15.5 COMBUSTION SECTION👌🏼

Question 1

Simply explain combustion process

Answer 1

• raises temperature of air
• releases energy contained in air/fuel mixture
• which drives turbine and compressor

Question 2

What are the 2 main components in a combustion chamber

Answer 2

• combustion chamber casing
• flame tube found inside casing

Question 3

What is the fuel-air mixture electrically ignited by

Answer 3

• igniter plug

Question 4

After the combustion has been started what occurs to the ignition

Answer 4

It is switched off

Question 5

What 2 primary conditions are necessary for correct and safe combustion

Answer 5

• ratio of air and fuel must be correct
• air velocity must be slow to ensure complete combustion inside combustion chamber

Question 6

What is the complete ratio for complete combustion

Answer 6

• 15 parts of air, 1 part of fuel

Question 7

Airflow are split into 2 parts

Answer 7

• primary airflow
• secondary airflow

Question 8

20% to 30% of the airflow from the compressor

Answer 8

• primary airflow

Question 9

What are the 3 types of combustion chambers used on gas turbine engines

Answer 9

• can-type combustion chamber
• can-annular combustion chamber
• annular combustion chamber

Question 10

Explain Can-type combustion chambers

Answer 10

• found on old gas turbine engines with centrifugal compressors

Question 11

Advantage of can-type combustion chambers

Answer 11

• simple in design
• very good structural strength

Question 12

Disadvantage of can-type combustion chambers

Answer 12

• heavy
• require a lot of space
  -need complicating air supply ducts from compressor

Question 13

Explain can-annular combustion chambers

Answer 13

• set of flame tubes installed around combuster section
• all flame tubes have common outer casing and inner casing

Question 14

Advantages of can-annular combustion chamber

Answer 14

• smaller, lighter than multiple can-type combustion chamber
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Question 15

Disadvantage of can-annular combustion chamber

Answer 15

• high aerodynamic losses
• ignition from one flame tube to another is difficult

Question 16

Which combustion chamber is used on modern gas turbine engines

Answer 16

• annular combustion chamber

Question 17

How many flame tubes does the annular combustion chamber have

Answer 17

1

Question 18

In a annular combustion chamber what is the flame tube supported by

Answer 18

• inner and outer combustion chamber casing

Question 19

What are the 3 major parts of a combustion chamber casing

Answer 19

• dome
• inner liner
• outer liner

Question 20

Advantages of annular combustion chamber

Answer 20

• Smaller, lighter
• better efficiency
• combustion is smokeless

Question 21

Disadvantage of annular combustion

Answer 21

• expensive to make
• removal is difficult and time consuming

Question 22

What does the dome have openings for

Answer 22

• fuel nozzles

Question 23

What are the fuel nozzles surrounded by

Answer 23

Swirl vanes

Question 24

Annular combustion chamber construction

Answer 24

• combustion case
• flame tube
• external components (fitted on outer wall)

Question 25

What is included in the combustion case assembly

Answer 25

• outer wall
• inner wall
• diffuser

Question 26

Explain Flame tube cooling

Answer 26

Done by secondary airflow, forms a cooling film

Question 27

What is a more sophisticated method of film cooling

Answer 27

• transpiration cooling (requires less air for cooling the flame tube liners)

Question 28

How is secondary airflow entered in the flame tube

Answer 28

• radial holes in the liner

Question 29

Explain rich mixture

Answer 29

-too much fuel for primary air in combustion chamber
- some fuel therefore cannot be burnt and released into the exhaust

Question 30

When does lean mixture occurs

Answer 30

If insufficient fuel is available in the combustion chamber

Question 31

What occurs to the remaining airflow from compressor (secondary airflow)

Answer 31

• bypasses and mixes with hot gas in the dilution zone

Question 32

Where is the flame stabilised. PRIMARY ZONE OR SECONDARY ZONE

Answer 32

primary zone