FR2710726A1 - Radiant gas burner for stove or hob. - Google Patents

Abstract

Gas burner, for stove or cooker hob, comprising a combustion head (1, 101) and a mixing chamber (11, 111), said head having a porous radiant element (4, 104), said chamber (11, 111) being arranged below the radiant element (4, 104) and receiving air and gas for feeding said radiant element with an air/gas mixture, at least one element (12, 112) forming an obstacle to the circulation of the air/gas mixture being arranged in said chamber (11, 111), characterised in that the element forming an obstacle (12, 112) defines, with the internal faces of the mixing chamber (11, 111), a circulation blade, in which the air/gas mixture is forced to circulate, being in contact with said internal faces so as to cool them.

Description

The present invention relates to gas burners of the radiant type,

  for cookers or hobs. Such a burner conventionally comprises a head having a porous radiant element, the front face of which defines the combustion face of the burner. Under this radiant element is arranged a chamber in which air and gas mix before reaching said element. Such a radiant type gas burner is for example used to produce hobs with an appearance close to that of hobs which include hobs made of glass ceramic material, the front face of the radiant element flush with the plane top of the table in which said burner is integrated. A hob of this type has in particular been described in the international patent application of the

  Applicant published under number WO-92/06334.

  Gas burners of the radiant type known to date nevertheless have the following major drawback: the containers to be heated being very close to the combustion faces of the radiant elements (the space between a container and a radiant element to allow the evacuation of combustion gas is only a few millimeters), it occurs by convection and conduction of significant heat transfers to the volumes which

  are located under the radiant elements.

  These heat transfers can cause untimely ignitions of the air / gas mixture in the mixing chamber, upstream of the normal combustion zone. They can also produce rapid deterioration of the seal which is interposed between the

  combustion head and the body that carries it.

  They can damage those of the electronic components which are located under the hob surface. A main object of the invention is to solve this problem. Gas burners are already known in which at least one element forming an obstacle to the circulation of the air / gas mixture is disposed in the mixing chamber. In this regard, it is advantageous to refer to patent EP-157,432 in which a gas burner of this type is described. The element forming an obstacle to the circulation of the air / gas mixture therein is a deflector which is arranged in the center of the chamber, and which serves to distribute

  uniformly the combustible mixture on the radiant element.

  The burner according to the invention is characterized in that the obstacle-forming element defines with the internal faces of the mixing chamber a circulation blade in which the air / gas mixture is forced to circulate while being in contact with said faces

  interior so as to cool them.

  In a preferred embodiment of the invention, the obstacle-forming element is a bell, this bell having a bottom surrounded by walls extending from said bottom towards the bottom of the mixing chamber, the interior of this bell being supplied with air and gas, the mixture formed in said bell discharging from the latter in the vicinity of the bottom of the mixing chamber, then rising to the radiant element by circulating in the circulation blade defined between the walls of the bell and the interior faces of the chamber

mixture.

  Other features and benefits of

  the invention will become more apparent from the description which follows

  of several particular embodiments. This

  description is illustrative and not limiting. She must

  be read with reference to the accompanying drawings in which: - Figure 1 is a sectional view of a gas burner of the radiant type according to a particular preferred embodiment of the invention; - Figures 2a to 2e schematically represent other possible variants for the invention. The burner in FIG. 1 is a gas burner of the radiant type integrated in a hob T. It consists of a combustion head 1 and a body 2 which

wear this head 1.

  The combustion head 1 has a cylindrical tubular skirt 3 by which it bears on the body 2. This head 1 is closed at its end opposite to the body 2 by a porous membrane 4, which constitutes the radiant element of the burner. This membrane 4 is made of a metal fiber material

sintered refractories.

  This material is advantageously of the type which is sold by the company ACOTECH under the name BEKITHERM AC 200 P1 and which has the particularity of being crossed by a multitude of perforations of diameter less than the distance of jamming of the flames. These perforations make it possible to considerably reduce the pressure drops that this material imposes on the gas mixture. This material also has excellent Nox performance: 40

  ppm at 500 kW / m2 and 10% excess air.

