Uniflow Scavenging

Function

The uniflow scavenging reduces the scavenging problems of the two-stroke engine. The outlet port is opened earlier after the power stroke and during the inflow into the cylinder it is closed earlier. An unsymmetrical valve timing diagram evolves.

How it works

Two pistons at the crankshaft header are guided such that one piston rashes on its way to BDC and the other on its way to TDC. Thus the outlet port is opened earlier after the power stroke, and before the intake into the cylinder the transfer port is opened earlier, too. You may achieve a similar effect by using a horizontal crankpin that is not parallel to the crankshaft. The piston turned on the way from BDC to TDC in one and from TDC to BDC into the other direction. With a diagonal piston crown ports on one side could also be opened earlier and be closed later.

Disadvantage

A combustion chamber spanning two cylinder spaces, leads to an unfavourable combustion because of its length. (more emissions, high fuel consumption, thermal problems). 06/08