EP0730122B1 - Gas burner with improved acoustical attenuation - Google Patents

Description

The present invention relates to burners with gases with improved acoustic discretion as described in the preamble of claim 1.

DE-A-22 63 471 describes an example of a like a gas burner.

The present invention aims to provide a burner with gas of the kind in question which does not have an entry forced air, but a venturi tube fitted with a gas and which is especially effective in mitigating noise generated by the operation of the gas injector and the venturi tube.

To this end, according to the invention, a gas burner of the genre in question is essentially characterized in that the interior volume includes a venturi tube having a upstream end which is provided with a gas injector combustible and which is shaped to draw air under the effect of fuel gas injection thereby generating the aforementioned noises, the space entrance opening anti-noise hollow communicating with the venturi tube and being disposed at a distance from the upstream end of the tube venturi which is between 0.2 k λ and 0.3 k λ, where k is an odd integer and where λ is the wavelength predetermined.

• le brûleur présente un plan de symétrie et comporte deux demi-coques embouties qui sont assemblées l'une à l'autre et qui délimitent chacune une moitié du volume intérieur du brûleur et de l'espace creux antibruit, ce qui permet une réalisation simple et peu coûteuse du brûleur ;
• l'espace creux antibruit est une cavité résonante fermée qui communique avec le volume intérieur dudit brûleur uniquement par l'ouverture d'entrée ;
• la cavité résonante est un tube résonant qui s'étend sur une certaine longueur entre l'ouverture d'entrée et une extrémité fermée, la longueur de ce tube résonant étant sensiblement égale à un multiple entier impair du quart de la longueur d'onde prédéterminée ;
• le tube venturi présente vers son extrémité d'amont une paroi annulaire extérieure pleine qui entoure une paroi annulaire intérieure pleine en délimitant avec la paroi extérieure un volume annulaire qui forme la cavité résonante, cette cavité résonante s'étendant selon l'axe longitudinal du tube venturi entre d'une part une extrémité d'amont fermée voisine de l'extrémité d'amont du tube venturi et d'autre part une extrémité d'aval qui forme une ouverture annulaire constituant l'ouverture d'entrée de la cavité résonante ;
• l'espace creux antibruit est un tube de liaison qui s'étend sur une certaine longueur entre des première et deuxième extrémités communiquant toutes les deux avec le volume intérieur dudit brûleur, la première extrémité du tube de liaison formant l'ouverture d'entrée susmentionnée, la deuxième extrémité étant située en aval de la première extrémité, l'air et le gaz combustible qui transitent dans le brûleur sans passer par le tube de liaison parcourant une longueur déterminée entre les deux extrémités du tube de liaison, et la longueur du tube de liaison différant de ladite longueur déterminée par une longueur n λ/2, où n est un nombre entier impair et où λ est la longueur d'onde prédéterminée ;
• la longueur du tube de liaison est supérieure à la longueur déterminée parcourue entre les deux extrémités dudit tube de liaison par l'air et le gaz combustible qui transitent dans le brûleur sans passer par le tube de liaison ;
• le tube venturi débouche dans une chambre de prémélange en amont de la tête de combustion, la chambre de prémélange s'étendant longitudinalement entre deux extrémités et communiquant avec le tube venturi à une seule de ses extrémités, le tube venturi étant disposé le long de la chambre de prémélange, et la longueur du tube de liaison étant inférieure à la longueur prédéterminée parcourue entre les deux extrémités dudit tube de liaison par l'air et le gaz combustible qui transitent dans le brûleur sans passer par le tube de liaison ;
• la deuxième extrémité du tube de liaison communique avec le tube venturi, est disposée à une distance de l'extrémité d'amont du tube venturi qui est comprise entre 0,2 q λ et 0,3 q λ, où q est un nombre entier impair supérieur à k ;
• k vaut 1 ou 3 ;
• le volume intérieur du brûleur présente, au droit de l'ouverture d'entrée de l'espace creux antibruit, une section de passage du mélange air-gaz qui est au moins 10 fois plus grande que la section de ladite ouverture d'entrée : on évite ainsi l'émission par l'espace creux antibruit de bruits de fréquences supérieures qui pourraient éventuellement renforcer les bruits émis par le brûleur à des longueurs d'ondes différentes de la longueur d'onde λ que l'on cherche à atténuer.

