Spectral radiation intensities of a turbulent buoyant ethylene flame: CFD-aided tomographic inversion

Radiation heat transfer has been found to dominate fire spread in large-scale fires. The radiation heat loss of buoyant turbulent fires is coupled with fluid mechanics, combustion processes, and soot/gas concentrations. Deconvolution of these combined phenomena can facilitate the development of combustion and radiation models for use in predictive fire modeling. Therefore, in this work, line-of-sight spectral radiation intensities have been measured from a buoyant turbulent pool-fire-like ethylene diffusion flame. In an attempt to be representative of practical turbulent fires, a burner of 15.2 cm in diameter was used. Temporal measurements of radiation intensity were obtained with a fast (400 Hz) mid-infrared spectrometer at a horizontal plane located at half a burner diameter above the burner. Measurement statistics, including mean, root mean square (RMS), probability density function (PDF) of line of sight intensity, and intermittency are reported herein for wavelengths dominated by soot and CO2 radiation. The data show that radiation is affected by large-scale vortical motions, resulting in varying flame intermittency in the radial direction. Radial distributions of local scalar properties (temperature and soot volume fraction) were calculated through tomographic inversion, using measured data at multiple soot radiation wavelengths. The inversion technique was coupled with the results of a computational fluid dynamics (CFD) fire simulation code. CFD results were used to construct PDFs and spatial correlations for the scalars of interest. The estimated scalars are shown to be consistent with values from the literature, and mean and RMS radiation intensities computed from these scalars are in good agreement with measurements.