Hydrodynamic effects of shock interactions on initial flame kernel development of close dual-point laser induced sparks
Hydrodynamic effects of shock interactions on initial flame kernel development of close dual-point laser induced sparks
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DOI：
10.1016/j.proci.2023.01.001
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发表时间：
2023-02
影响因子：
3.4
通讯作者：
S. Nakaya;Ren Eto;Takuto Yamaguchi;Takahiro Koseki;M. Tsue
中科院分区：
文献类型：
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作者：
S. Nakaya;Ren Eto;Takuto Yamaguchi;Takahiro Koseki;M. Tsue
对近双点激光诱导火花火焰核的形成进行了实验研究，重点研究了激光诱导火花产生的激波相互作用所引起的流体动力学效应。利用532 nm Nd:YAG激光器发射的射线劈裂，在燃烧室中心附近产生双火花。甲烷/空气混合物在静息条件下在定容室中点火，并详细测量了点火能量和压力历史。采用logistic回归法推导出最小点火能为可燃性为50%的点火能。用高速摄像机对火焰核的起裂过程进行了纹影摄影观察。通过调整反射镜和透镜的角度来调整激光诱导火花的偏移量。从最小点火能量和燃烧诱导时间两方面详细研究了单点和闭合双点激光击穿诱导火花的点火性能。时间分辨纹影照片表明，在一定条件下，在激光火花所定义的对称面附近，两个驼峰状核在初始阶段迅速生长。它们的形成是由于马赫数激波引起的水动力效应，是双激波相互作用的结果。近双点激光诱导火花在1.0 MPa时的最小点火能量远低于单点激光诱导火花在0.1 MPa时的最小点火能量，但大于单点激光诱导火花的最小点火能量。近双点激光诱导火花的燃烧诱导时间，即最大增压速率所对应的时间，在高压下明显缩短。在马赫数激波形成的条件下，近双点激光诱导火花形成了坚固的火焰核，提高了稀薄混合物在高压下的点火性能。
Flame kernel formations of close dual-point laser induced sparks were investigated experimentally, focusing on the hydrodynamic effects induced by an interaction of shock waves produced by the laser induced sparks. Dual sparks were produced near the center of the combustion chamber by splitting of a ray emitted by a 532 nm Nd:YAG laser. Methane/air mixtures were ignited under a quiescent condition in a constant volume chamber with detailed measurements of the ignition energy and the pressure history. The minimum ignition energy was derived as an ignition energy having an ignitability of 50% using the logistic regression method. The flame kernel initiation process was also observed by Schlieren photography using a high-speed video camera. The offset of laser induced sparks were adjusted by tuning angles of mirrors and lenses. The ignition performance of single- and close dual-point laser breakdown induced sparks was investigated in detail in terms of the minimum ignition energy and the combustion induction time. Time resolved Schlieren photographs indicated that two hump shaped kernels grew rapidly during the initial stage in the vicinity of the plane of symmetry defined by the laser sparks under certain conditions. Their formation was due to the hydrodynamic effects induced by Mach shock waves, which resulted from interactions of the dual shock waves. The minimum ignition energy of the close dual-point laser induced sparks near the lean limit at 1.0 MPa was much lower than that of single-point laser induced sparks, although it was greater than that of the single ones at 0.1 MPa. The combustion induction time, which was defined as the time corresponding to the maximum pressure increase rate, was shortened for close dual-point laser induced sparks, especially for lean mixtures at high pressure. Robust flame kernels were formed by close dual-point laser induced sparks with Mach shock wave formation, and improved ignition performance for lean mixtures at high pressure was observed.