EP1845306A1 - Gas burner for cooking oven - Google Patents

Abstract

The burner has a flame holding device (7) separating flame (27) from a mixing chamber receiving flow of main air and gas to constitute a gaseous mixture (26). The device has a lattice (35) with metallic wires, for passing the mixture. The lattice has a control ring (32) with thickness larger than the thickness of a central part (31a) of a main disc (31) based on a flame`s main direction (28) for slowing down the mixture crossing the part with respect to the mixture crossing the ring. Peripheral orifices (24) situated around the device permit an air flow (39) to be guided toward the flame.

Description

The invention relates to the field of gas burners for kitchen ovens, for example, ovens used in large commercial or institutional kitchens.

The energy produced by combustion is recovered in thermal form. The products of the combustion of gas pass through, for example, heat exchanger tubes where they are cooled to extract thermal energy. Apart from any pressure losses in the heat exchanger tubes or in chimney ducts, the combustion gases from the burner are substantially at atmospheric pressure. The mechanical energy of the combustion gases from the burner is a disadvantage generating vibrations and noise in the kitchen oven.

The patent application EP 698 768 (Electrolux, Zanussi) describes a gas stove equipped with hollow heating elements traversed by combustion products from a gas burner. A disadvantage of this type of burner is to be limited in thermal power. Indeed, when the rate of mixing of air and flammable gas increases, the propagation speed of the combustion of the flame in the gas mixture stream may be lower than the flow rate of the mixture and the flame is detached from the burner. If the phenomenon is not quickly corrected, the flame is blown and extinguished. Conversely, if the gas mixture flow rate is lower than the propagation of the flame, it can go upstream of the burner. Another disadvantage of this type of furnace is that under the effect of thermal variations and the mechanical effects of the flue gas flow, the heating elements, brought to high temperature, can come into vibration. This causes an unpleasant noise and shortens the life of the oven.

The patent application FR 2 708 083 (Gaz de France) describes a flame attachment plate for a gas burner. This plate acts as a sieve for distributing gaseous mixture fillets. She comprises a compressed network of intertwined wires. This structure allows a passage distributed, substantially uniformly, gas streams on the entire surface of the plate and a regular spread of the flame created. However, this type of burner has the disadvantage of being limited in thermal power per cm ² of attachment plate. In addition, this type of burner seeks to produce flames of relatively low height and where the thermal power is located close to the attachment plate. It seems that this type of burner is suitable for heating, from the outside, domestic boiler water coils, for example. However, for kitchen ovens, we want to heat from inside the heat exchanger tubes. It is advantageous to spread the flame to reduce hot spots.

The patent application EP 840 061 (Gaz de France) discloses a flame attachment device comprising a plurality of identical rings composed of a compressed network of interwoven wires. The gaseous mixture passes radially through the rings. Each of the rings gives rise to a radial circular flame. The rings are coaxial and superimposed on each other and separated by solid spacers not traversed by the gas mixture. The outer diameter of the solid spacers is smaller than the outer diameter of the compressed network rings. Pilot flames are formed in the grooves corresponding to the spacers. The previous drawback, namely, the fact of developing thermal energy only at the location of the burner attachment plate, is here accentuated because the combustion gases propagate radially with respect to the axis of the burner. burner.

Requirement US 2006/0 035 189 (Rational AG) discloses a burner having porous body members of tubular form. The wall of the tube is in a compressed network of wires. Several tubular shapes are interlocked axially to form a larger burner. The stabilization of the flame is improved by a deflector plate. In this type of burner, the thermal energy is disengaged radially with respect to the axis of the burner.

The patent US 5,199,416 (Rational GmbH) describes a burner head where a closed combustion chamber opens onto several heat exchanger tubes through which the combustion gases pass. An enclosure surrounding the combustion chamber brings fresh air to the inlet of the heat exchanger tubes to reduce the transition temperature between the combustion chamber and the heat exchange tubes. In this type of burner, the air contributing to the combustion of the flammable gas is entirely contained in the gas mixture upstream of the combustion chamber. The combustion products are evacuated through the exchanger tubes through an outlet manifold. The disadvantage of this type of burner is that in order to limit the non-oxidized combustion products by combustion, it is necessary to introduce into the gas mixture passing through the burner an excess of air relative to the stoichiometric proportions of the gas. For a given burner thermal power, the air supercharging can cause a detachment of the flame. Or, for the same limit of flame separation, the air supercharging reduces the thermal power of the flame.

