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A two-stroke engine has various advantages. It is simple in structure, light in weight, high in mechanical efficiency, superior in accelerating ability, etc. However, its fuel consumption is bad, its combustibility under partial load is poor and it is usually accepted that its exhaust gas is problematic. With increasing traffic flow volume, it has become recently necessary to operate transiently each vehicle with frequent stops and starts, as well as decelerations and accelerations. From this standpoint, the authors have formed a simple dynamic model of two-stroke engine, and by means of simulation investigated how its performance can be improved while it is transiently operated, in combination with experiment. The results confirm that the calculations from the model coincide approximately with experiment. The influences of various factors on the performance have been revealed.

It is important not only to increase a thermal efficiency of a spark ignition engine, but also to decrease a driving loss of auxiliary component of engine such as a cooling system. For example, there is a limitation of cooling performance when a requirement of aerodynamics design of a motorcycle or an automobile is severe. We propose an active application of ejector pump drove by exhaust energy to the cooling system. There were several applications of ejector system to the intake or exhaust system, but there was nothing for the design of it. In this report, one of the fundamental researches conducted in our laboratory, the effects of the dimensions of the ejector on the ejector performance are discussed. The results are followings: (1) The more the engine speed decreases, the more the ejector efficiency (G2/G1: G1 is the mass of charging air in the engine, G2 is the mass of entrained air by the ejector system) increases.