Influence of Fuel Injector Nozzle Geometry on Internal and External Flow Characteristics

The effects of upstream conditions, such as nozzle and entrance shapes, on external flow characteristics continue to challenge fuel injection modeling efforts, particularly in the case of high-pressure diesel sprays. In this research, flow details were investigated both experimentally and numerically in a fuel injector nozzle orifice using an integrated approach. Calculations using the SIMPLE algorithm were first performed for the scaled-up experimental nozzles with various length to diameter ratios (L/d). Measurements of internal flow velocities for these nozzles were made by laser Doppler velocimetry in order to verify the computational results. Mean and fluctuating velocities and discharge coefficients were obtained at various Reynolds numbers. The mean turbulence intensity and turbulent kinetic energy for a sharp inlet nozzle were generally higher than for a round inlet nozzle, except for the near-wall region beginning at about one nozzle diameter from the entrance. In order to verify the trends observed in the scaled-up nozzle, experimental observation of external spray behavior was made for corresponding actual-scale nozzles at various up-stream flow conditions. For these tests a set of nozzles were used which had a 0.3 mm hole diameter, L/d from 1 to 8, and round or sharp inlet shape. Five injection pressures were selected, from 2.5 to 10 MPa, and the ambient pressure was varied from 0.1 to 2.1 MPa. Phase/Doppler particle analyzer and laser sheet photography measurements indicated that droplet sizes produced from round inlet nozzle were generally larger than from the sharp inlet nozzle, and the spray angle of the round inlet nozzle was narrower than that from the sharp inlet nozzle. Discharge coefficient measurements and photographs allowed hydraulic flip and cavitation to be distinguished, and the effect of inlet shape on nozzle flow characteristics could be clarified. At lower injection pressures a longer breakup length was associated with the sharp inlet nozzles, which may be due to the higher near-wall turbulence intensity of the round inlet nozzles. Numerical predictions generally agreed well with the measured results, except for some variation in the boundary layer region.