A Simple and Realistic Model for the Scavenging Process in a Crankcase-Scavenged Two-Stroke Cycle Engine

E. Sher, R. Harari

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

A semi-empirical model for the scavenging process in a crankcase-scavenged two-stroke cycle engine is proposed. The model is based on the assumption that, typically, the time variation profile of the exhaust gas purity, β, exhibits a sigmoid-type curve while a rounded protuberance usually appears on its back, thus forming a ‘crest’ profile. The hump has been interpreted as the occurrence of an extensive short-circuiting. An exponential function of the form of is suggested to fit this curve, from which the scavenging efficiency has been derived. Two parameters, namely the mixing degree, b, and the short-circuiting degree, c, are to be calibrated. However, it was found that the selection of the best fitting values for b and c do not depend on the engine speed or on the engine load. Rather, b and c are inherent properties of the engine design. For modern engine design a value of 0.57 is recommended for b and a value of 0.81 for c/c-max. Calculations of the scavenging efficiency were found to be in excellent agreement with predictions of a detailed computer program for three small Schnürle-type different make engines. The present model does not consider a specific mechanism for the gas exchange process, and as such it is believed that it is applicable to other engine types (cross, loop or uniflow) to the same extent.

Original languageEnglish
Pages (from-to)129-137
Number of pages9
JournalProceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy
Volume205
Issue number2
DOIs
StatePublished - 1 Jan 1991

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