Definition
In a gas turbine engine, the ratio of the ideal work required to compress air to a given pressure to the actual work the compressor expends to achieve that same pressure rise. It is expressed as a percentage and reflects how much of the energy put into the compressor goes into useful pressure increase rather than being lost to heat, turbulence, and friction.
Plain English
A measure of how good the engine's compressor is at squeezing the air. The closer the actual work matches the perfect, theoretical amount needed, the higher the efficiency.
Context Anchor
Seen in turbine engine performance, engine design, and discussions of why an engine may make less power or run hotter than expected.
Derivation
Compressor comes from the Latin comprimere, meaning to press together. Efficiency comes from the Latin efficere, to accomplish. Together: how well the part that presses the air together accomplishes its job.
Why Pilots Care
Higher compressor efficiency delivers more engine power or thrust for the same fuel flow and keeps operating temperatures lower.
Grounding Statement
For the same increase in air pressure, a more efficient compressor needs less power and creates less wasted heat.
Intuition Check
Do not read “efficiency” here as a general compliment meaning “the compressor is good.” In this context, it specifically compares useful air compression with the power actually used to get it.
Example Sentence 1
Erosion of the compressor blades over time reduces compressor efficiency and shows up as higher EGT at cruise power.
Example Sentence 2
Reduced compressor efficiency caused higher TIT readings during the climb.