Eccentric needle displacement effect on spray formation from a multi orifice diesel injector

Abstract

As emission regulations becomes stringent, improving injection process in internal combustion (IC) engines, is one of the ways of enhancing combustion characteristics and reducing pollutants emissions. Hence in this study, the effect of on-axis and off-axis internal needle displacement on injection characteristics from a multi orifice injector, used in direct injection IC engines, were investigated and analyzed. Two stage off-axis needle movement was formulated for the investigation. The first stage was at the initial stage of the needle lift, where the needle continuously glides along the internal cone of the nozzle body, before it completely departs the body. The second stage was considered to be from the moment the needle completely departed the nozzle body. Two different direction of the two stage off-axis needle displacement, were analyzed and their effect on flow and spray characteristics compared to those from on-axis needle displacement. The results showed that, off-axis needle displacements in the immediate areas of the nozzle orifices, causes exponential increment in spray jet penetrations as compared to off-axis needle displacement around the maximum needle lift position. Also, the displacement at the early stages of injection, had more influence on the spreading angles of spray jets from the nozzle orifices than the needle displacement around full needle lift.