A Study of the Delivery Ratio Characteristics of Crankcase-Scavenged Two-Stroke Cycle Engines

In order to increase the air charge of crankcase-scavenged two-stroke cycle engines, the relations between delivery ratio and engine speed were investigated on a rotary disc-valve inlet port engine and on a conventional piston-valve inlet port engine by varying through wide limits the angle area and timing of the inlet port. For the inlet port configuration tested on the first engine, it was found that there was an optimum cut angle of the rotary disc valve, which produced a certain angle area. To improve the delivery ratio characteristics at a given speed, it was not necessary to change this angle area; it was effective to change only the timing of the inlet port by shifting the disc valve around the crankshaft. For the piston-valve inlet port engine, the results showed that a wide, low port, which was also found to have a higher flow coefficient, produced a higher delivery ratio over the entire engine speed range than a narrow, high port. For the configuration tested (with no inlet or exhaust pipes), the maximum delivery ratio of the wide, low port was nearly in proportion to the effective crankcase stroke.