Definition
A combustion cycle in which fuel is burned at an essentially constant pressure while the working gas expands in volume. It is the thermodynamic cycle used by gas turbine (jet) engines, where air is continuously compressed, mixed with fuel and burned in the combustion chamber at steady pressure, then expanded through the turbine and exhaust to produce thrust or shaft power.
Plain English
It is the way a jet engine makes power: air flows in, is squeezed, then fuel is burned at a steady pressure while the hot gas expands and rushes out the back. Unlike a piston engine, the burning happens continuously and the pressure stays roughly the same during combustion.
Context Anchor
Seen in powerplant theory when comparing gas turbine engines with piston engines.
Derivation
Constant means unchanging, and pressure here refers to the pressure of the gas inside the combustion chamber. The phrase highlights what stays the same during burning: pressure holds steady while volume increases, which is the opposite of the piston engine cycle where volume is held briefly constant and pressure spikes.
Why Pilots Care
It explains why turbine engines run smoothly and continuously rather than in pulses, why they need a steady airflow to operate, and why the design priorities (mass airflow, compressor efficiency, turbine inlet temperature) differ from those of a reciprocating engine.
Analogy
It is like heating air in an open-ended tube: the air can keep moving through, so pressure does not build sharply the way it would in a sealed container.
Grounding Statement
Picture a steady flame inside a tube with air rushing through it: the flame burns continuously at the same pressure while the heated air expands and accelerates out the back end.
Intuition Check
Do not read “constant-pressure” as meaning pressure never changes anywhere in the engine. It means the energy-release part of the cycle is treated as happening at nearly the same pressure.
Example Sentence 1
Turbine engines operate on the constant-pressure cycle of energy release, so combustion is continuous rather than occurring in separate power strokes.
Example Sentence 2
The constant-pressure cycle of energy release lets the engine run continuously as long as fuel is supplied.