Patent Publication Number: US-2019195499-A1

Title: Pilot burner assembly with central pilot fuel injection for a gas turbine engine combustor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2017/073672 filed Sep. 19, 2017, and claims the benefit thereof. The International Application claims the benefit of European Application No. EP16189714 filed Sep. 20, 2016. All of the applications are incorporated by reference herein in their entirety. 
    
    
     FIELD OF INVENTION 
     The present technique relates generally to burners for combustors of gas turbine engines and, more particularly to pilot burner assemblies for combustors of gas turbine engines. 
     BACKGROUND OF INVENTION 
     In a gas turbine engine combustor a fuel is combusted or burned to produce hot pressurised exhaust gases which are then fed to a turbine stage where they, while expanding and cooling, transfer momentum to turbine blades thereby imposing a rotational movement on a turbine rotor. Mechanical power of the turbine rotor can then be used to drive a generator for producing electrical power or to drive a machine. However, burning the fuel leads to a number of undesired pollutants in the exhaust gas which can cause damage to the environment. Therefore, it is generally desired to keep the pollutants as low as possible. One kind of pollutant is nitrogen oxide (NO x ). 
     Combustion in present day gas turbine engine combustors, for example Dry Low Emissions (DLE) combustors, is initiated and maintained by using a pilot fuel and a main fuel fed at different positions of the combustor and at different stages of operation, for example in some DLE combustors, the percentage split of pilot fuel is about 4% at full load and increases at part load, primarily to prevent combustion dynamics and flame out as the air-to-fuel ratio increases. However, the pilot fuel may burn in a non-premixed and/or partially premixed mode close to the burner face and generate high levels of thermal NO x . It is therefore desired to provide a technique that reduces emissions, particularly NO x . 
     SUMMARY OF INVENTION 
     Thus, an object of the present disclosure is to provide a technique that that reduces emissions, particularly NO x . 
     The above object is achieved by a pilot burner assembly, a combustor assembly equipped with such a pilot burner assembly, and a gas turbine engine having at least one such combustor assembly of the present technique. Advantageous embodiments of the present technique are provided in dependent claims. 
     In a first aspect of the present technique, a pilot burner assembly for a combustion chamber in a gas turbine engine is presented. The pilot burner assembly includes a pilot burner and a radial swirler. The pilot burner has a burner head face. A plurality of pilot fuel injection holes are present on, and open at, the burner head face. The pilot fuel injection holes, hereinafter also referred to as the holes, provide pilot fuel into the combustion chamber for combustion. The burner head face has a center. The radial swirler generates a swirling mix of a main fuel and air in the combustion chamber. The radial swirler has a plurality of swirler vanes. The swirler vanes are arranged circumferentially around the burner head face with respect to the center of the burner head face and are radially disposed around the center of the burner head face. The swirler vanes include radially inner thin ends. The thin ends positioned around or about the center of the burner head face together define a burner region on the burner head face. The burner region is concentric with the center of the burner head face, i.e. the center of the burner head face is also the center of the burner region. 
     In the pilot burner assembly of the present technique, each of the pilot fuel injection holes on the burner head face is positioned on the burner head face and within the burner region such that a distance of the pilot fuel injection hole from the center of the burner head face is equal to or less than 50 percent of a distance of an edge of the burner region from the center of the burner head face, when measured along a straight line that joins the center of the burner head face to the edge of the burner region and passes through the pilot fuel injection hole. The distance of the pilot fuel injection hole from the center may be measured from a geometric center of the hole or from a point on the edge of a pilot fuel injection hole boundary that is farthest from the center of the burner head face. 
