Local measurement of gas temperature with an infrared fiber-optic probe

A fibre-optic probe has been developed for measuring the gas temperature in flames. The principal feature of the method is that the probability distribution function of the gas temperature can be obtained locally in a particle-loaded gas flow. Instant gas temperatures are determined from infrared emission spectra obtained from the interior of a 1.3 MW pulverized coal flame. Thermal radiation from different positions in the furnace is collected with the infrared fibre-optic probe and the emission spectra are measured with a Fourier transform infrared spectrometer. The experiments show that the instant local gas temperature can be extracted from the brightness temperature spectrum at the 2350 cm(-1) fundamental band of CO2, at which self-absorption is minimized. The brightness temperature spectrum is very useful for evaluation of the measurement, in that the measuring conditions for applying the method are fulfilled. Good agreement is observed between the temperatures measured with the infrared probe and those measured with a suction pyrometer. The performance and characteristics of the infrared relative to the suction pyrometer method as well as laser methods in flames are compared and discussed. The gas temperature profile and probability distribution functions can be obtained even faster with the infrared probe than can the mean gas temperature with a conventional suction pyrometer.