HK1141859A - Gas burner for a cooktop - Google Patents

Description

Gas burner for cooktops

Technical Field

The present invention relates to a gas burner, in particular a gas burner with a plurality of combustion portions, intended to be used in a cooktop (cooktop) of a stove or similar appliance.

Background

Gas cooktops that are becoming popular on the market today typically include high heat input gas burners, for example burners having a heat input rating in excess of 3 kW. In such gas burners, the combustion portion usually comprises at least two concentric flame rings, in order to spread the heat generated by the burner as uniformly as possible over a relatively large and wide operating area, so as to be able to heat pans and pots, even of large size, as uniformly as possible.

In this connection, gas burners are known in the prior art in which the flame ring is provided by a single gas injection pipe, to which a cock for adjusting the gas flow is usually connected. In such gas burners, in particular in order to prevent the occurrence of the usual constraints in which the individual flame rings of the burner remain constantly operating (i.e. they burn together whether they are required or indeed not) in all cases (for example in the case where the surface area of the bottom of the vessel to be heated is not very large, i.e. small in size) and in order to optimize the distribution of the heat output of the gas burner in any environment, in fact the prior art has proposed many solutions.

Thus, for example, gas burners having a plurality of flame rings have been developed and provided, wherein the flame rings themselves are provided separately. A widely known example of such a gas burner is disclosed in patent application WO 9908046.

With reference to what is illustrated and described in the above-mentioned patent application, the sum of the components that make up the gas burner, when assembled together, forms inside it a lower chamber and an upper chamber, wherein these chambers are separated from each other by a horizontally extending partition. In the lower chamber there is a first gas injection pipe provided with an injector leading to a first air/gas mixing device formed by a venturi tube which is bifurcated into two ducts providing the outermost flame ring. In the upper chamber there is in turn a second gas injection pipe provided with an injector leading to a second air/gas mixing device formed by a venturi tube providing the innermost flame ring.

This makes it possible to vary the flow rate in the gas injection pipe and therefore also the heat output that a single flame ring can generate, i.e. it is possible to adjust by correctly setting the two-way gas tap with different operating settings. In one of the operating settings of the gas tap, the gas streams ejected from the injectors of the two nozzles or respectively the two gas injection pipes are mixed with air in two respective air/gas mixing devices, thereby providing two flame rings. In a different operating setting of the gas cock, the flow rate of the gas is reduced and the gas flow is injected only by the injectors of the second gas injection pipe, so as to flow only into the second air/gas mixing device, so that only the inner flame ring is fed with the relative combustion mixture. In order to be able to operate properly, the gas burner requires the ignition of both flame rings or only the inner flame ring, depending on the actual requirements (for example the size of the pan). In the above-mentioned patent application there is also another embodiment which is capable of adjusting the gas flow rate by means of two gas taps, which is considered but is not actually described any further.

The drawbacks of gas burners of the above type generally stem from the fact that: the different flame rings (i.e. the combustion section) are provided by means of a respective plurality of different injectors associated with the combustion section itself, so that the burner is rather complex in construction and of considerable size, requiring correspondingly large installation spaces, which is certainly not a satisfactory or even acceptable case, since these burners are applied in cooktops, in particular when these are of the type intended to be used at home.

Furthermore, gas burners (so-called catalytic burners) are known from the prior art, in which the combustion part is formed from a porous or ceramic material plate. In a typical embodiment, the domestic catalytic gas burner comprises a support of porous material, generally in the shape of a regular polyhedron, in which a suitable catalyst is dispersed in a zone, in this particular case generally defined as the reaction zone. One of the two faces of the support of porous material is exposed to and impinged by a jet of fuel emitted from at least one injector device located in proximity to the support of porous material. The fuel then spreads and diffuses through the support of porous material towards the reaction zone while mixing with the comburent (i.e. comburent) diffusing from the opposite face of the support of porous material, thus allowing the combustion process to take place.

In such catalytic gas burners, the support of porous material participates in combustion throughout, i.e. combustion takes place over the entire area of said support. In fact, the only possibility to regulate the heat generated by combustion is to control the reaction speed by adjusting the flow rate of the fuel, without the possibility to vary the surface area of the support of the porous material participating in the combustion.

