掺混NH_(3)/乙烯同向射流扩散火焰碳烟生成热化学效应分析

Analysis of thermal and chemical effects of soot formation in NH_(3)/C_(2)H_(4)co-flow diffusion flame

以氨气、乙烯和氩气同向射流扩散火焰为研究对象,采用消光法、快速插入测温法结合CHEMKIN模拟,研究了不同体积分数(0%,10%,20%和30%)氨气与乙烯混合燃烧后火焰中碳烟体积分数分布、中心线温度分布以及氨气热效应和化学效应对碳烟生成的影响。结果表明:随着NH_(3)掺混比增大,碳烟的最大体积分数减小,碳烟生成区域向火焰中心线与火焰下游移动;随着NH_(3)掺混比增大,火焰最高温度增大;CHEMKIN模拟中采用NH_(3)-C 2H 4-PAH燃烧机理和脱氢加乙炔(HACA)碳烟生长机理,运用虚拟氨气(FNH_(3))得到了NH_(3)的热效应与化学效应对碳烟生成的影响,模拟结果表明,随着NH_(3)掺混比增加,碳烟的最大体积分数减小;氨气热效应对碳烟的抑制作用在NH_(3)体积分数分别为0%,10%,20%,30%时几乎呈现线性变化,而化学效应在NH_(3)体积分数小于10%时能显著抑制碳烟生成,当继续增大NH_(3)掺混比,氨气化学效应对碳烟的抑制作用逐渐减小;NH_(3)的掺混使得多环芳烃(PAHs),H,C 2H 2,C 3H 3的浓度降低和CN的浓度升高,抑制了碳烟前驱物的形成,模拟结果也表明,NH_(3)的化学效应对升高火焰温度、降低PAHs摩尔分数和碳烟体积分数发挥重要作用,而热效应在抑制C 2H 2和C 3H 3的生成过程中作用更加明显。

In this paper,the co-flow diffusion flame of ammonia,ethylene and argon was investigated.The extinction light method,rapid insertion temperature measurement method combined with CHEMKIN simulation were used to study the volume fraction of soot distribu-tion,centerline temperature distribution,and the influence of ammonia thermal and chemical effects on soot formation in the ethylene flame blended with different volume fractions of ammo-nia(0%,10%,20% and 30%).The experimental results show that the maximum volume frac-tion of soot decreases,the maximum flame temperature increases and the soot formation area moves towards the flame centerline and downstream of the flame as the NH3 mixing ratio increa-ses.The NH_(3)-C_(2)H_(4)-PAH mechanism and hydrogen abstraction acetylene addition(HACA)soot growth mechanism were used in the CHEMKIN simulations,and the thermal and chemical effects of NH_(3)on soot formation were obtained by introducing the fictitious ammonia(FNH_(3)).The simulation results show that the maximum volume fraction of soot decreases with the increase of ammonia ratio.The inhibition of soot formation by the thermal effect of NH_(3)varies almost linearly from 0%,10%,20%,30%NH_(3)blending.The chemical effect can significantly inhibit soot formation when the ammonia blending ratio is less than 10%,and the inhibition of soot formation by the chemical effect of ammonia gradually decreases when the ammonia blending ratio continues to increase.The mixing of NH_(3)results in the reduction of the concentration of polycyclic aromatic hydrocarbons(PAHs),H,C_(2)H_(2),and C_(3)H_(3),and the increase of the concentration of CN,which inhibits the formation of soot precursors.The simulation results also indicate that the chemical effect of NH_(3)plays a more important role in raising the flame temperature and reducing the mole fraction of PAHs and the volume fraction of soot,while the thermal effect plays a more obvious role in inhibiting the formation of C_(2)H_(2)and C_(3)H_(3).