Experimental Fluid Dynamic Investigation of Urea–Water Sprays for Diesel Selective Catalytic Reduction–DeNOx Applications

Abstract

The injection process of urea–water solution determines initial conditions for reactions and catalysis and is fundamentally responsible for optimal operation of selective catalytic reduction (SCR) systems. In this study, injection and spray atomization characteristics of a pressure driven injector were investigated in varying crossflow conditions using shadow imaging, Mie scattering, and particle image velocimetry (PIV). Spray angle and tip propagation are described. Processed images characterize spray density and mass distribution. Velocity fields from PIV analyses indicate the entrainment of droplets in the spray. This is shown to be primarily dependent on the injection momentum ratio, in accordance with previous literature. The presence of a vortex pair is clearly evidenced at low gas flow momentums. Results indicate that fluid mechanic differences between the spray and gas flow are insufficient to induce substantial secondary breakup and interact extensively with the bulk of the spray. Spray wall impingement remains unavoidable; therefore, sufficient mixing lengths or devices are required for urea decomposition.