     As a result of the placement of the pilot fuel injection holes within a central region or in the vicinity of the center of the burner head face, i.e. because the holes in the present assembly are centrally positioned, the pilot fuel is injected into re-circulated hot product gases close to the burner head face in the combustion chamber, primarily at part load conditions of operations of the gas turbine engine, thus yielding an emission reduction, primarily a reburn NO x  reduction (destruction of NO by interaction with hydrocarbon radicals). There is a further improvement as the pilot fuel is injected into a region of low oxygen and hence the pilot fuel burns at a lower temperature. Later on in the combustion process, using the present pilot burner assembly a secondary burn may be achieved with a high influx of Oxygen in a main flame region of the combustion chamber during operation of the gas turbine engine. The cool main flame is further stabilized by the presence of additional heat and partially combusted products from the reburning of the pilot fuel. Thus the pilot burner assembly of the present technique reduces NO x , and optionally promotes main flame stabilisation. 
     In an embodiment of the pilot burner assembly, hereinafter also referred to as the burner assembly, the distance of the pilot fuel injection hole from the center of the burner head face is equal to or less than 30 percent of the distance of the edge of the burner region from the center of the burner head face. Thus the holes are nearer to the center of the burner head face and ensure the pilot fuel is injected into re-circulated hot product gases, even when the re-circulation of the hot product gases is confined into a leaner or smaller space around a longitudinal axis of the combustion chamber close to the burner head face in the combustion chamber. 
     In another embodiment of the burner assembly the distance of the pilot fuel injection hole from the center of the burner head face is equal to or less than 15 percent of the distance of the edge of the burner region from the center of the burner head face. Thus the holes are further near to the center of the burner head face and ensure the pilot fuel is injected into re-circulated hot product gases, even when the re-circulation of the hot product gases is confined into a further smaller space around the longitudinal axis of the combustion chamber close to the burner head face in the combustion chamber. 
     In another embodiment of the burner assembly the distance of the pilot fuel injection hole from the center of the burner head face is equal to or greater than 5 percent of the distance of the edge of the burner region from the center of the burner head face. Thus the holes are centrally located on the burner head face but not present at the center of the burner head face and ensure better mixing and distribution of the injected pilot fuel into re-circulated hot product gases. 
     In another embodiment of the burner assembly the distance of the pilot fuel injection hole from the center of the burner head face is equal to or greater than 10 percent of the distance of the edge of the burner region from the center of the burner head face. Thus the holes are centrally located on the burner head face but not present at the center of the burner head face and there is more area on the burner head face within which the holes are positioned thus ensuring better distribution of the holes on the burner head face and better distribution and mixing of the injected pilot fuel into re-circulated hot product gases. 
     In another embodiment of the burner assembly, the burner region is circular. This provides an embodiment of the assembly where the swirler vanes are symmetrically and circularly located on the burner head face. 
     In another embodiment of the burner assembly, each of the pilot fuel injection holes is adapted to provide pilot fuel in a radially outwards direction. This is a further improvement over the presently known pilot burners where the pilot fuel is provided in a radially inwards direction. As a result of providing pilot fuel in the radially outwards direction, better distribution and mixing of the injected pilot fuel into re-circulated hot product gases is ensured. 
     In another embodiment of the burner assembly, the radially outwards direction forms an angle with the burner head face between 30 degrees and 90 degrees, and advantageously between 30 degrees and 60 degrees. Thus the pilot fuel pilot fuel is injected into the re-circulated hot product gases in a distributed manner and even when the re-circulated hot product gases are not established in direct physical contact of the burner head face during the operation of the gas turbine engine. The mixing and distribution of the injected pilot fuel is increased. 
     In another embodiment of the burner assembly, the plurality of the pilot fuel injection holes includes at least a first pilot fuel injection hole and a second pilot fuel injection hole. Each of the first and the second pilot fuel injection holes to provide pilot fuel in the radially outwards direction at different angles with the burner head face. 
     Thus, different holes are used to inject pilot fuel at different angles into the combustion chamber and thereby into the re-circulated hot product gases, which provides a scattered distribution and mixing of the pilot fuel in the re-circulated hot product gases. 
     In another embodiment of the burner assembly, the pilot fuel injection holes are arranged in a two dimensional array, for example in a single circular arrangement around the center of the burner head face or in a two concentric circular arrangements having different radii. The mixing and distribution of the injected pilot fuel is increased. 
