There are three types of scavenging
1. Cross scavenging
2. loop scavenging
The air inlet and exhaust ports are angled at the same end of the cylinder liner and they are placed opposite to each other.
scavenging efficiency is 0.75 to 0.8
For Cross scavenging,scavenge and exhaust porrs are arranged diametrically opposite one another on the cylinder. When Piston uncovers, scavenge ports,super charge air is directed upward passing under the cylinder cover and down the opposite side. It pushes the exhaust stream and expels the exhaust gas through the exhaust port on the other side of the scavenge port.
The scavenge ports are usually sloped in an upward direction to give an upward angle to the air stream.
the air inlet and exhaust ports at the same end of the cylinder liner but the exhaust ports are on the top of the inlet ports.
Scavenging efficiency is 0.8 to 0.9
In loop scavenging, exhaust port are in the same side above the scavenge port on the cylinder. The pattern of supercharger air flow takes place nearly across the diameter of the cylinder. it is also required long Piston skirt or exhaust timing vakve to prevent scavenging air leak into exhaust.
The ports inlet are angled to provide the input air with a rotating swirling impact.
3.Uniflow scavenging :-
The air inlet and exhaust ports or valves are arranged the opposite ends of the cylinder liner.
scavenging efficiency is more than 0.9
In this,scavenge ports are at lower parts on the cylinder liner surface.In this system, the supercharged air enters at the lower end of the cylinder and leaves at the top. The exhaust gas is expelled through the centrally installed exhaust valve in the cylinder cover.
The scavenge ports are angled to generate a rotational movement of for rising air column . The air is forced out of the cylinder by the moving Piston leading to low flow resistance to effect it sometime to squeezing the contents out of the tube.