Disclosure of Invention

It is therefore a main object of the present invention to overcome the drawbacks and drawbacks of the gas burners with multiple combustion sections currently known in the prior art. Within this general object, a main object of the present invention is to provide a gas burner with a plurality of combustion sections, wherein a set of said plurality of combustion sections is provided by suitably adjusting the gas jet emitted from the injector.

Another object of the present invention is to provide a burner comprising a plurality of combustion sections, wherein a set of combustion sections intended to participate in the combustion process can be correctly and timely selected.

It is a further object of the present invention to provide a gas burner comprising a plurality of combustion portions and having a simpler and more compact structure.

It is a further object of the present invention to provide a gas burner comprising a plurality of combustion sections, wherein the area of the surfaces participating in the combustion process can be varied according to actual needs and requirements.

It is also an object of the present invention to provide a gas burner comprising a plurality of combustion portions, which is able to achieve the above aims and objects at a fully competitive cost and which is further able to be manufactured using manufacturing methods widely known and readily available in the prior art.

An important advantage of the gas burner according to the invention, comprising a plurality of gas portions consisting of a plurality of flame rings, is obtained by the fact that: the result of the turbulence generated by the gas jet is that the amount of air drawn into the jet is increased due to the improved combustion mixing.

The advantage of the gas burner according to the invention comprising a plurality of combustion sections consisting of porous or ceramic material portions is that the control of the reaction speed can be improved by a suitable fuel injection system.

Another advantage of the present invention is that cooktops for domestic and/or professional use can be manufactured, which are suitable for accurately heating pans and pots of the most varied size and shape.

According to the present invention, these objects, together with others which will become apparent from the following disclosure, are achieved in a gas burner comprising a plurality of combustion sections, said gas burner comprising the features and characteristics defined and detailed in the appended claims.

Drawings

The advantages and features of the invention will be understood more easily in any case by the description of some exemplary embodiments, which are given below by way of non-limiting example with reference to the accompanying drawings, in which:

FIG. 1a is a cross-sectional view of the controlled gas jet ejector shown in FIG. 1b, taken along line I-I;

FIG. 1b is a schematic top view of a controlled gas jet ejector;

FIGS. 1c and 1d are schematic views of the controlled gas jet ejector shown in FIG. 1a, seen in two different operating states;

FIGS. 2 and 3 are schematic views of a first preferred embodiment of a gas burner comprising a plurality of combustion sections using a controlled gas jet injector according to the invention, wherein the combustion sections are composed of a plurality of flame rings;

FIGS. 4 and 5 are schematic views of a modification of the first preferred embodiment described above, in which another gas burner having a plurality of flame rings is provided;

FIGS. 6 and 7 are schematic views of a second preferred embodiment in which a gas burner with a single flame ring with adjustable heat input is provided; and

fig. 9 and 10 are schematic views of a third preferred embodiment of a gas burner comprising a plurality of combustion sections using a controlled gas jet injector according to the invention, wherein the combustion sections consist of partially porous supports.

Detailed Description

The gas burner according to the invention is supplied by a gas flow formed in and ejected from an injector, published in the turbulence bullets 5 according to Vincent Faivre and Thierry poinst: 025(2004) (Journal of Turbulence 5: 025(2004)), manufactured and provided with the teachings of the paper entitled "Experimental and scientific Investigations into Active Control of jets for combustion applications" and which can be found at the following internet addresses:

http://www.cerfacs.fr/～cfdbib/repository/TR CFD 04 90.pdf

the objective of the research work described in the above paper was to develop an initiator device for controlling the mixing enhancement of axisymmetric non-reactive jets. The actuator consists of a small nozzle supplying a primary jet. The nozzles are positioned to add a directional angular component to the velocity field. In particular, the authors solve the following points and problems:

-an optimal orientation of the actuators (activators);

-influence of the distance of the initiator from the gas jet outlet of the injector;

-the effect of the ratio of the gas flow rate of the starter to the gas flow rate of the main conduit; and finally,

the angle of divergence of the gas jet.