     In a second aspect of the present technique, a combustor assembly for a gas turbine engine is presented. The combustor assembly includes a combustion chamber having a longitudinal axis, and a pilot burner assembly according to the first aspect of the present technique. The pilot burner assembly is arranged such that the longitudinal axis of the combustion chamber is aligned with the center of the burner head face. The pilot burner, the radial swirler and the combustion chamber are serially arranged along the longitudinal axis. A main burner may be present that provides a main fuel to the combustor chamber through the radial swirler. Thus, the combustor assembly of the present technique has the same advantages as the abovementioned aspect of the present technique. 
     In a third aspect of the present technique, a gas turbine engine is presented. The gas turbine engine includes at least one combustor assembly which in turn includes a pilot burner assembly according to the first aspect of the present technique. 
     All previously explained configurations may apply to pilot burners and combustor assemblies with gaseous or liquid fuel operation, or with dual fuel operation. Furthermore, the pilot burner may comprise one or more fuel injection openings differently positioned and in addition to the pilot fuel injection holes of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above mentioned attributes and other features and advantages of the present technique and the manner of attaining them will become more apparent and the present technique itself will be better understood by reference to the following description of embodiments of the present technique taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  shows part of a gas turbine engine in a sectional view and in which an exemplary embodiment of a pilot burner assembly and an exemplary embodiment of a combustor assembly of the present technique are incorporated; 
         FIG. 2  schematically illustrates an exploded view of an exemplary embodiment of the combustor assembly including an exemplary embodiment of the pilot burner assembly of the present technique are depicted; 
         FIG. 3  schematically illustrates a perspective view of a conventionally known pilot burner with a swirler; 
         FIG. 4  schematically illustrates a top view of the conventionally known pilot burner of  FIG. 3  along with the swirler; 
         FIG. 5  schematically illustrates a perspective view of a conventionally known pilot burner of  FIG. 3  with a conventionally known positioning of the fuel injection holes; 
         FIG. 6  depicts a schematic section illustrating injection of pilot fuel for a conventionally known pilot burner; 
         FIG. 7  schematically illustrates a pilot burner assembly of the present technique depicting a swirler and arrangement of pilot fuel injection holes in accordance with aspects of the present technique; 
         FIG. 8  schematically illustrates the pilot burner assembly of the present technique without the swirler depicting arrangement of the pilot fuel injection holes in accordance with aspects of the present technique; 
         FIG. 9  schematically illustrates the pilot burner assembly of the present technique without the swirler depicting another arrangement of the pilot fuel injection holes in accordance with aspects of the present technique; 
         FIG. 10  schematically illustrates the pilot burner of the present technique without the swirler depicting injection of the pilot fuel in accordance with aspects of the present technique; 
         FIG. 11  depicts a schematic section illustrating injection of pilot fuel from an exemplary embodiment of the pilot burner of the present technique; and 
         FIG. 12  depicts a schematic section illustrating injection of pilot fuel from another exemplary embodiment of the pilot burner of the present technique; in accordance with aspects of the present technique. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     Hereinafter, above-mentioned and other features of the present technique are described in details. Various embodiments are described with reference to the drawing, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be noted that the illustrated embodiments are intended to explain, and not to limit the invention. It may be evident that such embodiments may be practiced without these specific details. 
       FIG. 1  shows an example of a gas turbine engine  10  in a sectional view. The gas turbine engine  10  comprises, in flow series, an inlet  12 , a compressor or compressor section  14 , a combustor section  16  and a turbine section  18  which are generally arranged in flow series and generally about and in the direction of a rotational axis  20 . The gas turbine engine  10  further comprises a shaft  22  which is rotatable about the rotational axis  20  and which extends longitudinally through the gas turbine engine  10 . The shaft  22  drivingly connects the turbine section  18  to the compressor section  14 . 
