Effects of Group-Hole Nozzle Specifications on Fuel Atomization and Evaporation of Direct Injection Diesel Sprays

摘要

The group-hole nozzle concept is regarded as a promising approach to facilitate better fuel atomization and evaporation for direct injection diesel engine applications. In the present work, the spray and mixture properties of group-hole nozzle with close, parallel or a small included angle orifices were investigated experimentally by means of the ultraviolet-visible laser absorption-scattering (LAS) imaging technique, in comparison with the conventional single-hole nozzle. Three series of group-hole nozzles were designed to investigate the effect of group-hole nozzle specification while varying the included angle and interval between the orifices. The results suggested that: 1) Group-hole nozzle with very close, parallel orifices presents the similar spray characteristics with those of the single-hole nozzle. However, with the increase of injection pressure, the group-hole nozzle shows the potential to produce, to some extent, the better fuel atomization and evaporation without adversely affecting the spray spatial distributions. 2) Increasing the diverging angle between the orifices results in significant increase in mass of fuel vapor and reduction in overall Sauter Mean Diameter (SMD), indicating the evaporation improvement. 3) In the case of group-hole nozzle with large interval between orifices in this study, the restrained tip penetration, significant increase in the SMD, along with large liquid phase mass appearance around the spray tip can be found, which is considered to be a comprehensive result of the direct droplets collision in the overlapping part of the two jets and the droplets overtaken and coalescence inside the fuel spray due to the inferior spray tip penetration and ambient gas entrainment. 4) The liquid mass proportion and the SMD of the fuel spray from all test group-hole nozzles are greater than the estimated value by the LAS data of single-hole nozzle whose orifice diameter is the same as one of the group orifices. Thus, the interaction between the two jets has the effect of suppression of the ambient gas entrainment and fuel evaporation, though it has the effect of enhancement of the spray tip penetration.