Optimization of the location of injector in urea-selective catalytic reduction system

Urea–water solution (UWS) has been widely used in selective catalytic reduction (SCR) system as reductant to generate ammonia. The position where UWS nozzle should be located is a concerned issue and worth a deep investigation. Although UWS droplet evaporates and decomposes once it has been sprayed from the nozzle, the decomposition of droplet may be still incomplete if the distance between nozzle and reactor is not long enough. Thus, the incomplete decomposed UWS droplets will collect at the entrance of reactor, which is not beneficial for droplet evaporation, system flow and SCR efficiency. This paper presents the position where UWS nozzle should be placed from the perspective of evaporation and decomposition of UWS droplet. A numerical model of UWS droplet evaporation and decomposition was established in this paper and the droplet displacement is solved by adding droplet motion equation to the simulation model. The results can provide a practical help for designing a urea-SCR system.