柴油机SCR系统混合器优化设计与仿真分析

针对国六轻型柴油机混合器存在的NH₃均匀性问题,通过计算流体力学(CFD)对SCR系统内NH₃分布进行仿真研究,设计NH₃分布测试试验对仿真模型进行验证,优化设计混合器结构,研究了不同混合器方案对流场结构、SCR前端面NH₃均匀性和系统背压的影响。结果显示:仿真模型计算的NH₃分布与试验分布趋势具有较强的一致性;优化后的混合器B2方案NH₃均匀性可以达到0.97,远高于原混合器的0.88,同时背压由22.3 kPa降低到19.2 kPa;混合器多孔板从加强气流扰动和增加微小尿素液滴碰壁两个方面提升NH₃的均匀性;B3方案作为对照表明,与混合器不适用的多孔板会导致NH₃均匀性降低。

Optimization and Simulation for SCR Mixer of Diesel Engine

For the NH₃uniformity of SCR mixer for ChinaⅥlight-duty diesel engine,the NH₃distribution inside SCR system was simulated with CFD and the simulation model was verified by the test of NH₃distribution.The mixer structure was optimized and designed,and the influences of different static mixers on the structure of flow field,the uniformity of NH₃distribution before SCR and the pressure drop of aftertreatment system were investigated.The results show that the simulated results of NH₃distribution are consistent with the experimental results.Compared with the original mixer,the NH₃uniformity of B2 mixer increases to 0.97 from 0.88 and the back pressure decreases to 19.2 kPa from 22.3 kPa.Therefore,the porous plate at the rear of the mixer can improve the NH₃uniformity due to the enhancing air flow disturbance and increasing small urea droplet impact on the wall.B3 mixer shows that the porous plate that is not suitable for mixer will result in the decrease of NH₃uniformity.