| Summary: | 博士 === 國立成功大學 === 航空太空工程學系 === 87 === In recent Taiwan''s transportation market, the use of motorcycles and scooters has drastically experienced a rapid growth as convenient vehicles either in urban or rural areas. In order to strive for the market significance, there is a strong need of research and development (R/D) to develop the domestic small engine below 150c.c. in Taiwan. However, it is clear that the existing engine simulation model has been well developed, but is only suitable for larger-sized engine performance analysis and fails to have a well prediction for smaller engines, especially below 150 cc. This dissertation hence makes emphasis on the investigations of developing suitable combustion models for small-size four-stroke engines by experiments and developing an engine performance simulation through genetic algorithm (GA) optimization for small engine design. In the experiment, the 125cc four-stroke engine is used for investigations on a dynamometer test bench to measure such engine parameters as cylinder pressure, crank angle, Air-Fuel (A/F) ratio and ignition timing, etc. In the simulation of the cylinder volume variation and intake/exhaust wave phenomenon, the second-order Total Variation Diminution (TVD) scheme is adopted to enhance the calculation accuracy. Experimental results indicate that the values of the efficiency parameter and the form factor in the Wiebe function, commonly used as the combustion model in engine simulation, have to be modified for the small engine in comparison with the commonly suggested values in the larger-sized engine. In addition, the delay angle of combustion is insensitive to the A/F ratio, engine speed, and spark ignition timing. Although the rapid burning angle is relatively invariant with the A/F ratio, it does show a significant increase with the increase of the engine speed. In the simulation of engine performance optimization, the GA method has ensured that single-point and multi-point optimization can not only effectively seek their optimal parameters, but also the calculation time is reduced drastically. Meanwhile, the simulation results also suggest the appropriate valve timings of intake and exhaust for small engine design, which is also proved by experiments with the engine design data.
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