Comparative study of flow characteristics within asymmetric multi hole VCO and SAC nozzles

Abstract A three-dimension model of an asymmetric valve covered orifice (VCO) nozzle and an asymmetric blind hole nozzle (SAC) used in two valve engines were developed for investigating in-orifice flow characteristics. Two fluid model approach used for turbulence and cavitation modeling was used to replicate the turbulence and cavitation phenomenon within the nozzles. The formation and the subsequent development of cavitation phenomenon was comparatively more prevalent in the VCO nozzle orifices. Cavitation development intensity was observed to be more significantly influenced by orifice inclination angles in the VCO nozzle as compared to the SAC. Although in-orifice flow velocity of VCO are higher under cavitating condition, their corresponding injection rates are lower comparatively, due to the formation of smaller effective flow areas in the orifices. However under non-cavitating condition, the in-orifice flow velocities and effective injection velocities from the SAC orifices are higher, relative to that from the VCO. The cavitation phenomenal distribution within the SAC orifices were at the top areas while that of the VCO were mostly at the mid-sections of the orifices. Increasing orifice inclination angle increases the degree of cavitation phenomenon but decreases the uniformity of in-orifice flow velocity in the nozzles. The rate of non-uniformity in orifice flow velocity distribution is much higher within the VCO orifices as compared to the orifices in the SAC. With a comprehensive insight of in-orifice nozzle flow characteristics for asymmetric nozzles, the combustion efficiency and the rate of soot formation in a two valve engine can be managed and improve significantly by manufacturers.