The invention proposes a burner for a kitchen gas oven that overcomes the above drawbacks and in particular that increases the thermal energy of the burner, avoiding detachment of the flame, and spreading said flame.

According to one embodiment, the burner for a kitchen gas oven comprises a device for attaching the flame of the burner, separating a flame from a mixing chamber adapted to receive a main air flow and gas to constitute a gaseous mixture. The device for attaching the flame is provided with a lattice comprising metal wires, able to pass said gas mixture through the trellis, which trellis comprises at least one main zone and an adjacent pilot zone. The pilot zone has, in a main direction of the burner flame, a thickness greater than the thickness of the main zone, able to slow down the gaseous mixture passing through the pilot zone relative to the mixture crossing the main zone. The burner comprises at least one orifice adapted to receive a secondary air flow.

It is understood that in such a burner, the fact that a so-called "pilot zone" lattice zone is thicker in the direction of the burner flame, makes the gaseous mixture streams passing through the pilot zone are slowed down by a path traveled. in lattice longer than those crossing the main zone. The nets passing through the pilot zone have a lower speed than those crossing the main zone and can feed a small flame called "pilot flame" which is not likely to drop from said pilot zone. The flow rate of gaseous mixture in the main zone can be increased. The pilot flame initiates the start of combustion of the gas streams leaving the main zone. The thermal power of the burner is increased. This increase in power is accompanied by an increase in the length of the flame but not in its temperature. This can help prevent hot spots.

Advantageously, the main zone of the lattice has a porosity of between 60% and 90%.

Advantageously, the main zone of the compressed mesh has a thickness of between 3 and 8 mm.

Advantageously, the thickness ratio of the pilot zone on the main zone is between 2 and 5.

According to another embodiment, the burner comprises means for guiding the flow of secondary air towards the flame. It is conceivable that in this other embodiment, the secondary air stream burns the combustion residues from the mixing chamber. The mixed gas flow rate can be increased, for example up to the stoichiometric proportion of the main air flow, with a low risk of flame takeoff. The thermal power of the burner is increased, and the flame increases in temperature. The secondary air flow also makes it possible to regulate the flows of the combustion products, in particular to control the conditions of ignition and development of the flame, the quality of the combustion and the operating stability, irrespective of the aeration rate, optimal for combustion, chosen for the burner mixing chamber.

According to a variant, the flame attachment device comprises a main disk perpendicular to the direction of the burner flame and a coaxial pilot ring superimposed on the periphery and downstream of the main disk. The ring and the disc each comprise a wire mesh.

Advantageously, the orifice adapted to receive the secondary air flow is located at the periphery of the device for attaching the flame.

In this variant, the two possibilities of increasing the thermal power of the burner due to the pilot zone and the secondary air flow accumulate. This variant has the additional advantage that the pilot ring helps the separation of the secondary air flow and the flame leaving the main zone. This separation prevents secondary air from blowing the flame. In addition, fresh air arrives at the edge of the flame. This avoids having a hot spot at the location of the flame attachment device. This also helps to spread the flame lengthwise. In addition, the pilot zone and the main zone are adjacent and the pilot zone is further downstream than the main zone. These two characteristics have the effect that part of the nets leaving the pilot zone can join, at reduced speed, the nets leaving the main zone. This can allow a flow transition of the mixture between the main broadband zone and the pilot zone.

According to another variant, the burner comprises a sealed enclosure connected to a fan and surrounding the mixing chamber and the or the secondary air orifices. The fan is connected, inside the enclosure, to the mixing chamber by a leak connection means adapted to introduce into the mixing chamber the main air flow and to divert the flow of air towards the enclosure. secondary air.

