Patent Publication Number: US-11041624-B2

Title: Fuel spray nozzle for a gas turbine engine

Description:
FIELD OF DISCLOSURE 
     The present disclosure concerns a fuel spray nozzle for a gas turbine engine. 
     BACKGROUND TO THE INVENTION 
     In a gas turbine engine, fuel is mixed with air prior to delivery into a combustion chamber where the mixture is ignited. Arrangements for mixing the fuel and air vary. In prefilming arrangements, fuel is formed in a film along a prefilmer surface adjacent to a nozzle. Pressurised, turbulent air streams are directed against the prefilmer surface and serve to shear fuel from the surface and mix the sheared fuel into the turbulent air streams. In vaporiser designs fuel is forced through a small orifice into a more cavernous air filled chamber. The sudden pressure drop and acceleration of the fuel flow upon entering the chamber disperses the fuel into a spray. High temperatures subsequently vaporise the fuel. Turbulent air flows in the chamber again encourage mixing. 
     Both methods have associated advantages and disadvantages. Prefilming fuel injectors have highly complex and intricate designs that are expensive to manufacture. Design iterations are slow, due to complexity of the manufacturing process. Whilst relatively simple in design and generally cheaper in manufacture, vaporiser fuel injectors provide inferior fuel preparation when compared to prefilming fuel injectors thereby resulting in inferior engine performance. 
     It is desirable to provide a fuel injector which is simple in construction but has improved performance over prior art vaporiser designs. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention there is provided a fuel spray nozzle comprising a fuel injector and an air swirler and having the configuration as described in Claim  1 . The fuel injector component comprises a fuel passage having at least one inlet and at least one outlet, the outlet is configured for accelerating fuel exiting the fuel passage and ejecting a jet of fuel. The jet is directed in crossflow across a stream of relatively high velocity air exiting a swirl passage of a radially adjacent air swirler. The air swirler is arranged outboard of the fuel injector and comprises one or more passages that terminate in a single outlet chamber in which the fuel passage outlet(s) of the fuel injector sits. 
     Jet in crossflow′ is an airblast technique, in that the energy for atomisation is primarily provided by the airstream. It has some advantages over pre-filming injectors; the fuel is rapidly distributed over a range of radii, giving an opportunity for improved fuel/air mixing; and the mechanical design of the injector is simpler, permitting a reduction in manufacturing cost. 
     Desirably the fuel passage outlet and the air swirler outlet chamber are substantially axially coincident such that the jet is injected into the air stream after the air has been maximally accelerated and swirled in the swirler passages. This is assisted by walls of the swirler passages being radially convergent in a manner which directs the exiting air flow towards the fuel passage outlet to encourage mixing of the fuel and air in the outlet chamber and minimise filming of fuel on walls of the air swirler. The configuration ensures maximal atomisation of the fuel as it joins the relatively high velocity air stream. 
     The terms axial and radially herein are intended to refer to an axial centre-line passing through the air swirler and a radius around the axial centre-line. 
     Embodiments of the invention now described are configured in a jet in crossflow style of fuel spray nozzle. 
     In embodiments of the invention, the fuel outlet and the outlet chamber of the air swirler are positioned with respect to each other to maximise vaporisation of the fuel as it meets the air. The velocity and swirl imparted to the air in the swirler passages further assists in efficient mixing of the fuel and air on route to the combustion chamber. Optimal results can be achieved in part by optimising the angle of injection of the jet of fuel with respect to the direction at which the air exits a swirler passage and/or by the relative axial position of the fuel passage outlet relative to a terminus of the one or more swirler passages. 
     It will be appreciated that walls of the air swirler passages influence the predominant flow direction of an air stream exiting the swirler passages. The fuel passage outlet and walls of the swirler passages are directed towards each other so as to create a collision of the fuel and air streams which is within an optimum angle range (the vertex of the angle being downstream from the fuel outlet). The optimum angle is such that the fuel penetrates as far as possible across the radially adjacent swirl passage, without excessive impingement on the prefilming surface or any impingment on the outer wall of radially distal swirl passages. 
