Visualization and Analysis of Droplets Behavior in Aftertreatment Systems:II. Improvement of Vaporization Efficiency by Surface Texturing

Diesel engines contain Nitrogen oxides (NOx) in exhaust gases, and is considered to be problematic in view of the environment. For worldwide NOx emission control, Selective catalytic reduction (SCR) dosing systems are widely used in aftertreatment systems. A mixer of the urea aqueous solution is placed between the injector and SCR catalysts and is used to provide good ammonia uniformity in SCR catalysts. It is very important to mix and evaporate the urea aqueous solution at short-distance using the optimum the mixer blade geometry. In this paper, the collision behavior of droplets into textured mixer surface materials are investigated by visualization experiment by backlight method. Then, several surface texture types were proposed as a means to improve the atomization performance of droplets by the mixer. In order to verify the performance of droplet atomization by the textures, a visualization experiment of droplet behavior was conducted using a simple experimental device including high-speed camera. Furthermore, the droplet diameter distribution before and after collision was calculated using the visualization results. Various conditions of droplet diameters were measured and the vaporization performances of the surface textures were studied. According to the results, 30 micron of pitch texture demonstrated good micronizing and evaporating of the droplets. This time, our study has established new visualization experiment methods for the aftertreatment systems, especially micro-scale of SCR dosing systems. It was found that improvement of the vaporization efficiency by surface texturing on the mixer or exhaust pipes.