Is it normal to see the bulk fuel temperature colder than the engine fuel?

The correct answer reflects the nature of the fuel flow and temperature variations as fuel moves through different components of the aircraft's fuel system. It is indeed normal for the bulk fuel temperature to be colder than the engine fuel because the bulk fuel is typically stored in a tank where it is subject to ambient temperatures. Before entering the engine, the fuel passes through various parts of the fuel system, including the fuel heat exchanger, which can warm the fuel to ensure optimal combustion and engine performance.

In this context, the fuel heat exchanger is specifically designed to take the colder bulk fuel and warm it up before it reaches the engine. This process is crucial, particularly during normal operational conditions, as it helps in improving the efficiency of the combustion process within the engine. As the fuel moves closer to the engine, it is warmed up, leading to the engine fuel having a higher temperature compared to the stored bulk fuel.

Understanding this process is critical for maintaining optimal engine performance and ensuring that the fuel remains at appropriate temperatures for effective combustion, especially during various operational phases.