Numerical investigation into primary breakup of diesel spray with residual bubbles in the nozzle

The paper presents a three-dimensional numerical investigation of the high-pressure diesel injection with residual bubbles in the nozzle using the Multi-fluid-Quasi-VOF (volume of fluid) model based on the OpenFOAM framework. The validity of the model to simulate the near-field spray was verified. It was found that the predicted primary breakup process was in good agreement with experimental imaging. Furthermore, the evolution of the instability waves at the gas-liquid interface, the formation of ligaments and the effects of bubbles initially residual in the nozzle on the primary breakup were analyzed. The results demonstrate that drag force is one of the main reasons to trigger the instability waves and consequently enhance the primary breakup. The residual bubble initially inside the nozzle can also improve the primary breakup and the turbulent perturbation especially in the mushroom-structure region. The large residual bubble near the nozzle inlet can lead to the formation of liquid filaments at the neck of the spray plume. On the other hand, the large residual bubble near the nozzle outlet considerably promotes the fragmentation of the mushroom structure. Meanwhile, residual bubbles will impact the development of cavitation and consequently enhance instability waves.