  More generally, the different materials described in patents and patent applications EP-157,432 can be used to produce the radiant element 4,

EP-227.131, EP-390.255.

  The front face of the radiant element 4 constitutes the combustion face of the burner. It is flush with the upper face of the table T. The skirt 3 is surrounded externally, towards its end which carries the radiant element 4, by an annular collar 5. This collar 5 is itself annularly bordered by a flat 6. The latter comes to bear on the edge of the opening of the table T, which receives the said burner 1, in order to maintain the combustion head 1 relative to the table T. The body 2 is mainly constituted by a cylindrical wall 7 closed by a bottom 8. This cylindrical wall 7 has substantially the same inside and outside diameters as the skirt 3. In the assembled position of the head 1 on the body 2, the edge of the skirt 3 bears on that of edges of the wall 7,

which is opposite to the bottom 8.

  This section, referenced by 7a in FIG. 1, is extended by a collar 9 ensuring the centering of the

skirt 3 relative to the wall 7.

  An annular seal 10 for sealing and taking up is provided for interposing between the skirt 3 and the wall 7. This seal 10 is received in an annular housing of U-shaped cross section which the edge has

  7a near the inner face of the wall 7.

  The skirt 3 and the wall 7 define, with the membrane 4 and the bottom 8, a chamber 11 in which the air and the gas mix before reaching said membrane 4. In this chamber 11 is arranged an element 12 forming a bell , which is supported by its edge on the bottom 8. This bell element 12 is defined by a cylindrical body 14 closed by a bottom 13. The outside diameter of the body 14 is slightly less than the inside diameter of the chamber 11. Its height axial is significantly smaller than the height of the chamber 11,

  so that the bottom 13 is spaced from the membrane 4.

  The edge of this element 12 forming a bell is extended by several tabs 15, which project

  radially with respect to the external face of the body 14.

  These lugs 15 are distributed over the entire periphery of said body 14 and ensure the centering of said element 12 in the

mixing chamber 11.

  The edge of the element 12 forming a bell also has, between the legs 15, recesses 16 in the form of slots which are regularly distributed over its entire periphery. These recesses 16 ensure communication between the internal volume of the bell 12 and the circulation blade which is defined between the external faces of

  the bell 12 and the interior faces of the chamber 11.

  The bell 12 and the wall 7 are further crossed radially by a channel 17 which opens into said bell 12 and which supplies the chamber 11 with air and gas, the air and the gas being propelled into said channel by ventilation means arranged upstream of the mixing chamber. So that the bell can be removed from the bottom 8, the recess of the bell 12 through which the channel 17 is passed is a notch 17a formed on the edge of said

bell 12.

  The bottom 8 is crossed by an orifice 8a from which a tubular element 18 extends coaxially in the chamber 11, up to the radiant element 4. In said tubular element 18 extends an electrode 19 which opens out from said tubular element 18 at its end opposite the bottom 8. This electrode 19 is thus partially projecting

  relative to the front face of the radiant element 4.

  At this end, the tubular element 18 is embedded in a ring 20 of ceramic material which

  thermally insulates the membrane 4.

  A tubular cylindrical stopper 21 extends from this ring 20, towards the bottom 8, surrounding the tubular element 18. This stopper 21 is of a length less than the length of the element 18. It ends in its end opposite to the ring 20 by an external annular flange 22. Between this flange 22 and the bottom 8 is compressed a helical spring 23 also

  passed over the tubular element 18.

  Locking means (not shown) keep the combustion head 1 in place on the body 2, while the spring 23 is compressed. These locking means are for example electromagnetic means. The installation of such a burner is carried out from the

next way.

  Body 2 and channel 17 are previously

  integrated into the table T, during assembly thereof.

  To assemble the combustion head 1 on said body 2, the operator passes the spring 23 and the stopper 21 over the tubular element 18. Then, he introduces the bell 12 into the chamber 11, by positioning the notch 17a on the channel 17. It then covers the assembly by the combustion head 1, the ring 20 of which bears on the stopper 21 and exerts on said head 1, an effort to compress, via the flange 22, the spring 23. When the skirt 3 is in place on the edge of the wall 7, the operator locks the head

combustion 1 on the body 2.

