Measurement and Intra-Layer Modeling of Soot Density and Permeability in Wall-flow Filters

The objective of this study is to study the soot layer density and permeability in wall-flow diesel particulate filters. Knowledge of the soot morphology as function of the operating conditions is important for the design and on-board control of Diesel Particulate Filters (DPFs).

The experimental set-up relies on a specially designed soot loading procedure on single-channel cordierite filters. The experimental conditions simulate real-world as close as possible regarding the filtration velocity, temperature and soot quality, since the sampling is done in real exhaust. By cutting, weighing and imaging the single channel filters it is possible to measure with accuracy the soot layer thickness as deposited under different operating conditions. Combined with pressure drop measurements and modeling, it is further possible to evaluate the soot layer permeability.

The density values obtained ranged between 25 and 100 kg/m³ and were found to depend on flow velocity, pressure drop and soot loading. In order to de-couple the above effects on soot morphology, an intra-layer model able to account for locally variable soot properties and soot compressibility was developed. After calibration of the main parameters based on the single channel results, the model was integrated in a previously developed full-scale DPF model and validated under transient soot compression testing.