WO1996006304A1

WO1996006304A1 - A burner for gas cookers and hobs

Info

Publication number: WO1996006304A1
Application number: PCT/GB1995/001990
Authority: WO
Inventors: Gordon Edward Andrews
Original assignee: University Of Leeds Innovations Ltd.
Priority date: 1994-08-24
Filing date: 1995-08-22
Publication date: 1996-02-29
Also published as: AU3263395A; GB9417082D0

Abstract

A burner for a gas cooker or hob comprises a body (3) which defines a passage (10, 4) for the intake of primary air into the burner. A flame spreader (7) is mounted on the body (3) and defines therewith an annular gas/air mixing chamber (6). One or more orifices (7) are provided in the body (3) for connecting the air intake passage (10, 4) to the gas/air mixing chamber (6). A gas injector or needle (1) extends into the gas/air mixing chamber (6), and is spaced vertically from the inner surface of the flame spreader by a distance which causes the gas jet to impinge thereon.

Description

DESCRIPTION

A BURNER FOR GAS COOKERS AND HOBS

The present invention relates to a burner for gas cookers and hobs. The present invention also relates to a gas cooker or hob comprising one or more of said burners.

A common disadvantage associated with many known types of burners for gas cookers and hobs is that they are relatively tall. A principal reason for this is that gas/air mixing takes place within a chamber situated beneath the flame spreader part of the burner where gas and air mixing takes place by means of the so-called Venturi effect. This chamber essentially comprises a vertical sleeve or tube, the bottom end of which is closed and supports a gas nozzle, and the top end of which opens into the flame spreader. Primary air is drawn into the chamber through circumferentially spaced apertures in the side of the sleeve. Although the flame spreader itself may have a relatively small vertical height, this is offset by the sleeve beneath it. Space must be provided beneath the upper surface of the gas cooker or hob to accommodate this sleeve, as well as the gas pipes and control valves which connect the burners to a gas supply. A gas burner embodying the principals of design and construction described above is disclosed in GB-A-2190483A. Where primary air is drawn into a burner from beneath the upper surface of a hob, and the hob is mounted on a cupboard unit, problems can arise if the space directly beneath the hob is not isolated from the cupboard space. In this regard, whenever the doors of the cupboard are opened there will be fluctuations in the air pressure and hence in the flame intensity. Typically this manifests itself in flame flicker and in worst case situations the flame may go out. Increasingly there is a demand for gas cookers and hobs to be as compact and flat as is practicably possible. Accordingly, it is desirable and advantageous to design burners to be as flat as possible whilst remaining compatible with the installation requirements of the gas cooker or hob itself.

A burner which seeks to realise this objective is disclosed in GB-A-2100411. This burner comprises a cup shaped support which is mounted in an aperture in the upper surface or plate of a gas cooker or hob, and which carries a gas supply injector or needle in the bottom thereof. A substantially convex disc shaped body is removably supported above the upper surface of the plate on the cup shaped support and a flame spreader is, in turn, removably supported on the convex disc shaped member. A chamber is defined between the convex disc shaped body and the plate and between the convex disc shaped body and the flame spreader.

At the centre of the convex disc shaped body there is provided an open ended tubular portion which extends downwards into the throat of the cup shaped support so as to be concentric therewith and which opens at the top. into the chamber formed between the convex disc shaped body and the flame spreader. The convex disc shaped body is supported on the rim of, and centred with respect to, the cup shaped support by means of fins which extend radially outward from the open ended tubular portion. Between each adjacent pair of fins there is defined a radial passage which connects the chamber formed between the convex disc shaped body and the plate with the bottom end of the open ended tubular portion.

In use primary air for combustion is drawn into the burner through a circumferential gap provided between the perimeter of the convex disc shaped body and the upper surface of the plate. The primary air then passes through the radial passages defined between adjacent pairs of fins into the open ended tubular portion where it mixes with the gas from the gas supply injector or needle. The resultant gas/air mixture then passes into the chamber defined between the convex disc shaped body and the flame spreader and, after the normal fashion, through holes around the perimeter of the flame spreader, where combustion takes place. In this known burner, mixing of the gas with the primary air and distribution of the gas/air mixture is achieved by the so-called Venturi effect. This can be effective in ensuring complete and efficient combustion regardless of the type of gas used, whether natural or LPG, and even in the face of extensive gas pressure variations. However, in order to achieve Venturi mixing and distribution it is necessary to design the chamber between the convex disc shaped body and the flame spreader so that velocity increases and pressure recovers. This means that the cross-section of the chamber must increase as a function of radius from the centre to the perimeter.