In preferred embodiments, use is also made of one and / or the other of the following arrangements:

• the burner has a plane of symmetry and comprises two stamped half-shells which are assembled to each other and which each delimit one half of the internal volume of the burner and the hollow noise reduction space, which allows a simple and inexpensive burner;
• the anti-noise hollow space is a closed resonant cavity which communicates with the internal volume of said burner only through the inlet opening;
• the resonant cavity is a resonant tube which extends over a certain length between the inlet opening and a closed end, the length of this resonant tube being substantially equal to an odd integer multiple of a quarter of the predetermined wavelength ;
• the venturi tube has, towards its upstream end, a solid outer annular wall which surrounds a solid inner annular wall, delimiting with the outer wall an annular volume which forms the resonant cavity, this resonant cavity extending along the longitudinal axis of the tube venturi enters on the one hand a closed upstream end close to the upstream end of the venturi tube and on the other hand a downstream end which forms an annular opening constituting the entry opening of the resonant cavity;
• the noise reduction hollow space is a connecting tube which extends over a certain length between first and second ends, both communicating with the internal volume of said burner, the first end of the connecting tube forming the aforementioned inlet opening , the second end being located downstream of the first end, the air and the combustible gas which pass through the burner without passing through the connection tube traversing a determined length between the two ends of the connection tube, and the length of the tube link differing from said length determined by a length n λ / 2, where n is an odd integer and where λ is the predetermined wavelength;
• the length of the connecting tube is greater than the determined length traveled between the two ends of said connecting tube by the air and the combustible gas which pass through the burner without passing through the connecting tube;
• the venturi tube opens into a premix chamber upstream of the combustion head, the premix chamber extending longitudinally between two ends and communicating with the venturi tube at only one of its ends, the venturi tube being disposed along the premix chamber, and the length of the connecting tube being less than the predetermined length traveled between the two ends of said connecting tube by the air and the combustible gas which pass through the burner without passing through the connecting tube;
• the second end of the connecting tube communicates with the venturi tube, is disposed at a distance from the upstream end of the venturi tube which is between 0.2 q λ and 0.3 q λ, where q is an integer odd greater than k;
• k is 1 or 3;
• the internal volume of the burner has, at the level of the inlet opening of the noise-canceling hollow space, a cross section of the air-gas mixture which is at least 10 times larger than the section of said inlet opening: this avoids the emission by the noise-canceling hollow space of noises of higher frequencies which could possibly reinforce the noises emitted by the burner at wavelengths different from the wavelength λ which it is sought to attenuate.

Other characteristics and advantages of the invention will appear during the detailed description following of many of its embodiments given as examples, with reference to the drawings joints.

• la figure 1 est une vue schématique en coupe et en perspective montrant un brûleur atmosphérique à gaz selon une forme de réalisation de l'invention,
• la figure 2 est un graphe montrant les améliorations apportées à la discrétion sonore d'un brûleur atmosphérique à gaz grâce aux dispositions représentées sur la figure 1,
• les figures 3 à 5 sont des vues schématiques en coupe montrant des brûleurs atmosphériques à gaz selon trois autres formes de réalisation de l'invention,
• et la figure 6 est une vue partielle similaire à la figure 1, montrant l'extrémité d'amont du tube venturi d'un brûleur selon encore une autre forme de réalisation de l'invention.

In the drawings:

• FIG. 1 is a schematic sectional and perspective view showing an atmospheric gas burner according to one embodiment of the invention,
• FIG. 2 is a graph showing the improvements made to the acoustic discretion of an atmospheric gas burner thanks to the arrangements represented in FIG. 1,
• FIGS. 3 to 5 are schematic sectional views showing atmospheric gas burners according to three other embodiments of the invention,
• and FIG. 6 is a partial view similar to FIG. 1, showing the upstream end of the venturi tube of a burner according to yet another embodiment of the invention.

In the different figures, the same references denote identical or similar elements.

In all the embodiments considered below, reference 1 designates an atmospheric burner gas which is intended to be integrated in a boiler, in a water heater, in a bath heater or the like.

