JPH0743115B2 - Combustion type combustion device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a forced air combustion device, and more particularly to a forced air combustion device having a combustion plate gas burner provided with a large number of small holes.

[Prior Art] In a water heater or the like, a combustion unit including a burner that burns an air-fuel mixture premixed with fuel gas and combustion air in a combustion chamber under high load, and the combustion air is supplied to the combustion unit. A forced air combustor with a supply containing a fan is used as the heating means.

Generally, in a combustion apparatus, as a condition under which resonance vibrations associated with combustion grow, as disclosed in Japanese Patent Laid-Open No. 58-35308, the maximum amplitude of pressure vibrations in a combustion chamber, that is, so-called pressure vibrations. It is a necessary condition that the heat generation position for combustion (the burner hole position of the burner, that is, the vibration generation position due to combustion flame propagation) is located on the belly of
Further, it is a sufficient condition that the heat generation fluctuation (vibration due to combustion flame propagation) is synchronized with the pressure fluctuation in the combustion chamber.

That is, in the combustor, some kind of pressure vibration occurs due to the introduction of combustion air into the combustor and the discharge of combustion exhaust gas. In response to such pressure vibration, vibration due to flame propagation amplifies the pressure vibration. In such a state, pressure vibration increases, and resonance vibration is likely to occur.

The above requirement refers to the state in which the force acting on the pressure vibration most easily increases its amplitude, and as is clear from this, the heat generation position (generation of vibration due to combustion flame propagation) When the position) deviates from the antinode (local impedance maximum value) of the pressure oscillation and becomes further away, the effect on the pressure fluctuation decreases, and when the heat generation position is located at the pressure oscillation node (local impedance minimum value). The heat generation position does not satisfy the above requirement.

The latter sufficient condition indicates that the combustion vibration increases the amplitude of the pressure fluctuation when the vibration frequency of the heat generation vibration and the vibration frequency of the pressure fluctuation have the same or an integral multiple relationship.

Therefore, in order to prevent the resonance vibration from growing in the combustor, the combustor is provided with a structure such that the heat generation position, that is, the generation position of vibration due to flame propagation of combustion is located at the node of pressure vibration, or It will be understood that the frequency of heat generation vibration and the frequency of pressure fluctuation may not be the same or have an integral multiple relationship. The above-mentioned JP-A-58
The invention of -35308 gazette provides a burner having a plurality of fuel spray pipes so as to perform combustion with an oscillatory heating rate change different from the acoustic vibration mode of the combustion furnace,
The latter condition is not satisfied to prevent resonance vibration.

[Problems to be Solved by the Invention]

However, the frequency of the heat generation vibration is basically determined by the combustibility, specifically, the type of fuel gas, the air-fuel ratio, the shape of the gas burner, etc. In a large-scale combustion device such as this, the burner shape and other degrees of freedom are high, so it is easy to change the burner shape, etc. However, it is difficult to change the burner because there is a condition such that the amount of heat generated by the burner is determined with respect to the minimum required heating amount. For this reason,
It is difficult to change the frequency of heat generation vibration.

For this reason, in the forced-blowing combustion device that performs high-load combustion,
Vibration combustion (resonance sound) is likely to occur.

It is an object of the present invention to provide a forced air blowing type combustion device in which oscillating combustion is suppressed by setting the natural frequency of the supply unit and the natural frequency of the combustion unit to be substantially equal.

[Means for Solving the Problems] The present invention relates to a combustion section including a combustion chamber having an all-primary air burner for performing high-load combustion and an exhaust stack for exhausting combustion gas in the combustion chamber; A combustion device comprising a fan case equipped with a blower for forcibly supplying combustion air to a combustion section and a supply section composed of a mixing chamber of the all primary air burner, and a natural vibration occurring in the combustion section. The technical means is provided with means for making the number and the natural frequency generated in the supply section substantially equal.

Here, as means for making the natural frequency of the supply part and the natural frequency of the combustion part substantially equal, a bell mouth part is formed at the bell mouth-shaped inlet of the fan case so as to form an intake passage in the fan case. It is preferable to provide an extended cylindrical portion.

