Novel UWS mist 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 UWS mist generation technique. The SCR system helps to convert the harmful NOx emission into harmless by-products by injecting the UWS, which is converted into ammonia (NH3). Despite the proven technology, there are several challenges presented in the existing system which degrade the SCR performance: (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, the current work numerically investigates the effect of mist (contains very fine size droplets) injection on the droplet evaporation rate, solid deposition, and spatial distribution of NH3 at different locations of the mixing chamber. Note that the mist is generated using the compressed air (~3 bar) which flows through a fine orifice and interact with the UWS stored inside a mini tank. The Reynolds Average Navier Stokes (RANS) and discrete phase model (DPM) is used for simulating 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. Further observations show that there is a significant reduction in urea deposition on mixing chamber wall.