Abstract: A burner with a housing enclosing a combustion chamber and with an inlet for a gas/air fuel mixture and an outlet for combustion gas is disclosed. The combustion chamber is filled with a porous material whose porosity varies along the combustion chamber in such a way that the pore size increases in the direction of flow of the gas/air mixture so that a critical Peclet number for the pore size and accordingly for flame development results at a boundary surface or in a determined zone of the porous material, above which number a flame can develop and below which number the flame development is suppressed.