An extensive computational fluid dynamics (CFD) study has been performed in order to analyze the influence of nozzle geometry on the internal flow characteristics of a diesel injector. The flow through cylindrical and conical nozzles with different grades of hydro-grinding and at various needle lift positions and injection pressures was calculated to observe the individual effect of these parameters on the inception of cavitation. Most calculations were based on the assumption that the nozzle flow is axisymmetric. The set of calculations that was carried out to identify the most influential parameters for the onset of cavitation was determined by means of an experimental design technique. A correlation study was made in order to obtain a numerical expression that relates the critical cavitation number to geometric dimensions. Experiments were performed to validate both numerical calculations and conditions at which cavitation appears.

In order to analyze the influence of nozzle geometry on the internal flow characteristics of a Diesel injector, a CFD analysis of the flow through various nozzle geometries has been carried out with a commercial code. This program includes a numerical model simulating the effect of cavitation. For the flow simulation, cylindrical and conical nozzles with different grades of hydro-grinding were used in order to observe the individual effects of these geometrical parameters. The model predicts accurately the onset of cavitation, but is very limited for strongly cavitating flow, so that the analysis of the solution may only be qualitatively assessed. However, the simulations confirm the tendency observed in experiments, that the nozzle geometry significantly influences the inner flow characteristics. In particular, by increasing the hydro-grinding radius of the orifice inlet, the mean outlet velocity near the wall and the discharge coefficient are increased, while the zone of cavitating flow is reduced. In addition, it was found that conical nozzles do not produce cavitation.