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Module 15 - Gas Turbine Engines > 15.6 - Combustion > Flashcards

15.6 - Combustion Flashcards

1
Q

What are the 4 types of combustion sections?

A

Multiple-can
Can-annular
Annular-through flow
Annular-reverse flow

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2
Q

What is the ratio of fuel and air needed for a jet engine?

A

15 parts air to 1 part fuel

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3
Q

What is used to cool the flame tube?

A

Secondary air.
Either flowing between ceramic tiles and the interior walls, or by transpiration cooling where a film of air flows between laminations.

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4
Q

What is usually put on combustion liners?

A

A whitish coating which helps combat carbon deposits and erosion. Magnesium zirconate

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5
Q

Where would you see can type combustors?

A

Old gas turbine engines with centrifugal compressors

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6
Q

What are the advantages of can type combustors?

A

Simple design
Good structural strength
Can be maintained individually

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7
Q

What are disadvantages of can type combustors?

A

Large and heavy
Need lots of space
Complex compressor ducting (aerodynamic losses)
Ignition difficulties from one chamber to another

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8
Q

Where would you find a can-annular combustion chamber?

A

Older jet engines

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9
Q

What are advantages to a can-annular combustion chamber?

A

Smaller and lighter than multiple can design
Doesn’t need complex air ducting
Good strength

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10
Q

What are disadvantages to the can-annular combustion chamber?

A

High aerodynamic losses

Ignition difficulties from one chamber to another

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11
Q

Where would you find an annular combustion chamber?

A

Modern jet engines

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12
Q

How much shorter is the annular combustion chamber to its predecessors?

A

75%

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13
Q

What are the advantages of an annular combustion chamber?

A 
Smaller and lighter
High efficiency (larger combustion area)
Complete combustion and smokeless
Flame can spread easily
Better thermal load distribution 
Less cooling air required
Very high service life
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14
Q

What are the disadvantages to the annular combustion chamber?

A

Expensive

Removal is difficult and time consuming

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15
Q

What is the reverse flow combustion chamber?

A

A smaller annular combustion chamber that you would find on smaller engines or APU’s

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16
Q

What is a DAC?

A

Dual annular combustion chamber

17
Q

What is the purpose of using a DAC?

A

Reducing pollutants in the fuel;
Hydrocarbons
Carbon monoxide
Nitrogen oxides

18
Q

How is a DAC more efficient?

A

Has an inner and outer set of combustion areas, meaning the air-fuel ratio is controlled much better and reduces emissions.

19
Q

When is a flame-out more likely to occur?

A

During takeoff- if large amounts of water are ingested

During decent- when throttled back, less fuel but high airflow through engine

20
Q

What is the purpose of supplying air to the burner shroud and head?

A

It minimises carbon formation on the burner face

21
Q

How is the combustion chamber drain valve closed?

A

By the combustion chamber gas pressure. It will open on engine shut down.

22
Q

What is the purpose of the swirl vanes in the combustion chamber?

A

Gas re-circulation. They direct and slow the air as it enters the combustion chamber, and when it hits the secondary airflow, it creates a Toroidal Vortex.

23
Q

What type of welding is used for the fabricated liner of the flame tube?

A

Electric resistance welding

24
Q

What is the overall range of varying air/fuel ratio in a combustion chamber?

A

45:1 and 130:1

25
Q

What happens to the flow due to pressures in a duplex burner in terms of it’s main manifold?

A

It is restricted until the proper pressure is obtained.

26
Q

What does Carbon forming on fuel spray nozzles do?

A

Causes distortion of the fuel spray flow and direction. Can cause hot-spots within the combustion chamber

27
Q

What percentage of air is used in the combustion process?

A

40%

28
Q

What temperature is the flame in the combustion chamber?

A

2000 degrees C

29
Q

What is “Hot Streaking”?

A

A partially clogged fuel nozzle

30
Q

What is the purpose of the shroud placed around the fuel nozzles?

A

It prevents carbon build up

31
Q

Where does a vaporising burner inject fuel in comparison to airflow?

A

Against the airflow

32
Q

When is water/methanol injection used?

A

At high altitudes OR low air density

33
Q

In at atomising burner, where is the fuel atomised? (also known as a vaporiser)

A

Partly inside the swirl chamber and partly outside the injector

Module 15 - Gas Turbine Engines (22 decks)

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