There’s a major difference between a four stroke and two stroke engines. We’ll first start with the four stroke engine.
- Intake: the intake valve is opened; this helps the piston in travelling down the cylinder. Because the valve is opened this allows mixtures of fuel and air to come into the combustion chamber.
- Compression: once the intake valve is closed, the piston can travel back to the cylinder thus compressing the gases.
- Combustion: this causes the spark plug to ignite the condensed gas which causes it to explode. This then forces the piston to move down.
- Exhaust: the piston then rises up the cylinder which causes the exhaust valve to open. This also allows the piston to make room in the chamber which stars the process over again.
The motion of the piston rising and falling turns the crankshaft which is responsible for turning the wheels. This process is responsible for converting fuel into forward motion. The spark plug fires once every revolution. The four strokes are created by a set of mechanisms working in harmony. There’s also a camshaft that alternates to tip the rocker arm which is attached to either an exhaust valve or intake. A spring makes it possible for the rocker arm to return to its closed position.
To avoid compression leaks the valves need to be positioned properly. In a two stroke engine, the four events are incorporated into one downward and upward stroke, this makes it two strokes. Both the intake and exhaust are included in the condensing and combustion movements of the piston thus removing the requirement for valves. The piston travels down from combustion thus exposing the exhaust port.
This allows the exhausted gasses to escape the chamber. The downward stroke makes room for suction which pulls in new fuel through an inlet chamber. The piston will rise again blocking off the inlet and port also condensing the gasses at the top of the chamber.