A computational fluid dynamic toll was used to predict the performance of a prototype high-pressure swirl injector nozzle with respect to design parameters. Performance of the prototype nozzle was investigated in terms of the flow rate and the initial spray angle. Design parameters included needle lift, needle-seat angles, orifice diameter and length, and needle-seat contact diameter. The most important parameter was found to be the orifice diameter. Transient flow rate was also examined. The needle-opening time was found to have influence on the lineartiy of the dynamic flow rate.