摘要
选择性催化还原(SCR)是目前道路用国六柴油机降低NO_x排放的常用手段。但是,如果喷射的尿素水溶液得不到及时分解和反应,容易在喷嘴、混合器、壁面等处产生结晶,不仅降低NO_x的转化效率,还会增加排气背压,影响油耗。尿素结晶问题已成为发动机企业产品开发的难题之一。通过数值模拟方法,研究了某重型国六柴油机尿素喷射、排气和管路布置的相互作用,分析了SCR混合器内流动过程,针对结构上存在的问题提出了改进方案,并对混合器改进前后的内部流场、温度场、浓度场等作了对比分析。结果表明,优化后的混合器可以提高尿素水溶液和废气的混合效果,降低尿素结晶风险。
Urea/SCR systems have been proven effective at reducing NOx over a wide range of operating condition on mid/heavy duty diesel vehicles.However,Urea deposits are formed when urea-water solution is not decomposed and reacted in time,especially at low exhaust temperature.This phenomenon degrades the performance of the after-treatment system by decreasing overall mixing efficiency,lowering de-NOx efficiency and increasing pressure drop.Therefore,mitigating urea deposits is a primary design goal of modern diesel after-treatment systems.The interaction of urea injection,exhaust gas flow and pipe structure is analyzed for a certain China VI stage heavy duty diesel vehicle via numerical simulation,the flow process in SCR mixer is analyzed.Structural improvement was carried out,and the inner flow fields,temperature fields and concentration fields before and after the improvement are analyzed.Results show that the optimized SCR mixer is of better mixing effect and low-risk of urea deposits.
作者
战强
Zhan Qiang(School of Mechatronics and Vehicle Engineering,Weifang University(Weifang,Shandong,261000,China))
出处
《小型内燃机与车辆技术》
2020年第6期20-25,共6页
Small Internal Combustion Engine and Vehicle Technique
关键词
柴油机
氮氧化物
选择性催化还原
混合器
数值模拟
Diesel engine
Nitrogen oxides
Selective catalytic reduction
Mixer
Numerical simulation
