Search Results

A hybrid model for the atomization of Diesel sprays was developed [1]. The model was added to the KIVA code to better simulate spray evolution. Different implementation for low-medium and high injection pressure sprays are performed. It has already been validated for the low-pressure case [1,2] and in this work it was tested for high injection pressure systems, in a vessel at ambient conditions. It distinguishes between jet primary breakup and droplet secondary breakup. For the latter distinct models are used, as the droplet Weber number changes in the various regimes, in order to take into account the effects of the different relevant forces. For high pressure Diesel spray the effects of jet turbulence, cavitation and nozzle flow on liquid core primary breakup must be considered. Due to the high droplet velocity the catastrophic secondary breakup regime may occur.

In the present study, a commercial high pressure, common rail injection system for automotive DI diesel engines was fed with a conventional diesel fuel, a bio-derived fuel and a blend of them. The comparison of spray characteristics was carried out in terms of tip penetration and cone angles; the fuel spray, generated by rail pressures ranging from 60 MPa to 120 MPa, developed in an atmospheric chamber. The experimental set-up is based on a laser sheet technique. The radiation scattered by the spray, generated by a Nd-Yag pulsed laser, is collected by a CCD camera and fed to a frame grabber. A suitably set-up automatic image analysis process allows not only to determine the spray average development in terms of its geometric characteristics, but also to analyse in detail its internal structure. In particular, a suitable elaboration allowed the evaluation of the probability of presence in space of spray liquid fractions.