In 1876 Nikolaus August Otto constructed for the Deutz gas engine factory the first four-stroke engine in the world, a stationary single-cylinder engine. He had already invented the principle of the four-stroke engine in 1861.
Petrol engines are those piston engines with external carburation. (The FSI® petrol direct injection engine has internal carburation). The compression temperature of the fuel-air mixture at 400-600°C is still below the spontaneous combustion threshold, so it must be ignited by a spark. Unleaded fuels (super plus, super, regular grade petrol) are used in engines with a regulated catalytic converter.