Scavenging (engine)

If scavenging is incomplete, the remaining exhaust gases can cause improper combustion for the next cycle, leading to reduced power output.

This method requires that the exhaust pipe is long enough to contain the gas slug for the entire duration of the stroke.

The momentum of the gases assists in scavenging during the 'overlap' phase (when the intake and exhaust valves are simultaneously open).

However, the deflector piston was not very effective in practice - much of the gas flow took a shortcut path and still failed to reach the top of the cylinder - and the shape of the piston compromised the shape of the combustion chamber by causing long flame paths and excessive surface area.

This scavenging method does require a greater understanding of the 3-dimensional gas flow in the cylinder and more care in the placement, size, and angle of the various ports.

Uniflow scavenging is a design in which the fresh intake charge and exhaust gases flow in the same direction.