Further, a shield plate may be provided upstream of the suction port.

Alternatively, a shield plate provided upstream of the bellmouth-shaped suction port of the fan case may be used as means for making the natural frequency of the supply section and the natural frequency of the combustion section substantially equal.

[Operation and Effect of the Invention] As described above, the condition under which the resonance vibration associated with combustion grows is that the amplitude of the pressure vibration in the combustion chamber is at the maximum, that is, the antinode of the pressure vibration, at the heat generation position (burner) where combustion is performed. The position of the flame hole position, that is, the position where vibration is generated due to combustion flame propagation) is a necessary condition.
It is a sufficient condition that heat generation fluctuation (vibration due to combustion flame propagation) is synchronized with pressure fluctuation in the combustion chamber.

For this reason, in the present invention, in order to prevent combustion oscillation, it is necessary not to satisfy the former requirement,
In other words, we decided to use a method in which the heat generation position is located at the node of pressure oscillation.

By the way, in the combustor, the supply section and the combustion section are communicated with each other through a burner, and when the combustor has a natural frequency f ₀ , the position of the burner that generates heat generation vibration is It is not possible to specify the position where the pressure vibration of the natural frequency f ₀ of the entire combustor is located.

However, when the natural frequencies f ₁ and f ₂ are present in the supply section and the combustion section of the combustor, for example, the supply section and the combustion section are in the combustion chamber A as shown in FIG. When the burner B is arranged and the combustion air is supplied from the supply part C, as shown in FIG.
It is represented by a mass spring model resulting in a three-body problem with two springs D and E and three masses a, b, and c. At this time, the mass b at the center corresponds to the burner B. In this case, the natural frequencies f ₁ and f ₂ of each single unit except the burner B can be determined by the following equation according to Helmholtz's formula.

a ₁ : Sound velocity in the passage of the supply unit ▲ S ^* ₁ ▼: Equivalent cross-sectional area of the passage of the supply unit (dominated by the inlet of the scroll casing) ▲ l ^* ₁ ▼: Equivalent length of the passage of the supply unit (scroll casing Vented by the suction port of) ▲ V ^* ₁ ▼: Equivalent volume of the supply part (excluding passage) a ₂ : Sound velocity of exhaust pipe passage ▲ S ^* ₂ ▼: Equivalent cross-sectional area of passage such as exhaust pipe ▲ l ^* ₂ ▼: Equivalent length of exhaust pipe ▲ V ^* ₂ ▼: Equivalent volume of combustion chamber However, in general In general, the combustion device does not have a simple shape as shown in FIG. 7. For example, as shown in FIG. 9, a blower case F in which a blower for supplying combustion air is housed and a mixing chamber are stored. A supply part C is formed from G and in this case, as shown in FIG. 10, the combustion device has four springs H, I and J and four masses a, b, c and d. It may be an acoustic system represented by a mass-spring model that results in a problem.

Since the end of the combustor on the side of the supply unit and the end on the side of the combustion unit are open to the atmosphere, the natural frequency of the entire combustor
f ₀ is present, in the case where the natural frequency f ₁ of the supply and the natural frequency f ₂ of the combustion section are different, antinodes of vibration of the natural frequency f ₀ of the entire combustor to open tube resonance, It is not located in the burner, which is the communication section between the supply section and the combustion section, but is located on the side of the lower natural frequency of the natural frequency f ₁ of the supply section and the natural frequency f ₂ of the combustion section.

Therefore, at the time of combustion, for pressure fluctuations in the combustor,
Since the heat generation fluctuation of the burner (vibration due to combustion flame propagation) acts, oscillating combustion is likely to occur.

However, the natural frequency of the natural frequency f ₁ and the combustion section of the supply portion f ₂
Exists, the natural frequency f ₁ of the supply part and the natural frequency of the combustion part
If f ₂ is equal, the natural frequency f ₀ of the entire combustor is
It matches the natural frequency f ₁ of the supply part or the natural frequency f _{2 of the} combustion part.

