EP0651203A1 - Radiant gas burner for stove or cooker 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. <IMAGE>

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 applicant's international patent application published under the 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 uniformly distribute the combustible mixture on the radiant element.

Another burner of this type has also been described in patent application WO-84/04376. It is indicated in this patent application that the deflector returns the air / gas mixture to the side walls which define the mixing chamber, so as to cool these walls.

In these different burners, the cooling produced is only a secondary effect of the shape and geometry of the deflector, the main function of which is to distribute the air / gas mixture properly with respect to the radiant element. This cooling is insufficient to effectively oppose the heating of the mixing chamber.

It will be noted in particular that in these different burners of the prior art, a major part of the air / gas mixture reaches the radiant element of the burner without having been in contact with the lateral faces of the mixing chamber.

The invention proposes a burner which is characterized in that the obstacle-forming element has a general external contour which is similar to the inner contour of the mixing chamber and which defines therewith a circulation blade in which the air / gas mixture is forced to circulate before reaching the radiant element, to convectively exchange with the side wall or walls of the chamber mixture.

With such a structure, the entire air / gas mixture is forced to exchange by convection with the side walls of the mixing chamber; the volume of the blade in which the air / gas mixture circulates being reduced, the convective exchanges are much greater than in the case of the deflector mixing chambers of the prior art.

According to a particularly advantageous embodiment, the obstacle-forming element is a bell, this bell having a bottom surrounded by side walls extending from said bottom towards a bottom of the mixing chamber on which said bell is carried, l inside 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 blade circulation defined between the side wall or walls of the bell and the mixing chamber.

Such a structure makes it possible to achieve a satisfactory mixture of air and gas before they reach the radiant element of the burner: the air / gas mixture injected into the bell is homogenized there before being evacuated in the vicinity from the bottom of the bell to actively participate in cooling the walls of the mixing chamber.

• la figure 1 est une vue en coupe d'un brûleur à gaz du type radiant conforme à un mode de réalisation particulier préféré de l'invention ;
• les figures 2a et 2d représentent schématiquement d'autres variantes possibles pour l'invention.

Other characteristics and advantages of the invention will emerge from the following description of several particular embodiments. This description is illustrative and not limiting. It must be read in conjunction with the appended drawings in which:

• Figure 1 is a sectional view of a burner to gas of the radiant type in accordance with a particular preferred embodiment of the invention;
• Figures 2a and 2d 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 carries 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 material of sintered refractory metal fibers.

This material is advantageously of the type which is marketed 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 various materials described in patents and patent applications EP-157,432, EP-227,131, EP-390,255 can be used to produce the radiant element 4.

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 a annular flange 5. This flange 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 said burner 1, in order to maintain the combustion head 1 compared to 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 the edges of the wall 7, which is opposite 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 take-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 section which has the edge 7a near the face. inside 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 substantially 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 lugs 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 internal 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 dismantled relative to the bottom 8, the recess of the bell 12 through which the channel 17 has 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 with respect 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 it from 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 as follows.

The body 2 and the 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, by means of the flange 22, the spring 23 When the skirt 3 is in place on the edge of the wall 7, the operator locks the combustion head 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 diagrammatically by the arrows in FIG. 1.

They are homogenized there, then the mixture thus formed 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 ignites the burner by actuating the electrode 19.

The bell 12 defines with the cylindrical side face of the mixing chamber a circulation blade, in which the air / gas mixture is forced to circulate while being in contact with said lateral face over a major part of the height thereof. The walls which define said chamber 11 are thus 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 auto-ignition temperature (of the order of 500 ° C for LPG gases; of the order of 800 ° C for gas natural).

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 reserve of ventilation power to channel the mixture 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 / gas mixture also allows the cooling of the seal 10 which is arranged near the interior 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 distribution bell 12 .

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 grasp it.

As will have been noted, the disassembly of the combustion head 1 can take place without the user having to manipulate the electrode 19 and the high voltage connections to which it is connected, since the combustion head slides by relative to the tubular element 18 and the electrode 19.

