FAA Powerplant Written Practice Test

What is the compression ratio of an axial flow compressor primarily dependent on?

1. Number of compressor stages

2. Type of fuel used

3. Diameter of the compressor

4. Ambient air temperature

The correct answer is: Number of compressor stages

The compression ratio of an axial flow compressor is primarily dependent on the number of compressor stages. Each stage of an axial flow compressor consists of a rotor which accelerates the air and a stator which diffuses the air, converting kinetic energy into pressure energy. As the air progresses through successive stages, each stage contributes to an increase in the total pressure, thereby enhancing the overall compression ratio. The more stages that are included in the design of the compressor, the higher the potential compression ratio can be achieved. This design utilizes the principle that each stage incrementally increases the pressure of the air, culminating in a significant overall change in the air's pressure and density as it exits the compressor. While factors such as the type of fuel, diameter of the compressor, and ambient air temperature can influence the performance and efficiency of the compressor, they do not determine the compression ratio as directly as the number of stages does. The number of stages is a fundamental design characteristic that defines how much the compressor can compress air from its inlet to its outlet.