Behaviour of a Methane/Air Turbulent Diffusion Flame Expanding from a Porous Burner

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Abstract
This paper reports numerical simulations of unconfined CH4/Air turbulent diffusion flame which expands from a porous burner. Turbulent combustion is modelled using an Eddy Dissipation Concept (EDC) coupled with a RNG κ − ε statistical model for the turbulent flow. Radiation heat transfer which results from the formation of soot particles in the flame is represented using PI-approximation for the calculation of the irradiance field and transport submodels for the determination of soot volume fraction and soot number density. Appropriate source terms allow to reproduce the main phenomena (nucleation, coagulation, surface growth[tdot]) which appear during the expansion of soot field in the flaming zone. The set of coupled transport equations is solved numerically using a finite volume method, including a high order Ultra-Quick convective scheme to avoid numerical dissipation. The velocity-pressure coupling is treated with a projection technique. The numerical results obtained for pool fire regime show that the flow pattern is characterized by the development of large structures which appear during the expansion of the thermal plume above the flame. The corresponding flow regime is unsteady and induces large oscillations of the average flame height.

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