Engine Pressure Ratio (EPR) is defined as which of the following?

Engine Pressure Ratio (EPR) is defined as which of the following?

• A. Total Pressure Ratio Across The Engine
• B. Pressure Ratio Across The Turbine Exhaust To The Engine Inlet
• C. Ratio Of Compressor Discharge Pressure To Inlet Pressure
• D. Ratio Of Turbine Exhaust Pressure To Engine Inlet Pressure

Answer: (D)

Engine Pressure Ratio is a measure that compares the pressure left in the exhaust to the pressure at the engine inlet. In practical terms, this uses the turbine exhaust total pressure (the pressure as the gases exit the turbine and approach the nozzle) divided by the compressor discharge pressure at the engine inlet (the pressure entering the engine from the compressor). This ratio tracks thrust because as you increase throttle, the engine produces more energy and the exhaust pressure rises relative to the inlet pressure. The definition captures how much energy remains in the gas stream after passing through the turbine compared with what the engine ingests at the inlet, giving a direct indication of engine power. Other pressure ratios describe different things—for example, the overall engine total-pressure ratio or a ratio involving ambient inlet pressure—so they don’t define EPR. The standard expression matches the turbine exhaust pressure to the engine inlet pressure.

Engine Pressure Ratio is a measure that compares the pressure left in the exhaust to the pressure at the engine inlet. In practical terms, this uses the turbine exhaust total pressure (the pressure as the gases exit the turbine and approach the nozzle) divided by the compressor discharge pressure at the engine inlet (the pressure entering the engine from the compressor).

This ratio tracks thrust because as you increase throttle, the engine produces more energy and the exhaust pressure rises relative to the inlet pressure. The definition captures how much energy remains in the gas stream after passing through the turbine compared with what the engine ingests at the inlet, giving a direct indication of engine power.

Other pressure ratios describe different things—for example, the overall engine total-pressure ratio or a ratio involving ambient inlet pressure—so they don’t define EPR. The standard expression matches the turbine exhaust pressure to the engine inlet pressure.