JP2012225515A - Premixed combustion device and flame control method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure both characteristics of "reduction in NOx" and "stable combustion" in a premixed combustion device for burning a premixed gas obtained by mixing air and fuel in advance.SOLUTION: A stationary sound field is formed by a stationary sound field forming means (speaker 41, 42) within a cylindrical combustion chamber 30 and by applying the stationary sound field to a flame within the cylindrical combustion chamber 30, the flame is controlled by using a secondary flow in the direction vertical to the direction in which a pressure wave generated at the loop of speed vibration of the stationary sound field travels and wrinkles formed in the flame.

Description

  The present invention relates to a premixed combustion apparatus that performs continuous combustion, such as a rocket engine and a gas turbine engine, and a flame control method thereof.

  In recent years, in rocket engines, gas turbine engines, and the like, exhausted nitrogen oxides (NOx) cause acid rain, photochemical smog, and the like, and therefore, a premixed combustion system has been adopted to reduce NOx.

  The premixed combustion method can reduce NOx because combustion is possible while suppressing the flame temperature, but the range of stable combustion range is narrow, and unstable combustion such as misfire and flashback becomes a problem.

  Flame blow-off is a phenomenon that occurs because the flow rate of the premixed gas exceeds the combustion speed and the flame cannot propagate. Therefore, in order to suppress blow-off, it is indispensable to form a low speed region for the premixed gas.

  Therefore, in a conventional combustor, for example, flame holding is performed in a backflow region generated by applying a strong swirl to a premixed gas of fuel and oxidant with a swirler (see, for example, Patent Document 1).

  In addition, in an afterburner or the like, a flame holder is used to hold a flame in a recirculation region generated on the downstream side of the flame holder.

  In addition, it has been proposed to perform combustion control in a jet-type combustor by changing vibration of a rising jet flame by applying vibration excitation to the flow field upstream of the flame (see, for example, Patent Document 2).

JP-A-6-213445 JP 2008-281314 A

  By the way, as in the technology disclosed in Patent Document 1, if the flame is held in the reverse flow region generated by applying a strong swirl to the premixed mixture of fuel and oxidant with a swirler, combustion stability is improved while unburned There is a problem that pressure loss occurs because the gas passes through the swirler. Since the pressure loss greatly affects the efficiency for the gas turbine engine, it is desirable that the pressure loss be as small as possible.

  In addition, when using a flame holder, the flame holder is exposed to a flame, and thermal fatigue such as a decrease in strength due to heat becomes a problem.

  In addition, the disclosed technique of Patent Document 2 does not create a backflow region and aims at flame control, and flame holding cannot be performed at a high flow rate.

  Accordingly, an object of the present invention is to provide a premixed combustion apparatus capable of reducing pressure loss and performing stable combustion, and a flame control method therefor, in view of the conventional situation as described above.

  Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the description of embodiments described below.

  In the present invention, combustion is performed with reduced pressure loss by applying a standing sound field directly to the flame, thereby suppressing the blow-off by giving a disturbance to the flame.

  That is, the present invention is a premixed combustion apparatus for combusting a premixed gas obtained by premixing air and fuel, and forming a standing sound field in the combustion space of the premixed gas. Forming means, and applying the standing sound field to the flame in the combustion space, so that the vertical direction of the pressure wave generated at the antinode of the velocity vibration of the standing sound field The flame is held using the next flow and the soot formed in the flame.

  In the premixed combustion apparatus according to the present invention, the standing sound field forming means includes, for example, a resonance tube that surrounds the combustion space of the premixed gas, and in the combustion space of the premixed gas surrounded by the resonance tube. Creates a standing sound field.

  Further, in the premixed combustion apparatus according to the present invention, the standing sound field forming means generates, for example, sine waves of opposite phases from two speakers facing each other, and resonates at a half wavelength of the sine wave. By doing so, a standing sound field is formed in the combustion space of the premixed gas surrounded by the resonance tube.

