This report deals with a study concerning the scavenging performance of a two-stroke cycle gasoline engine under the following conditions: the throttle of the carburetor is set at variable levels, the delivery ratio is set at a predetermined level, the engine speed is varied, and the scavenging and exhaust ports are set at different heights. If the properly selected factors stipulated for a scavenging model are used, the calculated results can be made as consistent as the measured results of the carburetor set at full throttle, as discussed in the previous reports [1, 2]. The mass diffusion, mixing, and short-circuit factors make up the essential coefficients. The factors represent major characteristics: blow-back, return-blow, and the loss of fresh gases. These phenomena are more clearly illustrated by three-dimensional representations of the gas components in the scavenging passage and exhaust pipe. The analyses of these functions may provide an effective means of improving the scavenging performance, i.e., the delivery ratio, trapping efficiency, and charging efficiency.

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