Experimental determination of CO spectral line strengths and self-broadening coefficients at combustion-relevant temperatures.

This work examines the derivation of key spectral parameters of carbon monoxide (CO), including self-broadening coefficients, temperature dependence exponent, and line strengths, for eight transitions within the fundamental absorption band around 4.85 μm. Accurate characterization of these properties is essential for advancing CO sensors utilizing laser absorption spectroscopy (LAS). The selected spectral region exhibits strong absorption while effectively minimizing interference from combustion byproducts, including CO as well as HO. Using the selected quantum cascade laser (QCL) light source and a custom-built static chamber designed for elevated temperature and pressure conditions, a spectral measurement setup for high temperatures was built to obtain high-resolution absorption spectra in the range of 500-1000 K. Through fitting analysis, high-precision spectral parameters were inferred and compared with the HITRAN2020 database, showing a relative difference of less than 6 %. To validate precision and practical relevance of these parameters, the CO concentration was determined from the integrated absorbance of the CO absorption feature at 2055.4 cm in the ethylene(CH)-air flame, and flame temperature was determined using a dual-line thermometry method to validate the precision of the obtained parameters. The high-temperature spectral characteristics obtained not only ensure the effectiveness of target spectral line selection and the accuracy of measurement results in subsequent measurement system development, but also serve as a supplement and correction to existing molecular spectral databases.