摘要
采用计算流体动力学(CFD)与化学反应动力学结合的方法,建立了车用Urea-SCR排气后处理系统的数值模型,包括尿素水溶液蒸发及热解、催化还原化学反应等过程,NH3吸附/解吸附反应被视为"冻结"。采用一维CFD计算分析了不同温度下(260℃、280℃、320℃、408℃)n(NH3)/n(NOx)(物质的量之比)≤1对NOx转化率的影响;采用三维CFD计算比较了混合器对系统流场、浓度场及NOx转化率的影响。计算结果表明:NH3不过量时,高温下NOx转化率与n(NH3)/n(NOx)成正比,低温下存在一个临界n(NH3)/n(NOx),达到该临界值后NOx转化率趋于定值,NH3泄漏迅速增加;较好的混合器设计可以增加尿素热解时间和催化剂前NH3体积分数分布均匀性从而提高NOx转化率;仿真与试验结果吻合较好。
A modeling approach to optimize SCR （ Selective Catalytic Reduction） system with aid of CFD （Computation Fluid Dynamics） coupled with reaction dynamics was presented including evaporation of urea-water-solution, subsequent thermal decomposition and surface catalytic reactions in the monolith. Ammonia adsorption/desorption is treated as a frozen process and the kinetics is negligible in simulation. The influence of n（ NH3 ）/n（ NOx ） ≤1 on NOx conversion at different temperatures （260℃, 280℃,320℃, 408℃） was studied in a 1D model. A 3D model was implemented to evaluate the effect of mixer on flow, concentration distribution and NOx conversion efficiency. Results show that when ammonia is insufficient, NOx conversion efficiency is related to n （NH3 ）/n（ NOx） at high temperature, but NOx conversion efficiency tends to a constant with rapid increase in ammonia slip after a critical n （ NH3 ）/n （ NOx） is achieved at low temperature. The mixer before the monolith can improve NOx conversion with the longer residence time for urea decomposition and better NH3 concentration uniformity. The Simulation result shows good agreement with experimental data.
出处
《内燃机学报》
EI
CAS
CSCD
北大核心
2009年第3期249-254,共6页
Transactions of Csice
基金
国家自然科学基金资助项目(50876078)
