Spray Characteristics of Group-hole Nozzle for D.I. Diesel Engine

Reduction of orifice diameter of nozzle is advantageous to the fuel atomization in a D.I. diesel engine. However, the diameter reduction is usually accompanied with decrease of spray tip penetration, thus worsening fuel spatial-distribution and fuel-air mixing. In this paper, a group-hole nozzle concept was proposed to solve the problem resulting from minimization of orifice diameter. Compared to the conventional multi-hole nozzle, group-hole nozzle has a series group of orifices, and each group consists of two micro-orifices with a small spatial interval and small angle. For examining the characteristics of the spray injected by the group-hole nozzle, the ultraviolet-visible laser absorption-scattering (LAS) imaging technique was adopted to determine vapor concentration and droplets density as well as other spray characteristics such as spray angle and penetration of both vapor and liquid phases. The sprays were injected into a high-temperature and high-pressure nitrogen atmosphere in a constant volume vessel by a common rail injection system. The experimental results have shown that the group-hole nozzle spray has a smaller mean drop size and an equivalent tip penetration compared to a conventional single-hole nozzle with the same total section area of injection hole(s). The fuel-air mixture formation characteristics of the group-hole nozzles were also discussed taking into account the analysis based on the LAS measurement in this work.