Determination of Gas Temperatures at 295–1273 K Using CO Vibrational-Rotational Absorption Spectra Recorded with an FT-IR Spectrometer

Abstract

Fourier transform infrared absorption spectroscopy has been used to determine the rotational temperatures of high-temperature (≤1273 K) CO/N2 gas samples. To achieve this objective, a special gas cell was constructed which permitted the acquisition of absorption spectra of samples containing CO at concentrations of 1–10% by volume in N2 and at temperatures between 295 and 1273 K. The absorption spectra were recorded with the use of a moderate-resolution (0.25 cm−1) FT-IR spectrometer. The rotational temperatures were calculated from the spectra after rigorous correction for photometric errors. Temperatures calculated from the P branch of CO spectra had accuracies of 3.2% or better. In all cases, the calculated temperatures were lower than temperatures recorded with a thermocouple, which had an accuracy of ±0.75%. An important factor in the success of these determinations was the adoption of measures to prevent the modulated spectral emission of the hot gases from reaching the detector.

Application of FT-IR Absorption Spectroscopy for in Situ Gas Concentration and Temperature Measurements in Laboratory- and Pilot-Scale Combustion Environments

“…The largest percent difference, for any one spectrum was 4.9 %. These results are as good as those previously reported from a pure gas environment, 6 at similar temperatures. There is no evidence that the combustion environment has affected the accuracy of the calculation methodology.…”

“…A detailed explanation of the theory associated with the calculation of gas temperatures and concentrations from infrared absorption spectra has already been presented by Medvecz et al, [6][7][8] and will not be discussed here. For the pilot reactor, the beam traveled from the interferometer into a 48-in.…”

“…The quality of these spectra are as good as those obtained in a high temperature gas cell, reported in previous work. 6 , 7…”

“…5 More recently, calculation methodologies have been reported for the determination of gas concentrations and temperatures from high temperature (up to 1250 K) FT-IR absorption spectra. [6][7][8] These methodologies included corrections for photometric errors resulting from the limited resolution of the spectrometer (which cause distortions of the absorbance peak height and width) and corrections for the temperature dependence of the absorption coefficients for many CO and CO2 vibrational-rotational absorption lines.…”

“…In previous work by Medvecz, 6 , 7 CO and CO2 were the two gas species most thoroughly evaluated. This was done in anticipation of the application of FT-IR absorption spectroscopy to the combustion processes.…”