Particle emissions from combustion engines mainly consist of soot and additives from the lubrication oil. These emissions can be almost fully eliminated by using wall-flow filters in the exhaust aftertreatment system. During regeneration, the organic soot burns away, leaving only ash in the filter channels. The overall structure of the ash agglomerates and their distribution pattern within the channel of the wall-flow filter is influenced by a multitude of different factors. These include, for example, the temperature and velocity during filter regeneration. It is suspected that another influence is water that condenses on the filter surface during a cold start event. As ash consists of partially soluble components, such as CaSO₄, investigating the influence of condensed water on the restructuring and transportation of ash agglomerates in the filter channel will provide further insight into the deposition pattern.

A preexisting wind tunnel is modified to include a vaporizer to vary the relative humidity of the inlet air. An ash substitute can be dispersed into the wind tunnel and deposited in a wall-flow filter sample. Afterwards the filter sample can be subjected to humidifying and drying cycles. Parameters such as pressure drop, temperature, relative humidity and particle concentration can be measured. Changes in the density of the deposited particle layer alongside the filter channel wall can be determined by using an optical microscope. Additionally, structural changes of the agglomerated particles can be microscopically observed under variation of relative humidity using an Environmental Scanning Electron Microscope.

In this work, the first experimental setup will be presented. The different methodological approaches to examine the structural changes of particle agglomerates within the filter channel will be discussed.