RADIATION FROM TURBULENT DIFFUSION FLAMES
G. M. Faeth
The thermal radiation properties of nonluminous and luminous turbulent diffusion flames are reviewed, considering: the scalar structure of flames, excluding soot; soot properties of luminous flames; and turbulence/radiation interactions. Progress has been greatest for nonluminous flames. Scalar structure needed to analyze radiation properties is generally estimated using the laminar flamelet concept, e.g., approximating turbulent flames as wrinkled laminar flames, noting that the scalar properties of laminar flames are nearly universal functions of fuel-equivalence ratio. Estimates of spectral radiation intensities and radiative heat fluxes based on these ideas are typically within 20−30 percent of measurements. Extension of the laminar flamelet concept to the properties of soot which influence radiation from luminous flames has been studied. There is some evidence to support the extension and radiation predictions based on this idea; however, additional evaluation of the concept is needed. Turbulence/radiation interactions have been studied using stochastic analysis. The effects of turbulence/radiation interactions are most significant for luminous flames, where turbulent fluctuations can increase heat fluxes up to 2−3 times higher than estimates based on mean properties.
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