The spatial droplet size distribution directly determines the spatial uniformity of fuel-air mixture, and then further influences the combustion and emission performance. An imaging-based technique is employed in this study to capture spray droplets at different positions (eight positions along the spray axis and six positions on the spray periphery) under three injection pressures (60, 100, and 140 MPa). The ambient pressure is maintained at 2 MPa. Droplet characteristic parameters such as droplet velocity, droplet diameter, and minimum distance are analyzed. The experimental results indicate that regardless of injection pressure, the size distribution curve along the spray axis changes from unimodal to bimodal, and then from bimodal to unimodal. Meanwhile, the sauter mean diameter (SMD) along the spray axis firstly increases, and then stabilizes for a certain range before finally decreases. The SMD on the spray axis is larger than that on the spray periphery and no definite relationship exists between the droplet diameters on the spray periphery. Regardless of the measurement position, a higher injection pressure yields smaller spray droplets. The mean minimum distance between droplets increases along the spray axis, and the higher the injection pressure, the smaller is the mean minimum distance. However, at a measurement position near nozzle, a higher injection pressure contributes to a larger minimum distance. Relevant conclusions regarding the spatial distribution characteristics of the spray droplet size and minimum distance can be used to validate and improve the existing spray atomization model and droplet size distribution function.

中文翻译：

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基于成像技术的孔式喷嘴喷射柴油喷雾液滴粒径分布的实验研究——喷射压力的影响

液滴的空间尺寸分布直接决定了油气混合气的空间均匀性，进而影响燃烧和排放性能。本研究采用基于成像的技术在三种喷射压力（60、100 和 140 MPa）下捕获不同位置（沿喷雾轴的八个位置和喷雾外围的六个位置）的喷雾液滴。环境压力保持在 2 MPa。分析了液滴速度、液滴直径和最小距离等液滴特征参数。实验结果表明，无论喷射压力如何，沿喷雾轴线的粒径分布曲线均由单峰变为双峰，再由双峰变为单峰。同时，沿喷雾轴的索特平均直径（SMD）首先增加，然后在一定范围内稳定下来，最后才下降。喷雾轴上的 SMD 大于喷雾外围的 SMD，喷雾外围的液滴直径之间没有明确的关系。无论测量位置如何，较高的喷射压力会产生较小的喷雾液滴。液滴之间的平均最小距离沿喷射轴线增加，喷射压力越高，平均最小距离越小。然而，在喷嘴附近的测量位置，较高的喷射压力有助于较大的最小距离。关于喷雾液滴尺寸和最小距离的空间分布特征的相关结论可以用来验证和改进现有的喷雾雾化模型和液滴尺寸分布函数。