GB2586077A

GB2586077A - Domestic gas fire burner unit

Info

Publication number: GB2586077A
Application number: GB1911088.1A
Authority: GB
Inventors: Alan Charmer Robert
Original assignee: NU FLAME Ltd
Current assignee: NU FLAME Ltd
Priority date: 2019-08-02
Filing date: 2019-08-02
Publication date: 2021-02-03
Anticipated expiration: 2039-08-02
Also published as: GB201911088D0; GB2586077B

Abstract

A gas burner 100 for maintaining a continuously burning flame over one or more flame ports 130a-g. The burner includes a gauze sheet 520 set back behind the flame ports 130a-g. The gas flow area through the gauze sheet 520 may be larger than the gas flow area through the flame ports 130a-g, such that restriction of gas flow due to the reduced open area of the gauze sheet 520 is mitigated or eliminated, while preventing flashback into a mixing chamber 120 of the burner 100.

Description

Domestic Gas Fire Burner Unit

Technical Field

The present invention relates to gas burners, and in particular those used in domestic gas fires and outside burners for burning Natural Gas (NG) and/or Liquid Petroleum Gas (LPG).

Background

A fireplace is often the heart of the home, providing warmth and light during colder months. With concerns about pollution and air quality, particularly in big cities, coal and wood burning fires are increasingly being seen as being environmentally unfriendly. Gas fires, by contrast, are clean burning and so represent an environmentally friendly and attractive way to heat a room in a domestic building.

A modern domestic gas fire tends to be of a maximum Heat Input of 7kW net heat input, largely because fires up to this level of Heat Input do not require additional ventilation in order to burn safely. When installing higher Heat Input gas fires, ventilation has to be added to the building, such as in the form of an air brick. Such an air brick will necessarily allow cool outside air to be drawn into the property, which affects the room temperature. As a result, gas fires with heat inputs above 7kW are not the norm.

By way of further background, a gas fire typically includes a gas burner that is arranged to mix the fuel (NG or LPG) and air and to distribute the air and fuel across the width of the fire, as desired. Such a gas burner consists of a Venturi tube (often simply referred to as "a Venturi") sealed to a box or mixing chamber which has holes or ports in its upper surface for feeding the fuel-air mixture into the fire. When lit, the flames of the fire sit over the individual ports or holes in the burner top. The ports or holes may all be of the same size or of different sizes to vary the flame heights and/or widths. The mixing chamber of the burner may also have one or more baffles to even out the flame heights.

Typically the holes or ports are of a size and shape to provide the desired effect, be it tall or wide flames, with a sufficient level of aeration, (primary aeration) to create also a good degree of glow.

This principle has also been used with a so-called "outside burner" where, as its name implies, the burner is designed to be used outdoors and to provide a flame effect (tall flames) with little glow.

To explain the operation of a typical burner within an appliance: there is a gas supply provided from the gas main (Natural Gas) or from a gas bottle or tank (LPG) that passes to a controller or tap. The tap or other controller is configured both to turn the gas supply on and off and to vary the gas flow. From the tap, the gas passes via a pipe to an injector nozzle which limits the flow in order to obtain the desired maximum heat input or less.

The injector or nozzle can either have a single hole or be multi-hole. From there, the gas then flows through the smaller hole/holes of the injector and into the Venturi of the burner. Due to the velocity of the gas flow into the Venturi tube, the tube draws in air, (primary air) to mix with the supplied gas. The level of primary air typically will determine the colour of the flames in the fire when lit (which variation in flame colour most readers will have been seen when operating a Bunsen Burner).

As the gas flows along the Venturi, it mixes with the air and this mixing and equalizing of pressure continues into the burner body in a mixing chamber. The burner body is designed to be of a size and shape suited to the appliance in which it is installed, and the upper surface of the burner body will have holes/ports that allow the gas-and-air mixture to flow through them and, when ignited, create the flame effect.

As will be apparent, the size and shape of the burner vary according to the size and configuration of the appliance/fire, and the number of ports and their sizes vary dependent on the flame height and effect being sought. The sizes and number of the burner ports/holes are also selected to ensure the aeration provided to the injector and Venturi is not undesirably restricted, although some restriction may.

Such burners are designed for the flames to burn on or above the surface of the ports and not inside the burner. However, a phenomenon known as "light back" can still occur, as will be explained further.

