Numerical Simulation Research On The Performance Of Assisted Regeneration Of Catalyzed Diesel Particulate Filters

In recent decades,the automobile industry has been developed greatly,and the car ownership has increased year by year.However,it also caused a series of environmental pollution problems,especially the harm from particulate pollution to human health and living environment.Therefore,the new emission regulations have been continuous implemented in various countries,including more and more comprehensive testing methods,and lower and lower pollutant limits.It puts forward higher requirements for engine emission technology.As an effective aftertreatment technology to reduce particulate emissions,catalyzed diesel particulate filter（CDPF）has also caught extensive attention.Firstly,the geometric model of CDPF is constructed by AVL Fire software,and the discrete grid processing and grid independence verification are carried out for the simulation calculation.The simulation results are compared with the experimental results,and the max relative error is less than 3%.The accuracy and feasibility of the model are verified.Then,the change of pressure drop of the asymmetric CDPF is discussed with initial soot loading of 0-6 g/L.It is found that the pressure drop is mainly caused by depth layer at 0-1 g/L,and by soot cake layer at 2-6 g/L.So 0 g/L and 4 g/L are taken as their representative initial soot loading respectively.On this basis,the pressure drop components of CDPF with different asymmetric ratios are analyzed:when asymmetric ratio increases,the soot cake layer,depth layer,wall and inlet channel pressure drop are continuously decreasing,but the pressure drop of outlet channel has been largely improved with the highest percentage of total pressure drop with 46.66%and 41.08%at 0 g/L and 4 g/L respectively.Therefore,it is impossible to judge the overall pressure drop trend of CDPF based on part of the pressure drop change.In addition,the optimal asymmetric ratio of CDPF is researched:when soot loading of 0 g/L,for temperature less than 320℃,the optimal asymmetric ratio is 1.2,and for temperature greater than 320℃,the optimal asymmetric ratio is 1.1.When soot loading of 4 g/L,for the low temperature（260℃and 290℃）,optimal asymmetric ratio is 1.3,for moderate temperature（320℃and 350℃）,optimal asymmetric ratio is 1.2,and for high temperature（above 350℃）,optimal asymmetric ratio is 1.1.For mass flowrate,O₂ volume fraction and NO₂ concentration,when soot loading is 0 g/L,the optimal asymmetric ratio is 1.1,and when soot loading is 4 g/L,the optimal asymmetric ratio is 1.2.Finally,the regeneration characteristics of CDPF are studied.When temperature increases,the NO₂ concentration and NO₂/NOx ratio decrease.When the inlet O₂volume fraction and NO₂ concentration increase,the NO₂ concentration and NO₂/NOx ratio at the outlet both increase.For above studies,the NO₂/NOx ratio is between 29.19%and 50.81%.And as for the effect on outlet NO₂ concentration:temperature>inlet NO₂concentration>O₂volume fraction>mass flowrate At the same time,under the two initial soot loadings,when the temperature,O₂ volume fraction and NO₂ concentration increase,the regeneration efficiency also increases.With temperature increasing,the regeneration efficiency ranges from 58.85%to 97.38%,which is an obvious change.Under various working conditions,octagonal channel CDPF has the highest regeneration efficiency of over 95%,followed by hexagon.However,the pressure drop of the hexagon channel is about 14%lower than that of the asymmetric quadrilateral channel,while the pressure drop of the octagonal channel is 6.71%to 35.34%higher than that of the asymmetric quadrilateral channel.Therefore,the hexagonal channel has obvious advantages in NO₂ assisted passive regeneration.