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The combustion simulation based on CFD (Computational Fluid Dynamics) was attempted in order to visualize in-cylinder combustion phenomena of a small displacement, high speed four-stroke SI engine for motorcycle applications. To verify the results of the simulation, the steady state flow in a cylinder, the fuel spray behavior and the flame propagation behavior in an actual engine were measured and compared. The results were that an adequate correlation was confirmed in each phenomenon, proving that the CFD was applicable as a means of visualization. As the result of the investigation of the combustion system applying this technique, improvements such as the specific fuel consumption and the extension of the lean combustion zone were attained, assuring effectiveness of this technique for actual engine development. This technique has been applied to the development of the world's first four-stroke 50cm3 PGM-FI (Programmed Fuel Injection) engine.

An electronically controlled fuel injection system for controlling the air/fuel (A/F) ratio has been looked forward as a means for improving drivability, output characteristics, and fuel consumption of two-stroke cycle motorcycle racer engines. However, actual installation of such a system on a high output two-stroke cycle engine (which utilizes exhaust gas pressure pulsation effects) has been considered difficult for the following reasons. Fluctuation in the delivery ratio (L) during firing and misfiring becomes great due to effects from the exhaust pipe. Applying the control method used for conventional four-stroke cycle engines (by which the delivery ratio (L) is measured) would necessitate a large and heavy system. The authors have eliminated such problems by developing an electronically controlled fuel injection system, the PGM-FI (Programmed-Fuel Injection) system, which employs basic intake air flow data according to engine speed (NE) and throttle opening (θTH).