JP2000055318A - Combustor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustor, simple in constitution, inexpensive in cost and reduced in combustion vibration or combustion noise generated upon combustion. SOLUTION: A combustor is provided with a combustion chamber 1, a fuel supplying pipeline 12 for supplying fuel into the combustion chamber 1 and an oxidizing agent supplying pipeline for supplying oxidizing agent into the combustion chamber 1 to mix the fuel and oxidizing agent, supplied through respective supplying pipelines, and burn the mixture. In such a combustor, a sound resonance mode generating means 23, fluctuated with a frequency same as the pressure fluctuation in the combustion chamber 1 and making a flow speed fluctuation at the outlet port of combustion chamber side of the fuel supplying pipeline 12 zero, is provided in the fuel supplying pipeline 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustor, and more particularly, to a structure of a fuel supply system suitable for use in a combustor having high combustion vibration and combustion noise.

[0002]

2. Description of the Related Art A combustor uses diffusion combustion in which a fuel and an oxidant are mixed and burned in a combustion chamber, and premixed combustion in which a fuel and an oxidant are mixed in advance and then burned in a combustion chamber. In particular, in low NOx combustion, the amount of NOx generation is often suppressed by lowering the temperature of the premixed flame using a lean fuel, but the flame is likely to be unstable, so that combustion oscillation is likely to occur.

[0003] Combustion vibration is a phenomenon in which the pressure fluctuation inside the combustor increases with combustion, and the vibration may deform or break the structural material of the combustor, thereby impairing the soundness. The magnitude of the pressure fluctuation inside the combustor changes depending on the phase relationship between the heat generation amount fluctuation in the flame part and the pressure fluctuation inside the combustor.According to Rayleigh's generally known criteria, the heat generation amount in the flame part Vibration occurs when the time average of the product of the fluctuation and the pressure fluctuation becomes positive. That is, the vibration increases when the heat generation amount fluctuation and the pressure fluctuation change in the same phase. Therefore, if the phase relationship can be changed by controlling the feedback loop of the calorific value fluctuation and pressure fluctuation of the flame part,
Combustion vibration can be suppressed.

[0004] One of the factors constituting the feedback loop is considered to be a fluctuation in the flow rate of fuel or air. When the flow rate of fuel or air fluctuates in accordance with the pressure fluctuation in the combustor, the calorific value of the flame is changed and positive feedback is applied to the pressure fluctuation, and the vibration is amplified. Therefore,
As a technique for suppressing combustion oscillation, there has been known a method of detecting a pressure fluctuation inside a combustor and fluctuating a fuel flow rate to shift an in-phase relationship between a heat generation amount fluctuation and a pressure fluctuation inside the combustor. . This method is called active control of combustion oscillation and has been proved to be an effective means for suppressing combustion oscillation.

[0005]

However, the combustion vibration generated inside the combustor often oscillates at a frequency of several hundred Hz or more, and as in a gas turbine plant for power generation, there are a plurality of combustion cans of about 10 cans per turbine shaft. Vessels are installed and 10
When operating in a high-pressure field at or above the atmospheric pressure, a fuel flow control valve and a control mechanism that are driven at several hundred Hz or more per canister are required. For this reason, there was a problem in terms of cost and reliability for practical use.

SUMMARY OF THE INVENTION The present invention has been made in view of the foregoing, and it is an object of the present invention to provide a combustion apparatus of this kind which has no radical moving parts, has a simple structure, is inexpensive, and has little combustion vibration and combustion noise generated during combustion. To provide equipment.

[0007]

That is, the present invention comprises a combustion chamber, a fuel supply pipe for supplying fuel to the combustion chamber, and an oxidant supply pipe for supplying oxidant to the combustion chamber. A fuel and an oxidant supplied from a supply pipe are mixed and burned, wherein the fuel supply pipe fluctuates at the same frequency as the pressure fluctuation in the combustion chamber, and a combustion chamber side outlet of the fuel supply pipe. Thus, an acoustic resonance mode generating means for reducing the flow velocity fluctuation at zero is provided to achieve the intended purpose.

