Numerical Study On The Flow And Particle Traps In An Asymmetric Diesel Particulate Filter

Diesel engines have wide applications in the world,including the transportation,motor vehicles and industrial production.However,diesel particulate matter(PM)emission caused serious air pollution,threatening human health and the ecosystem.The PM emission is one of the key factors restricting its future development and application.Researchers all over the world have put forward various technologies to reduce the emission of the PM,and more stringent measures are introduced to limit the emission of the PM.Diesel particulate filter(DPF)is one of the most effective device to reduce particulate matter.The study of gas flow,particle deposition and pressure drop characteristics in DPF are of great scientific significance for DPF regeneration and structural optimization design.Firstly,the flow and static pressure in DPF are numerically studied using Eulerian–Lagrangian approach with three-dimensional model.The model is validated against the reference values,good agreement between the predictions and reference values is observed for the velocity and static pressure distribution.The results show that:(1)The velocity of the inlet channel first increases and then decreases,from 12.5 m/s to 17 m/s,and then decreases to 0 m/s,while the velocity of the outlet channel increases continuously.(2)The static pressure of the inlet channel first decreases and then increases,from 1000 Pa to 900 Pa,and then increases to 980 Pa.(3)The through-wall velocity first decreases and then increases along the axial direction,which depends on the static pressure difference between the inlet and outlet channles.Secondly,the Eulerian-Lagrangian method coupled with user defined scalar is used to solve the particulate concentration in the porous media.Particulate tracking method is used to research the particulate streamlines and deposition in DPF channel,in this model it is assumed that the particulates disappear after colliding with the porous wall.The main working parameters of DPF such as the inlet velocity,wall permeability and particulate size are studied to clarify the influence of the flow field on particulate deposition distribution in asymmetric pores.The results show that(1)As the entrance velocity increases,the velocity changes of channels are accelerated.The gradual increase in the static pressure difference between the inlet and outlet channels leads to a significant increase in the through-wall velocity.The increase in flow velocity has an increased impact on particle deposition,the number of deposited particles decreases at the front of channel,and increases at the end.(2)With the increase of wall permeability,the velocity changes of channels are accelerated.The static pressure of the inlet channel decreases,and the decrease of the static pressure of the outlet channel accelerates.The deposition efficiency of particles at the front of the channel decreases,and increases at the end.(3)As the particle size increases,the deposition at the front of the channel decreases,and increases at the end.Finally,the flow and pressure loss characteristics of DPF for cold and hot state under full load are studied.In this paper,it is assumed that DPF is in full load condition.The soot concentration in porous media reaches the maximum filling density,and the thickness of filter cake layer is 0.12 mm.In this study,the user defined functions are coupled to the mathematical model,and the source terms in the continuity equation and the component equation are solved by user defined function.The results show that the flow in DPF is not obviously affected by the thermal state,which is mainly due to the small heat release of soot reaction.The maximum temperature is only 15 K higher than the inlet temperature.However,the pressure loss in the DPF channel changes greatly from 30,000 Pa to 5,289 Pa,which also shows that the back pressure of the engine is constantly decreasing under the hot working condition of DPF.