     In operation of the gas turbine engine  10 , air  24 , which is taken in through the air inlet  12  is compressed by the compressor section  14  and delivered to the combustion section or burner section  16 . The burner section  16  comprises a burner plenum  26 , one or more combustion chambers  28  extending along a longitudinal axis  35  and at least one burner  30  fixed to each combustion chamber  28 . Generally, the burner  30  comprises a main burner (not shown) and a pilot burner (not shown in  FIG. 1 ) The longitudinal axis  35  passes through center of the burner  30 . The combustion chambers  28  and the burners  30  are located inside the burner plenum  26 . The compressed air passing through the compressor  14  enters a diffuser  32  and is discharged from the diffuser  32  into the burner plenum  26  from where a portion of the air enters the burner  30  and is mixed with a gaseous or liquid fuel. The air/fuel mixture is then burned and the combustion gas  34  or working gas from the combustion is channelled through the combustion chamber  28  to the turbine section  18  via a transition duct  17 . 
     This exemplary gas turbine engine  10  has a cannular combustor section arrangement  16 , which is constituted by an annular array of combustor cans  19  each having the burner  30  and the combustion chamber  28 , the transition duct  17  has a generally circular inlet that interfaces with the combustor chamber  28  and an outlet in the form of an annular segment. An annular array of transition duct outlets form an annulus for channelling the combustion gases to the turbine  18 . 
     The turbine section  18  comprises a number of blade carrying discs  36  attached to the shaft  22 . In the present example, two discs  36  each carry an annular array of turbine blades  38 . However, the number of blade carrying discs could be different, i.e. only one disc or more than two discs. In addition, guiding vanes  40 , which are fixed to a stator  42  of the gas turbine engine  10 , are disposed between the stages of annular arrays of turbine blades  38 . Between the exit of the combustion chamber  28  and the leading turbine blades  38  inlet guiding vanes  44  are provided and turn the flow of working gas onto the turbine blades  38 . 
     The combustion gas  34  from the combustion chamber  28  enters the turbine section  18  and drives the turbine blades  38  which in turn rotate the shaft  22 . The guiding vanes  40 ,  44  serve to optimise the angle of the combustion or working gas  34  on the turbine blades  38 . 
     The turbine section  18  drives the compressor section  14 . The compressor section  14  comprises an axial series of vane stages  46  and rotor blade stages  48 . The rotor blade stages  48  comprise a rotor disc supporting an annular array of blades. The compressor section  14  also comprises a casing  50  that surrounds the rotor stages and supports the vane stages  48 . The guide vane stages include an annular array of radially extending vanes that are mounted to the casing  50 . The vanes are provided to present gas flow at an optimal angle for the blades at a given engine operational point. Some of the guide vane stages have variable vanes, where the angle of the vanes, about their own longitudinal axis, can be adjusted for angle according to air flow characteristics that can occur at different engine operations conditions. 
     The casing  50  defines a radially outer surface  52  of the passage  56  of the compressor  14 . A radially inner surface  54  of the passage  56  is at least partly defined by a rotor drum  53  of the rotor which is partly defined by the annular array of rotor blade stages  48 . 
     The present technique is described with reference to the above exemplary turbine engine having a single shaft or spool connecting a single, multi-stage compressor and a single, one or more stage turbine. However, it should be appreciated that the present technique is equally applicable to two or three shaft engines and which can be used for industrial, aero or marine applications. Furthermore, the cannular combustor section arrangement  16  is also used for exemplary purposes and it should be appreciated that the present technique is equally applicable to annular type and can type combustion chambers. 
     The terms axial, radial and circumferential as used hereinabove are made with reference to the rotational axis  20  of the engine, unless otherwise stated. The terms axial, radial and circumferential as used hereinafter are made with reference to the longitudinal axis  35  of the combustor chamber  28  and the burner  30  associated with the combustion chamber  28 , unless otherwise stated. 
       FIG. 2  schematically shows an exploded view of an exemplary embodiment of the combustor assembly  100  including an exemplary embodiment of the pilot burner assembly  1  of the present technique. It may be noted that the assemblies  1  and/or  100  generally may include more parts, and in  FIG. 2  only those parts or components have been depicted that are important for understanding of the present technique. 
