DE69603389T2 - Gas burner with improved acoustic damping - Google Patents

Description

The present invention relates to gas burners with improved noise development as described in the preamble of claim 1.

The document DE-A-22 63 471 describes an example of such a gas burner.

The present invention aims to propose a gas burner of the type in question which does not have a pulsed air inlet but a venturi tube provided with a device for injecting gas and is particularly effective for dampening the noise generated by the operation of the gas injection device and the venturi tube.

For this purpose, a gas burner of the type in question is essentially characterized according to the invention in that the interior has a venturi tube with an inlet end, which is provided with a fuel gas injection device and is designed in such a way that it sucks in air under the effect of the injection of fuel gas, whereby the said noises are generated, the inlet opening of the anti-noise cavity is connected to the venturi tube and is arranged at a distance of between 0.2 kλ and 0.3 kλ from the inlet end of the venturi tube, where k is an odd whole number and λ is the predetermined wavelength.

In the preferred embodiments, one and/or other of the following arrangements is further used:

- the burner has a plane of symmetry and has two deep-drawn half-shells which are attached to each other and each delimit one half of the interior of the burner and of the anti-noise cavity, which allows a simple and inexpensive design of the burner;

- the anti-noise cavity is a closed resonance chamber that is only connected to the interior of the burner via the inlet opening;

- the resonance chamber is a resonance tube extending over a certain length between the inlet opening and a closed end, the length of this resonance tube being substantially equal to an odd integer multiple of a quarter of the predetermined wavelength;

- the venturi tube has, towards its inlet end, a solid annular outer wall which surrounds a solid annular inner wall so that, together with the outer wall, it delimits an annular space forming the resonance chamber, this resonance chamber extending along the longitudinal axis of the venturi tube between a closed inlet end adjacent to the inlet end of the venturi tube on the one hand and an outlet end on the other hand which forms an annular opening which represents the inlet opening of the resonance chamber;

- the anti-noise cavity is a connecting pipe extending over a certain length between the first and the second end, both of which communicate with the interior of the burner, the first end of the connecting pipe forming the said inlet opening, the second end being arranged downstream of the first end, the air and the fuel gas entering the burner without passing through the connecting pipe having a predetermined a given length between the two ends of the connecting tube, and the length of the connecting tube differs from the given length by a length λ/2, where n is an odd integer and λ is the given wavelength;

- the length of the connecting pipe is greater than the specified length between the two ends of the connecting pipe, traversed by the air and the fuel gas entering the burner without passing through the connecting pipe;

- the venturi tube opens into a premixing chamber arranged at the inlet side of the combustion head, the premixing chamber extending longitudinally between two ends and communicating with the venturi tube at only one of its ends, the venturi tube being arranged along the premixing chamber, and the length of the connecting tube being less than the predetermined length traversed by the air and the fuel gas, which enter the burner without passing through the connecting tube, between the two ends of the connecting tube;

- the second end of the connecting tube, which communicates with the venturi tube, is arranged at a distance from the inlet end 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;

- k has the value 1 or 3;

- the interior of the burner has a cross-section for the passage of the air/gas mixture straight ahead from the inlet opening of the anti-noise cavity which is at least ten times as large as the cross-section of the inlet opening: this prevents noise at higher frequencies from being emitted through the anti-noise cavity, which could potentially amplify the noise emitted by the burner at wavelengths other than the one to be attenuated.

Further features and advantages of the invention will become apparent in the course of the following detailed description of several exemplary embodiments with reference to the accompanying drawings.

In the drawing shows:

- Fig. 1 is a schematic sectional view and perspective view of an atmospheric gas burner according to an embodiment of the invention,

- Fig. 2 is a graphical representation of the improvements in the noise level of an atmospheric gas burner provided by the arrangements shown in Fig. 1,

- Fig. 3 to 5 are schematic sectional views of atmospheric gas burners according to three further embodiments of the invention, and

- Fig. 6 is a partial view similar to that of Fig. 1, showing the inlet end of the venturi tube of a burner according to another embodiment of the invention.

In the various figures, like reference symbols designate identical or similar components.

In all embodiments considered below, reference numeral 1 designates an atmospheric gas burner for integration into a boiler, water heater, instantaneous water heater or the like.

This burner 1 has a venturi tube 2 which extends on the inlet side of a combustion grate 6 or any other combustion head between an inlet end 3 connected to the atmosphere and an outlet end 4 connected to a premixing chamber 5. The premixing chamber 5 is delimited by a solid side wall, generally made of metal, and is only connected to the venturi tube 2 and to the combustion grate 6.

The venturi tube 2 conventionally has a short, tapering section, a constriction, and then a long, widening section in the direction from the inlet to the outlet side and is provided with a fuel gas injection device 7 at its inlet end 3.

