High-Temperature Spectral Emissivities of H_2O–CO_2 Mixtures in the 27-μ Region

Spectral emissivities in the 2.7-μ band were obtained for hot gas mixtures of CO2 and H2O between 1000°K and 2200°K for various (CO2/H2O) sample ratios. The emission measurements were made at the exit of a small tripropellant rocket burner which produced the variable (CO2/H2O) mixtures by burning hydrogen, oxygen, and carbon monoxide. The spectral emissivities were determined from a calibrated emission spectrum and a spectroscopic determination of the temperature of the hot gas. The composition was evaluated from a semiempirical fit to a thermochemical flow calculation. The hot CO2–H2O mixtures were observed at a total pressure of 1 atm in the optically thin absorption region with a constant geometric pathlength. The variations of the spectral emissivities as a function of temperature are given for constant density of CO2 and H2O in the optical path. The experimental results agree with semitheoretically derived predictions. The characteristic area ratios of the integrated emissivities or integrated radiances within portions of the 2.7-μ band were derived and given as a function of temperature and (CO2/H2O) sample ratio. These area ratios can be used to determine the (CO2/H2O) concentration in hot gas samples.