It is known that a condition can occur when operating a gas burner where the flames, rather than burning on the surface of the burner, can light back into the mixing chamber of the burner, affecting both the burner's combustion efficiency and the flames' appearance. It can also, under certain conditions, cause the burner to overheat, generating excessive temperatures. There is a risk that if this condition occurs then it could represent a danger of causing an explosion or another uncontrolled event.

In addition to what could be described as full light back, as detailed above, there is also a condition that arises, where, as the fire is turned off and the flames gradually diminish, the flame lights back into the burner, burning the last remaining gas in the mixing chamber and causing a "pop". Although this phenomenon does not in practice represent a danger, sometimes the pop can be quite loud and cause concern. Indeed, it does result in customer complaints, and so needs to be prevented.

Herein, the term light back is used to refer to any situation where flame is not burning on the surface of the burner, but instead the gas/air mixture undesirably transitions to burn within the burner.

This condition is known to be worse when the burner is operated at elevated temperatures, as would normally be the case in a gas fire with a so-called fuel effect above the burner, e. g. imitation coals, pebbles or wood pieces. Typically, when a gas fire has imitation coals/pebbles or wood pieces, it is referred to as a fuel effect gas fire, where the aim is to create a gas fire that mimics a traditional solid fuel fire, so as to produce a flame effect and glowing fuel effect pieces.

Light back can and does, however, occur with any burner, regardless of the temperatures involved, under certain conditions and where nothing is done to mitigate the effect. Indeed, over and above a fuel effect gas fire, any appliance where gas is burnt can be subject to light back conditions.

It is also known that for fires and appliances designed to burn LPG (Propane and/or Butane) then the tendency of a light back condition to occur can be far worse. In different countries there are variants of both Natural Gas (G20) and Liquid Petroleum Gas (e.g. Propane G31, Butane G32) with different calorific values and densities; however all can suffer from light back conditions if the burner is poorly designed.

As one solution to this problem, it is known for domestic gas fires that if the flame ports/holes of the burner are restricted to less than approximately 0.5mm in width or diameter then light back may be avoided. In addition, the depth of the port, i.e., the thickness of the burner body in the area of the flame port, can affect the tendency for light back problems to occur, with reduced likelihood of light back occurring with deeper ports. However, for many commercial applications, the burner bodies are made of sheet metal of a predetermined low thickness, such that light back will tend to occur.

The use of small-diameter, deep ports also conflicts with the desire to provide large sized flames, which require larger sized flame ports. Larger flame ports are also required to generate the required flow rate to ensure that enough primary air is entrained through the Venturi.

For most such applications, a sufficiently large sized flame port will be greater than 0.5mm wide. This is mainly because, from a design perspective, the sizes of the appliance/fuel bed, coupled with the desired heights of the flames and the gas volume available, there is a limit to the numbers of ports you can have. Therefore, with most such appliances, having ports restricted to 0.5mm in width/diameter is not possible.

The limitation on the port size comes from the requirement to have sufficiently large sized flames, and typically the size of the fire also dictates the maximum size of the burner. As an example, for a typical 7kW gas fire the ports may be approximately 5mm in diameter and there may be around 7ports, depending on the design of the burner, in order to provide flames of the desired size.

One means that is known to reduce light back is to dispose a thin gauze (a mesh with small openings) immediately, i.e., less than 0.5mm, behind the main port. The gauze is sealed around the port so that the gas and air mixture must pass through the gauze before flowing into the main port. However, a drawback of such an arrangement is that, typically, such a gauze will have an open area of only around 50%, which restricts the flow of the gas and air mixture and so brings into play a further design limitation.

Essentially, the gauze has the effect of reducing the effective open area of the flame port/hole, and in turn the aeration. To correct this issue, it is possible to add more flame ports; however, as will be understood, with a set flow and more ports the flame height will be shorter, which is not preferred.

As explained above, with a gas burner, the number and size of the flame ports/holes is important because they not only determine the size of the flames but they also affect the back pressure experienced by the Venturi, and hence the level of primary air intake. This in turn affects how fully and cleanly the gas is burned and consequently also the flame colour.

A balanced combination of port size with light back gauze therefore has to be provided, which however limits the flame effect and flame size options.

The future is also expected to bring about increasing fuel prices, better insulated homes and to result in higher-efficiency gas fires operating with lower heat inputs. It is therefore a challenge to try to generate the same flame effect while burning less gas, which calls for smaller or fewer ports, while still seeking to prevent light back.

