FAA Aviation Mechanic Powerplant (AMP)Reciprocating EnginesMedium
A turbocharged reciprocating engine uses a wastegate to control manifold pressure. What is the primary function of the wastegate?
- AIt cools the compressor discharge air before it enters the intake manifold
- BIt regulates the amount of exhaust gas directed to the turbine wheel to control boost
- CIt bypasses unmetered fuel around the fuel control unit at high altitude
- DIt relieves excess oil pressure supplied to the turbocharger bearings
Show answer & explanationAnswer & explanation
Correct answer: B. It regulates the amount of exhaust gas directed to the turbine wheel to control boost
The wastegate is a valve in the exhaust system that diverts a variable portion of exhaust gas away from the turbine wheel, controlling turbine (and thus compressor) speed and limiting manifold pressure to the desired setting.
Why the other options are wrong
- A. Cooling compressor discharge air is the job of an intercooler, not the wastegate.
- C. Fuel metering is handled by the fuel control/carburetor, not the wastegate.
- D. Oil pressure to turbo bearings is controlled by the engine oil system, not the wastegate.
Turbocharger Wastegate
A valve that controls the amount of exhaust gas routed through the turbine, regulating turbocharger speed and manifold pressure (boost).
- Located in exhaust system ahead of/around turbine
- Diverts exhaust overboard to limit boost
- Can be manually or automatically controlled
Memory trick: Wastegate = the exhaust's escape door that limits how hard the turbine spins.