Characterization of Diesel Common Rail Spray Behavior for Single- and Double-hole Nozzles

Double-hole nozzle and multiple injections have the potential for better fuel atomization and mixing in DI engine. In order to evaluate the behavior of the spray for the double-hole nozzles against traditional single-hole ones, high-speed spray visualization was carried out using a streak film camera and a copper vapor laser, and in combination with a long-distance camera when taking microscopic movies. The spray penetration and the cone angle were measured based on the images and compared for variable injection pressures, and for single and split injections, under ambient and elevated chamber pressure conditions. The results showed that the spray of the double-hole nozzle has comparable penetration but smaller cone angle when viewed from the nozzle end, compared to the single-hole nozzle with the same total hole discharge cross-sectional area. For microscopic view, it was observed that the interaction between the dual sprays is very dynamic. The fuel injection starts earlier and ends later from the lower hole, which also has smaller cone angle oscillations, possibly due to the hydro-erosion characteristic of the nozzle. The microscopic spray angle was observed to converge to a steady-state cone angle, which depends on the injection pressure, but it is smaller than the macroscopic spray angle. By multiple-injection testing, it was revealed that the pilot injection enhances the penetration of the main injection.