Advantageously, the metal wires of the lattice are arranged to constitute, in the direction of the flame, a succession deviating obstacles capable of deflecting the trajectory of a stream of the gas stream. This has the advantage that the gaseous mixture streams are distributed substantially uniformly over the entire surface of the mesh. In addition, the multiple deviating obstacles locally reduce the passage section of the gas nets. This locally increases the speed of the gas streams and prevents the flame from rising upstream of the trellis.

Advantageously, the mixing chamber is provided with a static suction device intended to be traversed by a main air flow and adapted to suck up flammable gas.

According to another embodiment, the burner for a kitchen gas oven comprises a device for attaching a flame of the burner separating the flame from a mixing chamber of the gas. The attachment device of the flame is provided with a lattice in the compressed state comprising metal son able to pass said gas mixture through the mesh. The trellis comprises at least one adjacent main area and an adjacent pilot area. The pilot zone has, in the direction of the burner flame, a thickness greater than the thickness of the main zone.

According to another embodiment, the burner for a cooking gas oven comprises a device for attaching a flame of the burner separating the flame from a mixing chamber adapted to receive a main air flow and gas. The burner comprises at least one orifice adapted to receive a secondary air flow, and means for guiding the flow of secondary air towards the flame.

According to another aspect, the invention relates to a cooking oven equipped with a burner described above wherein the flame of the burner is located in a combustion pipe, extended by at least one heat exchanger tube capable of driving gases. combustion; the oven comprising a cooking air fan and means for guiding the cooking air from the fan to the heat exchanger tube or tubes and a cooking zone of the oven.

• la figure 1 est une représentation schématique en coupe du brûleur; et
• la figure 2 est une vue de détail du dispositif d'accrochage du brûleur.

Other features and advantages will appear on reading the detailed description of some embodiments taken as non-limiting examples and illustrated by the accompanying drawings, in which:

• Figure 1 is a schematic sectional view of the burner; and
• Figure 2 is a detail view of the attachment device of the burner.

As illustrated in FIG. 1, the burner comprises a propulsion unit 1 fixed on a fixing plate 2 and surrounded by a box 3. The propulsion unit 1 comprises a fan 4, a venturi device 5, an upstream sleeve 6 and a device The fastening plate 2 also receives an ignition device 8 and an exchanger assembly 9. The exchanger assembly 9 successively comprises a combustion pipe 10 fixed to the fixing plate 2, at least one heat exchanger tube 11 and an outlet 12.

The fan 4 is of the centrifugal type and propels air sucked through the venturi device 5. The venturi device 5 is fixed rigidly opposite and at a distance from the outlet orifice of the fan 4. The connection device to leakage 16 comprises spacers 13, for example in the form of columns or washers which are pressed between an inlet plate 14 of the venturi device 4 and an outlet plate of the fan 4. The mechanical connection between the venturi device 5 and the fan 4 is rigid but not waterproof. The air from the fan 4 separates between a main flow 17 and a secondary flow 18.

The venturi device 5 has an axial cavity in the form of two opposite conical frustums, through which the main stream 17 passes. The cavity is of slow and continuous variation of its section and has a diameter restriction 19 situated between an upstream portion 5a and a downstream part 5b. The progressive expansion of the main air flow 17 in the downstream part 5b of the venturi device causes a depression on the wall of the cavity. A transverse channel 20 opens into the cavity where the main stream 17 has a depression. The venturi device 5 is a static suction device capable of sucking gas flammable through the transverse channel 20 connected to a gas supply.

The space delimited by the downstream part 5b of the venturi device 5, the upstream sheath 6 and the flame attachment device 7 constitutes a mixing chamber 21. The connection of the venturi device 5 and the upstream sheath 6 is sealed. The main stream of air 17 is mixed with the gas from the transverse channel 20 to form a gaseous mixture 26 which flows through the mixing chamber 21, passes through the attachment device 7, and is then ignited by the injection device. ignition 8.

The ignition device 8 is constituted by a central conductor 22 and an insulating sheath 23 surrounding the central conductor 22 and fixed on the fixing plate 2 and is of the incandescent or spark type.

