温度-浓度耦合变量下甲烷吸收谱线关联分析

采用可调谐激光吸收光谱技术对甲烷体积分数进行检测时,由于测量环境温度变化导致气体吸收谱线线强发生变化,将对测量结果造成不可避免的影响。基于直接吸收光谱法分析不同甲烷体积分数(1.0%～15.0%)在温度290～350 K时吸收谱线特性变化规律,采用多项式回归和共享参数全局线性拟合得到温度-甲烷体积分数耦合变量甲烷光谱吸光度关联式。结果表明:相同温度下,甲烷光谱吸光度A随甲烷体积分数升高而增大;相同甲烷体积分数下,由于总配分函数比值r_Q在甲烷吸收光谱线强随温度变化过程中占据主导作用,r_Q随温度增大的线性降低使得甲烷线强随温度升高而减小;在甲烷体积分数1.0%～15.0%、测量温度290～350 K时,温度-甲烷体积分数耦合变量甲烷光谱吸光度关联式的反演结果相对误差小于1.000%。

Correlation analysis of methane absorption lines with coupling variables of temperature and concentration

When using tunable diode laser absorption spectroscopy to detect methane on-line, the line intensity of methane absorption spectrum is affected by the change of ambient temperature, which has inevi-table impacts on measurement results. Based on the direct absorption spectroscopy method, the absorption spectrum properties of methane with different concentrations (1%~15%) and temperatures (290~350 K) were analyzed, and the correlation between temperature-concentration coupling variables and spectral absorbance of methane was obtained by polynomial regression and global linear fitting of shared parameters. The results show that the spectral absorbance A of methane increases with the increase of concentration at the same temperature. At the same concentration, the ratio of total partition function rQ plays a dominant role in the process of methane absorption spectrum line intensity changing with temperature and the linear decrease of rQ with the increase of temperature, which results that the methane line intensity decreases with temperature increasing. When the methane concentration is in the range of 1%~15% and the ambient temperature is 290~350 K, the relative error between the inversion result of correlation and the simulation data of HITEMP spectrum platform is less than 1%.