In the APU, what does the fuel control unit regulate?

The fuel control unit in an Auxiliary Power Unit (APU) plays a critical role in managing the fuel flow to the combustion chamber. This regulation is essential for maintaining the proper operation and efficiency of the APU. By controlling the amount of fuel that is supplied, the fuel control unit ensures that the correct mixture of air and fuel is achieved for combustion, which directly impacts performance, start-up, and overall functionality of the APU.

Control over fuel flow is vital because if too much fuel is supplied, it can lead to inefficient combustion and potential engine damage, while too little fuel can result in incomplete combustion and power loss. Ensuring the correct amount of fuel flow also helps in the management of temperature and emissions from the combustion process, making the APU operate smoothly and within safety parameters.

This regulation of fuel flow distinguishes the fuel control unit from systems that manage fuel pressure levels, air intake temperature, or oil circulation rates, which are all critical to other functions but do not directly correspond to the primary responsibility of the fuel control unit within the APU.