A numerical investigation of the flame stability in porous burners employing various ceramic sponge-like structures

In order to optimize the porous burner for the application as a pilot burner of stationary gas turbines aiming to reduce NOx emissions a fundamental study investigating the influence of the thermo-physical properties of the porous structure on the flame stabilization in a porous burner was conducted. This work presents a numerical study of the stability of one-dimensional laminar premixed flame in porous inert ceramic sponge structure. A set of steady computations are considered, using a numerical model that takes into account solid and gas energy equations as well as detailed chemistry. The model considers additionally the enhancement of both, thermal and species diffusivity by the flow dispersion, whereas the dispersion coefficients of the investigated structures have been determined from three-dimensional flow simulations using MRI (magnet resonance imaging) and CT (computer tomography) data to regenerate the real sponge structures. Hence, it was possible to calculate a thickened flame front as it was detected in experiments, too. The computations were conducted for different operational conditions and different burner configurations in respect to geometrical and material properties of the porous inert media. The numerical predictions showed very good agreement with the corresponding experimental stability data. The obtained numerical results were used for the formulation of a simple stability model based on the Pe number that enables a prediction of the lean blow-off limits in the combustion systems employing porous burner concept.