Therefore, in the communicating portion between the supply portion and the combustion portion, there is a node of pressure oscillation that does not cause a variation peculiar to the eigenmode of the natural frequency f ₀ of the entire combustor.

The mechanism of oscillatory combustion is as follows: the natural frequency of the combustion unit consisting of the combustion chamber and the exhaust stack (the minimum natural frequency when there are multiple) and the natural frequency of the supply unit consisting of the mixing chamber and the fan case (multiple Minimum natural frequency in some cases)
Oscillating combustion occurs when the time conditions affected by the combustion process are satisfied and the two shift without matching.

Here, the time condition that the combustion process affects is basically determined by the combustibility (type of fuel gas, air-fuel ratio, shape of gas burner, etc.), so it is difficult to change this as a measure for oscillatory combustion. Can not. In the present invention, in order to eliminate the oscillating combustion, the natural frequency f ₁ of the feed unit itself, by matching the natural frequency f ₂ of the combustion section alone, so as not to establish the acoustic conditions of the oscillating combustion.

This is because even in a complicated system as shown in FIG. 9, if the minimum natural frequency f ₁ of the single feed unit and the minimum natural frequency f ₂ of the single combustion unit match, the speed fluctuation Since the node b of B is in the burner B, it is possible to create an acoustic condition in which vibration combustion does not occur in the natural vibration mode of the coupled system.
This can be theoretically proved, and in general, the natural frequencies f ₁ and f ₂ of the supply section and the combustion section are obtained by measurement with an FFT analyzer or the like.

FIG. 11 shows an example of the speed fluctuation measurement at the burner B and the speed fluctuation measurement at the inlet F of the supply section C in the combustion apparatus shown in FIG.

As is clear here, at the inlet F of the supply section C, there is speed fluctuation, but at the burner B, there is almost no speed fluctuation. From this, it is understood that the burner B is located at the node of the natural frequency f ₀ of the entire combustion device, and the combustion vibration of the burner B does not act on the pressure vibration of the combustion device.

By the way, regarding the natural frequency f ₂ of the combustion part, the exhaust gas temperature in the exhaust passage part changes from the time of ignition to the steady combustion, so the sound velocity also changes, and therefore the natural frequency f ₂ is shown in FIG. In the graph of acoustic impedance of, the frequency shifts to the higher frequency side. On the other hand, since the fluid temperature of the supply part does not change much, its natural frequency f ₁ hardly changes.

That is, oscillating combustion occurs when the natural frequencies f ₁ and f _{2 in} the graph of FIG. 5 deviate and the values do not match. This can explain the phenomenon in which oscillatory combustion occurs or stops after a certain period of time.

Therefore, in order to eliminate oscillatory combustion, a relationship of f ₁ ≈ f ₂ (when each unit has one natural frequency) or f ₁ min ≈ f ₂ min (when each unit has multiple natural frequencies) is established. It will be good.

Where f ₁ min is the minimum natural frequency of the supply unit alone, and f ₁ min is
₂ min is the minimum natural frequency of the combustion unit itself during combustion.

However, the meaning of the supply unit alone and the combustion unit alone here are the respective elements separated in the sealed state of the burner surface.

That is, the equivalent length of the exhaust stack ▲ l ^※ ₂ ▼, the equivalent volume of the combustion chamber ▲ V ^※ ₂ ▼ is reduced, and the equivalent sectional area of the exhaust passage ▲ S
^※ ₂ ▼ to greatly to the case where increasing the natural frequency f _2, in order to match the natural frequency f ₁ of the supply unit to the natural frequency f ₂ of the combustion section, for example, corresponding cross-sectional area of the fan inlet ▲ S ^*
₁ ▼ is increased to a bellmouth-like suction port equivalent length ▲ l ^*
₁ ▼, the equivalent volume of the supply part ▲ V ^* ₁ ▼ can be considered as a way to reduce it.

With the above-described principle configuration, the forced air blowing type combustion device of the present invention has the following effects.