     The combustor assembly  100 , hereinafter referred to as the assembly  100 , includes a pilot burner  60  having a burner head face  62 , a radial swirler  70  having swirler vanes  72 , generally wedge shaped or pie-slice shaped, positioned on an annular base plate  71  around the burner head face  62  for creating a swirling mix of a fuel and air, an annular closing plate  92  to which the swirler vanes  72  of the swirler  70  are attached and a combustion chamber  28  defined by a combustion casing  98 , and optionally a transition piece referred to as a pre-chamber  96  located between the swirler  70  and combustion casing  98 . The combustion chamber  28  has a diameter larger than the diameter of the pre-chamber  96 . The combustion chamber  28  is connected to the pre-chamber  96  via a dome portion (not shown) comprising a dome plate (not shown). In general, the transition piece  96  or the pre-chamber  96  may be implemented as a one part continuation of the combustion casing  98  towards the pilot burner  60 , or as a separate part between the pilot burner  60  and the combustion casing  98 . The pilot burner  60  and the combustion chamber  28  show substantially rotational symmetry about the longitudinally axis  35 . In general, the longitudinal axis  35  is the axis of symmetry for the combustor assembly  100  and its components including the pilot burner assembly  1 . As shown in  FIG. 5 , the longitudinal axis  35  passes through a center  65  (not seen in  FIG. 2 ) of the burner head face  62 . 
     In the swirler  70 , a plurality, for example twelve, of the swirler vanes  72  are arranged circumferentially spaced around annular base plate  71  so as to form, between adjacent swirler vanes  72 , slots  75 . The annular base plate  71  includes at the radially outer end of each slot  75  a base injection holes  77  by means of which main fuel is supplied to the swirler  70 . Each swirler vane  72  may additionally include at the radially outer end of a side  73  thereof one or more side injection holes  76  by means of which main fuel is also supplied to the swirler  70 . A plurality of fixing holes  78  extend through swirler vanes  72  and the base plate  71  through which the swirler vanes  72  are fixed on the base plate  71 , as shown in  FIG. 2 . Alternatively, the swirler vanes  72  may be integrally formed, i.e. as one part extension, with the base plate  71 . Generally, the base plate  11  is fixed onto an adapter plate (not shown) positioned annularly around the burner head face  62 , however the swirler  70  along with the swirler vanes  72  may be positioned for the pilot burner assembly  1  by supporting the swirler  70  on other components (not shown). 
     As seen in  FIG. 3 , each swirler vane  72  has a thin end  74  that has a radially inner position. The radially inner thin ends  74  of swirler vanes  72  are set back from a radially inner edge  79  of annular base plate  71  thereby to define an annular ledge  80  (shown in  FIGS. 3 and 4 ) immediately radially outward of edge  79 . 
     The pre-chamber  96  is cylindrical in form and may be formed integrally with annular closing plate  92  or may be attached to the annular closing plate  92  through an intermediate component (not shown). Thus, on one face of the annular closing plate  92  the swirler vanes  72  are attached, through a plurality of fixing holes  94  included in the annular closing plate  92  aligned with the fixing holes  78  of the swirler vanes  72  by using nuts and bolts (not shown), and on the other face of the annular closing plate  92  the pre-chamber  96  is integrally formed or attached through an intermediate piece (not shown). It may be noted that the assembly of the swirler  70 , the swirler vanes  72 , the annular closing plate  92  and the pre-chamber  96  shown in FIGs of the present disclosure are for exemplary purposes only and that there may be other pieces or components, such as other annular plates (not shown) that connect one component to another, for example the swirler vanes  72  may be connected or integrally formed with a top plate (not shown) which may then be connected to the annular closing plate  92 . 
     As shown in  FIGS. 2 to 4 , air is supplied to the radially outer ends of slots  75  of the swirler  70  and travels generally radially inwardly along slots  75  confined between two adjacent swirler vanes  72  on the sides, the base plate  71  at the bottom, and the face of the annular closing plate  92  facing the swirler vanes  72 . Main fuel is supplied to base injection holes  77 , and optionally to the side injection holes  76  opening in the slots  75 , so as to enter slots  75  and mix with the air travelling along slots  75 . Thus, the swirler  70  creates a swirling mix of fuel and air in an annular region immediately radially inward of the radially inner ends of slots  75 . This swirling mix travels axially along the assembly  100  to combustion chamber  28 , passing through the annular closing plate  92 , and pre-chamber  96 . 
