An Investigation Of Particle Motion And Soot Deposition Distribution Inside Diesel Particulate Filter

As an effective exhaust purification approach of vehicles,after-treatment technology has been widely used and obtained a well developing in order to meet the strengthened emission regulations.Compared with gasoline engines,diesel engines have many advantages including higher power and thermal efficiency,lower fuel consumption and superior durability.However,the particulate matter(PM)emission amounts of diesel engines are significantly higher than equivalent gasoline engines due to the non-premixed combustion process,which makes PM become a principal emission pollutant of diesel engines.Diesel particulate filter(DPF),as one of the most effective after-treatment devices for particulate matter,has been widely used in diesel-fueled vehicles due to its extremely high particle filtration efficiency.In order to investigate the particle motion and deposition distributions inside DPF,a DPF microcosmic channel model based gas-solid two-phase flow model has been built in this paper,as well as the transient deep-bed filtration model.Using numerical simulation method,the particle motion trajectory and flow field inside DPF channels were studied,as well as DPF filtration efficiency and particle deposition distributions in DPF.The study on particle motion trajectory inside DPF inlet channels shows that within the range of sizes of particles emitted from diesel engines,the drag force and Brownian force are two main acting forces that significantly influence the motion trajectories of particles.For 10 nm particles,the impact of Brownian force on particle motion trajectories is obvious while for 100 nm and 1000 nm particles,the impact brought by the Brownian force is negligible.The increase of space velocity can suppress the effect of Brownian motion on particle motion trajectories and improve the straightness of particle motion.As for the flow field inside DPF channels,study shows that the space velocity and DPF wall permeability have obvious effects on DPF flow field inside DPF channels.When the space velocity is low,a good linear relationship can be observed for axial velocities along DPF inlet and outlet channel,and the through-wall velocity is uniform.However,with the increase of the space velocity,the linear relationship for axial velocities along the inlet and outlet channel weakens,and the through-wall velocity at the rear-part of the inlet channel rises.Besides,the lower the wall permeability is,the better the linear relationship for the axial velocities along the inlet and outlet channel is,and the more uniform the through-wall velocity is.The effect of space velocity on velocity field becomes slight when the wall permeability is low.The study on DPF filtration efficiency in this paper shows that compared with the filtration efficiency of 10 nm and 1000 nm particles,the DPF filtration efficiency of 100 nm particles is much lower.With the increase of space velocity,the DPF filtration efficiency of particles drops.Besides,it can be observed that there is a negative correlation between DPF filtration efficiency and through-wall velocity along the inlet channel.The area in which an obvious increase of through-wall velocity happens is also the area where an obvious drop of filtration efficiency occurs,especially for particles whose filtration efficiency are greatly influenced by Brownian diffusion collection mechanism.A uniform through-wall velocity distribution along the DPF channel brings a uniform distribution of DPF filtration efficiency along the DPF channel.As for the particle deposition distributions inside DPF,study shows that the particle deposition distribution on the wall surface along the inlet channel is dependent on the space velocity,DPF wall permeability and particle sizes.For 10 nm particles,the particle deposition distribution on the wall surface along the inlet channel is relatively uniform while for 100 nm particles,more particles deposits at the end of the inlet channel.With the increase of space velocity and wall permeability,the deposition distribution of particles on the wall surface along the inlet channel becomes less and less uniform,and the area where the particle deposition concentration increases is also the area where the through-wall velocity rises.As for the particle deposition distributions inside porous wall,study shows that the deep-bed filtration processes are different for particles with different sizes.The deep-bed filtration processes of 10 nm and 1000 nm particles are similar,which all indicates a shallow particle penetration depth inside porous wall.For 10 nm and 1000 nm particles,almost all the particles are collected in the top 20% thickness of the porous wall,especially the top 10% thickness of the porous wall,which is also the area where the porosity and permeability decrease most with the deposition of particles.However,for 100 nm particles,the penetration depth inside the porous wall is much deeper and the changes of porosity and permeability of the porous wall are slow.Moreover,with the deposition of particles inside porous wall,the increase rate of DPF pressure drop is much higher for 10 nm and 1000 nm particles than 100 nm particles,and the DPF filtration efficiency of particles rises gradually.The study on the dense thin layer covered inhomogeneous wall structure DPF in this paper shows that the presence of the layer can improve the uniformity of the through-wall velocity along DPF channel,raise the filtration efficiency of DPF and its uniformity along the DPF channel,and decrease the penetration depth of particles inside porous wall significantly.