Turbine Engine Systems: Fuel, Lubrication, Ignition, Starting, and Air
Domain 7 tests the fuel, oil, ignition, starting, and air systems that support turbine operation.
Fuel and oil
- The fuel system includes tank boost pumps, engine-driven HP pump, fuel control unit or FADEC, fuel/oil heat exchanger, filter, and nozzles.
- Fuel scheduling is by N1/N2, throttle position, altitude, and temperature; FADEC trims fuel for acceleration and limiting.
- Lubrication is dry sump with pressure and scavenge elements, chip detector, filter, and oil cooler.
- Oil pressure and temperature limits are type-specific; low oil pressure may indicate pump, seal, or sensor problems.
Ignition, starting, air
- Exciters provide high-energy sparks; igniters are used for start and selected operations, not continuously in all engines.
- Start sequence: motoring, ignition, fuel on, light-off, acceleration to idle; hot or hung starts require abort.
- Bleed air supplies anti-ice, cabin pressurization, and cooling; excessive bleed extraction reduces thrust.
Worked example
A turbofan burns 3,000 lb/hr at 4,000 lbf thrust. TSFC = 3,000 ÷ 4,000 = 0.75 lb/(lbf·hr). The reasoning: specific fuel consumption normalizes fuel flow by thrust so engines of different size can be compared.
Traps
Leaving ignition on continuously; ignoring bleed-air effects on performance; using automobile oil; assuming a hung start will self-correct; resetting a chip detector without inspection.