The spatio-temporal evolution of laser induced spark ignition of non-premixed gaseous methane and oxygen is investigated. The reactants are injected into an optically accessible combustion chamber from an oxidizer centered shear-coaxial injector. High-speed schlieren imaging and measurements of laser energy deposited are used to characterize ignition behavior at various spark locations throughout the chamber. A spatial map of ignition probability is generated from tests at multiple axial and radial locations from the point of propellant injection. The rate of pressure rise from successful tests reveals two modes of ignition dependent on the location of the laser-induced breakdown, and , based on laser-induced breakdown occurring within reactant jet or in the recirculation region, respectively. Physical processes occurring over multiple timescales throughout the direct ignition method are first discussed. Ignition outcomes associated with the indirect method are determined by the hydrodynamic ejection protruding from the laser spark, the behavior of which is explored in detail using flow statistics extracted from images taken at a single spark location. The spatial–temporal progression of this jet is found to be dependent on deposited laser energy, leading to a relationship between the amount of energy added to the flow and ignition outcome. General bounds for spark location, deposited laser energy, and ejection behavior are identified to predict ignition outcomes. Cases that are an exception from these bounds are investigated in detail to understand the cause of unique behavior. These cases lie within regions of the variable space that are susceptible to stochastic elements of the flow.

中文翻译：

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气态甲烷-氧气模型火箭燃烧室的激光诱导火花点火

研究了非预混合气态甲烷和氧气激光诱导火花点火的时空演化。反应物从以氧化剂为中心的剪切同轴喷射器喷射到光学可访问的燃烧室中。高速纹影成像和沉积激光能量的测量用于表征整个腔室中各个火花位置的点火行为。点火概率的空间图是通过从推进剂喷射点开始的多个轴向和径向位置的测试生成的。成功测试的压力上升速率揭示了两种点火模式，这两种点火模式取决于激光诱导击穿的位置，以及分别基于反应物射流内或再循环区域中发生的激光诱导击穿。首先讨论了整个直接点火方法中多个时间尺度上发生的物理过程。与间接方法相关的点火结果由激光火花突出的流体动力喷射确定，使用从单个火花位置拍摄的图像中提取的流量统计数据详细探索其行为。人们发现，这种射流的时空进展取决于沉积的激光能量，从而导致添加到流体中的能量与点火结果之间存在关系。确定火花位置、沉积激光能量和喷射行为的一般界限，以预测点火结果。对这些界限之外的例外情况进行详细调查，以了解独特行为的原因。这些情况位于易受流动随机元素影响的可变空间区域内。