Abstract:
A fuel supply method for a fuel injection device including a fuel injection unit, comprising: supplying fuel to a first fuel injection member of the fuel injection unit through a first fuel supply passage internally formed in a holding-and-supplying unit holding the fuel injection unit; and supplying fuel to a second fuel injection member of the fuel injection unit through a second fuel supply passage internally formed in the holding-and-supplying unit.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates to a fuel supply method and a fuel supply system and, more specifically, to a fuel supply method and fuel supply system for supplying fuel in a fuel injection device of a gas turbine so as to achieve low-NO x  operation. 
   2. Description of the Related Art 
   There has been a demand in recent years for a fuel injection nozzle for combustors, capable of injecting fuel such that the exhaust gas has a low NO x  concentration, owing to the recent progressively growing severity of controls concerning NO x  emission imposed on aero and industrial combustors. To achieve low-NO x  combustion, the fuel injection nozzle is required to inject fuel such that the mean flame temperature is low and temperature distribution in flames is uniform. Fuel must be mixed with a large amount of air to lower the mean flame temperature and to make temperature distribution in flames uniform. 
   When fuel is jetted by a conventional fuel injection nozzle N having a single fuel passage  101  as shown in  FIG. 3 , the fuel is mixed in a large amount of air for low-NO x  combustion, the spatial distribution of the fuel is liable to occur, and flame temperature is distributed. Such a mode of combustion is undesirable to reduce NO x  emission. Although no problem arises in combustion while the combustor is operating in a high power setting, the air-fuel mixture becomes excessively lean and combustion becomes unstable while the combustor is operating in a low-power or middle-power settings. 
   Unstable combustion that occurs in the low-power setting or middle-power setting may be avoided by an improved fuel injection nozzle obtained by altering the conventional fuel injection nozzle N. The improved fuel injection nozzle has a plurality of series of swirl vanes which are concentrically arranged in different radial positions, and a plurality of series of fuel injection mechanisms which are concentrically arranged in different radial positions. The operation of the fuel injection mechanisms is regulated according to engine power settings, and the amount of air into which the fuel is mixed is regulated for the so-called staging combustion. A fuel injection device provided with such fuel injection mechanisms is under development. 
   When the plurality of fuel injection mechanisms in different radial positions are used for staging combustion, problems arises in holding the fuel injection mechanisms and in a method of supplying fuel to the fuel injection mechanisms. 
   For example, if the fuel injection mechanisms are held individually on holding arms and the fuel is supplied through the arms, blockage of the air flow into combustor increases, and the air flowing into a fuel injection unit will be distorted. There is the possibility that joints of the fuel injection mechanisms and the arms are damaged due to difference in thermal expansion between the fuel injection mechanisms and the arms. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of such problems in the related art and it is therefore an object of the present invention to provide a fuel supply method and a fuel supply system for a fuel injection device for staging combustion or to a fuel injection device provided with a plurality of fuel injection mechanisms at different radial positions. 
   According to a first aspect of the present invention, a fuel supply method for a fuel injection device including a fuel injection unit and a holding-and-supplying unit holding the fuel injection unit, the fuel injection unit including a first fuel injection member, a first atomizing mechanism surrounding the first fuel injection member, a second fuel injection unit disposed radially outside the first atomizing mechanism, a second atomizing mechanism disposed radially outside the second fuel injection member, and an outer casing surrounding the second atomizing mechanism, comprises: supplying fuel to the first fuel injection member through a first fuel supply passage internally formed in the holding-and-supplying unit; and supplying fuel to the second fuel injection member through a second fuel supply passage internally formed in the holding-and-supplying unit. 
   Preferably, the first fuel supply passage and the second fuel supply passage are arranged so as to overlap each other with respect to a flowing direction of combustion air. 
   According to a second aspect of the present invention, in a fuel supply system for a fuel injection device including a fuel injection unit and a holding-and-supplying unit holding the fuel injection unit, the fuel injection unit including a first fuel injection member, a first atomizing mechanism surrounding the first fuel injection member, a second fuel injection member disposed radially outside the first atomizing mechanism, a second atomizing mechanism disposed radially outside the second fuel injection member, and an outer casing surrounding the second atomizing mechanism, the holding-and-supplying unit is internally provided with a first fuel supply passage through which fuel is supplied to the first fuel injection member and a second fuel supply passage through which fuel is supplied to the second fuel injection member. 
