Abstract:
An injection assembly for a combustor of a gas turbine has an outer body provided with inlet passages for comburent air, a conical tubular portion housed inside the outer body and delimiting partly an inner duct and an outer annular duct; a first and a second supply means for supplying a liquid fuel into the inner duct and, respectively, into the outer annular duct; at least one circumferential annular seat formed being carried by one of the tubular portion and the outer body, so as to collect a mass of liquid fuel advancing in the outer annular duct and make uniform the flow of liquid flowing out of the circumferential annular seat.

Description:
[0001]    The invention relates to an improved gas turbine combustor injection assembly. 
         [0002]    In particular, the invention relates to an injection assembly for injecting an air-liquid fuel mixture into a combustion chamber of a gas turbine for an aeronautical/aeroderivative engine. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the field of gas turbines, it is known to feed the air-liquid fuel mixture towards a combustion chamber of the turbine using a fuel injection, air-fuel mixing assembly of the type described in European patent application no. EP 2 385 307 A1 filed by the applicant. 
         [0004]    More specifically, the injection assembly comprises an outer tubular body and an inner conical tubular body, which partially extends inside the outer tubular body, is tapered towards the combustion chamber and separates two air liquid mixing ducts from one another, said ducts being an inner duct and an outer annular duct. The outer annular duct is delimited by the aforesaid outer tubular body. 
         [0005]    In each duct, the liquid fuel is introduced through a respective ring of nozzles. The nozzles of the outer annular duct are usually oriented so as to send the liquid fuel towards the inner conical tabular body. However, there are solutions in which the nozzles of the outer annular duct are oriented so as to direct the liquid fuel towards the outer tabular body. 
         [0006]    Regardless of the direction along which the liquid fuel is supplied, before entering the combustion chamber, the air and the liquid fuel must be properly mixed depending on the fuel flow rate and on the operating condition of the turbine. 
         [0007]    Experiments have shown that, in some operating conditions requesting a high degree of homogenization of the air-liquid fuel mixture sent to the combustion chamber, said mixture was not homogeneous, but, instead, it was different from area to area of the duct. This lack of homogeneity leads to the formation of fumes and, in general, of a great quantity of polluting combustion products. 
         [0008]    Experiments have also shown that the lack of homogeneity of the air/liquid fuel mixture was also partly due to a lack of homogeneity in the flow of liquid fuel fed in the outer annular duct, which, instead of being fed in the form of an annular meatus with a substantially constant thickness, as desired, in some operating conditions spontaneously divided itself forming fluid threads or a beam of fuel flows adjacent to one another and fed independently of one another towards the combustion chamber. 
       SUMMARY OF THE INVENTION 
       [0009]    The object of the invention is to provide an improved gas turbine combustor injection assembly, which can solve the problem described above in a simple and economic fashion and, in particular, can create, at the inlet of the combustion chamber, a homogeneous air-liquid fuel mixture. 
         [0010]    According to the invention, there is provided an improved gas turbine combustor injection assembly, the assembly comprising an outer body having inlet passages for comburent air and a first tubular portion extending coaxially to an axis; a second conical tubular portion housed at least partly inside said outer body and said first tubular portion coaxially to said axis and delimiting partly an inner duct and, with said first tubular portion, an outer annular duct having respective outlets; first and second supply means for advancing a liquid fuel in said inner duct and, respectively, in said outer annular duct, characterized by also comprising, at least, a first continuous circumferential annular seat formed on at least one of said first and second tubular portion and suitable to collect a predefined mass of liquid fuel advancing in said annular duct. 
         [0011]    Preferably, in the assembly defined above, the first seat has a constant depth. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention will now be described with reference to the accompanying drawings, which show a non-limiting embodiment thereof, wherein: 
           [0013]      FIG. 1  shows, in a cross-sectional view with parts removed for greater clarity, a gas turbine combustor provided with a preferred embodiment of an improved injection assembly according to the invention; 
           [0014]      FIG. 2  is a perspective perspective view, on a larger scale, of the injection assembly of  FIG. 1 ; 
           [0015]      FIG. 3  shows, in a cross-sectional view and on a significantly larger scale, a detail of  FIG. 1 ; 
           [0016]      FIG. 4  shows, in a cross-sectional view and on a significantly larger scale, a detail of  FIG. 3 ; 
           [0017]      FIG. 5  is a cross-section according to line V-V of  FIG. 3 ; 
           [0018]      FIGS. 6 and 7  are similar to  FIGS. 3 and 4  and show a variant of a detail of  FIGS. 3 and 4 ; and 
           [0019]      FIG. 8  shows a further variant of a detail of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    In  FIG. 1 , number  1  indicates, as a whole, a gas turbine combustor comprising a combustion chamber  2  and an injection assembly  3  to send a mixture of air and liquid fuel to the combustion chamber  2 . 
