Quantitative Measurement of Equivalence Ratios of Methane/Air Mixture by Laser-Induced Breakdown Spectroscopy: the Effects of Detector Gated Mode and Laser Wavelength
ZUO Peng1, LI Bo1*, YAN Bei-bei2, LI Zhong-shan1, YAO Ming-fa1
1. State Key Laboratory of Engines，Tianjin University，Tianjin 300072，China 2. School of Environment Science and Engineering，Tianjin University，Tianjin 300072，China
Abstract：Laser-induced breakdown spectroscopy (LIBS) has been increasingly used in combustion diagnostics as a novel spectral analysis method in recent years. The quantitative local equivalence ratio of methane/air mixture is determined by LIBS using different emission intensity ratios of H/O and H/N. The comparison between calibration curves of H656/O777 and H656/N746 is performed in gated mode, which shows that H656/O777 can achieve better prediction accuracy and higher sensitivity. More spectral intensity ratios (H656/O777, H656/N+500, H656/N+567 and H656/N746) can be used to make calibration measurements in ungated mode and H656/O777 is also tested best among them. The comparison between gated and ungated detection modes shows that gated mode offers better accuracy and precision. In addition, the effects of different laser wavelengths (1 064, 532 and 355 nm) on LIBS spectra and calibration curves are investigated with laser focal point size and laser fluence kept constant. The results show that with longer laser wavelength, the peak intensity and SNR of H, O and N lines increase, as well as the slope of calibration curve of H656/O777. Among these three wavelengths, 1 064 nm laser is best suited to measure the equivalence ratio of CH4/air mixture by LIBS. The experimental results are explained in terms of plasma electron density and temperature, which have a significant impact on the emission intensity and the partition function of hydrogen and oxygen, respectively.
Key words：Laser-induced breakdown spectroscopy;Equivalence ratio;Gated mode;Laser wavelength;Electron density;Electron temperature
左 鹏1，李 博1*，颜蓓蓓2，李中山1，尧命发1 . 基于激光诱导击穿光谱技术定量测量甲烷/空气混合当量比的实验研究：门控模式及激光波长的影响分析 [J]. 光谱学与光谱分析, 2015, 35(11): 2990-2995.
ZUO Peng1, LI Bo1*, YAN Bei-bei2, LI Zhong-shan1, YAO Ming-fa1 . Quantitative Measurement of Equivalence Ratios of Methane/Air Mixture by Laser-Induced Breakdown Spectroscopy: the Effects of Detector Gated Mode and Laser Wavelength . SPECTROSCOPY AND SPECTRAL ANALYSIS, 2015, 35(11): 2990-2995.
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