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How does a gasoline engine turn fuel into mechanical power?

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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.

A gasoline engine converts fuel into mechanical power through a process of internal combustion, where the energy released from burning a fuel-air mixture is used to perform work on moving engine components.1

In the most common type, the four-stroke cycle, this process occurs in four distinct stages:2

Intake: The piston descends, drawing a mixture of gasoline vapor and air into the cylinder.2
Compression: The piston ascends with both valves closed, compressing the mixture.2
Power: An electric spark ignites the compressed charge. The resulting expansion of burned gases creates high pressure that pushes the piston, performing mechanical work.23
Exhaust: The piston ascends again, forcing the spent combustion products out through the open exhaust valve.2

In piston-and-cylinder engines, this reciprocating motion drives the piston, while in rotary engines, gas pressure acts on a rotor to create rotational movement. Ultimately, this thermodynamic process transforms the chemical energy of gasoline into the mechanical force required to power machinery.31