A plurality of peripheral orifices 24 are formed in the fixing plate 2 around the hooking device 7 of the flame and open into the combustion pipe 10. The box 3 surrounds the propulsion assembly 1 and is connected to The fixing plate 2 and the casing 3 together form a sealed enclosure 25 traversed by an end 6a of the upstream sheath 6 receiving the attachment device 7, via the transverse channel 20, by the 4 and the peripheral orifices 24. The secondary air flow 18 escaping from the leakage connection device 16 is trapped in the enclosure 25 and can escape through the peripheral orifices 24. The space separating the inlet plate 14 of the venturi 5 and the outlet plate 15 of the fan 4 is adjusted so that the secondary air flow 18, escaping from the leakage connection device 16, has a higher pressure e at atmospheric pressure and greater than the pressure inside the combustion pipe 10. A secondary air flow 39 passes through the peripheral orifices 24 in the direction of the flame 27.

The combustion pipe 10 has an elongate shape surrounding the flame attachment device 27, the peripheral ports 24 and the ignition devices 8. The chemical reaction The flow direction of the gaseous mixture 26, downstream of the hooking device 7 of the flame 27, defines a main direction 28 of the flame 27 of the flame 27 of the flammable gas with the air. burner.

The chemical reaction converts the gaseous mixture 26 into combustion products and releases thermal energy. The thermal energy heats the combustion products which come into contact with the combustion pipe 10 and then flow inside the heat exchanger 11. The heat exchanger assembly 9 is also heated by direct radiation from the heat exchanger. thermal energy of the flame 27.

The fact that the orifices 24 are located near the flame 27, allows a reliable ignition and without noise. Indeed, when the ignition device 8 ignites the gas mixture 26, the pressure in the combustion pipe 10 increases sharply. The orifices 24 contribute to absorbing the transient effect of the ignition and avoid an explosion noise that is encountered in closed exchangers on the side of the device 7 for attaching the flame 27.

In addition, the possibility of being able to adjust the secondary air flow rate 39 makes it possible to regulate the flow rate passing through the exchanger assembly 9, and in particular the tube 11. This allows, without modifying the thermal power of the burner, to avoid the heating regimes. resonance of the exchanger assembly 9 and the noise that would result.

As illustrated in FIG. 2, the attachment device 7 of the flame 27 is housed inside the end 6a of the sheath 6 and comprises a main disc 31 passing through the entire internal cross section of the sheath 6. pilot ring 32, coaxial with the main disk 31, is superimposed downstream of the main disk 31, and is in radial contact with the inner surface of the end 6a of the sheath 6. The main disk 31 and the pilot ring 32 are all both consist of a mesh of wire 35, interwoven or knitted, then compressed. During compression, the metal wires undergo plastic deformation. The lattice 35 in the free state retains the shape obtained during its compression. The remaining space between the deformed metal son allows the passage of gaseous mixture threads 26 after multiple deviations. This makes it possible to harmonize the speeds of the threads passing through the trellis 35. An embodiment of such trellis is described in the patent application. FR 2 708 083 to which we can usefully refer.

A ring 33 is provided with ribs 33a in the form of braces and fixed upstream of the main disk 31. Lugs 34 extend radially inwardly of the sheath 6 and are arranged downstream and at the periphery of the pilot ring 32. The ring 33 and the lugs 34 enclose the main disk 31 and the pilot ring 32 to support them mechanically, despite the temperature rise of the attachment device 7 of the flame 27 which can reach 1000 ° C.

The pilot ring 32 may be of rectangular section, and has a singing surface 32a, downstream and perpendicular to the main direction 28, and an inner cylindrical surface 32b. One end 22a of the central conductor 22 of the ignition device 8 is disposed in the immediate vicinity of the edge surface 32a. During ignition, a spark springs from the end 22a of the central conductor 22 to the metal wires 35a of the mesh 35, connected to the electrical ground.

The main disc 31 comprises a central portion 31a and a peripheral portion 31b above which is superimposed the ring 32. The gas mixture 26 is shared, through the attachment device 7, between central threads 36 passing through the central portion 31a and peripheral threads 37 passing through the peripheral portion 31b and the ring 32. The central threads 36 have a homogeneous propagation speed over the entire surface of the central portion 31a. The peripheral threads 37 are distributed in a zone of slow propagation 38 located along the edge surface 32a and the inner surface 32b.