Further, the present invention comprises a combustion chamber, a fuel supply pipe for supplying fuel to the combustion chamber, and an oxidant supply pipe for supplying an oxidant to the combustion chamber. In the combustor for mixing and burning the fuel and the oxidant, an acoustic mode that resonates at a pressure fluctuation frequency generated in the combustion chamber is formed in the fuel supply pipe, and the acoustic mode is formed between the fuel supply pipe and the fuel supply pipe. An acoustic resonance mode generating means having a maximum value of the fluctuating pressure at a connection portion of the combustion chamber is provided.

In addition, the fuel supply system includes a combustion chamber, a fuel supply pipe for supplying fuel to the combustion chamber, and an oxidant supply pipe for supplying an oxidant to the combustion chamber. In a combustor for mixing and burning an oxidant, one end of the fuel supply pipe is communicated with the inside of the fuel supply pipe, the other end is closed, and the fuel flow rate at the fuel supply pipe outlet is reduced. A branch pipe having a length that generates an acoustic resonance mode in which the fluctuation becomes zero is provided.

In this case, the branch pipe is provided with a temperature control mechanism for controlling the temperature of the branch pipe, and the combustor is provided with a fluctuation measuring instrument for measuring a pressure fluctuation in the combustor. It is formed so that the set value of the temperature control mechanism is adjusted by the fluctuation signal of the vessel.
Further, the branch pipe is formed so that at least a part thereof has a bellows structure, or a piston is provided therein, so that the length of the branch pipe can be changed.

The present invention also includes a combustion chamber, a fuel supply pipe for supplying fuel to the combustion chamber, and an oxidant supply pipe for supplying an oxidant to the combustion chamber. In the combustor for mixing and burning the fuel and the oxidant, a bypass pipe connecting the upstream and the downstream is provided in the middle of the fuel supply pipe, and the fuel flow rate fluctuation in the bypass pipe and at the outlet of the fuel supply pipe. A closing mechanism for closing the flow rate of fuel in the bypass pipe is provided at a position where an acoustic resonance mode in which is zero is generated.

In this case, the branch pipe is provided with a temperature control mechanism for controlling the temperature of the branch pipe, and the combustor is provided with a fluctuation measuring instrument for measuring a pressure fluctuation in the combustor. It is formed so that the set value of the temperature control mechanism is adjusted by the fluctuation signal of the vessel. Further, the closing mechanism is formed so that its position can be changed.

That is, with the combustor thus formed, the fluctuation in the fuel supply pipe at the same frequency as the pressure fluctuation in the combustor and the fluctuation in the flow velocity at the outlet of the fuel supply pipe on the combustion chamber side are zero. Since the acoustic resonance mode generating means is provided, an acoustic resonance mode is formed inside the pipe to the fuel outlet during operation, and particularly at the fuel outlet,
The pressure fluctuation gradient becomes zero and the flow velocity fluctuation becomes zero. As a result, combustion oscillations caused by fluctuations in fuel flow rate are suppressed, and the reliability of equipment can be improved by suppressing combustion instability such as loss of flame or flashback, and suppressing wear of structural materials. .

In order to generate such an acoustic mode in the fuel supply pipe, it is necessary to devise a fuel pipe system. According to the present invention, a fuel pipe is provided with a branch pipe or a bypass pipe having a closing mechanism, and by changing the length, the cross-sectional area, or the temperature, an acoustic resonance mode in which the flow velocity fluctuation at the fuel pipe outlet becomes zero is generated. It is to let.

Since the flow velocity fluctuation becomes zero at the closed part of the branch pipe or the bypass pipe, if the flow velocity fluctuation is made zero at the fuel pipe outlet, when the cross-sectional area and the temperature in the pipe are constant, the acoustic resonance frequency f becomes become that way.

