EP0651203B1 - 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 burners with radiant gas, for stoves or tables cooking.

Such a burner conventionally comprises a head having a porous radiant element, the face of which front 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 by example used to make cooktops of a appearance close to that of tables with ceramic glass hob, the front frontal of the radiant element flush with the plane top of the table in which said burner is integrated. One such hob has been described in the international patent application of the Applicant published under number WO-92/06334.

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

These heat transfers can be at the origin inadvertent ignition of the air / gas mixture in the mixing chamber, upstream of the normal zone of combustion.

They can also produce an alteration quick seal that is interposed between the combustion head and the body that carries it.

They can damage the components which are located under the table plan cooking.

A main object of the invention is to solve this problem.

We already know gas burners in which at least one element forming an obstacle to the circulation of air / gas mixture is placed in the mixing chamber. We may in this respect advantageously refer to the patent EP-157.432 in which a gas burner of this type is described type. The element forming an obstacle to the circulation of air / gas mixture there is a deflector which is arranged at the center of the room, and that used to distribute uniformly the combustible mixture on the radiant element.

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

In these different burners, the cooling achieved is only a side effect of the form and deflector geometry whose main function is distribute the air / gas mixture appropriately in relation to the radiant element. This cooling is insufficient to effectively oppose room warming mixture.

Note in particular that in these different prior art burners, most of the mixture air / gas reaches the radiant element of the burner without having been in contact with the side faces of the mixed.

The invention proposes a burner which is characterized in that the obstacle element has a general exterior outline which is analogous to inner contour of the mixing chamber and which defines with this one a circulation blade in which the air / gas mixture is forced to circulate before reaching the radiant element, to convectively exchange with the or the side walls of the mixing chamber.

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

According to a particularly embodiment advantageous, the obstacle-forming element is a bell, this bell having a bottom surrounded by walls lateral extending from said bottom to a bottom of the mixing chamber on which said bell is carried, the interior of this bell being supplied with air and gas, the mixture formed in said bell discharging from this in the vicinity of the bottom of the mixing chamber, then going up to the radiant element by circulating in the circulation space defined between the wall (s) sides of the bell and the mixing chamber.

Such a structure makes it possible to mix satisfying air and gas before they reach the radiant element of the burner: the air / gas mixture injected in the bell is homogenized there before evacuating at neighborhood of the bottom of the bell to participate actively 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. It must be read in conjunction with the appended 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 and 2d schematically represent other possible variants for the invention.

The burner in Figure 1 is a gas burner from radiant type integrated in a T hob. consisting of a combustion head 1 and a body 2 which wear this head 1.

The combustion head 1 has a skirt 3 cylindrical tubular by which it is supported the body 2. This head 1 is closed at its end opposite the body 2 by a porous membrane 4, which constitutes the radiant element of the burner. This membrane 4 is made of a metallic 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 traversed 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 / m ² and 10% excess air.

More generally, we can use for make the radiant element 4 the different materials described in patents and patent applications EP-157,432, 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 compared to the upper face of table T.

The skirt 3 is surrounded externally, towards its end which carries the radiant element 4, by a annular collar 5. This collar 5 is itself annularly bordered by a flat 6. This comes in support 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.

Body 2 is mainly constituted by a cylindrical wall 7 closed by a bottom 8. This cylindrical wall 7 is substantially the same inner and outer diameters than the skirt 3. In 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 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 catch-up is provided to come between the skirt 3 and the wall 7. This seal 10 is received in a housing U-shaped annular section with the edge 7a near the inner face of the wall 7.

The skirt 3 and the wall 7 define, with the membrane 4 and bottom 8, a chamber 11 in which air and 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-shaped element 12 is defined by a cylindrical body 14 closed by a bottom 13. The diameter outside of body 14 is slightly less than the diameter inside of chamber 11. Its axial height 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 legs 15 which project radially with respect to the external face of the body 14. These legs 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 has also, between the legs 15, shaped recesses 16 of slots which are regularly distributed throughout its around. These recesses 16 ensure communication between the internal volume of the bell 12 and the blade circulation which is defined between the outer 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 in air and gas, the air and the gas being propelled into said channel by means of ventilation arranged upstream of the mixing chamber. So that the bell can be removed from the bottom 8, the recess of the bell 12 in which the channel 17 is past is a notch 17a formed on the edge of said bell 12.

The bottom 8 is crossed by an orifice 8a from from which a tubular element 18 extends coaxially in chamber 11, up to the radiant element 4. In said tubular element 18 extends an electrode 19 which opens out of 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 to from this ring 20, towards the bottom 8, surrounding the tubular element 18. This stopper 21 is of a length shorter than the length of element 18. It ends in its end opposite to the ring 20 by a flange outer annular 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 means electromagnetic.

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

In operation, air and gas, which arrive under the bell 12, circulate therein in the manner which has been represented schematically by the arrows on the figure 1.

They are homogenized there, then the mixture as well 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 turns on the burner by actuating the electrode 19.

The bell 12 defines with the side face cylindrical mixing chamber a blade of circulation, in which the air / gas mixture is forced to circulate while being in contact with said lateral face over most of its height. The walls which define said chamber 11 are thus cooled by the air / gas mixture, while this is preheated, which improves the efficiency of the burner. We ensures, of course, that the air / gas mixture does not reach its auto-ignition temperature (from around 500 ° C for LPG gases; around 800 ° C for natural gas).

The turbulence that the air and gas undergo the interior of the bell 12 also favor the convective exchanges between the gas and the walls of the bell 12. Note that the use for the burner a perforated type membrane 4, provides a ventilation power reserve to channel the mix and increase its turbulence.

Spring 23 is subtracted from the high temperatures, since it is arranged inside the distribution bell 12 and that it doesn't push the membrane 4 directly, but via the stopper 21.

