Model testing the two-phase scavenging system in a two-stroke petrol engine

摘要

Due to an inadequate scavenging process two-stroke petrol engines suffer from substantial fuel-specific consumption, as well as from considerable emissions of toxic components in exhaust gases. This paper describes the model testing and evaluation of a new scavenging system in a small two-stroke petrol engine with internal working mixture preparation. The scavenging process is performed by two different gas media in two successive phases and is more sophisticated and effective than the conventional single-phase (Schnurle) principle. Using the similarity principle and dimensional analysis, a new mathematical model was developed for evaluation of the effectiveness of the scavenging systems. This makes it possible to establish relationships between the most important parameters of the model engine and of the real engine, which are independent of the dimensional parameters. The effectiveness of the scavenging systems was defined by means of qualitative scavenging efficiency. A special testing device for the model engine has been developed and a liquid working media (instead of gaseous) is used. A qualitative as well as a quantitative evaluation of the predicted values and a simulation of the working medium exchange process at different working conditions is possible. A visual observation of the slowed-down scavenging process in a transparent model cylinder was also made. The mathematical model can be applied to any scavenging system of two-stroke engines or to similar periodic events in the process technique.