Summary of the Invention

According to the present invention, there is provided a burner for generating a flame by burning gas, the burner comprising: a burner body having an inlet for receiving gas from a gas source and having one or more flame ports, the burner body being arranged to direct a flow of the gas through the one or more flame ports to sustain a flame on the outside of the burner body adjacent each of the flame ports when the burner is lit; and a gauze disposed inside the burner body and set behind the one or more flame ports such that the flow of gas will pass through the gauze within the burner body before flowing into the flame ports.

In embodiments of the invention, the gauze may be mounted across one or more openings within the burner body, the one or more openings having a total cross-sectional flow area that is greater than a total cross-sectional flow area through the one or more flame ports. The gauze may present an effective flow area for the gas through each opening that is less than the cross-sectional flow area of the one or more openings, and the effective flow area for the gas through the gauze at each of the one or more openings may be equal to or greater than the cross-sectional flow area through respective ones of the one or more flame ports into which the gas passes after passing through the one or more openings.

In these embodiments, each port may have a respective opening, such that the flow of gas will pass through each opening and into the respective port. The gauze may be provided as a single sheet mounted across all of the one or more openings. Alternatively, where there are two or more openings, the gauze may be provided as a separate sheet mounted across each opening.

In alternative embodiments, there may be a single opening, such that the flow of gas will pass through the single opening and into all of the flame ports.

In the foregoing embodiments, the gauze may be mounted to a gauze plate defining the one or more openings. The gauze may be sandwiched between the gauze plate and another gauze plate.

In embodiments with a gauze assembly including a gauze and a gauze plate, the gauze assembly may be mounted in the burner body behind the one or more flame ports.

In further or in any of the foregoing embodiments, the gauze may be formed from a woven wire mesh.

In further or in any of the foregoing embodiments, the gauze may have an open area of 60% or less. The open area may be 50% or less.

In further or in any of the foregoing embodiments, the gauze may be set back behind the flame ports by at least 1.0 mm, preferably at least 1.2 mm.

In further or in any of the foregoing embodiments, the gauze may be set back behind the flame ports by at most 10 mm, preferably at most 8 mm.

In further or in any of the foregoing embodiments, one or more collection chambers may be disposed between the gauze and the ports such that the flow of gas will pass through the gauze and into a respective collection chamber before flowing into each flame port.

In further or in any of the foregoing embodiments, each flame port may define an outlet including a through hole with a minimum dimension greater than 0.5 mm, preferably greater than 2 mm.

In further or in any of the foregoing embodiments, the burner body includes 3 or more flame ports, preferably 5 or more flame ports, and more preferably includes 7 flame ports.

In further or in any of the foregoing embodiments, the burner further comprises a Venturi tube arranged to mix gas received from the gas source with air drawn into the Venturi tube by the gas flow, the mixed gas and air being directed into a mixing chamber in the burner body before passing through the gauze.

In further or in any of the foregoing embodiments, the burner body is made from sheet metal, preferably from steel.

In further or in any of the foregoing embodiments, the burner further comprises a baffle disposed in the burner body to improve the mixing of gas from the gas supply with ambient air and to help direct the flow of gas to the one or more flame ports.

Brief Description of the Drawings

To enable a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: Fig. 1A shows a top plan view of an embodiment of a gas burner according to the present invention; Fig. 1B shows a side cross-sectional view of the gas burner of Fig. 1A; Fig. 1C shows an end on view of the gas burner of Fig. 1A, illustrating the Venturi tube at the gas inlet; Fig. 2A shows a side view of a gauze assembly used in the embodiment of a burner of Fig. 1A; Fig. 2B shows a top plan view of the gauze assembly of Fig. 2A, illustrating the opening formed identically in the top and bottom gauze plates; Fig. 2C shows an end on view of the gauze assembly of Fig. 2A; and Fig. 3 shows a schematic cross-sectional view through the burner body of Fig. 1A, illustrating the gauze assembly mounted behind the flame ports.

Detailed Description

The present invention was made in order to address the aforementioned problems and design challenges associated with gas burner design. The invention is generally applicable to all gas burners, and is specifically beneficial when applied to domestic gas fires and outside burners facing increased design constraints to adapt to regulation and increasing fuel prices.

Embodiments of the invention are able to provide a means to prevent light back, while overcoming the flow rate restriction that arises when using a strip of gauze. Beneficially, such embodiments still use a sheet metal burner construction and permit sufficiently large sized ports to retain a good aerated flame effect, while using less gas.

