Patent Publication Number: US-2020284431-A1

Title: Combustor and combustor array

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a combustor and a combustor array. 
     Priority is claimed on Japanese Patent Application No. 2019-043169, filed Mar. 8, 2019, the content of which is incorporated herein by reference. 
     Description of Related Art 
     In general, in a combustor, fuel injected from a fuel nozzle is mixed and burned inside a cylindrical body to form a flame inside the cylindrical body. More specifically, the fuel nozzle includes a first nozzle disposed on a central axis of the combustor, and a plurality of second nozzles disposed around the first nozzle in a circumferential direction. Fuel is injected from the first nozzle. The fuel burns in the surrounding air. As a result, a diffusion flame is formed. On the other hand, a premixed gas in which fuel and air are mixed in advance is ejected from the second nozzles. When the diffusion flame touches the premixed gas, a premixed flame is formed. 
     Here, in the combustor as described above, one premixed flame extending in an axial direction is formed starting from the first nozzle. For this reason, the flame length tends to increase in the axial direction. When the length of the flame increases, since a retention time of the flame in the combustor also increases, there is a likelihood that the generation of NOx will be promoted. Thus, there is an increasing demand for a combustor capable of reducing the length of the flame, while the output is maintained. 
     In this way, as a combustor capable of reducing the flame size, for example, an apparatus described in Patent Document 1 below has been proposed. The combustor described in Patent Document 1 has a plurality of tubes extending in the same direction as each other. A fuel supply hole for injecting fuel is formed on an inner peripheral surface of each tube, and the air and fuel flowing from an upstream side are mixed and blown out of a distal end of the tube. By igniting the air-fuel mixture, a short flame is formed starting from the distal end of each tube. 
     PATENT DOCUMENTS 
     [Patent Document 1] U.S. Pat. No. 8,112,999 
     SUMMARY OF THE INVENTION 
     However, the combustor described in Patent Document 1 adopts a configuration in which fuel is supplied from the inner peripheral surface of the tube. For this reason, a region having a higher fuel concentration than other regions is formed along the inner peripheral surface of the tube. This may cause a phenomenon in which the flame flows backward toward an upstream side (a flashback). As a result, there is a risk of hindering a stable operation of the combustor. 
     The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a combustor and a combustor array that can be operated more stably. 
     A combustor according to an aspect of the present invention is equipped with a distal end portion which forms a nozzle extending along an axis and is open at a distal end; an intermediate portion having a mixing surface which defines a mixing space in which air and fuel are mixed, which gradually expands outward in a radial direction from the axis from the nozzle to a rear, behind the distal end portion; a proximal end portion which forms a fuel space to which fuel is supplied from outside, behind the intermediate portion; and a plurality of air introduction pipes which penetrate the proximal end portion in a direction of the axis, have a distal end communicating with the mixing space, are arranged in a circumferential direction with respect to the axis to surround the axis, and have a fuel supply hole formed on each inward side in a radial direction of the axis to communicate with the fuel space. 
     According to the aforementioned configuration, the air guided into the mixing space through the air introduction pipe is mixed with fuel in the mixing space to form an air-fuel mixture. By igniting the air-fuel mixture, a flame is formed on a downstream side from the nozzle of the distal end portion. Here, the fuel supply holes are formed in each of the portions on the inner side in the radial direction of the plurality of air introduction pipes, that is, portions close to the axis. Accordingly, in the mixing space, as a portion becomes closer to the axis, the fuel concentration becomes higher. Further, since the nozzle extends along the axis, the fuel concentration is highest in a region through which the axis passes, in a flame region formed on the downstream side of the nozzle. In other words, the fuel concentration is relatively low in an inner peripheral surface of the nozzle, an inner surface of the mixing space, and a region along the surface on an outward side in the radial direction of each air introduction pipe. As a result, it is possible to reduce the likelihood that flashback will occur along these surfaces. Furthermore, according to the aforementioned configuration, the mixing surface gradually expands to the outer side in the radial direction from the nozzle toward the rear. In other words, the mixing surface gradually reduces in diameter radially inward in the radial direction toward the nozzle. Therefore, for example, as compared with a configuration in which the mixing surface expands in the radial direction of the axis, the fuel and air can be gradually contracted and directed toward the nozzle, while promoting mixing of the fuel and air. As a result, a pressure loss in the mixing space can be reduced. 
