Porous burner as well as a method for operating a porous burner

Abstract

The invention relates to a porous burner with a housing, which has an inlet for a fuel-air mixture and an outlet for the exhaust gas mixture generated in the burner, where in flow-direction of the fuel-air mixture the housing contains an ignition space with an ignition device and adjacent to this space a porous burner medium. On the inlet side the ignition space is provided with a stabilizing element, which reduces the inlet cross-section and directs the flow of the fuel-air mixture essentially perpendicular to the inlet cross-section of the porous medium. The porous burner is provided with a device for controlling the mass flow of the fuel-air mixture, which serves to shift the combustion zone from the ignition space into the porous medium.

1 . A porous burner comprising a housing, which housing has an inlet for a fuel-air mixture and an outlet for the exhaust gas mixture generated in the burner, an ignition space with an ignition device and, following said ignition space, a porous medium being provided in the housing in flow direction of the fuel-air mixture, wherein the ignition space contains a stabilizing element at its inlet side, which reduces the inlet cross-section and directs the flow of the fuel-air mixture essentially perpendicular to the inlet cross-section of the porous medium, and wherein the porous burner is provided with a device for controlling the mass flow of the fuel-air mixture. 
   
   
       2 . A porous burner according to  claim 1 , wherein in front of the stabilizing element in flow direction of the fuel-air mixture, there is located a mixing chamber for pretreatment of combustion air and liquid fuel 
   
   
       3 . A porous burner according to  claim 2 , wherein the mixing chamber is heatable. 
   
   
       4 . A porous burner according to  claim 1 , wherein the stabilizing element is a perforated ceramic plate. 
   
   
       5 . A porous burner according to  claim 4 , wherein the perforated ceramic plate has a flow cross-section which amounts to 10% to 30% of the free flow cross-section of the porous burner. 
   
   
       6 . A porous burner according to  claim 4 , wherein the perforated ceramic plate has a flow cross-section which amounts to 15% to 20% of the free flow cross-section of the porous burner. 
   
   
       7 . A porous burner according to  claim 4 , wherein the diameters of the bores in the perforated plate are dimensioned such that the flames are quenched in the case of flame blowback, with the diameters of the bores amounting to 8% to 15% of the thickness of the perforated plate. 
   
   
       8 . A porous burner according to  claim 4 , wherein the diameters of the bores in the perforated plate are dimensioned such that the flames are quenched in the case of flame blowback, with the diameters of the bores amounting to approximately 10%, of the thickness of the perforated plate. 
   
   
       9 . A porous burner according to  claim 4 , wherein the perforated ceramic plate is attached to the inlet of the porous burner by means of a conical clamping ring. 
   
   
       10 . Method for operating a porous burner, which has an ignition space with an ignition device in flow direction of the fuel-air mixture in front of a porous medium, comprising:
 a) directing and accelerating the flow of the fuel-air mixture essentially perpendicular to the inlet cross-section of the porous medium by means of a perforated plate at the inlet of the ignition space;   b) ignition of the fuel-air mixture in the ignition space and stabilization of a flame front in a combustion zone on the side of the perforated plate facing the porous medium;   c) increasing the mass-flow of the fuel-air mixture and shifting the combustion zone into the porous medium.   
   
   
       11 . Method according to  claim 10 , wherein in the case of liquid fuels the fuel-air mixture is prepared in a heatable mixing chamber located in front of the perforated plate. 
   
   
       12 . Method according to  claim 10 , wherein the air ratio λ is increased for the purpose of increasing mass flow of the fuel-air mixture at the transition from start-up phase to steady-state operation.