Internal flow characteristics of an elliptical-orifice pressure-swirl injector under backpressure conditions

The internal flow evolution of pressure-swirl injectors strongly affects liquid-film formation and subsequent atomization behavior. However, the influence of elliptical-orifice geometry on the internal flow characteristics of pressure-swirl injectors under backpressure conditions remains insufficiently understood. This study aims to clarify the coupled effects of elliptical-orifice aspect ratio and backpressure on the internal flow evolution of pressure-swirl injectors. The internal flow characteristics of equal-area elliptical-orifice pressure-swirl injectors were numerically investigated using the Volume of Fluid (VOF) method under different aspect ratios (AR = 1.0–2.56) and backpressure levels (P c = 0.1–2.0 MPa). The effects of elliptical-orifice geometry and backpressure on chamber filling, air-core deformation, outlet liquid-film distribution, and near-outlet swirl characteristics were analyzed. The results show that increasing AR modifies the geometric constraint near the orifice, resulting in asymmetric liquid redistribution and delayed chamber filling compared with the circular-orifice case. With increasing AR, the outlet liquid film becomes increasingly nonuniform, and the dimensionless film-thickness span increases from 0.056 at AR = 1.0 to 0.46 at AR = 2.56 under P c = 0.1 MPa, indicating enhanced local liquid-film accumulation near the major-axis edge regions. Increasing backpressure further intensifies outlet liquid-film redistribution, especially for high-AR injectors, by promoting local thick-film formation and spatial nonuniformity. Moreover, high-aspect-ratio elliptical orifices weaken the organized tangential momentum transport near the outlet due to enhanced liquid-film nonuniformity, leading to reduced swirl intensity. These results demonstrate the strong coupling between elliptical-orifice geometry and backpressure in regulating internal liquid-film evolution and near-outlet flow characteristics of pressure-swirl injectors.