In a two-spool gas turbine engine, which statement correctly describes the LP and HP compressors?

• A. They are both mounted on the same shaft.
• B. The HP compressor handles initial low-pressure air, while the LP compressor finishes compression to higher pressure.
• C. The LP compressor handles initial low-pressure air; the HP compressor finishes the compression to higher pressure and drives the gas generator, on separate shafts.
• D. They operate in parallel to feed a single-stage combustor.

Answer: (D)

In a two-spool engine, two separate drive shafts carry the compressor stages: an outer low-pressure spool and an inner high-pressure spool. The air flow through the core is staged, with the air first entering the low-pressure compressor and then being further compressed by the high-pressure compressor before entering the combustor. The two compressors are on different shafts, and their outputs ultimately feed the same core combustor, not separate burners. The HP compressor does not start the cycle by handling the initial air; that is the job of the LP compressor, and the HP compressor then finishes the compression. The gas generator itself is driven by the turbine on the high-pressure spool, not by the compressor. Therefore, both compressors contribute to supplying the same combustor, which is why the statement describing them as operating to feed a single combustor is the best fit.