Near-nozzle dynamics of diesel spray under varied needle lifts and its prediction using analytical model

Due to the lack of sufficient measurement methods, great difficulties are still present in clarifying the relationship between the nozzle internal flow and liquid-jet dynamics, especially when considering the needle motion effect. In this study, by utilizing the X-ray phase-contrast imaging (XPCI) technique, the in-nozzle needle motion characteristics and the liquid-jet dynamics in the near-nozzle field have been measured within a wide range of injection-pulse durations, based on which the needle-lift dependence of liquid-jet dynamics has been discussed in detail. The study is important for the nozzle related investigations, especially in view of the increasingly widely adopted multiple-injection strategies in the injection systems. The results indicate that, ruled by the mass flow equilibrium inside the nozzle sac, the liquid-jet flow dynamics in the near-nozzle field is closely related to the needle lift and injection pressure. Insufficient needle lift under short injection-pulse duration hurts the liquid-jet momentum that should be highly considered in the multiple-injection strategies. An analytical model has also been proposed to predict the jet axial velocity in the near-nozzle field. The model was found to have good agreement with the experimental results at different conditions.