Radiation from Turbulent Nonluminous and Luminous Diffusion Flames PDF Download

Author: United States. National Bureau of Standards
Publisher:
ISBN:
Category :
Languages : en
Pages : 75

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Book Description
A theoretical and experimental study of the structure and radiation properties of turbulent buoyant diffusion flames is described. The results have application to modeling fires within structures, materials test methods, fire detection, and effects of materials on fire properties. The investigation consists of two phases, as follows: study of effects of turbulence/radiation interactions, considering the properties of nonluminous hydrogen/air diffusion flames; and study of extension of the laminar flamelet concept to soot properties needed to predict radiation from luminous acetylene/air and ethylene/air turbulent diffusion flames. Theory and experiment are considered in both phases of the investigation. Measurements in turbulent hydrogen/air diffusion flames yielded radiation fluctuation intensities of 20-110 percent, providing direct evidence of the importance of turbulence/radiation interactions. A stochastic analysis, based on the laminar flamelet concept, was developed which provided encouraging predictions of mean and fluctuating spectral radiation intensities (average discrepancies between predictions and measurements were roughly 30 percent), as well as temporal power spectral densities of radiation fluctuations. The temporal spectra exhibit energy-containing and inertial regions, very similar to other turbulence properties, although the rate of decay of the spectra with increasing frequency in the inertial region is somewhat greater than observed for scalar fluctuations. Measurements and predictions in the turbulent luminous flames concentrated on scalar properties (particularly soot volume fractions) in the overfire region. Predictions of scalar properties based on the laminar flamelet concept were very encouraging. Direct evaluation of soot volume fraction state relationships for the overfire region was hampered by effects of turbulent fluctuations and experimental uncertainties; nevertheless, within these limitations, soot volume fraction state relationships were nearly universal, and soot generation efficiencies nearly constant, for sufficiently long residence times. However, effects of finite-rate chemistry were noted for short residence time ethylene/air flames, causing spatial variations of soot generation efficiencies in the overfire region. For long residence times, present measurements of soot generation efficiencies were in reasonably good agreement with earlier findings for acetylene/air and ethylene/air diffusion flames.