CO2稀释对天然气掺氢预混层流火焰燃烧特性的影响

摘要

The laminar flame combustion characteristics of natural gas-hydrogen-carbon dioxide gas-air premixed gases were studied in a constant volume combustion bomb.The combustion velocity of laminar stretched flame was investigated in the experiment under the same hydrogen fraction and different carbon dioxide fractions,and the effect of increasing carbon dioxide fractions in the premixed gases on flame combustion characteristics was ana-lyzed.Results showed that the combustion velocity of premixed gases decreased with the increase of carbon dioxide fractions due to the effect of carbon dioxide gas diluting and absorbing heat effect.The ω-shape flame front appeared,and the contacting area between the combusted area and the unburned area decreased with the increase of carbon dioxide fractions;the propagating velocity of stretched flame obviously decreased.When carbon dioxide gas fraction was2COϕ≤5%,,the flame propagating velocity decreased with the increase of flame stretched rate,the Markstein length was positive,and the flame front tended to stablize.When carbon dioxide gas fraction was 2COϕ≥10%,,the change rule of Markstein length was no longer the specific rule to follow,which depended on the dominant role that combustible gas was hydrogen gas or natural gas.%在定容燃烧弹内研究了相同的掺氢比、不同的二氧化碳体积分数下，天然气-氢气-二氧化碳-空气的预混气体层流火焰燃烧特性；分析了二氧化碳体积的增加对火焰燃烧特性的影响。结果表明：随着二氧化碳体积分数的增加，二氧化碳气体的稀释作用和吸热作用使混合气燃烧速率降低，火焰半径随时间的增长率明显减小；同时火焰前锋出现“ω”形的火焰锋面，减小了已燃区和未燃区接触面积，拉伸火焰传播速率明显下降。当二氧化碳体积分数ϕCO2≤5%，时，拉伸火焰传播速率随拉伸率的增加而减小，马克斯坦长度为正值，火焰前锋面趋于稳定；当ϕCO2≥10%，时，马克斯坦长度随二氧化碳体积分数的增加没有统一的规律可循，由于氢气和天然气的马克斯坦长度随着稀释度的增加有相反的变化规律，所以其变化规律取决于可燃混合气中占主导地位的可燃气体是氢气还是天然气。