The charge density in a flame contains important information about the combustion processes that is difficult to obtain due to fast, complex, and highly exothermic reactions. This paper presents a study of using electrostatic probes to measure the charge density in methane fired diffusion and premixed flames. The sensing principle, practical design, and performance assessment of the electrostatic probe are presented. Comparative experimental studies with a reference ion-current sensor carried out on a combustion test rig indicate that the fluctuation of the signal from the electrostatic probe arises from the variation in the charge density in a flame. A dimensionless index, combining the average of local peak values in the electrostatic signal with the flame oscillation frequency, is adopted as an indicator of the charge density. Experimental results demonstrate that the charge density in a methane diffusion flame has an increasing trend with the fuel flowrate varying from 0.80 L/min to 1.20 L/min. The charge density in a methane-air premixed flame yields a decreasing trend with the equivalence ratio ranging from 0.54 to 0.75, then increases and reaches a local peak at the equivalence ratio of 1.03, and continues to increase when the equivalence ratio varies from 1.03 to 3.50. The charge density in the inner cone is higher than that in the outer cone for diffusion and premixed flames. The results obtained suggest that the developed electrostatic probe and the index can be used to indicate the charge density in diffusion and premixed flames.

中文翻译：

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使用静电探针测量甲烷燃烧扩散和预混火焰中的电荷密度


火焰中的电荷密度包含有关燃烧过程的重要信息，但由于快速、复杂且高度放热的反应，这些信息很难获得。本文介绍了使用静电探针测量甲烷燃烧扩散和预混合火焰中的电荷密度的研究。介绍了静电探针的传感原理、实用设计和性能评估。在燃烧试验台上进行的参考离子电流传感器的对比实验研究表明，静电探针信号的波动是由火焰中电荷密度的变化引起的。采用无量纲指标，将静电信号中局部峰值的平均值与火焰振荡频率相结合，作为电荷密度的指标。实验结果表明，随着燃料流量从0.80 L/min到1.20 L/min变化，甲烷扩散火焰中的电荷密度呈增加趋势。当量比在0.54~0.75范围内，甲烷-空气预混火焰中电荷密度呈下降趋势，当量比为1.03时，电荷密度增大并达到局部峰值，当量比在1.03~1.03范围内，电荷密度继续增大。 3.50。对于扩散和预混合火焰，内锥体中的电荷密度高于外锥体中的电荷密度。所得结果表明，所开发的静电探针和指数可用于指示扩散火焰和预混合火焰中的电荷密度。