This is primarily achieved by providing an arrangement in which the light back gauze is spaced away from the burner top, behind the ports, such that it has little or no restrictive effect on the gas flow through it. The gauze must of course be sealed around its edges and/or to adjacent portions of the burner so that the gas flow cannot bypass the gauze.

Without wishing to be bound by theory, it is believed that embodiments of the invention alleviate the effect of the gauze reducing (by around 50%) the effective open area of the flame port/hole. This is because, by disposing the gauze across a larger opening set back from the flame ports, the effective flow area across the gauze can be increased while maintaining the desired size of the flame port/hole.

In specific examples of the invention, this is achieved using a metal backing strip that has one or more holes that together have a larger combined area than the area of the flame ports, ideally at least twice the area. This allows the flow rate of mixed gas and air through the gauze to match the desired flow rate through the flame ports. Whether one hole is provided in the backing strip per flame port, or one or more larger communal holes are provided to each feed into two or more flame ports, the effect is to provide an increased flow area through the gauze behind the flame ports. As such, the gas and air mixture within the burner passes through the restrictive gauze across a wider open area than if it were positioned immediately behind or across the port, before then flowing essentially unrestricted into the smaller flame port. In this way, the restriction of the gauze is removed, but the gauze will still provide light back protection against the flames propagating into the burner body.

Turning now to the drawings, an embodiment of a burner 100 is shown in Figs. 1A-C, 2A-C and 3.

As shown in Fig. 1A, the burner includes a burner body 110 that defines a housing. The burner body 110 has a substantially rectangular shape in plan view, and includes a burner top exhibiting, in this instance, seven flame ports 130a-g distributed along its length. The burner body 110 is preferably formed from sheet metal such as steel that is cut, bent and welded into the desired housing shape. Of course, there is no restriction on the shape of the burner body 110, and any shape is possible; a rectangular construction is however desirably easy to make from sheet metal. The housing receives the further components of the burner, as detailed below.

The size and number of flame ports is not limiting on the invention, and may be adjusted according to the size, shape and distribution of flames desired to be produced by the burner. In this example, the flame ports 130a-g each have a width of 5mm, with the end flame ports 130a and 130g being wider and thinner than the intermediate flame ports 130b-f in order to produce a desired tapered flame effect. This arrangement is beneficial in a burner for a low depth profile gas fire, designed to be mounted to a flat wall without a cavity or chimneybreast behind the fire.

As seen in Fig. 1B, the burner body 110 is mounted on a burner base 400. A Venturi tube 200 is provided at one end at an inlet to the burner, as also seen in Fig. 1C, to receive gas from a gas supply, in a manner well known in the art. Gas fed into the Venturi tube will flow through the tube and entrain ambient air from outside the burner body, mixing the air into the gas flow. This entrained air is the primary air, and the ratio of primary air to gas in this mixture is substantially responsible for determining the colour and temperature of the flame produced by the burner 100 at the flame ports 130a-g.

After passing through the Venturi tube 200, the gas flow enters a mixing chamber 120 defined by the inside of the burner body 110. A baffle 300 is desirably disposed downstream of the Venturi tube to redirect the gas flow and help to distribute the gas and air mixture throughout the mixing chamber 120 and across all of the burner ports 130a-g. The baffle can be secured in place by a screw 310 passing through the burner base 400.

A gauze assembly 500 is mounted within the housing of burner body 110 directly behind the flame ports 130a-g, abutting the underside of the top sheet of metal defining the burner top. The gauze assembly 500is sealed around its edges and/or between its upper surface and the burner top to prevent gas flow from bypassing the gauze and ensuring the gas flow passes through the gauze.

In normal use, gas flows through the burner 100 and exist the flame ports 130a-g. The flow of gas through the flame ports 130a-g is set to support a continuously burning flame that sits above each flame port 130a-g. However, under light back conditions, the flame may propagate back through one or more of the flame ports 130a-g and burn the gas and air mixture within the mixing chamber 120. The gauze assembly 500, in particular gauze 520, prevents flames from propagating through it and therefore prevents light back within the mixing chamber 120.

Gauze assembly 500 is shown in more detail in Figs. 2A-C. The gauze assembly 500 includes an upper gauze plate 510, a lower gauze plate 530, and a gauze sheet 520 sandwiched between them. The upper and lower gauze plates 510, 530 in this example are identical, and each includes an opening 515, 535 respectively. It is not necessary for the gauze plates 510, 530 to be identical, although this may improve manufacturing speed and reliability, since a common component part can be used and easily combined to form the gauze assembly, rather than different parts having to be separately manufactured and correctly assembled.