One of the injectors described in the above cited publications is illustrated in fig. 1a to 1d, that is to say one that has been found to be particularly suitable for achieving the object of the present invention, wherein it is of course understood that even other types of injectors described in said publications can be applied to supply gas burners falling within the scope of the present invention.

In fig. 1a to 1d, the controlled gas jet injector 20 is provided with an inner main gas injection duct 22 having a circular cross-sectional shape, which extends along the axis 10 and is dimensioned to ensure a sufficient gas flow rate. At least one initiator conduit is provided to feed additional gas into the main conduit 22, the at least one initiator conduit having a smaller size than the main conduit.

In the preferred embodiment, two air flow regulating devices 24 and 25 are provided connected to the main conduit 22. The diameter of the gas flow regulating means 24 and 25 and their orientation are critical parameters related to the gas control efficiency and are chosen accordingly. On the other hand, the number of airflow moderators 24 and 25 to be or that can be applied depends on the size (i.e., cross-sectional area) of the main duct 22. Preferably, the axes 12 and 13 of the air flow conditioners 24 and 25 are both perpendicular to the injection axis 10 of the main conduit 22, and the air flow conditioners 24 and 25 are themselves connected tangentially to the main conduit 22, as best shown in fig. 1 b.

The gas jet injected by the injector 20 diverges along the flow direction or injection axis 10, thereby defining a divergence angle γ. The spread angle gamma of the gas jet emitted from the controlled gas jet ejector 20 is controlled by the gas injection in the gas flow regulating devices 24 and 25 so that the spread angle gamma of the gas jet can be varied between two different boundary angles, i.e. a minimum angle and a maximum angle, which are defined by the angles alpha and beta shown in fig. 1c and 1d, respectively. When gas flows from the main conduit 22 and the gas flow regulating devices 24 and 25 are inactive (i.e. not operating), the gas jet emitted from the controlled gas jet ejector 20 has a spread angle α (fig. 1 c). Conversely, when the gas flow regulating devices 24 and 25 inject gas tangentially into the main conduit 22, the gas jet ejected from the controlled gas jet injector 20 has a diffusion angle β, where β > α (fig. 1d), so that, downstream of the injection point, the movement of the gas flow is divided into a median rectilinear component along the injection axis 10 with high kinetic energy and a peripheral tangential component that rotates the peripheral portion of the gas flow about the injection axis 10. Thus, the angle β of the gas at the outlet of the controlled gas jet ejector 20 is greater than the angle α, so that the gas tends to expand turbulently. The variation of the angle y between its minimum value a and maximum value β can be made to occur equivalently, in a continuous manner and in a selective manner, according to practical needs and requirements. In the embodiments and related variants to be described below, the following two types of air flow regulating devices can be used equivalently: the gas flow regulating means enable the value of the angle γ defined by the jet of gas emitted by the injector to be regulated in a continuous manner, or preferably to vary said angle γ between predetermined values comprised between the above-mentioned minimum value α and maximum value β.

The gas burner according to the invention, comprising a plurality of combustion sections, comprises a controlled gas jet injector 20 supplying different elements of the burner with fuel, wherein said different elements are adapted to feed each combustion section associated therewith. The specific shape and configuration of some of the elements constituting the burner according to the invention are chosen so as to be able to receive the jets of gas emitted by the injector 20 most effectively in all the possible cases of their angle γ.

Fig. 2 and 3 schematically illustrate a first preferred embodiment of a gas burner 16, said gas burner 16 comprising a plurality of combustion sections and using a controlled gas jet injector 20, wherein the combustion sections are constituted by a plurality of flame rings (for example three such flame rings 40, 42 and 44) preferably arranged concentrically around the injection axis 10 of the gas.

The gas burner 16 with the plurality of flame rings comprises a first peripheral burner element comprising a bowl-shaped body 30 and an annular burner head 34, and a second intermediate burner element comprising a cylindrical body 36 and an annular burner head 39. The gas burner 16 also comprises a controlled gas jet injector 20 supplying fuel gas to its different combustion sections. The controlled gas jet type injector 20 includes gas injection devices 22, 24 and 25. An air flow adjustment device (not shown) of the type having a plurality of operational settings is provided in a conventional manner to adjust the heat output of the burner.

