Research On The Influence Characteristics Of Ash Deposition For Wall-Flow Diesel Particulate Filter

Haze has attracted much attention in recent years for its pollution to the atmospheric environment.According to the researches,the vehicle exhaust emission is the main source of the haze.Therefore,the vehicle emission control,especially the PM(Particulate Matter)emission control of diesel vehicle,has become the most effective method to reduce the pollution of haze and improve the atmospheric environment quality.For diesel vehicle,Diesel Particulate Filter(DPF)is the most efficient equipment to decrease the PM emission,and filtration efficiency,flow resistance,regeneration efficiency and service life are the main performance evaluation indexes of it.The service life determines the practicability and cost to use of DPF.Studies have shown that there are a lot of factors make an impact on the service life of DPF,and the ash is the main one.The Ash deposition in the filter of DPF will lead to the increase of flow resistance directly and affects the performance of both diesel engine and DPF.If the filter is under heavy ash load,DPF will fail to work.So ash deposition in filter will decrease the service life of DPF.The research of the effect of ash deposition on diesel particulate filter and the way to increase the ash load capacity of filter are great significance for increase the service life of DPF.This paper has mainly researched on ash deposition characteristics and its impact on the flow resistance and filtration efficiency of DPF.Considering the effects of ash on both filtration efficiency and flow resistance,this paper has researched how to optimize the method of application of DPF to improve the ash load capacity of it.Meanwhile,based on the characteristic of the asymmetric cells filter,this paper has put forward five different design schemes for asymmetric cells filter,and analyzed the flow resistance and ash load capacity of these five design schemes by the theoretical models.The main research work of this paper is summaried as follow:1.Based on the pattern of ash cake deposition and a single channel model,the mathematical model of ash deposition in cake has been proposed,and the influence of ash deep bed deposition and ash deposition distribution are taken into account.Calculated results show good agreement with the experimental data,indicating that the model can reasonably describe the flow resistance characteristic of filter for ash deposition in cake.In this model,the flow resistance characteristic of filter for ash deposition in cake is analyzed,which includes each individual flow resistance contribution to the total flow resistance,variation of flow resistance along with ash distribution and quality of ash and soot.Finally,the effect of calculation parameters on total flow resistance is analyzed using the grey correlation analysis.2.Based on the characteristics of ash cake deposition,the single channel model and the packed bed model,a mathematical model of filtration process of wall-flow filter for ash deposition in cake has been proposed.The effects of exhaust volume flow rate,exhaust temperature,the amount of ash load and the distribution of ash deposition in cake on the filtration characteristic of filter are analyzed.3.This paper has developed an optimization scheme to improve the ash load capacity of diesel particulate filter without changing the structural parameters of filter.Considering the effects of ash on both filtration efficiency and flow resistance,ash plug which deposits at the end of the inlet channel is better to alleviate the impact of the ash load on DPF and balance the relationship between flow resistance and filtration efficiency.Based on the characteristic of ash deposition,ashes tend to deposit at the end of the inlet channel for DPF with active regeneration.So the active regeneration can help to increase the ash load capacity of DPF.4.This paper has put forward five different design schemes for asymmetric cells filter.And a mathematical model of flow resistance of asymmetric cells filter has been proposed.The effect of five different design schemes on flow resistance and ash load capacity of asymmetric cells filter with the same I/E and the effect of different I/E on ash load capacity of asymmetric cells filter are analyzed.Finally,the effect of ash distribution on ash load capacity of asymmetric cells filter is analyzed.This paper mainly studies on the effect of ash deposition on the flow resistance and filtration efficiency of DPF,and the effect of the method of application of DPF and the design scheme of asymmetric cells on ash load capacity of filter.The research work in this paper can not only provide a theoretical basis for the accurate prediction of DPF flow resistance and filtration efficiency,but also can be a reference for select the appropriate DPF using method and provide a reference for the optimization design of structural parameters.It has practical significance to promote the application of DPF.