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 constructive restriction. On the other hand, the delivery ratio is considerably affected by the pressure pulsation in the exhaust and inlet systems. Changing the crankcase volume of a gasoline engine, the present authors have experimentally investigated its effect on the delivery ratio and the effect of the exhaust and inlet systems on the compensation for the drop of delivery ratio caused by the increase of crankcase volume. Finally they found out the conditions to improve conspicuously the delivery ratio by properly tuned exhaust and induction pipes.