EFFECT OF NOZZLE HOLE GEOMETRY ON NON-EVAPORATING DIESEL SPRAY CHARACTERISTICS AT HIGH-PRESSURE INJECTION

Abstract

Non-evaporating diesel sprays from a common-rail injection system were characterized to investigate the effect of nozzle hole geometry. Two valve covered orifice (VCO) injectors with cylindrical and tapered nozzle holes were used. The injection rate was measured using an injection rate meter via the Bosch tube method. The spray tip penetration was analyzed from macroscopic spray images in a constant volume chamber using a high-resolution charge-coupled device camera and a spark light. Spray characteristics near the nozzle hole exit were observed using a microscopic visualization technique. The velocity and size of the droplets were measured downstream using a phase Doppler anemometer system. At the initial stage, the slope of the injection velocity from the tapered nozzle hole was larger than that from the cylindrical nozzle hole at the same injection pressure. The maximum injection velocity from the tapered nozzle hole was also higher. Until the micro-spray cone angle reached a maximum value, the spray tip penetration of the two nozzles increased with the change of injection rate. Subsequently, the spray tip penetration increased linearly with time. At the initial stage, the length of the liquid column injected from the tapered nozzle hole was about twice as long as that from the cylindrical nozzle hole. During the injection period, the oscillation in the micro-spray angle of the tapered nozzle hole was smaller than that of the cylindrical nozzle hole. The velocity and size of a droplet downstream with the tapered nozzle hole were slower and smaller than the velocity and size of the cylindrical nozzle hole.