What happens during the power stroke of a gasoline engine?

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Labeled cross-sectional diagram of a V-type gasoline engine for an automobile, showing internal components such as pistons, crankshaft, camshaft, intake and exhaust valves, connecting rods, spark plugs, and intake manifold. — gasoline engine Cross section of a V-type engine.

During the power stroke of a four-stroke cycle gasoline engine, both the intake and exhaust valves remain closed. Following the ignition of the air-fuel mixture by an electric spark, the rapid expansion of the burned gases creates high pressure. This pressure acts upon the piston head, propelling the piston and converting the energy from combustion into mechanical work.12