How the internal combustion engine turns fuel into motion — types, construction and animated operation, with differences for ICE cars, hybrids and EVs
The internal combustion engine turns the chemical energy of fuel into mechanical work. Inside the cylinders an air–fuel mixture burns and pushes the pistons, which spin the crankshaft through the connecting rods, and from there torque flows to the transmission and wheels. The valvetrain opens and closes the valves at the right moment, the fuel and ignition systems prepare and ignite the mixture, and the cooling and lubrication systems keep the engine from overheating and wearing out. Engine design varies by cylinder layout and by fuel type, and in a hybrid it works together with an electric motor.
Engines are classified by cylinder layout and by fuel type
How the cylinders are arranged relative to one another
The cylinders sit in a single vertical row. The simplest, most compact and cheapest layout to build — used across the board on passenger cars with 3–4 cylinders.
Components
The cylinders are set in two banks at an angle, forming a V. This packs 6, 8 or more cylinders into a short block — used on powerful and premium cars.
Components
The cylinders lie flat in two opposing banks and the pistons move toward each other. This gives a low centre of gravity and good balance — typical of Subaru and Porsche.
Components
What ignites the mixture in the cylinders, and how
Runs on the Otto cycle: the air–fuel mixture is compressed and ignited by a spark plug. Revs higher more easily and is quieter and cheaper than a diesel.
Components
Runs on the Diesel cycle: fuel is injected into strongly compressed hot air and self-ignites, with no spark. More economical and torquier down low, but heavier and noisier.
Components
A petrol engine fitted with equipment to run on liquefied (LPG) or compressed natural (CNG) gas. Gas is cheaper and cleaner, and switching between fuels happens on the move.
Components
From a full-time ICE to no engine at all
The internal combustion engine is the only source of motion. It has to work across the whole load range — from idling in traffic to peak revs on the motorway — so its construction, cooling and transmission are built for constant, varied duty.
The engine works together with an electric motor and often uses the more efficient Atkinson cycle. The electronics decide when to start it and when to drive on electricity, so the ICE runs in its optimal range more of the time and can shut off entirely in traffic.
There is no internal combustion engine at all — an electric motor fed from the traction battery takes its place. The cylinders, valves, ignition, cooling and exhaust systems all disappear, leaving a compact and almost maintenance-free electric drive instead of a complex ICE.
The main parts and systems of an internal combustion engine
Click a part to see its description in the cards below
The engine's foundation, with the cylinders in which the pistons move. Coolant and oil passages are cast inside, and the crankshaft mounts underneath.
Moves up and down in the cylinder, taking the pressure of the burning gases and passing the force through the connecting rod to the crankshaft.
Links the piston to the crankshaft and turns the piston's motion into shaft rotation, taking large alternating loads.
Converts the pistons' up-and-down motion into rotation, which is passed on to the flywheel and the transmission.
Closes the cylinders from above and forms the combustion chambers. Its valves let fresh mixture in and let the exhaust gases out.
The camshaft's lobes open and close the valves at the right moment. The shaft is driven from the crankshaft by a timing belt or chain.
Creates an electric spark that ignites the air–fuel mixture in a petrol engine. In a diesel its job is done by compression ignition.
A heavy disc on the crankshaft that smooths out the jolts from individual power strokes and stores rotational energy for even running.
Distributes the incoming air (or mixture) among the cylinders, giving each one an even fill.
Regulates how much air enters the engine and thereby controls its power in response to the accelerator pedal.
Sprays a metered dose of fuel under pressure into the airflow or straight into the cylinder, forming the combustible mixture.
A pump circulates coolant through the block and radiator, carrying away excess heat and holding the engine at its working temperature.
Builds pressure in the lubrication system and feeds oil to the rubbing parts — the crankshaft bearings, the camshaft and the cylinder walls.
Uses the energy of the exhaust gases to force more air into the cylinders. This raises power without increasing engine displacement.