Scavenging

Scavenging-

It is the process of pushing exhaustedgas-charge out of the cylinder and drawing in a fresh draught of air or fuel/ air mixture for the next cycle. This process is essential in having a smooth-running internal combustion engine. If scavenging is incomplete, the following stroke will begin with a mix of exhaust fumes rather than clean air. This may be inadequate for proper combustion, leading to poor running conditions such as four-stroking. Scavenging is equally important for both two- and four-stroke engines. However it
is more difficult to achieve in two-stroke engines, owing to the proximity, or even overlap, of their induction and exhaust
strokes. Scavenging is also equally important to both petrol and diesel engines. Modifying the exhaust system, (i.e. modifying the exhaust gas velocity by changing exhaust tube diameters) can
detract from the "ideal" scavenging effects, and reduce fuel efficiency and power if not properly planned out and executed.