Engine pressure ratio
The engine pressure ratio (EPR) is the total pressure ratio across a jet engine, measured as the ratio of the total pressure in the engine nozzle (after the turbine) divided by the total pressure in the inlet section of the engine (ahead of the compressor).
In many gas turbine engines, the EPR is used as the engine rating parameter, i.e. as an easily measurable indication of the thrust that the engine is currently producing.
Integrated engine pressure ratio
The integrated engine pressure ratio (IEPR) is the ratio of the pressure at the core engine exhaust and fan discharge pressure compared to the intake pressure to the gas turbine engine. The IEPR is an engine indicator system unique to the Rolls-Royce RB211.
- The Boeing Company Engine thrust control system US Patent 4248042 Includes Boeing's discussion on EPR or IEPR being a better indicator of thrust.