Abstract The present work proposed an index to extend the previous lean blowout detection method to bluff-body stabilized flame at the condition of low Reynolds number. Dynamic characteristics near lean blowout of low Reynolds number bluff-body flame are not exactly same with that of high Reynolds number bluff-body flame. Thus lean blowout detection index requires modification for low Reynolds number bluff-body flame. The flame images show that, for a fixed fuel flow, increase of air flow to a certain value can cause flame liftoff-reattachment events, and further increase of air flow can lead to complete liftoff and even lean blowout. Temporal and spectral analyses of the ion current and CH* signals exhibit that both standard deviation and low frequency energy within 0.2–10 Hz of each signal first increase due to flame liftoff-reattachment and then decrease due to complete flame liftoff with the increase of air flow. This leads to that the lean blowout detection indexes including the normalized root mean square (NRMS), normalized cumulative duration (θ) and fraction of the fast Fourier transform (FFT) power at low-frequencies ( F F T % [ 0 - f 1 H z ] ) first increase and then decrease with the increase of air flow. As a result, the flame at the liftoff state may be wrongly classified as stable state. To avoid this, the histogram distributions of two signals were investigated. The number of small value sample points of each signal increases with increase of air flow, indicating that the percentage of small value sample points can be used to detect lean blowout. The mean value of each signal at the liftoff-reattachment state is used as the threshold value to classify small value sample points. For either the ion current signal or CH* signal, percentage of sample points below the corresponding threshold value ( P k ) is used to detect lean blowout. The flame is considered as close to lean blowout when P k reaches 50%. Experimental results show that P k can be used for reliable detection of lean blowout for bluff-body stabilized flame at the condition of low Reynolds number.

中文翻译：

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钝体稳定火焰的精益爆裂检测

摘要 本工作提出了一种指标，将以往的稀燃检测方法扩展到低雷诺数条件下的钝体稳定火焰。低雷诺数钝体火焰的接近贫燃喷出的动力学特性与高雷诺数钝体火焰的动力学特性并不完全相同。因此，对于低雷诺数钝体火焰，稀薄喷出检测指数需要修改。火焰图像表明，对于固定的燃料流量，空气流量增加到一定值会引起火焰升空-再附着事件，进一步增加空气流量会导致完全升空甚至贫燃。离子电流和 CH* 信号的时间和光谱分析表明，标准偏差和低频能量均在 0 以内。每个信号的 2-10 Hz 首先由于火焰升空-重新附着而增加，然后随着空气流量的增加，由于火焰完全升起而减少。这导致包括归一化均方根 (NRMS)、归一化累积持续时间 (θ) 和快速傅立叶变换 (FFT) 功率分数 (FFT % [ 0 - f 1 H z ] ) 随风量的增加先增大后减小。结果，处于升空状态的火焰可能被错误地归类为稳定状态。为了避免这种情况，研究了两个信号的直方图分布。每个信号的小值采样点的数量随着空气流量的增加而增加，表明小值采样点的百分比可用于检测稀燃。将每个信号在提离再附着状态下的平均值作为阈值对小值样本点进行分类。对于离子电流信号或 CH* 信号，低于相应阈值 (P k ) 的采样点百分比用于检测贫燃。当 P k 达到 50% 时，火焰被认为接近贫燃。实验结果表明，P k 可以可靠地检测低雷诺数条件下钝体稳定火焰的贫燃。