Under which condition is vaporisation of fuel most likely to occur?

Vaporisation of fuel is most likely to occur at a high power setting with hot fuel and low atmospheric pressure due to several factors related to thermodynamics and engine operation.

When an aircraft operates at high power settings, the engine demands more fuel to maintain performance. This increased fuel flow can lead to higher temperatures within the fuel system, especially if the fuel is already hot. On the other hand, the ambient atmospheric pressure plays a critical role in the vaporisation process.

Lower atmospheric pressure reduces the boiling point of the fuel, which means that it can change from liquid to vapor at a lower temperature than it would at standard atmospheric pressure. Therefore, when hot fuel is subjected to low atmospheric pressure, the conditions are ripe for vaporisation to occur, as the high engine demands combined with the lower ambient pressure facilitate the formation of vapour.

This understanding is based on the principles of fluid dynamics and thermodynamics, highlighting the balance between temperature, pressure, and fuel state. The other scenarios involve conditions that either reduce the likelihood of fuel vaporisation or create an environment where the fuel remains stable in its liquid form.