Study On The DPF Capturing Characteristics Of Diesel Engine Based On Bipolar Electrical Charge Agglomeration Technology

Modern diesel engines have the advantages of low fuel consumption,high thermal efficiency,and high reliability,and are increasingly widely used.However,the emission of particulate matter(PM)from diesel engines is 30 to 60 times that of gasoline engines.Controlling particulate emissions from diesel engines is the most important task at present.Although Diesel Particulate Filter(DPF)capture efficiency of accumulated modal(particle size at 50 nm to 1?m)is above 90%,for nuclear modal particles(particle size is less than 50nm)capture efficiency is only 42%.The use of Bipolar Electrical Charge Agglomeration(BECA)to pre-treat the particles entering the DPF can make the micronano-particles coagulate into larger particle size,improve the capture efficiency of the DPF for the micronano-particles.The study of bipolar charge coagulation technology on the DPF trapping performance is great important.In this paper,based on FLUENT software,the three-dimensional calculation model of DPF tunnel is established.The turbulence model,discrete phase model and porous media model are used to simulate and calculate the flow and deposition characteristics of charged particles in the tunnel under different charge voltage conditions.The results show that the increase of the charge voltage tends to linearly change the velocity distribution along the axis of the inlet and outlet tunnel,and the higher the charge voltage is,the more obvious the linear change is.The pressure in the inlet tunnel increases after the voltage is applied,but the pressure in the outlet tunnel little change.At the same time,the increase of the charge voltage tends to smooth the change of wall seepage velocity along the tunnel,and the distribution of particle deposition in the channel tends to be even.The higher the voltage is,the more uniform the particles deposition distribution is.By establishing a bipolar charge coagulation test platform,the influence of different charge voltages on the particle trapping performance of the DPF was studied.The test results show that bipolar charge coagulation can improve the DPF capture efficiency,and at the same time,reduce the number and the concentration of particles in exhaust.When the charge voltage is 20 kV,the capture efficiency of nuclear modal particles(in the range of 9.3~10.8nm)increases from 42% at 0kV to 69%,while the capture efficiency for particles with particle sizes larger than 90 nm increases from 70% to 92%;By the filter paper weighing method,on corresponding to charge voltage(0k V,10 kV,20kV),the measured average collection efficiency of DPF were 72.2%,81.2%,92.9%.The loaded DPF channels were measured by Scanning Electron Microscope(SEM)to obtain the particle deposition thickness in the tunnel under different charge voltages.The measurement results show that the increase of the charge voltage will make the particles deposition more uniform.And the higher the voltage,the greater the particle deposition thickness.When the charge voltage is 0kV,the particle deposition thickness at the inlet end of the DPF is less than about 48?m,while the deposition of particles at the end of the tunnel reaches a maximum value of about 60?m;when the charged voltage is 10 kV and 20 kV the particle deposition thickness is relatively uniform,the average deposition thickness was 69.74?m and 88.78?m,respectively.