Srilomsak M, Hanamura K
Department of Mechanical Engineering, Graduate School of Engineering, Tokyo Institute of Technology, Meguro, Tokyo, Japan.
J Microsc. 2020 Aug;279(2):85-97. doi: 10.1111/jmi.12905. Epub 2020 May 25.
Regeneration of diesel particulate filter (DPF) is a complicated process due to its high operating temperature and associated oxidation of soot on the filter substrate. Several oxidation mechanisms of diesel soot have been proposed based on reaction kinetics, but more information about the oxidation phenomena is needed in a practical system, that is, soot oxidation on a DPF substrate. In this work, the DPF regeneration process was, for the first time, visualized at the particle scale ex-situ, in time-lapse series, using field emission scanning electron microscopy (FE-SEM). Time-lapse transformation of soot cake layer on a real DPF was followed from initiation through the complete regeneration process. In parallel, transformation of the soot primary particle diameter was directly measured using high-resolution transmission electron microscopy. FE-SEM visualization clearly showed shrinkage of the soot cake layer on the DPF wall as oxidation progressed. Furthermore, diameter distribution analysis revealed a trend of shrinkage of the nanoscale soot primary particles during oxidation, supporting the FE-SEM observations of the micron-scale shrinkage of the agglomerated soot cake layer. Fragmentation of the shrunken soot cake layer was also observed and is suspected to be a result of locally higher gas flow that depends on surface pore morphology of the filter substrate. LAY DESCRIPTION: In this work, the DPF regeneration process was, for the first time, visualized at the particle scale ex-situ, in time-lapse series, using field emission scanning electron microscopy (FE-SEM). Time-lapse transformation of soot cake layer on a real DPF was followed from initiation through the complete regeneration process. In parallel, transformation of the soot primary particle diameter was directly measured using high resolution transmission electron microscopy. FE-SEM visualization clearly showed shrinkage of the soot cake layer on the DPF wall as oxidation progressed. Furthermore, diameter distribution analysis revealed a trend of shrinkage of the nano-scaled soot primary particles during oxidation, supporting the FE-SEM observations of the shrinkage of the micron-scale agglomerated soot cake layer. Fragmentation of the shrunken soot cake layer was also observed and is suspected to be a result of locally higher gas flow that depends on surface pore morphology of the filter substrate. Further detail mechanism about transformations of the soot cake layer was additionally discussed based on electrostatic attraction.
柴油颗粒过滤器（DPF）的再生是一个复杂的过程，这是由于其较高的工作温度以及过滤器基体上烟灰的相关氧化作用。基于反应动力学已经提出了几种柴油烟灰的氧化机制，但在实际系统中，即DPF基体上的烟灰氧化，还需要更多关于氧化现象的信息。在这项工作中，首次使用场发射扫描电子显微镜（FE-SEM）在颗粒尺度上对DPF再生过程进行了非原位的延时系列观察。跟踪了真实DPF上烟灰饼层从开始到完全再生过程的延时转变。同时，使用高分辨率透射电子显微镜直接测量了烟灰初级颗粒直径的变化。FE-SEM观察清楚地表明，随着氧化的进行，DPF壁上的烟灰饼层出现收缩。此外，直径分布分析揭示了氧化过程中纳米级烟灰初级颗粒的收缩趋势，支持了FE-SEM对团聚烟灰饼层微米级收缩的观察结果。还观察到收缩的烟灰饼层出现破碎，怀疑这是由于取决于过滤器基体表面孔隙形态的局部较高气流导致的。层次描述：在这项工作中，首次使用场发射扫描电子显微镜（FE-SEM）在颗粒尺度上对DPF再生过程进行了非原位的延时系列观察。跟踪了真实DPF上烟灰饼层从开始到完全再生过程的延时转变。同时，使用高分辨率透射电子显微镜直接测量了烟灰初级颗粒直径的变化。FE-SEM观察清楚地表明，随着氧化的进行，DPF壁上的烟灰饼层出现收缩。此外，直径分布分析揭示了氧化过程中纳米级烟灰初级颗粒的收缩趋势，支持了FE-SEM对团聚烟灰饼层微米级收缩的观察结果。还观察到收缩的烟灰饼层出现破碎，怀疑这是由于取决于过滤器基体表面孔隙形态的局部较高气流导致的。基于静电引力，还额外讨论了烟灰饼层转变的更详细机制。
