Effect of injection conditions on penetration and drop size of HCCI Diesel sprays

Abstract. The more recent development in Diesel engines and the ongoing study of the HCCI concept will probably require, in a next generation of engines, early fuel injection in air at low pressure and density to reach a correct mixing and to match evaporation and ignition requirements. In this work different common rail nozzles, fed with fuel supplied at constant pressure in the range from 30 to 100 MPa, were used to produce sprays in air at ambient temperature and pressure ranging from 1 to 7 bar, to investigate the spray penetration as a function of air and fuel pressure. From the experimental results a scaling low was then deduced, which is able to account for different penetration curves in the various tests by a unique common behavior: a linear penetration part, whose length is function of the air density and of the nozzle diameter, followed by a decrease of the tip velocity. Best fit interpolation of the scaled results allowed the definition of a correlation that can predict the spray tip penetration in a wide range of conditions. For a reduced set of experimental conditions drop size and velocity were measured by phase Doppler anemometry; phase averaged mean diameter was then computed and analyzed as a function of the fuel injection pressure, and showed a clear reduction of the drop diameter with increasing injection pressure.