The centrifugal compressor in an APU is responsible for what function?

The correct answer highlights the primary function of a centrifugal compressor, which is to raise the pressure of air. In an auxiliary power unit (APU), the centrifugal compressor plays a crucial role by taking in ambient air, compressing it, and increasing its pressure. This compressed air is vital for various functions, including providing airflow to the engine for starting or facilitating combustion processes.

The design of centrifugal compressors, characterized by rotating impellers, allows for significant increases in air pressure relative to the ambient atmospheric pressure, making them efficient for applications like APUs in aircraft. This functionality is essential for ensuring that engines can operate effectively, especially during starting or in challenging operational conditions.

The other functions listed, such as increasing mass airflow or generating electrical energy, do not accurately reflect the primary function of the centrifugal compressor itself. While these aspects may be indirectly influenced by the operation of the APU and its components, the key role of the centrifugal compressor is specifically to increase air pressure.