The bowl-shaped body 30 has a handle (shank) open at the bottom and bounded laterally by an inner conical ring (circlet)27 and an outer conical ring 28 (fig. 3). These conical collars 27 and 28 are preferably coaxial with each other and their longitudinal axes coincide with the injection axis 10. Said conical collars 27 and 28 taper upwards, i.e. in the direction of the advancing movement of the gas stream. The shank of the bowl-shaped body 30 extends radially outwardly at its upper portion, thereby forming a hollow disc with a cavity (bore) in its center, bounded by a lower surface 46 and a smaller diameter upper surface 47, forming an open-topped annular rim 49 at the end of the hollow disc. The circularly shaped spray head 34 is placed on top of said annular rim 49 of the hollow disc of the bowl-shaped body 30, so that the flame rings 42 and 44 can be formed in this way. Inside the peripheral burner element there are two venturi-forming chambers 31 and 32 (fig. 2) communicating with each other. A gas/air mixture is formed within the bowl-shaped body 30 and dispensed therein.

The cylindrical body 36 of the intermediate burner element rests on the bowl-shaped body 30 of the peripheral burner element, thereby being arranged coaxially with the bowl-shaped body 30 and forming two chambers 32 and 35 communicating with each other, the chambers 32 and 35 themselves forming a venturi tube in which the gas/air mixture is formed and distributed.

The constriction 32 of the venturi tube of the intermediate burner element is preferably accommodated in a coaxial arrangement in the constriction 31 of the venturi tube of the peripheral burner element. The arrangement of the two devices 31 and 32 for mixing gas and air according to the invention enables a single injector 20 of the controlled gas jet type described above to be used to feed one or more flame rings 40, 42 and 44.

The controlled gas jet injector 20 is located below the handle of the bowl-like body 30, where the controlled gas jet injector 20 is arranged facing (i.e. opening) the apertures of the two gas/air mixing devices 31 and 32. The gas flow fed into the main conduit 22 and the gas flow regulating devices 24 and 25 is regulated by regulating means, which may be for example a gas tap or a valve (not shown), and in which a plurality of operating settings are provided. In a first operating setting of the gas flow regulating device, the gas is injected only through the main pipe 22, the gas jet at the outlet of the controlled gas jet injector 20 being ejected at an angle γ ═ α, so that the gas jet is only directed to impinge on and enter the internal mixing device 32, thereby providing a unique flame ring 40, as illustrated in fig. 2. In a second operating setting of the gas flow regulating device, the gas jet passes through both the main duct 22 and the gas flow regulating devices 24 and 25, the gas jet at the outlet of the controlled gas jet injector 20 being ejected at an angle γ ═ β, so that the gas jet is directed to impinge on and enter the mixing devices 31 and 32, thereby providing all the flame rings 40, 42 and 44, as best shown in fig. 3. In this case, a greater amount of air is drawn into the two air/gas mixing devices 31 and 32, which contributes to the efficiency of the gas burner 16, due to the increase in the turbulence level caused by the gas jet expanding with a motion consisting of a central component oriented along the injection axis 10 and a peripheral tangential component around the injection axis 10.

Schematically illustrated in fig. 4 and 5 is a variant of the first preferred embodiment described above, in which all the components of a further gas burner 216 having a plurality of flame rings have a similar configuration to that of one of the first preferred embodiment described previously, and the only difference compared to the first preferred embodiment described previously is that: in this example the manner in which the gas is supplied to flame rings 240, 242 and 244, which are preferably concentrically arranged about the gas injection axis 210. That is, the bowl-shaped body 230 comprises internal air/gas mixing means 233 for supplying flame rings 242 and 244, while the cylindrical body 236 comprises external air/gas mixing and distribution means 231 connected with air/gas distribution means 235 for supplying flame rings 240. These inner and outer air/gas mixing means 232 and 231 are defined by conical collars 227 and 228, preferably arranged coaxially about the gas injection axis 210, similarly to what has been described above with reference to fig. 2 and 3.

