In the 18th century attempts were made to run engines by exploding gunpowder or burning turpentine in them. It was not until the end of the 19th century that easily vapourised oil products became available. These light oils (petrol) enabled a German engineer, Nikolaus Otto, to build the first practical internal combustion engine in 1876. The series of steps that takes place during the working of a petrol engine is known as the Otto.

Petrol vapour and air , into the where they are , and then by means of an electric . The resulting high-pressure gases the piston down inside the . The burned gases out of the cylinder the piston and the cycle is repeated over and over again. A movement of the up or down the is called a and it takes strokes (, , and ) to complete one complete Otto cycle during which the crankshaft turns around . Power is only produced during one of these four strokes (the stroke).

(From: The penguin book of the physical world, 1976)