Spray characterization of Urea-Water Solution (UWS) injected in a hot air stream analogous to SCR system operating conditions 2019-01-0738

The Selective Catalytic Reduction (SCR) system has great potential in reducing NOx emissions where the urea-water solution (UWS) spray, necessary to transform these gasses in nitrogen and water, plays an important role in the performance of this system. The UWS needs to be properly mixed with the exhaust gasses coming from the engine before entering the SCR, therefore the solution must be injected in the exhaust pipe in a way that it completely vaporizes in order to reduce deposit formation and guaranteeing a proper functioning and durability of the NOx reduction system. Achieving complete vaporization of the UWS spray is no easy task, mainly due to reduced space, and in order to understand the behaviour of the spray under operating conditions it is necessary to study the influence of numerous parameters that affect the development of the spray atomization and vaporization. The present article details a methodology to study the UWS injection process under different gas and injection conditions, varying the mass flow and the temperature of the gas, the inclination angle of the injector and the injection pressure in order to characterize the liquid spray. All experimental results were obtained in a new test vessel developed to study the UWS injection process which is capable of reaching an air flow of 400kg/h and air temperatures up to 400ºC (depending on the air mass flow). Experiments showed that the injection pressure plays an important role on the global spray performance as well as on the droplet size and droplet velocity near the nozzle exit.