Definition
The pressures generated inside an engine cylinder when the fuel-air mixture burns during the power stroke. These pressures push the piston down, turning the crankshaft, and they vary with engine power setting, mixture, and the timing of ignition.
Plain English
The push created inside each cylinder when the fuel and air burn. That push is what drives the engine.
Context Anchor
Seen in constant-speed propeller operation when discussing the relationship between engine speed, manifold pressure, and how hard the engine is being loaded.
Derivation
Combustion comes from the Latin 'combustio,' meaning 'burning up.' Pressure is the force pushing outward on the cylinder walls and piston as that burning happens. Together: the force created by burning fuel inside the engine.
Why Pilots Care
These pressures directly influence propeller blade angle and must be balanced by counterweights or oil pressure so the governor can maintain the selected RPM.
Intuition Check
Combustion pressures are not the pressure in the fuel line or the pressure shown directly on the manifold pressure gauge. They are the pressures produced inside the cylinders as the mixture burns.
Example Sentence 1
Operating with high manifold pressure and low RPM can create combustion pressures higher than the engine is designed to handle.
Example Sentence 2
The propeller governor uses oil pressure to overcome combustion pressures and keep the blades at the angle needed for the chosen RPM.