Experimental Studies of the Mixing Processes and Flow Configurations in Two-Cycle Engine Scavenging

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Abstract
The paper describes work carried out at various stages during the period 1944–54 and indicates the need for a new approach in the study of the scavenging process in two-stroke engines. Its main object is to outline various ways of studying the main features of the scavenge flow within the cylinder as distinct from the gas dynamics of the charging process. By using a special photo-electric cell probe in a scale model and determining the change in purity of the stream at any point it was possible to examine the basic characteristics of scavenging flow and consider the process as taking place in broadly three phases. The first of these, entailing the formation and development of the inlet jets, has been studied in a preliminary way with the aid of a colour reacting technique to show the mixing region together with the undiluted core of a jet starting from rest. This has thrown light on the rate of mixing in the initial phases of scavenge flow and has indicated the possibility of achieving higher efficiencies by a reduction in the size of inlet ports and an increase in their number. An experimental study carried out on a loop-type system has shown that the flow configuration can be substantially different from that usually assumed and that flow instabilities could occur leading to partial short-circuiting of the flow. Photographic records of the flow and the major axis of rotation under various conditions have been obtained and assist in showing qualitatively the effect of altering the angles of entry of the jets. It is further shown that under certain conditions an increase in the inlet air flow could nullify any gains in scavenging efficiency. End-to-end scavenge systems are also discussed, indicating the need for further study of some of the major parameters governing the flow.

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