This burner 1 comprises a venturi tube 2 which extends between an inlet end 3 communicating with the atmosphere and an outlet end 4 communicating with a premix chamber 5, upstream of a combustion grate 6 or any other combustion head. The bedroom premix 5 is delimited by a solid side wall, in general metallic and it communicates only with the venturi tube 2 and with combustion grate 6.

The venturi tube 2 conventionally comprises, from upstream to downstream, a short converging section, a pass, then a long divergent section, and it is provided at its inlet end 3 of a fuel gas injector 7.

During operation of the burner, air is sucked in at the inlet end 3 under the effect of the injection combustible gas. This air mixes with the combustible gas in the venturi tube 2 and in the premix chamber 5, then the premix thus produced is burned out of the premix chamber 5 by the combustion grate 6.

In all the examples shown, the burner 1 has a single venturi tube 2, but it could have possibly several venturis tubes opening into the same premix chamber, without departing from the scope of the present invention.

Furthermore, in the examples shown, the tube venturi 2 opens into the premix chamber 5 through the bottom 5a of this chamber, at a longitudinal end 5b of said chamber, and the venturi tube 2 is folded under the bottom 5a substantially parallel to the grid of combustion 6, towards the second longitudinal end 5b of the premix chamber.

Except in the particular case considered in the figure 4, the venturi tube 2 could however be arranged differently from the premix chamber 5, and in particular, it could be arranged under the bottom 5a of the premix chamber substantially perpendicular to the combustion grate 6.

In all the examples considered here, we create in the venturi tube or in the premix chamber 5 of counter-noises in phase opposition with vibrations acoustics generated by the injection of combustible gas and the concomitant air inlet at the inlet end 3 of the tube venturi, and also generated by the rapid circulation of gas mixture in the venturi tube. We thus mitigate these acoustic vibrations, which allows an operation quieter burner 1.

In the example in Figure 1, the noise barriers are generated by means of two resonant cavities in the form of tubes 10, called "quarter-wave" tubes. These tubes have a section of any shape and each extend longitudinally between on the one hand an open end 11 communicating with the inside of the venturi tube 2, and on the other hand a closed bottom 12.

The acoustic vibrations which take place inside the venturi tube 2 penetrate into each of the two tubes 10 through their open end 11, and these vibrations travel the longitudinal length, respectively l 1, l 2 of these tubes before being reflected on their bottom 12, then they again travel the longitudinal length of said tubes in the opposite direction before returning to the venturi tube 2.

In this way, when the interior of the venturi tube 2 is the seat of acoustic vibrations whose frequency corresponds to a wavelength equal to four times the longitudinal length l 1 or l 2 of one of the two tubes 10, this tube 10 returns in the venturi tube acoustic vibrations in phase opposition with the vibrations generated in the tube 2.

In other words, the two tubes 10 generate counter-noises in phase opposition with the noises generated in the venturi tube 2 in the vicinity of two predetermined frequencies corresponding to wavelengths λ1 and λ2 such that the lengths l 1 and l 2 tubes are respectively substantially equal to a quarter of the wavelengths λ1 and λ2, or more generally equal to odd integer multiples of a quarter of the wavelengths λ1 and λ2.

Advantageously, the inlet ends 11 of the tubes 10 are arranged to communicate with an area of the internal volume of the burner where the acoustic vibrations having the frequency to be absorbed have an amplitude maximum.

In particular, the inlet ends 11 of the tubes 10 are preferably arranged at respective distances l 3, l 4 from the inlet end 3 of the venturi tube which are respectively substantially equal to odd integer multiples of a quarter of the lengths of waves λ1 and λ2 of the noises which are respectively muffled by the two tubes 10.

More generally, the distance l 3 can be between 0.2 k1 λ1 and 0.3 k1 λ1, and the distance l 4 can be between 0.2 k2 λ2 and 0.3 k2 λ2, where k1 and k2 are odd whole numbers, preferably equal to 1 or 3.

As in all embodiments of the present invention the distances between the input end 3 of the venturi tube and the inlets 11 of the tubes (more generally the entrance openings of the noise-canceling hollow spaces) are curvilinear distances corresponding to the average path followed by the gases from the inlet end 3 of the tube venturi to the entry openings in question.

