15.13 STARTING AND IGNITION

Question 1

2 separate systems are required to ensure gas turbine engine will start satisfactory which are

Answer 1

• compressor and turbine to be rotated at an adequate speed (to produce sufficient air)
• ignition of air/fuel mixture

Question 2

Is it possible for the motor of the engine to operate without ignition

Answer 2

Yes

Question 3

How is a gas turbine engine simply started

Answer 3

Rotating high-pressure compressor

Question 4

The starter must continue to assist the engine until what?

Answer 4

• reaches self-sustaining speed

Question 5

Why must the torque supplied by the starter be excessive

Answer 5

• to overcome compressor inertia and friction loads of engine compressor

Question 6

Once there is sufficient airflow established through the engine, what occurs

Answer 6

• ignition turned on, followed by fuel

Question 7

Why must the starter continue to assist the engine above self-accelerating speed

Answer 7

• to avoid delay in the starting cycle

Question 8

Explain cartridge starter

Answer 8

• quick independent method of starting
• small impulse type turbine that is driven by high velocity gases from a burning cartridge

Question 9

How is the cartridge ignited

Answer 9

By applying voltage

Question 10

To achieve a cartridge start, it is first placed where

Answer 10

Breach cap

Question 11

Explain a air starter

Answer 11

• motor transmits power through a reduction gear and clutch to the starter output shaft

Question 12

Where is the air taken from for the starter turbine to rotate

Answer 12

• external ground supply
• APU
• cross feed from a running engine

Question 13

Only 1 source of around 30-50psi is used at a time to start the engines

Answer 13

True

Question 14

What happens to the clutch as the engine accelerates up to idling r.p.m

Answer 14

• automatically disengages

Question 15

What clutch assembly engages automatically as soon as the rotor starts to turn but disengages as soon as the drive coupling turns more rapidly than the rotor side

Answer 15

Sprag clutch assembly

Question 16

What oil does the starter use

Answer 16

Turbine oil

Question 17

Is the starter easy to remove for maintenance

Answer 17

Yes

Question 18

If the air starter valve fails to open what happens

Answer 18

• there is a manual valve which overrides to allow engine start

Question 19

What are the 2 electric starter systems

Answer 19

• direct cranking electrical systems
• starter generator systems

Question 20

Explain direct cranking electrical starter

Answer 20

• DC electric motor
• common on small turbine engines, such as APU and turbo-shaft engines

Question 21

Explain starter generator starting system

Answer 21

• most gas turbines are equipped with this
• Like direct cranking electrical systems, except they also contain a second series of windings

Question 22

Explain starter generator engagement

Answer 22

• permanently engaged with engine shaft necessary drive gears

Question 23

Explain direct cranking starter engagement?

Answer 23

• employ some means of disengaging the starter from the shaft after engine has started

Question 24

The starter generator is a shunt generator

Answer 24

True

Question 25

When would continuous ignition be used

Answer 25

• if there is a possibility of engine flame out
• e.g. used for landings

Question 26

Most turbine engines are equipped with what type of ignition system

Answer 26

• high-energy capacitor type ignition system which are air-cooled by fan airflow

Question 27

As a safety factor how many igniter plugs are fired

Answer 27

2

Question 28

Once combustion has been initiated what happens to the flame

Answer 28

It is continuous

Question 29

Each discharge circuit incorporates how many storage capacitors

Answer 29

2

Question 30

What is a exciter

Answer 30

• dual unit producing sparks at each of the 2 igniter plugs
• continuous series of sparks is produced until engine starts

Question 31

Explain annular gap ignitor plug

Answer 31

• projects slightly into combustion chamber liner to produce more effective spark
• known as ‘long reach ignitor’

Question 32

Explain constrained gap plug

Answer 32

• operates at cooler temp
• does not project into combustion chamber liner