When the burner is operating, air is sucked in at the inlet end 3 as a result of the injection of the fuel gas. This air mixes with the fuel gas in the venturi tube 2 and in the premixing chamber 5, whereupon the premix produced in this way is burned through the combustion grate 6 as it exits the premixing chamber 5.

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

Furthermore, in the examples shown, the venturi tube 2 opens through the bottom 5a of the premixing chamber 5 into this chamber, at one longitudinal end 5b of the chamber, and the venturi tube 2 is guided back under the bottom 5a essentially parallel to the combustion grate 6 in the direction of the second longitudinal end 5b of the premixing chamber.

However, with the exception of the particular case shown in Fig. 4, the venturi tube 2 could be arranged differently with respect to the premixing chamber 5 and could in particular be arranged under the bottom 5a of the premixing chamber substantially perpendicular to the combustion grate 6.

In all the examples considered here, counter-noises are generated in the Venturi tube or in the premixing chamber 5 with an opposite phase to that of the sound vibrations generated by the injection of the fuel gas and the simultaneous entry of air at the inlet end 3 of the Venturi tube and also by the rapid progression of the gas mixture in the Venturi tube. These sound vibrations are thus dampened, which makes it possible to achieve a quieter operation of the burner 1.

In the example of Fig. 1, the counter noises are generated by means of two tubular resonance chambers 10, so-called "quarter-wave" tubes. These tubes have an arbitrary cross-section and each extend in the longitudinal direction between an open end 11 connected to the interior of the Venturi tube 2 on the one hand and a closed bottom 12 on the other.

The sound vibrations occurring inside the venturi tube 2 enter each of the two tubes 10 through their open end 11, and these vibrations traverse the lengths 11 and 12 of these tubes, respectively, before breaking at their bottom 12, whereupon they again traverse the lengths of the tubes in the opposite direction before arriving again in the venturi tube 2.

If sound vibrations occur inside the Venturi tube 2, the frequency of which corresponds to a wavelength equal to four times the length /1 or /2 of one of the two tubes 10, this tube 10 conducts the Venturi tube produces sound vibrations whose phase is opposite to that of the vibrations generated in tube 2.

In other words, the two tubes 10 generate counter-noises which are in antiphase with the noises generated in the venturi tube 2, in the vicinity of two predetermined frequencies corresponding to wavelengths λ1 and λ2, so that the length h or 12 of the tubes is respectively substantially equal to a quarter of the wavelength λ1 or λ2, or, more generally, equal to integer odd multiples of a quarter of the wavelengths λ1 and λ2.

Advantageously, the inlet ends 11 of the tubes 10 are arranged in such a way that they are connected to a zone of the interior of the burner where the sound vibrations with the frequency to be absorbed have a maximum amplitude.

In particular, the inlet ends 11 of the tubes 10 are preferably arranged at a respective distance /3 and /4 from the inlet end 3 of the venturi tube, each of which is substantially equal to an integer odd multiple of the fourth part of the wavelengths λ1 and λ2 of the noises respectively suppressed by the two tubes 10.

More generally, the distance /3 may be between 0.2 k1 λ1 and 0.3 k1 λ1, and the distance 14 may be between 0.2 k2 λ2 and 0.3 k2 λ2, where k1 and k2 are odd integers, preferably equal to 1 or 3.

As with all embodiments of the present invention, the distances between the inlet end 3 of the venturi tube and the inlet 11 of the tubes (typically the inlet openings of the anti-noise cavities) are curved paths corresponding to the mean path. which the gases follow from the inlet end 3 of the venturi tube to the respective inlet openings.

In a particular embodiment, in order to attenuate two sound vibration peaks at approximately 1000 and 2300 Hz, tubes 10 with a circular cross-section were used, having an inner diameter of 3 millimeters, with the following parameters: /1 = 3.2 cm, /2 = 8.6 cm, 13 = 3.6 cm, /4 = 8.5 cm.

Fig. 2 shows a spectrum of sound vibrations that were measured in a particular embodiment of the burner 1 shown in Fig. 1, namely without the two tubes 10 (solid line) and with the two tubes 10 (dotted line).

It is seen that the spectrum without the two tubes 10 has two sound vibration peaks P1 and P2 in the vicinity of 1000 and 2300 Hz, and that these peaks are eliminated as a result of the addition of the two tubes 10.

It is understood that the burner 1 could be equipped with a single tube 10 or, if necessary, with more than two tubes 10, depending on the noise frequencies that are to be absorbed.

Furthermore, the tubes 10 could optionally be connected to the premixing chamber 5 instead of to the Venturi tube 2, they could optionally have a straight shape instead of the curved shape shown in Fig. 1, and they could optionally not be arranged in the plane of symmetry of the burner 1.