Other possible embodiments for the invention have been illustrated in FIGS. 2a to 2d. 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 air / gas mixture to circulate along the interior faces of the mixing chamber. , before its combustion.

In the variants shown in FIGS. 2a and 2b, the element 112 forming an obstacle is a solid element which has an external geometry complementary to the internal geometry of the mixing chamber 111. The circulation blade thus defined forces the air mixture / gas circulate in contact with the walls of the chamber 111 and thus participate in the cooling thereof. In the embodiment of FIG. 2a, the element 112 forming an obstacle and the mixing chamber 111 are of parallelepiped shape. In the embodiment of Figure 2b, the element 112 and the chamber 111 are substantially conical in shape and widen towards the radiant element of the burner head.

The bell shape of the obstacle, which corresponds in particular to the embodiments shown in FIG. 1 and in FIGS. 2c to 2d, 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. 2c, 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 placed near the bottom of said body 103, that is to say in a plane distant from the radiant element 104.

Also, as shown in FIG. 2d, 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 130, for example helical, which the body 102 and the combustion head 101 and which allow an operator to disengage 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 expected that the bell-shaped element has a helical profile, which forces the mixture which rises towards the radiant element to circulate in rotation outside said bell-shaped element, which promotes exchanges with the inside faces of the mixing chamber.

Claims (11)

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 the circulation of the mixture air / gas being disposed in said chamber (11, 111), said obstacle element (12, 112) sending the air / gas mixture to the side faces of the mixing chamber (11, 111) to cool them, characterized in that that the obstacle forming element (12, 112) has a general external contour which is analogous to the internal contour of the mixing chamber (11, 111) and which defines therewith a circulation blade in which the air / gas mixture is forced to circulate before reaching the radiant element, to exchange c onvectively with the side wall or walls of the mixing chamber (11, 111). Burner according to claim 1, characterized in that the obstacle-forming element is a bell (12, 112), this bell having a bottom (13) surrounded by side walls (14) extending from said bottom (13) towards a bottom (8) of the mixing chamber (11) on which said bell is carried, the interior of this bell (12, 112) being supplied with air and gas, the mixture formed in said bell (12, 112 ) evacuating therefrom in the vicinity of the bottom (8) of the mixing chamber, then rising to the radiant element (4) by circulating in the circulation blade defined between the side wall or walls of the bell (12, 112) and the mixing chamber (11). 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 spring element (23) being compressed between the bottom (8) of the mixing chamber (11) and a stop member (21) extending between said bottom spring (23) and the combustion head (1), said spring element (23) being disposed inside the bell (12, 112), the burner also comprising locking means for opposing the action of said spring element. Burner according to one of Claims 2 or 3, characterized in that the bell (12, 112) has at least one notch (17a) through which a lateral channel (17) passes for supplying the mixing chamber (11) in air and / or gas. Burner according to one of claims 1 to 3, characterized in that the mixing chamber is supplied with air and gas at its bottom, and in that the combustion head has a skirt in support, by means of a seal, on said bottom, said skirt defining, with said bottom and the radiant element, the mixing chamber. Burner according to one of the preceding claims, characterized in that the combustion head (1) is carried by a body (2) extending from a bottom (8) which has the mixing chamber (11), said body (2) defining said mixing chamber (11) with the combustion head (1). Burner according to claim 6, characterized in that said body (2) has an opening for the lateral supply of the mixing chamber (11) with air / gas mixture, the height of said body (1) from said bottom (8 ) to the combustion head being just greater than the height of said opening. Burner according to one of the preceding claims, 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 inside the mixing chamber (11) up to the radiant element (4) , said tubular element (18) electrically insulating the air / gas mixture with respect to said electrode (19). Burner according to claim 8, characterized in that the tubular element (18) passes through the radiant element (4) and is thermally insulated therefrom by a ring (20) of ceramic adhesive in which it is embedded. Burner according to one of claims 8 or 9, characterized in that the electrode (19) is positioned in the center of the radiant element (4). Burner according to one of the preceding claims, characterized in that the radiant element (4) is a membrane made of a porous material made of sintered refractory metal fibers, this membrane having a multitude of perforations.

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