  In operation, the air and the gas, which arrive under the bell 12, circulate in the latter in the manner which has been represented schematically by the arrows in FIG. 1. Then, they are homogenized there, and the mixture thus constituted escapes from said bell 12 by the slots 16, going up along the interior faces of the chamber 11, to the space between the radiant membrane 4 and the bottom 13 of the bell 12. The operator switches on the

  burner by actuating the electrode 19.

  Thus, the bell 12 defines with the internal faces of the mixing chamber a circulation blade, in which the air / gas mixture is forced to circulate while being in contact with the internal faces of the mixing chamber 11. The walls which define said chamber 11 is cooled by the air / gas mixture, while the latter is preheated, which improves the efficiency of the burner. Care is taken, of course, that the air / gas mixture does not reach its self-ignition temperature (of the order of 5000 ° C. for LPG gases;

  around 800 "C for natural gas).

  The turbulence undergone by the air and the gas inside the bell 12 also promotes convective exchanges between the gas and the walls of the bell 12. It will be noted that the use for the burner of a membrane 4 of the type perforated, provides a ventilation power reserve to channel the

  mix and increase its turbulence.

  The spring 23 is subtracted at high temperatures, since it is disposed inside the distribution bell 12 and that it does not push the membrane 4 directly, but through the stopper 21. The circulation of the air mixture / gas also allows the cooling of the seal 10 which is arranged near the inner faces of the skirt 3 and of the cylinder 7, and benefits from the temperature gradient in this wall. This cooling is all the better as this seal 10 is located just above the supply channel 17, so that it is cooled by a "fresh" gas mixture, directly coming from the bell 12

distribution.

  The central position of the electrode 19 has the advantage of being favorable for ignition. It is in fact the center of the porous membrane 4 which is least disturbed by the movements of ambient air. It is also at the center level that natural convection with

the ambient air is the weakest.

  The perforations in the membrane 4 make it possible to increase the range of the operating powers of the burner. Also, the ventilation means working with less back pressure, they rotate less quickly and

are therefore less noisy.

  When an operator wants to disassemble the combustion head 1 relative to the body 2 of the burner, he disengages the locking means. The compressed spring 23 then pushes back the combustion head 1 so as to cause it to protrude relative to the table T, in a

  position where the operator can easily enter it.

  As will have been noted, the disassembly of the combustion head 1 can take place without the user

  does not have to handle the electrode 19 and the high-

  voltage to which it is connected, since the combustion head slides relative to the tubular element 18

and electrode 19.

  Other possible embodiments for

  the invention have been illustrated in Figures 2a to 2e.

  In each of these variants, the burner comprises a head 101 and a body 102, which together define a

  chamber 111. The head 101 has a radiant element 104.

  The chamber 111 is supplied with air and gas by a channel 117. According to the invention, it is arranged in the mixing chamber 111, an element 112 which forms an obstacle for the circulation of the air / gas mixture and forces the mixture air / gas to circulate along the faces

  inside the mixing chamber, before combustion.

  In the variant shown in FIG. 2a,

  the element 112 forming an obstacle is a solid element.

  In the advantageous variants of FIGS. 2b and 2c, the mixing chamber 111 is reduced to a simple

  circulation lane, by the element 112 forming an obstacle.

  This is, in fact, of a geometry complementary to that of the mixing chamber and forces the air / gas mixture to circulate in contact with the walls of the latter

  and thus participate in the cooling of the chamber.

  In the embodiment of FIG. 2b, the interior volume of the chamber 111 is flat parallelepiped, the element 112 being a blade extending inside it. In the embodiment of FIG. 2c, the element 112

  and the chamber 111 are substantially conical in shape.

  The bell shape of the obstacle, which corresponds in particular to the embodiments shown in FIG. 1 and in FIGS. 2d to 2e, nevertheless constitutes a preferred solution for the invention, since the air / gas mixture injected into the bell is homogenized there, before being evacuated by recesses provided for this purpose in the vicinity of the edge of the bell 112, actively participating in the cooling of the walls of the

mixing chamber.

