SPRAY CHARACTERISTICS OF A GROUP-HOLE NOZZLE FOR DIRECT-INJECTION DIESEL ENGINES

The reduction of the orifice diameter of a nozzle is advantageous to fuel atomization in a direct-injection diesel engine. However, diameter reduction is usually accompanied by a decrease in spray-tip penetration, worsening fuel spatial distribution and fuel-air mixing. In this article, a group-hole nozzle concept is proposed to solve the problem resulting from minimization of the orifice diameter. Compared to the conventional multihole nozzle, a group-hole nozzle has several groups of orifices; each group consists of two micro-orifices separated by a small spatial interval, with or without a 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 distributions of vapor concentration and droplet density, as well as other spray characteristics, such as spray angle and penetration of both vapor and liquid phase. The experimental results on the spray characteristics (injected into a high-temperature and high-pressure nitrogen atmosphere in a constant volume vessel by a common rail injection system) 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 consideration the analysis based on the LAS measurement in this work.