Macroscopic Spray Parameters in Automotive Diesel Injector Nozzles With Different Hole Shape

The sprays generated from three nozzles for automotive diesel engines have been compared. The nozzles were characterized by the same stationary flux and they were designed for the same engine, but with holes of different shape: cylindrical, conical and with different internal edge finishing. The nozzles have been mounted on an injection system test bench in order to characterize their hydraulic behaviour at practical test conditions for the engine on which the nozzles have to be installed. Then, the injector has been mounted on a test chamber and sprays were generated at the test conditions previously defined. Digital images of every spray plume were acquired at the same optical and injector operative conditions. An automatic digital image procedure was defined in order to evaluate the macroscopic spray characteristics: penetration and dispersion angle. This procedure was based on the Karhunen-Loeve decomposition in order to choose the appropriate threshold level for each image. The effect of the intensity threshold level on the image analysis was analysed in terms of macroscopic spray characteristics. The temporal evolutions of the sprays generated by the three nozzles were compared with one-another and the effects of practical injection timing on spray penetration were analysed. A dimensionless spray penetration correlation was developed in order to take into account the effects of the injection rate profiles on the penetration.