     For example, the optimum angle range is 30 to 150 degrees. More preferably, the range is 60 to 150 degrees, for example between about 90 and 130 degrees. The optimum arrangement may be influenced by factors such as the flow rate of the air and fuel at their outlets. The optimum angle range ensures that the mix of fuel with air in the air swirler outlet chamber is maximised and the amount of fuel crossing to a wall of the air swirler minimised. 
     Any fuel not picked up in the cross flow may collect on a prefilming surface which forms part of the air swirler or fuel injector. For example, the prefilmer surface is in the form of a cone of the fuel passage which extends and converges in a direction downstream from the fuel outlet. Alternatively the prefilmer may be a radially inwardly facing surface of the air swirler. 
     The fuel passage may have an annular configuration. The fuel passage may comprise a plurality of outlets symmetrically arranged around an annulus. Additional fuel circuits may be arranged inboard of the air swirler within the fuel injector to permit staging of the engine. Optionally the additional fuel circuits are annularly arranged. 
     The air swirler may be nominally concentrically arranged with respect to the fuel passage. 
     Optionally, a separate seal component is arranged between the air swirler and the fuel passage and is configured to allow radial and/or angular and/or axial movement between the air swirler and fuel passage. The seal may be configured to allow controlled leakage flow (for example specific metered flow) to pass through the passage between the fuel passage and air swirler. 
     In some embodiments, the fuel spray nozzle further comprises a non-swirling air jet. The air jet supply passage can pass axially through an annularly arranged fuel passage. In other embodiments the air passage may be annular and arranged outboard of the fuel passage. The air jet is advantageous in preventing a recirculating vortex from penetrating into the fuel spray nozzle thereby reducing carbon deposition on, and aerodynamic blocking of, the nozzle exit. 
     In some embodiments the fuel passage is protected from the ambient air by means of one or more cavities filled with stagnant air that acts as an insulating layer. These cavities can be configured to protect the fuel from heat flowing from the air in the air swirler, between the air swirler and fuel injector, or from any other air passage built into the fuel injector. 
     Upstream of the single outlet, the air swirler may comprise one or more air passages (which may optionally be convergent), extending annularly which include vanes configured to impart swirl on transmitted air. These passages may be configured to drive an axial flow or a radial flow, or a flow in any combination of these directions. Multiple convergent air passages may be aligned to have axial overlap, the outer radial wall of a first convergent passage forming a radially inner wall of an adjacent, upstream convergent passage. The vanes can be arranged to extend between the radially outer and radially inner walls of the converging passage, being exposed beyond the downstream edge of the most upstream radially outer wall. 
     At the upstream edge, the walls of the convergent air passages can be arched or undulated such that the length from the outlet chamber to the upstream edge is variable around the radial outer wall. The arches can be uniform. Where two or more convergent passages are provided with undulations, the radially outer walls of the passage may be arranged at different angular rotations relative to each other. The leading edges of the vanes connecting adjacent annular structures can be arched or inclined. Such a configuration is well suited to manufacture using additive layer manufacturing (ALM) techniques, for example direct laser deposition (DLD). The ability to use such manufacturing techniques provides greater flexibility in design of vane and passage shapes, allowing these shapes to be optimised to enhance aerothermal performance. By optimising vane and passage configurations to provide high intensity air turbulence and speed, the efficient atomisation of fuel into a fine spray with substantially uniform droplet size distribution can be achieved. The air swirler outlet and convergent air passages can be provided with a throat profile which is configured to control the cone angle of the exiting air. Achievable results can be comparable to or even exceed the atomisation provided by complex prefilmer arrangements. 
     EP2772688 discloses one embodiment of an air swirler suitable for use in embodiments of the fuel spray nozzle of the invention. 
     It will be appreciated that as well as shape, the number of vanes and passages can also be varied to suit requirements without departing from the scope of the claimed invention. 
     The described arrangement is relatively insensitive in terms of effective area with respect to axial, radial and angular movement between the fuel injector (which comprises the fuel passage and outlet) and the air swirler. Thus the fuel injector and air swirler can be mounted independently. 
     The separation of the fuel injector from the air swirler reduces the complexity and the cost of the manufacturing process compared to prior art prefilmer design. 
