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 at the exit of the propelling nozzle divided by the total pressure at the entry to the compressor.
Jet engines use either EPR or compressor/fan RPM as an indicator of thrust. When EPR is used the pressures are measured anywhere convenient in the intake and exhaust ducts.
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.