Abstract: Homogeneous mixtures of CH4/air under moderate or intense low-oxygen dilution (MILD) combustion conditions were numerically studied to clarify the fundamental effects of exhaust gas recirculation (EGR), especially CO2 in EGR gases, on ignition characteristics. Specifically, effects of CO2 addition on autoignition delay time were emphasized at temperatures between 1200 K and 1600 K for a wide range of the lean-to-rich equivalence ratio (0.2-2). The results showed that the ignition delay time increased with equivalence ratio or CO2 dilution ratio. Furthermore, ignition delay time was seen to be exponentially related with the reciprocal of initial temperature. Special concern was given to the chemical effects of CO2 on the ignition delay time. The enhancement of ignition delay time with CO2 addition can be mainly ascribed to the decrease of H, O and OH radicals. The predictions of temperature profiles and mole fractions of CO and CO2 were strongly related to the chemical effects of CO2. A single ignition time correlation was obtained in form of Arrhenius-type for the entire range of conditions as a function of temperature, CH4 mole fraction and O2 mole fraction. This correlation could successfully capture the complex behaviors of ignition of CH4/air/CO2 mixtures. The results can be applied to MILD combustion as “reference time”, for example, to predict ignition delay time in turbulent reacting flow.

摘要： 为了更深入地理解烟气中二氧化碳在高温低氧条件下对甲烷燃料点火特性的影响，利用SENKIN Code及GRI-Mech 3.0详细化学反应机理研究了不同初始温度（1200-1600K），当量比（0.2-2.0），以及稀释比（0-0.6）下CO2稀释对甲烷-空气混合气点火延迟时间的影响。结果表明，自燃点火延迟时间随着当量比或CO2稀释比的增加而变大。在本文研究范围内，点火延迟时间与初始温度的倒数成指数关系。重点对CO2作为稀释气体的化学作用进行了研究，分析认为，在CO2的化学作用下，H、O以及OH基团浓度进一步降低，进而减缓甲烷氧化速率，从而导致点火延迟时间变长。CO2的化学作用对于燃烧温度、CO及CO2浓度等预测密切相关。此外，根据计算结果，得到了甲烷-空气-CO2混合气点火延迟时间的Arrhenius关联式，该式在本文研究范围内与详细化学反应机理预测值吻合较好。本文计算结果可作为预测高温低氧湍流燃烧点或延迟时间“参考值”。

关键词: MILD燃烧, 点火延迟时间, 自燃, 甲烷