Study Of Synergistic Effect During The Formation Of Some Key Aromatic Hydrocarbons In Pyrolysis Atmosphere

Soot,one of the main pollutants produced by combustion,is a major cause of urban haze and threatens human health seriously.Among the complex mechanism of soot formation,the gas phase formation mechanism of aromatics is considered to be the key sub-mechanism.Since the practical transport fuel is a mixture of a large number of components,the soot formation,particularly the formation of critical aromatic,is significantly affected by the interaction between different fuel components in the combustion process.Among them,synergistic effect not only shows that the interaction between the fuel components can dramatically promote the formation of pollutants such as polycyclic aromatic hydrocarbons(PAHs)and soot,but also indicates the diversity of the formation pathways of benzene,PAHs and other precursors of soot.Synergistic effects typically include that between non-aromatic components and aromatic components and that between non-aromatic components.For these two synergistic effects,the synergistic effect on the formation of PAHs between ethylene and benzene,toluene and ethylbenzene was investigated experimentally using the co-flow diffusion flame,and the synergistic effect on the formation of aromatic hydrocarbons in the 1,3-butadiene/propyne flow reactor co-pyrolysis experiments was investigated theoretically using the reaction kinetic model in this paper.Co-flow diffusion flame is one of the main types of diffusion flames.Since the flame surface is formed in the flow direction of fuel and air,the consumption of fuels inside the flame(i.e.,the fuel side)is mainly pyrolyzed,and a large amount of aromatics and soot are produced,which is an important system for soot formation mechanism study.Free radicals play an important role in the formation and growth of aromatic hydrocarbons,so the quantitative detection of free radicals in the co-flow diffusion flame will promote the development of aromatics models.In this work,a new experimental apparatus for co-flow diffusion flame was designed and constructed,with the instant sample and detection of all species on the axis of the flame by the use of quartz nozzle ultrasonic molecular beam sampling and vacuum ultraviolet photon ionization spectrometry.The experimental research of ethylene mixed with 10%or 15%carbon flux of benzene,toluene or ethylbenzene was carried out on this platform.A variety of free radicals such as methyl,propargyl,cyclopentadienyl,benzyl and indenyl were detected,and the distribution of a variety of stable products and active intermediates on the axis of the flame were obtained.The results show that the PAHs production in the flame increases with the increase of the length of alkyl branch and the synergistic effect between ethylene and toluene or ethylbenzene on PAHs formation is stronger than that between ethylene and benzene.The reason is that a lot of benzyl radical is formed in the toluene and ethylbenzene blending flame,while benzene blending flame produces lots of phenyl radical but a little benzyl radical.Therefore,The HACA pathway is the most important path for PAHs formation in benzene blending flame,while the benzyl radical contributes significantly to PAHs formation in the toluene and ethylbenzene blending flame,making the PAHs production is much higher and contributing to a stronger synergistic effect.Toluene pyrolysis also produces a large number of phenyl radical,and the synergistic effect between phenyl and benzyl radical in the toluene blending flame makes fluorine production much higher.A numerical investigation on the co-pyrolysis of 1,3-butadiene and propyne is performed in this work to explore the synergistic effect between fuel components on aromatic hydrocarbon formation.A detailed kinetic model of 1,3-butadiene/propyne co-pyrolysis with the sub-mechanism of fuel decomposition and aromatic hydrocarbon formation is developed and validated on previous 1,3-butadiene and propyne pyrolysis experiments.The model is able to reproduce both the single component pyrolysis and the co-pyrolysis experiments,as well as the synergistic effect between 1,3-butadiene and propyne on the formation of a series of aromatic hydrocarbons.Based on the rate of production and sensitivity analyses,key reaction pathways in the fuel decomposition and aromatic hydrocarbon formation processes are revealed and insight into the synergistic effect on aromatic hydrocarbon formation is also achieved.The synergistic effect results from the interaction between 1,3-butadiene and propyne.The easily happened chain initiation in the 1,3-butadiene decomposition provides an abundant radical pool for propyne to undergo the H-atom abstraction and produce propargyl radical which plays key roles in the formation of aromatic hydrocarbons.Besides,the 1,3-butadiene/propyne co-pyrolysis includes high concentration levels of C3 and C4 precursors simultaneously,which stimulates the formation of key aromatic hydrocarbons such as toluene and naphthalene.