How does a dual axial-flow compressor improve the efficiency of a turbojet engine?

How does a dual axial-flow compressor improve the efficiency of a turbojet engine?

• A. Higher compression ratios can be obtained
• B. Lower compression ratios
• C. No change in efficiency
• D. Increased turbine inlet temperature

Answer: (A)

The main idea is that using two axial-flow compressors in series lets the engine achieve a higher total pressure rise while keeping each stage operating at a comfortable loading. When the compression is distributed across two stages, each stage can do a moderate amount of work with better aerodynamic efficiency, reducing losses from high blade loading and flow disturbances. That means the overall compressor works more efficiently (higher isentropic efficiency) and the engine can reach a higher overall pressure ratio without pushing a single stage to its limits. A higher overall pressure ratio improves the Brayton cycle performance, boosting thermal efficiency and thrust for a given turbine inlet temperature limit. This is the practical reason why a dual axial-flow compressor can enhance engine efficiency: it enables higher compression ratios more efficiently. The other options don’t capture this effect: lowering the compression ratio or claiming no change misses the actual gain from distributing the work, and simply increasing turbine inlet temperature isn’t the outcome of adding a dual compressor.

The main idea is that using two axial-flow compressors in series lets the engine achieve a higher total pressure rise while keeping each stage operating at a comfortable loading. When the compression is distributed across two stages, each stage can do a moderate amount of work with better aerodynamic efficiency, reducing losses from high blade loading and flow disturbances. That means the overall compressor works more efficiently (higher isentropic efficiency) and the engine can reach a higher overall pressure ratio without pushing a single stage to its limits.

A higher overall pressure ratio improves the Brayton cycle performance, boosting thermal efficiency and thrust for a given turbine inlet temperature limit. This is the practical reason why a dual axial-flow compressor can enhance engine efficiency: it enables higher compression ratios more efficiently.

The other options don’t capture this effect: lowering the compression ratio or claiming no change misses the actual gain from distributing the work, and simply increasing turbine inlet temperature isn’t the outcome of adding a dual compressor.