The surface of the peripheral portion 31b is much smaller than the sum of the edge surface 32a and the inner surface 32b. This widening of the surface and the greater thickness of mesh 35 to be traversed by the peripheral threads 37, compared to the central threads 36, that the speed of the peripheral threads 37, downstream of the pilot ring 32, is greatly reduced with respect to the speed of the central threads 36 having passed through the central portion 31a.

The spark initiates the combustion of the gas mixture 37 in said slow propagation zone 38 in which the pilot flame is formed, which in turn initiates the combustion of the central threads 36. The fact that the pilot ring 32 has an inner surface 32b extending over a certain axial distance contributes to the efficiency of the pilot flame. The central threads 36 are in contact, over the entire axial distance, with the pilot flame to enter combustion. The propagation speed of the central threads 36 can be greatly increased without the main flame 27 picking up. Such an arrangement of the attachment device makes it possible to greatly increase the gas mixture flow rate 26 and the thermal power of the burner.

The secondary air stream 39, from the orifices 24, has a pressure greater than the pressure of the combustion products and constitutes a thermally insulating layer. This limits the temperature rise of an upstream portion 10a of the combustion pipe 10 located opposite the end 6a of the sheath 6 and the flame 27. This thermal insulation makes it possible to avoid a hot spot of the combustion pipe In particular, the secondary air flow 39 is guided in such a way that the connection zone between the fixing plate 2 and the burner is kept at a low temperature. This allows the use of common seals and improves the life of the entire burner. In addition, the secondary air 39 supplies oxygen to the flame 27 so as to reduce the proportion of unburned gases, or incompletely oxidized oxides such as carbon monoxides. The fact that the peripheral orifices 24 are located around the attachment device of the flame 27 allows the secondary air 39 to be naturally guided towards the flame 27. The flow 39 of secondary air contributes to the stabilization of the flame 27.

In a particular embodiment, the main disk 31 is constituted by a knitting of metal son. The metal wires may be stainless steel, for example type 304L and a diameter between 0.1 and 0.4 mm, preferably of the order of 0.2 mm. The disc 31 has an outer diameter of between 50 and 70 mm, preferably between 55 and 60 mm, and for example 57.8 mm. The thickness of the disk 31 is between 3 and 8 mm, preferably of the order of 5 mm.

The ring 32 consists of a knit of stainless steel wires, for example of the type 309, and of a diameter that is thicker than the wire of the main disc 31, preferably between 0.2 and 0.35 mm, for example of the order of 0.28 mm. The ring 32 has an inside diameter smaller than the diameter of the main disc 31, preferably between 35 and 45 mm, for example of the order of 40 mm. The ring 32 has an outer diameter preferably identical to the diameter of the main disk 31 and a height of between 5 and 25 mm, preferably between 10 and 20 mm, in particular between twice and five times the thickness of the main disk. 31. The thickness of the ring 32 may be of the order of 15 mm. The mesh 35 constituted by the compressed knit has, for the ring, as for the disc, a porosity between 60% and 90% of the outer volume of the mesh, preferably between 70% and 80% and for example about 75%. .

The thermal power of the burner can be adjusted over a range ranging for example from 8 to 40 kilowatts, including playing, in addition to flow rate variations, on the chemical composition of the flammable gas.

Other types of material could be suitable for the mesh 35 as soon as they have a random succession of deviating obstacles, randomly distributed over the entire volume of the mesh 35, so that the gas streams passing through said material are deflected. and distributed homogeneously over the entire surface of the mesh 35.

