Effects of curvature on triple flame propagation in fuel-oxidizer counterflow
Effects of curvature on triple flame propagation in fuel-oxidizer counterflow
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DOI：
10.1016/j.combustflame.2022.112353
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发表时间：
2022-11
影响因子：
4.4
通讯作者：
Shumeng Xie;Dehai Yu;J. Daou;Zheng Chen
中科院分区：
文献类型：
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作者：
Shumeng Xie;Dehai Yu;J. Daou;Zheng Chen
在这项研究中，我们分析了膨胀的三重火焰在燃料对流氧化剂的轴对称逆流中的传播。该问题被描述为一个具有一步全局反应的热扩散模型。在大激活能和弱应变速率的极限下进行了渐近分析。对应变率的任意值进行的数值模拟支持和补充了这项研究。除了与混合层内反应物浓度变化有关的火焰前沿曲率1/Rt外，扩展三重火焰的传播还取决于方位曲率1/Rf，其中Rf是前前缘径向距离。当三重火焰扩展到较大的径向距离时，其传播变得准稳定。在准稳态假设下，推导出三重火焰的位移速度与总曲率1/Rf+1/Rt成正比的显式表达式，并通过二维轴对称模拟验证了准稳态假设的正确性。其中包括对膨胀的三重火焰的瞬变模拟，并将其与准稳态假设下的定常特征值问题的数值解进行了比较。在瞬时着火阶段之后，当Rf(用化学计量的平面火焰厚度测量)超过5时，三重火焰以准稳态方式传播。虽然理论分析是在弱应变极限下进行的，但三重火焰速度与曲率1/Rf的线性关系在很大的应变率范围内都是适用的。此外，将分析推广到向内传播的三重火焰(火焰孔)，得到了描述三重火焰位移速度与曲率关系的相似表达式。
In this study, we analyze the propagation of an expanding triple flame in an axisymmetric counterflow of a fuel against an oxidizer. The problem is formulated as a thermo-diffusive model with one-step global reaction. An asymptotic analysis in the limit of large activation energy and weak strain rate is conducted. The study is supported and complemented by numerical simulations carried out for arbitrary values of the strain rate. In addition to the flame front curvature 1/R t associated with the variation in the reactants concentrations transverse to the mixing layer, the propagation of the expanding triple flame also depends on the azimuthal curvature 1/R f where R f is the front leading edge radial distance. As the triple flame expands to large radial distances, its propagation becomes quasi-steady. Under a quasi-steady state assumption, an explicit expression is derived for the displacement speed of the triple flame, which is found to be linearly proportional to the total curvature 1/R f+ 1/R t. Two-dimensional axisymmetric simulations are conducted to validate in particular the quasi-steady assumption. These include transient simulations of the expanding triple flame which are compared to the numerical solution of the steady eigenvalue problem obtained in a frame attached to the propagating front under a quasi-steady assumption. Following a transient ignition phase, the triple flame is found to propagate in a quasi-steady manner when R f (measured with the stoichiometric planar flame thickness) exceeds 5, approximately. Although the theoretical analysis is performed in the weak strain limit, the linear dependence of the triple flame speed on the curvature 1/R f is found to be applicable over a wide range of strain rates. Besides, the analysis is extended for inwardly propagating triple flames (flame holes) and similar expressions describing the relationship between displacement speed of the triple flame and curvatures are obtained.