In a particular embodiment, to attenuate two peaks of acoustic vibrations at around 1000 and 2300 Hz, tubes 10 of circular section with an inside diameter of 3 millimeters were used, with the following parameters: l 1 = 3.2 cm , l 2 = 8.6 cm, l 3 = 3.6 cm, l 4 = 8.5 cm.

FIG. 2 shows a spectrum of acoustic vibrations measured in an exemplary embodiment particular of the burner 1 represented in FIG. 1, on the one hand without the two tubes 10 (in solid lines), and on the other hand with the two tubes 10 (dotted lines).

We can see that without the two tubes 10, the spectrum presents two peaks P1 and P2 of acoustic vibrations at around 1000 and 2300 Hz, and that these peaks are suppressed thanks to the addition of the two tubes 10.

It goes without saying that burner 1 could be provided of a single tube 10 or possibly of more than two tubes 10, depending on the desired noise frequencies absorb.

In addition, the tubes 10 could possibly communicate with the premix chamber 5 rather than with the venturi tube 2, they could if necessary present a straight rather than curvilinear shape such as that shown in Figure 1 and they might possibly not not be arranged in the plane of symmetry of burner 1.

It is however advantageous that the tubes 10 are arranged with their longitudinal axes in the plane of symmetry of the burner 1, as shown in FIG. 1, insofar as this provision makes it possible to carry out simply burner 1 by stamping then assembly of two metal half-shells, one of these half-shells being shown schematically in Figure 1. Each half-shell then represents half of the venturi tube 2, of the side wall of the premix chamber 5, and of each tube 10.

In the case of such an embodiment, the grid of combustion 6 will usually be reported above the premix chamber 5 after assembly of the two half-shells. However, it is also possible to use place of the grid 6 a combustion head formed by air-fuel gas mixture outlet channels, these channels being achieved simply by the juxtaposition of the two half-shells.

As shown in Figure 3, the tubes 10 could be replaced by one or more cavities resonant 20 having another form. The resonant cavity 20 is in the form of a volume capacity V, called "Helmholtz resonator" designed to produce inside of the burner 1 against noise in phase opposition with noises presenting the frequency to be attenuated.

The resonant cavity 20 communicates with the interior of the venturi tube 2 or the premix chamber 5 via an entrance 21 and it is delimited by a wall waterproof 22.

où :

• f est la fréquence à atténuer, en Hertz,
• S est la section de l'orifice d'entrée 21,
• c est la vitesse de propagation des ondes acoustiques,
• V est le volume intérieur de la cavité 20,
• et h est la longueur de l'ouverture d'entrée 21, c'est-à-dire la distance entre le volume intérieur du brûleur et la capacité V au niveau de ladite ouverture d'entrée 21 : si la capacité V est accolée à la paroi du tube venturi 2 ou de la chambre de prémélange 5, h est simplement l'épaisseur de cette paroi.

For a cavity 20 having a single inlet orifice 21, the frequency to be attenuated is expressed by the following conventional formula:

or :

• f is the frequency to be attenuated, in Hertz,
• S is the section of the inlet orifice 21,
• c is the speed of propagation of the acoustic waves,
• V is the interior volume of the cavity 20,
• and h is the length of the inlet opening 21, that is to say the distance between the internal volume of the burner and the capacity V at the level of said inlet opening 21: if the capacity V is attached to the wall of the venturi tube 2 or of the premix chamber 5, h is simply the thickness of this wall.

Like the tubes 10 already described, the resonant cavity 20 can communicate with the venturi tube 2 or with the premix chamber 5, and one or more can be provided several resonant cavities depending on the number of frequencies to be attenuated.

As already indicated for the example of FIG. 1, the inlet 21 of the cavity 20 is preferably arranged in an area where the amplitude of the acoustic vibrations is maximum in the burner, for example at a distance l 5 from the upstream end 3 of the venturi tube which is between 0.2 and 0.3 times an odd integer multiple k of the wavelength λ of the noise to be attenuated, k preferably being equal to 1 or 3. The distance l 5 is preferably close to λ / 4 or more generally close to an odd integer multiple k of λ / 4, k being preferably equal to 1 or 3.

