## 3 Results and Discussion
### Spray Cone Angle  
Figure 14 shows the SCA of the circular and elliptical nozzles in two planes, the XZ plane and the YZ plane, while Figure 15 shows the average SCA of the circular and elliptical nozzles in two planes, the XZ plane and the YZ plane. At the initial stage of spraying, diesel fuel was just sprayed from the orifice, and the SCA fluctuated widely, gradually reducing to a relatively stable value. With the injection process, the fuel beam gradually began to diffuse radially, so the SCA gradually increased. After the SCA became relatively stable, the SCA of the elliptical nozzle was larger in both planes, compared with the circular nozzle. In the XZ plane, the average SCA of elliptical nozzles with aspect ratios of 1.25 and 1.5 increased by 76.90% and 77.17%, respectively, compared to that of the circular nozzle, and in the YZ plane, the average SCA of elliptical nozzles with aspect ratios of 1.25 and 1.5 increased by 27.04% and 37.43%. The reason may be that the initial cross-section of the spray with elliptical nozzles is asymmetric; to balance the surface tension in different directions, the spray will tend to make the cross-section more rounded during the axial development. The asymmetry of the spray results in the instability of the spray boundary layer, which causes the spray to break up and atomize earlier, resulting in the spray spreading faster in the radial direction. This also results in the contact area between the spray of the elliptical nozzles and the ambient gas being larger than that of the circular nozzle, resulting in the spray of the elliptical nozzles being subjected to greater aerodynamic drag in the spraying  
Figure 12: Axial velocity distribution in the YZ plane for circular and elliptical nozzles.  
process. As a consequence, the STP is reduced, and the SCA becomes larger, which is conducive to the atomization of the spray.  
Figure 14: Spray cone angle (SCA) for circular and elliptical nozzles: (**a**) SCA in XZ plane; (**b**) SCA in YZ plane.  
Figure 13: Axial velocity distribution at different positions within three nozzle orifices.  
Figure 16 shows the pressure distributions of circular and elliptical nozzles in the XZ plane. The low-pressure part was mainly distributed in the spray head and was interspersed with the high-pressure part. Compared with the circular nozzle, elliptical nozzles had more low-pressure parts during spraying, a larger area, and a wider distribution area, and the pressure difference moved the gas into the spray and mixed it with the diesel fuel, which resulted in the sprays of elliptical nozzles winding the gas from the outer part of the spray earlier, giving a better radial development. The high-pressure part of the elliptical nozzle spray was concentrated at the tip of the spray, which inhibited the axial development of the spray. Figure 17 shows the vorticity distributions of circular and elliptical spray nozzles in the XZ plane at ASOI of 1.2 ms. As seen from the figure, the vorticity of the elliptical spray was larger than that of the circular nozzle, while the vorticity field of the circular spray was more uniformly distributed compared to the elliptical nozzles. This indicated that the elliptical spray was subjected to stronger turbulence perturbation than the circular nozzle, which enhanced the interaction between the spray and the ambient gas.