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首页> 外文期刊>Combustion and Flame >Experimental analysis of laser-induced spark ignition of lean turbulent premixed flames: New insight into ignition transition
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Experimental analysis of laser-induced spark ignition of lean turbulent premixed flames: New insight into ignition transition

机译：稀薄湍流预混火焰的激光诱导火花点火实验分析：点火过渡的新见解

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Recently, Shy and his co-workers reported a turbulent ignition transition based on measurements of minimum ignition energies (MIE) of lean premixed turbulent methane combustion for a wide range of equivalence ratios. Our study used a similar approach to present an additional and complete MIE data set for laser-induced spark ignitions in a flow configuration and under turbulent conditions (i.e., for different ranges of length and time scales) that differed from those chosen by Shy and his colleagues. To extend the previous analyses to very lean premixed methane/air flames, the study examined a characteristic chemical time (τ_(cb)). which was defined as the start of the chain-branching reactions. Physically, this chemical time corresponded to the time when the initial chemical reactions of the ignition process released enough heat to compensate for heat losses and to enable a self-sustained reaction in successful ignition. Values for τ_(Cb), which were experimentally obtained from the temporal evolution of the mean hot kernel emissions (in laminar flow), strongly decreased with the equivalence ratio 0 for very lean flames and remained nearly constant and equal to 150 μs for O > 0.7. We obtained a clear turbulent ignition transition on the MIE as a function of the rms velocity (u') and reconfirmed the two modes of ignition. Temporal kernel emission recordings served to describe the transition through the study of the interaction between the turbulence and the hot kernel at the time t = τ_(Cb)- For low turbulence, when the smallest time scales of the turbulence τ_K were larger than the τ_(CB)b values, the hot kernel/turbulence interaction occurred after the initiation of the chemical reactions. The amount of deposited energy required to initiate the reactions and to attain a self-sustained flame kernel was consequently similar to that found under laminar conditions. After the transition, the smallest time scales of the turbulence were smaller than the τ_(Cb) values. Turbulence may have affected and interacted with the hot kernel before the initiation of chain-branching reactions occurred. Larger amounts of deposited energy were therefore required to compensate for this turbulent dissipation and to attain a self-sustained flame. A Peclet number (Pe_(CB)) was introduced, which is equal to the ratio of the turbulent diffusivity at the time of the initiation of the chemical reactions and the thermal diffusivity. These very scattering MIE data (dependent on O and u') are plotted as a function of Pe_(CB) and collapsed into a single curve with two drastically different increasing slopes showing the ignition transition.
机译：最近，Shy和他的同事报告了在较宽的当量比范围内，根据稀薄预混湍流甲烷燃烧的最小点火能量（MIE）的测量结果，湍流点火过渡。我们的研究使用了类似的方法来呈现额外的和完整的MIE数据集，该数据集用于在气流配置中以及在湍流条件下（即，对于不同的长度和时间范围）与激光所引起的火花点火，与Shy和他选择的方法不同。同事。为了将先前的分析扩展到非常稀薄的甲烷/空气预混合火焰，该研究检查了特征化学时间（τ_（cb））。定义为链支化反应的开始。在物理上，该化学时间对应于点火过程的初始化学反应释放出足够的热量以补偿热量损失并能够在成功点火中实现自我维持的时间。 τ_（Cb）的值是通过实验得出的平均热核发射量（层流中）的时间演变而得到的，对于非常稀薄的火焰，当量比为0时，τ_（Cb）急剧减小，对于O>，其值几乎保持恒定并等于150μs。 0.7。我们在MIE上获得了明显的湍流点火过渡，作为有效值速度（u'）的函数，并再次确认了两种点火模式。时间内核发射记录通过研究t =τ_（Cb）时湍流与热内核之间的相互作用来描述过渡过程-对于低湍流，当湍流τ_K的最小时间尺度大于τ_时（CB）b值表示，热核/湍流相互作用在化学反应开始后发生。因此，引发反应并获得自持火焰核所需的沉积能量与层流条件下的沉积能量相似。过渡之后，湍流的最小时间尺度小于τ_（Cb）值。在发生链支化反应之前，湍流可能已经影响了热谷粒并与之相互作用。因此，需要大量的沉积能量来补偿这种湍流耗散并获得自持的火焰。引入了佩克利数（Pe_（CB）），该数等于化学反应开始时的湍流扩散率与热扩散率之比。这些非常分散的MIE数据（取决于O和u'）被绘制为Pe_（CB）的函数，并折叠成一条曲线，其中两个截然不同的增加的斜率显示了点火过渡。

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