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Internal combustion engine

An internal combustion engineAn internal combustion engine A car is usually powered by a piston engine, a kind of internal combustion engine. It is so-called because fuel, usually petrol or diesel oil, but sometimes hydrogen or liquefied petroleum gas, is burned (combusted) inside it. In this way, the engine converts the chemical energy stored in its fuel into movement or kinetic energy. Inside the heavy engine block are cylinders: normally four in a car engine. Pistons fit snugly inside the cylinders. When the engine is running, the pistons turn the crankshaft via connecting rods, and the crankshaft turns the wheels.

An internal combustion engine in cutawayAn internal combustion engine in cutaway
Pistons turning the crankshaftPistons turning the crankshaftClick to play video

How it works

In a petrol engine, petrol, a liquid fuel, is pumped from the tank to an electronic fuel-injection system. There it is turned into a fine spray and mixed with air. Inlet valves let the fuel-air mixture into the engine’s cylinders where it is ignited by electric spark plugs. The opening and closing of the valves is precisely controlled and timed by the rotation of the camshaft. Four or more cylinders sparking one after the other very quickly produce a continuous power to the wheels.

Movement of a piston inside a cylinder Movement of a piston inside a cylinder During what is called the four-stroke cycle, the explosions that result when the spark plugs ignite the fuel-air mixture drive the pistons inside the cylinders up and down. The crankshaft, to which the pistons are attached, turns this up-and-down motion into a turning motion. The crankshaft is, via the gears, connected to the wheels, and so the car is driven along. Exhaust gases, meanwhile, escape from the cylinders via the exhaust valve, and are piped out of the engine through the exhaust manifold. Lubricating oil allows the engine’s moving parts to slide alongside one another smoothly. Oil passing through the filter is cleaned of any grit and other impurities.

Possibly the world's first internal combustion engine was invented by Nicéphore and Claude Niépce in 1807 (Nicéphore went on to produce the world's first photograph in 1827). Known as the Pyrélophore, it powered a boat that ran on the river Saône.  

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