WO2014049421A1

WO2014049421A1 - Method for regulating the heating power of a gas burner, and an improved gas burner which uses the method

Info

Publication number: WO2014049421A1
Application number: PCT/IB2013/002122
Authority: WO
Inventors: Carlo Paesani
Original assignee: Defendi Italy S.R.L.
Priority date: 2012-09-27
Filing date: 2013-09-26
Publication date: 2014-04-03
Also published as: ITVE20120036A1

Abstract

A method for regulating the heating power of a gas burner (2, 64) for cooking, characterised in that, when the burner (2, 64) operates under reduced throughput conditions, part of the heat generated by the reduced throughput flames (58, 102) is dissipated by an air flow of controlled throughput.

Description

METHOD FOR REGULATING THE HEATING POWER OF A GAS BURNER, AND AN IMPROVED GAS BURNER WHICH USES THE METHOD

The present invention relates to a method for regulating the heating power of a gas burner, and an improved gas burner which uses the method.

In the current state, market requirements are increasingly aimed at constructing burners able to also operate at very low minimum power in order to apply to the pan placed on the burner a heat quantity sufficient to maintain the required temperature.

However, in addition to this requirement for a very low minimum power, there is always the requirement for very high maximum power.

To operate at very high power, the area of the main apertures from which the air/gas mixture emerges must be sufficiently large to be able to generate good combustion with low carbon dioxide values; at the same time, however, the large area of the main apertures, when passing to minimum power operation, results in flame return or extinguishing phenomena which must be compensated by increasing the gas feed, causing in this manner an increase in the minimum power which can be developed by the burner.

In the current state, traditional burners attain high maximum powers, of the order of 18,000-20, 000 BTU/h, compared with minimum powers of the order of 2,500 BHU/h; this minimum power is still too high for low temperature cooking or for temperature maintenance.

Various solutions are currently available commercially.

A first known solution is the so-called dual burner. This uses two gas injectors, each connected to a corresponding outlet of a two-way valve, which is controlled such as to be able to send gas selectively to one or to both injectors. These generate air/gas mixture flows and feed them to two separate mutually concentric chambers. In particular, the outer main chamber, known as the "outer burner" is of annular shape and is provided on its outer edge with a plurality of radial apertures adapted to form the main flame ring. The inner chamber, known as the "inner burner", is of cylindrical shape, is smaller, and is positioned at the centre of the outer burner. This chamber is also provided externally with a series of radial apertures which give rise to a secondary flame ring. The diameter of the outer burner at the main apertures is of about 110-130 mm, while the diameter of the inner burner at its radial apertures is about 30-35 mm.

When in use at maximum power, the gas feeds both injectors, which then feed the air/gas mixture to both chambers, to hence generate the main flame ring and the secondary flame ring; by rotating the knob of the control valve, the mixture flow to the two chambers decreases until the valve completely closes gas feed to the outer chamber, hence interrupting feed to the main flame ring. By rotating the control valve to the end, the burner minimum throughput condition is reached, at which only a small quantity of mixture reaches the central chamber, to generate the secondary flame ring at minimum burner power. In this latter operating condition, in which only the inner burner is fed, this minimum power has an acceptable and low value, of the order of about 800 BTU/h; however the secondary flames, emerging from the radial apertures of the central chamber, are concentrated within a particularly small diameter, of about 30-35 mm; consequently the heat induced into the pan is not distributed over the entire pan and is not optimal for low temperature cooking. Another known solution consists of a burner provided with a simmering secondary flame ring and with a main flame ring which are separate and vertically superposed. This type of solution also comprises two gas injectors associated with corresponding exits of a two way control valve. Each injector feeds a chamber which is fluidically separate from the other. In greater detail, a main chamber is present which feeds a series of radial apertures positioned on its outer circumference and generating the main flame ring; the outer diameter of this type of burner is fairly large, about 90-100 mm, such as to be able to develop a maximum power of about 18,000-22,000 BTU/h. Below and above the main chamber a lower chamber is disposed of substantially the same diameter as the main chamber and feeds a secondary flame ring, of which the flames can be in the form of small individual flames or can join together to form a continuous annular flame.