A device 7 for hooking the flame 27 of the burner combining a pilot zone 32 associated with the orifices 24 gives the burner a great flexibility. A single burner can equip a wide variety of furnaces and accommodate the differences in pressure drop of the heat exchanger 9 according to the size of the furnaces equipped. The same device 7 with the associated orifices 24 can be used with the different types of gas usually encountered in kitchens. The same device 7, with the associated orifices 24 can equip burners whose nominal powers vary over a wide range, for example from single to double constant gas type, or more, including changing the type of gas. The fact that the same device 7 with the associated orifices 24 covers a wide range of applications, makes it possible to reduce the costs of production and storage of the spare parts necessary for the after-sales services of the commercial networks.

Claims (12)

Burner for a kitchen gas oven comprising a hooking device (7) for a flame (27) of the burner, separating the flame (27) from a mixing chamber (21) able to receive a main air flow (17) and gas to form a gaseous mixture (26), characterized in that the attachment device (7) of the flame (27) is provided with a mesh (35) comprising metal wires, adapted to passing said gaseous mixture (26) through the trellis (35), which trellis (35) comprises at least one adjacent main area (31a) and a pilot zone (32); the pilot zone (32) having, in a main direction (28) of the flame (27) of the burner, a thickness greater than the thickness of the main zone (31a), able to slow down the gaseous mixture (37) passing through the pilot zone (32) with respect to the mixture (36) passing through the main zone (31 a); the burner comprising at least one orifice (24) adapted to receive a secondary air flow (39). Burner according to claim 1, wherein the main zone (31a) of the mesh (35) has a porosity of between 60% and 90% and a thickness of between 3 and 8 mm. Burner according to any one of the preceding claims, wherein the thickness ratio of the pilot zone (32) on the main zone (31a) is between 2 and 5. Burner according to any one of the preceding claims, comprising means (10a, 6a) for guiding the secondary air flow (39) to the flame (27). Burner according to any one of the preceding claims, wherein the flame attachment device (7) comprises a main disk (31) perpendicular to the direction (28) of the flame (27) of the burner and a ring pilot (32), coaxial, superimposed on the periphery and downstream of the main disk (31), the ring (32) and the disc (31) each comprising a mesh (35) of metal son. Burner according to any one of the preceding claims, wherein the orifice (24) adapted to receive the secondary air flow (39) is located at the periphery of the attachment device (7) of the flame (27). Burner according to any one of the preceding claims, comprising an enclosure (25) connected to a fan (4) and surrounding the mixing chamber (21) and the orifices (24) of secondary air (39); the fan (4) being connected, inside the enclosure (25), to the mixing chamber (21) by a leaky connection means (16) suitable for introducing into the mixing chamber (21) the main air flow (17) and diverting to the enclosure (25) the secondary air flow (18). Burner according to claim 7, wherein the leaky connection means (16) comprises spacers (13), in particular in the form of columns or washers pressed between an inlet plate (14) of a venturi device (5). and a plate (15) for outputting the fan (4), the mechanical connection between the venturi device (5) and the fan (4) being rigid but not sealed, the air coming from the fan (4) separating between the main flow (17) and the secondary flow (18). Burner according to claim 7 or 8, wherein the secondary air flow (18) escaping from the leakage connection means (16) is trapped in the chamber (25) and can escape through the peripheral openings ( 24), the space separating the inlet plate (14) of the venturi (5) and the outlet plate (15) of the fan (4) being adjusted so that the secondary air flow (18), s' escaping from the leakage connection device (16), has a pressure greater than the atmospheric pressure and greater than the pressure inside a combustion pipe (10), a secondary air flow (39) passing through the orifices peripherals (24) towards the flame (27). Burner according to any one of the preceding claims, wherein the metal wires of the mesh (35) are arranged to form, in the direction (28) of the flame (27), a succession of deviating obstacles (35a) adapted to deflect the trajectory of a stream of the gas stream (36, 37). Burner according to any one of the preceding claims, wherein the mixing chamber (21) is provided with a static suction device (5) intended to be traversed by a main air flow (17) and able to suck flammable gas. Kitchen oven equipped with a burner according to any preceding claim wherein the flame (27) of the burner is located in a combustion pipe (10), extended by at least one heat exchanger tube (11) adapted to conduct flue gases; the oven comprising a fan of cooking air and means for guiding the cooking air from the fan to the heat exchanger tube or tubes (11) and a cooking zone of the oven.

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