## 1 Introduction
showed that diesel sprays with uncircular orifices suffer from axis switching; they also have larger spray areas (Sas) and SCAs compared to circular orifices, and they pointed out that uncircular orifices cause greater instability in the spray, which leads to faster atomization [20]. [PERSON] et al. found that the SCA of elliptical orifices is greater than that of circular orifices, the STP of circular orifices is longer than that of elliptical orifices, and the elliptical orifice spray also suffers from axis switching at high injection pressures [21; 22]. Some other studies were also conducted that found that the liquid-phase STP of elliptical orifices is smaller than that of circular orifices under evaporative conditions, and the application of elliptical orifices is favorable for reducing liquid-phase STP, thus avoiding fuel impingement in the combustion chamber of a small engine [23]. A unique dovetail spray structure emitted from an elliptical GDI injector with an aspect ratio of 4 was captured for the first time in a study by [PERSON] et al. The dovetail-shaped spray appeared only in the main view plane of the elliptical spray [24]. [PERSON] et al. found that elliptical nozzles have larger SCAs and air-entrained masses than circular nozzles, elliptical nozzles have reduced partial equivalence ratios and high-concentration regions in cylinders, and air-fuel mixing is more homogeneous [25]. [PERSON] et al. demonstrated that elliptical nozzle outlets have higher vorticity magnitudes than circular nozzle outlets for all injection conditions and that elliptical nozzles have a wider near-field SCA and long-axis projection area than circular nozzles [26]. [PERSON] et al. computationally investigated the differences between shrinkage cross-section elliptical nozzles and constant cross-section elliptical nozzles using \(\Sigma\)-Y modeling under cavitation and non-cavitation conditions, and the study showed that cavitation elliptical nozzles had the potential for enhanced air-fuel mixing [27]. [PERSON] et al. proposed a methodology for examining the discrepancy between the internal flow within the nozzle and the external spray, as well as the interrelationship between atomization. The findings revealed that elliptical nozzles exhibited superior atomization quality compared to their circular counterparts. Furthermore, it was observedthat an optimal increase in eccentricity led to enhanced atomization, which was attributed to the promotion of liquid decomposition and the reduction in the STP [28]. The impact of elliptical nozzles on fuel atomization remains a nascent area of investigation, with the majority of existing studies conducted under low ambient density. There is a clear need for further research to elucidate the influence of elliptical nozzles on fuel atomization characteristics under high ambient density. In this study, the effects of elliptical nozzles and circular nozzles on the macroscopic and microscopic characteristics of diesel fuel spray under high ambient density were investigated. The investigation was conducted under non-cavitation conditions, with an injection pressure of 120 Mpa and an ambient density of 65.6 kg/m\({}^{3}\). Optical testing techniques and numerical simulation were employed to gain insights into the fuel atomization characteristics of elliptical nozzles under high ambient density.