Mid-infrared CO2 sensor with blended absorption features for non-uniform laminar premixed flames

We develop a novel mid-infrared CO2 absorption sensor exploiting spectrally blended features to characterize thermochemical non-uniformity of laminar premixed flames. A new algorithm for interpreting spectra with significantly blended features is proposed for single line-of-sight multi-transition absorption thermometry. A CO2 sensor covering eight absorption transitions near 2378.0 cm−1 is demonstrated in a laminar premixed CH4/Air flame at an equivalence ratio of φ=1.0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\varphi =1.0$$\end{document}. The average signal-to-noise ratio is 1293 with a measurement time of 1.0 s, and the estimated CO2 detection limit is 42.8 ppm at 1543 K with 6 cm pathlength. Computational fluid dynamics (CFD) simulation with reduced GRI 1.2 mechanism is performed for comparison. Spatially resolved distributions are obtained with the laser absorption spectroscopy (LAS) measurements, combined with postulated distribution from CFD simulation. The LAS measurements agree with the CFD simulation, with a central-zone temperature difference of less than 1.1% and CO2 concentration difference of less than 1.0%. Discrepancy is observed in the boundary layer region due to pronounced mixing with the ambient surroundings. The sensor developed provides a lead for general LAS sensor design (blended absorption features, ambient interference, or under optically thick conditions), and can serve for practical combustion sensing.