Since the forced air blowing type combustion apparatus of the present invention is provided with means for making the natural frequency of the supply section and the natural frequency of the combustion section substantially equal to each other, it is possible to reliably suppress oscillatory combustion.

At this time, in order to make the natural frequencies of the supply section and the combustion section substantially equal, the volume of the mixing chamber, the passage length or cross-sectional area of the fan case corresponds to the volume of the combustion case, the passage length or cross-sectional area of the exhaust pipe. A large amount of combustion can be accommodated by providing an intake passage with a cylindrical portion to lengthen the passage length of the supply portion or providing a shielding plate upstream of the intake port to reduce the cross-sectional area of the supply portion. Therefore, the natural frequencies can be easily made substantially equal to each other in correspondence with the one in which the volume of the combustion chamber is increased and the one in which the exhaust passage is elongated to extend the exhaust gas.

Therefore, it is possible to easily suppress oscillatory combustion without significantly increasing the passage length, volume, etc. of the supply unit.
It can be a small combustion device.

[Embodiment] An embodiment of the forced air blowing type combustion apparatus of the present invention will be described with reference to the drawings.

FIG. 1 shows an instantaneous gas water heater 1 to which a first embodiment of a forced air blowing type combustion device of the present invention is applied, and FIGS. 2 and 3 show a centrifugal air blower 40 thereof.

The instantaneous gas water heater 1 includes a combustion section 2, a heat exchange section 3, a supply section 4 for supplying combustion air to the combustion section 2, and a gas supply path 8.
And an electronic control unit 9.

The combustion section 2 includes a combustion case 20 and a combustion plate type gas burner 22 which is attached to the combustion case 20 via a fixing member 21 and has a large number of ejection holes in a ceramic plate body.
23, an exhaust pan 25 attached to the upper portion of the combustion chamber 23 and having an exhaust port 24 for exhausting combustion gas burned by the gas burner 22, and an exhaust pipe (not shown) connected to the exhaust pan 25.
Consists of.

As a means to make the natural frequency f ₂ of the combustion section 2 substantially equal to the natural frequency f ₁ of the supply section 4 (for example, 200 Hz), the combustion section 2 is provided with a sound absorbing material 25a in the exhaust pan 25 or an exhaust stack. Equivalent sectional area of the passage such as the exhaust stack (▲ S ^*
₂ ▼), the equivalent length of the exhaust stack (▲ l ^* ₂ ▼), and the equivalent volume of the combustion chamber 23 (▲ V ^* ₂ ▼) are changed according to the equation 2, and the natural frequency f _{2 is set} to 200 Hz during combustion. Was set to be.

The heat exchange section 3 includes a plate fin group 31 for increasing the heat exchange rate.
And a water supply pipe 32 and a hot water supply pipe 33. The water, which is arranged between the gas burner 22 and the exhaust port 24 and is sent from the upstream of the water supply pipe 32, is heat-exchanged with the exhaust gas in the combustion chamber 23 to form hot water. It flows out from the hot water supply pipe 33.

The supply unit 4 includes a scroll casing 5, a mixing chamber 50,
Outer peripheral edge of a flat plate-shaped rotating plate 42 having a boss portion 41 at the center
The centrifugal blower 40 is provided with a fan 45, which is arranged in 43 and whose inner peripheral edge 44 is curved so as to have a concave shape in the rotation direction orthogonal to the rotary plate 42, and a drive motor 46 for the fan 45.
A rotary shaft 47 of a drive motor 46 is fastened to the boss portion 41 of the rotary plate 42. The centrifugal blower 40 is provided with a space 48 surrounded by the inner peripheral edge 44 of the fan 45.

The scroll casing 5 has a spiral shape and has three screw holes 52 formed in the side surface 51 and an inlet 27 of the combustion case 20.
To the side surface 51, and the tubular body 6 that is fastened to the side surface 51,
It comprises a shield plate 7 that is fastened to the tubular body 6.

