DOUBLE FLAME AND MULTIPLE SOLUTION COMPUTATIONS FOR A WETTED POROUS SPHERE VAPORIZING IN REACTIVE FLOWS

The flame and vaporization characteristics of an n-octane droplet burn ing in reactive flows are investigated through numerical analyses of a convective, reactive flow over a wetted porous sphere under various f low temperatures, Reynolds numbers, and ambient equivalence ratios. Th e Liquid fuel is assumed to come through the porous sphere and vaporiz e at the sphere's surface. The gas flow field is predicted by solving the quasi-steady conservation equations of mass, momentum, and energy, in which gas-phase combustion is modeled by a one-step global finite- rate chemical reaction. Numerical results reveal that multiple solutio ns for flame configurations and vaporization rates exist under certain flow conditions for both rarely oxidizing and reactive flows. Reactiv e flows increase the vaporization rate slightly at low ambient tempera tures, while significantly at high ambient temperatures. Double flames occur in both the upper and lower branch solutions. In the upper bran ch situation, both the premixed and nonpremixed flames merge at relati vely low ambient temperatures, low ambient equivalence ratios, or high Reynolds numbers. In the lower branch solution, however, double flame s do not exist at sufficiently low ambient temperatures or high Reynol ds numbers where the envelope flame does not appear.