Engine pressure ratio is defined as the difference between which two pressures?

The definition of engine pressure ratio is indeed focused on the relationship between pressures at specific points in a gas turbine engine's cycle. In this case, it refers specifically to the compressor inlet total pressure and the turbine discharge total pressure.

The compressor inlet total pressure is the total pressure of the air entering the compressor, which includes both the static and dynamic pressure contributions at that point. This is significant because it impacts the overall efficiency and performance of the engine, directly influencing how much air is compressed before entering the combustion process.

Conversely, the turbine discharge total pressure is the total pressure measured at the exit of the turbine, which indicates how much energy has been extracted from the exhaust gases after they pass through the turbine, slowing down significantly in the process.

The engine pressure ratio is crucial because it indicates the degree to which the engine compresses the incoming air compared to the pressure of the exhaust gases exiting the turbine. A higher pressure ratio typically signifies a more efficient engine design, as it indicates effective compression and turbine usage.

Understanding this ratio allows engineers and flight engineers to infer performance characteristics of the engine, which plays a significant role in determining fuel efficiency, thrust capabilities, and overall operational performance.