The Petrol Engine

The Otto engine (named after Nikolaus August Otto, 1832-1891) is an internal-combustion engine. During the combustion of a fuel-air mixture, energy is released and transformed into mechanical work, that is, motion.

That’s How It Works:

In a carburettor, the air required for combustion (only the air makes the ignition and the combustion of the fuel possible) is mixed with the liquid fuel and sucked into the cylinder by the piston that is sliding down (e). Afterwards, the generated mixture is compressed in the cylinder and ignited by the spark of a spark plug (b), as a result, combustion takes place. Due to the expansion of the generated gas, the piston in the cylinder is pushed downwards and the crankshaft (h) is set into motion by a connecting rod (g) connected to the piston. Eventually, the piston that is moving upwards expels the burned gas and a new fuel-air mixture is sucked in.

Otto engines are distinguished into four-stroke and two-stroke engines. A stroke is the period of time that the piston needs to move from one dead-centre (moment, where the piston changes its direction of motion) to the next.

The Four-Stroke Otto Engine

In the four-stroke engine the work process is split into four strokes (two turns of the piston):

Sucking in: Sucking in of the fuel-air mixture

Compressing: Compressing of the mixture by the piston

Working: Ignition and combustion

Expelling: Forcing out the burned mixture

The Two-Stroke Engine

The two-stroke engine generally has no valves, but a port control. This makes it possible that two work processes can take place simultaneously with every piston stroke (half a piston turn). So the entire work process happens during a single turn of the piston.

Sucking in/compressing

Working/Expelling

Where Are Otto Engines used?

In our cars we will usually find a four-stroke engine under the bonnet. Other engines are rarely used. In motor boots, four-stroke engines are often used as well. The two-stroke Otto engine is used for low-powered mopeds, mopeds, some small motorcycles and lawn mowers.