It is, of course, possible to use only a single gauze plate 510 or 530 with the gauze sheet 520, but the sandwich construction used in this example is relatively easy to manufacture by spot welding the plates 510, 530 together with the gauze sheet 520 between them, and can be reliably sealed to prevent gas leakage around the outsides of the gauze assembly 500. In particular, it is important that no gaps exist around the outside of gauze assembly 500 that allow the gas flow to bypass the gauze. Typically this will mean there should be no gaps that are 0.5 mm or greater, as this would permit light back to occur by flames bypassing the gauze assembly 500 and propagating into the mixing chamber 120. For some conditions, depending on the gas being burned and environmental conditions such as wind, even gaps as small as 0.5 mm would allow light back, and the gauze assembly 500 should be sealed accordingly.

As can be appreciated, also with reference to Fig. 3, the upper gauze plate 510 includes a through hole 515 that defines both an opening in the gauze plate 510 and a collection chamber between the gauze sheet 520 and the flame ports 130a-g. An identical through hole 535 in the lower gauze plate 530 defines an opening in the gauze plate 530. Through holes 515 and 535 are aligned so as to define a common flow passage, although they need not be identical in size and shape.

By setting the thickness of the gauze sheets, the depth of the collection chamber 515 between the gauze sheet 520 and the flame ports 130a-g, i.e., the set back distance of the gauze sheet 520 from the flame ports 130a-g, is defined. It has been determined that a set back distance of 1.0mm, and preferably at least 1.2mm, is sufficient to allow a free flow of gas through the gauze sheet 520 and into the flame ports 130a-g. The thickness of the upper gauze plate 510 is thus set to obtain this desired set back of the gauze sheet 520 by using a plate of 1.2mm thickness.

In other embodiments, the gauze assembly 500 need not abut the underside of the burner top, and may be set back further from the burner top in order to increase the set back distance between the gauze sheet 520 and the flame ports 130a-g. However, if the set back distance is made too large, flames can still propagate through the flame ports 130a-g and cause light back to occur within the collection chamber 515 (instead of within the mixing chamber 120). To prevent this, for most applications the set back distance should be less than 10mm, preferably less than 8mm.

In the present embodiment, the openings 515, 535 in the gauze plates 510, 530 are elongated to provide a common opening and collection chamber for all of the flame ports 130a-g. Of course, it would also be possible to provide separate openings and/or collection chambers for each flame port 130a-g, or for any subset of flame ports, as desired. For example, separate openings in lower gauze plate 530 may feed into common collection chambers formed by upper gauze plate 530, or a common opening in lower gauze plate 530 may feed into separate collection chambers in upper gauze plate 510. Similarly, each collection chamber may feed into one or more of the flame ports 130a-g.

The exemplary openings 515, 535 have a width of 7mm, providing a total flow area for the openings that is substantially larger than the total flow area through the flame ports 130a-g. In general, this is to overcome the flow restriction presented by gauze sheet 520. Gauze sheet 520 may be made from a woven wire mesh or any other suitable construction such as a slitted sheet or other braided material. Such constructions will exhibit a restricted flow area of less than 100% of the area of the opening across which they are disposed. This is referred to as the open area, being the percentage of the area of the gauze sheet that is open to gas flow through it compared with the percentage that is occluded by the presence of the gauze material. The gauze open area will typically be 60% or less, and in the present embodiment the gauze open area is around 50%.

The effective flow area for gas through the gauze assembly is the area AO of the (smallest) opening for gas to flow through the gauze plates 510, 530 multiplied by the open area of the gauze sheet. With reference to Fig. 3 in particular, it is desirable to ensure that the effective area for the gas flow through the gauze sheet 520, for each flame port 130a-g (where these do not have common openings and/or collection chambers) is at least equal to the flow area AP through the respective flame port(s). In this way, the effect of the flow restriction created by the provision of gauze sheet 520, on gas flow through the flame ports 130a-g, is effectively mitigated or eliminated.

The burner of the present invention is thus able to prevent light back occurring in a gas burner without limiting the design freedom to control the height and width of flames for a gas fire subject to restrictions on the permitted size, shape and total heat input, for example of 7kW.

