Physicochemical characteristics of ash-bridges in diesel particulate filter

Abstract

The diesel particulate filter (DPF) is one of the most effective devices for reducing particulate emissions from diesel engines so as to satisfy emission regulations, and it has been widely utilized worldwide. After prolonged operation of the DPF, the accumulated non-combustible ash particulates can be sintered with filter walls and form ash-bridges, which will deteriorate DPF performance and increase emissions. Understanding physicochemical characteristics of ash-bridges is essential for elucidating the generation and evolution mechanisms of ash-bridges. Since lubricant additives are the main source of ash particulates, this study prepared four DPFs containing ash-bridges through accelerate ash loading experiments based on Zn-based, Ca-based, Mg-based, and composite lubricant additives. Subsequently, X-ray computed tomography (X-CT), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were employed to analyze the structural characteristics, micro-morphology, and chemical composition of ash-bridges inside each DPF. The results indicate that Zn-based and composite ashes formed numerous fine ash-bridges in the middle of the DPF, whereas Ca-based and Mg-based ashes resulted in fully shaped and highly blocked ash-bridges. These ash-bridges aggregated into compact ash plugs downstream in all DPFs. The micro-morphology of Zn-based ash-bridges appeared as ball-and-stick, Ca-based ash-bridges aggregated into large ash aggregates in DPF downstream, Mg-based ash-bridges exhibited characteristics of high porosity, and the micro-morphology of composite ash-bridges is spherical in DPF downstream. The primary components of ash-bridges in Zn-based, Ca-based, and Mg-based DPFs are Zn2P2O7, CaSO4, and MgO, respectively. The main components of ash-bridges in composite DPF include Ca7Mg2P6O24, Zn3(PO4)2(H2O)4, and CaSO4. These findings provide valuable insights into the understanding of ash-bridges, contributing to the enhancement of DPF performance and durability.