,In 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.