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EGK Engines > Gas Turbine - Combustion > Flashcards

Gas Turbine - Combustion Flashcards

1
Q

Requirements for combustion section

A

High combustion efficiency
Stability
Reliable
Exit temp does not exceed blades temp limit
Low emissions/low fuel consumption

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2
Q

Where is the highest pressure found in turbine engine

A

The diffuser after the last compressor before combustion

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3
Q

1st stage of combustion

A

Fuel injector sprays fuel into recirculating air into chamber

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4
Q

2nd stage of combustion

A

Electric igniter plug starts combustion then switches off

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5
Q

3rd Stage of combustion

A

Mixture starts burning and flame spreads around combustion chamber and flame becomes self sustaining

15:1 - 2100 degrees

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6
Q

4th Stage of combustion

A

Self sustaining speed all engine spools have reached a self sustaining speed where assistance from air starter not needed.

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7
Q

How is the air starter disengaged

A

Coupling between engine N2 spool and starter by use of centrifugal forces

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8
Q

Distribution of air into combustion phase from diffuser as percentages

A

20% direct into core
80% secondary air flows around the tube and introduced after combustion

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9
Q

Swirl Vanes do what

A

Create recirculation to slow air for continuous combustion

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10
Q

What temperature do gases leave combustor

A

1000 degree to 1500 degrees

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11
Q

Types of combustion layouts

A

Multiple (old design tubes all around)

Annular (circles around each other)

Turbo annular (canned tubes and circles together)

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12
Q

Advantage of annular combustion layout

A

Shorter/stiffer and lighter engine
Even distribution

Less wall area required so less cooling so more air for combustion chamber emissions

No flame propagation problems during engine start

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13
Q

Types of fuel injectors for combustion

A

Air spray injector (simplex):
HP delivery through a swirl chamber then out of nozzle - inefficient at low RPM

Duplex fuel nozzle:
Has a small orifice for low RPM
Has a large orifice for high power
Powered via FADEC

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14
Q

Fuel Burner Drain purpose

A

Prevent unburned fuel in combustion section

Drains away at lowest points in each section

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15
Q

High Energy Ignition Unit

A

Delivers 60-100 sparks per minute
25,000 volts

High power output - 12 joules for short periods of high altitude starts/ground start

Lower power - 3-6 joule for continuous ignition

Basically a magneto that pumps up a capacitor until it cannot hold anymore charge

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16
Q

When would we use the high energy ignition system

A

Engine start
Using contaminated runways
Flying through conditions that could cause flameout

17
Q

What does the HPSOV do

A

Delivers fuel

18
Q

Purpose of swirl vanes

A

Angle airflow sideways using swirl vanes

Increase radial velocity but reduce axial velocity

19
Q

What happens to pressure in the combustion chamber

A

Pressure does not go up as we do not allow gases to expand

20
Q

Secondary air is used for

A

Cooling of the flame tube

21
Q

What reduces axial flow in chamber

A

Due to swirl vanes/perforated flare and airflow from the sides

22
Q

What types of combustion chamber has a flame tube

A

They all do

23
Q

Percentages of cooling and dilution air in the dilution zone

A

40% cooling
20% dilution

24
Q

Highest max temp in the engine is located at

A

Just before entry to turbine stator

25
Q

Primary Airflow

A

20% of the hot stream gassed used to actual combustion

26
Q

Secondary Airflow

A

80% of the hot gas stream
Used for cooling (60%)
Stabilise the flame (20%) (primary zone)

27
Q

Multiple Can - Combustion Chamber

A

Used in radial compressors
One fuel nozzle in each can
Ignition only present in two cans

28
Q

Turbo Annular

A

Used in axial flow compressors
In line with compressor and diffuser so no deflection losses
Can surrounded by single outer casing

29
Q

Annular Chamber

A

Main type in axial flow compressors
Single flame tube
2 igniters and lots of fuel nozzles
Less weight and less cooling required

30
Q

Types of Fuel Nozzles in combustion and where they are found

A

Simplex - single delivery poor atomisation at low fuel flows
Duplex - primary lower pressure /main orifice for high pressure

2 simplex nozzles in annular chamber near igniter and rest of the duplex type

31
Q

Fuel drains

A

Located at lowest point within chamber
Held shut by combustion pressure
Takes 30 secs to drain fuel

32
Q

Gas Behaviour in combustion

A

Highest temperature occurs during combustion
Constant pressure - constant stream of gas
Increase in pressure = stall

33
Q

Another advantage of an annular combustion chamber is

A

Reduced thermal stress on the turbine

34
Q

Diffuser is a very

A

Divergent duct increase pressure and reduce velocity

35
Q

Continuous Ignition - What does FADEC automatically switch on in response to

A

Engine anti ice
Maximum flex thrust selected
Idle thrust selected
Thrust control malfunction detected
Stall warning/stick shaker

EGK Engines (22 decks)

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