2-Stroke vs. 4-Stroke Engine: What are the Differences?

Contrary to what one might believe, the operating stages of a 2-stroke and 4-stroke engine are identical:

1. Admission

2. Compression

3. Explosion (gasoline)/Combustion (Diesel)

4. Exhaust

However, in a 2-stroke engine, oil, fuel and air are mixed in the combustion chamber, which is not the case in a 4-stroke engine where the fuel must not be mixed with the oil under any circumstances.

In a 2-stroke engine, the four stages are carried out in one piston back and forth, or 2 movements (one crankshaft revolution). The air/fuel/oil mixture is admitted during the piston rise by depression, followed very quickly by compression. The explosion that follows causes the piston to descend and the exhaust. The oil is therefore burned in the exhaust, which is not the case in a 4-stroke engine.

In a 4-stroke engine, the four operating stages are carried out in two piston back and forth movements, or 4 movements (two crankshaft revolutions). When the piston descends, air is admitted with the opening of the intake valves and mixes with the fuel thanks to the injectors. Compression then takes place when the piston rises and, under no circumstances (except in the event of a technical problem), does the oil mix with the fuel. With the explosion/combustion, the piston is sent back down and the exhaust occurs when it rises. Therefore, except in the event of a technical problem, the burnt oil is not evacuated through the exhaust.