15.13 Start and Ignition Flashcards
What two separate systems are required for an engine start?
- provision must be made for compressors and turbine to be rotated up to speed to provide adequate air for combustion
- provision must be made for ignition of the air/fuel mixture
Why must the torque supplied by starter motor be in excess of torque required?
To overcome compressor inertia and friction loads
What will happen if the starter was to cut out before self accelerating speed is attained?
Engine fails to accelerate to idle or potentially decelerate
What are the two starter types?
- cartridge starter
- air starter
What initiates the burning of the cordite cartridge charge?
Electrically fired detonator
How is the cartridge ignited ?
Applying a voltage
“Cartridge generates gas when ignited”
Where is the gas directed to and by what?
Directed to the turbine via a relief valve
Which starter type is used on most commercial jet engines?
Air starter
What does the air starter transmit its power through?
Reduction gear and clutch
What are the the external air supplies used for rotating the starter?
- external ground supply
- APU
- engine cross feed
What happens if the air starter valve fails to open?
Manual override
*with a man in the flight deck and another on the valve
What controls the air supply to starter?
Electrically operated control and pressure reducing valve
What does the transmission housing contain?
The clutch, reduction gear, drive coupling and oil reservoir
What type of valve is used on the regulating valve assy?
Butterfly valve
What are the two types of electric starter motors?
Direct cranking
Starter generator
What is type of engine uses direct cranking?
Small GTE
APU
Small turboshaft
What are the 4 types of field windings?
Series field (c-field)
Shunt field
Compensating field
Interpole or commutating
What are the 3 field windings used during a start?
C-field
Compensating field
Commutating
What 3 field windings are used as a generator?
Shunt
Compensating
Commutating
What 3 relays close when battery and starter are switched ON?
Motor relay
Ignition relay
Battery cut out relay
When is continuous ignition used?
When there is a possibility of a flame out
* can also be used during T/O, landing and emergencies
What does a capacitor type ignition system consists of?
2 individual identical ignition units, operating from a common low DC V power source
What voltage does the exciter receive?
24V DC
Describe the discharge from the 2nd capacitor in a ‘capacitor discharge exciter unit’
Low voltage but high energy
What are the two types of igniter plugs?
Annular gap (long reach)
Constrained gap
What is the key features of an Annular gap igniter plug?
Projects slightly into combustion chamber liner to produce and more efficient spark
