Effect of Dual-Hole Nozzle Injection Angle on Primary Breakup and Near-Nozzle Spray Dynamics of High-Pressure Diesel Jets: Volume-of-Fluid Numerical Investigation

Optimizing fuel injector geometry represents a critical pathway toward cleaner and more efficient diesel combustion. This study presents a comprehensive numerical investigation of the influence of the dual-hole nozzle injection angle on the primary atomization behavior and spray hydrodynamics of high-pressure diesel jets. The present analysis is deliberately restricted to cold-flow, near-nozzle primary breakup under isothermal conditions (293.15 K) so that the hydrodynamic and aerodynamic breakup mechanisms can be isolated in the immediate vicinity of the orifice before evaporation and combustion occur. Two-dimensional simulations are conducted using an Eulerian Volume-of-Fluid (VOF) framework with finite element discretization, three injection-angle configurations (0°, 5°, and 10°) under realistic engine conditions (injection pressure: 138 MPa; chamber pressure: 2.32 MPa; nozzle diameter: 100 µm). The numerical model was validated against the experimental and computational benchmark data of Ménard et al., showing reasonable qualitative agreement in jet morphology, although the 2D nature of the model leads to an exaggerated accumulation of liquid at the spray tip compared to the 3D reference. The validation therefore supports the qualitative trends and the relative angular comparison, but the absolute quantitative predictions remain subject to this 2D structural limitation. Results reveal that the injection angle exerts a decisive influence on the competition between axial momentum and radial dispersion. The neutral 0° configuration yields an overly concentrated jet with limited interfacial destabilization and poor air entrainment, whereas the 10° angle produces excessive radial spreading at the expense of axial penetration depth. By contrast, the 5° convergence angle provides the best trade-off among the three tested configurations under the studied conditions, promoting enhanced Rayleigh–Plateau instability growth, earlier ligament formation, and finer droplet generation—favorable to a more homogeneous air–fuel mixture. These findings provide quantitative guidance for dual-hole injector geometry design and demonstrate the suitability of high-fidelity VOF-based methods for resolving complex two-phase atomization phenomena relevant to low-emission diesel engine design. Quantitatively, the peak axial velocity is reached at the nozzle exit for all configurations; relative to the 0° baseline, the 5° convergence angle increases the fuel–air interfacial spreading by about 141% while retaining roughly 90% of its axial penetration at the monitoring positions P1–P3, whereas the 10° case loses about 26% of axial penetration for a comparable radial spread.