EPR is defined as the ratio of engine jet pipe pressure to compressor inlet pressure. Which option correctly states this ratio?

• A. Compressor Inlet Pressure To Engine Jet Pipe Pressure
• B. Engine Jet Pipe Pressure To Compressor Inlet Pressure
• C. Jet Pipe Pressure To Ambient Pressure
• D. Ambient Pressure To Compressor Inlet Pressure

Answer: (B)

EPR is a measure of thrust setting based on the engine’s internal pressure rise. It is defined as the pressure at the engine’s jet pipe (the exhaust section) divided by the pressure at the compressor inlet. This means the jet pipe pressure is the numerator and the compressor inlet pressure is the denominator. As the engine produces more power, the jet pipe pressure climbs relative to the compressor inlet, raising the ratio. It is not ambient pressure and not the inverse of the ratio.