Numerical Study On Pressure Drop And Regeneration Characteristics Of The Novel Asymmetric Channel Particulate Filter

Under the current and future emission regulations,particulate filter becomes the necessary device in the aftertreatment system,while the installation of the particulate filter will increase the fuel consumption of the engine.Asymmetric channel particulate filter can effectively reduce the exhaust back pressure and regeneration frequency,which can improve the fuel economy of the engine and decrease the regeneration loss.It is considered as the mainstream structure of the new generation of the filter body by major manufacturers and research institutions at home and abroad,and it is the inevitable choice under the new situation of the "Energy Saving and Reduction of Pollution".However,the current development of the asymmetric channel particulate filters are faced with the problems of the high initial total pressure drop and low utilization rate of filtration wall,so the effect of the reducing back pressure is greatly reduced.In order to effectively control the initial total pressure drop of the filter,reduce the pressure drop of the soot layer,and achieve the optimal pressure drop performance in the whole soot loading range,a novel asymmetric channel structure named HRT(Hexagon-Rectangle-Triangle)asymmetric channel structure was proposed in this paper.The structure of the HRT asymmetric channel filter is composed of regular hexagon,regular triangle and rectangular channels,among which the regular hexagon and regular triangle channels are the inlet channels and the rectangular channels are the outlet channels.The long side of the rectangle coincides with the regular triangle side,and the short side of the rectangle coincides with the regular hexagon side.With this structure,the utilization rate of the filtration wall can be fully improved,and the area of the filtration wall can be increased to a certain extent,so as to improve the pressure drop performance of the asymmetric channel particulate filter.Firstly,a one-dimensional flow and regeneration model of the HRT particulate filter was established.Since there is no calculation model of the particulate filter with three types of the channels at home and abroad,the model was based on the calculation model of the particulate filters with two types of the channels.The control equations of one type of the inlet channel were added.The one-dimensional flow and regeneration model of the HRT structure was theoretically deduced and obtained,and the source program of the calculation model was compiled with VC++2013.Then,the side length ratio of the HRT structure was determined.The results show that when the side length ratio of HRT is equal to 3,the distribution of the gas flow and the soot layer is uniform,and the total pressure drop performance is the best.Through the analysis of the influence law of the pressure drop under the clean wall condition,it is found that the initial total pressure drop of the HRT structure is only about 2-6%higher than that of the SQ structure under different structures and exhaust parameters,while the initial total pressure drop of the SQ_ACT structure is 38-49%higher than that of the SQ structure.The flow pattern in the channel shows that the working mechanism of the HRT structure which can effectively control the initial total pressure drop is:HRT asymmetric channel can increase the area of the filtration wall,and the utilization rate of the filtration wall can be fully improved,which can effectively reduce the penetration velocity in the filtration wall.At the same time,it can avoid too much reduction in the volume of the inlet and outlet channel,so as to restrain excessive increase of the flow velocity in the inlet and outlet channel.The influence law of the pressure drop under soot loading stage was analyzed.It is found that the HRT structure has the best pressure drop performance in the range of 0-8g/L soot load under different structure and exhaust parameters.The total pressure drop of the HRT structure is about 20-27%lower than that of the SQ structure under 8g/Lsoot load,which is about 4-12%lower than that of the SQ_ACT structure.It is worth noting that the SQ_ACT structure is the theoretical limit value,so the pressure drop performance of the HRT structure will be better than the SQ_ACT structure in practical application.The flow characteristics in the filters shows that the working mechanism of the HRT structure with the lowest total pressure drop of HRT in the process of soot loading is:HRT structure can increase the filtration wall area,and the utilization rate of the filtration wall can be fully improved,which can reduce the penetration velocity and the soot layer thickness.Based on the established model,the effects of different structures and exhaust parameters on the O2-NO2 regeneration performance of the HRT,SQ,SQ_ACT filters were predicted.The results show that the O2-NO2 soot oxidation rate of the HRT filter is slightly higher than that of the SQ structure under different parameters,which is basically the same as the SQ_ACT structure.Among them,the influence of the exhaust parameters on the regeneration performance is higher than that of the structure parameters,especially the inlet temperature,the mass ratio of the NOx to soot and the oxygen content.In general,the influence of the filter structure type on the regeneration performance is very small,so the HRT structure can meet the regeneration performance requirements of the post-treatment system.