Extinction timescales of periodically strained, lean counterflow flames
Extinction timescales of periodically strained, lean counterflow flames
复制标题
周期性紧张、稀薄逆流火焰的熄灭时间尺度
DOI：
10.1007/s003480050345
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发表时间：
1999
影响因子：
2.4
通讯作者：
J. Whitelaw
中科院分区：
文献类型：
--
作者：
K. Sardi;J. Whitelaw
非强制和周期性强制湍流逆流火焰的熄灭极限已经测量了当量比的相关稀燃燃气轮机。因此，相对的流包括在两个流中具有在0.5至0.7范围内的相同当量比的甲烷和空气的混合物，以及在一个流中具有小于0.7的当量比和在另一个流中具有0.9的当量比的混合物。的振荡施加扬声器和强制火焰熄灭被证明取决于脉动的总持续时间。通过用特定频率、振幅和持续时间的正弦信号强制流动来测量消光时间，如果没有发生消光，则增加脉动时间，并重复该过程直到发生消光。一种形式的化学发光被用来观察有和没有振荡的火焰前锋和轴向和径向速度分量的门控测量量化的相位滞后之间的输入信号和流量作为一个函数的frequency.Extinction应变率增加当量比和大于对称火焰相同的燃料总量和总当量比低于0.7，基于两种流的燃料和空气混合物。例如，总当量比为0.6的非对称火焰在比对称火焰高70%的体应变率下熄灭。强制火焰承受瞬时应变率大于非强制火焰熄灭的临界值，并存活了高达100个周期的频率范围从200到1000赫兹的瞬时应变率等于非强制熄灭的限制。 对称火焰具有较短的熄灭时间尺度，并且比相同燃料总量的不对称火焰对当量比的变化更敏感。可视化显示，从CH自由基发出的光强度随速度信号的相位而变化，使得它最初随着应变的增加而降低，并且随着应变的减少而增加，这与熄灭然后重新点亮的趋势一致。
The extinction limits of unforced and periodically forced turbulent counterflow flames have been measured with equivalence ratios of relevance to lean-burn gas turbines. Thus, the opposed flows comprised mixtures of methane and air with the same equivalence ratios in the two streams in the range of 0.5 to 0.7 and also mixtures with equivalence ratios less than 0.7 in one flow and the other with an equivalence ratio of 0.9. The oscillations were imposed by loudspeakers and forced flame extinction was shown to depend on the total duration of pulsation. Extinction times were measured by forcing the flow with a sinusoidal signal of specified frequency, amplitude and duration and, if extinction did not occur, the time of pulsation was increased and the procedure was repeated until extinction took place. A form of chemiluminescence was used to observe the flame front with and without oscillation and gated measurements of the axial and radial velocity components quantified the phase lag between the input signal and the flow as a function of frequency.Extinction strain rates increased with equivalence ratio and were greater for asymmetric than symmetric flames with the same total quantity of fuel and total equivalence ratios below 0.7, based on the fuel and air mixtures of both streams. For example, asymmetric flames of 0.6 total equivalence ratio extinguished at bulk strain rates 70% higher than those of symmetric flames. The forced flames withstood instantaneous strain rates larger than the critical values for unforced flame extinction and survived for up to 100 cycles in the frequency range from 200 to 1000 Hz with instantaneous strain rates equal to the unforced extinction limit. Symmetric flames had shorter extinction timescales and were more sensitive to changes in the equivalence ratio than asymmetric flames of the same total quantity of fuel. The visualisation showed that the light intensity emitted from CH radicals varied in phase with velocity signals so that it initially decreased with increasing strain and increased as the strain reduced, consistent with a tendency to extinguish and then re-light.