Working principle of two-stroke gasoline engine

The working cycle of a two-stroke internal combustion engine is completed in two piston strokes, that is, the crankshaft rotates one cycle. In a four stroke internal combustion engine, the exhaust and intake processes are commonly referred to as the ventilation process. In a two-stroke internal combustion engine, the gas exchange process refers to the process in which exhaust gas is swept away from the cylinder and replaced by fresh air. The main difference between the working cycles of the two internal combustion engines lies in the gas exchange process.
1. In the first stroke, the piston is driven by the crankshaft and moves from bottom dead center to top dead center.
When the piston is still at the bottom dead center, the inlet port is closed by the piston, and the exhaust port and scavenging port are opened. At this point, the combustible mixture in the crankcase enters the cylinder through the scavenging hole, sweeping away the exhaust gas inside. When the piston moves to the top dead center, the piston head first closes the scavenging hole and the scavenging is completed. But at this point, the exhaust hole has not yet been closed, and some exhaust gas and combustible mixture continue to be discharged through the exhaust hole, which is called additional exhaust. When the piston closes the exhaust port, the combustible mixture in the cylinder begins to be compressed. The compression process does not end until the piston reaches the top dead center.
2. In the second stroke, the piston moves from top dead center to bottom dead center.
At the end of the compression process, the spark plug generates an electric spark, igniting the combustible mixture in the cylinder. Gas expands to do work. At this point, the exhaust and scavenging ports are closed by the piston, but the inlet ports are still open. And air and gasoline continue to flow into the crankcase through the intake port until the piston skirt closes the intake port. As the piston continues to move towards the bottom dead center, the volume of the crankcase continues to decrease, and the mixture inside is pre compressed. Afterwards, the piston head first opens the exhaust hole, and the expanded combustion gas has become exhaust gas, which is discharged through the exhaust hole. At this point, the workflow ends and early exhaust begins. Then the piston opens the scavenging hole again, and the pre compressed combustible mixture enters the cylinder from the crankcase through the scavenging hole, sweeping out the exhaust gas and starting the scavenging process. This process will continue until the scavenging port closes on the next piston stroke.