Measurements and inverse calculations of spectral radiation intensities of a turbulent ethylene/air jet flame

Fast (6250 Hz) line-of-sight measurements of infrared spectral radiation intensities (Iλ) from a luminous flame and a new deconvolution technique for the estimate of local scalar properties using inverse radiation calculations are reported. Time series data of Iλ for one diametric and nine chord-like radiation paths in a representative horizontal plane were measured. Statistical properties of Iλ, including mean, root mean square (rms), probability density function, autocorrelation coefficient, and power spectral density, were obtained from the time series data. The measured statistical properties of Iλ at two representative wavelengths, which are dominated by carbon dioxide (CO2) and soot radiation, respectively, are reported. The autocorrelation coefficient data show large negative loops with repeatable zero crossings at 20 ms and minimum values as low as −0.2 at 30-40 ms. Radial distributions of mean and rms CO2 mole fractions and temperatures were estimated using inverse calculations of mean Iλ at two different wavelengths dominated by CO2 radiation in conjunction with the relationship of these quantities to mixture fractions. Soot volume fraction distributions were also estimated using inverse calculations of mean Iλ at a wavelength dominated by continuum soot radiation. The estimated local mixture fraction distributions were in reasonably good agreement with sampling data from similar flames. The calculated mean Iλ from 1.4 to 4.8 μm other than those used in the inverse calculations matched the experimental data well. The present method provides non-intrusive measurements of major gas species and temperature statistics in turbulent soot containing flames not accessible to other optical diagnostics.