Unveiling needle lift dependence on near-nozzle spray dynamics of diesel injector

A study on diesel spray characteristics is essential for the improvement of diesel combustion. However, information on diesel spray characteristics, especially those by the effect of injector needle lift, are lacking. In this study, the near-nozzle spray characteristic in a wide range of injection duration was investigated to understand the spray dynamics, which is vital to increase engine thermal efficiency in an engine with a multi injection strategy. The investigation has been done by conducting a high-speed visualization using X-ray, which is generated in Advanced Photon Source (APS) at Argonne National Laboratory, to obtain a phase-contrast image of a diesel spray. The needle lift inside the injector was also visualized and analyzed. The results show that the needle lift has a strong dominance on the spray angle that the spray angle is suppressed when the needle lift reaches a certain point regardless of the injection pressure and injection duration. The nozzle-exit spray velocity is strongly correlated with the needle lift and injection pressure. The spray velocity-decrease is significant when the needle lift is low and is independent of injection pressure and injection duration. The internal flow area is found to has an important role in determining the flow state.