[0016]

F = na / (2L) (n = 1, 2, 3,...) (1) where L is a pipe length from a closed portion of a branch pipe or a bypass pipe to a fuel pipe outlet, a Is the speed of sound depending on the temperature,
n is a natural number. Therefore, by adjusting the pipe length L and the temperature in the pipe, the resonance frequency in the pipe can be changed to match the frequency of the combustion vibration.
FIG. 2 shows an example of the mode of pressure fluctuation and flow velocity fluctuation when n = 1, where the flow velocity fluctuation is zero at the fuel pipe outlet.

More generally, when the pipe cross-sectional area is S, the pipe length is L, the sound velocity is a, the subscript of the fuel pipe is 1, and the subscript of the branch pipe or the bypass pipe is 2, the resonance frequency is as follows. It can be calculated by the formula.

[0018]

## EQU2 ## sin (2πf (L1 / a1 + L2 / a2) = A × sin (2πf (L1 / a1−L2 / a2)) (2)

[0019]

A = (S2 / S1-a2 / a1) = (S2 / S1 + a2 / a1) (3) Here, the length L1 of the fuel pipe is determined by the fuel from the branch of the branch pipe or the bypass pipe. The length of the pipe to the pipe outlet,
The length L2 of the branch pipe or the bypass pipe is the length from the closed part of the branch pipe or the bypass pipe to the branch part. FIG. 3 shows the relationship between the resonance frequency and the temperature of the branch pipe or the bypass pipe when L1 is 1 m, the temperature of the fuel pipe main pipe is 20 ° C., and the cross-sectional area of the fuel pipe and the cross-sectional area of the branch pipe or the bypass pipe are the same. An example is shown. As shown in FIG. 3, by adjusting the length and temperature of the branch pipe or the bypass pipe, an acoustic resonance mode of an arbitrary frequency can be generated in the pipe.

Further, especially when resonance may occur in a fuel pipe without a branch pipe or a bypass pipe,
(2) The specifications of the branch pipe or the bypass pipe may be determined so as to satisfy the expression (3), and the specifications of the branch pipe or the bypass pipe may be determined so that the pressure fluctuation at the branch portion becomes zero. That is, the following equation should be satisfied.

[0021]

F = (2n−1) a2 / (4L2) (n = 1, 2, 3,...) (4) Therefore, for the combustion oscillation frequency of the combustor, (2)
(3) S2, L2, temperature, and mode order n may be determined so as to satisfy Expression (4). At this time, in the short wavelength mode, the position where the flow velocity fluctuation is zero changes largely due to the change in temperature or frequency. Therefore, it is better to set the mode order n as small as possible. Also, by changing the cross-sectional area of the branch pipe or the bypass pipe in the axial direction of the branch pipe or the bypass pipe, the specifications of the branch pipe or the bypass pipe can be determined more freely.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 is a diagram illustrating an example in which the combustor is applied to a gas turbine combustor. In this gas turbine combustor, an outer cylinder 2 is provided outside a cylindrical main chamber (combustion chamber) 1, and air 3 flows through a flow path 4 between the main chamber 1 and the outer cylinder 2.

The air 3 passing through the flow path 4 between the main chamber 1 and the outer cylinder 2 is supplied to an air passage 5 for a diffusion burner and a sub-chamber 6 for a premix burner. The air supplied to the diffusion burner air passage 5 is burned in the main chamber 1 together with the fuel from the diffusion fuel nozzle 11. In addition, a part of the air 3 supplied to the sub-chamber 6 for the premix burner is mixed with the fuel 8 from the premix fuel nozzle 7 in the sub-chamber 6 to become a premix gas 9,
It flows out of the sub chamber 6 and burns inside the main chamber 1.

