Acetylene Premixed Jet Flame Soot Generation Mechanism Study

Polycyclic aromatic hydrocarbons（PAHs）and soot are among the major pollutants in the combustion process,and they have a non-negligible impact on the environment and human health.Therefore,an in-depth study of their generation processes is of great importance for the development of effective emission reduction measures.The objectives of this work were to determine the relationship between temperature and soot formation in a C₂H₂ premixed jet flame and to investigate the effects of flow field and chemical reactions on soot growth.（1）The effects of flow rate and equivalence ratio on flame temperature and structure were investigated.It was found that the growth of soot agglomerates was affected by both surface growth and aggregation at the lower position of the flame.The average initial particle diameter of soot increased by 9.8 nm as the flame height（Height Above burner,HAB）increased from 20 mm to 65 mm.soot agglomerates increased by 67 nm.at the higher position of the flame,aggregation was the main factor of soot agglomerate growth.Above 125 mm,soot agglomerates can reach a maximum size of 528 nm.the difference in reaction paths between poor and rich combustion causes expansion and contraction of the gas.The flow rate of a poor-combustion flame is higher than that of a rich-combustion flame.This is because the reaction at the flame face of the lean flame causes the gas to expand.The vortex between the rich flame surface and the surrounding air is created and broken to a greater extent.This will increase the probability of collision between soot particles and thus promote the growth of carbon soot.（2）Reax FF molecular dynamics simulations reveal the basic mechanism of nucleation and growth of nascent soot particles of PAHs.The effect of temperature on the growth of soot agglomerates is complex.The surface growth of soot particles is promoted at low temperatures,while the aggregation of soot is promoted at high temperatures.Among them,the aggregation ability of olefin is most significantly affected by temperature.Due to stronger physical interactions,larger PAH monomers have stronger aggregation ability and are more likely to form initial soot particles than smaller PAHs.After the soot particles reach a certain size,PAHs cannot continue to aggregate.（3）The effects of different equivalence ratios on flame combustion characteristics were investigated by numerical simulations of Computational Fluid Dynamics（CFD）.The OH radicals are related to the oxidation of carbon soot,and the higher their concentration,the faster the oxidation rate of carbon soot.The highest growth rate of soot surface was achieved at an equivalence ratio of 1.5,reaching 0.201kg·m^-3·s^-1.The growth rate of soot surface increased and then decreased with the increase of flame height,which was consistent with the experimental results.These results show that the combustion equivalent ratio has an important influence on the combustion characteristics of acetylene jet premixed flame,and the optimization of the combustion equivalent ratio can improve the combustion efficiency of the flame and the control of soot generation.