Furthermore, the resonant cavity 20 is preferably, but not exclusively, symmetrically arranged with respect to the plane of symmetry of the burner 1, so that the entire burner 1, except where applicable the grate combustion 6, can be achieved by stamping two metal half-shells assembled according to the plane of symmetry, as explained above with reference to FIG. 1.

In the examples shown in Figures 4 and 5, the counter-noises are generated by means of a tube of link 30, of any section, which extends between a share an upstream end 31 or communicating entrance opening with the venturi tube 2, and on the other hand an end downstream 32 communicating with the venturi tube or the premix 5.

The ends of the tube 30 can optionally both communicate with the premix chamber 5.

In the two cases shown in FIGS. 4 and 5, the gas mixture which passes through the burner 1 without passing through the connection tube 30 travels a distance L in the venturi tube and the premix chamber 5 between the ends 31 and 32 of the tube of connection, and the connection tube has a length, respectively l 6, l 7, which is either less than or greater than the distance L and which differs from the distance L by a length n λ / 2, where n is a number odd integer and where λ is the wavelength of the noises to be suppressed.

In practice, n will most often be equal to 1.

In the example of FIG. 4, the length l 6 of the connecting tube 30 is half a wavelength shorter than the length L, and in the example of FIG. 5, the length l 7 of the tube link 30 is half a wavelength longer than length L.

Due to its length, the connecting tube 30 generates in any case at its end 32 a noise counter phase opposition with the acoustic vibrations of the gas mixture for the predetermined frequency to be damped.

As in the previous examples, the tube 30 is preferably, but not exclusively, arranged in the plane of symmetry of burner 1, so that this burner, except the if necessary its combustion grate 6, can be produced by stamping two metal half-shells then assembly of these two half-shells along the plane of symmetry.

In the examples shown in Figures 4 and 5, the distance l 8 between the end 31 of the connection tube and the upstream end 3 of the venturi tube can be between 0.2 k λ and 0.3 k λ , this distance being advantageously close to k λ / 4, and the distance l 9 between the second end 32 of the connecting tube and the upstream end 3 of the venturi tube can be between 0.2 q λ and 0.3 q λ and advantageously close to q λ / 4, where k and q are two different odd integers and where λ is the wavelength of the noise to be attenuated (k is preferably equal to 1 or 3).

Finally, in the example shown in Figure 6, the counter-noises are generated by means of a resonant cavity annular 35 formed at the upstream end 3 of the tube venturi.

This annular resonant cavity is delimited radially outwards by an annular wall outer 33 full which laterally delimits the tube venturi 2, and radially inward by a wall full annular 34 having successively a section converge, a pass, then a divergent section,

The wall 34 is in sealed peripheral contact with of the outer wall 33 upstream (the upstream ends of these two walls are not necessarily confused), and it extends downstream inside the outer wall 33 to an open end 34a which communicates with the inside of the wall 33.

Thus, the annular resonant cavity 35 extends along the longitudinal axis of the venturi tube 2 between a upstream end 35a closed and a downstream end 35b which forms an annular opening constituting the entrance to the resonant cavity.

These upstream and downstream ends are separated from each other by an axial distance l 10 substantially equal to a quarter of the wavelength of the noise to be suppressed, or more generally substantially equal to an odd multiple of a quarter. of this wavelength (preferably λ / 4 or 3λ / 4), the distance between the inlet end 3 of the venturi tube and the inlet opening 35b of the resonant cavity being between 0.2 k λ and 0.3 k λ where k is an odd integer (preferably 1 or 3) and λ is the wavelength of the noise to be attenuated.

Preferably, in all embodiments of the invention, the internal volume of the burner has, at right of the entrance opening of the noise-canceling hollow space (resonant cavity or connecting tube), a section of passage of the air-gas mixture which is at least 10 times more large than the section of said inlet opening, the cross section of the air-gas mixture being the section of the internal volume of the burner taken perpendicular to the average direction of gas flow.

