Measurement of soot temperature, emissivity and concentration of a heavy-oil flame through pyrometric imaging

This paper presents the monitoring and characterization of emissive properties of soot particles in heavy oil flames based on pyrometric imaging techniques. The soot temperature is derived from the relationship between the primary colors of flame images captured by a RGB camera. The emissivity of soot particles is then estimated by using the gray-level ratio of a primary color of the image to that of a blackbody source at the same temperature. The soot concentration is represented and estimated by KL factor, which is derived from the Hottel and Broughton's model once the emissivity is determined. The imaging system is calibrated using a blackbody furnace as a standard temperature source. The measurement accuracy is verified by applying the system to measure the true temperature of a tungsten lamp. The maximum relative error is about 0.9%. Experiments were conducted on a 9MWth industrial-scale combustion test facility to investigate the impact of the ratio of overfire air to total air, and the location of overfire air ports on the soot temperature, emissivity and concentration of a heavy oil flame.