稀释剂对H2/CH4预混火焰熄灭特性影响

掺氢天然气在稀释气体作用下的熄灭特性研究对实际燃烧设备的设计和优化具有重要的指导意义。本文利用对冲火焰法测量了掺氢天然气层流火焰在N₂和CO₂作用下的熄灭拉伸率,并采用数值模拟耦合详细化学反应机理对N₂,CO₂和He的稀释剂效应展开研究。结果表明,Li、GRI Mech 3.0和FFCM-1机理均能定性反映燃料熄灭拉伸率随当量比的变化规律,且FFCM-1机理综合预测精度最高。实验和模拟发现,不同稀释剂气体对掺氢天然气熄灭拉伸率降低幅度满足:He22。进一步研究发现,CO₂由于热容大,在反应体系中会降低火焰温度,同时增强了链终止反应强度,通过热效应和化学效应两方面对火焰熄灭特性起作用。He则能显著改变燃料混合物的平均摩尔质量,从而改变体系中重要反应物和自由基的扩散特性,从扩散效应方面影响火焰的熄灭特性。

Dilution Effect on The Extinction of H2/CH4/Air Premixed Flames

Knowledge of dilution effect on the extinction of H2/CH4/air premixed flames is of significance to the design and optimization of combustion applications.In the present work,both the numerical modeling and experimental measurement were conducted to analyze the effects of N₂,CO₂ and He dilutions on the extinction of H2/CH4/air premixed flames.The results showed that all the three chemical kinetics models(including Li scheme,GRI Mech 3.0 scheme,and FFCM-1 scheme)were capable of qualitatively characterizing the variation of extinction limits.The extent of the dilution effect of the three tested diluents on the reduction of the extinction stretch rate was found to be in the following sequence,He22.Further investigation revealed that CO₂ dilution weakened the H2/CH4/air premixed flames by decreasing the flame temperature(thermal effect)and strengthening the termination reaction(chemical effect).He dilution was able to significantly change the average molar mass of the fuel/air mixtures,resulting in the profound diffusivity effect on the extinction limits,while the diffusivity effect was negligible for both CO₂ and N₂ dilutions.