In this embodiment, a branch pipe for resonance (acoustic resonance mode generating means) 23 is connected to a diffusion fuel pipe (fuel supply pipe) 12 connected to a diffusion fuel nozzle 11. A branch portion 13 is provided in the diffusion fuel pipe 12, and a branch pipe 23 is connected thereto. That is, a branch pipe having one end communicating with the inside of the fuel supply pipe and the other end closed is provided in the middle of the fuel supply pipe.

The branch pipe 23 is provided with a heater 17 and a thermometer 18 so as to adjust the fuel temperature inside. Further, a pressure fluctuation measuring device 19 provided in the main chamber 1
And a controller 20 for adjusting the amount of heat generated by the heater 17 based on signals from the thermometer 18.

When combustion oscillation occurs inside the main chamber 1,
The control device 20 measures the combustion oscillation frequency f based on the signal from the pressure fluctuation measuring device 19, and as described above (2) and (3).
The temperature and the mode order n are determined so as to satisfy the expression (4). Here, the mode order n is selected to be the lowest order, and the set temperature is selected so as to minimize the difference from the fuel temperature of the diffusion fuel pipe.

Here, L1, S1, a1, L2, S2, and a2 in the equations (2), (3), and (4) represent the diffusion fuel pipe 1 from the branch 13 to the diffusion fuel outlet 22, respectively.
2, the length, cross-sectional area, sound velocity, and the length, cross-sectional area, and sound velocity of the branch pipe 23 from the branch portion 13 to the closed end of the branch pipe 23.
With the settings of (2), (3) and (4), an acoustic resonance mode is formed inside the pipe from the closed end of the branch pipe 23 to the diffusion fuel outlet 22 through the branch 13, and in particular, the diffusion fuel outlet 22 Then, the pressure fluctuation gradient becomes zero and the flow velocity fluctuation becomes zero.

As a result, combustion oscillations caused by fluctuations in fuel flow rate are suppressed, and combustion instability such as loss of flame or flashback is suppressed, and wear of structural materials is suppressed, thereby improving the reliability of equipment. it can. In particular, the present embodiment
This is effective when the length of the branch pipe 23 may be short.

FIG. 4 is a diagram showing a second embodiment of the present invention. In this embodiment, a bypass pipe 15 is used instead of the branch pipe 23 of the first embodiment. Diffusion fuel pipe 12
Is provided with two branch portions 13 and 14, and a bypass pipe 15 connecting the branch portions 13 and 14 is connected thereto. The bypass pipe 15 is provided with a plurality of valves 16 and 21 so that the valve can be closed at any position.

The bypass pipe 15 is provided with a plurality of heaters 17 and a thermometer 18 so as to adjust the fuel temperature inside. Further, the signals from the pressure fluctuation measurement device 19 and the thermometer 18 provided in the main chamber 1 are used to control the valves 16, 2
Control device 20 for controlling the opening / closing of unit 1 and the amount of heat generated by heater 17
Is provided. Hereinafter, in the present embodiment, the case where the valve 21 is closed will be described, but the same applies to the case where the valve 16 is closed.

When combustion oscillation occurs inside the main chamber 1,
The control device 20 measures the combustion oscillation frequency f based on the signal from the pressure fluctuation measuring device 19, and determines the closing position, the temperature, and the mode order n of the bypass pipe 15 so as to satisfy the equations (2), (3), and (4). decide. Here, as in the first embodiment, the mode order n is selected to be the lowest order, and the set temperature is selected such that the difference from the fuel temperature of the diffusion fuel pipe is minimized.

