柴油机Urea-SCR系统内流场与化学反应耦合研究

Coupling Research of Flow Field and Chemical Reaction in a Diesel Urea-SCR System

提出三维流场与一维化学反应相耦合的方法对柴油机尿素(urea)-选择性催化还原(SCR)系统进行全尺寸模拟,真实反映SCR系统内部气流运动状态对化学反应的影响。选择柴油机典型工况的排气温度、流量及压力等物理信息作为边界条件,对SCR系统进行流场分析,截取催化器前端截面的速度切片,建立流速均匀性系数与工况的函数模型,研究各流速分布下运行参数对NO_x转化效率及副产物N_2O生成的影响,为优化SCR系统控制策略提供指导。结果表明,不同工况下柴油机SCR催化器前端各区域流速差异明显,且流速均匀性系数在0.6～0.8区间内,氨氮比为1.1且NO_2、NO_x之比在0.0～0.5区间内时,NO_x转化效率最高,副产物N_2O的生成最少。

A method of coupling a three-dimensional flow field with an one-dimensional chemical method was proposed to perform a full-scale simulation of a diesel engine selective catalytic reduction(SCR)system to study the effect of flow uniformity distribution on catalytic reduction reaction.Using the exhaust information measured by the engine bench test,a SCR three-dimensional flow field simulation was conducted to study the flow velocity changes at the front cross section of the SCR catalytic converter under different operating conditions,and then the effect of the operating parameters on NOx conversion efficiency and by-product N 2O formation was investigated under various flow rate distributions in order to provide a guidance for optimizing the control strategy of the SCR system.Results show that the difference in flow rates between the various regions of the front end of the SCR catalytic converter is obvious under different operating conditions.When the flow rate uniformity coefficient is within the range of 0.6 to 0.8,NH 3/NOx is 1.1 and NO 2/NOx is between 0.0 and 0.5,the NOx conversion efficiency is the highest,while the formation of by-product N 2O is the lowest.