柴油机尿素SCR氨分布均匀性的试验与模拟优化

在发动机排气温度300℃、排气流量400kg/h的条件下,测量了尿素SCR催化剂载体前端面的NH3浓度分布。测试结果表明:载体前端面NH3浓度分布均匀性较差,NH3浓度最大值约是最小值的6倍,试验NH3分布均匀性指数仅为0.791。为了提高NH3的分布均匀性,采用CFD软件建立了该SCR系统的流动以及尿素水溶液的喷雾、热解和水解反应等模型,并研究了混合器对NH3浓度分布的影响。模拟结果表明:尿素水溶液喷射后,部分液滴发生撞壁,在排气管直管段大部分液滴集中沿管壁方向运动,进入进口多孔管后液滴分散开,但整体液滴分布不均匀。安装混合器能够使NH3分布均匀性指数和NOx转化效率提高约10%。

Experiment and Simulation of Ammonia Distribution Uniformity for Diesel Engine Urea-SCR

The NH3 concentration before the substrate was measured under the conditions of 300 ℃exhaust temperature and 400 kg/h exhaust mass flow.The result shows that the NH3 concentration distribution is poor on the side of substrate.The maximum value is about six times as much as the minimum value and the NH3 distribution uniformity index is only 0.791.In order to improve the NH3 distribution,the flow model and the solution spray,pyrolysis and hydrolysis model of SCR system are established with the CFD software and the influence of mixer on NH3 distribution is also researched.The simulation results show that only part of the urea droplets hit onto the pipe wall and most of the urea droplets move along the pipe wall in straight sections of exhaust pipe after the urea solution is injected into the exhaust pipe.The urea droplets scatter after they go through the inlet porous pipe,but their distribution is not uniform.However,after fixing the mixer,the NH3 distribution uniformity index and the NOx conversion efficiency improve by about 10% separately.