When under maximum flow conditions the valve feeds gas to both injectors such that the gas/primary air mixture reaches both the chambers, to hence create the main flame ring and the simmering secondary flame ring. On rotating the control knob, the gas flow to the main chamber decreases, and consequently the main flame decreases, while the gas quantity fed to the chamber which feeds the simmering secondary flames remains constant. On further rotating the control valve the minimum gas flow condition is reached, in which the valve enables gas to be fed only to the injector associated with the secondary chamber, and no longer to that associated with the main chamber; under these conditions only the simmering secondary flames are generated, which can be used for low temperature cooking. In known burners of this type, the heat generated by the simmering secondary flames is distributed over a ring having a greater outer diameter; however this results in a higher minimum power value, of about 1200-1300 BTU/h which, distributed over a diameter of 90-100 mm, induces into the pan a temperature value of about 110- 30°C. Notwithstanding this, in the current state this temperature value must be further lowered in order to optimize minimal cooking conditions, and to facilitate controllability.

The main object of the invention is to eliminate the drawbacks of known solutions and to propose an improved gas burner able to optimize its cooking performance when used under minimum power conditions.

Another object of the invention is to provide an improved gas burner the minimum power of which can be modulated in order to regulate the pan temperature to the extent of achieving a condition of hot maintenance rather than of actual cooking.

Another object of the invention is to provide a gas burner the maximum power of which can be increased, while maintaining optimal mixture combustion conditions.

Another object of the invention is to provide an improved gas burner which can be constructed easily, quickly and at low cost.

All these objects and others which will be apparent from the ensuing description are attained according to the invention by a method with the characteristics indicated in claim 1.

The method of the invention is utilized in the improved burner, having the characteristics indicated in claim 11. The present invention is further clarified hereinafter in two preferred embodiments with reference to the accompanying drawings, in which:

Figure 1 shows a vertical section through an improved gas burner according to the invention, in its maximum throughput condition,

Figure 2 shows it in its minimum throughput condition,

Figure 3 shows a vertical section through a different embodiment thereof in its maximum throughput condition,

Figure 4 shows a different vertical section therethrough in its minimum throughput condition.

As can be seen from Figures 1 and 2, the burner 2 comprises a base 4 which is applied to the opening provided in the upper sheet metal 6 of a cooking hob. The base 4 is associated lowerly with an injector holder 8 provided with a first inlet 10, which is connected to a first injector 12 having a particularly large flow hole. It is also provided with a second inlet 14, which is connected to a second injector 16, having a particularly small flow hole.

Inside the injector holder 8, about the first injector 12, there extends an annular chamber 18, provided upperly with passages 20. Into said annular chamber 18 a conduit 22 extends associated with a forced air generator 24, which is controlled in its operation by the same knob, not shown, which controls the control valve for the gas feed to the two injectors 12, 16.

A first flame divider ring 26 rests on the base 4 to define, with said base, an annular chamber 28 communicating with the outside of the burner via a circumferential gap 30 defined between them. The first flame divider ring 26 presents a circumferential wall 32 extending upwards and having in its upper edge a plurality of grooves 34 which extend radially and are spaced apart. Moreover, at the injector 16, the first flame divider ring 26 presents a vertical conduit 36.

On the first flame divider ring 26 a second flame divider ring 38 rests, presenting a vertical venturi tube 40, facing the first injector 12; moreover at its outer portion, the second flame divider ring 38 presents a circumferential wall 42, which is inclined inwards and upwards and is provided with a series of first apertures 44, and a lower edge 46 provided with a series of second apertures 48. Both the series of apertures 44 and 48 extend radially and are equidistant along the circumference of the second flame divider ring 38.

A cover disc 50 rests on the upper edge of the wall 42 of the second flame divider ring 38 and defines therewith the first apertures 44.