In order to achieve an appropriate gas/air mixture it is also necessary to fit a sleeve within the open ended tubular portion the position of which relative to the bottom of the cup shaped support can be adjusted to regulate the primary air intake.

It will be apparent from the preceding description of the burner of GB-A-2100411 that whilst it may achieve the objective of having a relatively low profile, it is, nevertheless, still quite complex. Each of the component parts, and particularly the convex disc shaped body with its radially extending fins, requires careful design and is expensive to produce. Moreover, although the overall vertical height of the burner may be relatively small as compared with other conventional burners, it is still significant. In this regard, the presence of the sleeve defining the gas/air mixing chamber significantly increases the height of the burner above the upper surface of the gas hob or cooker. Whilst the cup-shaped support extends the height of the burner below the upper surface of the gas cooker or hob.

It is an object of the present invention to provide a burner for a gas cooker or hob which is of very low height, even compared to that of GB-A-2100411. It is another object of the present invention to provide a burner which is of very simple design and which is comparatively inexpensive to produce.

It is yet another object of the present invention to provide a burner which achieves more efficient combustion, i.e. a reduction in the level of unburnt hydrocarbons and carbon monoxide, over known burner designs.

It is still another object of the present invention to provide a burner which achieves flame stability without necessitating the provision of an annular gas flow around the lower edge of the flame spreader as is commonly found in conventional burners. It is still another object of the present invention to provide a burner which allows primary air to be drawn in from either above or below the surface of the gas cooker or hob as a matter of design choice. According to the present invention there is provided a burner for a gas cooker or hob comprising a body which defines a passage for the intake of primary air into the burner, a flame spreader mounted on the body and defining therewith an annular gas/air mixing chamber, and one or more orifices connecting the air intake passage to the gas/air mixing chamber, characterised in that a gas injector or needle extends into the gas/air mixing chamber, and is spaced vertically from the inner surface of the flame spreader by a distance which causes the gas jet to impinge thereon.

In this burner air is entrained in the gas by impingement of the gas against the inner surface of the flame spreader. Impingement jet mixing gives a radially spreading gas jet on the inner surface of the flame spreader with a greatly increased fuel surface area for mixing with the primary air than in a conventional burner design. This gives rapid mixing. For this reason the spacing of the gas injector or needle from the inner surface of the flame spreader is relatively small. It has been found that the spacing oi the gas injector or needle from the inner surface of the flame spreader can be as small as the diameter of the gas injector or needle hole without necessitating any change in the gas injection pressure or flow rate. However, good impingement gas/air mixing can be achieved for impingement gap to gas injector or needle hole diameter ratio of between 10 and 1. Thus, the size of the impingement gap is not required to be set to close tolerances, but can be set to achieve the required overall burner height. In this way the gas burner of the present invention meets the aforesaid objective being very small in height.

The rate of primary air flow into the gas/air mixing chamber is determined by the size of the orifice or orifices connecting the air intake passage to the gas/air mixing chamber. Conveniently, an aperture is provided between the said body and the flame spreader through which the gas injector or needle extends into the gas/air mixing chamber and the size of this aperture is such as to leave an annular orifice around the gas injector or needle through which primary air can flow from the passage to the gas/air mixing chamber. Alternatively, several separate orifices may be provided to connect the air intake passage to the gas/air mixing chamber.

In one embodiment of the present invention an annular gas/air mix chamber is defined by the upper surface of the gas cooker or hob and the flame spreader, which is mounted directly thereon, and the primary air intake passage is defined by an aperture in the said upper surface of the gas cooker or hob. The air intake passage may comprise an annular orifice around the gas injector or needle, in which case the gas injector or needle is maintained in position in the centre of the aperture by a support situated beneath the gas cooker or hob. Alternatively, a plurality of circumferentially spaced apertures may be provided in the upper surface of the gas cooker or hob around the gas injector or needle.

In order to achieve improved mixing of the gas and air baffles may be provided in the mixing chamber. The gas/air mixing baffle may take the form of walls or pillars situated within the gas/air mixing chamber to cause turbulence. As an alternative, the surfaces defining the gas/air mixing chamber may be rough.

Preferably, a radially outwardly extending surface is provided immediately adjacent to and beneath the burner holes in the flame spreader. This surface gives rise to the so-called Coanda effect which gives improved flame stability.

