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Module 15 > 15.5 > Flashcards

15.5 Flashcards

1
Q

What must you ensure about combustion in a combustion chamber?

A

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

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2
Q

What are the two main components of a combustion chamber?

A

Combustion chamber casing and flame tube

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3
Q

What can the casing be split into?

A

Inner and outer casing

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4
Q

What is the function of combustion chamber casing?

A

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

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5
Q

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

A

The housing (casing)

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6
Q

What does the flame tube do?

A

Controls and guides the flame

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7
Q

What is the flame tube made up of?

A

Segments with holes and slots

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8
Q

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

A

Fuel nozzles/Injectors. The fuel vaporises

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9
Q

What creates ignition of the fuel-air mixture?

A

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

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10
Q

Why does the ignitor plug turn off after combustion?

A

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

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11
Q

What are the two primary conditions necessary for safe combustion?

A

The ratio of air to fuel
The air velocity

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12
Q

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

A

To make sure that the combustion occurs in it

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13
Q

What is the ratio of air to fuel?

A

15:1

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14
Q

What are the two parts of compressor air?

A

The primary and secondary airflow

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15
Q

What airflow is used for the combustion process?

A

Primary (20-30%)

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16
Q

What does the rest of the airflow do?

A

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

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17
Q

What occurs in the primary zone?

A

The flame stabilisers

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18
Q

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

A

On old gas turbines with a centrifugal compressor

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19
Q

Each combustion chamber has its own what?

A

Air supply duct
Fuel nozzle
Flame tube
Casing

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20
Q

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

A

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

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21
Q

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

A

Single or multiple chambers

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22
Q

What are the three disadvantages of can type combustion chambers?

A

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

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23
Q

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

A

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

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24
Q

Advantage of ‘Can-annular’?

A

Smaller and lightweight

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25
Q

Disadvantage of ‘Can-Annular’?

A

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

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26
Q

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

A

Annualar

27
Q

How can you tell that a combustion chamber is annular?

A

It has one flame tube!

28
Q

The annular consists of what 3 major parts?

A

Inner lining
Outer lining
The dome

29
Q

What is the purpose of the dome?

A

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

30
Q

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

A

Can type and Annular type

31
Q

What combustion chamber is known as a reverse combustion chamber?

A

Annualar

32
Q

What are advantages of Annular combustion chambers?

A

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

33
Q

What are the disadvantages of annular combustion chambers?

A

They are expensive and time consuming for maintenance

34
Q

What are the three sections in an annular combustion chamber?

A

The flame tube
Combustion case
External components fitted to outer wall

35
Q

What does the combustion case contain?

A

An inner wall
An outer wall
Diffuser

36
Q

What are the 2 integral parts of a combustion case?

A

Stator vanes also known as exit guide vanes
A diffuser

37
Q

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

A

Bleed air that is fed to the pneumatic system

38
Q

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

A

Ignitor bosses
Fuel nozzle pads

39
Q

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

A

2 in the lower half of the combustion case

40
Q

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

A

A frame

41
Q

What does the combustion case also house?

A

Bearings for HP rotor

42
Q

Main components of the flame tube?

A

Inner and outer cowl
Inner and outer liner
Dome

43
Q

What does the dome section of the flame tube do?

A

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

44
Q

What do the inner and outer liners do?

A

They hold the flame tube to the combustion case

45
Q

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

A

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

46
Q

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

A

3

47
Q

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

A

The fact its fixed at the front

48
Q

What is the dome centred in the combustion case by?

A

Mounting pins

49
Q

What does primary airflow do?

A

Enters the flame tube through the swirl vanes

50
Q

What route does secondary airflow take?

A

Passes the cowl and enters the flame tube through the liners

51
Q

What is the purpose of secondary airflow?

A

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

52
Q

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

A

Transpiration as it requires less air

53
Q

How does transpiration work?

A

The inner surface of the flame tube liners has detachable tiles

54
Q

How does the secondary airflow enter the flame tube?

A

Through holes in the liner

55
Q

What is the main cause for pollution?

A

Unburnt fuel

56
Q

When do these pollutants occur?

A

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

57
Q

What is a rich mixture?

A

Too much fuel for primary air in the combustion chamber

58
Q

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

A

Exhaust

59
Q

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

A

Carbon Monoxide

60
Q

What is a lean mixure?

A

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

61
Q

How does increasing the temperature reduce carbon monoxide emissions?

A

Nitrogen oxide build up

62
Q

What happens in an annular flame tube?

A

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.

63
Q

What is the purpose of the diffuser?

A

Increase static pressure which the swirling vanes

64
Q

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

A

Rear

Module 15 (18 decks)

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