Gas burners

Abstract: A gas burner arrangement comprises a gas burner in which spark-gaps 20 are defined between a plurality of flame electrodes 15 supported by a cover plate 7 and opposing electrode 5, a spark generator 31 and a flame failure sensor 32. The sensor 32 senses the absence of flame only when there is an absence of flame extending from each flame electrode 15 to the opposing electrode 5 at the same time and, in response to such absence of flame, initiates energisation of the spark generator to effect sparking and reignition of the burner. The arrangement reduces the likelihood of so-called "nuisance" sparking which has been found to occur where a single sparking electrode is employed and the flame, without being extinguished, moves away from the sparking electrode.

Description: The present invention relates to gas burners and, more particularly, to gas burners having automatic reignition systems which, when the burner flame is extinguished while air/gas mixture is being supplied to the burner, are energised in order to reignite the air/gas mixture. The invention is especially, thought not exclusively, applicable to toroidal aerated gas burners of the kind in which a mixture of gas and air is supplied to a burner head and issues from main burner ports formed in the outer wall thereof where, commonly, secondary air is entrained or available for providing a gas/air ratio suitable for automatic ignition and combustion when a control for the burner is turned on, and in which such burners include a detachable cover plate disposed over the central air spaced bounded by the toroidal burner body and supported in spaced relationship with respect to the burner head so as to provide an annular gap therebetween through which secondary air from the central air space can be entrained at the main burner ports, and to provide protection for the ignition source of an electric spark ignition system. This kind of burner will hereinafter be referred to as a toroidal aerated gas burner as hereinbefore described. In prior known burners having flame detection and automatic reignition, a single sparking /flame detection electrode is provided with the flame detection based on either the flame rectification system or the flame conduction system. With such known burners, so-called 'nuisance' sparking has been found to occur if, without being extinguished, the flame moved away from the electrode due to draughts or the like since flame rectification or flame conduction would not be detected. US-A-2152790 discloses an automatic safety pilot burner associated with a main burner. The pilot burner comprises a plurality of equally spaced metal electrodes which define a spark gap with a generally central terminal part of the burner. A spark generating means is energised manually by the pressing of a push button in an associated electrical circuit to produce a spark at the spark gap to ignite fuel gas supplied to the pilot burner. If the flame of the pilot burner is accidentally extinguished the gas supply to the pilot burner and also to the main burner is shut off automatically. DE-A-1962708 discloses a fuel gas burner arrangement providing for ignition across a spark gap of the burner and, in the case of an abnormal extinguishing of the flame, the generation of a number of re-ignition impulses followed, if re-ignition is unsuccessful, by shut off of the gas to the burner and actuation of a warning device. The spark gap is defined between the actual burner body and a single electrode mounted in the immediate vicinity of the burner body. This single electrode fulfils a dual purpose: on the one hand, serving as part of the ignition system to produce sparks to ignite the gas at the burner; and on the other hand, serving to determine changes in the flame ionization in the spark gap due to the presence or absence of a flame. An object of the present invention is to provide a gas burner arrangement in which the occurrence of nuisance sparking is reduced. From one aspect, the invention consists in a gas burner arrangement comprising a gas burner wherein spark-gaps are defined between a plurality of flame electrodes and opposing electrode means, a spark generator and a flame failure sensing means which is electrically connected to the flame electrodes in order to sense the absence of flame only when there is an absence of flame extending from each flame electrode to the opposing electrode means at the same time and, in response to such absence of flame, the flame failure means initiates energisation of the spark generator to effect sparking and reignition of the burner. With such an arrangement no sparking will occur until none of the sparking gaps have a flame extending across them. Thus a draught or the like may extinguish flames in the regions of all of the sparking gaps, except one, and nuisance sparking will not occur. Thus, when a draught temporarily moves a flame to only a portion of the burner, re-ignition sparking need not, unnecessarily, occur. The flame failure sensing means may employ either flame rectification or flame conduction, each of which is well known to those skilled in the art of flame failure sensing means. However, the employment of flame rectification is