Patent Publication Number: US-2017370590-A1

Title: Fuel nozzle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation of U.S. patent application Ser. No. 14/505,765 filed Oct. 3, 2014, the entire content of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The application relates generally to gas turbines engines combustors and, more particularly, to fuel nozzles. 
     BACKGROUND OF THE ART 
     Gas turbine engine combustors employ a plurality of fuel nozzles to spray fuel into the combustion chamber of the gas turbine engine. The fuel nozzles atomize the fuel and mix it with the air to be combusted in the combustion chamber. The atomization of the fuel and air into finely dispersed particles occurs because the air and fuel are supplied to the nozzle under relatively high pressures. The fuel could be supplied with high pressure for pressure atomizer style or low pressure for air blast style nozzles providing a fine outputted mixture of the air and fuel may help to ensure a more efficient combustion of the mixture. Finer atomization provides better mixing and combustion results, and thus room for improvement exists. 
     SUMMARY 
     In one aspect, there is provided a fuel nozzle for a combustor of a gas turbine engine, the fuel nozzle comprising: a body defining an axial direction and a radial direction; an air passageway defined axially in the body; a fuel passageway defined axially in the body radially outwardly from the air passageway, the fuel passageway having an outer wall including an exit lip at a downstream portion of the outer wall, the exit lip having a surface treatment including a swirl-inducing relief. 
     In another aspect, there is provided a gas turbine engine comprising: a combustor; and a plurality of fuel nozzles disposed inside the combustor, each of the fuel nozzles including: a body defining an axial direction and a radial direction; an air passageway defined axially in the body; a fuel passageway defined axially in the body radially outwardly from the air passageway, the fuel passageway having an outer wall including an exit lip at a downstream portion of the outer wall, the exit lip having a surface treatment including a swirl-inducing relief configured to induce swirl to at least one of pressurised air exiting the air passageway and pressurised fuel exiting the fuel passageway. 
     In a further aspect, there is provided a method of inducing swirl in at least one of pressurised fuel and air exiting a fuel nozzle of a gas turbine engine, the method comprising: carrying pressurised air through an air passageway in the fuel nozzle and carrying pressurised fuel through a fuel passageway disposed radially outwardly from the air passageway in the fuel nozzle; and directing the pressurised fuel and the pressurised air through a swirl-inducing relief formed on an exit lip of the fuel passageway and inducing swirl in at least one of the pressurised air and the pressurised fuel, the exit lip being disposed at a downstream portion of an outer wall of the fuel passageway. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG. 1  is a schematic cross-sectional view of a gas turbine engine; 
         FIG. 2  is a partial schematic cross-sectional view of a first embodiment of a nozzle for a combustor of the gas turbine engine of  FIG. 1 ; 
         FIG. 3  is a partial schematic cross-sectional view of a second embodiment of a nozzle for the combustor of the gas turbine engine of  FIG. 1 ; and 
         FIGS. 4A to 4D  are schematic views of vanes for the nozzle of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a gas turbine engine  10  of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan  12  through which ambient air is propelled, a compressor section  14  for pressurizing the air, a combustor  16  in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section  18  for extracting energy from the combustion gases. The gas turbine engine  10  has one or more fuel nozzles  100  which supply the combustor  16  with the fuel which is combusted with the air in order to generate the hot combustion gases. The fuel nozzle  100  atomizes the fuel and mixes it with the air to be combusted in the combustor  16 . The atomization of the fuel and air into finely dispersed particles occurs because the air and fuel are supplied to the nozzle  100  under relatively high pressures. The fuel could be supplied with high pressure for pressure atomizer style or low pressure for air blast style nozzles providing a fine outputted mixture of the air and fuel may help to ensure a more efficient combustion of the mixture. The nozzle  100  is generally made from a heat resistant metal or alloy because of its position within, or in proximity to, the combustor  16 . 
     Turning to  FIG. 2 , a first embodiment of the fuel nozzle  100  will now be described. 
     The nozzle  100  includes generally a cylindrical body  102  defining an axial direction A and a radial direction R. The body  102  is at least partially hollow and defines in its interior a primary air passageway  103  (a.k.a. core air), a secondary air passageway  104  and a fuel passageway  106 , all extending axially through the body  102 . 
