Effects of Different Injector Hole Shapes on Diesel Sprays

Twelve different hole shapes for diesel injector tips were characterized with DF-2 diesel fuel for spray cone angle over a range of injection pressures from 21 MPa (3 kpsi) to 69 MPa (10 kpsi). A baseline and two of the most radical designs were also tested for drop-size distribution and liquid volume fraction (liquid fuel-air ratio) over a range of pressures from 41 MPa (6 kpsi) to 103 MPa (15 kpsi). All hole shapes were circular in cross-section with minimum diameters of 0.4 mm (0.016 in.), and included converging and diverging hole shapes. Overall hole lengths were constant at 2.5 mm (0.098 in.), for an L/d of 6.2. However, the effective L/d may have been less for some of the convergent and divergent shapes. For the cone angle measurements, the injector was operated as a single hole injector spraying continuously into ambient temperature air at a pressure of 0.86 MPa (125 psia) at an air density of 9.7 kg/m³, or about one-half the density of a typical engine at injection conditions. The drop-size measurements were made with the injectors spraying into air at 0.55 MPa (80 psia) at an air density of 6.2 kg/m³. The results showed little effect of hole shape on the fully developed downstream spray cone angle or drop-size distribution. Injection pressure had little effect on the spray shape, while increasing injection pressure reduced drop sizes modestly.