掺混甲醇对汽油层流扩散火焰碳烟生成的影响

摘要

在一台协流扩散燃烧器上,应用双色激光诱导炽光法(TC-LⅡ)得到了火焰内二维碳烟体积分数分布.在燃料流量和碳流量一定时,研究了甲醇掺混比对汽油火焰碳烟生成的影响.结果表明:燃料流量一定时,与纯汽油相比,M20(甲醇体积分数为20％)、M40、M60和M80的峰值碳烟分别降低了50.7％、74.8％、91.0％和97.8％,平均碳烟分别降低了53.4％、85.6％、97.3％和99.8％.碳流量一定时,峰值和平均碳烟的降幅相比燃料流量一定时略有降低.这表明燃料流量一定时,甲醇掺混引发的碳元素质量流量的降低对碳烟降低的贡献很小,甲醇对碳烟的降低主要通过对燃料中芳烃的稀释作用及化学反应动力学的影响.火焰整体碳烟生成的起始高度随甲醇掺混比的增加而升高.火焰中心碳烟的起始高度在燃料流量一定时,随甲醇掺混比的增加而降低,碳流量一定时,随甲醇掺混比的增加略有升高.火焰中心碳烟体积分数随高度的增加,呈3段变化趋势.不同高度上,火焰径向碳烟峰值随火焰高度的上升由火焰外侧向中心移动,且峰值先增加后降低.%In a coflow diffusion burner,the soot concentration distributions in laminar diffusion flames of gasoline blending with methanol were measured using TC-LⅡ technique.This study was carried out under both the same fuel flow and the same carbon flow conditions.The results show that compared with the gasoline,the peak and average soot concentration in the M20,M40,M60 and M80 flames decrease by 50.7％,74.8％,91.0％,97.8％and 53.4％,85.6％,97.3％,99.8％ respectively under the same fuel flow condition,while they appears only a slight reduction under the same carbon flow condition.Therefore,the reduction in mass flow of carbon due to methanol blending has little contribution to soot reduction under the same fuel flow rate.The soot reduction by methanol blending under the same fuel flow condition is mainly caused by the dilution of aromatics in gasoline and the influence of chemical reaction kinetics.In the whole flame,the initial height of soot formation increases with methanol ratio in creasing.In flame center line,the initial height of soot formation decreases with methanol ratio increasing under the same fuel flow condition,while it increases under the same carbon flow condition.In addition,it is also found that the soot concentration along the flame center line presents three variation stages with the flame height.The radial peak soot concentration of the flame moves from outside to inside gradually with flame height increasing,and the peak value increases first and then decreases.