As compressor pressure ratio increases, the main effect on the compressor work is:

As compressor pressure ratio increases, the main effect on the compressor work is:

• A. Compressor work increases, potentially offsetting efficiency gains if cooling or fuel supply cannot meet demand.
• B. Compressor work decreases and efficiency always improves.
• C. Compressor work remains unchanged.
• D. Compressor work becomes negligible.

Answer: (A)

Raising the compressor pressure ratio makes the air require more shaft work to reach the higher pressure. As the pressure ratio climbs, the temperature rise during compression grows, so the energy per unit mass you must supply (roughly Cp times that temperature rise) increases. In real machines, the actual work is higher than the ideal due to compressor efficiency, so the shaft power needed grows even more with higher PR. Although increasing the pressure ratio can improve cycle efficiency by enabling better expansion or other thermodynamic benefits, those gains can be offset if the system can’t provide enough cooling after compression or enough fuel to keep the desired mass flow and temperatures in balance. In short, compressor work increases with pressure ratio, and that rise can erode potential efficiency gains if cooling or fuel supply can’t meet the demand.

Raising the compressor pressure ratio makes the air require more shaft work to reach the higher pressure. As the pressure ratio climbs, the temperature rise during compression grows, so the energy per unit mass you must supply (roughly Cp times that temperature rise) increases. In real machines, the actual work is higher than the ideal due to compressor efficiency, so the shaft power needed grows even more with higher PR.

Although increasing the pressure ratio can improve cycle efficiency by enabling better expansion or other thermodynamic benefits, those gains can be offset if the system can’t provide enough cooling after compression or enough fuel to keep the desired mass flow and temperatures in balance. In short, compressor work increases with pressure ratio, and that rise can erode potential efficiency gains if cooling or fuel supply can’t meet the demand.