Laminar burning velocities and transition to unstable flames in H2/O2/N2 and C3H8/O2/N2 mixtures☆
Laminar burning velocities and transition to unstable flames in H2/O2/N2 and C3H8/O2/N2 mixtures☆
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DOI：
10.1016/0010-2180(92)90085-4
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发表时间：
1992-09
影响因子：
4.4
通讯作者：
Sejin Kwon;L. Tseng;G. Faeth
中科院分区：
文献类型：
--
作者：
Sejin Kwon;L. Tseng;G. Faeth
实验研究了自由传播球形火焰在稳定和不稳定优先扩散条件下，正火焰拉伸对层流燃烧速度的影响，以及向不稳定火焰过渡的条件。数据库包括H2/O2/ n2混合物在火焰拉伸值高达7600 s−1的新测量值，以及C3H8/O2/ n2混合物在火焰拉伸值高达900 s−1的现有测量值。层流燃烧速度随卡洛维茨数的增加呈线性变化——在稳定或不稳定的优先扩散条件下，卡洛维茨数或减少或增加——产生的马克斯坦数主要随燃料当量比而变化。然而，中性优先扩散条件被转移到最简单的优先扩散理论与中性稳定性相关联的最大层流燃烧速度条件的不稳定侧。所有的火焰都表现出向不稳定火焰的过渡：不稳定的优先扩散条件使火焰向不规则火焰表面的过渡提前，而稳定的优先扩散条件使火焰通过流体动力不稳定性延迟向细胞火焰的过渡。基于Istratov和Librovich的预测，H2/O2/ n2混合物的水动力不稳定转变条件与丙烷/空气火焰的Groff早期相关性一致。
Effects of positive flame stretch on laminar burning velocities, and conditions for transition to unstable flames, were studied experimentally for freely propagating spherical flames at both stable and unstable preferential-diffusion conditions. The data base involved new measurements for H2/O2/N2mixtures at values of flame stretch up to 7600 s−1, and existing measurements for C3H8/O2/N2mixtures at values of flame stretch up to 900 s−1. Laminar burning velocities varied linearly with increasing Karlovitz numbers—either decreasing or increasing at stable or unstable preferential-diffusion conditions—yielding Markstein numbers that primarily varied with the fuel-equivalence ratio. Neutral preferential-diffusion conditions, however, were shifted toward the unstable side of the maximum laminar burning velocity condition that the simplest preferential-diffusion theories associate with neutral stability. All flames exhibited transition to unstable flames: unstable preferential-diffusion coditions yielded early transition to irregular flame surfaces, and stable preferential-diffusion conditions yielded delayed transition to cellular flames by hydrodynamic instability. Conditions for hydrodynamic instability transitions for H2/O2/N2mixtures were consistent with an earlier correlation due to Groff for propane/air flames, based on the predictions of Istratov and Librovich.