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During the scavenging of a two-stroke engine, it can be assumed that a very small quantity of fresh mixture flows from the scavenging ports and also from the crankcase through the gap between the cylinder and the piston to the exhaust port, in order to assess the effects of these leakages on fuel economy and hydrocarbon emissions, the authors calculated the quantity of mixture lost using the time-areas of the flow paths and the pressure-time history in the crankcase, and found that this quantity was in the order of 1-3% of the inducted fresh mixture.

The scavenging picture means here the velocity distribution of the scavenging flow in the cylinder measured by a pitot tube. The picture is often used to investigate the suitability of the design of the scavenging system in a two-stroke cycle engine. In measurements by pitot tube only the upward component of the velocity has been measured until now. By this improvement, however, it is well possible to measure the velocity in three dimensions. In other words, it is now possible to measure also the scavenging flow toward the exhaust port after the flow turns downward at the cylinder head.