1 kHz MID-IR ABSORPTION SPECTROSCOPY FOR CO AND CO2 CONCENTRATION AND TEMPERATURE MEASUREMENT

A sensor for in situ combustion gas measurements of concentration and temperature of carbon monoxide (CO) and carbon dioxide (CO2) has been developed and tested on a temperature calibrated diffusion flame burner in order to measure combustion efficiency. The fundamental bands of both molecules are exploited using distributed feedback quantum cascade lasers near 4.40 and 4.58 mu m at which the absorption line-strengths are multiple orders of magnitude larger than overtone and combination bands at lower wavelengths. Spectra were taken at a rate of 1 kHz across a 50.8-mm path length of an ethylene (C2H4)air diffusion flame at heights of 5 to 25 mm above the burner and at equivalence ratios ranging from 0.5 to 1.5. Total combustion efficiency was measured using the concentrations of CO and CO2, and temperature was obtained from relative strengths of multiple CO2 absorption lines with differing lower state energies. The results are compared to previous coherent anti-Stokes Raman spectroscopy (CARS) temperature measurements and equilibrium chemical calculations.