     The primary air passageway  103 , the secondary air passage  104  and the fuel passageway  106  are aligned with a central axis  110  of the nozzle  100 . The fuel passageway  106  is disposed concentrically between the primary air passageway  103  and the secondary air passageway  104 . The secondary air passageway  104  and the fuel passageway  106  are annular. It is contemplated that the nozzle  100  could include more than one primary and secondary air passageways  103 ,  104  and that the primary and secondary air passageways  103 ,  104  could have a shape of any one of a conduit, channel and an opening. The size, shape, and number of the air passageways  103 ,  104  may vary depending on the flow requirements of the nozzle  100 , among other factors. Similarly, although one annular fuel passageway  106  is disclosed herein, it is contemplated that the nozzle  100  could include a plurality of fuel passageways  106 , annular shaped or not. 
     The body  102  includes an upstream end (not shown) connected to sources of pressurised fuel and air and a downstream end  114  at which the air and fuel exit. The terms “upstream” and “downstream” refer to the direction along which fuel/air flows through the body  102 . Therefore, the upstream end of the body  102  corresponds to the portion where fuel/air enters the body  102 , and the downstream end  114  corresponds to the portion of the body  102  where fuel/air exits. 
     The primary air passageway  103  is cylindrical and defined by outer wall  103   b . The primary air passageway  103  carries pressurised air illustrated by arrow  116 . The air  116  will be referred interchangeably herein to as “air”, “core flow of air”, “jet of air”, or “flow of air”. The outer wall  103   b  is shown straight but it is contemplated that it could be wavy or have grooves or protrusions to induce swirl. By “swirl”, one should understand any non-streamlined motion of the fluid, e.g. chaotic behavior or turbulence. The primary air passageway  103  ends at exit end  115 . 
     The secondary air passageway  104  is defined by inner wall  104   a  and outer wall  104   b . The secondary passageway  104  could be wavy or leave protrusions or grooves to induce swirl. The secondary air passageway  104  carries pressurised air illustrated by arrow  118 . The air  118  will be referred interchangeably herein to as “annular film of air”, “flow of air”, “flow”, or “air”. 
     The fuel passageway  106  is defined by inner wall  106   a  and outer wall  106   b . The fuel passageway  106  carries pressurised fuel illustrated by arrow  119 . The fuel  119  will be referred interchangeably herein to as “fuel film”, or “fuel”. The inner wall  106   a  ends with the exit end  115  of the primary air passageway  103 , while the outer wall  106   b  extends downstream relative to the inner wall  106   a . The outer wall  106   b  of the fuel passage  106  is defined at the downstream end  114  by a first axial portion  120 , a second converging portion  122  extending from a downstream end  126  of the axial portion  120 , and a third axial portion  124  extending from a downstream end  128  of the converging portion  122 . The third axial portion  124  forms an exit lip  127  of the nozzle  100  through which the fuel  119  is expelled into the combustor  16 . The exit lip  127  is disposed downstream from the exit end  115  of the primary air passageway  103 . A diameter D 1  of the outer wall  106   b  at the third axial portion  124  is slightly bigger than a diameter D 2  of the outer wall  103   b  of the primary air passageway  103 . 
     The secondary air passageway  104  and the fuel passage  106  are typically convergent (i.e. its cross-sectional area may decrease along its length, from inlet to outlet) in the downstream direction at the downstream end  114 . The outer wall  106   b  of the fuel passageway  106  converging at the downstream end  114  forces the annular fuel film  119  expelled by the fuel passageway  106  onto the jet of air  116  from primary air passageway  103 . Similarly, the outer wall  104   b  of the secondary air passageway  104  are converging at the downstream end  114 , thereby forcing the annular film of air  118  expelled by the secondary air passageway  104  onto the annular film of fuel expelled by the fuel passageway  106 . At the downstream end  114 , the annular fuel film  119  is impacted by the core flow of air  116  of the primary air passageway  103  and the annular flow of air  118  of the secondary air passageway  104 . The flows  116 ,  118  having different velocities than the fuel  119  shear the fuel  119  and facilitate its break down into droplets (i.e. atomization). 
