Single cylinder tractor is one of the simple engines. It has only one cylinder, which is the basic form of engine. The working cycle of single cylinder engine consists of four piston strokes, namely intake stroke, compression stroke, power stroke and exhaust stroke.

Intake stroke

When the intake valve is opened and the exhaust valve is closed, the piston moves from top dead center to bottom dead center, the volume of the cylinder above the piston increases, resulting in vacuum, and the pressure in the cylinder drops below the intake pressure. Under the effect of vacuum suction, the gasoline atomized by carburetor or gasoline injection device mixes with air to form a combustible mixture, which is sucked into the cylinder by the intake port and intake valve. The intake process continues until the piston passes the bottom dead center and the intake valve is closed. Then the upward piston begins to compress the gas.

Compression stroke

The intake and exhaust valves are all closed, the combustible mixture in the cylinder is compressed, the temperature and pressure of the mixture increase.

Exhaust stroke

At the end of the working stroke, the exhaust valve opens. Because the pressure in the cylinder is higher than the atmospheric pressure, the high-temperature exhaust gas is quickly discharged from the cylinder. This stage belongs to the free exhaust stage, and the high-temperature exhaust gas is discharged through the exhaust valve at the local sound speed. As the exhaust process goes on, it enters the forced exhaust stage. The piston moves beyond the bottom dead center to the top dead center to force the exhaust gas out of the cylinder. When the piston reaches the top dead center, the exhaust process ends.

Power stroke

When the compression stroke approaches the top dead center, the spark plug installed above the cylinder head emits electric spark to ignite the compressed combustible mixture.

After the combustion of combustible gas mixture, a lot of heat is released, the pressure and temperature of the gas in the cylinder rise rapidly, and the high temperature and high pressure gas pushes the piston to move down the dead center quickly, and works externally through the crank and connecting rod mechanism. At the beginning of the power stroke, the intake and exhaust valves are closed.

If we look from the continuity of the work, the single cylinder engine is not stable, the speed fluctuation is large, and it is easy to shut down. However, its structure is simple, the manufacturing cost is low, and the maintenance is not complex. Now single engine is still widely used in small motorcycles, tractors, karts, and automatic rickshaws.