Spray characteristics of SCR urea swirl nozzles: A comparative analysis using multiple optical particle sizing methods

Abstract

Selective Catalytic Reduction (SCR) systems are widely employed in power generation, diesel engines, and industrial processes to mitigate NOx emissions. The atomization performance of urea injector nozzles significantly affects NO_x conversion and urea crystallization. This study introduces a novel Droplet Tracking Velocimetry (DTV) technique integrating the circular Hough transform with Voronoi-based tracking to simultaneously measure droplet size and velocity in hollow-cone sprays from pressure-swirl nozzles. Comparative experiments with Phase Doppler Interferometry (PDI) and Malvern laser diffraction reveal that DTV achieves over 90% velocity reconstruction accuracy and droplet size error below 7%, outperforming the other two methods in resolving transient spray heterogeneity. Axial and radial analyses show that the Sauter Mean Diameter (SMD) increases progressively with distance from the nozzle and exhibits significant radial growth due to the interaction between high-speed large droplets and low-speed small droplets. The DTV method provides comprehensive spatially resolved data, offering critical insights for optimizing SCR injector design and improving NOx reduction efficiency.