What is the main controlling factor of an axial-flow compressor's pressure ratio?

The main controlling factor of an axial-flow compressor's pressure ratio is the number of stages in the compressor. Each stage of an axial-flow compressor consists of a rotor and a stator, which work together to increase the air pressure. The pressure ratio is a result of the cumulative effect of all stages, with each stage incrementally boosting the air pressure. Therefore, increasing the number of stages allows for a greater overall increase in pressure ratio, as each additional stage contributes to further compression of the air.

While compressor speed and inlet air temperature do influence performance, they do not fundamentally determine the pressure ratio in the way that the number of stages does. The type of fuel used is not relevant to the pressure ratio of the compressor, as it pertains more to the combustion process that occurs downstream in the engine. Thus, the number of stages is the definitive aspect that governs how much the pressure can be increased in an axial-flow compressor system.