In one embodiment of the present invention the gas/air mixing chamber is divided into upper and lower passageways by a dividing plate, each of which passageways leads to a respective set of burner holes. In this arrangement some of the primary air drawn into the burner passes through the lower passage and the rest is mixed with the gas. The rich gas/air mixture passing out of the upper burner holes is mixed with the lean gas/air mixture passing out of the lower burner holes during combustion. This rich/lean dual flame gas burner provides a reduction of nitrogen oxide emissions.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 shows a cross section of a burner according to the present invention mounted directly onto the upper surface or plate of a gas cooker or hob; Fig. 2 shows a cross section of an alternative design of the burner according to the present invention;

Fig. 3 shows a cross section of yet another design of the burner according to the present invention; Fig. 4 shows a cross section of a modified version of the burner of Fig. 1 with a circumferential mixing baffle provided within the flame spreader chamber;

Fig. 5 shows a cross section of another modified version of the burner of Fig. 1 with the flame spreader chamber split in two by a divider plate to give a rich mix and lean mix which reduces nitrogen oxide emissions;

Fig. 6 shows a detail of an alternative form of the plate which separates the air intake passage from the gas/air mixing chamber; and

Fig. 7 shows in cross section yet another gas burner embodying the present invention in which the flame spreader is mounted on the upper surface of a gas cooker or hob.

Referring firstly to Fig. 1 there is shown a gas supply needle or injector 1 which is mounted in an orifice formed in the upper surface 2 of a gas cooker or hob. Although not shown the needle or injector 1 is connected to a gas supply line via a control knob which regulates the gas flow rate in conventional fashion. The needle or injector 1 forms an air tight fit in the orifice and to this end it may, for convenience, be screwed into place.

The burner itself essentially comprises a circular plate 3 mounted on the upper surface 2 and defining therewith a first annular chamber 4, and flame spreader 5 mounted on the circular plate 3 and defining therewith a second annular chamber 6.

The circular plate 3 has a central aperture in it which is large enough to accommodate the needle or injector 1 and still leave an annular gap 7 around the needle or injector 1 which connects the chamber 4 to the chamber 6. This annular gap 7 defines an air controlling flow orifice through which primary air is drawn into the second annular chamber 6 to be mixed with gas from the needle or injector 1. The size of the annular gap 7 controls the primary air flow rate and ultimately determines the richness of the gas/air mix in the chamber 6. The circular plate 3 is supported above the upper surface 2 on an annular ring 8 and is located in position relative to the needle or injector 1 by means of locating pins (not shown) carried on the bottom edge of the annular ring 8 which engage in locating holes drilled in the upper surface 2. Holes or slots 10 are spaced around the annular ring 8 and these holes or slots 10 allow primary air to be drawn into the burner.

Primarily for cosmetic reasons the edge of the circular plate 3 extends downwards to lie proximate to the upper surface 2, but a gap 11 is retained between the two to leave a circumferential passage through which primary air can pass through to the primary air inlet holes or slots 10. The circular plate 3 also has on its upper surface, immediately proximate to the down-turned edge, an annular rib 12 which serves to locate and centre the flame spreader 5 on the circular plate 3.

It will be appreciated that the holes or slots 10 and the gap 11 each define a flow area which is much greater than the annular gap 7 in order not to impede the flow of primary air into the chamber 6.

The flame spreader consists of two separable component parts - a ring 13 having a plurality of burner holes or slots 14 in it, and a cap 15 which is located on and centred in the ring. It will be readily appreciated that both of these components can be produced easily and inexpensively. They may, for example, be pressed from sheet metal or cast.

In use primary air is drawn into the burner from above the upper surface 2 through the air intake holes 10 and forms a gas/air mixture in the chamber 6 of the flame spreader 5. This gas/air mixture passes out through the burner holes 14 in the ring 13 where combustion occurs. The burner of the present invention relies upon impingement of the gas jet on the lower surface of the cap 15 to achieve mixing of the gas with the primary air. This contrasts with the burner of GB-A-2100411 which relies on the Venturi effect to achieve gas/air mixing. With gas jet impingement mixing the spacing of the gas injector or needle 1 from the inner surface of the plate 15 is quite important and in tests it has been found that the best results are obtained by spacing the gas injector or needle 1 from the lower surface of the plate 15 by a distance of between 1 to 10 times the inside diameter of the gas injector or needle hole. The richness of the gas/air mixture for combustion in the chamber 6 can be varied by increasing or decreasing, as required, the size of the annular gap 7.

The circular rib 12 on the upper surface of the circular plate 3 not only serves to locate the flame spreader 5 in position, but also serves to stabilise the flames and direct them in an upward arc. In this regard, the circular rib 12 forms a ledge immediately beneath and adjacent to the burner holes 14 which gives rise to the so-called Coanda effect on the flames exiting therefrom. It will be appreciated that it is very much easier and less costly to provide a burner with a ledge or surface immediately beneath and adjacent to the burner holes to achieve flame stability through the Coanda effect than it is to provide an annular gas flow around the burner, as is commonly found in conventional burners. However, should this method of flame stabilisation not be required, the conventional annular gas flow technique can be used instead without adding to the gas burner height.

