Diffusion Supporting Passive Filter Regeneration- A Modeling Contribution on Coated Filters

Wall flow particulate filters have been used as a standard exhaust aftertreatment device for many years. The interaction of particulate matter (PM) regeneration and catalytically supported reactions strongly depends on the given operating conditions. Temperature, species concentration and mass flow cause a change from advective to diffusive-controlled flow conditions and influence the rate controlling dominance of individual reactions. A transient 1D+1D model is presented considering advective and diffusive transport phenomena. The reaction scheme focuses on passive PM conversion and catalytic oxidation of NO. The model is validated with analytical references. The impact of back-diffusion is explored simulating pure advective and combined advective diffusive species transport. Rate approaches from literature are applied to investigate PM conversion at various operating conditions. Spatial NO/NO2 profiles over the cake/wall height and length are discussed and the transient evolution of axial cake heights is presented. The results reveal that the impact of back-diffusion on PM cake conversion cannot be purely assessed by the Péclet number. The comparison of different spatial coating designs shows that front-end coatings feature superior performance in passive PM cake conversion.