Online Measurement of the Flame Temperature and Emissivity during Biomass Volatile Combustion Using Spectral Thermometry and Image Thermometry

In this paper, a method for the simultaneous measurement of the flame temperature and emissivity using spectral thermometry and image thermometry was proposed; experiments were conducted using a laboratory furnace burning solid particle fuel derived from biomass. First, a non-gray emissivity model with a third-order polynomial function was established, and the accuracy of the temperature estimates obtained from the gray emissivity model, the non-gray emissivity model, and the Hottel and Broughton emissivity model was determined. The results showed that the proposed non-gray emissivity model had the highest accuracy and the maximum relative error compared to the thermocouple measurements was less than 1.5%. Second, the spectral emissivity obtained from the spectral thermometry was used to correct the image pyrometer data. The two-dimensional distributions of the flame temperature and emissivity are measured after correction using image pyrometry. It showed that the results of the spectral thermometry and image thermometry were highly consistent with the thermocouple measurements and the maximum relative errors were 1.5 and 3.2%, respectively. Finally, the effects of the equivalent ratio on the temperature and spectral emissivity were investigated. The results showed that the maximum temperature of the volatile combustion flame was 1000-1250 K and the maximum emissivity of the flame ranged from 0.05 to 0.25 in the equivalent ratio range of 0.91-0.71. The maximum temperature and emissivity decreased as the equivalent ratio decreased.