15.13 - Starting and Ignition Systems Flashcards
Does idle RPM of a jet engine change?
Yes, with altitude and with anti-icing switched on
What does the start master switch control?
Prepares electrical system - placing all AC power to the starter (if electric)
Ensures engine gauging systems are powered for the start in all conditions
What are the two main methods of starting a jet engine?
Electric and air starters
What is the purpose of a starter jaw?
It engages the starter motor axially with the gearbox and once started, moves back disengaging with the gearbox.
What is a sprag clutch?
Another way of engaging the starter to the gearbox. The ratchet pawls/sprags rotate with the engine and engage with lower centrifugal forces, ensuring the engine starter is connected below idling speed
What is the main advantage of using a starter generator?
One unit required to perform starter and generator functions, saving weight and less spare parts required
Where does an air starter get its air from?
A ground supply truck
The APU
Engine compressor air (from another running engine)
What are the requirements of the ignition system?
Engine starting
Relight at altitude if necessary
Continuous operation during critical flight conditions
What are the two circuits called in ignition systems?
Continuous duty (low energy) Intermittent duty (high energy)
What is the trembler mechanism?
A switch which vibrates in a DC ignition system; creating a spark and storing it in the primary capacitor until there is enough charge to jump the discharge gap
Where would you find a DC ignition system?
On a jet, where there is no APU and battery input voltage isn’t hugely there for starting
What are igniter plugs made from?
Nickel-chromium alloy
Why is a ceramic semiconductor igniter plug the one used today?
Resistance of the semiconductor increases as it heats up. The air gap between electrodes becomes ionised and the resistance is lower than the semiconductor; which causes a high energy spark as it discharges across the air gap
How can ceramic igniter plugs be cleaned from carbon deposits?
With a solvent and soft metallic brush
How is the depth of an igniter plug maintained?
A boss is installed on the outer engine casing into the combustor liner.
