Fractal Diffusion Limited Aggregation Of The Soot Particles Of Diesel Tail Gas

Soot is the main component of particulate matter emitted from diesel engine exhaust,and it is also one of the main pollutants of air pollution caused by transportation.Soot is formed by soot particles nucleation,collision condensation,surface growth,surface oxidation and deposition.And because the size of soot is very small,it can be suspended in the air for a long time and not easy to settle.When the concentration of soot pollutants in the atmosphere reaches a certain level,it will cause harm to the human body.Diesel particles filter(DPF)is a ceramic filter installed in diesel engine exhaust system,which can capture particulate matter before it enters the atmosphere.The physical characteristics of soot,such as its external shape,volume,density,heat and mass transfer,and electromagnetic will affect the efficiency of the DPF.Therefore,it is necessary to study the motion process of soot particles and the final morphology of the aggregates.Fractal theory is a very popular and active new theory and discipline in non-linear science,and has been widely used in the preparation of thin film materials,oil exploitation,heat transfer and heat dissipation of objects and other fields.Its research object is mainly irregular and non-differentiable geometry generated in the non-linear system.It is found that the complex structure of soot under the electron microscope is actually a fractal structure.Combining with the complex process of soot formation in diesel engine,this thesis introduces the Diffusion-limited aggregation(DLA)model to study the dynamic process of soot particles diffusion and condensation in two-dimensional space.And for the first time,the non-linear relationship between the step size of particles and the angle of particles motion is expressed by using the fuzzy membership function.By changing the parameters of the fuzzy membership function,the changes of the movement modes of soot particles with single particles size and soot particles with different particles sizes are studied,and the morphology control of soot aggregates is realized.The main contents are as follows:1.Modeling of soot particles Diffusion-limited aggregationIn this thesis,distance matrix,parallel algorithm and new geometric relationship to solve particles collision problem are introduced into classical DLA model.A more efficient off-lattice DLA model of soot particles is established by Monte Carlo method.The fractal morphology of aggregates,fractal dimension and running time of soot condensates under different parameters are analyzed through simulation experiments.2.Difffusion-limited aggregation of soot particles based on fuzzy membership functionIn this thesis,the idea of fuzzy control is first introduced into the soot particles DLA model.The membership function is used to express the non-linear relationship between the soot particles motion step and the particles motion angle.By changing the parameters of membership function,the morphological structure of the agglomerate can be changed from loose to compact,and the soot is more conducive to settling,thus realizing the control of the morphology of soot particles agglomerate.Relevant conclusions can be used for reference to improve soot purification technology.3.Diffusion-limited aggregation of soot particles with different particles sizes in accordance with Rosin-Rammler distributionThe particles sizes of soot particles emitted from diesel engine varies in a certain range.In this thesis,Rosin-Rammler distribution,which is widely used in practice,is introduced to describe the particles sizes distribution of soot particles.By changing the non-linear parameters of Rosin-Rammler distribution function,the distribution probability and range of different particles sizes are adjusted.Based on the single particles sizes model of soot particles diffusion-limited condensation,the fuzzy membership function DLA model of soot particles with different particles sizes was proposed.The movement mode of soot particles with different particles sizes was controlled by changing the membership function parameters of soot particles with different particles sizes,and the morphology of soot particles with different particles sizes was controlled.The above conclusions have important theoretical and practical significance for studying the motion and condensation mechanism of real soot particles and promoting the development of soot particles capture technology in diesel engine exhaust.