The tubular body 6 forms a bell mouth-shaped suction port 61 that is open to the outside, and the tip portion 62 has an air volume of the centrifugal blower 40,
A cylindrical part 63 that fits into the fan 45 by a predetermined size (▲ l ^* ₁ ▼) considering the opening area (▲ S ^* ₁ ▼) of the suction port.
And a curved portion 64 bent outward, and an annular portion 65 whose outer periphery extends from the curved portion 64. Cylindrical part 63
Are provided parallel to the inner peripheral edge 44 of the fan 45 and the rotation shaft 47 of the drive motor 46, and are provided so as to be orthogonal to the rotation plate 42. The inside of the cylindrical portion 63 serves as an intake air passage 66. The annular portion 65 is a screw hole formed so as to overlap with the screw hole 52 of the scroll casing 5.
67, and screw holes 67a, 67b, 67c formed on the same circumference,
A first convex portion 68 having a threaded hole 67b, and the first convex portion 68
2nd with a slightly higher height and a screw hole 67c
And the convex portion 69 of.

As shown in FIG. 4, the shielding plate 7 is a bell mouth-shaped suction port.
A conical part 72 having a point 71 at the center of 61, and the conical part
It is composed of a disc portion 74 whose outer circumference extends from the other end 73 of 72 and three mounting leg portions 75 hanging from the disc portion 74. The mounting leg portion 75 is formed with screw holes 76 that selectively overlap the screw holes 67a, 67b, 67c of the tubular portion 6. The cylindrical body 6 and the shielding plate 7 are selected for various screw holes depending on the mounting condition at the site, and the opening degree of the bellmouth-shaped suction port 61 is changed, and the combustion chamber flows into the bellmouth-shaped suction port 61. The air flow rate and the natural frequency f ₁ are changed.

On the contrary, the minimum natural frequency f ₂ (for example, 20
0 Hz), as a means for making the minimum natural frequency f ₁ of the supply unit 4 substantially equal, in the supply unit 4, an intake air passage 66 is formed in the fan 45 at the bellmouth-shaped intake port 61 of the scroll casing 5. To extend the cylindrical portion 63, change the mounting position of the shield plate 7,
And an equivalent volume of the mixing chamber 50 (▲ V ^* ₁ ▼), a predetermined dimension of the cylindrical portion 63 of the tubular pair 6 (▲ l ^* ₁ ▼), and a bellmouth-shaped suction set at the attachment position of the shielding plate 7. Depending on the opening area of the mouth 61 (▲ S ^* ₁ ▼), the minimum natural frequency of the supply part 4
The f ₁ is changed according to the equation ₁ and set to 200 Hz so that the natural frequency f ₂ becomes substantially the same value.

The gas supply unit 8 is integrally molded with the scroll casing 5, and is a gas ejection nozzle 81 for ejecting fuel gas, and a gas supply pipe for supplying fuel gas to the gas ejection nozzle 81.
It consists of 82 and a gas control unit 83. The gas control unit 83 is provided between the gas ejection nozzle 81 and the gas supply pipe 82, and is an electromagnetic on-off valve 84 that opens and closes by energization or de-energization.
And a governor valve (not shown) that is provided on the downstream side of the opening / closing valve 84 to adjust the gas flow rate, and an electromagnetic type that is provided on the downstream side of the governor valve and whose opening ratio is variable according to the energization amount. It is provided with a proportional control valve 85. An orifice 86 for adjusting the supply pressure and the flow rate of the fuel gas is attached to the other end of the gas ejection nozzle 81.

The electronic control unit 9 is turned on when the instantaneous gas water heater 1 is used.
A combustion switch of the gas burner 22 at the time of ignition in response to an input of a start switch (not shown) for operating, a temperature control volume (not shown) for setting the temperature of the hot water flowing out from the hot water supply pipe 33 operated by the user. Control of energization and de-energization of the spark electrode 92 for blowing sparks, the motor of the centrifugal blower 40, the gas control unit 83, and the like. Reference numeral 91 indicates a thermocouple for detecting the oxygen supply state of the flame of the gas burner 22.

