混合器对国六柴油机选择性催化还原系统尿素结晶的影响

Effects of Mixer on Urea Deposit in Selective Catalytic Reduction for ChinaⅥDiesel Engines

针对国六柴油机选择性催化还原(selective catalytic reduction,SCR)后处理系统尿素结晶问题,设计了两种不同的混合器结构。利用计算流体动力学(computational fluid dynamics,CFD)技术对两种混合器方案的尿素碰壁位置、尿素轨迹、气流速度、流速均匀性、NH_3均匀性、压力损失等进行了仿真分析和对比,最后通过发动机台架试验验证两种方案的排放性能和结晶性能。CFD分析及试验结果表明:方案二的气流速度、流速均匀性和NH_3均匀性都优于方案一,而方案一的压力损失小于方案二;方案一台架试验的结晶质量为608g,不满足主机厂要求,方案二台架试验的结晶质量为6g,满足主机厂要求。CFD分析和试验结果趋势一致,表明CFD分析是合理有效的。

In order to solve the problem of urea deposit in the selective catalytic reduction(SCR)aftertreatment system of a ChinaⅥdiesel engine,two mixers of different structures were designed.Simulation analysis and comparison of urea impingement,urea track,air flow velocity,uniformity of velocity,uniformity of NH3 and pressure loss was carried out through the computational fluid dynamics(CFD)technology.Finally,the emissions and deposit performance of the two mixers were tested by engine bench.The CFD and test results show that Mixer 2 is superior to Mixer 1 in the air flow velocity,the uniformity of velocity and the uniformity of NH3,but has bigger pressure loss.The deposit weight of Mixer 1 was measured as 608 g by engine bench test,which fails to meet the requirements of OEMs.And the deposit weight of Mixer 2 was measured as 6 g,which meets the requirement of OEMs.The trends of the CFD analysis and test results are consistent,indicating that the CFD analysis is appropriate and effective.