Thus, in a first operating setting of the gas flow regulating device, the gas jet at the outlet of the injector 220, which is directed to impinge on and enter the internal mixing device 232, is ejected at an angle γ ═ α, providing flame rings 242, 244, as illustrated in fig. 4; conversely, in a second operating setting of the gas flow regulating device, the gas jet at the outlet of the controlled gas jet injector 220, which is directed to impinge on and enter the mixing devices 231 and 232, is ejected at an angle γ ═ β, where β > α, thereby providing all the flame rings 240, 242 and 244, as best shown in fig. 5.

Fig. 6 and 7 schematically illustrate a second preferred embodiment of the invention, in which a gas burner 316 with a single flame ring with adjustable heat output is provided, wherein the aforementioned combustion section is constituted by a plurality of primary flame ports 350 and a plurality of secondary flame ports 352, respectively. The single flame ring is formed by a combination of the flame ports 350 and 352 described above.

The gas burner 316 with a single flame ring with adjustable heat output consists of a base comprising a bowl-shaped body 330 and a top member comprising a cylindrical body 336 and an annular spray head 339. The bowl body 330 has a handle with an open bottom and is bounded laterally by an inner conical ring 327 and an outer conical ring 328. These conical rings 327 and 328 are preferably coaxial with each other and taper upwardly (i.e., in the direction of the advancing movement of the gas stream). The stem of the bowl-shaped body 330 extends radially outwardly at its upper portion, thereby forming a hollow disc having a cavity in the center defined by a lower surface 346 and an upper surface 347 having the same diameter. The peripheral perimeters 357 and 359 of the surfaces 346 and 347, respectively, come into contact with one of the opposite edges of the side surface 354 of the base portion in which said plurality of holes 352 are formed. What is actually provided in this way is the air/gas mixing and distribution device 331, 333 which feeds the plurality of auxiliary flame ports 352.

The base is assembled coaxially along the axis 310 with a top member obtained by placing a spray head 339 over the cylindrical body 336 forming a plurality of primary flame ports 350. The plurality of primary flame ports 350 may of course be formed directly on the side surface of the cylindrical body 336. The cylindrical body 336 fits into or is associated with the side surface 354 of the base without interrupting any cylindrical continuity; thus, the plurality of flame ports 350 and 352 are located on the same cylindrical surface, thereby constituting the same flame ring, which is therefore capable of delivering an adjustable heat output, since the plurality of flame ports 350 and 352 can be supplied independently of each other.

The overall combination of the different elements and components making up the gas burner 316 enables further the formation of two chambers 332 and 335 communicating with each other, the chambers 332 and 335 forming a venturi tube in which the gas and air are mixed, the air/gas mixture thus formed being distributed to feed the plurality of primary flame ports 350. The constriction 332 of the venturi of the top burner part is accommodated in the constriction 331 of the venturi of the bottom burner part. This arrangement of the two devices 331 and 332 for mixing gas and air according to the invention enables a single injector 320 of the aforementioned controlled gas jet type to be used to provide a plurality of flame ports 350, 352.

The controlled gas jet injector 20 is located below the handle of the bowl body 330 where the controlled gas jet injector 20 is arranged to face (i.e., open) the apertures of the two gas/air mixing devices 331 and 332.

The principle of operation is similar to one of the previously described embodiments, so that in this case any further explanation is intentionally omitted.

However, for the sake of greater clarity, it seems appropriate here to be the only characteristic part of the reminder operation, namely to supply fuel gas to the heating portion of the burner formed by the plurality of flame ports 350 by the controlled gas jet injector 320 when the injection angle γ of the gas is equal to α (fig. 6), and to supply fuel gas to the combustion or heating portion of the burner formed by the plurality of flame ports 350 and 352 when the injection angle γ of the gas is equal to β, where β > α (fig. 7).

Of course, the gas supply means may be arranged to be able to feed only one set of said plurality of flame ports 350 and 352 depending on (i.e. depending on) the value taken by the angle γ, so that individual burner sections can be activated partially, i.e. only individual sections of said burner sections can be selectively ignited.