It will be apparent from the above description and from the drawing of Fig. 1 that the burner of the present invention is of very low height compared to that of GB-A-2190483A and of GB-A-2100411A. All of the burner lies on and above the upper surface 2 of the gas cooker or hob and only the gas injector or needle 1 itself is actually mounted in the upper surface 2.

Furthermore, the design of the burner of the present invention readily lends itself to being dismantled to gain access to the gas injector or needle 1. Finally, the burner of the present invention is of much simpler design than that of known burners and as a consequence it is comparatively easy and inexpensive to produce. Referring now to Fig. 2 there is shown another design of a gas burner according to the present invention in which the same reference numerals have been used to identify component parts which are common to the design of Fig. 1. This burner is essentially identical to that of Fig. 1 except that the flame spreader 5 comprises a single component which for convenience is formed from a sheet metal pressing, and the support for the circular plate 3 takes the form of a shallow dish shaped member 8 having a hole in the centre which serves to locate it relative to the gas needle or injector 1. As shown, the dish shaped member 8 sits on the upper surface 2 of the gas cooker or hob, and may, if required, be secured thereto by means of grub screws. Holes or slots 10 are formed in the upwardly extending sides of the dish shaped member 8 and these allow primary air to be drawn through into the burner for combustion. Pins or lugs 16 are provided on the upper edge of the dish shaped member 8 and these engage in correspondingly positioned holes in the circular plate 3 to locate the two components relative to each other. As shown, the profile of the periphery of the circular plate 3 differs from that of Fig. 1 but this is of no great significance and the profiles are essentially interchangeable, save that shown in Fig. 2 particularly lends itself to being pressed in sheet metal, as indeed do the designs of the other two components 5 and 8.

Referring now to Fig. 3 of the drawings there is shown yet another design of a gas burner according to the present invention. In this design the circular plate 3 comprises a shallow dish shaped portion 20 having a hole in the centre thereof which locates it over a gas needle or injector 1 mounted in the upper surface 2 of a gas cooker or hob. Holes or slots 21 are provided in the upwardly extending sides 22 of the dish shaped portion 20 and these provide inlets for the intake of primary air. A raised ledge 23 extends radially outwards from the side 22 of the dish shaped portion 20 on which is supported a shallow dish shaped member 24. This shallow dish shaped member 24 is centred on and retained in place on the ledge 23 by an annular abutment face 25. It will be noted that between them the dish shaped portion 20 and the dish shaped member 24 define a chamber 4 as found in the previous two designs. Holes or slots 26 are provided in and around the side of the dish shaped member 24 and the top is closed by a cap 27. Together the dish shaped member 24 and the cap 27 define a flame spreader having a gas/air mixing chamber 6 as found in the previous two designs. The circular plate 3 and the dish shaped member 24 may conveniently be pressed from sheet steel, whilst the cap 27 may be cast. Operation of the burner shown in Fig. 3 is as described with reference to the burner shown in Fig. 1.

Referring now to Fig. 4 of the drawings there is shown a modified version of the burner of Fig. 1. In this burner improved gas and air mixing is achieved by providing an annular baffle 30 on the inside of the cap. This baffle 30 ensures that the gas jet impinging against the inner surface of the cap is directed downwards to mix with the primary air passing through the annular gap around the gas injector or needle 1 before passing on to the burner holes. Of course, the annular baffle 30 may be replaced by pillars and even by making the surface of the gas/air mixing chamber 6 rough. Referring now to Fig. 5 of the drawings there is shown yet another modified version of the burner of Fig. 1. In this burner the ring 13 is provided with upper and lower burner holes 40 and 41, respectively, and with a radially inwardly extending plate 42. The plate 42 divides the gas/air mixing chamber 6 into two separate radially extending passages 43 and 44 of circular extent leading from the immediate vicinity of the gas injector or needle 1 to a respective one of the upper and lower burner holes 40 and 41. A hole is provided in the centre of the plate 42 through which the gas needle or injector 1 passes to leave an annular gap 45. The plate 42 serves to split the primary air being drawn into the burner so that only a limited amount thereof passes though into the upper passage 43 to be mixed with the gas, whilst the rest passes through into the lower passage 44. The result of this is that a rich gas/air mixture is obtained in the upper passage 43 and passed to the upper burner holes 40, where combustion occurs. However, as combustion occurs air is drawn into the flame from the lower burner hole, thus giving a rich/lean fuel mixture which helps to reduce nitrogen oxide emissions from the gas burner.

