One of the ways internal combustion engines work. Alternatives include the four stroke engine cycle (Otto cycle), and the one used in rotary engines (Wankel engines, though they technically use the Otto cycle, but in an odd way).

Like the four stroke engine cycle, the 2-stroke engine cycle -using engine is of the reciprocating type, with pistons moving back-and-forth in a column. Fuel mixed with air is burned, and the increase in pressure and volume is used to generate useful work.

The cycle is:

  • intake/compression - the piston moves into the combustion chamber, with fuel and air being introduced at the beginning of the stroke. At maximum compression, the fuel/air is ignited, usually by a spark plug
  • exhaust/power stroke - the piston is moving out of the combustion chamber, pushed out by the force of the burning fuel. At near the end of the cycle, the exhaust gasses leave the combustion chamber

Because there are twice as many power cycles compared to the Otto cycle, more power should be generated by two cycle engines. However, the inefficient exhaust and intake phases cancel out the benefits. However, there are some benefits to two cycle engines, with simplicity being perhaps the most important.

Due to the construction of two cycle engines, they usually have lubrication mixed in with the fuel.

Two cycle engines are used in lawn mowers, some motorcycles and snowmobiles, and other light vehicles.