FAA Powerplant Written Practice Test

What factor influences the operation of an automatic fuel control on a turbojet engine?

1. A Ambient temperature

2. B Burner pressure

3. C Fuel viscosity

4. D Engine RPM

The correct answer is: B Burner pressure

The operation of an automatic fuel control system on a turbojet engine is primarily influenced by burner pressure. This system is designed to optimize the fuel flow to the engine in response to changes in operating conditions. Burner pressure is critical as it directly relates to combustion efficiency and power output. The automatic control system adjusts the fuel flow based on the pressure within the combustion chamber to ensure that the correct air-to-fuel ratio is maintained for efficient combustion, thereby optimizing engine performance. While ambient temperature, fuel viscosity, and engine RPM do have some influence on engine performance, they are not the primary factors that the automatic fuel control directly regulates in response to operational changes. Ambient temperature affects air density and may indirectly influence fuel flow calculations, but the immediate feedback for fuel control adjustments comes from burner pressure. Fuel viscosity, while important for ensuring proper fuel atomization, does not directly govern the automatic control's operation. Engine RPM is an indicator of engine speed but does not provide the necessary feedback on how fuel should be adjusted in the combustion process as effectively as burner pressure does.