Understanding the operation and preparation of diesel particulate filters using a multi-faceted nuclear magnetic resonance approach

Abstract

In the present study, a range of magnetic resonance techniques have been applied to investigate two aspects associated with the preparation and operation of diesel particulate filters (DPFs). First, magnetic resonance techniques are used to investigate the evolution of the water distribution within a DPF during a drying process, typical of that associated with the preparation of a catalyzed DPF. For comparison, the drying characteristics of a flow-through monolith were also studied. In the flow-through monolith, which has impermeable walls, the drying front was observed to propagate from the very start of drying. Conversely drying in the DPF was characterized by uniform, axial drying up to a critical point, after which a drying front moved progressively through the DPF until it was fully dried. An explanation of this two-stage process, by taking into consideration the permeability of the channel walls, is suggested. Second, magnetic resonance imaging velocimetry was used to investigate the flow through a DPF. It is demonstrated that magnetic resonance imaging velocimetry is able to quantitatively and non-invasively characterize the flow fields in two DPF substrates, with asymmetric and symmetric channel geometries, respectively.