of the last stage of the HP compressor called?

A

Exit guide vanes.

36
Q

What is the integral part of the combustion case called?

A

The diffuser.

37
Q

What can be found on the outer wall of the combustion case?

A

Fuel nozzle pads and igniter bosses.

38
Q

What is located in the lower half of the combustion case?

A

2 igniter plugs.

39
Q

What are the main components of the flame tube?

A

Inner and outer liner.
Inner and outer cowl.
Dome.

40
Q

What is the purpose the dome in the flame tube?

A

To connect the inner and outer liner.

41
Q

What is outer liner attached to?

A

The dome.

42
Q

What is the inner liner attached to?

A

Bolted to the inner flange of HP turbine nozzle guide vanes.

43
Q

Describe flame tube film cooling ?

A

Secondary air passes cowl and enters flame tube through liners forming a cooling film on inner line surface.

44
Q

How does transpiration cooling differ from film cooling?

A

Uses less air.
The flame tube inner surface of liners is covered with detachable tiles.

45
Q

Describe transpiration cooling?

A

Secondary air enters the flame tube through radial holes.
Then flows through gaps between the liner segments and liners.

46
Q

What is a rich mixture in the combustion chamber?

A

Too much fuel for primary air.

47
Q

What is a lean mixture in the combustion chamber?

A

insufficient fuel is available in the chamber.

48
Q

How does a dual dome combustion chamber differ from a standard combustion chamber?

A

It’s much shorter.

49
Q

Why is a dual dome combustion chamber used?

A

It reduces the time that the exhaust gas is in the hot area, reducing the build up of nitrogen oxides.

M15 (18 decks)

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