     In the combustor, the mixing surface may be curved convexly outward in the radial direction of the axis in a cross-sectional view including the axis. 
     According to the aforementioned configuration, since the mixing surface is curved to be convex to the outer side in the radial direction of the axis, the fuel and air can be more gradually contracted. Therefore, it is possible to further reduce a pressure loss in the mixing space. 
     In the combustor, the nozzle may extend eccentrically in the radial direction with respect to the axis from the distal end side to the rear. 
     According to the aforementioned configuration, the nozzle extends while being eccentric in the radial direction with respect to the axis from the distal end side to the rear. Therefore, for example, as compared with a case in which the nozzle extends linearly along the axis, more turbulent flow components can be imparted to the flow of the fuel and air in the nozzle. As a result, the mixing of fuel and air in the nozzle can be further promoted. 
     In the combustor, the air introduction pipe may extend, while being eccentric in the radial direction with respect to an auxiliary axis extending parallel to the axis from the intermediate portion side to the rear. 
     According to the aforementioned configuration, the air introduction pipe extends while being eccentric in the radial direction with respect to the auxiliary axis that is a central axis of the air introduction pipe, from the intermediate portion side to the rear. Therefore, for example, as compared to a case in which the air introduction pipe extends linearly along the auxiliary axis, more turbulent flow components can be imparted to the air flow in the air introduction pipe. As a result, it is possible to further promote mixing of fuel and air in the mixing space. 
     In the combustor, the air introduction pipe may be twisted to be directed from one side in the circumferential direction of the axis toward the other side, from the intermediate portion side to the rear. 
     According to the aforementioned configuration, the air introduction pipe is twisted to be directed from one side in the circumferential direction of the axis toward the other side from the intermediate portion side to the rear. Therefore, a swirl component directed from one side in the circumferential direction toward the other side can be imparted to the flow of the air which passes through the air introduction pipe. As a result, it is possible to further promote mixing of fuel and air in the mixing space. 
     In the combustor, a lightening part as a hollow part may be formed in a portion closer to an outer peripheral side than the nozzle is at the distal end portion. 
     According to the aforementioned configuration, the lightening part as a hollow part is formed in a portion closer to the outer peripheral side than the nozzle at the distal end portion. As a result, convection is generated in the air exposed to a high temperature of the flame in the lightening part. Since unevenness in a temperature distribution along the nozzle is reduced by the convection, the flame formed from the nozzle can be more effectively held. 
     The combustor may further have a protruding part provided on a front side of the proximal end portion and protruding into the mixing space along the axis, the fuel supply hole being formed on an outer peripheral surface of the protruding part. 
     According to the aforementioned configuration, the protruding part protruding into the mixing space along the axis is provided on the front side of the proximal end portion. Further, the fuel supply hole is formed on the outer peripheral surface of the protruding part. Therefore, fuel can be supplied to a region in the mixing space closer to the nozzle. As a result, it is possible to further promote mixing of fuel and air in the mixing space. 
     A combustor according to an aspect of the present invention is equipped with a distal end portion which forms a nozzle extending along an axis and opening at a distal end; an intermediate portion which forms a mixing space expanding from the nozzle in a direction intersecting the axis behind the distal end portion; a proximal end portion which forms a fuel space to which fuel is supplied from outside behind the intermediate portion; and a plurality of air introduction pipes which penetrate the proximal end portion in a direction of the axis, have a distal end communicating with the mixing space, and are arranged in a circumferential direction of the axis to surround the axis, in which a fuel supply hole through which the fuel space and the mixing space communicate with each other is formed on a surface facing the distal end side of a portion surrounded by the plurality of air introduction pipes in the proximal end portion, and an extension cylinder part, which extends in the direction of the axis to cover the fuel supply hole from a side of the outer periphery and has an air hole formed to communicate with the mixing space, is provided on the surface facing the distal end side. 
