Structure and Radiation Properties of Luminous Turbulent Acetylene/Air Diffusion Flames

Abstract

An experimental and theoretical study of the structure and radiation properties of luminous, round, turbulent acetylene/air diffusion flames is described. Measurements were made of mean and fluctuating velocities, mean concentrations, laser extinction (514 and 632.8 nm), spectral radiation intensities (1200–5500 nm), and radiative heat fluxes. The measurements were used to evaluate structure predictions based on the laminar flamelet concept, and radiation predictions based on a narrow-band model both ignoring and considering turbulence/radiation interactions. State relationships needed for the laminar flamelet concept were found from auxiliary measurements in laminar flames. Predictions were encouraging; however, quantitative accuracy was inferior to earlier findings for luminous flames. This is attributed to the large radiative heat loss fractions of acetylene/air flames (approaching 60 percent of the heat release rate); coupled structure and radiation analysis should be considered for improved results. The findings suggest significant turbulence/radiation interactions (increasing spectral intensities 40–100 percent from estimates based on mean properties); and that soot volume fractions may approximate universal fractions of mixture fraction in turbulent acetylene/air diffusion flames.