On transition to cellularity in expanding spherical flames
On transition to cellularity in expanding spherical flames
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DOI：
10.1017/s0022112007005885
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发表时间：
2007-07
影响因子：
3.7
通讯作者：
G. Jomaas;C. Law;J. Bechtold
中科院分区：
文献类型：
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作者：
G. Jomaas;C. Law;J. Bechtold
在大气压和高压下，在燃料-氧化剂混合物的反应环境中，使用高速纹影成像实验确定了中心点燃、向外传播的球形火焰转变为细胞结构的瞬间，并随后根据流体动力学和扩散热不稳定性进行了解释。实验结果表明，对于混合物化学计量、氧气浓度和压力范围较宽的近等扩散乙炔火焰，转变佩克莱特数Pec = RcℓL几乎呈恒定值，其中Rc是转变时的火焰半径，ℓL是层流火焰厚度。然而，对于非等扩散的氢气和丙烷火焰，Pec 分别随混合物当量比呈线性增加和减少。使用先前理论对 Pec 的评估显示出完全的定性一致性和令人满意的定量一致性，证明了 Pec 对等扩散混合物的所有系统参数不敏感，以及 Markstein 数 Ze(Le – 1) 在非等扩散混合物的不稳定中占主导地位，其中 Ze 是 Zel'dovich 数，Le 是 Lewis 数。在评估 Pec 时，强调了使用局部评估的 ℓL、Ze 和 Le 值的重要性，这些值是从具有详细化学和传输的计算模拟一维火焰结构中提取的，或者是通过实验确定的拉伸火焰响应。
The instant of transition to cellularity of centrally ignited, outwardly propagating spherical flames in a reactive environment of fuelx–oxidizer mixture, at atmospheric and elevated pressures, was experimentally determined using high-speed schlieren imaging and subsequently interpreted on the basis of hydrodynamic and diffusional–thermal instabilities. Experimental results show that the transition Péclet number, Pec = RcℓL, assumes an almost constant value for the near-equidiffusive acetylene flames with wide ranges in the mixture stoichiometry, oxygen concentration and pressure, where Rc is the flame radius at transition and ℓL the laminar flame thickness. However, for the non-equidiffusive hydrogen and propane flames, Pec respectively increases and decreases somewhat linearly with the mixture equivalence ratio. Evaluation of Pec using previous theory shows complete qualitative agreement and satisfactory quantitative agreement, demonstrating the insensitivity of Pec to all system parameters for equidiffusive mixtures, and the dominance of the Markstein number, Ze(Le – 1), in destabilization for non-equidiffusive mixtures, where Ze is the Zel'dovich number and Le the Lewis number. The importance of using locally evaluated values of ℓL, Ze and Le, extracted from either computationally simulated one-dimensional flame structure with detailed chemistry and transport, or experimentally determined response of stretched flames, in the evaluation of Pec is emphasized.