However, it is 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, this arrangement making it possible to easily produce the burner 1 by deep drawing followed by assembly of two metal half-shells, one of which is shown diagrammatically in Fig. 1. Each half-shell thus represents half of the venturi tube 2, the side wall of the premixing chamber 5 and each tube 10.

In the case of such an embodiment, the combustion grate 6 is essentially placed on the premixing chamber 5 after the two half-shells have been assembled. However, it is also possible to use a combustion head instead of the grate 6, which is formed by outlet channels for the air/fuel gas mixture, these channels being simply formed by arranging the two half-shells next to one another.

As shown in Fig. 3, the tubes 10 could be replaced by one or more resonance chambers 2G with a different shape. The resonance chamber 20 has the shape of a chamber with the volume V, a so-called "Helmholtz resonator" designed to generate counter noises inside the burner 1 that are in antiphase with the noises with the frequency to be attenuated.

The resonance chamber 20 is connected to the interior of the Venturi tube 2 or the premixing chamber 5 via an inlet 21 and is delimited by a tight wall 22.

For a cavity 20 with a single inlet opening 21, the frequency to be damped is expressed by the following classical formula:

at the:

- f is the frequency to be attenuated in Hertz,

- S is the cross-section of the inlet opening 21,

- c is the speed of propagation of the sound waves ,

- V is the interior of the cavity 20,

- and h is the length of the inlet opening 21, i.e. the distance between the interior of the burner and the volume V at the level of the inlet opening 21: if the volume V is attached to the wall of the venturi tube 2 or the premixing chamber 5, h is simply the thickness of this wall.

Like the tubes 10 already described, the resonance chamber 20 can be connected to the venturi tube 2 or to the premixing chamber 5, and depending on the number of frequencies to be attenuated, one or more resonance chambers can be provided.

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

Furthermore, the resonance chamber 20 is preferably, but not exclusively, arranged symmetrically to the plane of symmetry of the burner 1, so that the entirety of the burner 1, except possibly the combustion grate 6, can be made by deep drawing two metallic half-shells. which are attached to each other along the plane of symmetry, as set out above with reference to Fig. 1.

In the examples shown in Fig. 4 and 5, the counter noises are generated by means of a connecting pipe 30 with any cross-section, which extends between an input-side end 31 or inlet opening connected to the Venturi tube 2 on the one hand and an output-side end 32 connected to the Venturi tube or the premixing chamber 5 on the other hand.

The ends of the pipe 30 can, if necessary, both be connected to the premixing chamber 5.

In the two cases shown in Figs. 4 and 5, the gas mixture passing through the burner 1 without passing through the connecting tube 30 travels a distance L in the venturi tube and the premixing chamber 5 between the ends 31 and 32 of the connecting tube, and the connecting tube has a length /5 or /7, respectively, which is either smaller or larger than the distance L and differs from the distance L by a length λ/2, where n is an odd integer and λ is the wavelength of the noise to be suppressed.

In practice, n is usually equal to 1.

In the example of Fig. 4, the length 15 of the connecting tube 30 is half a wavelength smaller than the length L, and in the example of Fig. 5, the length 17 of the connecting tube 30 is half a wavelength larger than the length L.

Due to its length, the connecting tube 30 generates in all cases at its end 32 a counter noise with the opposite phase to that of the sound vibration of the gas mixture for the specified frequency to be attenuated.

As in the previous examples, the tube 30 is preferably, but not exclusively, arranged in the plane of symmetry of the burner 1, so that the burner, with the possible exception of its combustion grate 6, can be made by deep-drawing two metal half-shells, followed by the mutual attachment of these two half-shells along the plane of symmetry.

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

Finally, in the example shown in Fig. 6, the counter noises are generated by means of an annular resonance chamber 35 provided at the inlet end 3 of the Venturi tube.

This ring-shaped resonance chamber is radially delimited on the outside by a solid ring-shaped outer wall 33, which laterally delimits the Venturi tube 2, and radially inward by a solid ring-shaped wall 34, which successively has a tapering section, a constriction, and then a widening section.

The wall 34 is in sealing circumferential contact with the outer wall 33 on the inlet side (the inlet-side ends of these two walls do not necessarily merge into one another) and extends towards the outlet side inside the outer wall 33 up to an open end 34a, which is connected to the interior of the wall 33.

Thus, the annular resonance chamber 35 extends along the longitudinal axis of the Venturi tube 2 between a closed input-side end 35a and an output-side end 35b, which represents an annular opening forming the entrance to the resonance chamber.

