What is the primary purpose of scavenging in a 4-stroke engine?

The primary purpose of scavenging in a 4-stroke engine is to enhance airflow to the combustion spaces. This process involves effectively removing the exhaust gases from the cylinder after combustion and allowing fresh air (or air-fuel mixture) to enter for the next power stroke.

In a 4-stroke engine, scavenging occurs in the overlap period when both the exhaust and intake valves are open. This overlap allows the incoming charge to help push out the residual exhaust gases, thereby improving the efficiency of the engine. Good scavenging ensures that the engine operates smoothly, maintains higher performance, and reduces the risk of unburnt fuel remaining in the cylinder, ultimately leading to a more complete combustion process.

While scavenging may also have an indirect effect on reducing emissions by ensuring complete combustion, its primary aim is to maximize the intake of fresh air into the combustion space, which enhances overall engine performance.