Investigation On Soot Particle Deposition And Distribution In DPF Based On Lattice Boltzmann Method

As the issues of energy security and atmospheric pollution become more prominent,strengthening the energy saving and emission reduction of internal combustion engines has become an urgent task for the internal combustion engine industry.Due to its advantages of high thermal efficiency,strong power and wider power coverage,diesel engines are widely used in transportation,agricultural machinery and engineering machinery.However,particulate emissions are still one of the key factors restricting their future development and application.Wall-flow DPF has become the standard configuration for diesel engines to meet the emission limits of PM and PN in current or upcoming emission regulations.The soot particle distribution,on the one hand,directly affects pressure drop characteristics and capture efficiency of DPF.On the other hand,as the initial conditions,the soot particle distribution affects the development process and characteristics of the regeneration process.Therefore,studying the soot distribution characteristics is of great significance for optimizing the filtration and regeneration performance of DPF,and improving the economy,power and emissions of diesel engines.In this paper,the soot distribution characteristics in the micro-channel of DPF are studied with considering the microstructure of porous walls.The gas-solid two-phase flow model based on the lattice Boltzmann method is used as the research method.Aiming at the shortcomings of the existing LB-CA model,the model is improved by introducing the incompressible Boltzmann model and the quantitative cell automation probabilistic model.The accuracy of the gas model and solid model in the developed model are verified by the channel model where the flow passes a square block.A DPF single-channel model is established based on the QSGS method.The developed LB-CA model is used to study the flow field characteristics and soot particle deposition and distribution characteristics.It is found that the upstream velocity has a significant effect on the flow field in the DPF channels.At the same upstream velocity,as the particle size increases,the particles gradually deposit to the rear part of the inlet channel.For particles with the same particle size,as the upstream velocity decreases,the uniformity of particle deposition distribution in inlet channel gradually becomes better.Compared with the effect of the particle size,the upstream velocity is more influential on the particle deposition distributions.At the top of the porous wall,there exists a gradient of deposited particle across the porous wall.The deposition distributions of particles with different diameters inside the porous wall are similar to the distributions of wall velocity along the channel length.The first appearance of particle clusters composed of deposited particles is consistent with the area with high probability of particle deposition.Overall,the deposited particles increase the axial pressure and reduce the axial velocity of the inlet channel gradually,but the axial velocity increases in the region where the channel narrows.A new method for generating porous media based on pore size distribution and porosity of porous wall is proposed,which can realize parameterized control to generate porous structures.The domain decomposition-based lattice Boltzmann-cell automation probabilistic model(DDLB-CA model)is proposed.The accuracy of DDLB-CA model is verified by the channel model.On these bases,the deposition and development law of soot particles in porous wall are studied.The formation process and influencing factors of the bridge structure are also investigated.It is found that the soot particles are first deposited on the windward side of the porous medium and at the narrow porous channels,gradually forming a bridge structure.Subsequent soot particles are influenced by the structure of the bridge structure,and the deposition position gradually moves forward,while the new bridge structure gradually forms in the upstream narrow porous channels.The interception,inertia,and diffusion mechanism of the porous media play an important role in the early stage of filtration process,but with the formation of the bridge structure,the bridge structure capture mechanism dominates the capture of soot particles.The formation speed of the bridge structure is affected by the flow velocity and particle size.For particles with the same particle size,the smaller the flow velocity,the earlier the bridge structure is formed.At the same flow velocity,for medium particles with the best capability to follow flow line,the formation of the bridge region is the fastest.The effects of different porous wall structures on the flow field distribution,particle deposition distribution and particle cluster deposition distribution are investigated.It is found that the structure of the porous wall significantly affects the distribution of its initial pressure field and velocity field.The distribution characteristics of the initial upstream pressure,pressure gradient and velocity in the porous walls can be optimized by adjusting the pore size distribution and porosity.The probability characteristics of the particle deposition distribution and the distribution of particle clusters(or bridges)are obviously affected by the structural parameters of the porous wall.The position of the particle clusters(or bridges)affects the pressure and velocity distribution characteristics.Therefore,the pressure and velocity distribution characteristics can be optimized by adjusting the structural parameters of the porous wall.The formation of particle clusters makes soot particles more inclined to deposit in the front of the porous wall,and improves the particle filtration efficiency.A denser soot particle layer is formed on the surface of porous wall with a smaller average pore diameter.