In simple terms
An internal combustion engine generates power by burning a fuel-air mixture inside a set of enclosed cylinders, rather than burning fuel externally to heat a separate working fluid. [1] The pressure from that burning mixture pushes a piston, and the engine converts that push into rotation.
How it works
Most car engines run on a four-stroke cycle. In the intake stroke, a piston moves down, drawing a mixture of air and fuel into the cylinder. In the compression stroke, the piston moves back up, squeezing that mixture into a small space. In the power stroke, the mixture is ignited, either by a spark plug in a gasoline engine or by the heat of compression alone in a diesel engine, and the rapidly expanding gases force the piston back down with considerable force. [1] Finally, in the exhaust stroke, the piston pushes the spent gases out of the cylinder, and the cycle repeats.
Each piston connects to a crankshaft through a connecting rod, and the crankshaft converts the pistons’ straight up-and-down motion into the rotating motion that ultimately drives the wheels, propeller, or other output. [1]
Why it matters
Only a fraction of the energy released by burning fuel becomes useful mechanical work; a large share is lost as heat through the exhaust and cooling system, which is why engine efficiency, and reducing that waste, has been a central focus of automotive engineering for decades. [2]
Where you’ll see it
- Most cars, trucks, and motorcycles on the road today
- Lawn mowers, generators, and other small gasoline-powered equipment
- Diesel engines in trucks, ships, and heavy construction equipment
- Piston aircraft engines in smaller planes
Example
A car accelerating from a stoplight is drawing air and fuel into its cylinders, compressing and igniting that mixture dozens of times per second in each cylinder, and converting the resulting force through the crankshaft into the torque that turns the wheels.
Often confused with
An electric motor produces rotation directly from electromagnetic forces and has no combustion, fuel, or exhaust at all; it is a fundamentally different way of producing motion, not a variation on the internal combustion engine.
Key facts
- Most internal combustion engines in cars run on a four-stroke cycle: intake, compression, power, and exhaust.1
- Ignition is either spark-triggered, as in gasoline engines, or triggered by compression alone, as in diesel engines.1
- The burning fuel-air mixture rapidly expands, pushing a piston down, and that linear motion is converted into rotation by a crankshaft.1
- Only a portion of the fuel's energy becomes useful mechanical work; a large share is lost as heat, which is why engines need cooling systems and exhaust management.2
In the news
Quick checkWhat is the basic job of the crankshaft in an internal combustion engine?Show answer
It converts the up-and-down, linear motion of the pistons into the rotating motion that ultimately turns the wheels or other output.
Sources
- Encyclopaedia Britannica. Internal combustion engine. Undated (accessed 1 November 2026)
- U.S. Department of Energy. How Do Gasoline Car Engines Work?. Undated (accessed 1 November 2026)
Editorially reviewed by Last reviewed November 1, 2026Researched and drafted with AI assistanceReport an issue