Questions people actually ask

In an internal-combustion engine the fuel and air burn inside the engine itself, and the hot gases push on a moving surface such as the face of a piston. Encyclopaedia Britannica: Internal-combustion engine Each four-stroke cycle takes four strokes of the piston (intake, compression, power and exhaust) and two turns of the crankshaft. Encyclopaedia Britannica: Gasoline engine

Intake stroke: with the inlet valve open, the piston moves down and draws a mixture of petrol vapour and air into the cylinder. Encyclopaedia Britannica: Gasoline engine Compression stroke: with both valves closed, the piston moves up and squeezes the mixture; near the top an electric spark sets it alight. Encyclopaedia Britannica: Gasoline engine Power stroke: with both valves still closed, the expanding burnt gas presses the piston down. Encyclopaedia Britannica: Gasoline engine Exhaust stroke: the rising piston pushes the burnt gases out through the open exhaust valve, and the cycle starts again. Encyclopaedia Britannica: Gasoline engine

A petrol engine burns a volatile liquid fuel, petrol or a petrol mixture such as ethanol, and an electric spark starts the burning. Encyclopaedia Britannica: Gasoline engine In a diesel engine, air is squeezed until it is hot enough to set alight the diesel fuel sprayed into the cylinder. Encyclopaedia Britannica: Diesel engine Diesel engines are also called compression-ignition engines, because the fuel is lit by air heated by squeezing, not by a spark. Encyclopaedia Britannica: Diesel engine

The diesel engine’s most outstanding feature is its efficiency: by squeezing air alone it can use higher compression ratios than a spark-ignition engine. Encyclopaedia Britannica: Diesel engine Diesel engines are generally about one-third more efficient than petrol engines. US Department of Energy and EPA, fueleconomy.gov: Where the energy goes (petrol vehicles)

A spark plug fits into the cylinder head and has two electrodes with a small air gap; current jumps the gap as a spark that lights the air-fuel mixture. Encyclopaedia Britannica: Spark plug

A turbocharger is a blower driven by a small turbine that is spun by the engine’s own exhaust gases. Encyclopaedia Britannica: Supercharger

In a car engine the flywheel smooths out the pulses from the cylinders and gives energy for the pistons’ compression strokes. Encyclopaedia Britannica: Flywheel

If the driven gear has twice as many teeth as the small driving gear, it turns at half the speed with twice the torque. Encyclopaedia Britannica: Gear

One horsepower is 33,000 foot-pounds of work a minute: enough to lift 33,000 pounds one foot in one minute. Encyclopaedia Britannica: Horsepower One horsepower is 746 watts. Encyclopaedia Britannica: Horsepower

The French inventors Nicéphore and Claude Niépce built an early internal-combustion engine, the Pyréolophore, in 1807. Encyclopaedia Britannica: Étienne Lenoir Étienne Lenoir, a Belgian inventor, devised the first commercially successful internal-combustion engine, patented on 24 January 1860. Encyclopaedia Britannica: Étienne Lenoir In 1876 Nikolaus Otto built an engine using the four-stroke cycle; because he was the first to build one, it is called the Otto cycle. Encyclopaedia Britannica: Nikolaus Otto

A Wankel rotary engine has no pistons going up and down: a curved triangular rotor orbits inside a closed casing. Encyclopaedia Britannica: Wankel engine In a Wankel engine the output shaft turns three times as fast as the rotor, and one turn of the rotor completes intake, compression, expansion and exhaust. Encyclopaedia Britannica: Wankel engine

A hybrid car has a petrol or diesel engine and one or more electric motors; the battery is charged by regenerative braking and by the engine, not by plugging in. US Department of Energy, Alternative Fuels Data Center: How do hybrid electric cars work? An all-electric car has an electric motor instead of an internal-combustion engine, with no tailpipe exhaust and no fuel pump, fuel line or fuel tank. US Department of Energy, Alternative Fuels Data Center: How do all-electric cars work?