Modelling of diesel filters for particulates removal

Diesel particulate filter (DPF) is regarded as the most useful technology to reduce particulate matter from exhaust gas of a diesel engine, with filtration efficiencies in excess of 90%. Exhaust gas entering the channel is forced to flow through the ceramic porous walls into the adjoining cells and thus leaving the particulates behind. The collected particulate matter inside the trap has to be periodically oxidized to regenerate the DPF. We have developed a transient spatially 2D model of the filter, soot deposition and its regeneration. The momentum, mass and enthalpy balances of the gas and the solid phase were employed in the model including the description of heat conduction, diffusion in the solid phase and complex soot combustion kinetics. Detailed kinetics of soot combustion is considered: combustion by O2—both the thermal initiated one and the catalyzed one and the oxidation by NO2. The results of simulations include the prediction of development of concentrations, temperature, pressure, flow pattern and soot layer thickness along the filter. Effect of NO2-assisted soot oxidation coupled with catalytic NO/NO2transformation is examined. The filtration model includes cake and deep-bed filtration and it is used to predict porosity, permeability, filtration efficiency of the soot layer and the wall. Optimized numerical methods and software for the solution of the above mentioned models are described and results for various operation conditions are presented and discussed.