Turbine Engine Combustion Section

Question 1

Why is the velocity of the airflow slowed significantly as it enters the combustion chamber?

Answer 1

To reduce the velocity to below the flame propagation speed and thereby reduce the possibility of a flame out.

Question 2

What is the purpose of burning fuel in a combustion chamber?

Answer 2

To increase the volume (velocity) of the gases.

Question 3

How does the velocity of the gas vary through the combustion chamber?

Answer 3

The velocity is reasonably constant through the burner, but it increases significantly through the nozzle guide vanes as it exits the combustion chamber.

Question 4

What are the basic combustion chamber design configurations? 3

Answer 4

Can, can-annular and annular.

Question 5

What is the configuration/description of a can combustion chamber?

Answer 5

Combustors external to the engine, and most easily serviced.

Question 6

What is the configuration/description of a can-annular combustion chamber?

Answer 6

Multiple, separate interconnected chambers, encircling the turbine. An efficient combination of the other two designs.

Question 7

What is the configuration/description of an annular combustion chamber?

Answer 7

A segmented chamber made up of partitions and baffles, mounted co- axially about the engine axis, receiving primary air through a cylindrical shroud. ( Dual ring system).

Question 8

What is the function of the inter-connectors between the chambers of multiple chamber combustion sections?

Answer 8

To equalise operating pressures and to allow combustion propagation between chambers.

Question 9

What are the two types of can-annular or annular combustion chamber?

Answer 9

Through flow and reverse flow.

Question 10

What does reverse flow mean with respect to combustion chamber design?

Answer 10

If a combustion chamber is described as reverse flow, the direction of the air/gas flow is changed through 180 degree, at least once but normally twice as it progresses through the engine core.

Question 11

Why is reverse flow used in combustion chamber design?

Answer 11

To reduce the length of the engine

Question 12

What are the advantages of an annular combustion chamber? 6

Answer 12

1. Less cooling air required.
2. Improved combustion efficiency.
3. No flame propagation problems.
4. Compact, i.e. maximum utilisation of available space, with minimum length and diameter.
5. Less weight.
6. Lower cost.

Question 13

What is a disadvantage of an annular combustion chamber?

Answer 13

Less structural integrity.

Question 14

Why is far more air than is needed for combustion fed into the combustion chamber?

Answer 14

To supply air for cooling.

Question 15

What is the purpose of the combustion chamber liner and its associated metering and air flow distribution devices?

Answer 15

To separate and meter the air flow for cooling and combustion and to create a region of low velocity re-circulation of the air in the primary zone.

Question 16

What proportion of the air passing from the compressor/diffuser into the inner combustor is used for combustion?

Answer 16

Conventionally about 25% of the air passing from the compressor/diffuser into the inner combustor is used for combustion, however as turbine engine design becomes more refined this proportion is increasing toward 40% and in some cases 50% is claimed. i.e less air required for cooling.