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Module 15 Richard > 15.05 Combustion Section > Flashcards

15.05 Combustion Section Flashcards

1
Q

What is the purpose of the combustion section?

A

It produces a hot stream of gas for the turbines and jet nozzle by continuous combustion of a fuel-air mixture

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2
Q

What are the requirements for safe and efficient combustion?

A
  • safe ignition
  • stable combustion
  • complete combustion
  • equal temperature distribution
  • combustion with minimum pressure loss
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3
Q

What properties must the combustion chamber have?

A
  • lightweight and small
  • have a cooling system
  • high operating lifetime
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4
Q

What is the purpose of the combustion chamber casing?

A

It protects the internal and external engine parts from the hot gases and also takes air pressure loads

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5
Q

When are the igniters turned off?

A

After the engine has been started and is self-sustaining

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6
Q

What are the two primary conditions for safe combustion?

A
  • the ratio of air to fuel must be correct

- the air velocity must be slow enough for complete combustion

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7
Q

What happens to the airflow from the compressor?

A

It splits into the primary airflow and secondary airflow

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8
Q

What is the primary airflow from the compressor?

A

It is approximately 20% to 30% of the air which is used for the combustion process

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9
Q

What ratio of kerosene to air mixture is required for complete combustion?

A

15 parts air to 1 part fuel

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10
Q

What is the secondary airflow from the compressor?

A
  • bypasses the primary combustion zone and mixes with hot gas in dilution zone
  • used for cooling (as temperature 2000°C in centre of flame)
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11
Q

How does the secondary airflow bypass the primary combustion zone?

A

It enters the dilution zone of the flame tube via dilution air holes

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12
Q

What are the three types of combustion chamber?

A
  • the can-type combustion chamber
  • the can-annular combustion chamber
  • the annular combustion chamber
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13
Q

Where would you find a single-chamber combustion chamber?

A

Small gas turbine engines such as APU

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14
Q

What is the purpose of the interconnector tubes in a multiple-can type combustion chamber?

A

They connect all chambers together and ensure equal pressure throughout and also ignition from the two chambers with the igniter plugs

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15
Q

What are the advantages of a can-type combustion chambers?

A
  • simple design
  • very good structural strength
  • can be installed and removed individually
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16
Q

What are the disadvantages of a can-type combustion chambers?

A
  • difficult ignition from one chamber to another
  • heavy and require a lot of space
  • complicated air supply ducts
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17
Q

What type of combustion chamber has flame tubes surrounding it?

A

The “can-annular” combustion chamber

18
Q

What are the advantages of can-annular combustion chambers?

A
  • simple air supply ducts
  • good structural strength
  • smaller and lighter than the simple multiple can-type
19
Q

What are the disadvantages of using the can-annular combustion chambers?

A
  • Aerodynamic losses are high

- ignition from one flame tube to another is difficult

20
Q

What type of combustion chamber is the most commonly used one on modern gas tubing engines?

A

The annular combustion chamber

21
Q

What is important about the annular combustion chamber’s outer casings?

A

They are part of the load carrying engine structure

22
Q

What are annular combustion chambers also known as because of their special design?

A

Reverse flow combustion chamber

23
Q

What are the advantages of annular combustion chambers?

A
  • better thermal load distribution
  • smaller and lighter
  • larger combustion area = better efficiency and smokeless combustion
  • flame is easier to spread over the flame tube
24
Q

What are the disadvantages of annular combustion chambers?

A
  • expensive to make

- removal is difficult and time consuming

25
Q

Why are annular combustion chambers used if they have disadvantages?

A

The disadvantages are compensated for by a very high service life

26
Q

What makes up an annular combustion chamber?

A
  • a combustion case
  • a flame tube
  • external components fixed to outer wall
27
Q

On the outer wall of an annular combustion case, what are the mounting flanges for?

A

They are for bleed air tubes and cooling air tubes

28
Q

What is the purpose of the flame tube in an annular combustion chamber?

A

It stabilises the flame during combustion

29
Q

What are the stator vanes of the last part of the HP compressor also known as?

A

Exit guide vanes

30
Q

What is a design feature of the inner wall of an annular combustion chamber?

A

It is usually removable so that the flame tube can be installed

31
Q

Where are the igniter bosses installed in comparison to the fuel nozzles?

A

They are installed slightly behind the fuel nozzles

32
Q

The fuel nozzle openings and the igniter plug openings can also be used as…?

A

Borescope inspection ports of the flame tube

33
Q

What is the purpose of the bore in a swirl vane?

A

It holds the nozzle tip in the centre

34
Q

How is the flame tube bolted to the combustion case?

A

By a fixed point at one end and a movable point at the other (thermal expansion)

35
Q

What is important about the mounting principle of a combustion chamber?

A

It allows for long service life for the flame tube

36
Q

What is film cooling?

A

The secondary airflow that enters the flame tube through liners instead of the swirl vanes creates a film of cooling air on the inner surface of the liners.

37
Q

What flame tube cooling methods are used on modern combustion chambers?

A
  • machined cooling rings
38
Q

What flame tube cooling methods were used in older combustion chambers?

A
  • Corrugated strips

- splash cooling strips

39
Q

What is the most sophisticated method of film cooling in the combustion chamber?

A

Transpiration cooling method

40
Q

What is a thin coating of ceramic material on the inner surface of the combustion chamber used for?

A

Heat protection

Module 15 Richard (18 decks)

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