Effects of nozzle design parameters on nozzle flow and spray characteristics in common-rail diesel injectors

Abstract

The purpose of this study is to quantitatively analyze the effects of nozzle design parameters on the nozzle flow and spray development characteristics of the common-rail diesel injector to present the direction of nozzle design for high-pressure diesel injectors. The main nozzle design parameters are number of nozzle holes, hydraulic flow rate, nozzle length/diameter ratio, and k-factor. The injection rate measurement and spray visualization were performed using nozzles with various shapes to compare nozzle flow characteristics, nozzle outlet conditions, and spray characteristics. Based on the experimental results, the main parameters that affect flow rate, injection duration, spray tip penetration and spray cone angle were selected and the effects of each independent nozzle design parameter on the spray behavior were analyzed. Various measurement techniques were applied to identify the nozzle flow and spray development characteristics, such as Bosch tube method, spray visualization using a high-speed camera and CCD camera with an Nd:YAG laser. The spray boundary and developmental index were measured using MATLAB image processing to satisfy the reliability of spray tip penetration and spray cone angle results in the analysis of the spray behavior depending on the nozzle design parameters. Experiments were conducted for various injection pressure conditions from 20 MPa to 200 MPa to compare the flow and spray characteristics of the diesel injector over the operating range in the vehicle. To simulate the density condition in the combustion chamber of the engine, where the diesel fuel is injected, a constant-volume chamber was pressurized inside to 2.0 MPa in the spray visualization. The injection rate, injection duration, steady state flow rate, spray tip penetration and spray cone angle were compared for various nozzles by the injection rate measurement and spray visualization experiment. An Nd:YAG laser and a CCD camera were synchronized to observe the atomization process in the initial stage of injection.