15.5 Combustion Section

Question 1

What is the purpose of the combustion section?

Answer 1

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

Question 2

What are the requirements of the combustion chamber?

Answer 2

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

Minimum pressure loss.

Question 3

The combustion chamber must what?

Answer 3

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

Question 4

What is the air to fuel ratio?

Answer 4

15:1

Question 5

What percentage is primary airflow?

Answer 5

20-30%

Question 6

What percentage is secondary airflow?

Answer 6

70-80%

Question 7

What are the main components of the combustion chamber?

Answer 7

Flame tube and casing.

Question 8

What is the purpose of the casing?

Answer 8

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

Question 9

What is the purpose of the housing ?

Answer 9

Gives support to the flame tube.

Question 10

What is the purpose of the flame tube?

Answer 10

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

Question 11

Where is the flame tube ?

Answer 11

Inside the casing.

Question 12

Describe the process of the combustion section?

Answer 12

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.

Question 13

What are the conditions necessary for safe and correct combustion?

Answer 13

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

Question 14

Which zone of the combustion chamber does the flame stabilise?

Answer 14

The primary zone.

Question 15

What is the combustion chamber split into?

Answer 15

Primary and secondary zones.

Question 16

What are the 3 types of combustion chambers?

Answer 16

Can type.
Can annular .
Annular.

Question 17

Where is the can type combustion chamber used?

Answer 17

On old gas turbine engines with centrifugal compressors.

Question 18

What are the types of can type combustion chambers?

Answer 18

Single can or multiple can.

Question 19

What are the advantages of the can type combustion chamber?

Answer 19

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

Question 20

What are the disadvantages of the can type combustion chamber?

Answer 20

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

Question 21

Describe a can annular combustion chamber?

Answer 21

A set of flame tubes installed around the combustion section.

Question 22

Describe the casing of the flame tubes?

Answer 22

The flame tubes have a common outer and inner casing.

Question 23

What is the advantage of the can annular combustion chamber?

Answer 23

Smaller and lighter.

Question 24

What are the disadvantages of the can annular combustion chamber?

Answer 24

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

Question 25

What type of combustion chamber is most common?

Answer 25

Annular type.

Question 26

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

Answer 26

Dome Inner liner. Outer liner.

Question 27

How many flame tubes does the annular combustion chamber have?

Answer 27

1

Question 28

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

Answer 28

A reverse flow combustion chamber.

Question 29

What were the advantages of the annular combustion chamber?

Answer 29

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

Question 30

What are the disadvantages of an annular combustion chamber?

Answer 30

Expensive to make. Difficult and time consuming removal.

Question 31

What are the sections of the annular combustion chamber?

Answer 31

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

Question 32

What makes up the combustion case?

Answer 32

Inner and outer wall. Diffuser.

Question 33

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

Answer 33

Attaches nozzle guide vanes to HP turbine.

Question 34

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

Answer 34

Compressor Discharge Pressure seal.

Question 35

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

Answer 35

Exit guide vanes.

Question 36

What is the integral part of the combustion case called?

Answer 36

The diffuser.

Question 37

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

Answer 37

Fuel nozzle pads and igniter bosses.

Question 38

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

Answer 38

2 igniter plugs.

Question 39

What are the main components of the flame tube?

Answer 39

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

Question 40

What is the purpose the dome in the flame tube?

Answer 40

To connect the inner and outer liner.

Question 41

What is outer liner attached to?

Answer 41

The dome.

Question 42

What is the inner liner attached to?

Answer 42

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

Question 43

Describe flame tube film cooling ?

Answer 43

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

Question 44

How does transpiration cooling differ from film cooling?

Answer 44

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

Question 45

Describe transpiration cooling?

Answer 45

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

Question 46

What is a rich mixture in the combustion chamber?

Answer 46

Too much fuel for primary air.

Question 47

What is a lean mixture in the combustion chamber?

Answer 47

insufficient fuel is available in the chamber.

Question 48

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

Answer 48

It’s much shorter.

Question 49

Why is a dual dome combustion chamber used?

Answer 49

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