15.5

Question 1

What must you ensure about combustion in a combustion chamber?

Answer 1

Combustion must be completed (No unburnt fuel must leave the combustion chamber)

Question 2

What are the two main components of a combustion chamber?

Answer 2

Combustion chamber casing and flame tube

Question 3

What can the casing be split into?

Answer 3

Inner and outer casing

Question 4

What is the function of combustion chamber casing?

Answer 4

To take air pressure loads and protects the internal and external parts from the hot combustion gases.

Question 5

What gives to the flame tube, and other chamber components such as fuel nozzles and igniter plugs?

Answer 5

The housing (casing)

Question 6

What does the flame tube do?

Answer 6

Controls and guides the flame

Question 7

What is the flame tube made up of?

Answer 7

Segments with holes and slots

Question 8

What sprays fuel into the centre of the airflow? And what happens after its ejected?

Answer 8

Fuel nozzles/Injectors. The fuel vaporises

Question 9

What creates ignition of the fuel-air mixture?

Answer 9

Electrically by the ignitor plug which switches off as soon as combustion occurs

Question 10

Why does the ignitor plug turn off after combustion?

Answer 10

Because combustion continues as long as fuel and air are supplied to the engine?

Question 11

What are the two primary conditions necessary for safe combustion?

Answer 11

The ratio of air to fuel
The air velocity

Question 12

Why must air velocity be slow enough in the combustion chamber?

Answer 12

To make sure that the combustion occurs in it

Question 13

What is the ratio of air to fuel?

Answer 13

15:1

Question 14

What are the two parts of compressor air?

Answer 14

The primary and secondary airflow

Question 15

What airflow is used for the combustion process?

Answer 15

Primary (20-30%)

Question 16

What does the rest of the airflow do?

Answer 16

Bypass the combustion come and mixes with the hot gas in the dilution zone

Question 17

What occurs in the primary zone?

Answer 17

The flame stabilisers

Question 18

Where can ‘Can-Type’ combustion chambers be found?

Answer 18

On old gas turbines with a centrifugal compressor

Question 19

Each combustion chamber has its own what?

Answer 19

Air supply duct
Fuel nozzle
Flame tube
Casing

Question 20

What are the 3 advantages of Can- type combustion chambers?

Answer 20

Simple design
They can be removed and replaced individually
Great structural strength

Question 21

What are the two types of Can-type combustion chambers?

Answer 21

Single or multiple chambers

Question 22

What are the three disadvantages of can type combustion chambers?

Answer 22

Heavy, need a lot of space
Complicated air supply ducts
Difficult to ignite different chambers

Question 23

What is a common feature of a ‘Can-annular’?

Answer 23

All the flame tubes have a common inner and outer casing.

Question 24

Advantage of ‘Can-annular’?

Answer 24

Smaller and lightweight

Question 25

Disadvantage of 'Can-Annular'?

Answer 25

Aerodynamic losses are high and ignition from one flame tube to the other is difficult

Question 26

What type of combustion chamber is commonly used of modern gas engines?

Answer 26

Annualar

Question 27

How can you tell that a combustion chamber is annular?

Answer 27

It has one flame tube!

Question 28

The annular consists of what 3 major parts?

Answer 28

Inner lining Outer lining The dome

Question 29

What is the purpose of the dome?

Answer 29

It has openings for the fuel nozzles which are surrounded by the swirl vanes

Question 30

What two types of combustion chambers are ideal for use in the APU?

Answer 30

Can type and Annular type

Question 31

What combustion chamber is known as a reverse combustion chamber?

Answer 31

Annualar

Question 32

What are advantages of Annular combustion chambers?

Answer 32

Smaller and lighter Large combustion area for greater efficiency Flame can spread easily Combustion is complete and smokeless

Question 33

What are the disadvantages of annular combustion chambers?

Answer 33

They are expensive and time consuming for maintenance

Question 34

What are the three sections in an annular combustion chamber?

Answer 34

The flame tube Combustion case External components fitted to outer wall

Question 35

What does the combustion case contain?

Answer 35

An inner wall An outer wall Diffuser

Question 36

What are the 2 integral parts of a combustion case?

Answer 36

Stator vanes also known as exit guide vanes A diffuser

Question 37

What Is fed through the outer wall after the last compressor stage?

Answer 37

Bleed air that is fed to the pneumatic system

Question 38

Other than openings for bleed air, what is also located on the outer wall?

Answer 38

Ignitor bosses Fuel nozzle pads

Question 39

How many ignitor plugs are installed on the outer wall of the combustion case?

Answer 39

2 in the lower half of the combustion case

Question 40

The combustion case/the compressor rear frame is classed as a what?

Answer 40

A frame

Question 41

What does the combustion case also house?

Answer 41

Bearings for HP rotor

Question 42

Main components of the flame tube?

Answer 42

Inner and outer cowl Inner and outer liner Dome

Question 43

What does the dome section of the flame tube do?

Answer 43

It connects inner liner with outer liner Houses swirlers with swirl vanes

Question 44

What do the inner and outer liners do?

Answer 44

They hold the flame tube to the combustion case

Question 45

What stays the same across all engines in regards to a flame tube?

Answer 45

The flame tube is fixed at one end and moveable at the other

Question 46

How many dimensions is the flame tube fixed in at the aft end?

Answer 46

3

Question 47

What SOMETIMES allows the flame tube to expand at the rear?

Answer 47

The fact its fixed at the front

Question 48

What is the dome centred in the combustion case by?

Answer 48

Mounting pins

Question 49

What does primary airflow do?

Answer 49

Enters the flame tube through the swirl vanes

Question 50

What route does secondary airflow take?

Answer 50

Passes the cowl and enters the flame tube through the liners

Question 51

What is the purpose of secondary airflow?

Answer 51

Forms a cooling film on inner surface of liners to protect it from heat (film cooling)

Question 52

What is a more sophisticated method for film cooling, and why?

Answer 52

Transpiration as it requires less air

Question 53

How does transpiration work?

Answer 53

The inner surface of the flame tube liners has detachable tiles

Question 54

How does the secondary airflow enter the flame tube?

Answer 54

Through holes in the liner

Question 55

What is the main cause for pollution?

Answer 55

Unburnt fuel

Question 56

When do these pollutants occur?

Answer 56

If combustion is incomplete due to an incorrect fuel to air ratio

Question 57

What is a rich mixture?

Answer 57

Too much fuel for primary air in the combustion chamber

Question 58

If a rich mixture doesn't burn all of its fuel, where will it dump it?

Answer 58

Exhaust

Question 59

Excessive fuel and low combustion also supports the build up of what?

Answer 59

Carbon Monoxide

Question 60

What is a lean mixure?

Answer 60

If there is insufficient fuel available in combustion chamber which causes less pollution but flame can extinguish

Question 61

How does increasing the temperature reduce carbon monoxide emissions?

Answer 61

Nitrogen oxide build up

Question 62

What happens in an annular flame tube?

Answer 62

Fuel nozzle releases fuel, igniter ignites fuel and swirl vanes ensure the primary air is reversing to ensure the flame doesn't extend through. Secondary airflow is used to cool the inner lining and ensure it creates a vortex that makes the air stay in.

Question 63

What is the purpose of the diffuser?

Answer 63

Increase static pressure which the swirling vanes

Question 64

What part of the inner wall is removable to allow for installation of the flame tube?

Answer 64

Rear