     According to the aforementioned configuration, the air guided into the mixing space through the air introduction pipe is mixed with fuel in the mixing space to form an air-fuel mixture. By igniting the air-fuel mixture, a flame is formed on a downstream side from the nozzle of the distal end portion. Here, the fuel supply hole is formed on a surface facing the distal end side of the portion surrounded by the plurality of air introduction pipes in the proximal end portion. That is, the fuel is injected from the fuel supply hole in the direction of the axis. Further, the fuel supply hole is covered with the extension cylinder part from the outer peripheral side. In addition, in the extension cylinder part, an air hole through which the mixing space communicates with the space is formed on the inner peripheral side of the extension cylinder part. Therefore, after mixing the fuel and air to a certain extent in the space on the side of the inner periphery of the extension cylinder part, the air-fuel mixture can be supplied to the mixing space. That is, it is possible to further promote mixing of fuel and air in the mixing space. 
     Furthermore, since the fuel supply part is provided along the axis, the fuel concentration increases in the mixing space as the portion is closer to the axis. Therefore, in a flame region formed on the downstream side of the nozzle, a fuel concentration becomes the highest in a region through which the axis passes. In other words, the fuel concentration is relatively low on the inner peripheral surface of the nozzle, the inner surface of the mixing space, and a region along the surface on an outer side in the radial direction of each air introduction pipe. As a result, it is possible to reduce the likelihood that flashback occurs along these surfaces. 
     A combustor array according to an aspect of the present invention has a plurality of combustors according to any one of the above aspects. The plurality of combustors are arranged in the plural in a plane orthogonal to the axis. 
     According to the aforementioned configuration, it is possible to provide a combustor array that has a high output and can be stably operated, by arranging a plurality of combustors in which the likelihood of occurrence of flashback is reduced. 
     In the combustor array, the plurality of combustors may be arranged in a grid shape in the plane orthogonal to the axis. 
     In the combustor array, each of the plurality of combustors may have a hexagonal shape when viewed from the direction of the axis, and they may be arranged in a honeycomb shape due end faces thereof coming into contact with each other. 
     In the combustor array, the plurality of combustors may be arranged in an annular shape. 
     In the combustor array, the plurality of combustors may be arranged in a staggered manner so that positions of the axis differ from each other in the plane orthogonal to the axis. 
     In the combustor array, the plurality of combustors may be disposed along a curved concave surface which becomes convex from one side toward the other side. 
     According to the aforementioned configuration, the flame distribution is made uniform and a more stable flame can be obtained. 
     According to an aspect of the present invention, it is possible to provide a combustor and a combustor array capable of being operated more stably. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing a configuration of a combustor array according to a first embodiment of the present invention. 
         FIG. 2  is a cross-sectional view showing the configuration of the combustor according to the first embodiment of the present invention. 
         FIG. 3  is a cross-sectional view showing a configuration of a combustor according to a second embodiment of the present invention. 
         FIG. 4  is a cross-sectional view showing a configuration of a combustor according to a third embodiment of the present invention. 
         FIG. 5  is a cross-sectional view showing a configuration of a combustor according to a fourth embodiment of the present invention. 
         FIG. 6  is a plan view showing the configuration of the combustor according to the fourth embodiment of the present invention. 
         FIG. 7  is a cross-sectional view showing a configuration of a combustor according to a fifth embodiment of the present invention. 
         FIG. 8  is a cross-sectional view showing a configuration of a combustor according to a sixth embodiment of the present invention. 
         FIG. 9  is a cross-sectional view showing a configuration of a combustor according to a seventh embodiment of the present invention. 
         FIG. 10  is a plan view showing a first modified example of a combustor array according to an embodiment of the present invention. 
         FIG. 11  is a plan view showing a second modified example of the combustor array according to an embodiment of the present invention. 
         FIG. 12  is a plan view showing a third modified example of the combustor array according to the embodiment of the present invention. 
         FIG. 13  is a plan view showing a fourth modified example of the combustor array according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     A first embodiment of the present invention will be described with reference to  FIGS. 1 and 2 . A combustor array  100  according to the present embodiment is equipped with a plurality of combustors  1 . Each combustor  1  is a small device that forms a small-size flame. That is, the combustor array  100  is configured as a so-called micro flame combustor. 
