FAA Aviation Mechanic Powerplant (AMP)Turbine EnginesEasy
A mechanic removes a turbine engine igniter plug and notices it does not fire across a fixed narrow gap like an automotive spark plug. Instead, it stores electrical energy and releases it in an intense spark across a resistive surface. Which igniter type is this, and why is it used?
- AMassive electrode automotive-type igniter, because it withstands high compressor discharge pressure
- BShielded platinum igniter, because it uses low voltage supplied directly from the aircraft battery bus
- CFine-wire igniter, because it produces continuous low-energy sparking suitable for idle operation
- DAnnular gap (semiconductor) igniter, because it stores high energy in a capacitor and discharges it across a semiconductor material to produce a very hot, intense spark
Show answer & explanationAnswer & explanation
Correct answer: D. Annular gap (semiconductor) igniter, because it stores high energy in a capacitor and discharges it across a semiconductor material to produce a very hot, intense spark
Turbine ignition systems use high-energy capacitor discharge (CD) units feeding annular gap igniter plugs with a semiconductor material bridging the gap; this allows energy to build up and release in a very hot, high-energy spark needed to ignite fuel in the combustor, even in adverse conditions.
Why the other options are wrong
- A. Turbine igniters are not automotive-style fixed-gap plugs.
- B. Turbine ignition systems use high voltage/high energy CD units, not low battery voltage directly.
- C. Fine-wire plugs are used on reciprocating engines, not turbine igniters.
Turbine Igniter Plug
A high-energy annular gap igniter with a semiconductor material bridging the electrode gap, fired by a capacitor discharge ignition exciter.
- Semiconductor surface allows current path even before high energy discharge
- Produces very hot, intense sparks needed for combustor light-off
- Used with high-energy CD ignition exciters, not automotive-type systems
Memory trick: Semiconductor plug = a tiny capacitor bomb bridging the gap