     The pilot fuel is fed to the combustion chamber  28  through one or more pilot fuel supply lines  61 , schematically represented in  FIG. 2 , integrated in the pilot burner  60 . The pilot fuel exits the pilot burner  60 , particularly the burner head face  62  through pilot fuel injection holes  2  shown in  FIGS. 5, 6 and 8 to 12  in accordance with aspects of the present technique. The pilot fuel is a gas. 
       FIGS. 3 to 6  are now explained to provide a conventionally known arrangement of the pilot fuel injection holes  2 , which is later used, in reference to  FIGS. 7 to 12 , to explain the inventive arrangement of the pilot fuel injection holes  2  of the present technique. 
     In the conventionally known pilot fuel burners, the pilot fuel injection holes  2 , hereinafter also referred to as the holes  2 , are present at the periphery of the burner head face  62  usually positioned immediately radially inwards of the edge  79  of the base plate  71  (shown in  FIG. 2 ). In the conventional arrangement, the holes  2  are generally covered by a lip  8  as shown in  FIGS. 3, 4 and 6 . As shown in  FIGS. 4, 5 and 6 , the pilot fuel is injected from under the lip  8 , i.e. from the holes  2  present under the lip  8 , in a radially inward direction  86  towards the center  65 , i.e. towards the axis  35  as shown in  FIGS. 5 and 6 . In  FIG. 5 , the triangles formed by dotted line represent the relative position of the swirler vanes  72  with respect to the holes  2  on the burner head face  62 . 
       FIG. 6  shows a central re-circulation zone  95  formed by re-circulated hot gases  82 , relative to a direction  84  of flow of the main fuel/air and to the direction  86  of the flow of the pilot fuel from the holes  2  of the conventional arrangement. 
       FIGS. 7 to 12  have been explained hereinafter to describe the arrangement of the pilot fuel injection holes  2  on the pilot burner face  62 . The explanation of the form and the components of the pilot burner assembly  1 , the combustor assembly  100  and the gas turbine engine  1  provided in reference to  FIGS. 1 to 6  still apply for  FIGS. 7 to 12 , except the conventional arrangement of the holes  2  explained in reference to  FIGS. 3 to 6 . 
       FIGS. 7, 8 and 9  explain the inventive arrangement of the pilot fuel injection holes  2  on the pilot burner face  62  of the present pilot burner assembly  1 , the combustor assembly  100  and the gas turbine engine  1 .  FIG. 7  schematically illustrates a top view of an exemplary embodiment of the pilot burner assembly  1 , hereinafter also referred to as the burner assembly  1  of the present technique depicting the swirler  70  and the pilot burner  60 , hereinafter also referred to as the burner  60 , having the pilot burner face  62 , hereinafter also referred to as the face  62 , and an exemplary embodiment of an arrangement of pilot fuel injection holes  2 , hereinafter also referred to as the holes  2 , in accordance with aspects of the present technique.  FIG. 8  schematically illustrates the burner assembly  1  of  FIG. 7  with the swirler  70  removed for more clearly depicting the arrangement of the holes  2  on the face  62 , whereas  FIG. 9  schematically illustrates another exemplary embodiment of the burner assembly  1 . 
     As depicted in  FIGS. 7 to 9 , the burner assembly  1  has the burner  60  with the face  62  having the holes  2  for providing pilot fuel for combustion. The face  62  has a center  65 . The holes  2  are multiple in number, for example there may be twelve holes  2  in an embodiment of the burner assembly  1 , that are arranged in a symmetrical manner, for example in a circular arrangement around the center  65 . The holes  2  may also be arranged in other shapes forming two dimensional arrays, for example the arrangement of the holes  2  may be such that the holes  2  form two concentric circular shapes (not shown) around the center  65 . 