  Furthermore, in the premixed combustion apparatus according to the present invention, for example, a lean premixed gas of propane gas is burned in a combustion space surrounded by the resonance tube, and flame holding is performed by a standing sound field of 155 dB or more.

  The present invention is a flame control method in a premixed combustion apparatus for burning a premixed gas obtained by premixing air and fuel, forming a standing sound field in the combustion space of the premixed gas, By applying the standing sound field to the flame in the combustion space, the secondary flow in the direction perpendicular to the traveling direction of the pressure wave generated at the antinode of the velocity vibration of the standing sound field, and the flame The flame is held using the formed soot.

  According to the present invention, in a premixed combustion apparatus for combusting a premixed gas obtained by premixing air and fuel, a standing sound field is directly applied to the flame so as to disturb the flame. By suppressing, pressure loss can be reduced and stable combustion can be performed.

It is a schematic diagram which shows schematic structure of the premixing combustion apparatus to which this invention is applied. It is a figure which shows typically the secondary flow generate | occur | produced in the orthogonal | vertical direction with respect to the advancing direction of a pressure wave by giving a density change to the antinode of the velocity vibration of a standing sound field. It is a figure which shows the result of having observed the floating height of the flame in the said premixing combustion apparatus, and the change of a flame shape. It is a figure which shows the relationship between the burner nozzle exit flow velocity and the equivalent ratio at the time of blowing in each frequency and sound pressure in the said premixed combustion apparatus. It is a figure which shows the observation result of the maximum burner nozzle exit flow velocity which can hold a flame when a sound pressure is changed in the said premixed combustion apparatus.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  The present invention is applied to, for example, a combustion apparatus 100 configured as shown in FIG.

  As shown in FIG. 1A, this combustion apparatus 100 is a premixed combustion apparatus that burns a premixed gas obtained by previously mixing air and fuel, and is a premixed combustion apparatus that mixes combustion air and fuel. A mixing chamber 10, a burner nozzle 20 for injecting a premixed gas in which combustion air and fuel are mixed in the premixing chamber 10, and a cylindrical combustion chamber for burning the premixed gas injected from the burner nozzle 20 30.

  Flowmeters 11 and 12 for measuring the flow rates of the combustion air and the fuel are provided in the combustion air and fuel supply paths supplied to the premixing chamber 10.

  The fuel air is supplied to the premixing chamber 10 via the surge tank 13.

  The combustion chamber 30 is provided with an opening 32 for allowing the premixed gas injected from the burner nozzle 20 to enter the chamber at the center bottom of the peripheral wall 31 and for discharging the combustion gas to the outside. The exhaust port 33 is provided at the central top of the peripheral wall 31.

  Here, in FIG. 1A, a part of the combustion chamber 30 is shown longitudinally cut in the longitudinal direction, and a sectional view taken along line AA of the combustion chamber 30 in FIG. 1 (B).

  Further, the premixed combustion apparatus 100 is provided with two speakers 41 and 42 facing each other at both ends of the cylindrical combustion chamber 30.

  The two speakers 41, 42 facing each other are driven by sine wave signals having opposite phases and supplied via an amplifier 44 that amplifies the sine wave signal output from the sine wave signal generator 43, and have opposite phases to each other. The sine wave acoustic output is generated and resonated with a half wavelength of the sine wave, thereby functioning as a standing sound field forming means for forming a standing sound field in the cylindrical combustion chamber 30.

  That is, in the premixed combustion apparatus 100, the standing sound field forming means generates sine waves having opposite phases from the two speakers 41 and 42 facing each other, and resonates at a half wavelength of the sine wave. Thus, a standing sound field is formed in the combustion space of the premixed gas surrounded by the resonance tube. The cylindrical combustion chamber 30 functions as a resonance tube that surrounds the combustion space of the premixed gas in which the combustion air and fuel are mixed.

  When a density change is applied to the antinode of the velocity vibration of the standing sound field, as shown in FIG. 2, a secondary flow is generated in a direction perpendicular to the traveling direction of the pressure wave. Moreover, under strong sound pressure, soot is formed in the flame by acoustic vibration.

