Experimental Study On Deposition Characteristics Of Particulate Matter In Metal Foam Particulate Filter

The pollution of mobile sources such as vehicles has become an important source of air pollution.Diesel particulate trap(DPF)is the most effective aftertreatment for particulate emission reduction.The traditional ceramic wall flow DPF is easily damaged and broken under high temperature.Metal foam has the advantages of high porosity,good permeability,large specific surface area,high temperature resistance,easy processing and good impact resistance,and metal foam can effectively reduce exhaust back pressure and improve fuel economy.However,the characteristics of particulate matter deposition and filtration efficiency in metal foams have not been well studied.The study of this paper is for the influence of the basic structural parameters of metal foam filter on the filtration efficiency and the deposition characteristics of particulate matter.First,a rapid particulate loading system was established,which effectively reduced the loading time of particulate matter.The dynamic deposition process and deposition characteristics of particulate matter in metal foam filter were studied,and an image characterization method of particulate matter deposition was proposed.The rapid particulate loading system is mainly composed of a particulate matter generating device,a particulate matter filtrating device,and a data acquisition system.The dynamic deposition characteristics of particulate matter in the filter are characterized by the stereo microscope,and the filtration efficiency is calculated by the exhaust smoke value before and after the filter(AVL-415 smoke meter).Stereo microscope images show that most of the particulate matter will be deposited in the first and second layers of filter.In terms of particle deposition and distribution,the area covered by particulate matter on the first layer of the filter element is the largest,and the proportion of the area of the pores at the end portion is basically reduced to 0%(the area covered by the particle matter is nearly 100%);The particle deposition distribution is the most uniform in the axial direction,and the particle deposition uniformity in other layers decreases gradually in the radial direction.The average pore diameter of the filter element directly determines the filtration efficiency and deposition characteristics of the particulate matter.Three materials with different pore sizes were selected for the study: 30 ppi,90 ppi,and 130 ppi(ppi,pores per inch).The results show that the soot mass concentration filtration efficiency of the metal foam with a smaller pore size is higher,but the filtration efficiency is not much different after the filter cake layer is formed.The filtration efficiency of the combined filter elements(30 ppi,90 ppi,and 130 ppi)was initially low,but gradually increased to a level slightly below 90 ppi over time.The smaller the pore diameter,the higher the pressure drop.Although the combined filter can effectively reduce the pressure drop,it will sacrifice part of the filtration efficiency.In addition,the thickness of the filter will directly affect its filtration performance,especially the particulate matter deposited on the first layer.The results show that the thick filter will maintain a high filtration efficiency throughout the test,and will first stabilize.When the thickness is the same,the pressure drop of the filter with a small pore diameter is high.Although the filtration efficiency of the 90 ppi filter of the same thickness is lower than that of the 130 ppi filter at the initial stage,but the difference in the later stage is almost the same,but the pressure drop of the 90 ppi filter element is more advantageous.It can reduce the pressure drop without sacrificing the filtration efficiency.