Two-dimensional simulations of steady perforated-plate stabilized premixed flames

Abstract

The objective of this work is to examine the impact of the operating conditions and the perforated-plate design on the steady, lean premixed flame characteristics. We perform two-dimensional simulations of laminar flames using a reduced chemical kinetics mechanism for methane–air combustion, consisting of 20 species and 79 reactions. We solve the heat conduction problem within the plate, allowing heat exchange between the gas mixture and the solid plate. The physical model is based on a zero-Mach-number formulation of the axisymmetric compressible conservation equations. The results suggest that the flame consumption speed, the flame structure, and the flame surface area depend significantly on the equivalence ratio, mean inlet velocity, the distance between the perforated-plate holes and the plate thermal conductivity. In the case of an adiabatic plate, a conical flame is formed, anchored near the corner of the hole. When the heat exchange between the mixture and the plate is finite, the flame acquires a Gaussian shape stabilizing at a stand-off distance, that grows with the plate conductivity. The flame tip is negatively curved; i.e. concave with respect to the reactants. Downstream of the plate, the flame base is positively curved; i.e. convex with respect to the reactants, stabilizing above a stagnation region established between neighboring holes. As the plate's thermal conductivity increases, the heat flux to the plate decreases, lowering its top surface temperature. As the equivalence ratio increases, the flame moves closer to the plate, raising its temperature, and lowering the flame stand-off distance. As the mean inlet velocity increases, the flame stabilizes further downstream, the flame tip becomes sharper, hence raising the burning rate at that location. The curvature of the flame base depends on the distance between the neighboring holes; and the flame there is characterized by high concentration of intermediates, like carbon monoxide.

Keywords:

• laminar premixed flames
• perforated-plate stabilized flames
• flame–wall interactions
• flame consumption speed
• stand-off distance

Acknowledgments

This work was supported by Research and Technology Center, Robert Bosch LLC, Palo Alto, CA, King Abdullah University of Science and Technology (KAUST), Award No KUS- I1-010-01, and US Department of Energy, University Turbine Systems Research Program, grant DE-FC26-02NT41431.

Notes

¹The corrected equations in [26] are: Equation (31): C _ρ≡ρ/T(v−1/c _pReSc Z).∇ T Equation (33): E _ρ≡∑ _{i = 1} ^N ∇.(ρv Y _i )+(1/ReSc)∇.(ρ Y _i V _i )− Y _i ∇.(ρv)/W _i Equation (35): ε_ρ≡− ∑ _{i = 1} ^N Daw _i /W _i

²The surface temperature of the plate is undefined in the case when conductivity is zero, since the boundary wall acts as an insulating boundary. In this case, there is no flame–wall heat exchange. The temperature on the surface and within the plate, thus, is an artifact of the initial conditions, which does not impact the flow-field.