The circulation of the air / gas mixture also allows the cooling of the seal 10 which is arranged nearby 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 joint seal 10 is located just above the channel supply 17, so that it is cooled by a "fresh" gas mixture, directly from bell 12 distribution.

The central position of the electrode 19 presents the advantage of being favorable to ignition. It is indeed the center of the porous membrane 4 which is the least disturbed by the movement of ambient air. It's also at the center level, that natural convection with the ambient air is the weakest.

The perforations in the membrane 4 allow increase the range of operating powers of the burner. Also, the ventilation means working with less back pressure, they rotate more slowly and are therefore less noisy.

When an operator wants to disassemble the head combustion 1 relative to the burner body 2, it disengages the locking means. Compressed spring 23 then pushes back the combustion head 1 so as to protruding from table T, in a position where the operator can easily enter it.

As will be noted, the disassembly of the head 1 can intervene without the user do not have to handle the electrode 19 and the high connections voltage to which it is connected, since the head of combustion slides in relation to the tubular element 18 and electrode 19.

Other possible embodiments for the invention have been illustrated in Figures 2a to 2d. In each of these variants, the burner has a head 101 and a body 102 which together define a chamber 111. The head 101 has a radiant element 104. 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 a obstacle for the circulation of the air / gas and force mixture the air / gas mixture to circulate along the faces inside the mixing chamber, before combustion.

On the variants shown in Figures 2a and 2b, the element 112 forming an obstacle is a solid element which is of an external geometry complementary to the interior geometry of the mixing chamber 111. The blade of circulation thus defined obliges the air / gas mixture to circulate in contact with the walls of room 111 and at thus participate in the cooling thereof. In the embodiment of FIG. 2a, the element 112 forming obstacle and the mixing chamber 111 are shaped parallelepiped. In the embodiment of the Figure 2b, the element 112 and the chamber 111 are substantially conical in shape and widens towards the element radiant from the burner head.

The bell shape of the obstacle, which corresponds in particular to the embodiments represented on the Figure 1 and Figures 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, in actively participating in cooling the walls of the mixing chamber.

In another variant, as shown on FIG. 2c, the mixing chamber 111 can be supplied with air / gas mixture from 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, i.e. in a plane distant from the element radiant 104.

Also, as shown on the Figure 2d, the means which allow the combustion head 101 relative to the body 102 of the burner can be made up of complementary ramps 130, for example helical, which have the body 102 and the combustion head 101 and which allow a operator to release head 101 from 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 shaped element bell has a helical profile, which forces the mixture which goes up towards the radiant element to circulate in rotation outside of said bell-shaped element, which promotes exchanges with the interior faces of the mixing chamber.

Claims (11)

1. A gas burner for a cooker or a hob, the burner 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 beneath the radiant element (4, 104) and receiving air and gas to feed said radiant element with an air/gas mixture, at least one element (12, 112) forming an obstacle to the flow of the air/gas mixture being disposed in said chamber (11, 111), said obstacle-forming element (12, 112) sending the air/gas mixture over the side faces of the mixing chamber (11, 111) to cool them, the burner being characterized in that the general external outline of the obstacle-forming elements (12, 112) is analogous to the internal outline of the mixing chamber (11, 111) and co-operates therewith to define a flow slot through which the air/gas mixture is forced to flow before reaching the radiant element, so as to exchange heat by convection with the side wall(s) of the mixing chamber (11, 111).
2. A burner according to claim 1, characterized in that the obstacle-forming element is a bell (12, 112), said bell having a top (13) surrounded by side walls (14) extending from said top (13) towards a bottom (8) of the mixing chamber (11) on which said bell is carried, the inside of the bell (12, 112) being fed with air and with gas, the mixture formed in said bell (12, 112) escaping therefrom in the vicinity of the bottom (8) of the mixing chamber, and then rising to the radiant element (4) by flowing in the flow slot defined between the side wall(s) of the bell (12, 112) and of the mixing chamber (11)·
3. A 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-forming element (23) being compressed between the bottom (8) of the mixing chamber (11) and an abutment member (21) extending between said spring (23) and the combustion head (1), said spring-forming element (23) being disposed inside the bell (12, 112), the burner also including locking means for opposing the action of said spring-forming element.
4. A burner according to claim 2 or 3, characterized in that the bell (12, 112) has at least one notch (17a) through which there passes a lateral pipe (17) for feeding the mixing chamber (11) with air and/or with gas.
5. A burner according to any one of claims 1 to 3, characterized in that the mixing chamber is fed with air and with gas through its bottom, and in that the combustion head has a skirt bearing via a sealing ring on said bottom, said skirt co-operating with said bottom and the radiant element to define the mixing chamber.
6. A burner according to any preceding claim, characterized in that the combustion head (1) is carried by a body (2) extending from a bottom (8) of the mixing chamber (11), said body (2) co-operating with the combustion head (1) to define said mixing chamber (11).
7. A burner according to claim 6, characterized in that said body (2) has an opening for feeding the mixing chamber (11) laterally with an air/gas mixture, the height of said body (2) from said bottom (8) to the combustion head being just greater than the height of said opening.
8. A burner according to any preceding claim, characterized in that it includes an electrode (19), part of which projects from the front face of the radiant element (4), said electrode (19) being received in a tubular element (18) extending inside the mixing chamber (11) to the radiant element (4), said tubular element (18) insulating the air/gas mixture electrically from said electrode (19).
9. A 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.
10. A burner according to claim 8 or 9, characterized in that the electrode (19) is positioned in the center of the radiant element (4).
11. A burner according to any preceding claim, characterized in that the radiant element (4) is a membrane of porous material made of sintered refractory metal fibers, said membrane having a multitude of perforations.

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