What is the purpose of the fuel control unit in a gas turbine?

• A. Measure ambient conditions and adjust fuel accordingly.
• B. Filter fuel and ignore temperature effects.
• C. Control lubricating oil pressure.
• D. Meter and schedule fuel flow to maintain the desired speed/power, regulate for altitude/temperature, and protect the engine from over-temp.

Answer: (D)

Fuel control is about precisely metering and scheduling the fuel that fires the combustor so the engine meets the desired speed or power. The fuel control unit takes the commanded operating point and translates it into the exact amount of fuel to inject, while continuously adjusting for changing conditions. It uses sensor data on engine speed, temperatures, and sometimes turbine inlet temperature, along with ambient conditions like altitude and air temperature, to keep the engine running at the required point without overstressing it. It also provides protection by limiting fuel flow if signs of over-temperature or other unsafe conditions appear, preventing damage to the turbine and compressor. That combination—metering fuel to meet speed/power goals, correcting for altitude and temperature, and protecting against overheating—is why this option is the best description.

The other ideas fall short because the fuel control unit’s purpose isn’t simply measuring ambient conditions or filtering fuel without regard to temperature effects, and it isn’t about controlling lubricating oil pressure. While ambient conditions inform the adjustments, the core function is to meter and schedule fuel flow to achieve the desired operation and safety limits.