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Role of instability on the limits of laterally strained detonation waves

机译：不稳定性对横向拉伸波浪极限的作用

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The present work examines the role of instability and diffusive phenomena in controlling the limits of detonations subject to lateral strain. Experiments were conducted in mixtures with varying levels of cellular instability, i.e., stoichiometric methane-oxygen (CH4/2O(2)), ethylene-oxygen (C2H4/3O(2)), and ethaneoxygen (C2H6/3.5O(2)). These detonations were propagated in channels with exponentially enlarging cross-sections, following the recent works of Radulescu and Borzou (2018) and Xiao and Radulescu (2020). Steady detonation waves were obtained at the macro-scale, with the near-limit reaction zone structures characterized by significant unreacted gas pockets. The turbulent flame burning velocity of these pockets was evaluated to be 30 m/s to 70 m/s, which is larger than the theoretical laminar value by a factor of 2 to 7 and smaller than the CJ deflagration speed by a factor of 2 to 3. For all the mixtures tested, the characteristic D - K relationships, relating the detonation mean propagation speed with lateral flow divergence, were obtained directly from experiments and as well from the generalized ZND model with lateral strain rates using detailed chemical kinetics. The results showed that the degree of departure between experiments and the theoretical predictions increases significantly with the detonation instability level. As compared to the laminar ZND wave, the more unstable detonations are much more detonable than the more stable detonations, with substantially larger limiting divergence rates and maximum velocity deficits. Such enhanced detonability with detonation instability can be manifested in the significantly enhanced global rates of energy release with the notably suppressed thermal character of ignition for the more unstable detonations. This globally enhanced burning mechanism is found to be realized by the intensified auto-ignition assisted by the turbulent diffusive burning of the unreacted gas pockets, substantially shortening the characteristic reaction zone lengths. Finally, the relatively good universality of the D/D-CJ - K-eff lambda relations implicitly suggests that cell size is also a function of the detonation wave stability, since it is controlled by the reaction zone thickness of unstable detonations. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
机译：目前的作品研究了不稳定性和扩散现象在控制受横向菌株的爆炸的限制方面的作用。在具有不同水平的细胞不稳定性水平的混合物中进行实验，即化学计量甲烷 - 氧（CH 4 / 2O（2）），乙烯 - 氧（C 2 H 4 / 3O（2））和乙烯氧基（C2H6 / 3.5O（2）） 。在最近的Radulescu和Borzou（2018）和Xiao和Radulescu（2020）的最新作品之后，这些爆炸在具有指数扩大的横截面的通道中传播。在宏观级别获得稳定的爆震波，近极限反应区结构以显着的未反应气囊为特征。这些口袋的湍流火焰燃烧速度被评估为30米/秒至70米/秒，比理论层的层数大于2至7的倍数，小于CJ丝液速度为2倍3.对于所测试的所有混合物，将爆轰平均传播速度与横向流动分歧的爆轰平均传播速度相关，并通过使用详细的化学动力学与横向应变速率的广义ZnD模型一起获得。结果表明，随着爆轰不稳定水平，实验与理论预测之间的出发程度显着增加。与层流ZnD波相比，更不稳定的爆炸比更稳定的爆炸更令人淤积，具有基本上更大的限制性速度和最大速度缺陷。这种具有爆轰不稳定性的这种增强的可恶性可以在显着增强的全球能量释放速率下表现出与爆炸的较大抑制出点火的热性特征，以便更不稳定的爆炸。发现该全球增强的燃烧机构是通过由未反应的气囊的湍流扩散燃烧的强化自动点火来实现，基本上缩短了特征反应区长度。最后，D / D-CJ - K-EFF Lambda关系的相对良好的普遍性地表明，电池大小也是爆轰波稳定性的函数，因为它由不稳定的爆炸的反应区厚度控制。 （c）2020燃烧研究所。由elsevier Inc.出版的所有权利保留。

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