A numerical model has been developed to simulate unsteady cavitation processes in plain-orifice pressure atomizers typically used in diesel engine fuel injectors. The model is implemented via solution of the two-phase Navier Stokes equations formulated with the use of a pseudo-density which varies between vapor and liquid densities. Results for sharp-edged orifices indicate that partial cavitation flows are typically periodic, with a period of the order of the orifice transit time. Reducing orifice diameter tends to inhibit both the initiation and the overall extent of the cavitated region. Evert a slight rounding of the orifice inlet lip has dramatic effects on both cavitation and orifice discharge characteristics. Rounding tends to inhibit cavitation substantially, and also increases orifice discharge coefficient under both cavitated and noncavitated conditions. Finally, the cavitation field appears to develop quite rapidly (on the order of a few nozzle transit times) at the initiation of the infection process.