| Summary: | 博士 === 國立臺灣大學 === 生物產業機電工程學研究所 === 89 === This study was called for to investigate the emission characteristics and spray simulation of the single cylinder, small DI diesel engine operated with conventional and alternative fuels, such as DME, B20 and B30. It contained experiment part and numerical simulation part. In the experiment part, the emission characteristics of particle size distributions and number concentrations of the engine operated with alternative fuels was investigated, and compared them with diesel fuel. In the numerical simulation part, the flow field was simulated with KIVA—3 CFD code. The flow field characteristics of combustion chamber without fuel injection and with diesel, DME and biodiesel fuel injections were investigated, respectively. We attempted to understand the behaviors of spray droplet and how the spray interacted with the gas flow fields.
In this research, we have successfully set up a diesel engine fueled with DME facility. The results of the experimental on the present work on the diesel engine fueled with DME showed that the smoke and PM emissions reduction ratio factor was above 15 as compared with that of diesel fuel. The PM2 particle number concentration of the DME operated engine was about 0.47 to 0.23 times that of diesel fuel. Both of the two engines had PM2 particle number concentration as high as above 107（particle/liter）at all engine speed range. This presented hazard to public health and the environment. This study aimed to develop a new domestic biodiesel production procedure which made use of waste fryer vegetable oil by transesterification method, and further investigated the emission characteristics of a small DI diesel engine using B20, B30 and diesel fuels, respectively. We have found that those of the three fuels had PM2 particle number concentrations as high as above 106—107（particle/liter）at most of the engine speed ranges. This presented a magnificent hazard to public health and the environment. We also found that B30 emited more PM2 particle number concentrations than that of diesel fuel, and PM2 number concentration increased as biodiesel concentration increased.
The simulated results showed that the bowl with squish lip in piston generated squish flow, tumble flow and reverse squish flow. DME and diesel fuels showed very different spray behaviors. The spray cone angle of DME was affected by significantly increased vaporization gas density and ultra low liquid viscosity. There were also the cause of small spray penetration length. The air entrained along spray axle mixing phenomenon for DME was completely different from that of diesel fuel / air mixing process. Biodiesel and diesel fuels showed very similar spray behaviors. However the biodiesel spray droplet showed that the more faster evaporation, deeper spray penetration length and better fuel/air mixing.
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