Double Flame and Multiple Solution Computations for a Wetted Porous Sphere Vaporizing in Reactive Flows

Abstract

The flame and vaporization characteristics of an n-octane droplet burning in reactive flows are investigated through numerical analyses of a convective, reactive flow over a wetted porous sphere under various flow temperatures, Reynolds numbers, and ambient equivalence ratios. The liquid fuel is assumed to come through the porous sphere and vaporize 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 solutions for flame configurations and vaporization rates exist under certain flow conditions for both rarely oxidizing and reactive flows. Reactive flows increase the vaporization rate slightly at low ambient temperatures, while significantly at high ambient temperatures. Double flames occur in both the upper and lower branch solutions. In the upper branch situation, both the premised and nonpremixed flames merge at relatively low ambient temperatures, low ambient equivalence ratios, or high Reynolds numbers. In the lower branch solution, however, double flames do not exist at suffficiently low ambient temperatures or high Reynolds numbers where the envelope flame does not appear.

Key Words:

• Theoretical analysis
• droplet ignition
• droplet vaporization
• porous sphere

Additional information

Notes on contributors

T. L. JIANG

To whom correspondence should be addressed.