A Single-Cycle Test Apparatus for Studying “Loop Scavenging” in a Two-Stroke Engine

Abstract

An apparatus is described for studying the process of scavenging the cylinders of loop-scavenged two-stroke engines. This consists essentially of a full-scale single-cylinder model of the engine with means for driving it for a single porting cycle. Tests upon the apparatus are made at atmospheric temperature and different gases are used at appropriate pressures to simulate the correct densities of the engine air charge and exhaust gas. The choice of suitable gases permits an easy analysis of the trapped charge for the determination of the efficiency of the scavenging process. Some experimental results and conclusions are presented, including the effects of operating with high charge densities and exhaust back pressures. A method is developed of expressing, from the experimental results, the scavenging performance of a given design of ports. This takes the form of curves relating the volumetric total charge supplied and the charging efficiency with the pressure ratio across the ports. These relationships are otherwise independent of the mass charge, the intake density, the exhaust back pressure, and the pressure loss across the cylinder. The influence of crankshaft speed is examined, as also are some causes of lost efficiency.