     More specifically, as shown in  FIG. 1 , the combustor array  100  is equipped with a plurality of (9) combustors  1  arranged in a grid shape in a plane orthogonal to an axis O that is a central axis of the combustor  1 . When viewed from a direction of the axis O, the combustor  1  has a rectangular (square) cross-sectional shape. Outer surfaces of a pair of adjacent combustors  1  about each other without a gap. 
     Next, the configuration of the combustor  1  will be described with reference to  FIG. 2 .  FIG. 1  is a cross-sectional view taken along a line A-A of  FIG. 2 . As shown in  FIG. 2 , the combustor  1  is equipped with a distal end portion  31 , an intermediate portion  32 , a proximal end portion  33 , and an air introduction pipe  12 . 
     A nozzle  11  which extends along the axis O and has a distal end  11 T opening outward is formed in the distal end portion  31 . As shown in  FIG. 1 , the nozzle  11  has a circular cross-sectional shape centered on the axis O. 
     The intermediate portion  32  is integrally provided on a side opposite to the distal end  11 T of the distal end portion  31  in a direction of the axis O (a rear end  11 R). In the following description, a side at which the distal end  11 T is located when viewed from the rear end  11 R in the direction of the axis O is called a “front” and a “front side”, and an opposite side thereto is called a “rear” and a “rear side”. A mixing space  32 V communicating with the nozzle  11  is formed inside the intermediate portion  32 . The mixing space  32 V expands in a direction (a radial direction) intersecting the axis O. More specifically, the mixing space  32 V is defined by a conical mixing surface S 1  that has a diameter gradually expanding outward in the radial direction from a rear end  11 R of the nozzle  11  to the rear along the axis O, and a cylindrical surface S 2  extending in a cylindrical shape from an end edge on a rear side of the mixing surface S 1  along the axis O. That is, the mixing space  32 V is gradually reduced in diameter from the rear side toward the nozzle  11 . 
     The proximal end portion  33  is integrally provided on the side to the rear of the intermediate portion  32 . A fuel space  33 V as a hollow part is formed inside the proximal end portion  33 . Fuel supplied from the outside is stored in the fuel space  33 V. A surface facing the front side of the proximal end portion  33  is configured by an annular surface S 3  connected to the cylindrical surface S 2  of the mixing space  32 V and a central surface S 4  located on the inner peripheral side of the annular surface S 3 . The annular surface S 3  and the central surface S 4  expand at the same position in the direction of the axis O. Further, both the annular surface S 3  and the central surface S 4  expand in a direction orthogonal to the axis O. 
     The air introduction pipe  12  is a flow path that penetrates the proximal end portion  33  in the direction of the axis O. Air supplied from the outside is guided into the aforementioned mixing space  32 V through the air introduction pipe  12 . A plurality (four) of air introduction pipes  12  are provided to surround the axis O at intervals in the circumferential direction. Each air introduction pipe  12  extends along an auxiliary axis O 2  that extends parallel to the axis O. An inner diameter of the air introduction pipe  12  is constant over the entire region in the direction of the auxiliary axis O 2 . End portions on a front side of each air introduction pipe  12  communicate with the above-described mixing space  32 V. End portions on the rear side of each air introduction pipe  12  communicate with an air supply source (not shown). 
     Each one fuel supply hole  40  is formed on the introduction pipe inner side surface  12 A, which is a portion on an inner side in the radial direction of the axis O, in the inner peripheral surfaces of the plurality of air introduction pipes  12 . The introduction pipe inner side surface  12 A is a region facing the axis O side when the air introduction pipe  12  is viewed from the direction of the axis O. In the inner peripheral surface of the air introduction pipe  12 , a region except the introduction pipe inner side face  12 A (that is, a region facing a side opposite to the axis O) is an introduction pipe outer side surface  12 B. Each fuel supply hole  40  communicates with the fuel space  33 V and the space inside the air introduction pipe  12 . The fuel stored in the fuel space  33 V is guided into the air introduction pipe  12  through the fuel supply hole  40 . 