  In the premix combustion apparatus 100, the standing sound is applied by applying the standing sound field to a flame in the cylindrical combustion chamber 30 in which the premixed gas injected from the burner nozzle 20 is burned. The premixed flame is blown away by holding the flame using the secondary flow in the direction perpendicular to the traveling direction of the pressure wave generated in the antinode of the field velocity vibration and the soot formed in the flame. Eliminates unstable combustion, etc., and realizes stable combustion.

  That is, in the premixed combustion apparatus 100, a sine wave is generated from the two directly opposed speakers 41 and 42 and resonated to generate a standing wave in the combustion chamber 30. This standing wave is flamed. The blow-off of the flame is suppressed by the backflow region due to the secondary flow generated by direct application and the wrinkles associated therewith.

  Here, in the premixed combustion apparatus 100, the flow rates of the combustion air and propane gas are measured by the flow meters 11 and 12, and the premixed gas in which the combustion air and the fuel are mixed at a predetermined ratio in the premixing chamber 10. The premixed gas injected from the burner nozzle 20 was burned in the cylindrical combustion chamber 30 and an experiment was performed in which the standing sound field was applied to the flame. Results were obtained.

  In the experiment, a stainless steel tube burner having an inner diameter of 10 mm and a rim thickness of 1 mm was used as the burner nozzle 20 to form a flame at room temperature and atmospheric pressure, and the cylindrical combustion chamber 30 was made of stainless steel having a diameter of 267 mm. And 300 mm and 400 mm long tubes were used. A standing sound field was formed by generating sine waves with opposite phases from the two directly facing speakers 41 and 42 and resonating them in a circular tube. The frequency was about 620 Hz for a 300 mm long tube and about 480 Hz for a 400 mm long tube so as to resonate at ½ wavelength. During combustion, the temperature inside the tube changes and the resonance frequency changes due to the change in sound speed. The frequency was finely adjusted each time.

  In forming the flame, the burner nozzle outlet flow velocity was increased in order to avoid flame holding at the burner rim. In this state, since the flame blows off, the flame is held by using a flame holder 50 having a diameter of 12 mm as shown by a broken line in FIG. 1, and then the standing sound is set so that the flame position coincides with the velocity vibration belly. Form a field, remove the flame holder 50 in that state, create a state to hold the flame only with the sound field, reduce the flow rate of propane gas under a constant sound pressure, and from the flow rate at the time of blowout, The equivalent ratio of flame holding limit was calculated.

  The sound pressure was measured with an oscilloscope 70 at the position of the antinode of pressure vibration by a piezoresistive differential pressure sensor (PR-10 manufactured by KELLER) 60, and the flame was held in the sound field. The sound pressure at a constant equivalent ratio was lowered and the sound pressure at the time when blow-off occurred was read using an oscilloscope 70. Moreover, the flame was image | photographed with the high-speed video camera (MEMRCAM GX-8 by Nac Image Technology Co., Ltd.) and a still camera which are not shown in figure.

  Result of observing changes in flame height and flame shape due to differences in sound pressure Ps under the conditions of equivalent ratio φ = 0.7, burner nozzle outlet flow velocity Uu = 36 m / s, and frequency f = 640 Hz. Is shown in FIG. In the figure, the white line indicates the burner nozzle outlet, the white dotted line indicates the resonance tube inlet, and the hatched portion indicates the flame holder 50.

  When there is no sound, the flame blows off without the flame holder 50 as shown in FIG. 3A, but without the flame holder 50, the flame of Ps = 0.8 kPa as shown in FIG. The flame holding position can be set to a burner rim by setting the sound pressure level SPL = 155 dB as shown in FIG. 3 (C) in the case of the flame of Ps = 1.1 kPa in the case of the flame of the sound pressure level SPL = 153 dB. Further, the flame with Ps = 2.0 kPa adhered to the burner rim with a sound pressure level SPL = 160 dB as shown in FIG.

