When does scavenging occur in the four-stroke diesel cycle?

Scavenging in a four-stroke diesel cycle refers to the process of clearing out exhaust gases from the combustion chamber at the end of the exhaust stroke and making space for fresh air to enter during the intake stroke. This process is facilitated by the valve overlap, which occurs when both the intake and exhaust valves are open simultaneously at the end of the exhaust stroke and the beginning of the intake stroke.

During this overlap, the incoming fresh air helps to push out the remaining exhaust gases, enhancing the engine's efficiency by ensuring that the combustion chamber is filled with as much fresh air as possible for the next power cycle. This is crucial for better combustion, increased power output, and reduced emissions.

The other strokes do not involve scavenging. The compression stroke is primarily focused on compressing the air-fuel mixture, the power stroke involves the combustion and expansion of gases to produce power, and the intake stroke's main function is to draw air into the cylinder, not to clear out exhaust gases. Thus, scavenging specifically occurs during the phase of valve overlap where both valves are open to optimize the intake of fresh air while expelling exhaust gases.