一氧化碳添加对甲烷/空气贫燃预混火焰的影响(英文)

通过对贫燃条件下(燃料与空气化学计量比φ=0.60-0.80)的甲烷/一氧化碳/空气火焰结构进行数值模拟,研究燃料中一氧化碳添加量对层流燃烧速度、氮氧化合物的排放以及熄火拉伸率的影响.随着燃料中一氧化碳添加量的不断增加,层流燃烧速度有所下降,这与燃料中加入氢气产生的现象有所不同.为了解释这一现象,本文深入探讨了层流燃烧速度与H+OH浓度峰值之间的关系,结果表明,一氧化碳的增加导致H+OH浓度峰值呈线性下降,与层流燃烧速度下降趋势完全一致.随着一氧化碳的增加,氮氧化合物排放量有所下降.探讨了NO的生成机理,且由敏感性分析得到生成NO的重要反应,分析当一氧化碳量增大时,NO的浓度以及重要反应的NO生成率均下降.此外,利用数值模拟求解径向拉伸率,深入分析燃料中添加一氧化碳时拉伸率对贫燃火焰稳定性的影响.由计算结果得到熄火拉伸率,发现燃料中一氧化碳的添加在一定程度上能够增强火焰的稳定性.

Effects of CO Addition on the Lean Premixed CH4/Air Flame

A numerical study was carried out to determine the effects of CO addition on the laminar burning velocity, NO, emission, and extinction strain rate in a premixed CH4/CO/air flame under the lean condition (equivalence ratio of fuel to air (φ)=0.60-0.80). When more CO was added to the fuel, the laminar burning velocity decreased, which is different from that observed for H2 addition. To explain this, we studied the strong correlation between laminar burning velocity and H+OH peak concentrations. Results showed that the H+OH peak concentrations decreased linearly with an increase in CO content. This tendency is in good agreement with that of the laminar burning velocity. For NOx, we observed that increments in CO addition led to a remarkable reduction in the NO, emission. In addition, we investigated the NO formation mechanism and determined the relevant reactions for NO production using a sensitive analysis. The NO concentrations decreased significantly with enrichment by CO and the NO production rate also clearly decreased. We calculated the radial strain rate Srad and discussed the influence of strain rate on lean flame stability with regards to the addition of different CO mole fractions to the fuel. The extinction strain rates indicated that the lean flammability limits were extended by CO addition in some way.