Direct Determination of Effective Spectral Emissivity of Hot Burnt Gas using Absolutely Calibrated Radiometric Spectrometer

Measurement of the radiative characteristics of a flame is important in the field of combustion diagnostics to better understand combustion processes, fuel performance, and combustion engine efficiency. Flame emissivity is one of the most important parameters for investigating such characteristics. This paper proposes a method to directly measure the effective spectral emissivity of a hot burnt gas in flame. We calibrate the radiometric measurement of a mid-infrared (IR) emission spectrometer using a directly heated graphite blackbody in a national standards laboratory, and determine the flame temperature by fitting the spectrum detected with the emission spectrometer to the color ratio calculated with HITEMP using the species concentrations predicted by ICT thermodynamic calculation. For proof of concept, we determine the spectral effective emissivity of the flame of an IR countermeasure flare in the spectral range of 2–5 μm. We estimate the uncertainty in the measurement to be 11.48 %.