     The second converging portion  122  and the third axial portion  124  (i.e. exit lip  127 ) have a surface treatment including a swirl-inducing relief in the shape of a plurality of grooves  130 . The grooves  130  define a plurality of ridges  131  between them. The ridges  131  form transitions in the outer wall  106   b  and induce swirl in the core flow of air  116  as it exits the air passageway  103 . The grooves  130  induce a swirl in the annular fuel film  119  as it exits the first axial portion  120  of the fuel passage  106  and gets in contact with the core flow of air  116 . The grooves  130  are formed in the third axial portion  124  up to a downstream end  132  of that portion (i.e. downstream end of exit lip  127 ). In the embodiment shown in the Figures, the grooves  130  are circumferential, helicoidal and of round cross-section. It is contemplated that the grooves  130  could have various shapes, for example, the grooves  130  could be axial, circular, of a rectangular cross-section, or of a triangular cross-section. The grooves  130  could be more or less thick. The grooves  130  could even be replaced by ridges (or various protrusions). An example of said protrusion is shown and described in  FIG. 3 . It is contemplated that the grooves  130  could be disposed only on the third axial portion  124  or on a downstream portion thereof. It is also contemplated that the grooves  130  could be disposed on the third axial portion  124  and on a portion of the second converging portion  122 . The grooves  130  could be continuous or discontinuous. 
     By inducing swirl to the fuel film  119 , turbulence or a chaotic behavior to the fuel film  119  develops as the fuel film exits the lip  127 . A thickness of the fuel film  119  may thus be reduced, and in turn mixing of the fuel  119  with the air  116 ,  118  from the primary and secondary air passageways  103 ,  104  is increased. The increase of the mixing may reduce a size of the droplets of fuel formed, favours atomization, and as a result enhances combustion. In addition, the ridges  131  define relatively sharp edges of the outer wall  106   b  and may act as fuel atomization sites, which in turn may increase a number of the available atomization sites for the fuel to enhance combustion compared to if the grooves  130  were not present. 
     The grooves  130  may be easily machined into the nozzle  100 . They may allow to improve the nozzle atomization performance without changing the nozzle overall geometrical envelope or altering the nozzle air-distribution. 
     Turning now to  FIG. 3 , a second embodiment of a fuel nozzle  200  will be described. 
     The nozzle  200  includes generally a cylindrical body  202  defining an axial direction A and a radial direction R. The body  202  is at least partially hollow and defines in its interior a primary air passageway  203  (a.k.a. core air), a secondary air passageway  204  and a fuel passageway  206 , all extending axially through the body  202 . 
     The primary air passageway  203 , the secondary air passage  204  and the fuel passageway  206  are axially defined in the body  202 . The fuel passageway  206  is disposed concentrically between the primary air passageway  203  and the secondary air passageway  204 . The secondary air passageway  204  and the fuel passageway  206  are annular. It is contemplated that the nozzle  200  could include more than one secondary air passageway  204  and that the secondary air passageway  204  could have a shape of any one of a conduit, channel and an opening. The size, shape, and number of the fuel passageway  206  and air passageways  203 ,  204  may vary depending on the flow requirements of the nozzle  200 , among other factors. 
     The body  202  includes an upstream end (not shown) connected to sources of pressurised fuel and air and a downstream end  214  at which the air and fuel exit. The terms “upstream” and “downstream” refer to the direction along which fuel/air flows through the body  202 . Therefore, the upstream end of the body  202  corresponds to the portion where fuel/air enters the body  202 , and the downstream end  214  corresponds to the portion of the body  202  where fuel/air exits. 
     The primary air passageway  203  is defined by outer wall  203   b . The primary air passageway  203  carries pressurised air illustrated by arrow  216 . The air  216  will be referred interchangeably herein to as “air”, “core flow of air”, or “jet of air”. The outer wall  203   b  is shown straight but it is contemplated that it could be wavy or have grooves or protrusions to induce swirl. The primary air passageway  203  ends at exit end  215 . 
     The secondary air passageway  204  is defined by an inner wall and an outer wall (not shown), and has a plurality of round exits  204   c . The secondary air passageway  204  carries pressurised air illustrated by arrow  218 . The air  218  will be referred interchangeably herein to as “flow of air”, or “air”. 