     Next, the operation of the above-described combustor  1  will be described. When operating the combustor  1 , fuel and air are supplied to the combustor  1 , respectively. Air flows from the rear toward the front through the plurality of air introduction pipes  12 . Fuel is supplied (sprayed) into the air flow from the fuel space  33 V through the aforementioned fuel supply hole  40 . The fuel flows from the rear toward the front along the introduction pipe inner side surface  12 A in the air introduction pipe  12 . Thereafter, the fuel and air are mixed in the mixing space  32 V to form a premixed gas. At this time, a region having a relatively high fuel concentration (a high concentration region X) is formed to cover the introduction pipe inner side surface  12 A and the central surface S 4  from the outside. The premixed gas is guided by the mixing surface S 1  of the mixing space  32 V to contract toward the inner side in the radial direction of the axis O. The contracted premixed gas is guided to the outside through the nozzle  11 . By igniting the premixed gas with an ignition device (not shown), a premixed flame extending forward from the nozzle  11  is formed. When such a phenomenon occurs simultaneously in each combustor  1 , the combustor array  100  operates as a micro flame combustor that forms a plurality of small-scale flames. 
     As described above, according to the aforementioned configuration, the air guided into the mixing space  32 V through the air introduction pipe  12  is mixed with fuel in the mixing space  32 V to form a premixed gas. By igniting the premixed gas, a flame is formed on a downstream side from the nozzle  11  of the distal end portion  31 . Here, the fuel supply holes  40  are formed in each of the portions on the inner side in the radial direction of the plurality of air introduction pipes  12 , that is, portions close to the axis O (the introduction pipe inner side surface  12 A). Accordingly, in the mixing space  32 V, as the portion is closer to the axis O, the fuel concentration becomes higher (a high concentration region X is formed). Further, since the nozzle  11  extends around the axis O, the fuel concentration is highest in a region through which the axis O passes, in a flame region formed on the downstream side of the nozzle  11 . In other words, the fuel concentration is relatively low in the inner peripheral surface of the nozzle  11 , the inner surface of the mixing space  32 V, and ae region along the surface on an outer side in the radial direction (the introduction pipe outer side surface  12 B) of each air introduction pipe  12 . As a result, it is possible to reduce a likelihood that flashback occurs along the surfaces. Therefore, the combustor  1  and the combustor array  100  can be operated more stably. 
     Furthermore, according to the aforementioned configuration, the mixing surface S 1  gradually expands to the outer side in the radial direction from the nozzle  11  toward the rear. In other words, the mixing surface S 1  is gradually reduced in diameter toward the nozzle  11  from the outer side to the inner side in the radial direction. Therefore, for example, as compared with a configuration in which the mixing surface S 1  expands in the radial direction of the axis O, the fuel and air can be gradually contracted and directed toward the nozzle, while promoting the mixing of the fuel and air. As a result, the pressure loss in the mixing space  32 V can be reduced. Therefore, the combustor  1  and the combustor array  100  can be operated more stably. 
     In addition, according to the aforementioned configuration, by arranging a plurality of combustors  1  in which the likelihood of occurrence of flashback is reduced, it is possible to provide a combustor array  100  that has a high output and can be more stably operated. In particular, according to the aforementioned configuration, the plurality of combustors  1  are arranged in a grid shape in a plane orthogonal to the axis O. Therefore, the distribution of the flame in the plane orthogonal to the axis O is made uniform, and a more stable flame can be obtained. 
     The first embodiment of the present invention has been described above. Further, various changes and modifications can be made to the aforementioned configuration without departing from the gist of the present invention. 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described with reference to  FIG. 3 . In addition, components similar to those of the first embodiment are denoted by the same reference numerals, and repeated description will not be provided. As shown in  FIG. 3 , in a combustor  1  according to the present embodiment, a shape of a mixing surface S 1   b  is different from that of the first embodiment. The mixing surface S 1   b  has a curved surface shape that is curved to be convex to the outer side in the radial direction of the axis O in a cross-sectional view including the axis O. The mixing surface S 1   b  is smoothly connected to a cylindrical surface S 2  located on the rear side. 