The operation of the instant gas water heater 1 of this embodiment will be described with reference to the drawings.

In the instant gas water heater 1, when the start switch is turned on, the fan 45 of the centrifugal blower 40 rotates and the scroll casing 5
Combustion air is supplied to the gas burner 22 through the bellmouth-shaped inlet 61 of the tubular body 6.

Then, the electronic control unit 9 outputs to the opening / closing valve 84 and the proportional control valve 85 of the gas control unit 83 to open the opening / closing valve 84 and the proportional control valve 85.

When the drive motor 46 starts, the fan 45 starts to rotate at high speed, sucks the combustion air existing in the space 48 surrounded by the inner peripheral edge 44 of the fan 45 in the centrifugal direction, and the centrifugal force causes the fan 45 to rotate.
And is discharged to the mixing chamber 26. Further, the combustion air existing outside the scroll casing 5 is sucked into the space 48 through the intake flow passage 66 while the flow rate of the combustion air is reduced by the curved portion 64 of the tubular body 6. At the same time, a predetermined flow rate fuel gas is supplied from the gas supply passage 8 to the mixing chamber 26.

Here, as a noise countermeasure, in order to reduce combustion noise, the exhaust pan 25 is provided with a sound absorbing material 25a or the exhaust pan 25 is bent to change the shape of the exhaust system. Since the shape is changed, pressure loss may occur, causing oscillating combustion.

However, in the present embodiment, when the combustion air passes through the intake air passage 66, the tip portion 62 takes into consideration the air volume of the centrifugal blower 40 and the opening area (▲ S ^* ₁ ▼) of the bellmouth-shaped inlet 61. Cylindrical part that fits in the fan 45 by the specified size (▲ l ^* ₁ ▼)
Pass 63. In addition, a shielding plate 7 is provided above the bellmouth-shaped suction port 61 at a position where the opening area (▲ S ^* ₁ ▼) of the suction port is changed. That for the smallest natural frequency f ₁ of the supply unit 4 so as to substantially coincide with the natural frequency f ₂ of the combustion section 2 (e.g. 200 Hz), oscillating combustion it does not occur at the time of combustion.

That is, in the present embodiment, the natural frequency f ₂ of the combustion section 2 composed of the combustion chamber 23 and the exhaust stack and the natural frequency f ₁ of the supply section 4 composed of the mixing chamber 50, the scroll casing 5 and the like match. Oscillating combustion does not occur even when the time conditions affected by the combustion process are satisfied. Further, in this embodiment, stable and good combustion can be always performed from the time of ignition to the time of steady combustion and further to the time of extinction.

FIG. 6 shows a second embodiment of the forced air blowing type combustion apparatus of the present invention.

This embodiment is a plate 12 in which a large number of small holes (φ2.2 mm × 60 pieces) 127 are formed in the exhaust port 24 of the exhaust pan 25 of the first embodiment.
Exhaust passage 128 formed by exhaust pan 25 with 6 attached
Since the equivalent length of ▲ l ^* ₂ ▼ was changed according to the formula 2,
The occurrence of oscillatory combustion can be prevented as compared with the first embodiment.

Exhaust port of this embodiment in which a large number of small holes 127 of the plate 126 are formed
Since the opening area of 24 is smaller than the opening area of the exhaust port of the first embodiment in which the plate 126 is not provided, it is possible to reduce the passage amount of combustion noise, and thus combustion is performed while preventing occurrence of oscillatory combustion. It is also possible to reduce noise. According to this embodiment, the bellmouth-shaped suction port 61 of the supply unit 4
It can be confirmed that the forced ventilation type combustion device in which the number of holes is one and the number of holes of the exhaust port 24 is large is that the effect of reducing oscillatory combustion is remarkably good.

In the present embodiment, the shape of the hole of the plate 126 is a small hole,
It may be oval. The size of one hole is φ2.0 mm to 2.5 mm in the case of a circular hole, and 0.8 mm to one side in the case of a rectangular hole.
1.4 mm is preferable, but the size of one hole is not limited.

