Definition
In a gas turbine engine, the ratio of the air pressure at the compressor outlet (discharge) to the air pressure at the compressor inlet. It expresses how many times the compressor multiplies the pressure of the air passing through it before that air enters the combustion section.
Plain English
A number that tells you how much the engine's compressor squeezes the air. If the air leaves the compressor at eight times the pressure it came in at, the compressor pressure ratio is 8 to 1.
Context Anchor
Seen in turbine engine descriptions, engine performance discussions, and maintenance or systems training for jet and turboprop aircraft.
Derivation
Compressor comes from the Latin comprimere, meaning to press together. Ratio comes from the Latin for reckoning or relation between two quantities. Together the term simply describes the relationship between pressure going in and pressure coming out.
Why Pilots Care
It directly affects engine thrust, fuel efficiency, and operating temperatures; higher ratios allow more power but require stronger components and careful monitoring.
Analogy
It is like comparing the pressure in a bicycle pump before and after you push the handle. The useful idea is not just the final pressure, but how much the pump increased it.
Intuition Check
Compressor pressure ratio is not the same as compressor pressure. It is a comparison: pressure out divided by pressure in.
Example Sentence 1
Modern high-bypass turbofans can achieve a compressor pressure ratio of 40 to 1 or more, which contributes to their fuel efficiency.
Example Sentence 2
Engines with higher compressor pressure ratios typically deliver better fuel economy at cruise altitudes.