         [0021]    With reference to  FIGS. 1 and 2 , the assembly  3  comprises an air-liquid fuel supply head  5 , which is conveniently manufactured as one single piece, and a support arm  6  for the head  5 , which makes up—together with the head  5 —part of a body  7 , which is also manufactured as one single piece. 
         [0022]    The head  5  projects from the arm  6  coaxially to an axis  9  and comprises a casing or outer tubular body  10 , which ends with a tubular portion  11  delimiting a duct  12 . The duct  12  communicates with the combustion chamber  2  through an axial outlet opening  13  of its and with the main air flow supply area through two rings  15  and  16 , besides one another, made of known shaped openings indicated with  15   a  and  16   a.    
         [0023]    With reference to  FIGS. 1 and 3 , the duct  12  houses a body  20 , which is, in longitudinal section, substantially T-shaped and comprises an annular attachment portion  21 , substantially shaped like a plate, coaxial to the axis  9  and extending between the opening rings  15  and  16 . The body  20  comprises, furthermore, a conical tubular portion  22 , which extends from an inner edge of the portion  21  coaxially to the axis  9 , is tapered towards the chamber  2  and towards a free ends of its and is delimited, on the outside, by a surface  23  having a straight generatrix  24  ( FIG. 3 ). The body  20  partially extends inside the tubular portion  11  and divides the duct  12  into an inner duct  26  communicating with the ring  15  of openings  15   a  and into an outer annular duct  27 . The annular duct  27  communicates with the ring  16  of openings  16   a  and is delimited, on one side, by the surface  23  and, on the other side, by the inner surface  28  of the tubular portion  11 . 
         [0024]    With reference to  FIGS. 1 and 2 , again, the assembly  3  comprises, furthermore, two hydraulic circuits  29  and  39 , which are separate from one another and are designed to supply a liquid fuel to the inner duct  26  and, respectively, to the annular duct  27 . Given the circuits  29  and  30 , the circuit  29  comprises a conveying duct  31  extending through the arm  6  and an injector  32  arranged along the axis  9 , whereas the circuit  30  comprises a conveying duct  33  of its own, whose outlet leads into an annular chamber  34  obtained in the annular portion  21  ( FIG. 3 ). 
         [0025]    In the particular example described herein and with reference to  FIG. 3 , the circuit  30  comprises, furthermore, a ring  35  of adjusted straight ducts  36  extending through the portion  21  and having respective axes  36   a  that are parallel to the generatrix  24 . Each duct  36  has a relative inlet communicating with the chamber  34  and a relative outlet obtained through a surface  37  and in a position spaced apart from the surface  23 . The surface  37  extends orthogonally to the axis  9  and delimits the portion  21 . 
         [0026]    In this way, the ducts  36  direct the liquid introduced into the annular duct  27  towards a smooth portion of the surface  23  externally delimiting an inlet section  38  of the conical tubular portion  22  extending starting from the surface  37 . 
         [0027]    With reference, again, to  FIG. 3  and, in particular, to  FIG. 4 , the conical tubular portion  22  comprises, furthermore, an outlet section  39 , which is also delimited by a smooth surface, and an intermediate section  40  extending between the sections  38  and  39  and delimited, in the example shown herein, by a corrugated surface, as explained more in detail below. 
         [0028]    With reference to  FIGS. 4 and 5 , the section  40  comprises a plurality of continuous circumferential ribs, in the case described herein three ribs, which are spaced apart from one anther in the feeding direction of the liquid fuel and along the axis  9 . 
         [0029]    According to a variant that is not shown herein, the intermediate section  40  comprises one single circumferential rib  41 . 
         [0030]    Regardless of their number, each rib  41  has a thickness S, measured starting from the surface  23  in a radial direction, that is constant along the entire length of the rib  41  itself. The thicknesses S of the ribs  41  are conveniently equal to one another, but they could also be different. Preferably, the thickness S ranges from 1/20 to ⅕ of the difference between the corresponding inner and outer radius of the annular duct. 
         [0031]    Each rib  41  also has a radial half-section ( FIG. 5 ) with a triangular shape and a circular perimeter edge  43 . 
         [0032]    Alternatively, each rib  41  has a radial half-section with a trapezoidal shape, preferably—though not necessarily—tapered towards the inside of the annular duct  27 , or with a square, rectangular or circular shape. In the last cases, each rib  41  is delimited by a free end surface, which is coaxial to the axis  9 . 
         [0033]    Regardless of the geometry of the radial half-section, each rib  41  is coupled to the intermediate section  40  of the conical body  20  in a fluid-tight manner. Preferably, each rib  41  and the body  20  or at least the section  40  of the tubular portion  22  make up part of a body manufactured as one single piece, as you can see in  FIGS. 4 and 5 , for example through the forming technique known as “additive manufacturing”. 
         [0034]    Alternatively, each rib  41  consists of a relative closed ring, which is distinct from the body  20  and is fitted and forced on the section  40  with an axis of its coaxial to the axis  9 . 