The space bounded upperly by the cover disc 50 and lowerly by the second flame divider ring 38 defines a main distribution chamber 52, while the space bounded upperly by the second flame divider ring 38 and lowerly by the first flame divider ring 26 defines a secondary distribution chamber 54.

The operation of the burner according to the invention derives from the aforegoing description.

Under conditions of use at maximum throughput (see Figure 1), the burner control valve, not shown here, is open and, consequently, the gas reaches the injectors 12 and 16 through the inlets 10 and 14.

In particular, the limited gas quantity which emerges from the small hole of the second injector 16 draws into the passage chamber 28 a primary air flow 56 through the gap 30 and from there entrains it along the vertical conduit 36 causing them to mix, the mixture reaching as far as the secondary distribution chamber 54 and from there it leaves through firstly the second apertures 48 of the second flame divider ring 38 and then through the grooves 34 of the first flame divider ring 26, to generate a series of secondary small flames 58.

In contrast, the considerable quantity of gas which emerges from the first injector 12 draws a flow of primary air from the base of the vertical venturi tube 40 and entrains it along this to cause their mixing; the mixture reaches the main distribution chamber 52, from which it emerges through the first apertures 44 of the second flame divider ring 38, to generate the ring of main flames 60.

On rotating the burner control knob, the valve associated with it causes progressive reduction of the gas feeding the injector 12 from maximum value to zero while, at the same time, maintaining the gas quantity feeding the injector 16 constant or, depending on the type, causing it to reduce from a maximum value to a minimum value, at which only the secondary flames 58 are fed.

On further rotating the burner control knob, the generator 24 is activated which, via the conduit 22 feeds a forced air flow 62 into the annular chamber 18, from where the air 62 enters the venturi tube 40 to reach the main distribution chamber 52, from which it then emerges through the first apertures 44, which are positioned above the secondary flames 58, and acts such as to graze then and to dissipate part of the heat generated by them.

On further rotating the burner control knob, while the gas quantity fed to the injector 16 continues to remain constant, the flow from the generator 24 can be regulated to increase the quantity of forced air 62 fed thereby and hence increase the dissipation of the heat generated by the flames 58. Moreover the forced air 62 which leaves the first apertures 44 grazes the cover disc 50 and cools it, so contributing to further lowering the pah temperature.

According to a first mode of operation of this first embodiment, when the burner is used at minimum throughput, the first main injector 12 is closed and, consequently, the venturi tube 40, the main distribution chamber 52 and the first apertures 44 are traversed only by the forced air 62; in contrast, when the burner is not used at minimum throughput, the generator 24 is deactivated, while the first injector 12 receives the gas and consequently, the venturi tube 40, the main distribution chamber 52 and the first apertures 44 are traversed only by the gas/primary air mixture.

Advantageously, according to a different mode of operation of this first embodiment, the forced air generator 24 can be activated even when the burner 2 operates under maximum throughput conditions, such that the forced air 62 can be added to the primary air drawn in with the gas and be mixed with it. In greater detail, the forced air 62 is added to the primary air drawn in by the injector 12 within the venturi 40, to form a particularly oxygen-rich mixture, which enables the maximum power of the burner to be increased while maintaining low carbon dioxide values.

From that stated, it is apparent that the improved burner according to the invention is very advantageous compared with traditional burners, in that it enables the minimum burner power to be modulated and reduced, and the pan temperature to be brought to 40°C, such that its contents are neither cooked nor burned, but merely maintained hot. As for traditional burners, the fact that the secondary flames 58 are fed

1

separately from the main flames 60 enables a low minimum condition to be reached, characterised by the presence of only the flames 58; however, in the improved burner of the invention, said minimum does not constitute the final condition reached, but the starting condition from which forced air 62 starts to be blown in to further reduce the burner power.

In a second embodiment, shown in Figures 3 and 4, the burner 64 comprises an injector holder 66 which is applied at the opening formed in the upper sheet metal of the cooking hob; the injector holder 66 is provided with an aperture 68 communicating with an inlet 70 connected via a conduit 72 to a forced air generator 74.

