带压环境中CO2/H2O/N2气体稀释对合成气层流火焰速度的影响

合成气稀释燃烧是燃气轮机高效低污染燃烧的重要运行方式。本文以CO₂、H₂O和N₂为稀释气体，利用数值模拟方法研究稀释比对不同压力下合成气（CO/H₂/CH₄）层流火焰速度（S_L）的影响规律，并从自由基浓度变化、敏感性数值和生成速率（rate of production，ROP）三个方面解析三种气体的物理和化学作用机理。结果表明，S_L随燃烧压力和稀释比的增大而不断减小，其中CO₂对层流火焰速度的抑制最为显著。稀释气体的物理效应对层流火焰速度的影响远大于化学效应，但CO₂和H₂O的化学效应不能忽略。化学效应则是通过改变H和OH自由基浓度影响S_L，其中CO₂稀释降低H和OH自由基浓度，H₂O稀释则是降低H自由基浓度，从而降低合成气的层流火焰速度。进一步反应动力学分析发现了H/OH浓度变化在低压、加压下的主要化学反应路径，且受H₂O稀释的化学反应速率对压力较CO₂更为敏感。

Effect of CO2/H2O/N2 gas dilution on laminar flame speeds of syngas at elevated pressure

Syngas dilution combustion is an important mode of operation for gas turbines with high efficiency and low pollution. CO₂, H₂O and N₂ were used as dilution gases to study the effect of dilution ratio on the laminar flame speed of syngas (CO/H₂/CH₄) at elevated pressures with numerical simulation, and the physical and chemical mechanisms of the three gases were also analyzed in radical concentration change, sensitivity value and ROP(rate of production) analysis. The results show that the laminar flame speed decreases with the increase of combustion pressure and dilution ratio, and the suppression of CO₂ on the laminar flame speed is the most significant. The physical effect of the diluent gas on the laminar flame velocity is far greater than the chemical effect, but the chemical effects of CO₂ and H₂O cannot be ignored. The chemical effect is to affect S_L by changing the concentration of H and OH radicals, where CO₂ dilution reduces the H and OH radical concentration, and H₂O dilution decreases the H radical concentration, thereby reducing the laminar flame velocity of the syngas. Further reaction kinetics analysis finds the main path of change of H/OH concentration at low and high pressure, and the chemical reaction rate diluted by H₂O is more sensitive to pressure than CO₂.