preferred. This is because in connection with single sparking electrode burners it has been found that condensation or a build up of deposits of dust, grease or soot on a burner may occur and, if so, bridge the sparking gap to cause electrical tracking which in the case where flame conduction is utilised simulates the presence of a flame and flame conduction with the result that reignition sparking can be suppressed when required on the extinction of a flame; whereas in the case where flame rectification is utilised, such electrical tracking does not produce such problems and thus the required reignition sparking can be more reliable should the flame be extinguished. The gas burner arrangement may incorporate or be associated with other equipment such as safety devices and/or control devices or systems which are energised or operated either in response to the cessation of energisation of the spark generator when successful ignition or reignition of the burner has occurred, or in response to failure of ignition or reignition of the burner to occur within a predetermined sparking time period from the start of the energisation of the spark generator. For example, when ignition or reignition of the burner occurs an extractor fan or cooker hood may be energised and in addition, or alternatively, if the burner fails to ignite or re-ignite after the predetermined period a valve, such as a solenoid valve, may be operated so as to close or turn off the supply of gas to the burner. The gas burner may comprise an annular burner head which has main burner ports around the periphery thereof and opening outwardly of the burner head. In one form, the gas burner may be a toroidal aerated gas burner of the kind hereinbefore described having a detachable cover plate which comprises an electrically insulating material from which the plurality of electrodes depend, an electrical contact region about which the electrodes are disposed, and electrically conducting means substantially concealed by the insulating material and connecting the electrodes with the electrical contact region, and wherein the burner head provides the opposing electrode means. Preferably, the dimensioning and arrangement of the electrodes and burner ports are such that, when the burner is in use, the electrodes are bathed in the flames from the main ports, even when the burner is turned down to simmer rate, whereby there is a reliable sufficient flame current which facilitates good flame rectification response. Conveniently, the connection means comprises a plurality of lengths of electrically conducting material equal in number to the number of electrodes with each conducting length connected to a respective one of the electrodes. Each conducting length may extend through a respective passageway in the insulating material. The passageway may extend from, or from closely adjacent to, the peripheral edge of the cover plate. The electrical contact region may comprise an electrical conducting projection or spigot which depends from the insulating material. Conveniently, the electrically conducting projection or spigot is fitted into a socket mounted within the central air space of the toroidal burner, with the socket having electrical conducting means which is contacted by the projection thereby providing an electrical connection connecting the plurality of electrodes to the spark ignition/reignition system and flame failure sensing means. For example, the electrical conducting means may comprise a metallised layer on the internal surface of the socket. Preferably, the electrodes lie on an imaginary circle, are substantially equally spaced from each other, and are substantially equi-distant from the electrical contact region. From another aspect the invention also consists in a cover plate for use in a gas burner arrangement wherein the gas burner is of the kind hereinbefore described, the cover plate comprising an electrically insulating material, a plurality of electrodes which depend from the insulating material and which are disposed about an electrical contact region, and electrically conducting means substantially concealed by the insulating material and connecting the electrodes with the electrical contact region. From further aspects, the invention consists in a cooker hob plate having mounted thereon at least one gas burner arrangement according to this invention, and also in a gas cooker incorporating such a hob plate or otherwise comprising one or more gas burner arrangements according to this invention. In order that the invention may be more readily understood, reference will now be made, by way of example only, to the accompanying drawings, in which :- Figure 1 is a plan view from above of one embodiment of gas burner arrangement according to the invention, Figure 2 is a central vertical sectional view on the line II-II in Figure 1 of the burner arrangement, with the spark generator and flame failure sensing means using the flame rectification principle shown schematically, Figure 3 is an exploded perspective view of the cover plate and burner head shown in Figures 1 and 2, and Figure 4 is a block diagram showing schematically a circuit in which an extractor fan and solenoid valve are connected to