In this study, the flow rate and swirling characteristics of the swirl injector for Urea-SCR corresponded to its changed design parameters. They were identified through unsteady flow analyses that employed the overset mesh technique. Also, the internal flow and spraying characteristics of an improved model with combined factors for optimal performance were analyzed. To improve the injector’s internal flow characteristics, the number of swirlers, the nozzle angle round, and the needle end shape length were taken as design factors. The following numbers were summed to check the reliability of the overset mesh technique: 1) the rate of theoretical mass change of the control volume that varies according to a needle’s movement of and 2) the rate of mass change inside of the control volume computed by a simulation.
The flow characteristics corresponding to various injector designs were analyzed: the flow rate of the injector’s single spray appeared to increase with the increasing number of swirlers, nozzle angle rounds, and with the shortened length of needle end shapes. The swirling characteristics of the injector were examined and the rotary flow created by the swirl disk found to affect the outlet 0.3 ms later with the swirling coefficient continuously increasing until the spraying’s termination. The average swirling coefficient values corresponding to respective design changes were compared and revealed that a lesser number of swirlers, a bigger nozzle angle round, and an extended needle length was advantageous for enhancing swirling intensity. Based on results obtained from the internal flow analyses, a combination of a single spray’s amount, the average flow coefficient and the average swirling coefficient were determined as the design factors for the improved model, which consisted of 8 swirlers, a 0.4 mm of nozzle angle round, and a 0.95 mm needle end shape length.
The internal flow of the improved model was analyzed and a comparison with the base model showed that the amount of a single spray and the average coefficient increased approximately by 2% while the average swirling coefficient grew by about 12%. In addition, an improved axial flow attributable to the bigger nozzle angle round was also found. The spraying characteristics of the base and improved models were identified by analyzing the spray where the spraying angle of approximately 30° was found optimal for both models. However, with regard to the spray’s range, the improved model appeared to have a range approximately 4.2% longer than the base model. The results obtained from the Urea-SCR injector analyses conducted in this study are thus expected to be useful for the design and performance improvement of single injectors.