     According to the aforementioned configuration, since the mixing surface S 1   b  is curved to be convex to the outer side in the radial direction of the axis O, the fuel and air can be more gradually contracted. Therefore, it is possible to further reduce a pressure loss in the mixing space  32 V. 
     The second embodiment of the present invention has been described above. Further, various changes and modifications can be made to the aforementioned configuration without departing from the gist of the present invention. 
     Third Embodiment 
     Subsequently, a third embodiment of the present invention will be described with reference to  FIG. 4 . In addition, configurations similar to those of each of the aforementioned embodiments are denoted by the same reference numerals, and repeated description will not be provided. As shown in  FIG. 4 , in a combustor  1  according to the present embodiment, shapes of a nozzle  11   b  and an air introduction pipe  12   b  are different from each of the aforementioned embodiments. The nozzle  11   b  extends while being eccentric in the radial direction with respect to the axis O from the distal end  11 T toward the rear end  11 R. More specifically, the nozzle  11   b  is formed by alternately connecting a portion which is eccentric with respect to the axis O (an eccentric portion E 1 ) and a portion centered on the axis O (a centered portion C 1 ). Further, the eccentric portion E 1  and the centered portion C 1  are connected in a smooth curved surface shape. 
     Furthermore, the air introduction pipe  12   b  extends while being eccentric in the radial direction with respect to the auxiliary axis O 2  from the intermediate portion  32  side toward the rear. More specifically, the air introduction pipe  12   b  is formed by alternately connecting a portion which is eccentric with respect to the auxiliary axis O 2  (an eccentric portion E 2 ) and a portion centered on the auxiliary axis O 2  (a centered portion C 2 ). Further, the eccentric portion E 2  and the centered portion C 2  are connected in a smooth curved surface shape. 
     According to the aforementioned configuration, the nozzle  11   b  extends while being eccentric in the radial direction with respect to the axis O from the distal end  11 T side to the rear. Therefore, for example, as compared with a case in which the nozzle  11   b  extends linearly along the axis O, more turbulent flow components can be imparted to the flow of the fuel and air in the nozzle  11   b . As a result, it is possible to further promote the mixing of fuel and air in the nozzle  11   b.    
     Furthermore, according to the aforementioned configuration, the air introduction pipe  12   b  extends while being eccentric in the radial direction with respect to the auxiliary axis O 2  that is the central axis of the air introduction pipe  12   b  from the intermediate portion  32  side to the rear. Therefore, for example, as compared to a case in which the air introduction pipe  12   b  extends linearly along the auxiliary axis O 2 , more turbulent flow components can be imparted to the air flow in the air introduction pipe  12   b . As a result, it is possible to further promote mixing of fuel and air in the mixing space  32 V. 
     The third embodiment of the present invention has been described above. Further, various changes and modifications can be made to the aforementioned configuration without departing from the gist of the present invention. 
     Fourth Embodiment 
     Next, a fourth embodiment of the present invention will be described with reference to  FIGS. 5 and 6 . In addition, configurations similar to those of each of the aforementioned embodiments are denoted by the same reference numerals, and repeated description will not be provided. As shown in  FIGS. 5 and 6 , in the present embodiment, a configuration of an air introduction pipe  12   c  is different from those of each of the aforementioned embodiments. The air introduction pipe  12   c  has an upstream part  12   c   1  extending along the aforementioned auxiliary axis O 2 , and a downstream part  12   c   2  connected to a downstream side (a front side) of the upstream part  12   c   1 . As shown in  FIG. 6 , the downstream part  12   c   2  is gradually twisted from the one side in the circumferential direction of the axis O toward the other side, from the intermediate portion  32  side to the rear. That is, the downstream part  12   c   2  is inclined with respect to the axis O in a cross-sectional view including the axis O. 
     According to the aforementioned configuration, the air introduction pipe  12   c  is twisted to be directed from one side in the circumferential direction of the axis O toward the other side from the intermediate portion  32  side to the rear. Therefore, the swirl component directed from one side in the circumferential direction toward the other side can be imparted to the flow of the air which passes through the air introduction pipe  12   c . As a result, it is possible to further promote mixing of fuel and air in the mixing space  32 V. 
