柴油机选择性催化还原系统氨泄漏及控制研究

Research on Ammonia Slip and Control of Diesel Engine SCR System

氨泄漏的预测和控制是选择性催化还原系统的关键问题。开展选择性催化还原系统小样试验,研究V_2O_5-WO_3/TiO_2催化剂的氨吸附脱附特性以及氨氮比和温度对氨泄漏量的影响。结果表明:氨泄漏一旦发生氨泄漏量将会迅速升高,氨泄漏临界点的预测和控制对氨泄漏量的控制至关重要;氨泄漏临界点对应的氨存储饱和度不随氨氮比和催化剂温度的变化而改变;氨氮比分别为0.7、1.0和1.4时,氨泄漏临界点对应的氨存储饱和度维持在76.7%附近波动,分别为79%、75%和76%.氨存储饱和度与氨泄漏临界点有较强的相关性,基于这种相关性设计开发了以氨存储饱和度为控制目标的控制算法,并进行了欧洲瞬态测试循环。采用该控制方法后催化剂出口的氮氧综合比排放为2.45 g/(kW·h),氨泄漏体积浓度均值为3.7×10^(-6),峰值为12.8×10^(-6),达到国家第Ⅳ阶段机动车污染物排放标准要求。

The prediction and control of ammonia slip are the key issues of selective catalytic reduction （SCR） system. A SCR sample test bench was built. The adsorption and desorption characteristics of am- monia in V2Os-WO3/TiO2 catalyst are studied, and the effects of NH3/NOx ratio and catalyst temperature on ammonia slip are analyzed. The results show that the ammonia slip increases rapidly once ammonia leaks. The prediction of critical point of ammonia slip is very crucial for the control of ammonia slip. When the ammonia slip reachs to a critical point, the ammonia storage saturation level is not changed with the change in NH3/NOx ratio and catalyst temperature. When NHJNOx ratio is set to 0.7, 1.0 and 1.4, the ammonia storage saturation level is 79% , 75% and 76%. The value of ammonia storage satura- tion level maintains fluctuations in the rangg of about 76.7% when the ammonia slip reachs to the critical point. The ammonia storage saturation level is related to the ammonia slip critical point. The control method of ammonia slip is designed based on the correlation between ammonia saturation level and ammonia slip critical point. The control method was used for SCR, and the European transient cycle （ETC） test of engine reduced to 2. 12.8× 10-6, was performed. 45 g/（kW-h）, which meet the The ETC test results show that the brake specific emission of outlet NOx is the average ammonia slip is 3.7 ×10-6, and the peak ammonia slip is requirements of national IV emission regulations.