     The position of the fuel injector within the air swirler means that the air swirler can be combustor-mounted, reducing stress within both the combustion module casing and the fuel injector and thereby reduces the requisite size, aerodynamic drag, cost and weight of the fuel spray nozzle and combustion module casing compared to prior art arrangements. 
     The nozzle may further incorporate a thermal management system. A thermal management system might comprise a cooling circuit and/or a heat shield. In some embodiments an integral heat shield may extend radially outwardly from the outlet to provide an axially upstream facing heat shield surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described by way of example only, with reference to the Figures, in which: 
         FIG. 1  is a sectional side view of a gas turbine engine; 
         FIG. 2  is a section of a fuel spray nozzle in accordance with a first embodiment of the invention, showing the air swirler, fuel injector and (optional) seal components; 
         FIG. 3  is a section of a fuel spray nozzle in accordance with a second embodiment of the invention, showing the air swirler, fuel injector and (optional) seal components; 
         FIG. 4  is a section of a fuel spray nozzle in accordance with a third embodiment of the invention, showing the air swirler, fuel injector and (optional) seal components; 
         FIG. 5  is a section of a fuel spray nozzle in accordance with a fourth embodiment of the invention, showing the air swirler, fuel injector and (optional) seal components and combustor heat shield; 
         FIG. 6  shows an example of an air swirler configuration suitable for use in fuel spray nozzles in accordance with the invention; 
         FIG. 7  shows the interaction of air flowing from a swirler passage and fuel flowing from a fuel injector in an embodiment of a fuel spray nozzle in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION 
     With reference to  FIG. 1 , a gas turbine engine is generally indicated at  10 , having a principal and rotational axis  11 . The engine  10  comprises, in axial flow series, an air intake  12 , a propulsive fan  13 , an intermediate pressure compressor  14 , a high-pressure compressor  15 , combustion equipment  16 , a high-pressure turbine  17 , and intermediate pressure turbine  18 , a low-pressure turbine  19  and an exhaust nozzle  20 . A nacelle  21  generally surrounds the engine  10  and defines both the intake  12  and the exhaust nozzle  20 . 
     The gas turbine engine  10  works in the conventional manner so that air entering the intake  12  is accelerated by the fan  13  to produce two air flows: a first air flow into the intermediate pressure compressor  14  and a second air flow which passes through a bypass duct  22  to provide propulsive thrust. The intermediate pressure compressor  14  compresses the air flow directed into it before delivering that air to the high pressure compressor  15  where further compression takes place. 
     The compressed air exhausted from the high-pressure compressor  15  is directed into the combustion equipment  16  where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines  17 ,  18 ,  19  before being exhausted through the nozzle  20  to provide additional propulsive thrust. The high  17 , intermediate  18  and low  19  pressure turbines drive respectively the high pressure compressor  15 , intermediate pressure compressor  14  and fan  13 , each by suitable interconnecting shaft. 
     In  FIGS. 2 to 5 , embodiments of the invention have an axis passing centrally through the fuel passage with the air swirler arranged radially outboard of the axis. 
     In  FIG. 2 , a fuel passage  1  extends to form an annular fuel channel having fuel outlet ports  1   a . Air swirler  3  is coaxially aligned and radially outboard of the annular fuel channel wherein swirl passages  4  converge to a common outlet chamber  5 . It is to be noted that the outlet ports  1   a  are directed at an angle which is between the co-axial centre-line and a radius of the air swirler  3 . Furthermore, the outlet is arranged to substantially coincide with outlet chamber  5  of the air swirler  3 . Thus, a jet of fuel exiting the fuel injector by outlet  1   a  is directed in cross-flow with air exiting an air swirler passage  4  and entering outlet chamber  5 . An annular cavity  2  (for example containing stagnant air or another insulator) surrounds the fuel passage  1  and serves as a heat shield. Optional seal components  8   a  and  8   b  sit between the annular fuel channel and swirler  3 . The seal components  8   a ,  8   b  ensure air is predominantly directed through the air swirler  3  and inside the radially outer annular chamber. As can be seen, male and female parts of the seal components  8   a ,  8   b  engage in a radial direction, however, they are not locked in position, radial space between walls of the male and female parts allow radial movement of the swirler  3  relative to the fuel injector  1 . Axial and angular movement is allowed for by sliding or rotation of the fuel injector inside the air swirler. For this purpose, a spherical section is included on the body of the fuel injector, which is free to slide inside the interfacing cylindrical section of the air swirler. 
