Investigation On Soot Formation Characteristics During The Pyrolysis And Oxidation Of C₂ Hydrocarbons Under A Wide Range Of Equivalence Ratios

Soot is a byproduct produced from the pyrolysis or incomplete combustion of hydrocarbon fuels.On one hand,it is harmful to the environment and the human body;on the other hand,it is a widely-used functional material named as carbon black.It is therefore very important to control its emission and production.In order to reduce the interference of the complex environment in the practical industrial production,a laminar premixed stag nation flame configuration and a laminar flow tube reactor combined with small orifice samling method were used in this study.A variety of measurement methods were applied to obtain accurate and detailed sooting characteristics including total soot yield,particle size distribution,particle morphology,and soot induction delay time.This study is aimed at investigating the soot particle formation characteristics in fuel-rich combustion and pyrolysis of C₂ hydrocarbons and exploring the effects of the fuel structure,temperature,equivalent ratio,and reaction atmosphere.Numerical simulation was also conducted to analyze the experimental results.Firstly,the detailed soot characteristics were explored in the laminar premixed flames of C₂ hydrocarbon fuels.The results show that under a certain flame temperature and C/O ratio,the soot yield presented a trend of ethane>ethylene>acetylene.In the acetylene flame,the starting point of soot formation is the latest,the evolution of PSDs is the slowest,and the structure of the aggregates is the simplest.The reaction pathway analysis reveals that the paths to produce benzene are similar in all three flames.The soot yield is the largest in the ethane flame since the equivalence ratio is highest due to the lo west C/H ratio in the fuel molecule.Secondly,the orifice dilution sampling technique was applied at the outlet of the flow reactor to quantitatively obtain the particle size distribution of soot particles during fuel pyrolysis.It was found that there w as a bimodal distribution during the soot formation process and the particle size distribution as well as the soot yield are strongly affected by the fuel concentration and temperature.The soot induction delay time in the flow tube was determined and was found to follow the Arrhenius law.Thirdly,the effects of low temperature and high equivalent ratio on the formation of soot particles were further explored.It was found that at higher temperatures,the soot yield monotonically increased with the equiva lence ratio,while at lower temperatures soot formation increased first then decreased as equivalence ratio rised.A small amount of oxygen would promote the formation of PAHs and thus nucleation,while a large amount of oxygen would inhibit soot formation.Finally,the effect of CO₂ addition on soot formation was explored.An increase of CO₂ concentration will first promote and then inhibit soot yield during ethylene pyrolysis.The specific reason is that CO₂ can generate hydroxyl radicals,and a small amount of hydroxyl radicals intensifies PAHs formation through C₃ reaction pathways,which accelerates soot nucleation and growth process,while a large number of hydroxyl radicals would have a strong oxidation effect.In this thesis,the soot formation characteristics of C₂ hydrocarbons were studied through experimental measurements and modeling.The effects of fuel structure,temperature,equivalent ratio and reaction atmosphere on soot formation were explored,which deepened the understanding of the soot formation mechanism and provided reliable data for soot model development.