CO2稀释对甲烷-高温空气扩散燃烧及NO生成特性影响的化学动力学分析

基于GRI-Mech 3.0详细化学反应机理,利用OPPDIF Code研究了CO2稀释比、预热温度及拉伸率对甲烷-高温空气层流对冲扩散火焰温度、热释放率、组分摩尔分数及NO生成特性的影响.研究结果表明,CO2稀释助燃空气能有效降低火焰中H、O及OH等基团摩尔分数,抑制燃烧过程链传播及链引发反应,从而减缓CH4氧化速率.随着助燃空气中CO2稀释比的增加,火焰最高温度逐渐降低,主氧化区及第二氧化区放热峰值变小,燃烧反应高温区变窄,NO生成指数E显著降低.当稀释比大于20%时,热力型NO随助燃空气温度升高规律并不明显.随着CO2稀释比的增加,快速型NO对NO生成量影响逐渐增强,成为高CO2稀释比下甲烷-高温空气扩散燃烧NO生成的主要路径.

Chemical Effects of CO2 Dilution on Flame Structure and NO Formation Properties in Methane-Preheated Air Counterflow Diffusion Flame

The present aims at charactering the effects of CO2 dilution on methane-high temperature air counterflow diffusion flames.Flame temperature,heat release ratio,species distribution and NO formation were calculated by using OPPDIF Code with GRI-Mech 3.0,mechanism.The results indicate that the suppression of CH4 oxidation with CO2addition can be mainly ascribed to the decrease of H,O and OH radicals involved in chain propagation and chain initiation reactions.Flame temperature and heat release rate decrease with the increase of the dilution ratio in the oxidation.As a result,the hot spot of reaction zone is suppressed with the addition of CO2.If the dilution ratio is greater than 20%,the effects of combustion air temperature on thermal NO emission are limited.NO formation by the fenimore route is dominant compared with other routes especially when the air is highly diluted with carbon dioxide.