Novel UWS Injection Technique for SCR Performance Improvement

The present study aims to meet the Euro-VII compliance applicable for internal combustion engines (diesel and hydrogen) by improving the performance of selective catalytic reduction (SCR) system using a novel urea water solution (UWS) mist injection technique. In SCR system, the interaction of exhaust gas and UWS resulted into ammonia (NH₃) species, which is mixed with harmful NO_x emission and converted into harmless by-products. Despite the proven technology, there are several challenges presented in the existing system which restricts the ideal performance of SCR system especially during cold starting condition: (i) incomplete droplet evaporation (ii) solid deposit formation (iii) non uniformity of NH₃ distribution at the catalyst entrance. The past studies shows that the droplet size plays a major role in this context. Further, it is noted that the smaller size droplets are desirable to overcome the impediments and enhance the efficiency of SCR application. Therefore, it is decided to investigate the effect of mist (contains very fine size droplets) injection on the important factors of SCR system such as formation and spatial uniformity of NH₃ species, and urea solid deposition on the mixing chamber wall. For this purpose, the study is carried out using the numerical simulation where the Reynolds Average Navier Stoke (RANS) and discrete phase model (DPM) is used to simulate the exhaust gas and mist, respectively. The results highlight that using the mist injection is a promising solution as it not only promotes the droplet evaporation rate but also enhances the NH₃ distribution which leads to a homogeneous mixture of NH₃/NO_x. Further, it is noted that the amount of urea solid deposition is significantly smaller on the mixing chamber wall.