Which device is commonly used to regulate fuel flow to a gas turbine APU to control its RPM?

• A. Fuel (Governor) FCU
• B. Fuel Pump
• C. Electronic Control Unit
• D. Ignition System

Answer: (A)

Maintaining the APU’s RPM requires a regulator that adjusts fuel flow based on speed feedback. This is provided by the Fuel Control Unit with a governor. The governor continuously monitors the turbine speed and meters fuel to the combustor to keep the RPM at the desired level. If the speed drops, it opens the fuel metering valve to increase fuel flow; if the speed climbs, it trims fuel flow to slow it down. This automatic regulation allows the APU to respond to changing loads and conditions while staying at a stable speed.

The fuel pump only delivers fuel under pressure; it doesn’t regulate RPM. The ignition system is for starting and flame stability, not steady-state RPM control. An electronic control unit can manage engine functions in some systems, but the device that directly regulates fuel flow in response to speed for APUs is the fuel control unit with a governor.