What does Engine Pressure Ratio (EPR) refer to?

What does Engine Pressure Ratio (EPR) refer to?

• A. Ratio of engine inlet to exhaust pressure
• B. Ratio of exhaust pressure to engine inlet pressure
• C. Ratio of compressor outlet to turbine inlet pressure
• D. Ratio of fuel-air ratio

Answer: (B)

Engine Pressure Ratio is a way to gauge thrust by comparing pressures before and after the core of the engine. It uses the total (stagnation) pressure at the engine inlet and the total pressure in the exhaust. In practice, EPR = Pt_exhaust / Pt_inlet. As you increase throttle, more fuel raises turbine power and the engine develops more exhaust pressure relative to the inlet, so the ratio climbs and correlates with thrust. It’s not the inlet-to-exhaust ratio, not the compressor outlet to turbine inlet ratio, and not related to fuel-air ratio.

Engine Pressure Ratio is a way to gauge thrust by comparing pressures before and after the core of the engine. It uses the total (stagnation) pressure at the engine inlet and the total pressure in the exhaust. In practice, EPR = Pt_exhaust / Pt_inlet. As you increase throttle, more fuel raises turbine power and the engine develops more exhaust pressure relative to the inlet, so the ratio climbs and correlates with thrust. It’s not the inlet-to-exhaust ratio, not the compressor outlet to turbine inlet ratio, and not related to fuel-air ratio.