     The face  62  is generally circular and substantially fits into the opening of the annular base plate  71  of the swirler  70 . The swirler vanes  72 , shown in  FIG. 7 , arranged circumferentially with respect to the center  65 , i.e. as well as the longitudinal axis  35 , are radially disposed around the center  65 . The swirler vanes  72 , hereinafter also referred to as the vanes  72 , have pie-slice shape or tapering shape or wedge shape and thus include the thin ends  74  that are positioned radially inwards, i.e. towards the center  65 . Tips of the thin ends  74  may be imagined to be joined, as shown in  FIG. 7 , to define a region referred to as the burner region  64 . In other words, the burner region  64  results from a shape inscribed by the tips of the thin ends  74 . Joining of the tips of the thin ends  74  is advantageously performed by maintaining the general symmetry of the vanes  72 , for example since the vanes  72  are circumferentially arranged the burner region  64  defined may be circular. Similarly, the joining may also be performed by maintaining the shape and symmetry of the face  62 . The burner region  64  may be larger than the face  62  and may include the ledge  80  and the face  62 . In cases where difference in the axial distance of planes of the face  62  and the tips of the thin ends  74  is substantial, the burner region  64  may be understood as a projection along the axis  35  of the shape, i.e. circle formed of dotted line in  FIG. 7 , on a plane of the face  62 . 
     In case (not shown) the tips of some of the thin end  74  of the vanes  72  are aligned in such a way so as to be radially displaces with respect to one or more of the other vanes  72 , the burner region  64  is defined by joining the inner most of the tips of the vanes  72  maintaining the general symmetry of the swirler  70 , for example if the vanes  72  are arranged in such a way that the tips of the thin ends  74  of some of the vanes  72  form shape or region say a first circular region, whereas the tips of the thin ends  74  of the other vanes  72  form another shape or region say a second circular region, then radially inner one of the two circular regions is considered to be the burner region  64 . 
     The burner region  64  is concentric with the center  65  of the face  62 , or in other words the burner region  64  has a center which is a point on the axis  35  which in turn passes through the center  65 . 
     In the inventive arrangement of the holes  2  in the burner assembly  1 , each of the holes  2  on the face  62  is positioned within the burner region  64  such that a distance  3  of the hole  2  from the center  65  of the is equal to or less than  50  percent of a distance  4  of an edge  66  of the burner region  64  from the center  65 . The distance  3  of the holes  2  may be defined by the periphery of the lip  8  beneath which the holes  2  are arranged as shown in  FIG. 7 . The distance  3  and the distance  4  are measured along a straight line  99 , as shown in  FIGS. 8 and 9  that joins the center  65  to the edge  66  of the burner region  64 , i.e. the boundary of the geometrical shape of the burner region  64 , and also passes through the pilot hole  2 . 
       FIGS. 8 and 9  provide two ways of measuring the distance  3 . As shown in  FIG. 8  the distance  3  may be measured from the center  65  to a point on an edge (not shown) of the hole boundary (not shown) that is farthest from the center  65  and on the straight line  99 , and thus the distance  3  includes the diameter of the hole  2 , in other words includes the hole  2 . Alternatively, as shown in  FIG. 9  the distance  3  may be measured from the center  65  to a geometric center (not shown) of the hole  2 . 
     In another embodiment of the burner assembly  1 , the distance  3  is equal to or less than 30 percent of the distance  4 . In yet another embodiment of the burner assembly  1 , the distance  3  is equal to or less than 15 percent of the distance  4 . 
     As shown in  FIGS. 7 to 9 , it may be noted that the holes  2  may not be located at the center  65  of the face  62 . The holes  2  may be located in the vicinity of the center  65  compared to the edge  66  of the burner region  64  albeit not at the center  65 . In one embodiment of the burner assembly  1 , the distance  3  is equal to or greater than 5 percent of the distance  4 . In another embodiment of the burner assembly  1 , the distance  3  is equal to or greater than 10 percent of the distance  4 . 