  In another variant, as shown in FIG. 2d, the mixing chamber 111 can be supplied with an air / gas mixture through its bottom and not laterally. The seal 110 between the body 102 of the burner and the combustion head 101 is then advantageously disposed near the bottom of said body 103, that is to say in a plane distant from the element.

radiant 104.

  Also, as shown in FIG. 2e, the means which allow the combustion head 101 to come out relative to the body 102 of the burner can be constituted by complementary ramps, for example helical, which the body has. 102 and the combustion head 101 and which allow an operator to release the head 101 relative to the body 102 by axially pivoting said head 101 relative to

said body 102.

  In yet another advantageous variant (not shown), it is provided that the contact element has a helical profile, which forces the mixture which rises towards the radiant element to circulate in rotation in the mixing chamber, which favors the exchanges with the interior faces thereof. 5

Claims (10)

  1. Gas burner for stove or hob, comprising a combustion head (1, 101) and a mixing chamber (11, 111), said head having a porous radiant element (4, 104), said chamber ( 11, 111) being disposed under the radiant element (4, 104) and receiving air and gas to supply said radiant element with an air / gas mixture, at least one element (12, 112) forming an obstacle to circulation of the air / gas mixture being disposed in said chamber (11, 111), characterized in that the obstacle forming element (12, 112) defines with the interior faces of the mixing chamber (11, 111) a circulation blade in which the air / gas mixture is forced to circulate while being in contact with said faces   interior so as to cool them.   2. Burner according to claim 1, characterized in that the obstacle-forming element is a bell (12), this bell having a bottom (13) surrounded by walls (14) extending from said bottom (13) towards the bottom (8) of the mixing chamber (11), the interior of this bell (12) being supplied with air and gas, the   mixture formed in said bell (12) evacuating therefrom   ci in the vicinity of the bottom (8) of the mixing chamber, then up to the radiant element (4) by circulating in the circulation blade defined between the walls of the bell (12) and the interior faces of the chamber of mixture (11).   3. Burner according to claim 2, characterized in that the combustion head (1) can be moved away from the bottom (8) of the mixing chamber (11), at least one element (23) forming a spring being compressed between the bottom (8) of the mixing chamber (11) and a stop member (21) extending between said spring (23) and the combustion head (1), said spring element (23) being disposed inside the bell (12), the burner also comprising locking means for   oppose the action of said spring element.   4. Burner according to one of claims 2 or 3,   characterized in that the bell (12) has at least one notch (17a) through which a lateral channel (17) passes for the supply of air to the mixing chamber (11) and / or in gas.   5. Burner according to one of claims   above, characterized in that the mixing chamber is supplied with air and gas via its bottom, and in that the combustion head has a skirt bearing, by means of a seal, on said bottom, said skirt defining, with said bottom and the element radiant, the mixing chamber.   6. Burner according to one of claims 1 to 4,   characterized in that the mixing chamber (11) is supplied laterally with air and gas, the combustion head (1) being carried by a body (2) extending from the bottom (8) of the mixing chamber (11) and defining said chamber with said combustion head (1), said body (2) having at least one opening for the supply of air / gas mixture, the height of said body (2) from said bottom (8) up to the combustion head (1) being just greater than the height of said opening.   7. Burner according to one of claims   above, characterized in that it comprises an electrode (19) partially projecting from the front face of the radiant element (4), this electrode (19) being received in a tubular element (18) extending the interior of the mixing chamber (11) up to the radiant element (4), said tubular element (18) electrically insulating the air / gas mixture from said electrode (19).   8. Burner according to claim 7, characterized in that the tubular element (18) passes through the radiant element (4) and is thermally insulated from it by a   ring (20) of ceramic glue in which it is embedded.   9. Burner according to one of claims 7 or 8,   characterized in that the electrode (19) is positioned at the center of the radiant element (4).   10. Burner according to one of claims   above, characterized in that the radiant element (4) is a membrane made of a porous material made of sintered refractory metal fibers, this membrane   with a multitude of perforations.