MEASUREMENTS OF PARTICLE FLAME TEMPERATURES USING 3-COLOR OPTICAL PYROMETRY

A three-color near-infrared optical pyrometer, with wavelengths center ed at 998, 810, and 640 nm, was used to monitor the combustion of poly mer particles. Individual spherical poly(styrene) particles, 47-355 mu m in diameter, burned in air at 1050-1400 K gas temperatures, surroun ded by sooting, diffusion envelope flames. The pyrometric results were interpreted in view of two models for soot radiation: (a) A conventio nal model, which assumes that the flame is optically thin and isotherm al and thus, the spectral emissivity is inversely proportional to the wavelength. With this method the calculated flame temperatures are ave rages, biased to areas with high temperature and/or soot concentration . (b) An alternative model, in which the envelope flames are assumed t o be again optically thin but nonisothermal in the radial direction. T he theoretical development of the latter model is included herein. For nonisothermal flames the spectral emissivity was shown to be nearly i ndependent of the wavelength. This model in conjunction with three-col or pyrometry may provide a way of estimating the highest temperature o f soot in the flame, as well as the temperature gradient across the fl ame. Temperatures calculated this way were higher by 200-230 K than th ose calculated using the conventional model. Experimental results sugg est that the agreement among the three individual temperatures obtaine d from three-color pyrometry depends on which of the above models for soot radiation is used. Based on the agreement between temperatures, t he degree of isothermality of the flame may be determined and thus, in dications about the controlling processes during combustion (oxygen di ffusion or volatile combustion) may be obtained. However, additional w ork is needed, involving simpler, one-dimensional flame configurations to confirm this model.