Effect of Crankcase Volume on the Delivery Ratio of a Crankcase-Scavenged Two-Cycle Engine

In order to increase the delivery ratio and the scavenge pressure in a crankcase-scavenged two-cycle engine, the crankcase volume must be made as small as possible. However, there exists the constructional restriction. On the other hand, the delivery ratio is considerably affected by pressure fluctuations in the exhaust and inlet systems. The present authors have experimentally investigated the effects of the crankcase volume and of the exhaust and inlet systems on the delivery ratio. It was confirmed that the drop in the delivery ratio caused by the increase in the crankcase volume could be fairly well compensated by tuning the exhaust and induction pipes. Finally they found out the conditions to improve vastly the delivery ratio by the properly tuned exhaust and induction pipes.