     The swirler comprises annular channels  4  crossed by swirl vanes  3   a . The channels  4  converge to a common outlet chamber  5 . 
     Referring now to  FIG. 3 , a fuel spray nozzle comprises a centrally arranged fuel injector passage  31  having an outlet  31   a . An annular space  32  is radially adjacent the fuel injector passage  31  and serves as a heat shield. Arranged coaxially with the fuel injector passage  31  at the outlet  1   a  end, is an air swirler  33  comprising coaxially arranged swirler passages  34  converging towards a common outlet chamber  35  which sits adjacent the fuel passage outlet  31   a . It is to be noted that the outlet ports  31   a  are directed at an angle which is between the co-axial centre-line and a radius of the air swirler  33 . Furthermore, the outlet is arranged to substantially coincide with outlet chamber  35  of the air swirler  33 . Thus, a jet of fuel exiting the fuel injector by outlet  31   a  is directed in cross-flow with air exiting an air swirler passage  34  and entering outlet chamber  35 . An annular wall  36  between the air swirler  33  and the fuel passage  31  channels non swirling air towards a centrally arranged air jet outlet  37 . Optional seal components  38   a ,  38   b  ensure air is predominantly directed through the air swirler  33  and inside the chamber  36   a  defined by the annular wall  6  towards the air jet outlet  37 . An optional integrated cooling system is associated with the nozzle and has cooling air inlets  34   a  and outlets  34   b.    
     Air swirler  33  comprises coaxially aligned air passages  34  having inlets  34   a  which converge towards a common outlet chamber  35 . Swirler vanes  33   a ,  33   b  extend between walls of coaxially adjacent passages  34 . 
     In  FIG. 4 , a fuel passage  41  extends to form an annular fuel channel having fuel outlet ports  41   a . A non-swirling air passage  46   a  passes through the centre of the annular fuel channel and has an outlet  47 . It is to be noted that the outlet ports  41   a  are directed at an angle which is between the co-axial centre-line and a radius of the air swirler  43 . Furthermore, the outlet is arranged to substantially coincide with outlet chamber  45  of the air swirler  43 . Thus, a jet of fuel exiting the fuel injector by outlet  41   a  is directed in cross-flow with air exiting an air swirler passage  44  and entering outlet chamber  45 . Air swirler  43  is coaxially aligned and radially outboard of the annular fuel channel wherein swirl passages  44  converge to a common outlet chamber  45 . An annular heat shield surrounds the fuel passage  41 . Optional seal components  48   a  and  48   b  sit between the annular fuel channel and swirler  4  downstream of the entrance to non-swirling air channel  46   a . An annular void space  42  is radially adjacent the fuel injector passage  41  and serves as a heat shield. 
     In  FIG. 5 , an annular fuel passage  51  sits centrally of the nozzle. An air swirler  53  is arranged coaxially with the annular fuel passage  51  and converges to a chamber  55  immediately downstream of the passage  51  outlet  51   a . It is to be noted that the outlet ports  51   a  are directed at an angle which is between the co-axial centre-line and a radius of the air swirler  53 . Furthermore, the outlet is arranged to substantially coincide with outlet chamber  55  of the air swirler  53 . Thus, a jet of fuel exiting the fuel injector by outlet  51   a  is directed in cross-flow with air exiting an air swirler passage  54  and entering outlet chamber  55 . A downstream facing combustor heat shield  52  extends from a downstream end of the swirler in a radially divergent manner. The heat shield  52  could be inclined or perpendicular to the central axis of the fuel injector, and could be of any shape. This heat shield could be cooled (for example but without limitation) by impingement of air on the cold side, effusion of air from the hot side or a combination of these. 