Claims (11)

1. A gas burner, comprising an internal volume (2,5) which receives air as well as a combustible gas and which discharges to the atmosphere through a combustion head (6), this burner generating noises in its internal volume during its operation and comprising in addition a hollow noise-reducing space (10, 20, 30, 35) for generating counter noises in its internal volume (2,5), in phase opposition to the aforementioned noises. at least for absorbing a certain frequency corresponding to a pre-specified wavelength, this hollow noise-reducing space being delimited by a solid wall and communicating with the internal volume (2, 5) of the burner at least through one inlet opening (11, 21, 31, 35b), the counter noises being obtained only by the geometry of said hollow noise-reducing space, the internal volume including a venturi tube (2) having an upstream end (3) which is provided with a combustible gas injector (7) and which is shaped to induce air under the effect of the combustible gas injection thus generating the aforementioned noises, the inlet opening (11, 21, 31, 35b) of the hollow noise-reducing space communicating with the venturi tube, characterised in that the inlet opening (11, 21, 31, 35b) is arranged at a distance from the upstream end (3) of the venturi tube which is between 0.2 k λ and 0.3 k λ, where k is an odd integer and where λ is the pre-specified wavelength.
2. A burner according to claim 1, having a plane of symmetry and comprising two fitted half-shells which are assembled together and which each delimit one half of the internal volume (2, 5) of the burner and the hollow noise-reducing space.
3. A burner according to any one of the claims 1 and 2, wherein the hollow noise-reducing space is a closed resonant cavity (10, 20, 35) which communicates with the internal volume (2, 5) of said burner only through the inlet opening (11,21,35b).
4. A burner according to claim 3, wherein the resonant cavity is a resonant tube (10) which extends over a certain length (l1, l2) between the inlet opening (11) and a closed end (12), the length of this resonant tube being approximately equal to an odd whole multiple of a quarter of the pre-specified wavelength.
5. A burner according to claim 3 wherein the venturi tube (2) has towards its upstream end (3) an external solid annular wall (33) which surrounds an internal so!id annular wall (34) delimiting with the external wall an annular volume (35) which forms the resonant cavity, this resonant cavity extending along the longitudinal axis of the venturi tube (2) between on the one hand a closed upstream end (35a) near the upstream end (3) of the venturi tube and on the other hand a downstream end (35b) which forms an annular opening constituting the inlet opening of the resonant cavity, and these upstream and downstream ends being separated from each other by an axial distance (110) approximately equal to an odd multiple of a quarter of the pre-specified wavelength.
6. A burner according to any one of claims 1 and 2, wherein the hollow noise-reducing space is a connection tube (30) which extends over a certain length (16, 17) between first and second ends (31, 32) both communicating with the internal volume (2, 5) of said burner, the first end (31) of the connection tube forming the aforementioned inlet opening, the second end (32) being located downstream from the first end (31), the air and the combustible gas which passes through the burner without passing through the connection tube (30) travelling a specified length (L) between the two ends of the connection tube, and the length of the connection tube differing from said specified length (L) by a length n λ/2, where n is an odd integer.
7. A burner according to claim 6, wherein the length (l6, l7) of the connection tube (30) is greater than the specified length (L) travelled between the two ends (31, 32) of said connection tube by the air and the combustible gas which pass through the burner without passing through the connection tube.
8. A burner according to claim 6, wherein the venturi tube discharges into a pre-mixing chamber (5) upstream of the combustion head (6), the pre-mixing chamber (5) extending longitudinally between two ends (5b, 5c) and communicating with the venturi tube (2) at only one (5b) of its ends, the venturi tube being arranged along the pre-mixing chamber, and the length (16) of the connection tube (30) being less than the pre-specified length (L) travelled between the two ends (31, 32) of said connection tube by the air and the combustible gas which passes through the burner without passing through the connection tube.
9. A burner according to any one of the claims 6 to 8, wherein the second end (32) of the connection tube communicates with the venturi tube (2), is arranged at a distance (19) from the upstream end (3) of the venturi tube which is between 0.2 q λ and 0.3 q λ, where q is an odd integer greater than k.
10. A burner according to any one of the previous claims, wherein k is 1 or 3.
11. A burner according to any one of the previous claims, wherein the internal volume of the burner has, at right angles to the inlet opening (11, 21, 31, 35b) of the hollow noise-reducing space, a passage section for the air-gas mixture which is at least 10 times greater than the section of said inlet opening.

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