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The aim of this work is the development of an energy-based model to predict primary break-up of urea and water (Ad Blue) sprays in condition typical of Selective Catalyst Reduction (SCR) systems. The atomization model for Ad Blue injection, developed in the present investigation, performs an energy balance of the liquid column to asses its deformation near the nozzle exit and to predict the dimension of droplets after the primary break-up. To formulate the energy balance it is necessary to evaluate several terms: the theoretical kinetic energy of the jet in absence of dissipation, its real kinetic energy, the fraction of energy dissipated due to turbulence effects, the surface energy before break-up, the surface energy of the droplets after the break-up. The model was implemented in the KIVA3v code and experimental data from Malvern analysis were used for the validation.

The present study focuses on the causes of dissimilarity in the flow structures of sprays produced by different holes of the same direct injection high-pressure diesel nozzle. To assess the effect of nozzle geometry on the transient spray structure, photographs of the spray plumes produced by VCO, mini-sac and reduced sac nozzles at different delays from the start of injection were acquired. Injected fuel volume, feeding pressure, injection duration, spray penetration and cone angle were measured for all the investigated nozzles. A statistical analysis of the acquired images and data showed that sprays from the same hole were highly repeatable even with clear hole-to-hole variation of the spray structure. In particular, for the three investigated nozzle geometries the effect of nozzle flow rate, hole inlet and outlet diameter, needle geometry and working time under engine conditions were investigated. Microscope pictures of the nozzle holes were also acquired.