Visualization and Analysis of Droplets Behavior in Aftertreatment Systems: I. Experimental Study by Acrylic SCR Dosing Simulator

Diesel engines have been extensively used as a primary power source for truck and off-road applications. Exhaust gas emissions from the engines, in particular Nitrogen oxides (NOx) is reduced using Selective catalytic reduction (SCR) dosing systems in aftertreatment systems. The injection of urea aqueous solution spray in the exhaust pipe of the small off-road diesel engines significantly eliminate NOx emissions. However, the crystallization of urea from the evaporative aqueous solution droplets and wall deposit formation in exhaust pipes are main issues in SCR dosing systems. The issues are critical deterioration of performance in aftertreatment systems. Nevertheless, the visualization study hasn't been investigated for the inside of exhaust pipes yet. This paper describes visualization experiments of the injected droplets behavior by Acrylic SCR dosing simulator. First visualization technique was applied measuring the gas flow distribution and directions with a smoke generator. Then, the injected spray and droplets behavior are validated with actual application conditions. The details of droplets behavior with gas distributions were confirmed by multiple Highspeed video cameras and PIV (Particle image velocimetry) analysis. From the visualization results show the details of SCR spray impingements, injected droplet directions and evaporated behavior in the exhaust pipe conditions. The results were clarified complicated gas and droplets flows inside of exhaust pipes. This time, our study has established new visualization experiment methods for the aftertreatment systems, especially Macro-Meso scale of SCR dosing systems. As a result, we have found that the visualization study shows effective utilization of SCR dosing systems.