Here, L in the equations (2), (3) and (4)
1, S1, a1, L2, S2, and a2 are diffusion fuel pipes 12 from the branch portion 13 to the diffusion fuel outlet portion 22, respectively.
, Cross-sectional area, sound speed, length, cross-sectional area, and sound speed of the bypass pipe 15 from the branch portion 13 to the valve 21. (2)
By setting the formulas (3) and (4), an acoustic resonance mode is formed inside the pipe from the valve 21 to the diffusion fuel outlet 22 through the branch 13, and especially, the flow velocity fluctuation becomes zero at the diffusion fuel outlet 22. In addition, the combustion oscillation caused by the fluctuation of the fuel flow rate is suppressed. Thereby, the reliability of the device can be improved by suppressing combustion instability such as loss of flame or flashback, and suppressing wear of structural materials.

This embodiment is effective when the length of the bypass pipe 15 is long. When there is a possibility that the inside of the pipe becomes a gas reservoir, the valves 16 and 21 are opened to purge the gas from the bypass pipe 15. It is. In this embodiment,
Although the case where two valves, two heaters, and two thermometers are installed in the bypass pipe 15 is shown, the same applies to the case where more are installed.

FIG. 5 is a diagram showing a fourth embodiment of the present invention. In the present embodiment, the pipe diameter of the branch pipe 23 of the first embodiment is changed at the position 24. That is, a part of the pipe has a bulging portion. In this case, (2)
(3) Although an equation taking into account the cross-sectional change is required instead of the equation (4), the condition can be obtained by using an acoustic analysis method such as a generally known transfer function method. FIG. 6 shows an example in which the pipe diameter of the branch pipe 23 is changed. By increasing the pipe diameter of the branch pipe 23,
It can be seen that the length of the branch pipe 23 can be reduced. According to the present embodiment, the specifications of the branch pipe 23 can be set more freely, and a more compact piping system can be constructed. In this embodiment, the pipe diameter of the branch pipe is changed, but the same effect can be obtained with the bypass pipe.

FIG. 7 is a diagram showing a fifth embodiment of the present invention. In this embodiment, the branch pipe 15 of the first embodiment is replaced with a bellows 25, and the length of the bellows 25 can be changed by a driving mechanism 26. With this drive mechanism 26,
Fine adjustment of the length of the bellows 25 is possible, (2)
(3) In addition to easier setting of the condition of the expression (4),
It is possible to improve the followability with respect to the change in the combustion oscillation frequency due to the change in the operating condition.

Although this embodiment has movable parts such as expansion and contraction of bellows, it is not necessary to follow the combustion vibration frequency of several hundred Hz, but it is only necessary to be able to follow the change of the combustion vibration frequency due to the average temperature change inside the combustor. Therefore, it is more advantageous in terms of control and equipment reliability than a method in which the fuel flow rate is varied at the combustion oscillation frequency.

FIG. 8 is a diagram showing a sixth embodiment of the present invention. In this embodiment, a piston 26 is provided inside the branch pipe 15 of the first embodiment, and the length of the branch pipe 15 can be changed by changing the position of the piston 26. The length of the branch pipe 15 can be finely adjusted by the piston 26, and the conditions of the equations (2), (3), and (4) can be more easily set, and the operating conditions can be adjusted similarly to the fifth embodiment. The ability to follow the change in the combustion oscillation frequency due to the change can be improved.

Although this embodiment also has a movable part such as a piston, the piston response time may be slower than the method of varying the fuel flow rate at the combustion oscillation frequency, which is advantageous in terms of control and equipment reliability. is there.

FIG. 9 is a diagram showing a seventh embodiment of the present invention. In the present embodiment, the present invention is applied to a premixed fuel pipe 27. The configuration is the same as the first embodiment,
In this embodiment, the fuel fluctuation of the premixed fuel 8 can be suppressed. In addition, the same change as the second to sixth can be made for the premixed fuel 8, and the combustion oscillation mainly caused by the fluctuation of the premixed fuel 8 can be effectively suppressed.

