1, the first stroke: the piston moves upward from the bottom dead center, and after the three air holes are closed at the same time, the mixed gas entering the cylinder is compressed; When the air intake is exposed, the combustible mixture flows into the crankcase.

2. The second stroke: When the piston is compressed to near the top dead center, the spark plug ignites the combustible mixture, and the gas expands to push the piston to move down to do work. At this time, the air inlet is closed and the combustible mixture sealed in the crankcase is compressed; When the piston approaches the bottom dead center, the exhaust hole opens and the exhaust gas rushes out; Then, the air exchange hole is opened, and the pre-compressed combustible mixture rushes into the cylinder to drive away the exhaust gas and carry out the air exchange process.

Extended data:

Advantages of two-stroke engine

1 and two-stroke engines have no valves, which greatly simplifies the structure and reduces the dead weight.

2. The two-stroke engine is ignited once every revolution, while the four-stroke engine is ignited once every other revolution. This provides an important power base for the two-stroke engine.

3. The two-stroke engine can run in any direction, which is very important in some equipment such as chain saw. When the oil sloshes, the standard four-stroke engine may fail unless it is upright. Solving this problem will greatly increase the flexibility of the engine.

These advantages make the two-stroke engine lighter, simpler and cheaper to manufacture. A two-stroke engine also has the potential to put twice the power into the same space, because it has twice the power stroke every revolution. The combination of lightness and dual power makes it have an amazing "thrust-to-weight ratio" than many four-stroke engines.

Baidu encyclopedia-two-stroke engine