发动机排气流中PM在DPF内的分布特性与催化剂涂覆策略的耦合

Vehicle particulate matter(PM) emissions are important incentives for atmospheric haze. Diesel Particulate Filter(DPF) can effectively capture PM, however, it is necessary to accelerate PM oxidation by catalyst, to continuously and efficiently remove them. Unsteady two-phase flow composed of PM with different particle sizes, pass through complex configuration of exhaust channels, will deposited in DPF porous media structure, and come into being different properties of soot cake. Conventional DPF adopt single catalytic formula containing noble metals and uniform coating. Soot cake in thick zones lack precious metals, PM oxidation efficiency is low. Soot cake in thin areas result in excessive precious metals. In this study, PM distribution characteristics in DPF are studied by constructing exhaust channel and DPF porous media model, combining two-phase flow calculation, laser testing, PM loading and soot cake nondestructive sampling technique. Soot cake samples were analyzed by SEM, XPS, TG analysis, to design Pt-LaBO3 catalytic formulation matching with microstructure and physicochemical characteristics of samples. Utilize optimization algorithm programming, to optimize the coating program. PM distribution and the coating strategy are coupled by applying flexible coating technology, to realize PM highly efficient oxidation in DPF with using low content precious metal.

汽车排放颗粒物PM是大气雾霾的重要诱因。颗粒捕集器DPF可有效捕集PM，但需借助催化剂加速其氧化，才能维持对PM的持续、高效去除。由废气与不同粒径PM组成的非定常两相流，穿过构型复杂的排气通道，会在DPF多孔介质内形成结构、性质各异的滤饼Soot Cake。传统DPF采用含贵金属的单一催化配方、均匀涂覆，在Soot Cake厚实区，表现为贵金属不足，PM氧化效率低；而在Soot Cake稀薄区，则贵金属过度。本研究通过构建排气通道及DPF多孔介质模型，结合两相流计算、激光测试，以及PM加载Soot Cake无损取样技术，研究DPF内的PM分布特性；并对分块Soot Cake样本进行SEM、XPS、TG理化分析，设计与其微观结构及理化特性相匹配的Pt-LaBO3催化配方，利用最优化算法编程，优化涂覆方案；应用灵活涂覆技术，使PM分布与涂覆策略耦合，实现DPF在低贵金属用量下的PM高效氧化。

汽车排放颗粒物PM是大气雾霾的重要诱因。颗粒捕集器DPF可有效捕集PM，但需借助催化剂加速其氧化，才能维持对PM的持续、高效去除。本项目研究了不同粒径的颗粒、soot cake的堆积密度、堆积形状、soot cake的不同尺寸及厚度，对其在孔道内的二次运动与分布的影响特性。基于上述特性，制备了LaBO3系列催化剂，由于LaCu0.7Fe0.3O4表面能吸附较多活性强的晶格氧，因而具有氧化碳烟的良好活性。通过开展涂覆催化剂的CDPF被动再生试验、主被动相结合的台架试验，结果表明，耐久循环工况下，催化剂涂覆量为15g/ft3CDPF的被动再生效率为87.5%，18g/ft3CDPF的再生效率则达到93.1%，而采取主被动相结合的15g/ft3CDPF，其再生效率则高达96.4%。基于量子化学计算，从微观方面研究了NO2及O2-NO2对soot的氧化机理，研究发现，NO2吸附在芘基表面形成的中间体-C(NO2)、-C(ONO2)构型，分解产生CO与CO2需要75.7 KJ/mol和53.5 KJ/mol的活化能；而O2-NO2对soot的活性位有竞争吸附作用，NO2易与O2产生C(O)反应，生成的NO3-可有效氧化活性C*，实现O2-NO2对soot氧化的协同效应。联合发动机的缸内燃烧与CDPF再生特性探究，发现主喷定时从-10.6°CA继续推迟至1.4°CA，CPF残余颗粒、压降以及NO2排放迅速降低；当主喷定时在-22.6°CA时，提高喷油压力有利于CDPF再生；后喷油量从5mg增大到10mg时，CDPF残余颗粒大幅度降低；EGR率为0%时，后喷时刻为18°CA时CDPF残余颗粒、压降及NO2排放最低，CDPF再生性能最佳；EGR率增大至25%时，CDPF再生性能最佳对应的后喷时刻为10°CA。通过开展机内与机外净化相互耦合的高效清洁燃烧与排气后处理研究，可以为机动车满足国六b排放法规的先进后处理系统的设计与开发服务。