Operating conditions for the deposition of monolayer and bilayer particulate coatings from aqueous 20-nm-diameter silica dispersions are identified in the context of a drag-out operation assisted by forced convection. The dry film thickness, uniformity, and morphology are assessed within an operating window parametrized by the capillary number and silica dispersion weight fraction. Three film deposition regimes with respect to the capillary number are observed: convective film deposition at low process rates, film entrainment at moderate process rates, and a thin-film transition regime at intermediate process rates. Locally ordered particulate films of variable layering thickness, including (i) a discontinuous submonolayer or (ii) a mixed submonolayer and monolayer, (iii) a mixed monolayer and bilayer, and (iv) multilayers, are dominant under convective deposition conditions. A map of morphologies is presented within the capillary number-weight fraction operating window, where monolayer and mixed monolayer-bilayer films are demonstrated in the thin-film transition regime at an intermediate dispersion weight fraction. A complementary map of the morphologies formed by the drag-out of 110 nm silica dispersions reveals a broader applicability to this type of operability diagram. These operating maps are constructed using model silica dispersions and are therefore relevant to particulate coatings of other inorganic materials.

Aluminum titanate (AT)-based Diesel Particulate Filter (DPF) with hexagonal cell geometry has previously been presented as a promising media showing extremely lower pressure drop, coming from its specific hexagonal channels of DPF. In addition these AT characteristics, the investigation on an engine bench verified that AT filter with the hexagonal cell structure exhibited different combustion behavior from the one with the standard cell structure. To understand this behavior, direct observation inside the filter on its microscopic scale was carried out. It was found that the hexagonal channels induced multiple steps on particulate matter accumulation.

The phenomena of soot trapping and oxidation in a hexagonal cell geometry DPF made of aluminum titanium oxide were investigated through microscopic visualization experiment and a simple analysis based on Darcy's law through the wall and the deposited soot layer. There were two types of flow: one was a flow through a wall between inlet and outlet channels (inlet/outlet wall flow), and the other was a flow which was introduced into a wall between inlet and inlet channels, and was turned toward the direction parallel to the wall, and finally exited into the outlet channel (bypass flow). The flow rate of the bypass flow was increased with a thickness of soot layer deposited on the inlet/outlet wall. As a result, the soot was trapped even on the inlet/inlet wall surface. In the regeneration process, depending on the flow rate of the bypass flow, the maximum temperature for the hexagonal cell DPF became lower compared with that for the conventional DPF.

No abstract