Why do turbine engine ignition systems typically use high-energy capacitor-discharge (CD) exciter units rather than the magneto-type ignition systems used on reciprocating engines?
- ATurbine engines require continuous sparking from the igniters throughout every phase of flight to sustain combustion
- BMagneto systems cannot generate sufficient voltage at high altitudes due to reduced air density inside the magneto
- CTurbine ignition is needed mainly for starting and occasional relight, and must produce an intense, high-voltage spark to ignite fuel in a high-velocity airstream
- DCD ignition systems eliminate the need for spark igniter plugs entirely
Show answer & explanationAnswer & explanation
Correct answer: C. Turbine ignition is needed mainly for starting and occasional relight, and must produce an intense, high-voltage spark to ignite fuel in a high-velocity airstream
Once combustion is established in a gas turbine, it is self-sustaining, so igniters are needed only for starting and occasional in-flight relight. Because fuel must be ignited in a fast-moving, often lean airstream, a very high-energy, intense spark from a capacitor-discharge exciter is required, far exceeding what a magneto can supply.
Why the other options are wrong
- A. Turbine combustion is continuous and self-sustaining once started, so igniters are turned off after light-off.
- B. Magneto voltage limitations relate to design, not altitude-related air density inside the magneto housing.
- D. CD systems still require igniter plugs to deliver the spark into the combustor.
Turbine Ignition System
A high-energy capacitor-discharge (CD) system that provides an intense spark for engine starting and occasional relight, unlike continuously firing reciprocating engine magnetos.
- Used only during start and relight, not continuously
- Exciter unit stores and discharges high-voltage energy
- Delivers spark via igniter plugs, not spark plugs
Memory trick: 'CD system: Charge, Discharge, Done' — one big spark to start, then quiet.