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Diesel injections with various nozzle geometries were tested to investigate the spray characteristics by optical imaging techniques. Sac-nozzle and VCO nozzle with single guided needle coupled with rotary-type mechanical pump were compared in terms of macroscopic spray development and microscopic behavior. These nozzles incorporated with common-rail system were tested to see the effect of high pressure injection. Detailed investigation into spray characteristics from the holes of VCO nozzles, mostly with double guided needle, was performed. A variety of injection hole geometries were tested and compared to give tips on better injector design. Different hole sizes and taper ratio, represented as K factor, were studied through comprehensive spray imaging techniques. Global characteristics of a diesel spray, such as spray penetration, spray angle and its pattern, were observed from macroscopic images.

Spray characteristics of diesel fuel injection is one of the most important factors in diesel combustion and pollutant emissions especially in HSDI (High Speed Direct Injection) diesel engines where the interval between the evaporation of atomized fuel and the onset of combustion is relatively short. An investigation into various spray characteristics from different holes of VCO nozzles was performed and its results were compared to standard sac nozzle. The global characteristics of spray, including spray angle, spray tip penetration, and spray pattern were measured from the spray images which were frozen by an instantaneous photography with a spark light source. For better understanding of spray behavior, SMD of the fuel sprays from each hole in the multi hole nozzles were measured with back light imaging while the sprays from the other holes were covered by a purpose-built nozzle cap.