Validation and calibration of a spectroscopic technique for determination of gas plume temperature

Results are reported from a continuing program of research into the physics and spectroscopy of heated stack plumes. Simultaneous thermocouple and spectrometer measurements are used to study sideways-directed plumes from an internal combustion engine and a propane-burning plume generator. A previously-reported result, that the ratio of optically thin signals from two CO2 transitions can be used to determine plume temperature, is confirmed by comparison of thermocouple and spectrometer measurements over a wide range of temperatures. The basic physics of molecular emission and absorption of radiation is discussed and is used to calibrate the relationship between the spectroscopic ratio and plume temperature. The result is a spectroscopic plume temperature diagnostic that contains no adjustable parameters, and can be calibrated by use of published absorption spectra. Data relating to the accuracy of the technique are discussed.