What does P4 refer to in turbine engine terminology?

In turbine engine terminology, P4 refers to the pressure measured at the turbine inlet, which is the pressure in the combustion area just before the hot gases enter the turbine section. This pressure is critical because it greatly influences the efficiency and performance of the engine.

When discussing engine operation, measuring the pressure at this point allows engineers to assess how well the engine is performing and how effectively it is converting thermal energy from combustion into mechanical energy. High turbine inlet pressure often correlates with increased power output, as the turbine can extract more energy from the high-temperature gas flow generated by combustion.

Thus, P4 is significant in the context of understanding engine performance characteristics, thermodynamic cycles, and overall efficiency calculations within turbine engines.