Definition
In a turbine engine, the ratio of the air pressure at the compressor discharge (the air leaving the compressor on its way to the combustion section) to the air pressure at the compressor inlet. It expresses how much the compressor has squeezed the incoming air before fuel is added and burned.
Plain English
How many times denser the air is after the compressor has squeezed it, compared to the air entering the front of the engine.
Context Anchor
Seen in turbine engine descriptions, maintenance manuals, and performance discussions involving how efficiently the engine prepares air for burning fuel.
Derivation
Compression comes from Latin words meaning “to press together.” Ratio comes from Latin meaning “a reckoning or comparison.” Together, the term means a comparison of how much the air has been pressed together.
Why Pilots Care
Higher values improve efficiency and thrust but must stay within limits to avoid overheating or damage.
Analogy
It is like comparing the pressure in a bicycle pump before and after you push the handle down. The number tells you how much the pressure increased.
Intuition Check
Compression ratio does not mean the physical size of the engine or the amount of fuel being used. In a turbine engine, it means the pressure increase across the compressor.
Example Sentence 1
Modern high-bypass turbofans achieve much higher compression ratios than the early jet engines, which is one reason they burn far less fuel per pound of thrust.
Example Sentence 2
After overhaul the technician confirmed the compression ratio still met the manufacturer's limits.