         [0035]    Regardless of how the ribs  41  are coupled to the intermediate section  40 , each rib  41  lies on a plane P of its that is orthogonal to the axis  9  and spaced apart from the other planes. 
         [0036]    Regardless of the number, the geometry and the relative position of the ribs  41  along the annular portion  22 , each rib  41  defines a barrier to the feeding movement of the liquid and partially delimits a relative continuous circumferential annular seat  44  extending along the outer periphery of the annular portion  22  and suited to collect, in use, a predefined mass of liquid fuel fed in the annular duct  27 . 
         [0037]    As the ribs  41  have a constant thickness S, each seat  44  has a constant depth that is equal to, or different from, the one of the other seats  44 . 
         [0038]    In the variant shown in  FIGS. 6 and 7 , the assembly  3  has no ribs  44  and each seat  44  is defined by a relative circumferential grooves  45  obtained in the wall of the tubular portion  22 . The grooves have constant or variable depth, measured in a circumferential direction. Conveniently, the grooves  45  have a depth ranging from 0.1 to 3 millimetres. 
         [0039]    In the further variant shown in  FIG. 8 , the channels  36  are inclined relative to the generatrix, so as to direct the liquid fuel towards an inlet section  46  of the surface  28 . In this variant, the ribs  41 , conveniently with a shape and a geometry equal to the ones carried by the tubular portion  22 , are carried by the tubular portion  11  ( FIG. 8 ) and extend inside the annular duct  27  towards the surface  23 . In this position, again, each rib  41  makes up an obstacle to the feeding movement of the liquid and defines a relative seat  44  for collecting a mass of liquid fuel. 
         [0040]    Like the case of the tubular portion  22 , even for the tubular portion  11 , the ribs  41 , according to a variant that is not shown herein, are replaced by grooves obtained in the wall of the tubular portion  11 . 
         [0041]    Regardless of the fact that the collecting seats  44  are obtained on the tubular portion  22  or on the tubular portion  11 , the seats  44  generate a liquid barrier crossed by the liquid flowing through the annular duct  27  towards the combustion chamber  2 . 
         [0042]    Experiments have shown that the presence of the liquid barrier and, in particular, the fact that the liquid fuel is forced to pass over a continuous circumferential obstacle defined by the ribs  41  or by the grooves  45  produce a mixing of the liquid fuel getting in and create, at the outlet, a compact liquid meatus, which is uniform and has a substantially constant thickness. 
         [0043]    In other words, compared to known solutions, the presence of the ribs  41  or of the grooves  45  prevents the liquid from following preferential feeding paths and, therefore, avoids the formation of flows or fluid threads transversely spaced apart from one another. 
         [0044]    The formation of a compact meatus without discontinuity, obtained with the invention, allows manufacturers not only to obtain an optimal air-liquid mixing in each section of the annular duct  27 , but also, especially, to obtain a mixture entering the chamber  2  that is perfectly homogeneous and does not change in time, whatever the quantity of air and/or the flow rate of the fuel introduced through the circuits  29  and  30 . 
         [0045]    The presence of the liquid fuel collecting seats  44 , then, increases the liquid fuel-air interface area, which leads, compared to known solutions, to an improvement of the air-fuel mixture entering the combustion chamber  2 . 
         [0046]    The thrust exerted by the air upon the liquid on the inside of the annular duct  27  generates a partial evaporation of the liquid fuel in the annular duct  27  and a simultaneous settlement of the remaining drops of liquid fuel on the surface against which the liquid flowing out of the seats  44  flows, thus stabilizing the liquid fuel film. Close to the outlet opening  13 , the strong turbulence generated by the mixing of the air flows coming from the ducts  26  and  27  contributes to the atomization of the film before entering the combustion chamber  2 . 
         [0047]    This translates into a significant reduction of the polluting products resulting from the combustion, especially as the temperature in the combustion chamber  2  increases. 
         [0048]    Owing to the above, it is evident that assembly  3  described herein can be subject to changes and variations, without for this reason going beyond the scope of protection set forth in the independent claims. In particular, the ribs  41  or the grooves  45  and, therefore, the seats  44  could be available in a number different from the one described above by mere way of example, have geometries that are different from the one mentioned above and/or a different spacing along the tubular portions  11  or  22 . 
         [0049]    Finally, the seats  44  could be obtained partly on the tubular portion  11  and partly on the tubular portion  22 , with the double purpose of making the flow of liquid fuel uniform, on the one hand, and of increasing the interaction of the air with the liquid fuel, on the other had, thus increasing the turbulence of the air. As a matter of fact, in these conditions the turbulence of the air getting in is amplified by the contact with the ribs  41  or the grooves  45  that are not affected by the liquid fuel. 
         [0050]    Moreover, at least one of the seats  44  could be defined partly by a relative rib  41  and partly by a relative groove  45 . In this case, the groove  45  could have a constant depth, equal to or different from the one of the possible other grooves  45 , or a variable depth.