MODELING GRAVITY EFFECT ON DIFFUSION FLAMES STABILIZED AROUND A CYLINDRICAL WICK SATURATED WITH LIQUID FUEL

Abstract

The familiar flames from candles and oil lamps are representative examples of wick-stabilized diffusion flames. The shape and burning characteristics of these flames depend strongly on gravity-induced buoyant flows. To obtain a better understanding of the gravity effect, a diffusion flame model has been formulated and numerically solved. In the computation, gravity is treated as a parameter, spanning from zero to the high blowoff limit. The model includes realistic wick and candle geometry but assumes that the wick surface is coated with liquid fuel. The gas-phase formulation consists of the full Navier–Stokes equations with a one-step finite-rate overall chemical reaction. Gas-phase flame radiation, important in low gravity near the quenching limit, is included by solving the axisymmetric radiation transfer equation using the S _N discrete ordinates method. The computed results include flame and flow structures, heat flux distributions, the energy budget, and the overall burning characteristics as a function of gravity and wick diameter.

Keywords:

• diffusion flame
• candle flame
• gravity effect

ACKNOWLEDGEMENTS

This research has been supported by a grant from the NASA Office of Biological and Physical Sciences with Dr. Daniel Dietrich as the grant monitor. Ammar Alsairafi wishes to thank the fellowship support from Kuwait University.

Notes

¹We note, however, that the flame shape as represented by the reaction rate contour has an inward hook toward the wick while the visible flame does not. This is a common shortcoming of using one-step kinetics to represent the visible flame in the stabilization zone. From the fundamental point of view, visible flame comes from the chemiluminescence of species in the reaction zone (Takahashi and Katta, 2002; Walsh et al., 1998).

^aFrom Villermaux and Durox (1992).

^bFrom Arai and Amagai (1993).