How does increasing compressor pressure ratio affect engine performance and stability?

• A. Increases efficiency and power but reduces surge margin unless stability controls are used.
• B. Decreases efficiency and reduces power.
• C. Has no effect on engine performance.
• D. Reduces fuel consumption significantly.

Answer: (A)

Increasing the compressor pressure ratio raises the pressure rise the compressor must achieve, which boosts the Brayton cycle efficiency and the engine’s potential power output. But pushing the ratio higher also tightens the margin before the compressor surges or becomes unstable. Surge and stall are more likely when the airflow is limited or transients occur, because the compressor map shifts and the operating point can move toward the surge line. To safely push higher ratios, stability controls are required—things like variable geometry, bleed valves, and sophisticated engine control strategies that keep the flow and pressure in a stable range. When these controls are in place, the performance gains from a higher pressure ratio are realized; without them, surge margin is reduced and stability becomes a major concern.