Molecular Dynamics Study On Primary Soot Particle Formation And Coagulation Process

As a product of incomplete combustion of fuel,the generation of soot particles will bring a series of negative effects.Including the reduction of combustion efficiency,enhancement of radiation heat transfer in the furnace,damage to burner structure and so on.It is extremely unfavorable to promote the clean and efficient utilization of fuel and to reach the goal of carbon neutralization.The formation process of soot particles is a complex physical process with cross-scale,multiphase and multicomponent features.During the process,the formation and merging of primary soot particles spans the molecular scale and nano particle scale.At present,the main approach of the researches on the micro-scale generation process of soot particles is sampling measurement and numerical simulation.In such approaches,there are some problems,such as measurement difficulties,difference between simulations and experiments,lack of pertinence,etc.Therefore,this paper explores the formation and collision process of primary soot particles by four steps.Firstly,this paper explores the inhomogeneous multi-scale distribution characteristics of micro-scale thermodynamic parameters in macro-scale homogeneous system and its correlation mechanism with chemical reaction.In this part,we explore the heterogeneity of micro-scale thermodynamic parameters caused by molecular thermal motion and its cross-scale characteristics.It is found that in the statistical scale below 100 nm,the above-mentioned heterogeneity will form a large difference between the statistical temperature and the macro-scale average temperature.The heterogeneity of temperature under different scales will affect the process of chemical reaction so that most chemical reactions occur in the local high-temperature area.These aera only accounting for very small proportion of the actual volume.Based on the above-mentioned research results,a cross-scale theoretical tool for micro-scale simulation to restore the actual working conditions is also formed in this paper.Based on the above mentioned cross-scale characteristics,this paper also explores the reaction mechanism of the soot particle precursors formation and evolution by micro-scale simulation.An all-atom molecular model of coal particle is established.The influence mechanism of many factors,including the influence mechanism of initial fuel configuration,temperature,pressure and atmosphere,on the formation process of soot particle precursors is also disclosed.Based on the above-mentioned research,this paper further explored the nucleation mechanism of acetylene and the binary nucleation mechanism of acetylene and polycyclic aromatic hydrocarbons(PAHs).The effects of important parameters such as temperature,precursor types and nucleation inhibitors on the nucleation process is obtained.It is found that in the binary chemical nucleation mechanism,the individual nucleation mechanism of acetylene and PAHs combine with each other through the key intermediate product of carbon chain,which improves the nucleation rate and the polymers stability.In the binary physical nucleation mechanism,there is almost no synergy between the two precursors.The acetylene molecules are only adsorbed in the void of polycyclic aromatic hydrocarbon polymers as gas molecules.Finally,this paper analyzes the physical properties of primary soot particles,。It is found that the main difference between them and the typical nanoparticles is their non-uniform charge distribution.This characteristic leading to a large electric dipole moment,which will produce additional interaction force between particles and have a great impact on the collision between particles.It is found that this effect significantly weakens the particle collision.The main sources of the inhibition effect are the decrease of the approaching velocity between particles and the direction change of particles in the repulsion side approaching.To sum up,this paper clarifies the non-uniform multi-scale distribution characteristics of micro-scale thermodynamic parameters in the thermodynamic uniform system.The micro-scale simulation of precursor generation,primary soot particle generation and the primary soot particle collision is completed.Therefore,the whole process mechanism of primary soot particle formation and collision is obtained.As a result,the theoretical basis for the accurate control of soot particle formation process is provided.