The spray atomization process plays a critical role in achieving high efficiency and reducing emissions in internal combustion engines. The fuel injection atomization process, especially the spray primary atomization process, is significantly influenced by turbulent flow and cavitation phenomena within the nozzle. In this study, based on the coupled large eddy simulation(LES) and a volume-of-fluid (VOF)method, the effects of four typical nozzle internal flow patterns on the spray primary breakup in the near-nozzle region were investigated. To realize this objective, the generation of four distinct flow patterns was accomplished through the design and construction of corresponding nozzle structures: (1) nearly single-phase flow in a tapered-orifice nozzle with low orifice location, (2) strong geometry-induced sheet cavitation flow with sheet region extending to the nozzle orifice exit in a normal cylindrical orifice, (3) vortex-induced string cavitation flow in a tapered-orifice nozzle with relative high orifice location, and (4) geometry-induced sheet cavitation is partially suppressed while it is enhanced in the orifice region close to exit in a convergent-divergent orifice. The numerical results unequivocally reveal that the initial atomization of the spray exhibits remarkable efficacy in the case of the conventional cylindrical nozzle, characterized by internal regions of substantial sheet cavitation, despite a relatively minimal flow discharge coefficient. Conversely, the normal tapered-orifice nozzle, lacking significant cavitation, demonstrates a larger flow discharge coefficient, yet its initial atomization performance is notably suboptimal.It is worth noting that the appropriate vortex-induced cavitation in the nozzle can correspond a higher flow rate with a thin string-type cavitation and simultaneously a better spray atomization quality with a strong vortex flow. Also it is concluded that a convergent-divergent nozzle with appropriate transition location can achieve strong atomization .

中文翻译：

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采用 LES-VOF 方法研究柴油机喷嘴空化流型对近场喷雾雾化特性的影响

喷雾雾化过程在实现内燃机高效率和减少排放方面发挥着关键作用。燃油喷射雾化过程，特别是喷雾初级雾化过程，受喷嘴内湍流和空化现象的影响显着。本研究基于耦合大涡模拟（LES）和流体体积（VOF）方法，研究了四种典型喷嘴内部流型对近喷嘴区域喷雾初级破碎的影响。为了实现这一目标，通过设计和构造相应的喷嘴结构，实现了四种不同流型的生成：（1）低孔口位置的锥形孔口喷嘴中的近单相流，（2）强几何诱导片状空化流，片状区域延伸至普通圆柱形孔口中的喷嘴孔口出口，(3) 具有相对高孔位置的锥形孔口喷嘴中涡流引起的串空化流，以及 (4) 几何形状引起的片状空化部分抑制，而在收敛-发散孔口中靠近出口的孔口区域则增强。数值结果明确地表明，在传统的圆柱形喷嘴的情况下，喷雾的初始雾化表现出显着的功效，其特征是内部区域具有大量的片状空化，尽管流量系数相对较小。相反，普通锥孔喷嘴由于缺乏明显的空化现象，具有较大的流量系数，但其初始雾化性能明显欠佳。值得注意的是，喷嘴中适当的涡流诱导空化可以对应较高的流量细弦式空化，同时具有较强的涡流，喷雾雾化质量更好。并得出结论：具有适当过渡位置的收敛-扩散喷嘴可以实现强雾化。