     As shown in  FIGS. 7 to 9  in combination with  FIG. 10 , the holes  2  of the burner assembly  1  of the present technique provide pilot fuel in a radially outwards direction  88 , i.e. directed away from the center  65  or the axis  35 , as compared to the holes  2  of a prior art burner assembly wherein the holes  2  provide pilot fuel in a radially inwards direction  86  i.e. directed towards the center  65  or the axis  35 , as shown in  FIGS. 4 to 6 . As shown in  FIG. 10 , the radially outwards direction  88  forms an angle  5  with the face  62 . The angle  5  is between 30 degrees and 90 degrees, and advantageously between 30 degrees and 60 degrees. All the holes  2  may provide pilot fuel in such a way that the angle  5  is equal or substantially equal for all the holes  2 . It should be appreciated that a centre-line of the holes  2  of the burner assembly  1  are in the radially outwards direction  88 , such that fuel immediately issuing from the holes  2  is in the direction  88 . Further, the fuel will tend to diverge in a general cone shape after exiting the holes; however, the bulk direction of the fuel is at least initially in the direction  88 . The direction  88  is not intended to indicate the direction  88  plus the divergent cone angle. 
     Alternatively, as shown in  FIG. 10 , in one embodiment of the burner assembly  1 , the plurality of the holes  2  may include two or more types of holes  2  depending on the angle  5  formed by the pilot fuel ejected from them, for example the plurality of the holes  2  may include one or more of a first pilot fuel injection hole  6  and one or more of a second pilot fuel injection hole  7 . The first pilot fuel injection hole  6  and the second pilot fuel injection hole  7 , both provide pilot fuel in the radially outwards direction  88  but at different angles  58 , 59 , respectively, for example the angle  58  may be 60 degrees whereas the angle  59  may be 45 degrees. 
       FIGS. 11 and 12  depict two exemplary embodiments of the burner assembly  1  with respect to the combustion chamber  28 , during an operation of the gas turbine engine  10 , and may be compared with  FIG. 6  that represents the operation of a prior art pilot burner with respect to the pilot fuel injection into the combustion chamber  28 . As depicted in  FIGS. 11 and 12 , the central recirculation zone  95  formed around the axis  35  continuous with or very close to the face  62 , but not extending through the entire area of the face  62 . The pilot fuel in this condition is injected directly into the central recirculation zone  95  because of the positioning of the holes  2  in the burner assembly  1  of the present technique, i.e. because the holes  2  are closer to the center  65  in the burner assembly  1  of the present technique as compared to the holes  2  of the prior art pilot burner. As shown in  FIG. 12 , the holes  2  may be formed angularly with the face  62  so that the injection of the pilot fuel is at the angle  5  or may be covered or positioned under a substructure (not shown) integral with the face  62  such that the pilot fuel when exiting the substructure acquires the angle  5 . 
     The present burner assembly  1  having the arrangement of the holes  2  on the face  62  described hereinabove with respect to  FIGS. 7 to 12  may be included in the combustor assembly  100  of  FIG. 2 , by aligning the burner assembly  1  in the combustor assembly  100  in such a way that the center  65  of the face  62  of the pilot burner  60  is aligned on the axis  35 , i.e. the axis  35  passes through the center  65 . The combustor assembly  100  having the burner assembly  1  may be included in the gas turbine engine  10  of  FIG. 1 . It may be noted that the shape of the holes  2  in the present disclosure has been shown as circular for exemplary purposes only and other shapes of the holes  2 , for example an oblong shape of the holes  2 , is well within the scope of the present technique. 
     While the present technique has been described in detail with reference to certain embodiments, it should be appreciated that the present technique is not limited to those precise embodiments. It may be noted that, the use of the terms ‘first’, ‘second’, etc. does not denote any order of importance, but rather the terms ‘first’, ‘second’, etc. are used to distinguish one element from another. Rather, in view of the present disclosure which describes exemplary modes for practicing the invention, many modifications and variations would present themselves, to those skilled in the art without departing from the scope and spirit of this invention. The scope of the invention is, therefore, indicated by the following claims rather than by the foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.