the burner arrangement. With reference to the drawings, a toroidal aerated gas burner arrangement according to the invention and designed for use on a hob plate 1 of a gas cooker or other gas appliance comprises a metal toroidal body 2 of generally U-shaped cross-section, a flared annular retention ring 3 supported at its lower edge on a recessed shoulder 4 of the body 2, an annular metal burner head 5 provided with a series of main burner ports 6 formed circumferentially around its outer peripheral wall, and a detachable cover plate in the form of a spillage protection cap 7 is supported in spaced relationship with respect to the burner head 5 by means of upstanding projections 8 formed on the upper surface of the burner head, as will be described below. The annular ring 3 supports the burner head 5 which is located by an annular boss 9 on the toroidal body 2. The annular ring 3 is located in position on the shoulder of the body 2 so as to define an annular gap 10 which communicates with an annular space 11 of the toroidal body through slots 12 formed in the lower edge of the ring 3 for the emission of an air/gas mixture for producing a small flame ring designed to retain and stabilise the main burner flame at the ports 6. The air/gas mixture can be supplied to the burner through an inlet 13 which communicates with the annular space 11. The spillage cap 7 (shown also in Figure 1) is comprised of an electrically insulating material, for example a ceramic material, such as cordierite and three flame electrodes 15 depend from the underside and adjacent the periphery of, the cap. The electrodes 15 are disposed about a central recess 16 in the underside of the cap so as to lie on an imaginary circle, be substantially equally spaced from each other and be substantially equi-distant from the central recess. A cylindrical metal projection or spigot 17 is located in the recess 16 to form an electrical contact region, the function of which will be described below. Each of three lengths 18 of electrically conducting material, such as metal wire or rod, connect a different electrode to the projection. In the present embodiment, each length 18 is integral with respective electrode 15 and extends through a respective bore or channel 19 formed in the insulating material 14. The bores 19 form passageways which extend radially from the recess 16 to the peripheral edge 19 of the cap 7. The three passageways 19 lie substantially in a common plane. The projection 17 has three openings or recesses 17a at 120° intervals around its circumference which, when the projection is located in the recess 16, are aligned with the radially inner ends 19a of the bores 19 which open into the recess. This enables the lengths 18 of electrically conducting material to be inserted at the periphery of the cap into the bores 19 and push fitted into the recesses 17a in the projection 17. The burner arrangement as shown in the present embodiment has three spark gaps 20. Each spark gap is defined between a respective one of the flame electrodes 15 and an opposing portion 5a of the metal burner head 5 which serves as the opposing electrode means. As can be seen from Figure 3, the tips of the flame electrodes terminate at a position which is outwards of the outer peripheral surface 22 of the outer wall 21 of the burner head. Opposite each electrode 15 a respective orifice 23 extends through the outer wall of the burner from the inner peripheral surface 24 in the direction upwardly and outwardly to the outer peripheral surface 22 of the outer wall towards the electrode. When the burner arrangement is in use air/gas mixture to be combusted is directed from the toroidal body 2 towards the electrodes 15 by the respective orifices 23 to produce ignition flames which ignite the air/gas misture issuing from the main burner ports 6. The underside of the cap comprises recesses 25 for fitting over the upstanding projections 8 on the top of the burner head to ensure that the cap and burner head are mounted in a correct relative orientation so that the ignition flame orifices 23 are aligned with the electrodes 15. The depths of the recesses 25 are less than the heights of the upstanding projections 8 and thus the underside 7b of the spillage cap 7 is in spaced relationship above the upper surface 5b of the burner head 5. The metal projection 17 is fitted into a socket 26 which is made of an electrically insulating material and mounted within the central air space of the toroidal burner by means of a bracket 27 projecting inwardly from the inner wall of the toroidal burner. The internal surface of the socket comprises a metallised layer 28 which provides electrical connection between the projection 17 and a terminal 29 which extends through the base 30 of the socket 26 and is also in contact with the metallised layer. High tension voltage is supplied to the electrodes 15 via the terminal 29 which is connected to a spark generator 31 to effect sparking across the spark gaps 20 to ignite the burner when the supply of gas is turned on and a flame failure sensing means 32 using the flame rectification principle to sense the presence/absence of flame across the spark gaps. Although referenced separately in Figure 