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Magnetic resonance imaging (MRI) has been used to investigate gas flow in diesel and gasoline particulate filters, exploring gas flow both within the channels and also at the entrance and exit of the filters (expansion and contraction effects). The latter measurement can be used to measure turbulent diffusivity in the filter bulk flow characteristics, and therefore estimate the importance of entrance and exit effects in contributing to overall filter back pressure as the filter properties and/or exhaust flow changes (i.e. with Reynolds number). The former measurement gives information that can be used to evaluate filter performance, in particular with respect to filtration efficiency, and examples will be shown from our measurements on diesel filter systems.

In recent years magnetic resonance imaging (MRI) has been shown to be an attractive method for fluid flow visualization. In this work, we show how MRI velocimetry techniques can be used to non-invasively investigate and visualize the hydrodynamics of exhaust gas in a diesel particulate filter (DPF), both when clean and after loading with diesel engine exhaust particulate matter. The measurements have been used to directly measure the gas flow in the inlet and outlet channels of the DPF, both axial profiles along the length and profiles across the channel diameter. Further, from this information we show that it is possible to indirectly ascertain the superficial wall-flow gas velocity and the soot loading profiles along the filter channel length.