The injection of small amount of diesel fuel is mainly achieved through the shortening of energizing signal. Consequently, in such injection phases, the needle does not reach the mechanical stroke-end and its displacement may be defined as ballistic.

By means of a detailed 3D-CFD modeling, the behavior of nozzle flow is investigated under typical pilot/split injection conditions, namely high injection pressure and low needle lift. The investigation focuses on the effects of the restricted flow passage on fuel flow at hole inlets. Once the modeling details are described, the influence of different elements on the internal fuel flow is shown and discussed, pointing out the role of different driving factors; investigations take into account actual injector tip layouts and the response to the needle off-axis operating conditions. Results are presented highlighting the flow pattern features within the nozzle and their reflects on the hole-to-hole differences.

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