2, spark generator 31 and flame failure sensing means 32 are commonly manufactured as a single unit. The flame failure sensing means 32 senses the absence of flame only when there is an absence of flame extending from each flame electrode 15 to the burner head 5 at the same time. In response to such absence of flame the flame failure sensing means 32 initiates energisation of the spark generator 31 to effect sparking again and reignition of the burner. In the present embodiment, Applicants have found that ignition and reignition may occur across any of the three spark gaps. The flame electrodes 15 are bathed in the flames from the main burner ports 6 and this results in desired relatively high flame currents being sensed by the flame rectification detection system. Suitable spark generators and flame failure sensing means using the flame rectification principle are known. In Figure 4 there is shown in schematic form an electric circuit in which the spark generator/flame failure sensing unit 31,32 is connected to a timer/control unit 33 which is connected to and sends electrical signals to an extractor fan 34 associated with a gas cooker (not shown) in which the burner arrangement is incorporated and a solenoid valve 35 located in a fuel gas supply pipe leading to the burner. Unit 31,32 and timer/control unit 33 are also connected to an electrical power supply. The circuit is so designed that when the energisation of the spark generator ceases on the completion of successful ignition or re-ignition of the burner, the extractor fan is activated, and if the burner fails to ignite or re-ignite within a predetermined time period from the start of the energisation of the spark generator, the solenoid valve is operated to close off the supply of gas through the pipe to the burner. The operations of the extractor fan and solenoid valve are under the control of the timer/control unit 33 which in turn receives signals at the appropriate times from the spark generator/flame failure sensing unit. By using the above described three flame electrode/detection points around the periphery of the burner head and by employing flame rectification (as opposed to flame conduction) as a means of flame sensing, there is good flame current even at low gas rates; flame detection continues when draughts blow the flames away from one (or even two) of the three electrodes whereby nuisance sparking is substantially alleviated or eliminated; and electrical tracking caused by any deposits on insulating material between electrodes and the burner head does not produce the problem of flame simulation because of the use of flame rectification. Applicants have found that good results have been obtained not only with high aeration burners but also with burners with lower, more conventional levels of primary aeration. It will be appreciated that the provision of three flame electrodes is only by way of example. Instead, two or four or five etc. electrodes could be used in a burner arrangement according to the invention. Applicants have found that three electrodes spaced equally around the spillage cap give very satisfactory results. In a different embodiment the flame electrodes may be located outwardly of the periphery of an annular burner head with generally radially outwardly facing main burner ports. A different means of connection to a spark generator would be needed but it is believed that this could readily be achieved by a person skilled in art. The burner head may again serve to provide the opposing electrode means. However, alternatively, each flame electrode may be operably associated with its own specific opposing electrode which is separate from the burner head.

Claims: A gas burner arrangement comprising a gas burner, wherein spark-gaps (20) are defined between a plurality of flame electrodes (15) and opposing electrode means (5), a spark generator (31) and a flame failure sensing means (32) which is electrically connected to the flame electrodes in order to sense the absence of flame only when there is an absence of flame extending from each flame electrode (15) to the opposing electrode means (5) at the same time and, in response to such absence of flame, the flame failure means (32) initiates energisation of the spark generator (31) to effect sparking and re-ignition of the burner. A gas burner arrangement as claimed in claim 1, in which the gas burner comprises an annular burner head (5) which has main burner ports (6) around the periphery thereof and opening outwardly of the burner head. A gas burner arrangement as claimed in claim 2, in which the gas burner is a toroidal aerated gas burner of the kind hereinbefore described having a detachable cover plate (7) comprising an electrically insulating material from which the plurality of electrodes (15) depend, an electrical contact region (17) about which the electrodes are disposed, and electrically conducting means (18) substantially concealed by the insulating material and connecting the electrodes (15) with the electrical contact region (17), and wherein the burner head (5) provides the opposing electrode means. A gas burner arrangement as claimed in claim 3, in which the connecting means (18) comprises a plurality of lengths