   Preferably, the first fuel supply passage and the second fuel supply passage are arranged so as to overlap each other with respect to a flowing direction of combustion air. 
   Preferably, the holding-and-supplying unit includes an integral assembly of an outer ring joined to the outer casing, an inner ring joined to the second fuel injection member, a cylindrical part joined to the first fuel injection member, and a fuel feed arm joined to the outer ring, and air passages are formed between the outer ring and the inner ring and between the inner ring and the cylindrical part. 
   According to the present invention, fuel can be supplied to the fuel injection device including the fuel injection unit without causing troubles attributable to the increase of blockage of the air flow into combustor and the difference in thermal expansion between the connected parts. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of a fuel injection device including a fuel supply system in a preferred embodiment according to the present invention; 
       FIG. 2  is a front elevation of the fuel injection device shown in  FIG. 1 ; and 
       FIG. 3  is a view of a conventional fuel injection nozzle. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2  show a fuel injection device A for a gas turbine to which a fuel supply method and a fuel supply system in preferred embodiments according to the present invention are applied. The fuel injection device A includes, as principal components, a fuel injection unit  10  that provides a combustion chamber (not shown) with an air fuel mixture, and a holding-and-supplying unit  20  that holds the fuel injection unit  10 . 
   The fuel injection unit  10  includes a first fuel injection member  30  disposed in a central part of the fuel injection unit  10 , a first atomizing mechanism  40  surrounding the first fuel injection member  30  and capable of atomizing fuel injected from the first fuel injection member  30 , a second fuel injection member  50  surrounding the first atomizing mechanism  40 , a second atomizing mechanism  60  surrounding the second fuel injection member  50  and capable of atomizing fuel injected from the second fuel injection member  50 , and an outer casing  70  surrounding the second atomizing mechanism  60 . 
   The first fuel injection member  30  has a cylindrical shape and is provided with a fuel supply passage  31  extended coaxially with the first fuel injection member  30  from a base end part to a middle part of the first fuel injection member  30 , and a fuel reservoir  32 . The fuel reservoir has a side wall provided with a predetermined number of radial fuel jetting holes  33  arranged on a circle. A joining part  34  is formed on the base end part of the first fuel injection member  30 . 
   The joining part  34  is joined to the holding-and-supplying unit  20 . A reduced part  34   a  is formed at the base end part of the first fuel injection member  30  as shown in  FIG. 1 . 
   The second fuel injection member  50  has the shape of a cylindrical tube and is provided with a fuel reservoir  51 . The fuel reservoir  51  has a side wall provided with a predetermined number of radial fuel jetting holes  52  arranged on a circle. 
   A joining part  55  is formed on the base end part of the second fuel injection member  50 . The joining part  55  is joined to the holding-and-supplying unit  20 . A projection of a predetermined length is formed in the base end part of the second fuel injection member  50  as shown in  FIG. 1 . 
   The first atomizing mechanism  40  has an annular air passage  41  defined by the outer circumference of the first fuel injection member  30  and the inner circumference of the second fuel injection member  50 , and an air swirling mechanism  43  disposed between the first fuel injection member  30  and the second fuel injection member  50 . 
   The second atomizing mechanism  60  has an annular air passage  61  defined by the outer circumference of the second fuel injection member  50  and the inner circumference of the outer casing  70 , and an air swirling mechanism  63  disposed between the second fuel injection member  50  and the outer casing  70 . 
   As shown in  FIGS. 1 and 2 , the holding-and-supplying unit  20  has an outer ring  21  joined to the outer casing  70 , an inner ring  22  joined to the second fuel injection member  50 , a central cylindrical part  23  joined to the first fuel injection member  30 , a fuel feed arm  26  formed integrally with the outer ring  21 , and a combining structure  25  connecting those components  21 ,  22 ,  23  and  26 . Fuel passages  28  are formed through the fuel feed arm  26  so as to be connected to fuel passages penetrating a gas turbine casing. Combustion air is supplied through the space between the inner ring  22  and the central cylindrical part  23  to the first atomizing mechanism  40 , and combustion air is supplied through the space between the outer ring  21  and the inner ring  22  to the second atomizing mechanism  60 . 
