柴油机SCR尿素分解详细化学反应机理模型研究

Detailed Chemical Reaction Mechanism Model of SCR Urea Decomposition for Diesel Engine

从分子结构化学层面解析尿素分解的反应路径,在此路径分析及前人研究的基础上,构建了包含14步反应和11种组分的SCR尿素喷射系统详细化学反应模型,该模型不仅考虑了氨气和异氰酸的生成,还涉及到缩二脲、三聚氰酸和三聚氰酸一酰胺等重要固体副产物的形成。基于量子化学计算方法解决了模型中两个反应无法通过文献获取的活化能和指前因子的动力学参数难题。针对尿素在喷射点到催化器入口前端间的排气管路中的分解过程构建三维模型,分别调入详细机理模型与总包反应机理模型,计算结果表明,两种机理模型预测的NH3浓度生成趋势相符,缩二脲、三聚氰酸一酰胺生成是造成NH3浓度在200℃左右出现预测误差的主要原因。

The reaction path of urea decomposition was analyzed from the perspective of molecular structure chemistry. The detailed chemical reaction model of SCR urea injection system including 14 steps and 11 components was constructed based on the path analysis and previous research experience, which considered both the formation of ammonia and isocyanic acid and the formation of important solid by-products such as biuret, cyanuric acid and cyanuric acid monoamide. The problem that the kinetic parameters of activation energy and pre-exponential factor in the two reactions of model that cannot be obtained by literature was solved according to the quantum chemical calculation method. A three-dimensional model was built for the decomposition process of urea in the exhaust pipe from the injection point to the front end of catalyst inlet. The detailed mechanism model and the total package reaction mechanism model were introduced respectively. The calculation results showed that the trend of NH 3 concentration generation predicted by the two mechanism models was consistent. The formation of biuret and cyanuric acid monoamide was the main reason for the prediction error of NH 3 concentration at about 200 ℃.