Approximate two-color emission pyrometry

Approximate methods for the determination of a temperature field using pure emission pyrometry applied to a two-dimensional nonoptically thin flame wi thout variation along a line of sight are presented. In the absence of an a bsorption measurement, emission pyrometry depends on theoretical spectral i nformation. Limitations of existing techniques stem from the fact that spec tral information is a function of temperature only for the optically thin s ituation, by and large the situation to which current techniques apply, and temperatures above 1000 K. Through extensive narrow-band calculation using a simulated flame over polymethylmethacrylate, we show that the spectral i nformation contained in the equivalent bandwidth ratio is approximately a c onstant for the 2.8 mum/1.8 mum band pair and appropriate bandwidths. The c onstant can be evaluated from emission measurements at a point where the te mperature is known or can be estimated using, e.g., the maximum flame tempe rature of a stimulated flame and the peak band intensities. The temperature field evaluated with this approximately constant value of the equivalent b andwidth ratio, A(r), is accurate to within five percent for temperatures d own to 450 K.