In the foregoing, the invention has been described with reference to an embodiment of a gas burner for a domestic gas fire. Regardless of this, the principle of this novel and inventive concept can be used with any aerated burner, in a wide range of applications. For example, an outdoor burner may not be limited to the same heat input restrictions as a burner for a domestic gas fire, and may for example be designed with a heat input of 14kW instead of 7kW, giving much greater freedom to control flame size and shape. Such outdoor burners may however encounter different environmental effects, for example from wind, which may tend to initiate an undesirable light back event. The burner of the present invention is equally applicable to such other uses, by preventing light back past the gauze sheet while maintaining a relatively unrestricted gas flow to the burner ports.

As such, the invention should not be considered to be restricted to domestic gas fires and may also be used with outside burners and in other gas flame applications. In particular, as social and regulatory pressure increases to move away from burning fossil fuels, other gases may be burned to provide heat and flame, such as hydrogen. This may include 100% hydrogen, or mixtures of hydrogen and natural gas, for example. The present invention is suitable to prevent light back in all such applications.

List of Reference Numerals -burner/burner unit 110 -burner body/housing 120 -mixing chamber 130a-g -flame ports 200 -Venturi tube 300 -baffle 310 -screw 400 -burner base 500 -gauze assembly 510 -upper gauze plate 515 -upper gauze opening 520 -gauze sheet 530 -lower gauze plate 535 -lower gauze opening

Claims

Claims 1. A burner for generating a flame by burning gas, the burner comprising: a burner body having an inlet for receiving gas from a gas source and having one or more flame ports, the burner body being arranged to direct a flow of the gas through the one or more flame ports to sustain a flame on the outside of the burner body adjacent each of the flame ports when the burner is lit; and a gauze disposed inside the burner body and set behind the one or more flame ports such that the flow of gas will pass through the gauze within the burner body before flowing into the flame ports.
2. The burner according to Claim 1, wherein the gauze is mounted across one or more openings within the burner body, the one or more openings having a total cross-sectional flow area that is greater than a total cross-sectional flow area through the one or more flame ports.
3. The burner according to Claim 2, wherein the gauze presents an effective flow area for the gas through each opening that is less than the cross-sectional flow area of the one or more openings, and wherein the effective flow area for the gas through the gauze at each of the one or more openings is equal to or greater than the cross-sectional flow area through respective ones of the one or more flame ports into which the gas passes after passing through the one or more openings.
4. The burner according to Claim 2 or 3, wherein each port has a respective opening, such that the flow of gas will pass through each opening and into the respective port.
5. The burner according to Claim 2, 3 or 4, wherein the gauze is provided as a single sheet mounted across all of the one or more openings.
6. The burner according to Claim 2, 3 or 4, wherein there are two or more openings and the gauze is provided as a separate sheet mounted across each opening.
7. The burner according to Claim 2 or 3, wherein there is a single opening, such that the flow of gas will pass through the single opening and into all of the flame ports.
8. The burner according to any one of Claims 2 to 7, wherein the gauze is mounted to a gauze plate defining the one or more openings.
9. The burner according to Claim 8, wherein the gauze is sandwiched between the gauze plate and another gauze plate.
10. The burner according to Claim 8 or 9, wherein a gauze assembly includes the gauze and gauze plate, the gauze assembly being mounted in the burner body behind the one or more flame ports.
11. The burner according to any preceding claim, wherein the gauze is formed from a woven wire mesh.
12. The burner according to any preceding claim, wherein the gauze has an open area of 60% or less.
13. The burner according to any preceding claim, wherein the gauze is set back behind the flame ports by at least 1.0 mm, preferably at least 1.2 mm.
14. The burner according to any preceding claim, wherein the gauze is set back behind the flame ports by at most 10 mm, preferably at most 8 mm.
15. The burner according to any preceding claim, wherein one or more collection chambers are disposed between the gauze and the ports such that the flow of gas will pass through the gauze and into a respective collection chamber before flowing into each flame port.
16. The burner according to any preceding claim, wherein each flame port defines an outlet including a through hole with a minimum dimension greater than 0.5 mm, preferably greater than 2 mm.
17. The burner according to any preceding claim, wherein the burner body includes 3 or more flame ports, preferably 5 or more flame ports, and more preferably includes 7 flame ports.
18. The burner according to any preceding claim further comprising a Venturi tube arranged to mix gas received from the gas source with air drawn into the Venturi tube by the gas flow, the mixed gas and air being directed into a mixing chamber in the burner body before passing through the gauze.
19. The burner according to any preceding claim, wherein the burner body is made from sheet metal, preferably from steel.
20. The burner according to any preceding claim, further comprising a baffle disposed in the burner body to improve the mixing of gas from the gas supply with ambient air and to help direct the flow of gas to the one or more flame ports.