EXPERIMENTAL STUDY ON SPATIAL DROPLET SIZE DISTRIBUTION OF DIESEL SPRAY INJECTED BY HOLE-TYPE NOZZLE USING IMAGING-BASED TECHNIQUE-EFFECT OF AMBIENT PRESSURE

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.