Cross-flow filters are central components in exhaust gas aftertreatment systems of modern combustion engines and are used to filter soot and ash particles from the exhaust gas. This causes a layer of particles to form on the filter surface, which increases the pressure drop of the filter. To maintain proper filter operation, the filter is regenerated regularly. The filters are regenerated by oxidizing the deposited particle layer with oxygen at high temperatures (723-873 K) or with nitrogen dioxide at moderate temperatures (523-723 K). Experiments on discontinuous NO₂-assisted regeneration in a wall-flow model filter channel are presented.

For this purpose, a particle layer is deposited on the filter surface using a propane soot generator and exposed to a NO₂-containing (500 ppm NO₂) atmosphere during filter regeneration. The process parameters, such as gas velocity and regeneration temperature are varied. The temporal course of the regeneration, as well as the visible layer break-up and rearrangement of particle structures, are recorded along the length of the channel using a high-speed camera (100-1000 fps).