It will of course be appreciated that the following is also contemplated for the first and second preferred embodiments described above: each burner may be provided with a second air/gas mixing device 32 housed in a non-coaxial arrangement; 232; 332, the first air/gas mixing device 31; 231; 331. moreover, the air/gas mixing devices 31 housed one inside the other; 231; 331 and 32; 232; 332 may be provided in more than two, for example three, so that in this case three distinct combustion sections may be supplied separately with the fuel mixture.

Fig. 8 and 9 schematically illustrate a catalytic gas burner of a third preferred embodiment comprising a plurality of combustion sections, wherein said combustion sections may be defined as part of a support 464 of porous material.

The catalytic gas burner 416 comprises a support 464 of said porous material, a chamber 466 and the aforementioned controlled gas jet injector 420. The support 464 of porous material is comprised of a polyhedral structure having a plurality of channels or capillaries 468 extending substantially along the axis 410. These channels or capillaries 468 can be independent of each other (i.e., not in communication with each other), as represented in fig. 8 and 9, or can constitute a segment comprising a plurality of communicating channels, wherein, however, the different segments are independent of each other. Catalysts (catalyst means) capable of causing the combustion process to take place, i.e. to cause the combustion process, are further dispersed in the support 464 of porous material. The chamber 466 is a fixed fixture that holds the porous material support 464 with the aid of means generally known in the art (not shown in the figures). To this end, the chamber is in fact provided with a suitably polyhedral shaped first open end capable of ensuring a hermetic and airtight bond with the support 464 of porous material. In a second end of the chamber 466, opposite to the above-mentioned first open end, a cavity is provided which allows the controlled gas jet injector 420 to be inserted therein, the controlled gas jet injector 420 being associated with said chamber 466 by means widely known in the art.

The controlled gas jet injector 420 is oriented to open (i.e. face) to one side of the porous material support 464 so that it is exposed to the gas stream injected against it, which can be combusted by mixing with air there. The gas flow rate may be adjusted by providing suitable actuating means (not shown), such as gas taps or valves, with a plurality of operational settings, and the gas flow regulating means 424, 425 may be controlled to control the ejection angle gamma of the gas accordingly. In a first operating setting of the starting device, the gas jet is emitted at an angle γ ═ α, so that the gas jet is directed only to strike a first portion 460 of the support 464 of porous material, said first portion 460 consisting of a first set of channels (i.e. combustion portions) 468. The portion 460 is thus supplied with fuel mixture and combustion can occur. In a second operating setting of the activation device, the air flow adjustment device 424, 425 changes the angle γ described above to a value of γ ═ β. Whereby the gas jets are directed to impinge on a second portion or group 464 of the combustion portion, other than the above-mentioned first portion 460, thereby allowing combustion to take place over substantially the entire surface of the support 464 of porous material. The air flow adjustment means 424, 425 are able to allow the angle γ to vary between a minimum value α and a maximum value β, continuously or in discrete steps, so that the actual area of the porous support 464 participating in the combustion will have a variable range depending on the value of said angle γ.

The arrangement according to the invention is therefore fully effective for achieving the objects indicated above. In particular, it ensures that a group of combustion sections can be supplied in a controlled manner from a single controlled gas jet injector 20 in an efficient manner according to the actual needs. Thanks to the arrangement according to the invention, it is possible to provide the following cooktop: wherein a single burner can have a heating zone adapted to the size of the vessel, i.e. the pan or pot to be heated. This achieves the advantageous effect of saving fuel while ensuring improved cooking performance and results.

It will be readily understood that the invention may be carried out in a variety of ways other than those described above, and that various other modifications may be made without departing from the scope of the invention.

Claims (18)

1. A gas burner (16, 216, 316, 416) comprising a plurality of combustion portions (40, 42, 44; 240, 242, 244; 350, 352; 468) adapted to receive a gas flow from a gas supply means (20, 30, 36; 220, 230, 236; 320, 330, 336; 420, 466), said gas supply means (20, 30, 36; 220, 230, 236; 320, 330, 336; 420, 466) comprising injector means (20, 220, 320, 420) adapted to inject a gas flow, said gas flow diverging along a flow direction (10, 210, 310, 410) so as to define a diffusion angle γ, characterized in that: gas flow regulating means (24, 25; 224, 225; 324, 325; 424, 425) are provided for varying the diffusion angle γ, so that the gas flow can be supplied to one or more of the plurality of combustion sections (40, 42, 44; 240, 242, 244; 350, 352; 468) in dependence on the regulation of the diffusion angle γ.

