확장테이퍼분공 GDI노즐의 미립화 향상 및 출구적심 저감 성능에 대한 고찰

초록

The concept of the diverging-tapered-hole nozzle has been introduced recently for the combustion improvement and PM/PN reduction in GDI engines. Its superior atomization performance and potential of injector-tip-wetting suppression have been reported in a previous study based on the experimental observations of macroscopic and microscopic spray characteristics. However, detailed mechanisms associated with these performances have not been clarified so far, which is essential to extract the best performance from this nozzle concept. In this study, the internal and near-nozzle flow characteristics of the diverging-tapered-hole GDI nozzle are investigated using X-ray phase-contrast and absorption imaging techniques. Based on the results, the mechanisms related to the above performances are thoroughly discussed. The results show that the diverging-tapered-hole nozzle generates the three-dimensionally expanding crescent-moon-like flow structure which can increase the fuel-air contact area and also possess the additional tearing force assisting in the liquid flow breakup. This crescent-moon-like flow structure is normally confined within the lower half circle of the hole cross-section which helps the low-velocity flow region does not leak through the upper half circle so that the fuel leak during the injection can be minimized. Also, the expanding hole space in the diverging-tapered-hole nozzle helps the dribbling fuel after the needle close can be better released rather than sticking into the nozzle tip. These three-dimensionally expanding crescent-moon-like flow, confined flow area, and the expanding hole space are discussed to be the key mechanisms related to performances of the diverging-tapered-hole nozzle.