柴油机选择性催化还原技术研究进展

Review on selective catalytic reduction technology of diesel engines

柴油车是大气中氮氧化物(NO_(x))的重要来源。选择性催化还原(SCR)系统是降低柴油机NO_(x)排放的主要后处理装置。我国柴油车(达到国VI法规)较多采用高效SCR技术路线,该技术路线需要SCR的NO_(x)转化效率达到95%左右。要实现全工况的低NO_(x)排放,需要开发宽域高活性高耐久性催化剂,保证SCR在宽温度窗口具有较高的NO_(x)转化效率,同时改善催化剂水热老化、硫中毒等问题。新法规对冷启动阶段NO_(x)排放的限值要求更加严格,紧耦合SCR和选择性催化还原捕集技术能够在发动机排气温度较低的工况下使SCR内的排气快速到达尿素起喷温度,有利于降低冷启动阶段的NO_(x)排放。SCR系统喷射控制策略优化是保证NO_(x)高转化效率且避免NH 3泄漏的关键因素,SCR控制策略开发要考虑硬件测量的不确定性,后处理系统构型复杂度的提高给SCR系统控制策略的开发提出了新的挑战。新型SCR还原剂如固态铵和还原性气体(碳氢、氢气和CO)能显著改善尿素作为还原剂载体的弊端,但是现阶段还无法实现大规模应用。

Diesel vehicles are an important source of nitrogen oxide(NO_(x))emissions in the atmosphere.Selective Catalytic Reduction(SCR)systems are the primary post-treatment devices for reducing NO_(x)emissions from diesel engines.In China,diesel vehicles mostly adopt the high-efficiency SCR technology route to meet the China VI emission regulations,which requires a NO_(x)conversion efficiency of around 95%for SCR.To achieve low NO_(x)emissions in full working condition,it is necessary to develop wide-temperature-range,high activity,and high durability catalysts to ensure that SCR has a high NO_(x)conversion efficiency in a wide temperature window,and to improve catalyst hydrothermal aging and sulfur poisoning.The new regulations require stricter NO_(x)emission limits during cold-start phases,and close-coupled SCR and SCR capture technology can enable exhaust gas in SCR to quickly reach the urea injection temperature under low engine exhaust temperature conditions,which is beneficial for reducing NO_(x)emissions during the cold-start phases.The optimization of SCR system injection control strategy is a key factor in ensuring high NO_(x)conversion efficiency and avoiding NH 3 leakage.The development of SCR control strategy should consider the uncertainty of hardware measurements,and the increasing complexity of the post-treatment system configuration brings new challenges to the development of SCR system control strategies.New SCR reductants such as solid ammonium and reducing gases(hydrocarbons,hydrogen,and CO)can significantly improve the drawbacks of urea as a reductant carrier,but large-scale application of these new reductants has not been realized.