CH_(4)/NH_(3)/空气预混稀燃火焰结构及吹熄特性实验研究

Structure and Blow-Off Characteristics of Lean Premixed CH_(4)/NH_(3)/Air Flames

本实验对稳定在钝体旋流燃烧器上的NH_(3)/空气及NH_(3)/CH_(4)/空气预混稀燃紧凑火焰开展了宏观结构及吹熄特性的研究.CH_(4)/空气预混火焰也被用于对比.利用PIV和OH-PLIF同步测量技术捕获流场和瞬时OH分布,获得火焰-流场耦合信息.结果表明,NH_(3)/空气火焰面的流体过量拉伸是导致其局部熄火,促使火焰整体吹熄的主要原因.NH_(3)/CH_(4)/空气火焰根部在临吹熄时也出现过量拉伸和局部熄灭,这将导致火焰最终吹熄.过量拉伸的主要来源为流体剪切变形.NH_(3)/空气火焰的内剪切层涡会进一步促进火焰吹熄.掺混CH_(4)能极大地提高极限拉伸率,增强稀燃火焰稳定性,拓宽火焰的稀燃极限.同时掺混CH_(4)也使火焰的燃烧速度及温度提高,有利于稳定火焰.

In this experiment,the macrostructure and blow-off characteristics of the compact lean premixed NH_(3)/air and NH_(3)/CH_(4)/air flames stabilized on a bluff-body and swirl burner were studied.Premixed CH_(4)/air flame was also used for comparison.Particle imaging velocimetry(PIV)and the hydroxyl planar laser-induced fluores-cence(OH-PLIF)synchronous measurement techniques were used to capture the flow field and instantaneous OH distribution,and the flame-flow coupling information was obtained.The results show that the flow excessive stretching on the NH_(3)/air flame surface is the main reason for the local extinguishment and the overall blow-off of the flame.Excessive stretching and local extinction also occur at the root of NH_(3)/CH_(4)/air flame near the blow-off,which will lead to the final blow-off of the flame.The main reason for excessive stretching is flow shear deforma-tion.The inner shear layer vortex of the NH_(3)/air flame will further promote the flame blow-off.Blending CH_(4)can greatly improve the extinction strain rate,enhance the stability of lean flame and broaden the lean blow-off limit.At the same time,the addition of CH_(4)can also increase the burning velocity and flame temperature,which is conducive to stabilizing the flame.