Theoretical and Experimental Analysis of Ash Accumulation and Mobility in Ceramic Exhaust Particulate Filters and Potential for Improved Ash Management

Ash accumulation in the channels of ceramic, honeycomb-type particulate filters is controlled by several key parameters, which are the focus of this study. Ultimately, it is the formation of ash deposits, their transport, and the manner in which the ash accumulates in the particulate filter, which determines the useful service life of the filter and its resulting impact on engine performance. Although significant variations in ash deposit properties and their spatial distribution within the filter channels have been reported, depending on the filter's application, understanding the key parameters and mechanisms, such as the effects of exhaust flow and temperature conditions, as well as the processes occurring during filter regeneration events (whether passive or active) are critical in developing improved filter ash management strategies. This work combines fundamental modeling studies with in-situ optical investigations clearly showing the processes whereby ash deposits are formed within the particulate filter, and subsequently transported down the length of the filter channel. A one-dimensional model was developed to describe the ash particle transport inside the filter channels, estimating the flow friction force imposed on the ash particles based on the local mean flow velocity. Size-dependent effects (critical mass) are accounted for in the model, which includes the re-entrainment of smaller, micron-sized ash particles, as well as the transport of larger agglomerated ash deposits (larger than 500 μm) through surface rolling or sliding. The results of the simplified 1-D model are compared and contrasted with experimental results from the in-situ optical studies, as well as three-dimensional analysis of the flow fields within particulate filter channels reported in the literature. Consistent with experimental observations, the theoretical analysis presented in this work provides a framework for understanding, and potentially controlling, the fundamental processes governing the mobility and accumulation of ash deposits within particulate filters, whether they are used as diesel particulate filters (DPF) or gasoline particulate filters (GPF).