2. Gas burner (16, 216, 316, 416) according to claim 1, wherein said plurality of combustion sections (40, 42, 44; 240, 242, 244; 350, 352, 468) are fed by a single injector device (20, 220, 320, 420).

3. Gas burner (16, 216, 316) according to claim 1 or 2, wherein said plurality of combustion portions (40, 42, 44; 240, 242, 244; 350, 352) is fed by a plurality of venturi tubes having a portion (27, 28; 227, 228; 327, 328) facing said injector means (20, 220, 320) and arranged coaxially around a gas flow injection axis (10, 210, 310).

4. A gas burner (16, 216) according to any of the preceding claims, wherein said plurality of combustion portions (40, 42, 44; 240, 242, 244) are in the form of a plurality of flame rings.

5. The gas burner (16, 216) of claim 4 wherein the plurality of flame rings (40, 42, 44) are concentrically arranged about a gas stream injection axis (10, 210).

6. A gas burner (316) according to any of claims 1 to 3, wherein the plurality of combustion portions (350, 352) is in the form of a first and a second plurality of flame ports arranged to form a single flame ring extending around the gas stream injection axis (310).

7. Gas burner (16, 216, 316, 416) according to claim 1, comprising a support (464) of porous material, wherein said combustion portion is formed by a plurality of channels or capillaries (468).

8. The gas burner (16, 216, 316, 416) of claim 8, wherein said plurality of channels or capillaries (468) are independent of each other.

9. The gas burner (16, 216, 316, 416) of claim 7, wherein said plurality of channels or capillaries (468) are arranged to form separate sections independent of each other, and wherein said plurality of channels or capillaries (468) within each of said sections are in communication with each other.

10. Gas burner (16, 216, 316, 416) according to any of claims 7 to 9, wherein a catalyst adapted to cause a gas combustion process is dispersed in the support (464) of porous material.

11. A gas burner (16, 216, 316, 416) according to any one of the preceding claims, wherein said diffusion angle γ varies between a first minimum value α when said gas flow regulating means (24, 25; 224, 225; 324, 325; 424, 425) are not activated and a second maximum value β under the influence produced by said gas flow regulating means (24, 25; 224, 225; 324, 325; 424, 425) being operated, wherein β > α.

12. Gas burner (16, 216, 316, 416) according to claim 11, wherein said gas flow regulating means (24, 25; 224, 225; 324, 325; 424, 425) are adapted to vary continuously or selectively, i.e. in discrete steps, between said first minimum value a and said second maximum value β.

13. A gas burner (16, 216, 316, 416) according to claim 12, wherein said plurality of combustion sections (40, 42, 44; 240, 242, 244; 350, 352; 468) is arranged such that at least one of said combustion sections is activated when γ ═ α and all of said combustion sections are activated when γ ═ β.

14. Gas burner (16, 216, 316, 416) according to any of the preceding claims, wherein said gas flow regulating means (24, 25; 224, 225; 324, 325; 424, 425) are formed on said injector means (20, 220, 320, 420).

15. Gas burner (16, 216, 316, 416) according to claim 14, wherein said gas flow regulating device (24, 25; 224, 225; 324, 325; 424, 425) comprises a pair of ducts extending perpendicularly to a longitudinal axis (10, 210, 310, 410) of a main duct (22), said pair of ducts being tangentially connected to said main duct (22).

16. A gas burner (16, 216, 316, 416) according to claim 15, wherein said gas flow regulating device (24, 25; 224, 225; 324, 325; 424, 425) is adapted to inject a gas flow into the main conduit (22), thereby varying the diffusion angle γ between a minimum value α and a maximum value β, where β > α.

17. Cooking top comprising at least one gas burner (16, 216, 316, 416) according to any of the preceding claims.

18. Cooking top according to claim 17, wherein said gas flow regulating means (24, 25; 224, 225; 324, 325; 424, 425) are activated by means of a knob operated gas tap or valve means.