Above the injector holder 66 a flame divider ring 76 is positioned, presenting internally two conduits, namely a first vertical conduit 78 associated with an injector 80 connected to a gas inlet 82, and a second vertical conduit 84 positioned at the aperture 68. In addition, the flame divider ring 76 comprises a perimetral band 86 having a series of first apertures 88 extending radially and spaced apart.

A separator disc 90 is associated upperly with the flame divider 76, to upperly close the first apertures 88 and lowerly define with the same flame divider 76 a first annular chamber 92.

A cover 94 rests on said separator disc 90 such as to define a second circular chamber 96 which communicates with the second vertical conduit 84. An annular gap 98 is defined between the cover 94 and the separator disc 90 at their circumferential edge. The operation of the burner in this second embodiment derives from the aforegoing description.

Under conditions of use at maximum throughput, the gas which enters via the gas inlet 82 and emerges from the injector 80, draws in a flow of primary air and entrains it along the first vertical conduit 78, causing them to mix; the mixture reaches the first annular chamber 92, from which it leaves through the first apertures 88, giving rise to the main flames 100.

On rotating the control knob for the burner 64, the valve associated with it causes the gas quantity to gradually decrease until a minimum throughput condition is reached, in which the limited gas quantity which arrives from the inlet 82, again following the same identical path, emerges from the first apertures 88, to create the small flames 102, which generate a limited power, of about 2200-2500 BTH/h.

On further rotating the burner control knob, the generator 74 is activated, to feed forced air 104 through, in order, the conduit 72, the inlet 70, the aperture 68, the second vertical conduit 84, to reach the second circular chamber 96, from which it emerges radially through the annular gap 98; in this manner, the forced air flow 104 acts on the flames 102, to dissipate part of the heat generated thereby, and at the same time grazing the cover 94, to contribute to its cooling.

In this second embodiment, the small flames 102 are not obtained separately from the main flames 100, given that they both emerge from the same aperture 88. Consequently, it is not possible to reduce the minimum starting power more than a certain amount, in fact to about 2000-2500 BTU/h, which is substantially double the value of about 1300 BTU/h of the first embodiment. Consequently the second embodiment of the burner requires a greater quantity of forced air 104 to cool the minimum flames 102. However against this, this second embodiment is particularly advantageous in that it uses a single, not double control valve, making the burner construction more economical.

An advantageous use of the present invention is in its application to the central part of a traditional dual burner. This type of burner is known to be able to operate at minimum power with only the central part active, and under these conditions the minimum power is about 800 BTU/h, with the heat concentrated on a smaller diameter. Feeding forced air thus has the double effect of reducing the impact of the flame and hence the pan temperature, and of dissipating the heat, which is no longer concentrated in a reduced diameter.

The forced air generator can be of various types, such as a minicompressor or a fan.

Moreover, the forced air exit can be positioned either above or below the small flames to be ventilated and can have virtually the desired distance therefrom.

In a third embodiment, not shown in the drawings, the forced air flow leaves the burner not to correspond with the minimum throughput flames, but upwards, directly onto the base of the pan placed on the burner. In this case there is again diminution of the effect of the minimum throughput flames, but without any direct intervention thereon.

Claims

C L A I M S

1. A method for regulating the heating power of a gas burner (2, 64) for cooking, characterised in that, when the burner (2, 64) operates under reduced throughput conditions, part of the heat generated by the reduced throughput flames (58, 102) is dissipated by an air flow of controlled throughput.

2. A method as claimed in claim 1 , characterised by blowing forced air (62, 104) in controlled quantity into correspondence with the reduced throughput flames (58, 102).

3. A method as claimed in one or more of the preceding claims, characterised by blowing forced air (62, 104) and making it emerge to the outside of the burner through at least one aperture (44, 98) with which the burner body (2, 64) is provided.