of electrically conducting material equal in number to the number of electrodes (15) with each conducting length connected to a respective one of the electrodes. A gas burner arrangement as claimed in claim 4, in which each conducting length (18) extends through a respective passageway (19) in the insulating material. A gas burner arrangement as claimed in any of claims 3 to 5, in which the electrical contact region (17) comprises an electrically conducting projection which depends from the insulating material. A gas burner arrangement as claimed in claim 6, in which the electrically conducting projection (17) is fitted into a socket (26) mounted within the central air space of the toroidal burner, said socket having electrical conducting means (28) which is contacted by the projection thereby providing an electrical connection connecting the plurality of electrodes (15) to the spark ignition/re-ignition system (31) and flame failure sensing means (32). A gas burner arrangement as claimed in claim 6 or claim 7 as dependent on claim 4 or claim 5, in which the conducting projection (17) and conducting lengths (18) are fitted together. A gas burner arrangement as claimed in any of the preceding claims, in which the electrodes (15) lie on an imaginary circle and are substantially equally spaced from each other. A gas burner arrangement as claimed in any of claims 3 to 8, or claim 9 as dependent on any of claims 3 to 8, in which the electrodes (15) are substantially equi-distant from the electrical contact region (17). A gas burner arrangement as claimed in claim 3, or any of claims 4 to 10 as dependent directly or indirectly on claim 3, in which for each electrode (15) a respective orifice (23) extends through the outer wall of the burner head (5) from the inner peripheral surface in a direction generally towards the associated electrode so that when the burner arrangement is in use air/gas mixture to be combusted is directed from the toroidal body towards the associated electrode by the respective orifice. A gas burner arrangement as claimed in claim 11, in which the tip of each electrode (15) terminates at a position which is outwards of the outer peripheral surface (22) of the outer wall (21) of the burner head (5) and each orifice (23) extends upwardly in its respective direction away from the burner head. A gas burner arrangement as claimed in claim 12, in which each orifice (23) extends from the inner peripheral surface (24) to the outer peripheral surface (22) of the outer wall (21) of the burner head (5). A gas burner arrangement as claimed in any of the preceding claims, in which the flame failure sensing means (32) uses the flame rectification principle to detect or sense the absence/presence of flame. A gas burner arrangement as claimed in any of the preceding claims in combination with a valve (35) located in a fuel gas supply line for supplying gas to the burner, said valve being operable to close off the supply line and thus the supply of gas to the burner in response to the burner failing to ignite or re-ignite after a predetermined period of attempted ignition or reignition. A gas burner arrangement as claimed in any of the preceding claims in combination with an extractor fan (34) or cooker hood which is caused to operate in response to the burner igniting or re-igniting. A cover plate for use in the gas burner arrangement as claimed in claim 3, comprising an electrically insulating material, a plurality of electrodes (15) which project from the insulating material and which are disposed about an electrical contact region (17), and electrically conducting means (18) substantially concealed by the insulating material and connecting the electrodes with the electrical contact region. A cover plate as claimed in claim 17, in which the connecting means (18) comprises a plurality of lengths of electrically conducting material equal in number to the number of electrodes (15) with each conducting length connected to a respective one of the electrodes. A cover plate as claimed in claim 17 or claim 18, in which the electrical contact region (17) comprises an electrically conducting projection which depends from the insulating material. A cover plate as claimed in claim 19, as dependent on claim 18, in which the conducting projection (17) and conducting lengths (18) are fitted together. A cover plate as claimed in any of claims 17 to 20, in which the electrodes (15) lie on an imaginary circle and are equally spaced from each other. A cover plate as claimed in any of claims 17 to 21, in which the electrodes (15) are substantially equi-distant from the electrical contact region (17). A cover plate as claimed in any of claims 17 to 22, which is intended to serve as a spillage cap. A cooker hob plate having mounted thereon at least one gas burner arrangement as claimed in any of claims 1 to 16. A gas cooker incorporating one or more gas burner arrangements as claimed in any of claims 1 to 16. A gas cooker incorporating a hob plate as claimed in claim 24.

Inventors: FORRESTER FLOOD JOHN JEREMY, SOOD SHIV KUMAR, FORRESTER FLOOD, JOHN JEREMY, SOOD, SHIV KUMAR
Applicants: BRITISH GAS PLC
Application year: 1991
Main classification: F24C3
IPC codes: F23Q3, F24C3