FIG. 10 is a diagram showing an eighth embodiment of the present invention. In this embodiment, the present invention is applied to a gas water heater. The air 3 is sent into the sub-chamber 6 by the fan 30 and mixes with the premixed fuel 8. The premixed gas 9 passes through the flame holding plate 31 and burns in the main chamber 1. Combustion gas 33
Is exhausted after heat exchange in the heat exchanger 32. The premixed fuel 8 flows into the sub-chamber 6 through the branch 13.
A branch pipe 23 is attached to the branch section 13.
A heater 17 and a thermometer 18 are installed in the
The amount of heat generated is adjusted accordingly. The water 34 is supplied to the heat exchanger 32
After the heat exchange, the water is discharged as hot water 35.

Also in such a gas water heater, the length, temperature and cross-sectional area of the branch pipe 23 are adjusted so that the premixed fuel pipe 7 and the inside of the By generating the acoustic resonance mode, it is possible to prevent the occurrence of combustion vibration and the generation of combustion noise due to fluctuations in the flow rate of the premixed fuel.

In the above description, when the branch pipe is provided, it is described that the branch pipe is provided at the bent portion of the fuel supply pipe. However, it is not always necessary to provide the branch pipe at this portion. As shown, it is a matter of course that this branch pipe may be provided in the middle of the fuel supply pipe 12 which is provided linearly.

As described above, in the combustor formed as described above, the fluctuation of the fuel flow rate can be suppressed by a simple method using acoustic resonance, and the combustion vibration generated in the combustor is suppressed. be able to. In particular, combustion vibration can be effectively suppressed by an inexpensive and highly reliable structure with few movable parts. As a result, combustion oscillations caused by fluctuations in the fuel flow rate are suppressed, and the reliability of equipment can be improved by suppressing combustion instability such as loss of flame or flashback, and suppressing wear of structural materials. .

[0044]

As described above, according to the present invention, it is possible to obtain a combustor of this type which has no radical moving parts, has a simple structure, is inexpensive, and has little combustion vibration and combustion noise generated during combustion. Can be.

[Brief description of the drawings]

FIG. 1 is a vertical sectional side view showing one embodiment of a combustor of the present invention.

FIG. 2 is a diagram illustrating an acoustic resonance mode.

FIG. 3 is a diagram showing a relationship between frequency and pipe temperature.

FIG. 4 is a vertical sectional side view showing another embodiment of the combustor of the present invention.

FIG. 5 is a longitudinal sectional side view showing another embodiment of the combustor of the present invention.

FIG. 6 is a diagram showing a relationship between a pipe diameter and a pipe length.

FIG. 7 is a longitudinal sectional side view showing another embodiment of the combustor of the present invention.

FIG. 8 is a vertical sectional side view showing another embodiment of the combustor of the present invention.

FIG. 9 is a vertical sectional side view showing another embodiment of the combustor of the present invention.

FIG. 10 is a longitudinal sectional side view showing another embodiment of the combustor of the present invention.

FIG. 11 is a longitudinal sectional side view showing another embodiment of the combustor of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Main chamber (combustion chamber), 2 ... Outer cylinder, 3 ... Air, 4 ... Air passage, 5 ... Diffusion burner air passage, 6 ... Sub chamber, 7 ... Premix fuel nozzle, 8 ... Premix fuel, 9 ... Premixed air, 10 ...
Diffusion fuel, 11: Diffusion fuel nozzle, 12: Diffusion fuel pipe (fuel supply pipe), 13: Branch, 14: Branch, 15
... bypass pipe, 16 ... valve, 17 ... heater, 18 ... thermometer, 19 ... pressure fluctuation measuring instrument, 20 ... control device, 21 ... shut-off valve, 22 ... diffusion fuel outlet, 23 ... branch pipe (acoustic resonance mode generation Means), 24 ... Position where the pipe diameter changes, 25
... bellows, 26 ... bellows drive mechanism, 27 ... piston, 28 ... piston drive mechanism, 29 ... premixed fuel pipe,
30 ... fan, 31 ... flame holding plate, 32 ... heat exchanger, 33 ...
Burned gas, 34 ... water, 35 ... hot water.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tomoya Murota 7-2-1, Omika-cho, Hitachi City, Ibaraki Pref. Hitachi, Ltd. Power and Electricity Development Division (72) Inventor Yoshitaka Hirata Omika-cho, Hitachi City, Ibaraki Prefecture No. 7-2-1 F-term in the Electric Power & Electric Development Division, Hitachi, Ltd. (Reference) 3K019 AA01 AA02 AA05 AA06 AA08 BA04 BA05 BD02 3K064 AA01 AC07 AC13 AD01 AD04 CA01

