Abstract This paper describes an analysis of the near-lean blow off (LBO) dynamics of spray flames, including the influence of fuel composition upon these dynamics. It is motivated by the fact that, while reasonable correlations exist for predicting blowoff conditions, the fundamental reasons for why flames supported by flow recirculation actually blow off are not well understood. Prior work on gaseous systems has shown that the blowoff event is a culmination of several intermediate processes, initiating with local extinction of reactions (“stage 1”), followed by large scale changes in flame and flow dynamics (“stage 2”), finally leading to blowoff. In this study, near-LBO dynamics were characterized for ten liquid fuels with widely varying kinetic and physical properties. Results were compared at two air inlet temperatures, 450 and 300 K, as this influences the relative importance of physical and kinetic properties in controlling LBO. Extinction, re-ignition, and recovery of the flame are evident from these data, and grow in frequency as blowoff is approached. Results show that after a near-blowoff event, the flame can move upstream at velocities much faster than the flow velocity, corresponding to re-ignition. Nonetheless, the majority of the flame recovery events appear to be associated with convection of hot products back upstream, not re-ignition. In contrast, downstream motion of the flame faster than the flow, which would correspond to bulk flame extinction, was never observed. This indicates that “extinction events” actually correspond to convection of the flame downstream by the flow when it loses its stabilization point. The dependence of the equivalence ratio when these events appear, their frequency, and event duration were quantified as a function of fuel composition and air inlet temperature. For example, the data shows a higher percentage of recovery from near-blowoff events through re-ignition for high DCN fuels at the 450 K air temperature condition. These extinction/re-ignition results suggest that high DCN fuels are harder to blow off than low DCN fuels through two mechanisms: (1) by delaying the onset of LBO precursor events, and (2) because they are able to recover from these precursor events through re-ignition more often.

中文翻译：

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液体燃料燃烧器中的近贫排放动力学

摘要 本文描述了对喷射火焰的近贫吹散 (LBO) 动力学的分析，包括燃料成分对这些动力学的影响。其动机是这样一个事实，虽然存在合理的相关性来预测吹气条件，但流动再循环支持的火焰实际吹气的根本原因尚不清楚。先前对气体系统​​的研究表明，吹出事件是几个中间过程的高潮，以反应的局部消失开始（“阶段 1”），然后是火焰和流动动力学的大规模变化（“阶段 2”），最后导致吹气。在这项研究中，对 10 种具有广泛变化的动力学和物理特性的液体燃料的近 LBO 动力学进行了表征。结果在两个进气口温度 450 和 300 K 下进行比较，因为这会影响物理和动力学特性在控制 LBO 中的相对重要性。从这些数据可以明显看出火焰的熄灭、重新点燃和恢复，并且随着接近吹气而增加频率。结果表明，在接近吹散事件之后，火焰可以以比流速快得多的速度向上游移动，对应于重新点燃。尽管如此，大多数火焰恢复事件似乎与热产品返回上游的对流有关，而不是重新点燃。相比之下，从未观察到火焰的下游运动比流动快，这对应于整体火焰熄灭。这表明“熄灭事件”实际上对应于流动失去稳定点时火焰下游的对流。当这些事件出现时，当量比的相关性、它们的频率和事件持续时间被量化为燃料成分和进气温度的函数。例如，数据显示，在 450 K 空气温度条件下，对于高 DCN 燃料，通过重新点火，从接近吹散事件中恢复的百分比更高。这些消光/重燃结果表明高 DCN 燃料比低 DCN 燃料更难通过两种机制吹掉：(1) 通过延迟 LBO 前体事件的发生，以及 (2) 因为它们能够从这些前体中恢复通过重新点火更频繁地发生事件。数据显示，在 450 K 空气温度条件下，通过重新点燃高浓度 DCN 燃料，从接近爆燃事件中恢复的百分比更高。这些消光/重燃结果表明高 DCN 燃料比低 DCN 燃料更难通过两种机制吹掉：(1) 通过延迟 LBO 前体事件的发生，以及 (2) 因为它们能够从这些前体中恢复通过重新点火更频繁地发生事件。数据显示，在 450 K 空气温度条件下，通过重新点燃高浓度 DCN 燃料，从接近爆燃事件中恢复的百分比更高。这些消光/重燃结果表明高 DCN 燃料比低 DCN 燃料更难通过两种机制吹掉：(1) 通过延迟 LBO 前体事件的发生，以及 (2) 因为它们能够从这些前体中恢复通过重新点火更频繁地发生事件。