Turbulent flame speeds in ducts and the deflagration/detonation transition
Turbulent flame speeds in ducts and the deflagration/detonation transition
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DOI：
10.1016/j.combustflame.2008.03.011
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发表时间：
2008-07
影响因子：
4.4
通讯作者：
D. Bradley;M. Lawes;Kexin Liu
中科院分区：
文献类型：
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作者：
D. Bradley;M. Lawes;Kexin Liu
提出了一种方法来确定火焰沿着带有挡板的管道传播（在点火端关闭）是否可能发生爆燃到爆炸的转变（DDT）。可燃混合物可以获得最大湍流燃烧速度。如果该值足够高，则会在火焰之前形成强烈的冲击。假设很快就会达到最大燃烧速度，并且根据先前的研究，可以在给定条件下获得该值。由于冲击，反应物温度和压力的增加进一步增加了最大湍流燃烧速度。火焰前方的气体速度与数值分析中的一维冲击波方程相关。预测的管道火焰速度与适当的最大湍流燃烧速度与在一系列 CH4-空气和 H2-空气混合物的慢速和快速火焰状态下测量的结果非常一致。如果反应物在可用时间内发生自燃，并且在相同温度和压力下预计的火焰速度接近查普曼-茹格速度，则滴滴涕是可能的。第一个条件的预测需要混合物在冲击温度和压力下的自燃延迟时间值。第二个预测需要层流燃烧速度和马克斯坦数的值。通过这些参数的适当值，可以从数字上看出CH4-空气中不存在DDT。对于氢气-空气，DDT 的起始值接近于实验观察到的当量比值。尽管无法预测 DDT 的细节，但不同管道尺寸的影响也可以预测。将研究扩展到更广泛的燃料需要更多关于较高温度和压力下的层流燃烧速度和马克斯坦数以及较低温度和压力下的自燃延迟时间的数据。
A methodology is proposed for determining whether a deflagration-to-detonation transition (DDT) might occur for flame propagation along a duct with baffles, closed at the ignition end. A flammable mixture can attain a maximum turbulent burning velocity. If this is sufficiently high, a strong shock is formed ahead of the flame. It is assumed that this maximum burning velocity is soon attained and on the basis of previous studies, this value can be obtained for the given conditions. The increase in temperature and pressure of the reactants, due to the shock, further increases the maximum turbulent burning velocity. The gas velocity ahead of the flame is linked to one-dimensional shock wave equations in a numerical analysis. The predicted duct flame speeds with the appropriate maximum turbulent burning velocities are in good agreement with those measured in the slow and fast flame regimes of a range of CH4–air and H2–air mixtures. DDTs are possible if autoignition of the reactants occurs in the time available, and if the projected flame speed approaches the Chapman–Jouguet velocity at the same temperature and pressure. Prediction of the first condition requires values of the autoignition delay time of the mixture at the shocked temperatures and pressures. Prediction of the second requires values of the laminar burning velocity and Markstein number. With the appropriate values of these parameters, it is shown numerically that there is no DDT with CH4–air. With H2–air, the onset of DDT occurs close to the values of equivalence ratio at which it has been observed experimentally. The effects of different duct sizes also are predicted, although details of the DDT cannot be predicted. Extension of the study to a wider range of fuels requires more data on their laminar burning velocities and Markstein numbers at higher temperatures and pressures and on autoignition delay times at lower temperatures and pressures.