Development of multicolor pyrometers to monitor the transient response of burning carbonaceous particles

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Abstract
A three‐color ratio pyrometer has been developed to obtain surface temperatures and high‐temperature combustion rates of burning carbonaceous particles. The features and performance of this instrument are contrasted to those of a two‐color ratio pyrometer, constructed earlier for similar studies. The three‐color pyrometer employs a visible (0.65 μm) and two near‐infrared (0.80 and 0.975 μm) wavelengths. The instrument uses a single optical fiber to capture radiation emitted from a particle burning in a high‐temperature laminar flow furnace. Monitoring of the combustion events takes place coaxially with the particle flow, from observation windows located at the top of the furnace injectors. Thus, the temperature‐time history of burning particles can be recorded. The radiation flux is split into three beams using dichroic edge filters. Narrow (or medium) bandwidth interference filters guide monochromatic radiation to solid‐state silicon photodetectors. The associated amplification is linear and/or logarithmic. In contrast, the two‐color pyrometer used a bifurcated optical fiber bundle to split radiation to two medium bandwidth interference filters centered at 0.80 and 1.0 μm. Silicon detectors were employed, associated with linear amplification. Both instruments were used to monitor the combustion temperature‐time behavior of burning highly homogeneous, spherical, and monodisperse carbonaceous particles, and their performance is discussed herein.