Compressor performance at altitude Compared with operation at sea level, the performance (capacity and pressure ratio capability at a given speed) of an air compressor operating at high altitudes will be __________.

Introduction / Context:
Ambient conditions strongly influence compressor performance. At higher altitudes, air density and ambient pressure are reduced, affecting mass flow capacity, surge margin, and achievable pressure ratios at a given rotational speed.

Given Data / Assumptions:

• Same mechanical speed and geometry at altitude as at sea level.
• Lower ambient static pressure and density at altitude.
• No variable geometry or control changes assumed for the comparison statement.

Concept / Approach:
Mass flow rate m_dot = rho * V_dot. For the same volumetric flow capability, lower ambient density rho directly reduces m_dot. The compressor map referenced to corrected conditions shows that at altitude the corrected speed and flow shift, reducing surge margin and practical pressure ratio at fixed speed.

Step-by-Step Solution:
Recognize density and inlet pressure drop with altitude.At fixed volumetric flow, mass flow decreases proportionally to density.Lower inlet pressure reduces achievable absolute delivery pressure for a given pressure ratio, impacting useful performance.Therefore, overall performance is lower compared to sea level.

Verification / Alternative check:
Engine and compressor manufacturers publish altitude derating curves showing reduced capacity and different surge/choke boundaries at higher altitudes.

Why Other Options Are Wrong:
“The same” ignores density effects. “Higher” contradicts basic continuity and compressor map behavior.

Common Pitfalls:
Confusing corrected (standardized) performance with actual performance; corrected data hides ambient effects by design.

Final Answer:
lower