## 3 Results and Discussion  
### Spray Tip Penetration  
Figure 10 shows the comparison of STP between circular and elliptical nozzles. According to Figure 10, it can be seen that the STP of elliptical nozzles was substantially reduced compared to that of the circular nozzle, and the difference between elliptical spray nozzles with different aspect ratios was not significant. In the initial phase of the spraying process, the gap in STP was small, and then the gap gradually increased. After the start of injection (ASOI) of 1.2 ms, the STP of elliptical nozzles with aspect ratios of 1.25 and 1.5 decreased by 19.29% and 20.96%, respectively, compared with that of the circular nozzle, and the elliptical nozzle with larger aspect ratio had the smallest STP. Figures 11 and 12 show the axial velocity distributions of circular and elliptical spray nozzles in the XZ plane and YZ plane. The axial velocity of the red part exceeded 200 m/s. It is obvious from the figure that the red part of the circular nozzle was longer than that of the elliptical nozzle, indicating that the spray velocity of the circular nozzle decreased more slowly and was subjected to less aerodynamic drag. The difference in the spray penetration distance of elliptical orifices with aspect ratios of 1.25 and 1.5 was not significant, probably due to the fact that after the spray was ejected from the orifices, they had an elliptical cross-section, and the spray from elliptical orifices tended to make the cross-section more rounded during axial development, resulting in faster diffusion of the spray in the radial direction, which inhibited the axial development of the spray. It also had a correlation with high environmental density. [PERSON] et al. mentioned that the high backpressure can inhibit the instability fluctuation and deformation of the spray [22]; at a high ambient density of 65.6 kg/m\({}^{3}\), the spray was more affected by ambient gases, which suppressed the differences between them. Three cross-sections were taken at 0.8 mm, 0.4 mm from the nozzle outlet and at the nozzle outlet. At ASOI of 0.4 ms, the velocity distributions on the three cross-sections are shown in Figure 13. From Figure 13, it can be seen that there was no significant decrease in the velocity of the circular nozzle, while the decrease in the velocity of the elliptical nozzle was more pronounced. Under the condition of the same cross-sectional area and the length of the nozzle, the inner wall surface area of the elliptical orifice nozzle was larger than that of the circular orifice nozzle, and the diesel fuel lost more kinetic energy in the inside of the nozzle, resulting in a reduction in the Initial kinetic energy of the spray. The axial velocity of the elliptical nozzle decreased more rapidly at the centerline of the spray than at the outside of the spray, causing the spray to move radially in the direction of aerodynamic drag, drawing in more gas from the outside of the spray and consuming the kinetic energy of the spray, Increasing the area of contact with the gas, and also being subjected to greater aerodynamic drag, resulting in smaller STP. The axial velocity fields of circular spray were similar in both planes, while the axial velocity fields of elliptical spray differed greatly in both planes, mainly because the curvature of the major axis of elliptical nozzles was smaller, and the spray was subjected to a larger shear force in the direction of the major axis. Due to the uneven distribution of the shear force in the direction of the major and minor axes of the elliptical nozzles, the flow velocity of elliptical spray was different in the direction of the major and minor axes, and thus, it was easier to generate stronger turbulence. The enhanced turbulence led to faster kinetic energy dissipation of the spray, thus reducing the STP.