Study On The Characteristics Of Soot Formation In The Diffusion Flame Of Hydrocarbon Fuels

Soot is a kind of particulate matter produced by incomplete combustion of hydrocarbon fuel and pyrolysis at high temperature.The emission process of soot will take part of the heat away,which will reduce the utilization of fuel and affect the thermal efficiency of combustion equipment.At the same time,the soot particles will be suspended in the air for a long time,which will promote the formation of haze and harm human health.The actual combustion conditions are mostly carried out under high pressure,so it is great significance to study the characteristics of soot generation under high pressure.In addition,the study of the characteristics of soot formation in dilute conditions such as H₂,CO,CO₂has guiding significance for the control of particulate pollutants in the process of Blended Combustion and exhaust gas recirculation.In this study,firstly,experiments were carried out on the high pressure axisymmetric diffusion combustion experimental system to study the soot emission characteristics of CH₄ laminar diffusion flame under different pressures and different CO₂ dilution ratios.The open source code,CoFlame,was used to simulate the laminar diffusion flame of CH₄.The working conditions of the simulation were consistent with the experimental conditions.Diffusion 2D-LOSA was used to measure the volume fraction distribution of soot and the temperature distribution in the flame.The temperature field,component concentration field,soot volume fraction,nucleation rate,number density and soot particle dynamics evolution are calculated by numerical simulation.By comparing the experimental and numerical simulation results,it is found that the experimental results are consistent with the simulation results,which verifies the accuracy and effectiveness of the open source program,CoFlame,in the prediction of soot generation in laminar diffusion flame.Experimental and simulation results show that the increase of pressure increases the volume fraction of soot and the temperature of flame,and the radius of soot formation area narrows.With the increase of CO₂ dilution ratio,the volume fraction of soot in CH₄ flame decreased and the flame temperature decreased.Secondly,on the basis of verifying the accuracy and validity of CoFlame program in the prediction of soot generation in laminar diffusion flame,the formation of soot in laminar diffusion flame of different kinds of hydrocarbon fuels?C₂H₄,C₂H₆,C₃H₈,C/H ratio are different?under different pressure and dilution ratio of H₂ and CO is comprehensively simulated by CoFlame program.The numerical simulation results show that with the increase of H₂ and CO addition ratio in the C₂H₄,C₂H₆,C₃H₈ diffusion flame,the temperature increases,the volume fraction of soot and the diameter and number density of primary soot particles decrease,and the inhibition effect of CO on soot formation is weaker than that of H₂;With the increase of pressure,the volume fraction of soot in C₂H₄,C₂H₆ and C₃H₈ flames increased,and the temperature increased;With the increase of C/H ratio of hydrocarbon fuel,the volume fraction of soot in the diffusion flame of hydrocarbon fuel increases gradually,and the distribution area of soot increases along the height direction and shrinks along the radius direction.In this study,the characteristics of soot formation during the combustion of various hydrocarbon fuels under different conditions are obtained,which is helpful to reveal the mechanism of soot formation during the combustion of hydrocarbon fuels,and to guide the emission control of particulate pollutants in the process of high pressure and dilution combustion.