Experimental Study on the Basic Phenomena of Flame Stabilization Mechanism in a Porous Burner for Premixed Combustion Application

One solution to intensify heat recirculation in a premixed burner and, thus, to enhance the flame stability is to employ porous inert material. Through the highly stable premixed flames low temperature combustion can be achieved employing high excess air ratios which beneficially results in a reduction of the NO x formation by the thermal pathway. Additionally, minimization of temperature and flow inhomogeneities, insensitivity to the fuel supply fluctuation, and damping of flow pulsations are beneficial properties of a porous burner leading to high power dynamic range. Heat transport properties of the solid porous inert media and the strongly tortuous flow path through this structure play a key role for the internal heat recirculation and for flame stabilization as its macroscopic manifestation. These properties strongly depend on the structure geometry and/or physical properties of the material. With an aim to quantify the contribution of the basic physical processes in a porous burner and to optimize its performance the present work reveals a comprehensive experimental study on the flame stability and emissions of such a burner containing different reticulate ceramic sponge structures. It was shown that in order to quantify the contribution of each heat transport mechanism of the global heat recirculation phenomenon and to estimate its relative importance experiments along a three-dimensional matrix (geometry, material, thermodynamic conditions) are required. The quantification of each relevant heat transport mechanism contribution was achieved using one-dimensional volume averaged analysis and comparison with experiments. Furthermore, such comprehensive experimental data with defined boundary conditions provide a necessary prerequisite for numerical validation cases.