Definition
The third stroke in the four-stroke cycle of a reciprocating engine, during which the burning fuel-air mixture expands rapidly inside the cylinder, driving the piston downward and producing the mechanical work that turns the crankshaft. It follows the compression stroke and precedes the exhaust stroke, and is the only stroke of the four that actually produces power.
Plain English
It is the part of the engine cycle where the fuel burns and pushes the piston down, which is what actually makes the engine turn and produce power.
Context Anchor
Seen in piston-engine theory, engine operation discussions, and descriptions of the intake, compression, power, and exhaust cycle.
Derivation
Stroke here means a single full movement of the piston from one end of the cylinder to the other. Power names what this particular stroke produces, distinguishing it from the other three strokes (intake, compression, exhaust), which consume or move energy rather than produce it.
Why Pilots Care
Recognizing this phase helps pilots understand power output, fuel efficiency, and symptoms of combustion problems.
Intuition Check
Do not read power stroke as any time the engine is making power. It means one specific piston movement: the burning mixture pushes the piston down after compression.
Example Sentence 1
During the power stroke, the expanding gases push the piston down with enough force to turn the crankshaft and drive the propeller.
Example Sentence 2
A rough-running engine may show weak power strokes on a cylinder analysis.