FAA Powerplant Written Practice Test

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

1. Altitude

2. Burner pressure

3. Fuel temperature

4. Engine speed

The correct answer is: Burner pressure

The correct choice indicates that burner pressure is a key factor influencing the operation of an automatic fuel control system on a turbojet engine. In turbojet engines, the combustion chamber pressure—commonly referred to as burner pressure—plays a crucial role in determining the optimal fuel flow required for balanced and efficient combustion. The automatic fuel control system adjusts the fuel flow rate based on feedback from various engine parameters, including the pressure within the combustion chamber. By monitoring burner pressure, the fuel control system can ensure that the combustion process maintains the desired thrust and efficiency under varying operating conditions. As the pressure changes, whether due to throttle inputs or varying flight circumstances, the fuel control system can respond accordingly to provide the appropriate amount of fuel, thus optimizing performance. Other factors like altitude, fuel temperature, and engine speed do influence engine performance but are not as directly impactful on the immediate control of fuel flow in relation to combustion as burner pressure is. Altitude typically affects air density and, therefore, airflow dynamics, while fuel temperature can impact combustion efficiency and the viscosity of the fuel but does not play a direct role in the rate of fuel delivery controlled by the automatic system during normal operations. Engine speed is relevant for overall performance but is more of a consequence of fuel flow and burner