Effect Of Oxygen Concentration On Soot Formation And Temperature In Methane/Ethylene Laminar Diffusion Flame

Soot was inevitably produced in conventional hydrocarbon fuel/air combustion process.Soot formation is a complex physical and chemical reaction process,in the past few decades,the relevant scholars have done a lot of investigation on the mechanism of soot formation,and have also had a comprehensive understanding of the various stages of soot evolution.However,systematic studies on the effects of different oxygen concentrations on the CH₄/C₂H₄ co-flow diffusion flame characteristics,the evolution of soot morphology at radial and axial of flame and the temperature distribution on the characteristics of soot particles have not been reported yet.In this dissertation,the laminar co-flow diffusion flame of CH₄/C₂H₄ under air and oxygen-enrich（O₂+N₂）atmosphere is taken as the experimental object.Thus experiments are carried out by changing the oxygen concentration and fuel flow rate.The main research contents and results are as follows:The temperature distribution and structural changes of CH₄ and C₂H₄ coflow jet flames were studied by changing the fuel flow rate and oxygen concentration.The results show that from the air atmosphere to the pure oxygen atmosphere,the flame length of the two fuels decreased by 79%,and the flame centerline temperature was233.6 K and 337.3 K lower than the edge temperature,respectively.C₂H₄ flame tip bifurcation appeared"flame wing",and it did not appear in the CH₄ flame from beginning to end.In the C₂H₄ oxygen-enriched combustion,the“golden area”appears at the middle of the flame front where the flame is stratified.To investigate the effect of oxygen concentration on the morphological evolution of soot deposition in a CH₄/C₂H₄ coflow jet diffusion flame,a 12-μm SiC fiber deposition sampling method combined with field emission scanning electron microscopy（FESEM）observations and thermocouple thermometry were used.Result show that the morphology of soot deposits strongly depend on its radial and axial position in the flame and oxygen concentration.TSPD-TEM method was used to obtain the soot morphology and agglomerate characteristics at different heights of the centerline of methane and ethylene co-flow diffusion flames,the morphology evolution process of soot particle and the diameter of primary particle（Dp）were obtained.Emphasis was placed on the analysis of the effects of oxygen concentration,temperature,and flame height on soot formation.The results show that the soot inception zone is advanced when oxygen concentration increased,and the nucleation,surface growth,coagulation,agglomeration and oxidation of the soot are significantly enhanced.The Dp increases first and then decreases with increasing flame height.At the root of the flame,the Dp increases continuously with increasing oxygen concentration,while the Dp at the higher flame position shows the opposite trend.CH₄-C₂H₄ blending combustion under the same number of carbon atoms,the impact of doping on Dp is more like a"neutralization".That is,the value of Dp in blended fuel combustion is between methane and ethylene.