     The fourth embodiment of the present invention has been described above. Further, various changes and modifications can be made to the aforementioned configuration without departing from the gist of the present invention. 
     Fifth Embodiment 
     Subsequently, a fifth embodiment of the present invention will be described with reference to  FIG. 7 . In addition, configurations similar to those of each of the aforementioned embodiments are denoted by the same reference numerals, and repeated description will not be provided. As shown in  FIG. 7 , in the present embodiment, a lightening part VL as a hollow part is formed in a portion of the distal end portion  31  on the outer peripheral side of the nozzle  11 . The lightening part VL has a cross-sectional shape along the outer shapes of the nozzle  11  and the mixing surface S 1 . The lightening part VL communicates with the outside. That is, air can circulate in the lightening part VL. 
     According to the aforementioned configuration, the lightening part VL as the hollow part is formed in the portion closer to the outer peripheral side than the nozzle  11  at the distal end portion  31 . As a result, convection is generated in the air exposed to the high temperature of the flame in the lightening part VL. Since the uneven temperature distribution along the nozzle  11  is reduced by the convection, the flame formed from the nozzle  11  can be more effectively held. 
     The fifth embodiment of the present invention has been described above. Further, various changes and modifications can be made to the aforementioned configuration without departing from the gist of the present invention. 
     Sixth Embodiment 
     Next, a sixth embodiment of the present invention will be described with reference to  FIG. 8 . In addition, configurations similar to those of each of the aforementioned embodiments are denoted by the same reference numerals, and repeated description will not be provided. As shown in  FIG. 8 , in the present embodiment, a protruding part  33 P protruding toward the mixing space  32 V side along the axis O is provided on a surface facing the front side of the proximal end portion  33  (that is, a central surface S 4 ). The protruding part  33 P has a columnar shape centered on the axis O, and a fuel supply hole  40   b  through which the fuel space  33 V and the mixing space  32 V communicate with each other is formed on the outer peripheral surface (a protruding part outer peripheral surface  33 S). A plurality of fuel supply holes  40   b  are formed at intervals in the circumferential direction of the axis O. That is, the fuel guided by the fuel supply hole  40   b  is directly supplied (sprayed) into the mixing space  32 V. 
     According to the aforementioned configuration, the protruding part  33 P protruding into the mixing space  32 V along the axis O is provided on the front side of the proximal end portion  33 . Further, the fuel supply hole  40   b  is formed on the outer peripheral surface (the protruding part outer peripheral surface  33 S) of the protruding part  33 P. Therefore, fuel can be supplied to a region in the mixing space  32 V closer to the nozzle  11 . As a result, it is possible to further promote mixing of fuel and air in the mixing space  32 V. 
     The sixth embodiment of the present invention has been described above. Further, various changes and modifications can be made to the aforementioned configuration without departing from the gist of the present invention. 
     Seventh Embodiment 
     Subsequently, a seventh embodiment of the present invention will be described with reference to  FIG. 9 . In addition, configurations similar to those of each of the aforementioned embodiments are denoted by the same reference numerals, and repeated description will not be provided. As shown in  FIG. 9 , in the present embodiment, a cylindrical extension cylinder part  33 T centered on the axis O is provided on a central surface S 4  of the proximal end portion  33 . Furthermore, a cylindrical outer extension cylinder part  33 U centered on the axis O is provided on an annular surface S 3   c  of the proximal end portion  33 . The fuel supply hole  40   c  is formed on the central surface S 4 . One fuel supply hole  40   c  is formed on the axis O. A plurality of air holes  50  penetrating the extension cylinder part  33 T in the radial direction are formed in the extension cylinder part  33 T. The mixing space  32 V and the space on the inner peripheral side of the extension cylinder part  33 T communicate with each other by the air hole  50 . 
