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Microscopic visualization experiments and simple numerical calculations using Darcy's law have been conducted for soot (PM) deposition in hexagonal channel diesel particulate filters (HEX DPFs) made of aluminum titanium oxide. In the HEX DPFs, a flow rate of the conventional wall-through flow crossing over a wall between inlet and outlet channels (an Inlet/Outlet wall) changes drastically during surface pore filtration, because a part of working gas with soot is distributed to an Inlet/Inlet wall as a bypass flow which is introduced into a wall between inlet and inlet channels (an Inlet/Inlet wall), then turning toward the direction parallel to its wall surface, and finally exiting into the outlet channel. In this case, the thickness of soot deposited on the surface of the Inlet/Inlet wall becomes thinner for the dependence on the distance from the outlet channel. On the other hand, during soot cake layer filtration, since the difference between both superficial flow velocities for Inlet/Inlet and Inlet/Outlet walls become smaller, growth rates of soot cake layers are almost uniform on both wall surfaces. Consequently, the thickness of soot deposited on the Inlet/Inlet wall has a distribution from the minimum height at the center of the channel width to the maximum around the edge.

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