On a Modified VCO Nozzle Layout for Diesel Common Rail Injectors under Actual Needle Displacement

The mechanical-hydraulic behavior of the nozzle and the features of the internal flow are two fundamental factors in the spray formation process. In the current multi-injection strategies, short injections with reduced values of the needle lift are usual. In these cases, the nozzle can give rise to abnormalities in spray development, highlighted by irregularities and asymmetries. The main hole to hole differences are encountered in the rate of injection, in the spray shape and in the atomization process. The off-axis of the needle, the characteristics of the volume upstream of the holes and their geometry play a key role in causing such anomalies. In the paper, an unconventional VCO nozzle layout has been defined and analyzed by modeling. The study is oriented at evaluating its capability on reducing the dispersion among the flow features of the holes, when the pure axial needle displacement is perturbed. The investigated nozzle is based on a multihole layout but, referring to the injector axis, nozzle holes have a non-radial arrangement. In comparison with the standard VCO nozzle configuration, 3D-CFD simulations have been devoted to highlight the influence of the alternative nozzle layout on the internal flow and on the resulting spray features in the external ambient. In the modelling process, data concerning rate of injection, spatial distribution of velocity and cavitation behaviour at hole exit have been computed; specific attention has been focused on the fuel flow distribution among the holes; the computations have evidenced the behaviour of the unconventional layout when off-axis needle displacement is considered. Results have been resumed indicating how the internal flow pattern properties are reflected by the spray features.