4. A method as claimed in one or more of the preceding claims, characterised by blowing forced air (62, 104) and making it emerge through apertures provided above said reduced throughput flames (58, 102).

5. A method as claimed in one or more of the preceding claims, characterised by blowing forced air (62, 104) and making it emerge through apertures provided below said reduced throughput flames (58, 102).

6. A method as claimed in one or more of the preceding claims, characterised in that said forced air (62) is made to emerge through a first ring of apertures (44) provided in the burner and is blown onto the reduced throughput flames (58) which emerge from a separate ring of apertures (34) of the burner.

7. A method as claimed in one or more of the preceding claims, characterised in that said forced air (104) is made to emerge through an annular extending passage gap (98) defined in the burner and is blown onto the reduced throughput flames (102) which emerge from a separate ring of apertures (88) of the burner.

8. A method as claimed in . one or more of the preceding claims, characterised in that said forced air (62) is made to emerge through a ring of apertures (44) for the main flames (60) when these are not fed with gas, and is blown onto the reduced throughput flames (58) which emerge from a separate ring of apertures (34) of the burner.

9. A method as claimed in one or more of the preceding claims, characterised by controlling said forced air flow (62, 104) by the same means used to control the burner gas flow.

10. A method as claimed in one or more of the preceding claims, characterised by using the same forced air (62) which dissipates part of the heat generated by the reduced throughput flames (58) to increase the primary air which forms the combustible mixture feeding the main flames (60).

11. An improved gas burner (2, 64) for cooking appliances, characterised by comprising:

- an injector holder (8, 66) associated with at least one injector (12, 16, 80) connected to at least one gas inlet (10, 14, 82) controllable by means for controlling said gas inlet;

- a generator (24, 74) for forced air (62, 104) controllable by means for controlling said generator; - at least one flame divider element (26, 38, 76, 90) positioned above said injector holder (8, 66);

- at least one cover (50, 94) positioned above said flame divider element (26, 38, 76, 90);

- a first chamber (54, 92) provided with a circumferential wall provided with at least one aperture (34, 88), through which a ring of reduced throughput flames (58, 102) emerges;

- a second chamber (52, 96) fluidically separated from said first chamber (54, 92) and connected to said generator (24, 74), said second chamber being provided with at least one aperture (44, 98) through which said forced air (62, 104) emerges.

12. A burner as claimed in one or more of the preceding claims, characterised in that said aperture (44, 98) through which the forced air emerges is directed at least partly onto said ring of reduced throughput flames (58, 102).

13. A burner as claimed in one or more of the preceding claims, characterised in that said at least one aperture (44) through which the forced air flow (62) emerges coincides with the apertures (44) through which main flames (60) of the burner emerge.

14. A burner as claimed in one or more of the preceding claims, characterised in that said aperture (88) through which said reduced throughput flames (102) emerge coincides with an aperture (88) through which main flames (100) of the burner emerge.

15. A burner as claimed in one or more of the preceding claims, characterised by comprising a single annularly extending continuous gap (98) through which said forced air (104) emerges.

16. A burner as claimed in one or more of the preceding claims, characterised in that said aperture (44, 98) through which said forced air (62, 104) emerges is positioned above said aperture (34, 88) through which said reduced throughput flames (58, 102) emerge.

17. A burner as claimed in one or more of the preceding claims, characterised in that said means for controlling said generator (24, 74) aare provided with means for deactivating said forced air flow (62, 104) when said main flames (60, 100) are fed.

18. A burner as claimed in one or more of the preceding claims, characterised in that said means for controlling said generator (24, 74) are provided with means for activating said forced air flow (62, 104) when said main flames (60, 100) are fed.

19. A burner as claimed in one or more of the preceding claims, characterised in that said means for controlling said gas injector (12, 16, 80) coincide with the control means for said generator (24, 74).

20. A burner as claimed in one or more of the preceding claims, characterised by comprising two injectors (12, 16) and control means operationally associated with a two-outlet valve, each outlet being associated with an injector (12, 16).