Diffusion-flame burning of fuel-vapor pockets in air

• Published in: Combustion and flame Vol. 98; no. 3; pp. 180 - 196
• Main Authors: Fendell, F.E., Bush, W.B., Mitchell, J.A., Fink, S.F.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.08.1994; Elsevier Science
• Subjects: 400800 - Combustion, Pyrolysis, & High-Temperature Chemistry; Applied sciences; CHEMICAL REACTION KINETICS; COMBUSTION KINETICS; Combustion. Flame; DIFFUSION; Energy; Energy. Thermal use of fuels; Exact sciences and technology; FLUID FLOW; FUEL-AIR RATIO; FUELS; GAS FUELS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; KINETICS; MATHEMATICAL MODELS; REACTION KINETICS; SUPERSONIC FLOW; Theoretical studies; Theoretical studies. Data and constants. Metering; Diffusion flame; Ignition; Theoretical study; Combustion; Models; Gas phase; Flame propagation
• ISSN: 0010-2180; 1556-2921
• DOI: 10.1016/0010-2180(94)90234-8

We examine analytically, with numerical assistance, the unsteady, diffusively limited burnup of initially unmixed fuel vapor and gaseous oxidizer. We study three simple spherical geometries: (1) an initially uniform sphere of fuel vapor immersed in an unbounded expanse of oxidizer; (2) a variant on case 1 in which only a finite concentric annulus of enveloping oxidizer is available for the burning of the initially uniform sphere of fuel vapor; and (3) an impervious sphere, consisting initially of one uniform hemisphere of fuel vapor and one uniform hemisphere of oxidizer. Of particular interest is the time interval for the exhaustion of the lean reactant, as a function of the fuel-to-oxidizer stoichiometry and the sphere radius. The motivation for these studies is to ascertain the fate of inhomogeneous blobs that arise as a consequence of imperfect fuel/air mixing, e.g., in the context of a supersonic combustor. In such a context, an inhomogeneous blob of gaseous mixture, idealized to have the geometry of a sphere, is examined as a Lagrangian element, as it is convected downstream, without slip, by the surrounding gaseous flow. The longest time for diffusional burnup, for the spherically enclosed geometries, arises for the case in which the fuel vapor and oxidizer are present in stoichiometric proportion.