Time-resolved imaging of flame kernels: Laser spark ignition of H2/O2/Ar mixtures
Time-resolved imaging of flame kernels: Laser spark ignition of H2/O2/Ar mixtures
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DOI：
10.1016/0010-2180(94)00278-z
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发表时间：
1995-08
影响因子：
4.4
通讯作者：
T. A. Spiglanin;A. Mcilroy;E. Fournier;R. B. Cohen;J. Syage
中科院分区：
文献类型：
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作者：
T. A. Spiglanin;A. Mcilroy;E. Fournier;R. B. Cohen;J. Syage
研究了激光诱导火花点火氢气/空气混合气体中火焰核的形状和结构随气体成分和时间的变化规律。使用平面激光诱导荧光（PLIF）来测量反应区内产生的OH自由基的空间分布，我们已经记录了一系列的图像后，激光诱导火花的初生火焰核的演变。该系列提供了火焰增长的速率，火焰形状的演变，以及PLIF信号的强度作为点燃火焰和非点燃事件的时间的函数。反应区在早期快速增长，但随着火焰核内能量密度的降低，传播速率缓慢下降。在扩展火花和火焰核中观察到明显的各向异性。在短时间内（t < 100 μs），观察到的环形形状类似于以前在甲烷/空气中的电极火花点火和激光点火所看到的环形形状。火焰也有向点火激光器方向生长的趋势。在最初的100 μs内，成功点火与失败点火几乎相同。在火花之后的100和500 μs之间出现显著的差异，特别是在强度上。这些观察结果意味着，早期的火焰核心增长占主导地位的气体运动引起的短持续时间的火花。点火的最终命运取决于反应的化学性质，它决定了气体是否经历了从热等离子体到传播火焰的转变。
The shape and structure of developing flame kernels in laser-induced spark ignited hydrogen/air mixtures is investigated as a function of gas composition and time. Using planar laser-induced fluorescence (PLIF) to measure the spatial distribution of OH radicals produced inside the reaction zone, we have recorded the evolution of the nascent flame kernel in a series of images following the laser-induced spark. This series provides the rate of flame growth, the evolution of the flame shape, and the intensity of the PLIF signal as a function of time for both igniting flames and nonignition events. The reaction zones grow quickly at early times, but slowly decrease in propagation rate as the energy density within the flame kernel decreases. A distinct anisotropy is observed in the expanding spark and flame kernel. At short times (t < 100 μs), a toroidal shape is observed similar to that seen previously for electrode-spark ignitions and for laser ignitions in methane/air. There is also a tendency for the flame to grow back toward the ignition laser. Successful ignitions appear virtually identical to failed ignitions during the first 100 μs. Significant differences, notably in intensity, appear between 100 and 500 μs following the spark. These observations imply that early flame kernel growth is dominated by gas motion induced by the short-duration spark. The ultimate fate of an ignition lies with the chemistry of the reactions which determines whether the gas undergoes a transition from hot plasma to propagating flame.