The spatial uniformity of the fuel-air mixture is influenced by the droplet size spatial distribution characteristics. An experimental investigation of the droplet size distribution of a diesel spray, injected by a hole-type nozzle, is conducted using an imaging-based technique to better understand the spatial droplet size distribution characteristics under different ambient pressures. The injection pressure is fixed at 100 MPa, while the absolute ambient pressure varies at 0.2, 0.5, 1,2, and 3 MPa. The droplet velocity, We number, droplet size distribution, Sauter mean diameter (SMD), and minimum distance between droplets, under different experimental conditions, are analyzed herein. The discussion is divided into two categories to better understand the influence of the ambient pressure: "higher ambient pressure" (1, 2, and 3 MPa), and "near-atmospheric pressure" (0.2 and 0.5 MPa). Under higher ambient pressure, the curve of the droplet size distribution along the spray axis initially changes from unimodal to bimodal, then changes back to unimodal. The SMD along the spray axis initially increases, then stabilizes in a certain range, and finally decreases. The rate of increase in the mean minimum distance in the region close to the spray tip is the largest. However, under near-atmospheric pressure, the curve of the droplet size distribution along the spray axis remains unimodal, and the variation of the SMD along the spray axis tends to be linear. The curve of the mean minimum distance has a wide descending region near the nozzle. The results of this study can be used to validate and improve the current functions of spray droplet size distribution and spray breakup models.

中文翻译：

---

基于成像技术的孔式喷嘴喷射柴油机喷雾液滴尺寸空间分布的实验研究-环境压力效应

燃料-空气混合物的空间均匀性受液滴尺寸空间分布特性的影响。使用基于成像的技术对通过孔型喷嘴喷射的柴油喷雾的液滴尺寸分布进行实验研究，以更好地了解不同环境压力下的空间液滴尺寸分布特征。注射压力固定在 100 MPa，而绝对环境压力在 0.2、0.5、1.2 和 3 MPa 变化。本文分析了不同实验条件下的液滴速度、We 数、液滴尺寸分布、Sauter 平均直径 (SMD) 和液滴之间的最小距离。讨论分为两类，以便更好地理解环境压力的影响：“更高的环境压力”（1、2 和 3 MPa），和“近大气压”（0.2 和 0.5 MPa）。在较高的环境压力下，沿喷雾轴的液滴尺寸分布曲线最初从单峰变为双峰，然后又变回单峰。SMD沿喷雾轴线先增大，然后稳定在一定范围内，最后减小。在靠近喷嘴尖端的区域中平均最小距离的增加率最大。然而，在接近大气压的压力下，液滴尺寸沿喷雾轴分布的曲线仍然是单峰的，SMD沿喷雾轴的变化趋于线性。平均最小距离曲线在喷嘴附近有一个较宽的下降区域。