Direct imaging of primary atomisation in the near-nozzle region of diesel sprays

In this publication we report on progress made with ongoing experimental investigations of the atomisation of n-dodecane using microscopic imaging and high-speed video with an ECN 'Spray A' injector. A long-distance microscope was used to visualize the near-nozzle region (1.025x0.906 mm). Our study focuses on the primary atomisation during the start, the steady-state and the end of the injection process. The spray formation and breakup of n-dodecane was investigated experimentally on a common rail diesel injector using a long working distance microscope. The objectives were to further the fundamental understanding of the processes involved in the initial stage of diesel spray formation under engine-like operating conditions, and provide validation data for numerical models. The end of injection was characterized by large ligaments and deformed droplets along with spherical droplets. It was noted that formation of large droplets during end of injection was not related to injection pressure. The large droplets were found to be in the range of up to 50 μm, which were moving with relatively low velocity. Typical velocity range for large droplets (30-50 μm) was between 1.5 to 5 m/s. The trajectory of individual droplets appeared to be random from injection to injection.