This paper deals with an investigation of the scavenging and power performances of a two-stroke cycle gasoline engine having poppet valves in the cylinder head but no cylinder ports.
In a previous experiment, a model test apparatus was used to carry out the experimental analysis of scavenging performance. We found as a result of this analysis that better scavenging efficiency could be obtained by improving the flow pattern of scavenging gas in the cylinder by means of scavenging valves with shroud than by perfect diffusion scavenging.
The present experimental study using a real engine was conducted according to this finding. The basic engine is a four-stroke motorcycle engine, one cylinder, 250 cm3, twin-cam, four-valve. The engine was modified into a two-stroke cycle engine by altering the camshafts so as to have twice the engine speed of the four-stroke cycle engine, and the valve timings were adjusted by a pin that connected the camshaft and sprocket. A deflector was set near the valve seat within each scavenging passage as a substitute for the scavenging valves with shroud. A volute-blower operated by a inverter motor was also used as a means to improve scavenging and a carburetor was used to supply fuel.
The experimental result indicated that the scavenging performance was nearly equal to the perfect diffusion scavenging that can be applied to a practical engine. The power of the two-stroke cycle engine was shown to be better than that of the basic four-stroke cycle engine when compared at the same engine speed.