Characterization of urea SCR using Taguchi technique and computational methods

Use of biodiesel in diesel engine helps to reduce HC, CO, and smoke emissions due to their enormous oxygen content, whereas NOx emissions formed by Zeldovich mechanism shoot up. Implementation of Bharat Stage (BS) VI by April 2020 in India has created extreme pressure on automobile manufacturers to include after treatment technology in their systems. Selective catalytic reduction (SCR), a NOx control technology, is operated using aqueous urea solution as the reductant. There are several parameters that need to be monitored to enhance the NOx conversion efficiency of SCR retrofit. The uniformity index of ammonia, which determines the conversion efficiency, is greatly influenced by parameters like exhaust gas temperature, injection angle, injector position, mass flow rate, and SCR geometry. This paper considers two types of SCR design, namely SCR with and without mixer design and their impact on NOx reduction. The effect of mass flow rate on urea conversion in SCR design without mixer is 27%, but the impact is reduced greatly in SCR design with mixer with less than 2% variation. The UI resulting from different cases ranges from 0.59 to 0.83. Using Taguchi technique and CFD tool, the impact of parameters on both the SCR designs has been investigated and the optimum SCR design is reported.

     

冰雹结构异质性的分析：大气条件及其潜在的环境意义

冰雹是球状或不规则冰块形式的降水，它一般产生于与复合单体、超级单体和冷锋锋面有关的对流云中。冰雹开始时是一些微小的冰球，这些小冰球与周围的小水滴不断发生碰撞，当附着的小水滴冻结起来，这些小冰球就增大了。当一个冰块混合体的直径达到或超过5 mm 时，就称为雹块[1]。一般来说，雹块是存在过冷水滴的雷暴积雨云内部上升气流和下沉气流共同作用的结果。过冷却的水滴不断沉积在冰晶上，使其起生长为雹块，这一般经过了从软雹（第一阶段）到小冰雹、再到雹块的不同阶段。一个雹块在云中上升、下沉的次数越多，所形成的雹块也就越大。当雹块降落到地面上时，其速度可以达到 90 mph (140 km /h)!