15.13 STARTING AND IGNITION Flashcards
2 separate systems are required to ensure gas turbine engine will start satisfactory which are
- compressor and turbine to be rotated at an adequate speed (to produce sufficient air)
- ignition of air/fuel mixture
Is it possible for the motor of the engine to operate without ignition
Yes
How is a gas turbine engine simply started
Rotating high-pressure compressor
The starter must continue to assist the engine until what?
- reaches self-sustaining speed
Why must the torque supplied by the starter be excessive
- to overcome compressor inertia and friction loads of engine compressor
Once there is sufficient airflow established through the engine, what occurs
- ignition turned on, followed by fuel
Why must the starter continue to assist the engine above self-accelerating speed
- to avoid delay in the starting cycle
Explain cartridge starter
- quick independent method of starting
- small impulse type turbine that is driven by high velocity gases from a burning cartridge
How is the cartridge ignited
By applying voltage
To achieve a cartridge start, it is first placed where
Breach cap
Explain a air starter
- motor transmits power through a reduction gear and clutch to the starter output shaft
Where is the air taken from for the starter turbine to rotate
- external ground supply
- APU
- cross feed from a running engine
Only 1 source of around 30-50psi is used at a time to start the engines
True
What happens to the clutch as the engine accelerates up to idling r.p.m
- automatically disengages
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
Sprag clutch assembly
What oil does the starter use
Turbine oil
Is the starter easy to remove for maintenance
Yes
If the air starter valve fails to open what happens
- there is a manual valve which overrides to allow engine start
What are the 2 electric starter systems
- direct cranking electrical systems
- starter generator systems
Explain direct cranking electrical starter
- DC electric motor
- common on small turbine engines, such as APU and turbo-shaft engines
Explain starter generator starting system
- most gas turbines are equipped with this
- Like direct cranking electrical systems, except they also contain a second series of windings
Explain starter generator engagement
- permanently engaged with engine shaft necessary drive gears
Explain direct cranking starter engagement?
- employ some means of disengaging the starter from the shaft after engine has started
The starter generator is a shunt generator
True
When would continuous ignition be used
- if there is a possibility of engine flame out
- e.g. used for landings
Most turbine engines are equipped with what type of ignition system
- high-energy capacitor type ignition system which are air-cooled by fan airflow
As a safety factor how many igniter plugs are fired
2
Once combustion has been initiated what happens to the flame
It is continuous
Each discharge circuit incorporates how many storage capacitors
2
What is a exciter
- dual unit producing sparks at each of the 2 igniter plugs
- continuous series of sparks is produced until engine starts
Explain annular gap ignitor plug
- projects slightly into combustion chamber liner to produce more effective spark
- known as ‘long reach ignitor’
Explain constrained gap plug
- operates at cooler temp
- does not project into combustion chamber liner
