氧化剂含氧浓度对甲烷反扩散火焰光谱特性影响实验研究

Experiment Study of Effects of Oxygen Mole Fraction in Oxidizer on Inverse Methane/Air Diffusion Flame Emission Spectrum Properties

关键词:  反扩散火焰  光纤光谱仪  辐射  燃烧

Key words:  Inverse diffusion flame  Fiber optical spectrometer  Emission  Combustion

摘要:

为了研究氧化剂的含氧浓度对同轴射流甲烷反扩散火焰光谱特性分布的影响，采用光纤光谱仪对富氧层流甲烷反扩散火焰中发射谱线分别为314nm和430nm的激发态自由基OH*和CH*进行了光谱特性实验研究，分析了OH*，CH*辐射强度随氧化剂含氧浓度[XO₂]的变化规律，及其沿反扩散火焰轴向与径向的分布特征。研究表明:甲烷反扩散火焰具有明显的内外双层结构，当氧化剂含氧浓度从21%增加到50%，反扩散火焰反应核心区直径增宽75%，而对火焰高度的变化却非常微弱。OH*和CH*辐射强度沿火焰轴向与径向均呈现先增后减的趋势。随着氧化剂含氧浓度增加，OH*辐射强度呈指数型增加，在距喷嘴出口2/3直径高度处处出现OH*和CH*辐射强度峰值，且峰值的轴向位置不随氧化剂含氧浓度[XO₂]的增大而改变。

Abstract:

In order to study the effects of oxygen mole fraction in the oxidizer on spectrum properties of the coflow methane inverse diffusion flames，spontaneous emissions from excited state radicals OH*(314nm) and CH* (430nm) have been measured in oxygen-enhanced methane inverse diffusion flames emission spectrum by the fiber optical spectrometer，the effects of oxygen mole fraction in the oxidizer on the radiant intensity of OH* and CH*，and the axial and radial distribution of OH* and CH* radiant intensity in various oxygen-enhanced conditions were analyzed. The results show methane inverse diffusion flame has internal and external double-layer structure，the diameter of chemical reaction core zone in IDFs (inverse diffusion flame) broaden 75% with improving the oxygen mole fraction in the oxidizer from 21% to 50%，however，the flame heights have no significant change almost at different oxidizer conditions. The distribution of OH* and CH* radiant intensity along the flame axial and radial direction showed a trend of decrease after a first increase. With increasing oxygen mole fraction in the oxidizer，the peak intensity of OH* growing exponentially，however，the peak intensity of the OH* and CH* appears at a distance of 2/3 oxidizer nozzle diameter away from the nozzle exit，and the axial peak position does not change with oxygen mole fraction in the oxidizer increase.