A Study on the Exhaust System of a Small Two-Stroke Engine : Effect of Exhaust Throttling on Engine Performance and Noise

Abstract

A symmetrically scavenged two-stroke engine generally loses a part of its fresh cylinder charge through the exhaust port at the last stage of the scavenging process. As a remedy for this, the authors propose a method of throttling the exhaust by an orifice, which reflects a positive pressure wave so as to prevent an outflow of the cylinder charge. A series of experiments was performed on the effect of location, configuration and throttle ratio of the throttling orifice on the performance of an engine. It was confirmed that remarkable effects were obtained from both the improvements of engine output and fuel consumption, and the reduction of exhaust noise in comparison with the other types of exhaust system and, moreover, that an exhaust throttle of the multi-orifice type improved the engine performance over a wide range of engine speeds.