These input and output ends are separated from each other by an axial distance 110 which is substantially equal to a quarter of the wavelength of the noise to be suppressed, or more generally expressed substantially equal to an odd multiple of a quarter of this wavelength (preferably λ/4 or 3 λ/4), the distance between the inlet end 3 of the venturi tube and the inlet opening 35b of the resonance chamber 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 interior of the burner straight ahead from the inlet opening of the anti-noise cavity (resonance chamber or connecting pipe) has a cross-section for the passage of the air/gas mixture that is at least ten times as large as the cross-section of the inlet opening, the cross-section for the passage of the air/gas mixture being the cross-section of the interior of the burner perpendicular to the mean flow direction of the gases.

Claims (11)

1. Gas burner with an interior (2, 5) which takes in air as well as a fuel gas and discharges it to the atmosphere via a combustion head (6), whereby this burner generates noises in its interior during operation and furthermore has an anti-noise cavity (10, 20, 30, 35) for generating counter-noises with an opposite phase to the said noises in its interior (2, 5) at least for a certain frequency to be absorbed, which corresponds to a predetermined wavelength; the anti-noise cavity is delimited by a solid wall and is connected to the interior (2, 5) of the burner via at least one inlet opening (11, 21, 31, 35b); the counter-noises are generated solely by means of the geometry of the anti-noise cavity; the interior has a venturi tube (2) with an inlet end (3) which is provided with a fuel gas injection device (7) and is designed in such a way that it sucks in air under the effect of the injection of fuel gas, whereby the said noises are generated; the inlet opening (11, 21, 31, 35b) of the anti-noise cavity is connected to the venturi tube, characterized in that the inlet opening (11, 21, 31, 35b) is arranged at a distance of between 0.2 kλ and 0.3 kλ from the inlet end (3) of the venturi tube, where k is an odd whole number and λ is the predetermined wavelength. 2. Burner according to claim 1, which has a plane of symmetry and with two deep-drawn half-shells which are attached to each other and each form one half of the Interior (2, 5) of the burner and the anti-noise cavity. 3. Burner according to one of claims 1 and 2, in which the anti-noise cavity is a closed resonance chamber (10, 20, 35) which is connected to the interior (2, 5) of the burner only via the inlet opening (11, 21, 35b). 4. Burner according to claim 3, in which the resonance chamber is a resonance tube (10) which extends over a certain length (/1, /2) between the inlet opening (11) and a closed end (12), the length of this resonance tube being substantially equal to an odd integer multiple of the fourth part of the predetermined wavelength. 5. Burner according to claim 3, in which the venturi tube (2) has a solid annular outer wall (33) towards its input end (3), which surrounds a solid annular inner wall (34) so that it delimits with the outer wall an annular space (35) forming the resonance chamber, this resonance chamber extending along the longitudinal axis of the venturi tube (2) between a closed input end (35a) adjacent to the input end (3) of the venturi tube on the one hand and an output end (35b) on the other hand, which forms an annular opening which represents the inlet opening of the resonance chamber, and the input and output ends are separated from one another by an axial distance (/10) which is substantially equal to an odd multiple of the fourth part of the predetermined wavelength. 6. Burner according to one of claims 1 and 2, wherein the anti-noise cavity is a connecting pipe (30), which extends over a certain length (16, /7) between the first and the second end (31, 32), both of which are connected to the interior (2, 5) of the burner, the first end (31) of the connecting pipe forming said inlet opening, the second end (32) being arranged downstream of the first end (31), the air and the fuel gas which pass into the burner without passing through the connecting pipe (30) passing through a predetermined length (L) between the two ends of the connecting pipe, and the length of the connecting pipe differs from the predetermined length (L) by a length λ/2, where n is an odd integer. 7. Burner according to claim 6, in which the length (16, 17) of the connecting pipe (30) is greater than the predetermined length (L) traversed by the air and the fuel gas, which enter the burner without passing through the connecting pipe, between the two ends (31, 32) of the connecting pipe. 8. Burner according to claim 6, in which the venturi tube (2) opens into a premixing chamber (5) arranged on the inlet side of the combustion head (6), the premixing chamber (5) extending in the longitudinal direction between two ends (5b, 5c) and communicating with the venturi tube (2) at a single (5b) of its ends, the venturi tube being arranged along the premixing chamber, and the length (/6) of the connecting tube (30) being less than the predetermined length (L) traversed by the air and the fuel gas, which pass into the burner without passing through the connecting tube, between the two ends (31, 32) of the connecting tube. 9. Burner according to one of claims 6 to 8, wherein the second end (32) of the connecting pipe connected to the Venturi tube (2) is arranged at a distance (19) from the inlet end (3) of the Venturi tube which is between 0.2 q λ and 0.3 q λ, where q is an odd integer which is greater than k. 10. Burner according to any preceding claim, wherein k has the value 1 or 3. 11. Burner according to any preceding claim, in which the interior of the burner straight ahead from the inlet opening (11, 21, 31, 35b) of the anti-noise cavity has a cross-section for the passage of the air/gas mixture which is at least ten times as large as the cross-section of the inlet opening.