   As shown in  FIG. 1 , the inner ring  22  is provided with an annular groove  22   a  of a predetermined depth formed in a shape corresponding to that of the base end part of the second fuel injection member  50  in its surface facing the second fuel injection member  50 . A fuel supply hole  22   b  is formed in the annular groove  22   a.  A fuel supply passage  27  (second fuel supply passage  27   b ) is formed through the fuel feed arm  26  and the combining structure  25  and is connected to the fuel supply hole  22   b.    
   The central cylindrical part  23  is provided with a recess  23   a  of a predetermined depth having a shape corresponding to that of the base end part of the first fuel injection member  30  as shown in  FIG. 1 . A fuel supply passage  27  (first fuel supply passage  27   a ) formed through the fuel feed arm  26  and the combining structure  25  opens into the bottom of the recess  23   a.    
   The combining structure  25  has an upper connecting part  25   a  connecting the inner ring  22  to an upper part of the outer ring  21 , a central connecting part  25   b  connecting the inner ring  22  and the central cylindrical part  23 , and a lower connecting part  25   c  connecting the inner ring  22  to a lower part of the outer ring  21 . The fuel supply passages  27  connected to the fuel supply passages  28  of the fuel feed arm  26  are extended in the combining structure  25 . The first fuel supply passage  27   a  and the second fuel supply passage  27   b  formed in the upper connecting part  25   a  and the central connecting part  25   b  are arranged so as to overlap each other with respect to a direction in which combustion air flows as shown in  FIG. 1  to form each of the upper connecting part  25   a,  the central connecting part  25   b  and the lower connecting part  25   c  in the least necessary width, i.e., a dimension along the direction perpendicular to the direction in which combustion air flows. Thus, the increase of blockage of the air flowing into combustor and un-uniformity in air flowing into combustor caused by the upper connecting part  25   a,  the central connecting part  25   b  and the lower connecting part  25   c  can be limited to the least unavoidable extent. The words upper and lower are used for designating upper and lower parts as viewed in  FIGS. 1 and 2  for convenience and do not necessarily designate upper and lower parts on the combustor of an actual gas turbine. 
   The fuel injection device A jets fuel only by the first fuel injection member  30 , atomizes the jetted fuel by the first atomizing mechanism  40 , and supplies an air-fuel mixture into combustion chamber while the gas turbine is operating in low-power settings. 
   The fuel injection device A jets fuel by both the first fuel injection member  30  and the second fuel injection member  50 , atomizes the jetted fuel by the first atomizing mechanism  40  and the second atomizing mechanism  60 , and supplies an air-fuel mixture into combustion chamber while the gas turbine is operating in a high-power settings. 
   In the fuel injecting device A having the fuel supply system in the present embodiment and capable of carrying out the fuel supply method in this embodiment, the fuel supply passages  27  are formed in the holding-and-supplying unit  20  holding the fuel injection unit  10  and are connected to the fuel passages  28  formed in the fuel feed arm  26  combined with the holding-and-supplying unit  20 . Therefore, any additional fuel supply pipes are not necessary, and hence the fuel supply system has simple construction. Since any fuel supply pipes are not necessary, the fuel supply system is free from troubles attributable to laying fuel supply pipes. For example, preventive means for preventing the breakage of fuel supply pipes liable to occur in installing a fuel supply system are unnecessary, and hence the fuel supply system can be efficiently assembled. The fuel supply system is free from troubles due to the difference in thermal expansion between fuel supply pipes and a supporting part. 
   Various modifications of the foregoing fuel supply system are possible. For example, the fuel supply system may be provided with a third fuel injection member surrounding the second fuel injection member  50  in addition to the first fuel injection member  30  and the second fuel injection member  50 . When the fuel injection device A is disposed under the annular combustor instead of over the combustor as mentioned above, “upper” and “lower” used in the foregoing description are replaced with “lower” and “upper”, respectively. 
   Although the invention has been described in its preferred embodiment, obviously many changes and variations are possible therein. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein without departing from the scope and spirit thereof.