基于PLIF的甲烷/空气富燃层流半预混半扩散火焰试验研究

Experimental Study on CH 4/Air Rich Laminar Premixed Flame Based on PLIF

为获得高当量比甲烷预混燃烧特性,利用平面激光诱导荧光技术研究本生灯甲烷/空气富燃层流预混火焰中氢氧自由基(OH)和一氧化氮(NO)的分布。结果表明:OH主要分布在火焰扩散层锋面两侧,火焰顶端基本无OH分布;当量比φ<1.31和φ≥1.31时本生灯富燃预混火焰外部扩散层分别以0.5 s和0.4 s为一个周期不断收缩膨胀;层流燃烧速度随当量比增加而减少,当φ=1.10时为最大燃烧速度33 cm/s,当φ>1.50时,层流燃烧速度基本保持不变,维持在15 cm/s左右;在火焰顶端存在强烈的负拉伸作用,负拉伸率的绝对值随着当量比的增加先减小后增加,其中火焰拉伸率是影响层流燃烧速度测量误差的主要因素;对立体火焰结构研究发现,φ=1.54时在火焰扩散层内部发生局部熄火现象;对火焰中NO的分布研究发现,NO主要分布在火焰内锥外部的扩散层,工程应用时应尽量减少火焰扩散燃烧区域的分布,以降低NO的排放。

In order to obtain high equivalent ratio CH 4 premixed combustion characteristics,the distribution of OH radical and NO in the premixed flame of CH 4/air rich laminar flow of Bunsen burner are studied by using planar laser induced fluorescence technique.The results show that OH radical is mainly distributed on both sides of the flame diffusion layer front,and there is basically no OH radical distribution at the top of the flame.The external diffusion layer of the Bunsen burner rich premixed flame shrinks and expands with a cycle of 0.5 s and 0.4 s respectively when the equivalent ratioφ<1.31 andφ≥1.31;laminar burning velocity decreases with the increase of the equivalent ratio,whenφ=1.1 for the maximum burning speed of 33 cm/s,whenφ>1.5,and laminar burning velocity basically remains the same,maintaining at about 15 cm/s.There is a strong negative stretching effect at the top of the flame,and the absolute value of the negative stretching rate decreases first and then increases with the increase of the equivalent ratio,and flame stretch ratio is the main factor affecting the measurement error of laminar combustion velocity.The study of the three-dimensional flame structure finds that local flameout occurs inside the flame diffusion layer atφ=1.54;and the study of the distribution of NO in the flame finds that NO is mainly distributed in the diffusion layer outside the inner cone of the flame.During engineering application,the distribution of flame diffusion and combustion area should be minimized to reduce NO emission.