Browse Publications Technical Papers 2019-01-0738

Spray Characterization of the 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. The urea-water solution (UWS) is the preferred method on vehicles for obtaining the ammonia, the required reductant for SCR. The UWS spray is necessary to transform exhaust gas into nitrogen and water and plays an important role in the performance of this system.
The UWS needs to be properly mixed with the exhaust gas 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 not an easy task, mainly due to reduced package space. Another challenge for converting UWS to ammonia is the latent energy in the exhaust. In order to understand the behavior 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 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 400°C (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.


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