Influence Of Ash Distribution And Asymmetric Structure On Diesel Particulate Filter Performance

The emission of PM(Particulate Matter),PN(Particulate Number)and NOX from diesel engines is one of the important reasons resulting in the fog and haze weather at present.DPF(Diesel Particulate Filter)can reduce particulate matter and particulate number emission effectively.But ash deteriorates DPF performance.The article researched the influence of ash and ash distribution on DPF performance,which lays the foundation of improving DPF performance.And then asymmetric DPF pressure drop and its influencing factors were studied.Asymmetric DPF can increase ash capacity and extend its service life according ash deposition characteristics.Firstly,the effect of ash distribution on inlet velocity,wall velocity and soot deposition was studied based on numerical computation.And then the effect of ash distribution on DPF pressure drop was researched by establishing evaluating function f.The results show that,when ash distribution factor increases,inlet velocity increases and wall velocity decreases.The holistic distribution of ash and soot approaches uniformity when the ash distribution on the wall is uneven.The holistic distribution is more uniform as soot deposition.The relative values of ash,soot,wall permeability decide the tendency of ash distribution affecting DPF pressure drop.Channel diameter,wall thickness,ash mass and soot mass change the extent of ash distribution affecting DPF pressure drop.Secondly,the influencing of ash distribution on DPF maximum regeneration temperature was studied by establishing evaluating function g,combining variation of DPF parameters and emission gas parameters.The results show that function can evaluate the effect of ash distribution on maximum regeneration temperature effectively.The negative value implies that the maximum regeneration temperature decreases when the ash is at the rear of the inlet channel.The extent of influence of ash distribution on maximum regeneration temperature enhances with ash mass and wall thickness increasing.When flux and O2 fraction increase,the extent enhances and then weakens.The extent weakens with ratio of inlet and outlet diameter and cell density increasing.The ratio of length and diameter and NO2 fraction have little effect on the extent.Lastly,the pressure drop characteristics of asymmetric DPF were further researched.The results show that,when the ratio of inlet and outlet diameters increases,inlet velocity decreases,and the decreasing extent weakens along axial DPF,the frontal wall velocity decreases and real wall velocity increases,outlet velocity decreases,the decreasing extent enhances along axial DPF.Increasing the ratio of inlet and outlet diameters can reduce DPF pressure drop effectively as the increasing of soot mass,ash mass,and flux.The change of DPF pressure drop is little when the ratio of inlet and outlet diameters is greater than 1.4.The optimal cell density decreases as the ratio of inlet and outlet diameters increasing.