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Shapes of Buoyant and Nonbuoyant Laminar Jet Diffusion Flames

Shapes of Buoyant and Nonbuoyant Laminar Jet Diffusion Flames

Shapes of Buoyant and Nonbuoyant Laminar Jet Diffusion

Shapes of Buoyant and Nonbuoyant Laminar Jet Diffusion Flames P. B. SUNDERLAND* National Research Council, Cleveland, OH 44135 B. J. MENDELSON Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544 Z.-G. YUAN National Center for Microgravity Research, Cleveland, OH 44135 D. L. URBAN NASA Lewis Research Center, Cleveland, OH 44135 Flame shapes were measured for buoyant and nonbuoyant laminar gas jet diffusion flames burning, methane, ethane, and propane in quiescent air. Test conditions involved burner diameters of 0.19–5.5 mm, ambient pressures of 0.25–2 atm, and fuel flowrates of 0.04–4.6 mg/s. Care was taken to minimize interference from soot emissions and from ignition disturbances. Microgravity conditions were obtained in the 2.2-s drop tower at the NASA Lewis Research Center. Normalized lengths of both buoyant and nonbuoyant flames were proportional to source Reynolds number, but the nonbuoyant flames were 40% longer on average. Normalized widths of the nonbuoyant flames were constant for Re 100, whereas buoyant flame widths scaled with source Froude number. Several nonbuoyant flame models are evaluated with the present shape data. © 1998 by The Combustion Institute NOMENCLATURE D mass diffusivity d burner inside diameter Fr source Froude number: Fr u 2 /gd g acceleration of gravity L stoichiometric or luminous flame length ṁ fuel mass flowrate p ambient pressure Re source Reynolds number: Re ud/ 4ṁ/d St source Stokes number: St Fr/Re T temperature t time after ignition t ch characteristic time u area-averaged fuel source velocity: u 4 ṁ/d 2 w maximum stoichiometric or luminous flame width z axial distance source fuel dynamic viscosity at 298 K source fuel density at p and 298 K *Corresponding author. NASA Lewis Research Center, M.S. 500-115, 21000 Brookpark Rd., Cleveland, OH 44135. E-mail: pbs@einstein.lerc.nasa.gov INTRODUCTION Laminar gas jet diffusion flames are fundamental to combustion. Their study has contributed to myriad advances in combustion science, including the development of theoretical, computational, and diagnostic combustion tools. Laminar jet flames are pertinent to the turbulent flames of more practical interest via the laminar flamelet concept [1, 2]. Flame shape is an important characteristic of laminar diffusion flames that has been modeled and measured using numerous techniques. Shape can be profoundly affected by gravity; thus observations of shapes at varying gravitational level are especially useful in the evaluation of models. Until now there has been no robust set of measurements of microgravity gas jet stoichiometric flame shapes and, in contrast to numerous correlations of flame length, empirical correlations of widths of laminar gas jet flames are conspicuously absent from the literature. The proportionality between laminar jet flame length and fuel mass flowrate, and the independence of length from pressure and COMBUSTION AND FLAME 116:376–386 (1999) 0010-2180/99/$19.00 © 1998 by The Combustion Institute PII S0010-2180(98)00045-5 Published by Elsevier Science Inc.

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