     The fuel passageway  206  is defined by inner wall  206   a  and outer wall  206   b . The fuel passageway  206  carries pressurised fuel illustrated by arrow  219 . The fuel  219  will be referred interchangeably herein to as “fuel film”, or “fuel”. The inner wall  206   a  is wavy. It is contemplated that the fuel passageway  206  could be straight or have various swirl-inducing reliefs on either or both of the inner wall  206   a  or outer wall  206   b . The outer wall  206   b  of the fuel passage  206  includes a first axial portion  220 , a second converging portion  222  extending from a downstream end  226  of the axial portion  220 , and a third axial portion  224  extending from a downstream end  228  of the converging portion  222 . The third axial portion  224  forms an exit lip  227  of the nozzle  200 . The exit lip  227  is disposed downstream from the exit end  215  of the primary air passageway  203 . A diameter D 21  of the outer wall  206   b  at the third axial portion  224  is slightly bigger than a diameter D 22  of the outer wall  203   b  of the primary air passageway  203 . 
     The fuel passageway  206  is typically convergent (i.e. its cross-sectional area may decrease along its length, from inlet to outlet) in the downstream direction at the downstream end  214 , thereby forcing the annular film of fuel  219  expelled by the fuel passageway  206  onto the jet of air  216  of the primary air passageway  203 . At the downstream end  214 , the annular film of fuel  219  is impacted by the core flow of air  216  of the primary air passageway  203  and the annular flow of air  218  of the secondary air passageway  204 . 
     The exit lip  227  of the fuel passageway  206  has a surface treatment including a swirl-inducing relief in the form of a plurality of vanes  230  disposed in a circumferential array at a downstream end  232  of the exit lip  227 . The vanes  230  extend radially inwardly from the outer wall  206   b  at the exit lip  227  toward the axial axis A. 
     Referring to  FIGS. 4A to 4D  each of the vanes  230  includes a pin  240  and an airfoil portion  242  extending downstream from the pin  240 . The pin  240  has a generally circular cross-section. The vanes  230  are impacted by the air  216  from the primary air passageway  203  and the fuel film  219  from the fuel passageway  206 . The primary air passageway  203  being disposed concentrically inside the fuel passageway  206 , a first portion  246  of the vane  230  is impacted by fuel  219  only and a second portion  248  of the vane  230  is impacted by air  216  only. The pin  240  has a radial height H 1  bigger than a radial height H 2  of the airfoil portion  242 . As best shown in  FIG. 4B , in one embodiment, a transition between the radial height H 1  and the radial height H 2  is smooth (i.e. curved). The radial height H 2  may be chosen to correspond to a radial height at which the vane  230  is impacted by fuel  219  only. As a result, the first portion  246  of the vane  230  impacted by fuel  219  only includes a lower portion  240   a  of the pin  240  and the airfoil portion  242 . The second portion  248  of the vane  230  impacted by air only includes an upper portion  240   b  of the pin  240  only (i.e. no airfoil portion  242 ). A virtual separation between the air  216  and the fuel  219  impacting the vane  230  is illustrated by wavy line  249  in  FIG. 4B . An orientation of the vanes  230  may be set to match a fuel injection angle. 
     Having a different structure of the vane  230  depending whether it is affected by air  216  or fuel  219 , allows to modulate the effect of the vane  230  on the air  216  and fuel  219 . In the example shown in the figures, the circular cross-section of the pin  240  induces turbulence and recirculation/swirl (indicated by arrow  251 ) downstream of the pin  240  (see  FIG. 4D ). The turbulence may enhance atomization of the fuel  219 . The airfoil portion  242 , however, having a streamlined shape, boundary layer and turbulence are minimized. Recirculation of the fuel  219  may be avoided to favor fuel velocity increase and thus shear between the air  216  and the fuel film  219 . Minimizing the recirculation zone of the fuel  219  may also prevent coking. 
     The vanes  230  could have various shapes. For example, the airfoil portion  242  could be omitted, or the pin  240  could have a same radial height as the airfoil portion  242 . The vanes  230  could also be designed independently of the virtual separation  249  between the air  216  and the fuel film  219 . The vanes  230  could also induce turbulence in both the fuel  219  and the air  216 . There could be more than one row of vanes  230 , and the vanes  230  may not be disposed circumferentially. 
     The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.