Prevention of Backflow in a Crankcase-Scavenged Two-Stroke Engine by Fluid Diodes

概要

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A crankcase-scavenged two-stroke engine with piston controlled ports has inevitable backflow of inlet charge at low speed in case where the inlet port timing is designed to be suitable for high speed operation. This paper describes an attempt that was made to prevent the backflow by a fluidic device which has diode characteristics, namely a fluid diode. A comparison of the effects on delivery ratio produced by two typical types of fluid diodes, i.e. a scroll diode and a vortex diode, is made and it is shown that the former is more effective than the latter. Experimental evidence of prevention of backflow by the scroll diode is provided showing the data compared with those for its acoustically equivalent device. The inlet system with the scroll diode is theoretically analyzed to give the trend of the delivery ratio with engine speed, by simulating the engine having a straight inlet pipe with an acoustically equivalent length and with flow resistance which varies with flow direction.
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