  Therefore, the higher the sound pressure, the more the flame base moves upstream, and the flame can be held even at a higher burner nozzle outlet flow velocity.

  Further, when focusing on the flame shape, no significant change could be confirmed from Ps = 0.8 kPa to Ps = 1.1 kPa, but the flame of Ps = 2.0 kPa is from Ps = 0.8 to Ps = 1. A low-flame flame on the downstream side that could be confirmed with a 1 kPa flame could not be confirmed. Moreover, soot was confirmed in all flames.

  Next, the relationship between the burner nozzle outlet flow velocity and the equivalent ratio at the time of blowing off at each frequency and sound pressure is shown in FIG.

  In the low flow rate region where the flow velocity was about 35 m / s or less, the flame base adhered to the burner nozzle rim during high sound pressure. In this case, not only the sound but also the flame holding mechanism of the rim may not be ignored, so it is not measured. Lean combustion was possible even at a higher flow rate at 1.8 kPa than at a sound pressure of 0.8 kPa. Moreover, at f = 480 Hz and PS = 1.8 kPa, the blow-off limit equivalent to the flame holder 50 having a diameter of 12 mm was confirmed.

  The cause of the formation of soot in the premixed flame in the standing sound field is thought to be baroclinic torque, and is a term that appears on the right side of the vorticity equation of the following equation (1).

Here, ω is a vorticity vector, ρ is density, and p is pressure. It is assumed that the density gradient ∇ρ is constant regardless of the frequency, and the pressure gradient ∇p is a pressure gradient caused by sound described below. The pressure vibration in the standing sound field is expressed by the following equation (2).

Here, P0 is the pressure amplitude, f is the frequency, c is the speed of sound, t is the time, and the x-axis is taken in the propagation direction of the pressure wave with the vibration surface of the speaker as O. Therefore, the pressure gradient at the antinode of the velocity vibration takes the spatial gradient of P in the equation (2) and is expressed by the following equation (3).

  Therefore, the baroclinic torque is directly proportional to the sound pressure and the frequency from the equations (1) and (3). However, the time required for the baroclinic torque to act on the flame surface is inversely proportional to the frequency, so that the time required for the deformation of the flame surface is shortened. Therefore, it is considered that the degree of deformation of the flame surface is not affected by the frequency, and therefore it is appropriate to arrange the blow-off limit by using the sound pressure P0 or its effective value PS as a parameter.

  The observation result of the maximum burner nozzle outlet flow velocity that can hold the flame when the sound pressure is changed is shown in FIG. As shown in FIG. 5, in order to achieve an improvement in the burner nozzle outlet flow velocity at the blow-off limit, the sound pressure must be higher, and the relationship was almost proportional. This is consistent with the flame height shown in FIG. 3 and the estimation from the previous analysis. Further, a slight difference was confirmed in the sound pressure at the time of blow-off limit due to the difference in frequency, and flame holding could not be performed unless the sound pressure was generally higher at 480 Hz than at 620 Hz.

  As is clear from the above experimental results, in the premixed combustion apparatus 100, the standing sound with respect to the flame in the cylindrical combustion chamber 30 in which the premixed gas injected from the burner nozzle 20 is combusted. By applying a field, a baroclinic is created by the secondary flow in the direction perpendicular to the direction of the pressure wave generated in the antinode of the velocity vibration of the standing sound field, the pressure gradient due to sound, and the density gradient due to combustion. A flame formed in the flame due to the torque is used to hold the flame, so that unstable combustion such as blowing of the premixed flame is eliminated and stable combustion can be realized.

  That is, in the premixed combustion apparatus 100, the blow-off limit can be improved by burning the premixed gas of propane gas and holding the flame with a standing sound field of 155 dB or more. Specifically, in the premixed combustion apparatus 100, the flammability limit of propane is reached up to a flow rate of about 50 m / s under a condition of a frequency of 480 Hz and an effective sound pressure of 1.8 Kpa (SPL = 159 dB). The flame could be held to the vicinity (near the equivalent ratio of 0.5) without causing the flame to blow without the flame holder 50.

