Impact of Choice of Spray Inputs on Simulations of Urea-Based Selective Catalytic Reduction Systems

Spray simulations based on the Eulerian-Lagrangian framework are the industry norm to predict ammonia (NH₃) uniformity and wallfilm formation in a urea-based selective catalytic reduction (SCR) system. However, key spray inputs such as drop size distribution, initial velocity, and cone angle required for these analyses can be obtained from various sources, which can affect the reliability of simulation results. In this work, a single-hole pressure-swirl diesel exhaust fluid (DEF) injector was first experimentally characterized using various apparatus and measurement methods including high-speed shadowgraphy (HSS), laser diffraction (LD)-based drop size analyzer, laser sheet imaging (LSI), laser Doppler velocimetry (LDV), and phase Doppler anemometry (PDA). Subsequently, spray simulations were conducted in a quiescent chamber using different sources of spray inputs. The impact of varied sources of spray inputs was found to be negligible for velocity-drop size correlation, but differences were observed in radial distribution profiles of mass flow, velocity, and Sauter mean diameter. Finally, spray simulations were conducted on a representative SCR aftertreatment system. They revealed that the choice of spray inputs can lead to differences in spray mass distribution at the mixer inlet. However, the NH₃ uniformity index (UI) at the SCR inlet was found to be relatively unaffected. On the other hand, wallfilm formation was significantly affected by the choice of spray inputs.