Investigation of sooting flames by color-ratio pyrometry with a consumer-grade DSLR camera.

The accurate measurement of temperature in sooty flames remains a challenging task. In this study, the procedure for calibration and use of a consumer-grade digital single-lens reflex (DSLR) camera for the measurement of temperature in sooty flames using color-ratio pyrometry (CRP) is elucidated. Owing to the necessity of acquiring RAW images for CRP, investigations conducted thus far have been limited to stable flames. In this work, the potential of a CANON EOS 550D DSLR camera for measuring temperature during a transient process such as a droplet combustion event at frame rates up to 50 fps is demonstrated. The spectral response curves of the camera-lens system were obtained with the help of a tunable laser source and a laser power meter, which were subsequently used to generate lookup tables for blackbody as well as soot radiation. Soot radiation was assumed to vary with wavelength (λ) as λ, where α is the soot dispersion exponent. The blackbody lookup table was validated against blackbody calibration data from 1023 to 1773 K. Experiments were conducted on a candle flame as well as a McKenna flat flame burner with ethylene-air mixtures of equivalence ratios 2.1 and 2.3. For estimating temperatures using CRP, soot particles were classified as nascent and mature soot with soot dispersion exponent (α) values of 4 and 1.38, respectively. The CRP results were found to yield a decent match with thermocouple measurements as well as data reported in the literature.