  Therefore, in the premixed combustion apparatus 100, the lean premixed gas of propane gas is burned in the combustion space surrounded by the resonance tube, and flame holding is performed by a standing sound field of 155 dB or more, thereby reducing “NOx”. And "stable combustion" can be secured.

  Thus, in the present invention, in the premixed combustion apparatus 100 that burns the premixed gas obtained by premixing air and fuel, a standing sound field is formed in the combustion space of the premixed gas surrounded by the resonance tube. By forming a standing sound field by means and applying the standing sound field to the flame in the combustion space, the traveling direction of the pressure wave generated in the antinode of the velocity vibration of the standing sound field Using the secondary flow in the vertical direction and the soot formed in the flame, the flame can be held, pressure loss can be reduced, and stable combustion can be performed.

  In the premixed combustion apparatus 100, the standing sound field is formed by the standing sound field forming means in the cylindrical combustion chamber 30 that functions as a resonance tube that resonates at ½ wavelength. The chamber 30 does not need to be cylindrical, and may function as a resonance tube that resonates at one wavelength or two wavelengths. In the premixed combustion apparatus 100, a standing sound field is generated in the combustion chamber 30 by the two speakers 41 and 42. However, the premixed combustion apparatus 100 is fixed in the combustion chamber 30 by the self-excited vibration of the combustor itself. A structure that generates a sound field can also be used. Further, by combining many sound sources instead of two and optimizing their arrangement, it is possible to suppress blow-off even if the flow rate of the premixed gas is higher. In addition, the present invention also includes suppression of flame blow-off in an engine combustor using a stationary flame such as a gas turbine engine, a ramjet engine, a scramjet engine, etc., flame holding of an afterburner of a jet engine, boilers, a gas stove, etc. The present invention can be applied to all combustion devices using a stationary flame.

  10 Premixing chamber, 11, 12 Flow meter, 13 Surge tank, 20 Burner nozzle, 30 Combustion chamber, 31 Perimeter wall, 32 Opening, 33 Exhaust port, 41, 42 Speaker, 43 Sine wave signal generator, 44 Amplifier, 50 Flame, 60 piezoresistive differential pressure sensor, 70 oscilloscope, 100 premixed combustion device

Claims (5)

A premixed combustion apparatus for burning a premixed gas obtained by premixing air and fuel,
A standing sound field forming means for forming a standing sound field in the combustion space of the premixed gas,
By applying the standing sound field to the flame in the combustion space, the secondary flow in the direction perpendicular to the traveling direction of the pressure wave generated at the antinode of the velocity vibration of the standing sound field, and the flame A premixed combustion apparatus for holding a flame by using a soot formed on the flame.   The standing sound field forming means includes a resonance tube surrounding the combustion space of the premixed gas, and forms a standing sound field in the combustion space of the premixed gas surrounded by the resonance tube. The premixed combustion apparatus according to claim 1.   The standing sound field forming means generates sine waves of opposite phases from two speakers facing each other, and resonates at a half wavelength of the sine wave, so that the premixing surrounded by the resonance tube 3. A premixed combustion apparatus according to claim 2, wherein a standing sound field is formed in the combustion space of the gas.   3. The premixed combustion apparatus according to claim 2, wherein a propane gas lean premixed gas is burned in a combustion space surrounded by the resonance tube, and flame holding is performed by a standing sound field of 155 dB or more. A flame control method in a premixed combustion apparatus for burning a premixed gas obtained by premixing air and fuel,
By forming a standing sound field in the combustion space of the premixed gas and applying the standing sound field to a flame in the combustion space, a pressure wave generated at the antinode of the velocity vibration of the standing sound field A flame control method characterized by performing flame holding using a secondary flow in a direction perpendicular to the traveling direction of the flame and a soot formed in the flame.

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