Module 15.13 Start & Ignition Flashcards
How are gas turbine engines started?
By rotating the high-pressure compressor to provide sufficient air to support combustion in the combustion section.
Once ignition and fuel have been introduced what must continue running?
The starter
Why must the starter keep running after fuel have been introduced?
To assist the engine until the engine reaches a self-sustaining speed.
When is the ignition turned on?
As soon as the starter has accelerated the compressor sufficiently to get enough airflow through the engine.
What would happen if assistance from the starter was cut off below the self-accelerating speed?
The engine would either fail to accelerate to idle speed or might even decelerate (a hot or hung false start).
What is a cartridge starter?
A small impulse-type turbine that is driven by high velocity gases from a burning cartridge.
The power output of the turbine is passed through a reduction gear and an automatic disconnect mechanism to rotate the engine.
What type of starter is used on most commercial jet engines?
The air starter.
How does an air starter work?
It transmits power through a reduction gear and clutch to the starter output shaft which is connected to the engine.
Where does an air starter get air from?
External ground supply, auxiliary power unit (A.P.U.) or cross-feed from a running engine.
What psi of air is used at a time in an air starter?
30-50 psi
When does the sprag clutch in an air starter engage and disengage?
Engages automatically as soon as the rotor starts to turn, but disengages as soon as the drive coupling (engine) turns more rapidly than the rotor side.
How is the engine started if the air starter valve fails to open?
There is usually some form of manual valve override to allow engine start.
How many engineers are need to manually one the air starter valve?
Two
What are the two types of electric starting systems?
Direct cranking electrical systems
Starter-generator systems
What is a direct cranking electric starter?
A direct current (D.C.) electric motor coupled to the engine.
What engines use a direct cranking electric starter?
Small turbine engines, such as Auxiliary Power Units (APUs).
What is a starter generator starting system?
A starter system that acts like a direct cranking electrical starter system, except after that, they switch to a generator once the engine has reached a self-sustaining speed.
What does the ignitor do?
Ignites the fuel in the combustion chamber.
When is the ignitor switched off?
After the fuel has been ignited and there’s a constant flame.
When is the continuous ignition mode used?
If there a possibility of engine flame out.
What type of ignition system do most turbine engines use?
A high-energy capacitor-type.
What are ignition systems cooled by?
Fan air
When is cooling of the ignition system important?
When the continuous ignition is used for a period of time.
What are the three power sources of the ignition system?
Battery
115 AC
Permanent magnet generator
Where is ignitor energy stored?
In capacitors
How many capacitors does each ignition discharge circuit incorporate?
Two
Where are the capacitors for the ignition discharge circuit located?
In the exciter unit.
What is an exciter?
A dual unit that produces sparks at each of the two igniter plugs.
How many ignitor plugs are there?
Two
What is an annular gap igniter plug sometimes referred to?
A long-reach igniter.
Why are annular gap igniter referred to as long-reach igniters?
Because they protrude slightly into the combustion chamber liner to produce a more effective spark.
Why does a constrained gap ignition plug operate at much cooler temperatures?
It does not project into the combustion chamber liner.
What is the most likey way for an igniter to accidentally discharge?
By touching the igniter
What is the correct procedure for disconnecting the igniter?
Disconnect igniter lead coupling nuts at the exciter end first.
What should you ensure of before touching the ignition units?
That there’s no electricity left in them.
How long should you not touch the ignition units for after opening the circuit breakers?
3 minutes
What type of turbine does a cartridge starter use?
Impulse type
