Numerical Study on Forced Regeneration of Wall-Flow Diesel Particulate Filters

A computational model which describes the combustion and heat transfer that takes place during forced regeneration of honeycomb structured wall flow type diesel particulate filter was developed. In this model, heat released by the soot- oxygen reaction, convection heat transfer in the gas phase, conductive heat transfer in solid walls, and heat transfer between the gas and wall of each honeycomb cell at various radial positions in a filter are calculated. Each honeycomb cell was modeled as one solid phase and two gas phases and these three phases were divided in the axial direction into small elements. Conductive heat transfer between the small solid elements and convection heat transfer between the small gas elements were calculated for each small time increment. Conductive radial heat transfer between honeycomb cells was also calculated. By comparison between calculated results with this model and experimental results under available limited conditions, the accuracy of the calculation model was verified. Filter temperature distributions were calculated for a wide range of material thermal properties, various cell structures and various filter shapes. Using the calculated temperature distributions, thermal stress analyses were performed for various filter designs and materials to discuss the relative merits of materials and structures. As conclusions, effects of material properties and structural design on filter durability in respect to thermal stress during forced regeneration are presented and favorable material selection and an example of stress relief design are proposed.