Dynamics of Radiative Low-Stretch Diffusion Flames

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This is an experimental and theoretical investigation of the structure and extinction behavior of gaseous diffusion flames at low stretch rates. The low-stretch condition is created by bottom-burning of a fuel mixture discharged from a porous axisymmetric burner of very large radius. Fuels studied include methane, hydrogen, carbon monoxide/hydrogen, and carbon monoxide/methane. Spatially resolved species, temperature, and velocity profiles are measured with laser diagnostics. Flame radiation and burner-surface radiation are also examined. Corresponding theoretical models are developed incorporating a narrowband radiation model. The study consists of five elements: (1) experimental determination of the flammability limit boundaries as functions of stretch rate and the amount of fuel dilution with emphasis on the radiation- induced extinction; (2) experimental exploration for the existence of "flamelets"; (3) experimental mapping of flame structure including hydrodynamic, thermal, and species profiles and radiation intensities from the flame and burner surface; (4) detailed modeling of low-stretch diffusion with detailed chemistry, transport properties, and flame/surface radiation; and (5) development of detailed radiation models including flame-surface interaction in a spectral manner and reevaluation of mean band parameters.