Abstract: A simulation model for selective catalytic reduction (SCR) of exhaust gas from diesel engine is established, and a concept of urea decomposition efficiency is proposed. Effects of exhaust gas temperature, NH₃ storage, NO₂/NO_x ratio and NH₃/NO_x ratio on the NO_x conversion efficiency are studied. The results show that the urea decomposition efficiency increases with decreasing exhaust gas flow rate and rising exhaust gas temperature. Special evaluating experiments for NO_x conversion efficiency under various temperatures were performed. The data obtained by simulation show good agreement with the experimental results. The results show that the NO_x conversion efficiency increases with the NH₃ storage capacity rising. Similarly, the NO_x conversion efficiency increases with rising exhaust gas temperature, and it gets stable when the exhaust gas temperature reaches a certain value. Increasing NO₂/NO_x ratio can also improve the NO_x conversion efficiency, but the opposite phenomenon occurs when the NO₂/NO_x ratio is greater than 50%. With increase of NH₃/NO_x ratio, the NO_x conversion efficiency ascends, and the influence is obvious when the exhaust gas temperature is high.

Key words: SCR, diesel engine, pollution, model, urea decomposition efficiency, NO_x conversion efficiency, operating parameter

摘要： 建立了柴油机选择性催化还原SCR系统的仿真模型，提出了尿素分解效率的概念。研究了排气温度、NH₃存储量、NO₂/NO_x、NH₃/NO_x等关键运行参数对NO_x转化率的影响。研究结果表明，随着排气流速的减小和排气温度的增加，尿素分解效率总体呈升高趋势。进行了不同温度下NO_x转化率的评价试验研究，仿真结果和试验结果吻合良好。随NH₃存储量的增加，NO_x转化率呈上升趋势。随排气温度的升高，NO_x转化率持续上升，当温度超过某一值后趋于稳定。随NO₂/NO_x的增加，NO_x转化率逐渐上升，当NO₂/NO_x超过50%后，NO_x转化率则有所下降；NO_x转化率随NH₃/NO_x的增大而上升，当排气温度较高时，其影响较为明显。

关键词: SCR, 柴油机, 污染, 模型, 尿素分解效率, NO_x转化率, 运行参数