Ignition and Combustion Characteristics of Wall-Impinging Sprays Injected by Group-Hole Nozzles for Direct-Injection Diesel Engines

The concept of two closely spaced micro-orifices (group hole nozzle) has been studied as a promising technology for the reduction of soot emission from direct injection (DI) diesel engines by improving the fuel atomization and evaporation. One of the main issues on group hole nozzle is the arrangement of orifices with various distances and angles. In this study, the ignition and combustion characteristics of wall-impinging diesel sprays from group-hole nozzles were investigated with various angles between two micro-orifices (included angles). A laser absorption scattering (LAS) technique for non-axisymmetric sprays, developed based on a LAS technique for axisymmetric spray, was applied to investigate the liquid/vapor mass distribution of wall-impinging sprays. The direct flame images and OH radical images inside a high pressure constant volume vessel were captured to analyze the effect of included angle on spray ignition and combustion characteristics. The group hole nozzles showed improved fuel evaporation and increased spray tip penetration compared to the conventional single hole nozzle. In group hole nozzles, the longer spray penetration after impingement was observed at parallel direction compared to the vertical direction and the same trend was observed in the flame geometry. The spray penetration in parallel direction was increased at high included angles while there was not so much change in vertical direction. The vapor mass concentration in both view directions was enhanced when the included angle was increased due to the reduced droplet collision region. Owing to the enhanced fuel evaporation, the ignition delay of wall-impinging sprays was shortened and the intensity of OH chemiluminescence increased at high included angles. The shorter flame length and longer flame height were observed at high included angles since the ignition occurs before the spray-wall interaction is fully developed.