     According to the aforementioned configuration, the air guided into the mixing space  32 V through the air introduction pipe  12  is mixed with fuel in the mixing space  32 V to form a premixed gas. By igniting the premixed gas, a flame is formed on a downstream side from the nozzle  11  of the distal end portion  31 . Here, the fuel supply hole  40   c  is formed on a surface facing the distal end  11 T side of the portion surrounded by the plurality of air introduction pipes  12  in the proximal end portion  33  (a central surface S 4 ). That is, the fuel is injected from the fuel supply hole  40   c  in the direction of the axis O. Further, the fuel supply hole  40   c  is covered with the extension cylinder part  33 T from the outer peripheral side. In addition, the extension cylinder part  33 T is formed with an air hole  50  through which the mixing space  32 V communicates with the space on the inner peripheral side of the extension cylinder part. Therefore, after mixing the fuel and air to a certain extent in the space on the inner peripheral side of the extension cylinder part  33 T, the air-fuel mixture can be supplied to the mixing space  32 V. That is, it is possible to further promote mixing of fuel and air in the mixing space  32 V. 
     Furthermore, since the fuel supply hole  40   c  is provided on the axis O, the fuel concentration increases in the mixing space  32 V as the portion is closer to the axis O. Therefore, in the flame region formed on the downstream side of the nozzle  11 , a fuel concentration becomes the highest in the region through which the axis O passes. In other words, the fuel concentration is relatively low in the inner peripheral surface of the nozzle  11 , the inner surface of the mixing space  32 V, and a region along the surface on an outer side in the radial direction of each air introduction pipe  12  (an introduction pipe outer side surface  12 B). As a result, it is possible to reduce the likelihood that flashback occurs along these surfaces. Therefore, the combustor  1  and the combustor array  100  can be operated more stably. 
     The seventh embodiment of the present invention has been described above. Further, various changes and modifications can be made to the aforementioned configuration without departing from the gist of the present invention. As a modified example common to the each of the above embodiments, the number of the combustors  1  included in the combustor array  100  is not limited to nine, and may be eight or less or ten or more. Further, the number of air introduction pipes  12  in the combustor  1  is not limited to four, and may be three or less or five or more. 
     Furthermore, the combustors  1  in the above-described combustor array  100  can also be disposed in a staggered manner as shown in  FIG. 10  (a first modified example). Specifically, a plurality of combustors  1  are arranged in a plane orthogonal to the axis O in a staggered manner so that the positions of the axes O are different from each other. Moreover, as shown in  FIG. 11 , it is also possible to form each combustor  1  in a hexagonal shape when viewed from the direction of the axis O, and to arrange the combustors in a honeycomb shape by bringing their end faces into contact with each other (a second modified example). In addition, as shown in  FIG. 12 , it is also possible to configure an annular combustor array  100  by forming outer diameters of each of the combustors  1  in a circular arc shape and connecting the combustors  1  in the circumferential direction (a third modified example). 
     Further, in each of the above-described embodiments and modified examples, examples in which the combustor  1  is arranged on a plane have been described. However, as shown in  FIG. 13 , it is also possible to adopt a configuration in which the combustors  1  are arranged along a curved surface (a fourth modified example). Specifically, these combustors  1  are arranged along a curved concave surface that is convex from one to the other. Note that such a curved surface may be one continuous surface. It may be a polyhedron formed by a plurality of planes connected to each other. 
     While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims. 
     EXPLANATION OF REFERENCES 
     
         
         
           
               100  Combustor array 
               1  Combustor 
               11 ,  11   b  Nozzle 
               11 R Rear end 
               11 T Distal end 
               12 ,  12   b ,  12   c  Air introduction pipe 
               12   c   1  Upstream part 
               12   c   2  Downstream part 
               12 A Introduction pipe inner side surface 
               12 B Introduction pipe outer side surface 
               31  Distal end portion 
               32  Intermediate portion 
               32 V Mixing space 
               33  Proximal end portion 
               33 P Protruding part 
               33 S Protruding part outer peripheral surface 
               33 T Extension cylinder part 
               33 U Outer extension cylinder part 
               33 V Fuel space 
               40 ,  40   b ,  40   c  Fuel supply hole 
               50  Air hole 
             C 1 , C 2  Centered part 
             E 1 , E 2  Eccentric part 
             O Axis 
             O 2  Auxiliary axis 
             S 1 , S 1   b  Mixing surface 
             S 2  Cylindrical surface 
             S 3  Annular surface 
             S 4  Center plane 
             VL Lightening part 
             X High concentration region