Fig. 6 shows a modification to the plate 3 which separates the air intake passage 4 from the gas/air mixing chamber 6. Instead of providing a large central aperture a plurality of circumferentially spaced holes 7 are provided in the plate 3 around the gas injector or needle 1. This design has the advantage of supporting the fuel pipe in the gas burner rather than in the cooker or hob top 2. It also ensures that the plate 3 is accurately centred on the gas injector or needle 1.

Referring finally to Fig. 7 of the accompanying drawings there is shown a gas burner embodying the present invention in which the fleune spreader 5 is mounted directly on the upper surface of a gas cooker or hob 2. Primary air is drawn into the chamber 6 defined by the fleune spreader 5 and the surface 2 through an annular orifice 50 in the said surface 2 at the centre of which is situated the gas injector or needle 1. The gas injector or needle 1 is maintained in this position by support means situated beneath the gas cooker or hob or by the inherent rigidity of the gas supply pipe to which it is connected. However, as an alternative a plurality of circumferentially spaced holes may be provided in the said surface around the gas injector or needle 1 in much the same way as is shown in Fig. 6.

The gas burner shown in Fig. 7 has the advantage of having an even smaller vertical height than the gas burners shown in Figs. 1 to 5, wherein a separate body is used to provide a primary air intake passage into the gas/air mixing chamber. However, because air is drawn from the space beneath the cooker or hob problems may arise if this space is subject to variations in air pressure such as may occur if the gas cooker or hob is mounted on a cupboard. As the doors of the cupboard ^are opened flame flicker may occur.

Claims

1. A burner for a gas cooker or hob comprising a body (3) which defines a passage (10,4) for the intake of primary air into the burner, a flame spreader (7) mounted on the body (3) and defining therewith an annular gas/air mixing chamber (6), and one or more orifices (7) in the body (3) for connecting the air intake passage (10,4) to the gas/air mixing chamber (6), characterised in that a gas injector or needle (1) extends into the gas/air mixing chamber (6), and is spaced vertically from the inner surface of the flame spreader by a distance which causes the gas jet to impinge thereon.

2. A burner according to claim 1, characterised in that the vertical spacing of the gas injector or needle (1) from the inner surface of the flame spreader (5) is between 1 to 10 times the diameter of the gas injector or needle hole.

3. A burner according to claim 1 or 2, characterised in that a single annular orifice (7) is provided in the said body (3) between the said air intake passage (4) and the said gas/air mixing chamber (6) for the admission of primary air to the said chamber (6), and the gas injector or needle (1) is situated at the centre of the said orifice (7).

4. A burner according to claim 1, 2 or 3, characterised in that a plurality of circumferentially spaced orifices (7) are provided in the said body (3) between the said air intake passage (4) and the said gas/air mixing chamber (6) for the admission of primary air to the said chamber (6), which orifices (7) are radially spaced from the gas injector or needle (1).

5. A burner according to any preceding claim, characterised in that the said body (3) comprises a circular plate (3) and annular support means (8) for supporting the circular plate (3) above the upper surface (2) of a gas cooker or hob, the said annular support means (8) having radial passages (10) therein for admitting primary air into the annular passage (4) defined by the said body (3), the said upper surface (2) and the said annular support means (8).

6. A burner according to any one of claims 1 to 4, characterised in that the said body is defined by the upper surface (2) of a gas cooker or hob, the said flame spreader (5) being supported therein, and primary air for combustion is drawn into the said gas/air mixing cheunber (6) from below the said upper surface (2) through one or more orifices (50) therein.

7. A burner according to any preceding claim, characterised in that the said flame spreader

(5) comprises an annular ring (13) having a plurality of burner holes or slots (14) in it, and a cap (15) which is supported on and centred in the ring (13).

8. A burner according to any preceding claim, characterised in that the gas/air mixing chamber (6) is divided vertically into upper and lower radial passageways (43 and 44) by a radially extending dividing plate (42), each of which radial passageways leads to a respective set of burner holes (40 and 41).

9. A burner according to any preceding claim, characterised in that air baffles are provided in the said gas/air mixing chamber.

10. A burner according to any one of claims

1 to 8, characterised in that the surfaces defining the gas/air mixing chamber are roughened.

11. A burner according to any preceding claim, characterised in that a radially outwardly extending surface is provided immediately adjacent to and beneath the burner holes in the flame spreader, which surface gives rise to the so-called Coanda effect and provides improved flame stability.

12. A gas cooker or hob comprising one or more gas burners according to any of the preceding claims.