A Numerical Study of the Influence of Diesel Nozzle Geometry on the Inner Cavitating Flow

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.