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

Abstract. The development of direct injection strategies in modern Diesel engines needs increasingly high injection pressures and better fuel distribution in the combustion chamber. The ongoing study of the HCCI concept will probably require early fuel injection in air at low pressure and density, and also fuel composition will probably require some modification to reach a perfect 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, are 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 experimental results a scale low is then deduced, which is able to account for different penetration curves in the various tests by a unique common behaviour: 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. For a reduced set of experimental conditions drop size and velocity are measured by phase Doppler anemometry; time averaged mean diameter is then computed and analysed as a function of the fuel injection pressure, and shows a clear reduction of the drop diameter with increasing injection pressure.