Claims (10)

[Claims] 1. A fuel supply system comprising: a combustion chamber; a fuel supply pipe for supplying fuel to the combustion chamber; and an oxidant supply pipe for supplying an oxidant to the combustion chamber. In a combustor that mixes and burns with an oxidant, an acoustic wave that fluctuates in the fuel supply pipe at the same frequency as the pressure fluctuation in the combustion chamber and has zero flow velocity fluctuation at a combustion chamber side outlet of the fuel supply pipe. A combustor comprising resonance mode generating means. 2. A combustion chamber, a fuel supply pipe for supplying fuel to the combustion chamber, and an oxidant supply pipe for supplying an oxidant to the combustion chamber, wherein the fuel supplied from each of the supply pipes In a combustor that mixes and burns with an oxidant, an acoustic mode that resonates at a pressure fluctuation frequency generated in the combustion chamber is formed in the fuel supply pipe, and the acoustic mode is defined by the fuel supply pipe and the combustion chamber. A combustor comprising an acoustic resonance mode generating means having a maximum value of a fluctuating pressure at a connection portion. 3. A fuel supply system comprising: a combustion chamber; a fuel supply pipe for supplying fuel to the combustion chamber; and an oxidant supply pipe for supplying an oxidant to the combustion chamber. In a combustor that mixes with an oxidant and burns, in the middle of the fuel supply pipe, one end communicates with the inside of the fuel supply pipe, and the other end is closed, and the fuel flow rate at the fuel supply pipe outlet is A combustor characterized in that a branch pipe having a length for generating an acoustic resonance mode in which the fluctuation becomes zero is provided. 4. A temperature control mechanism for controlling a temperature of the branch pipe is provided in the branch pipe, and a fluctuation measuring instrument for measuring a pressure fluctuation in the combustor is provided in the combustor. 4. The combustor according to claim 3, wherein a set value of the temperature control mechanism is adjusted by a signal. 5. The combustor according to claim 3, wherein the branch pipe has a variable length or diameter. 6. The combustor according to claim 3, wherein at least a part of the branch pipe is formed in a bellows structure. 7. The branch pipe has a piston therein, and is formed so as to change the distance from the branch portion of the branch pipe to the piston by changing the position of the piston. Or the combustor according to 4. 8. A fuel supply system comprising: a combustion chamber; a fuel supply pipe for supplying fuel to the combustion chamber; and an oxidant supply pipe for supplying an oxidant to the combustion chamber. In a combustor that mixes and burns with an oxidant, a bypass pipe that connects upstream and downstream is provided in the middle of the fuel supply pipe, and a fuel flow rate fluctuation in the bypass pipe and at an outlet of the fuel supply pipe is reduced to zero. A combustor characterized in that a closing mechanism for closing a fuel flow rate in a bypass pipe is provided at a position where an acoustic resonance mode is generated. 9. A temperature control mechanism for controlling a temperature of the bypass pipe is provided in the bypass pipe, and a fluctuation measuring instrument for measuring a pressure fluctuation in the combustor is provided in the combustor, and the fluctuation of the pressure fluctuation measuring instrument is provided. 9. The combustor according to claim 8, wherein a set value of the temperature control mechanism is adjusted by a signal. 10. The combustor according to claim 8, wherein the position of the closing mechanism is variably formed.