In combustion engines the inner energy set free by combustion (e.g. of gasoline or diesel fuel) is changed partly into mechanical energy. Beside the four-stroke engine, the two-stroke engine is used (e.g. in lawn-mowers or in power saws). Every second stroke the engine is operating - there are no valves. It is necessary to use a mix of gasoline and oil (two-stroke oil) as fuel. This is used to lubricate the piston and the crank shaft.

The principle of the way the 2-stroke engine works:

1st stroke

The compressed fuel-air mixture ignites and thereby the piston is pressed down. At the same time the intake port I is covered by the piston. Now the new mixture in the crankcase becomes precompressed. Shortly before the piston approaches the lower dead centre, the exhaust port and the overflow conduit are uncovered. Being pressurized in the crankcase the mixture rushes into the cylinder displacing the consumed mixture (exhaust now).

2nd stroke

The piston is moving up. The overflow conduit and the exhaust port are covered, the mixture in the cylinder is compressed. At the same time new fuel-air mixture is sucked into the crankcase.

By means of a crank shaft the up and down motion is converted into a rotational motion.

Click here, to find out more detailed information about the Otto-engine.