Numerical Modelling and Experimental Characterization of a Pressure-Assisted Multi-Stream Injector for SCR Exhaust Gas After-Treatment

Simulations for a pressure-assisted multi-stream injector designed for urea-dosing in a selective catalytic reduction (SCR) exhaust gas system have been carried out and compared to measurements taken in an optically accessible high-fidelity flow test rig. The experimental data comprises four different combinations of mass flow rate and temperature for the gas stream with unchanged injection parameters for the spray. First, a parametric study is carried out to determine the importance of various spray sub-models, including atomization, spray-wall interaction, buoyancy as well as droplet coalescence. Optimal parameters are determined using experimental data for one reference operating condition. The model is subsequently applied to all operating conditions with unaltered parameters and validated by means of the measured droplet velocity fields, droplet diameter distributions and spray-tip propagations which have been characterized by means of Particle Image Velocimetry (PIV), Phase Doppler Anemometry (PDA) and shadow imaging. Finally, the model is used to investigate in detail phenomena characteristic of inclined sprays in cross-flows. Effects such as formation of vortices behind the spray core for low cross flow velocities, greater entrainment of droplets at high flow rates as well as wall film dynamics and the interaction of droplets also with the side walls are discussed in detail, highlighting the importance of the respective phenomena at the different operating conditions.