Flame morphology and self-acceleration of syngas spherically expanding flames
Flame morphology and self-acceleration of syngas spherically expanding flames
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合成气球形膨胀火焰的火焰形态和自加速
DOI：
10.1016/j.ijhydene.2018.07.140
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发表时间：
2018
影响因子：
7.2
通讯作者：
Huang Zuohua
中科院分区：
文献类型：
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作者：
Cai Xiao;Wang Jinhua;Zhao Haoran;Zhang Meng;Huang Zuohua
在定容燃烧室中研究了初始压力为0.2 ~ 0.6MPa、CO/H2比为50/50 ~ 10/90、当量比为0.4 ~ 1.5的范围内CO/H2/O2/N2混合气体球形膨胀火焰的自加速特性。在不同当量比下，通过调节O2/N2比来保持绝热火焰温度恒定。记录纹影图像，研究球形膨胀火焰的火焰前锋演变。利用适当的方程提取局部加速指数，研究火焰自加速过程。结果表明，由于流体动力学和热扩散不稳定性的作用，火焰胞在光滑的火焰前缘发展，最终形成分形结构，导致火焰自加速传播。临界Peclet数对应于自加速的开始，Pecr随着Markstein长度Ma非线性地增加。观察进一步揭示了自加速的开始主要受热扩散效应的控制。自加速过程中存在两种不同的火焰传播区，即快速过渡加速区和准自相似加速区。快速转捩区受流体动力学扰动的失稳效应和火焰拉伸的稳定效应控制。而准自相似区主要受流体动力学不稳定性控制的火焰阵元级联过程的影响。自相似加速指数α s随初始压力和刘易斯数Le而变化。测得的α萨雷值为1.1-1.25（小于1.5），表明火焰未达到自湍流。
The self-acceleration of spherically expanding flames were investigated using a constant volume combustion chamber for CO/H2/O2/N2mixtures over a wide range of initial pressure from 0.2 to 0.6 MPa, CO/H2ratio from 50/50 to 10/90 and equivalence ratio from 0.4 to 1.5. The adiabatic flame temperature was kept constant by adjusting O2/N2ratio at different equivalence ratios. Schlieren images were recorded to investigate the flame front evolution of spherically expanding flames. Local acceleration exponents were extracted using a proper equation to study the process of flame self-acceleration. Results show that the flame cells develop on the smooth flame fronts and finally reach fractal-like structures due to the hydrodynamic and diffusional-thermal instabilities, resulting in flame self-accelerative propagation. The critical Peclet number corresponding to the onset of self-acceleration,Pecrincreases nonlinearly with the Markstein length,Ma. The observation further reveals that the onset of self-acceleration is mainly controlled by the diffusional-thermal effect. There exists two distinct flame propagation regimes in the self-acceleration, namely quick transition accelerative and quasi self-similar accelerative regimes. The quick transition regime is controlled by the destabilization effect of hydrodynamic perturbation and stabilization effect of flame stretch. While the quasi self-similar regime is primarily affected by the cascading process of flame front cells controlled by hydrodynamic instability. The self-similar acceleration exponent,αsvaries with the initial pressure and Lewis number,Le. The values ofαsare measured to be 1.1–1.25 (smaller than 1.5), indicating the flame dose not attain self-turbulization.