       FIG. 6  shows an air swirler suitable for use in a nozzle in accordance with the invention. The swirler has an axis Y and comprises a first swirler  64 , a second swirler  66  and an additional swirler  68 . The first swirler  64  comprises a plurality of vanes  70 , a first member  72  and a second member  74 . The second member  74  is arranged coaxially around the first member  72  and the vanes  70  extend radially between the first and second members  72  and  74 . The vanes  70  have leading edges  76  and the second member  74  has an upstream end  78 . The leading edges  76  of the vanes  70  extend with radial and axial components from the first member  72  to the upstream end  78  of the second member  74  and the radially outer ends  80  of the leading edges  76  of the vanes  70  form arches  82  with the upstream end  78  of the second member  74 . In particular the leading edges  76  of the vanes  70  extend with axial downstream components from the first member  72  to the upstream end  78  of the second member  74 . 
     The second swirler  66  comprises a plurality of vanes  84  and a third member  86 . The third member  86  is arranged coaxially around the second member  74 . The vanes  84  of the second swirler  66  extend radially between the second and third members  74  and  86 . The vanes  84  of the second swirler  66  have leading edges  88  and the third member  86  has an upstream end  90 . The leading edges  88  of the vanes  84  of the second swirler  66  extend with radial and axial components from the upstream end  78  of the second member  74  to the upstream end  90  of the third member  86  and the radially outer ends  92  of the leading edges  88  of the vanes  84  of the second swirler  66  form arches  94  with the upstream end  90  of the third member  86 . In particular the leading edges  88  of the vanes  84  extend with axial downstream components from the upstream end  78  of the second member  74  to the upstream end  90  of the third member  86 . 
     The first member  72 , the second member  74  and the third member  86  are generally annular members with a common axis Y. Thus, the upstream end of the first member  72  is upstream of the upstream end  78  of the second member  74  and the upstream end  78  of the second member  74  is upstream of the upstream end  90  of the third member  86 . 
     The outer surface of the downstream end of the first member  72  tapers/converges towards the axis Y of the fuel injector head  60 . The first member  72  The downstream end of the second member  74  tapers/converges towards the axis Y of the fuel injector head  60  and the inner surface of the downstream end of the third member  86  initially tapers/converges towards the axis Y of the fuel injector head  60  and then diverges away from the axis Y of the fuel injector head  60 . An annular passage  104  is defined between the first member  72  and the second member  74  and an annular passage  106  is defined between the second member  74  and the third member  86 . A central passage  108  is defined within the first member  74  in which a fuel passage can be received in accordance with the invention. 
     It is seen that the fuel injector head  60  is arranged such that the leading edges  76  and  88  of the vanes  70  and  84  respectively are arranged to extend with axial downstream components from the first member  72  to the upstream end  78  of the second member  74  and from the second member  74  to the upstream end  90  of the third member  86  respectively. In addition it is seen that the fuel injector head  60  is arranged such that the radially outer ends  80  and  92  of the leading edges  76  and  88  of the vanes  70  and  84  respectively form arches  82  and  94  with the upstream ends  78  and  90  of the second and third member  74  and  86  respectively. These features enable the fuel injector head  60  and in particular the first and second swirlers  64  and  66  of the fuel injector head  60  to be manufactured by direct laser deposition. These features enable the vanes  70  of the first swirler  64  to provide support between the first member  72  and the second member  74  and the vanes  84  of the second swirler  66  to provide support between the second member  74  and the third member  86  during the direct laser deposition process. 
       FIG. 7  shows in closer detail a fuel passage  101  having a fuel passage outlet  101   a  which is shaped and proportioned to generate a substantially parallel sided jet of fuel  100 . A swirler passage  104  of an air swirler  103  sits radially outboard of the fuel passage  101  and has radially converging walls which direct an air flow having a predominant flow  105  to meet the jet  100  in cross flow at an angle α. The angle α is within an optimum range as discussed above. The two streams  101  and  105  mix thoroughly and the mixture  106  is carried downstream to a combustion chamber. 
     The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects of the invention may be applied mutatis mutandis to any other aspect of the invention. 
     It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.