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The four-stroke engine How does an up-and-down movement turn a wheel?
Save to notebook Inside a petrol engine, burning fuel heats the gas above a piston. The expanding gas pushes the piston down. A connecting rod and an off-centre crank turn that push into rotation. Slow it down and follow one complete cycle.
Explore the model and follow its moving parts.
Read the full explanation ↓ Enable JavaScript for the interactive model. The written explanation and references are available on this page. Drag to rotate · Scroll to zoom · Select a part Four strokes. Two crankshaft turns. One power stroke per cylinder. How many crankshaft turns complete all four strokes? A One turnB Two turnsC Four turns
How the parts work together Intake The piston descends. An open intake valve lets a fresh mixture of air and fuel enter.
Compression Both valves close. The rising piston squeezes the mixture into a smaller space.
Power A spark ignites the mixture. Hot, high-pressure gas pushes the piston down and turns the crank.
Exhaust The exhaust valve opens. The piston rises, pushing spent gases out before the cycle repeats.
The main parts
Cylinder The chamber that guides the piston. The space above it grows and shrinks through each stroke.
Piston A sliding part that receives the force of the hot gas and passes it to the connecting rod.
Connecting rod The link between the sliding piston and the rotating crank. Its angle changes as the crank turns.
Crankshaft Its offset connection converts the piston’s back-and-forth movement into a turning shaft.
Flywheel A heavy rotating wheel that stores energy and helps smooth the motion between power strokes. What this model leaves out A simplified petrol-engine cutaway. Motion is slowed for learning; colours indicate cycle stages. Valve timing is prescribed; a cam or follower mechanism and open head ports are not modeled. Combustion, friction, and cooling are simplified.
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