GB2153988A - Gas burner - Google Patents

Abstract

In a gas burner at least one of the gas outlet ports (6') feeds gas directly to a gas ignition chamber (7) formed in the body (2) of the burner. A high tension electrode (8) and an earthed target (10) are provided to ignite gas fed to the chamber (7) thereby to cause ignition of gas supplied to the other ports. Safe ignition of the burner can be achieved even when gas is supplied to the burner at below the full flow rate. <IMAGE>

Description

SPECIFICATION Gas burner The present invention relates to a gas burner for use in a cooking hob.

In a conventional gas cooker, the ignition system has a high tension electrode spaced from an earthed metal target such that a spark is formed in the gas when required. It is important that the electrode is protected from spillage of foods and from accidental damage when cleaned, and so in the type of burner with a solid cap and radial ports the ignition system is located away from the radial ports which feed the main flame. Thus ignition is effected by means of a separate unit with its own gas supply distinct from the radial ports, although of course its outlet must be close to the outlets of the radial ports.

One disadvantage of the construction described above is that the burner can only be ignited successfully at high gas flow rates approaching, and at, the maximum value, because at low rates there may be difficulty in the ignited gases bridging the spacing between the ignition chamber and the outlets of the ports.

A further disadvantage of the construction is that the electrode cannot reliably be used to sense the presence of the main frame, using conventional flame conduction or rectification principles, because of its remoteness from the main flame. There can therefore be no certainty of a continuous flame between the electrode and the main flame over the wide range of flame conditions associated with gas rates at or between maximum and minimum values.

An object of the present invention may be to provide a burner which can be safely ignited at low flow rates.

Another object of the present invention may be to provide a burner of economic construction.

Another object may be to enable accurate monitoring of the operating condition of the burner.

In the present invention, an ignition chamber is provided downstream of at least some of the main flame outlet ports.

The present invention provides a gas burner comprising a central chamber connectable to a gas supply and a plurality of outlet ports, spaced apart around the central chamber, to form the main burner flame, wherein at least one of said outlet ports feeds an ignition chamber formed in the hob and means are provided to ignite gas, fed to the ignition chamber, and to sense the state of the main flame.

In this way, the burner need not be at, or close to, full flow rate for there to be safe ignition of the main flame.

Preferably, a high tension electrode and an earthed target are located at or adjacent an outlet of the ignition chamber, the electrode and target comprising both the igniting means and the sensing means.

Thus, a single electrode and target can be used both to ignite the gases in the ignition chamber and to sense directly the state of the main flame. Alternatively a separate flame sensing device (e.g. on the electrode and target) may be used. Hence a burner embodying these features has an economic construction and enables accurate and precise monitoring of the operating condition of the burner.

In one form of the invention, a plurality of main flame outlet ports communicate with the ignition chamber, and one or more of these ports may be of reduced cross-section compared to the remainder of these ports. In one example, three main flame outlet ports communicate with the ignition chamber, the middle of these three ports having a smaller bore than the other two, this arrangement providing efficient combustion in the ignition chamber. This may be because the amount of gas entering the chamber is restricted, thereby ensuring that there is an ignition flame sufficiently small to ensure that it stays within the chamber however large the gas rate is, and/or because there is a non-uniform flow of gas into the ignition chamber, which may encourage turbulence and hence permits an increased degree of mixing with secondary air, thereby providing increased efficiency of combustion.

In order that the invention may more readily be understood, a description is now given by way of example only, reference being made to the accompanying drawings, in which: Figure 1 is a cross-sectional view in elevation of a gas hob burner embodying the present invention; and Figure 2 is a view in the direction of arrows Il-Il in Fig. 1.

The Figures show a solid-cap gas burner 1 for use on a cooking hob. The burner 1 has a main body 2 with a supply conduit 3 connected to the gas mains; the conduit 3 feeds a gas/air mixture to a central chamber 4 whose boundary is defined primarily by the internal surface of a solid-cap burner top 5 which sits on the top of main body 2. Burner top 5 has a number of horizontal ports 6 which extend radially outward from the chamber 4.

Whereas the majority of the ports 6 lead directly to the atmosphere, three of them (designated 6' in the Figures) lead to another chamber 7 defined between burner top 5 and main body 2. At the open end of this chamber is located a high tension electrode 8 (suitably surrounded by a ceramic insulating shroud 9) and an earthed metal target 1 0.

When electrode 8 is at a high voltage, it discharges by producing a spark in the gap between it and target 10, this spark then igniting the gas/air mixture in chamber 7.

Once a flame is established in ignition chamber 7, it can readily ignite the gas/air mixture exiting from the remaining ports 6 and thereby produce the main flame. Due to proximity of the ignition chamber 7 to outlet ports 6 as compared to prior art burners, burner 1 can be ignited without risk at gas flow rates substantially below the maximum value.

In this example, the electrode 8 is suitable positioned to sense directly the main flame once this has been established, thereby ensuring that the operating state of the burner 1 can be continuously and precisely monitored without requiring any additional equipment to act as a sensor.

Alternatively, a separate flame sensing device could be used. This may take the form of another high tension electrode in combination with an earthed target. In these circumstances, it is convenient to position the ignition and sensing electrodes on opposite sides of the burner so as to ensure that the main flame has propagated around the burner from the point of ignition. Clearly, any other suitable sensing device could be used, e.g. a thermistor.

The three ports 6', which feed the ignition chamber 7, are arranged such that the middle one is of smaller bore than the other two, as it has been found that this contributes significantly to maximising the combustion efficiency in the chamber 7. This may be because, by limiting the gas supply into the ignition chamber, the ignition flame is maintained at a size which ensures that it remains beneath the top and in contact with the electrode irrespective of the gas rate being used; this necessitates that there be adequate secondary air in the ignition chamber, because otherwise combustion cannot take place under the top and the flame will be forced out from under the top. Another reason for this arrangement of bores maximising combustion efficiency may be because the amount of gas/air mixture is limited to a value which produces an optimum combination with secondary air input from that existing in the chamber. Another reason may be that the non-uniformity of the gas/air flow into the chamber 7 produces turbulence which promotes further mixing with the air existing in the chamber.

It will be appreciated that although, in the above-described example, the electrode and target are arranged within the ignition chamber this need not necessarily be the case.

Alternatively, the electrode, at least, could be arranged outside the chamber so as to reduce the possibility of unesirable sparking to earthed regions of the ignition chamber adjacent the target.

Claims (8)

1. A gas burner comprising a central chamber connectable to a gas supply and a plurality of outlet ports, spaced apart around the central chamber, to form the main burner flame, wherein at least one of said outlet ports feeds an ignition chamber formed in the burner and means are provided to ignite gas, fed to the ignition chamber, and to sense the state of the main flame.

2. A gas burner according to Claim 1 wherein more than one of said outlet ports feeds gas directly to the ignition chamber.

3. A gas burner according to Claim 1 or Claim 2 wherein a high tension electrode and an earthed target constitute both the igniting means and the flame sensing means.

4. A gas burner according to Claim 1 or Claim 2 wherein a high tension electrode and an earthed target constitute the igniting means and further means are provided to sense the state of the main burner flame.

5. A gas burner according to Claim 4 wherein said further means comprises a further high tension electrode and an earthed target.

6. A gas burner according to any one of Claims 3 to 5 wherein said igniting means is within the ignition chamber.

7. A gas burner according to any one of Claims 2 to 6 wherein at least one of said outlet ports feeding the ignition chamber is of reduced cross-sectionai as compared with the remaining outlet ports.

8. A gas burner substantially as hereinbefore described by reference to and as illustrated in the accompanying drawings.