Influence of the Diesel Injector Hole Geometry on the Flow Conditions Emerging from the Nozzle

Engine performances are correlated to the overall fluid dynamic characteristics of the injection system that, in turns, are strictly correlated to the fluid dynamic performance of the injector geometry. It is particularly true for actual GDI and Diesel engines where micro-orifice configurations are associated to very high injection pressure. In relation to the Common Rail Diesel engines, over the last decade different injector hole shapes have been tested. Actually, the most used configurations are: cylindrical, k, and ks. In this paper, the performance of all these three injector hole shapes are evaluated in order to find out the influence of orifice conicity and hydro-grinding level on the main fluid dynamic characteristics like cavitation evolution inside the injector as well as the flow properties at nozzle exit. The fluid dynamic behavior of each considered hole is evaluated over the injection time by performing a fully transient CFD multiphase simulation (i.e. the needle motion is reproduced during the simulation). By the proposed simulation methodology, the evaluation of the cavitating flow evolution inside the injector is performed not only from the point of view of the overall spray characteristics emerging from the injector holes but also from the cavitation erosion risk over needle, nozzle, and hole internal surfaces. © 2013 The Authors