In the present embodiment, the rotating plate of the centrifugal blower has a flat plate shape, but may have a conical shape.

In the present embodiment, the tubular portion extending to the bellmouth-shaped suction port of the scroll casing is formed into a cylinder, but the central portion of the tubular portion may be curved.

In this embodiment, the cylindrical portion 63 and the shielding plate 7 are provided at the bellmouth-shaped suction port of the scroll casing.
One that does not use either 63 or the shielding plate 7 may be used.

An intake extension pipe may be provided upstream of the bellmouth-shaped intake port of the centrifugal blower of the present invention.

In addition to this embodiment, the inner peripheral diameter of the discharge port of the scroll casing may be appropriately changed so that the natural frequency of the supply section and the natural frequency of the combustion section match.

The forced ventilation type combustion device of the present invention may be applied to a heating device or other forced ventilation type combustion device.

[Brief description of drawings]

FIG. 1 is a schematic view showing an instantaneous gas water heater to which the first embodiment of the forced air blowing type combustion apparatus of the present invention is applied, and FIG. 2 applies the first embodiment of the forced air blowing type combustion apparatus of the present invention. The moment when the centrifugal blower attached to the gas water heater is applied, FIG. 3 is a side cross-sectional view of FIG. 2, and FIG. 4 is the moment when the first embodiment of the forced air combustion device of the present invention is applied. FIG. 5 is a perspective view of a shield plate attached to the gas water heater, FIG. 5 is a graph showing acoustic impedance of the combustion section and the supply section, and FIG. 6 is a perspective view showing a second embodiment of the forced air combustion apparatus of the present invention. Figures, 7 to 10
The drawings are all for explaining the principle of the present invention. FIGS. 7 and 9 are schematic views of a combustion apparatus, and FIGS. 8 and 10 are FIGS. 7 and 9 respectively showing a mass spring model. It is a principle diagram represented by speed fluctuations. FIG. 11 is a diagram showing measurement results of speed change at the inlet of the supply section and speed change in the burner of the combustion apparatus shown in FIG. In the figure, 1 ... Instantaneous gas water heater, 2 ... Combustion section, 3 ... Heat exchange section, 4 ... Combustion air supply section, 5 ... Scroll casing, 6 ... Cylindrical body, 7 ... Shielding Plate, 8 ... Gas supply unit, 9 ... Electronic control unit, 40 ... Centrifugal blower, 42 ...
Rotating plate, 43 …… outer edge, 44 …… inner edge, 45 …… fan,
46 …… Drive motor, 50 …… Mixing chamber, 61 …… Bellmouth inlet.

Claims (5)

[Claims] 1. A combustion section comprising a combustion chamber having an all-primary air burner for performing high-load combustion and an exhaust stack for exhausting combustion gas in the combustion chamber, and compulsion combustion air to the combustion section. A combustion device comprising a fan case provided with a blower for supplying electricity and a supply section composed of a mixing chamber of the all primary air burner, the natural frequency occurring in the combustion section and the natural frequency occurring in the supply section. A forced air blowing type combustion device comprising means for making the frequencies substantially equal to each other. 2. A means for making a natural frequency generated in the combustion section and a natural frequency generated in the supply section substantially equal to each other is a minimum natural vibration among natural frequencies generated in the combustion section and the supply section. The forced-blowing combustion device according to claim 1, wherein the numbers are made substantially equal. 3. A means for making the natural frequency of the supply section and the natural frequency of the combustion section substantially equal to each other is such that a bell mouth-shaped inlet of the fan case forms an intake passage in the fan case. The forced air combustion device according to claim 1, wherein the bell mouth portion is a cylindrical portion that is extended. 4. The forced air blowing type combustion device according to claim 3, wherein a shield plate is provided upstream of the suction port. 5. The means for making the natural frequency of the supply section and the natural frequency of the combustion section substantially equal to each other is a shield plate provided upstream of the bell mouth-shaped suction port of the fan case. The forced air blowing type combustion device according to claim 1.