大功率柴油机尿素-选择性催化还原系统混合器仿真与试验研究

Simulation and Experimental Study of Urea-Selective Catalytic Reduction Mixer for a High Power Diesel Engine

针对大功率柴油机选择性催化还原技术(SCR)应用需求,设计了两种混合器方案,两方案的差别在于是否在喷射点前安装前置混合器。利用计算流体动力学(CFD)技术对两方案的气流轨迹、尿素分解率、分布均匀性及压力损失进行了仿真分析,并进行D2排放循环测试验证两方案的NOx转化效率。仿真及试验结果表明:安装前置混合器可以产生旋流,促进尿素液滴与气流充分混合,提高尿素分解率和NH3分布均匀性,压力损失增高;安装前置混合器能够提高SCR催化器的NOx转化效率,并可以通过标定优化使NOx比排放满足欧盟第五阶段排放限值要求。研究表明,前置混合器更能适应当前及未来大功率柴油机NOx排放法规限值要求。

According to the requirements of the selective catalytic reduction (SCR) technology of a high power diesel engine, two schemes of installing and not installing a pre-mixer before the injection point were designed. The computational fluid dynamics (CFD) technology was used to simulate the gas-flow trajectory, urea decomposition rate, NH3 distribution uniformity and pressure loss of the two schemes, and the D2 emission cycle test was carried out to verify the NOx conversion efficiency of the two schemes. The simulation and experimental results show that compared to the solution without a pre-mixer, the pre-mixer can generate a swirl to promote the full mixing of urea droplets with gas flow, and increase the urea decomposition rate and NH3 distribution uniformity at a higher pressure loss, thereby improving the NOx conversion efficiency of the SCR system, which makes the NOx emissions meet EU Stage V emission regulations, and provides a bright future for the development of higher power diesel engines.