Abstract:
A method of reducing engine noise generation by decoupling: acoustic and hydrodynamic fluctuation generated by a compressor and a fuel supply system; from acoustic and hydrodynamic fluctuation of a combustor, by: deflecting fuel jets into a fuel nozzle mixing chamber in a number of counter-rotating adjacent pairs of fuel laden vortices; emitting a resulting fuel-air mixture into the combustor downstream from the fuel nozzle mixing chamber.

Description:
RELATED APPLICATION 
     This application is a divisional of Ser. No. 10/320,488 filed Dec. 17, 2002, now U.S. Pat. No. 6,886,342 issued: May 3, 2005. 
    
    
     TECHNICAL FIELD 
     The invention relates to a method of reducing engine noise levels and improving fuel/air mixing using a fuel nozzle with cross-currents of fuel and air vortices. 
     BACKGROUND OF THE ART 
     Gas turbine engines include a pressurized fuel supply system that is mechanically linked to the rotation of the compressor through an accessory gear box. The combustor receives compressed air from the compressor and therefore the supply of pressurized fuel and compressed air to the combustor is significantly affected by fluctuation in the engine operation. 
     Evidence indicates that there is a strong coupling effect between: (1) the acoustic and hydrodynamic fluctuation generated by the compressor and fuel supply system; and (2) the acoustic and hydrodynamic fluctuation generated by the combustor. Combustion instability is introduced into the combustion system by perturbations imposed on the fuel nozzle injection ports by the fuel supply system and by the air supply system through the compressor and diffuser upstream of the combustor. 
     Objects of the invention will be apparent from review of the drawings and description of the invention below. 
     DISCLOSURE OF THE INVENTION 
     The invention provides a method of reducing engine noise generation by decoupling: acoustic and hydrodynamic fluctuation generated by a compressor and a fuel supply system; from acoustic and hydrodynamic fluctuation of a combustor, by: deflecting fuel jets into a fuel nozzle mixing chamber in a number of counter-rotating adjacent pairs of fuel laden vortices; emitting a resulting fuel-air mixture into the combustor downstream from the fuel nozzle mixing chamber. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       In order that the invention may be readily understood, embodiments of the invention are illustrated by way of example in the accompanying drawings. 
         FIG. 1  is an axial cross sectional view through a typical turbofan gas turbine engine showing general arrangement of the components and in particular showing the fuel supply, air compressor sand combustor arrangement. 
         FIG. 2  is a detailed axial cross-sectional view through a reverse flow combustor with a fuel nozzle in accordance with a first embodiment of the invention. 
         FIG. 3  is a like detail axial sectional view through a reverse flow combustor with the fuel nozzle disposed in a different location in accordance with the second embodiment of the invention. 
         FIG. 4  is a partially cut away isometric view of a fuel nozzle in accordance with the invention. 
         FIG. 5  is a sectional view along lines  5 — 5  of  FIG. 4  showing details of the internal components of the fuel nozzle. 
         FIG. 6  is a detailed view showing a section through the fuel nozzle along lines  6 — 6  of  FIG. 5  showing miniature fuel injection tubes directing fuel jets at cusps in the fuel deflecting surface of the fuel vortex generator. 
         FIG. 7  is a like sectional view showing counter rotating adjacent pairs of airflow vortices created as airflow over the airflow separation edges disposed between fuel jets. 
     
    
    
     Further details of the invention and its advantages will be apparent from the detailed description included below. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows an axial cross-section through a turbofan gas turbine engine. It will be understood however that the invention is also applicable to any type of engine with a combustor and turbine section such as a turboshaft, a turboprop, industrial gas turbine or auxiliary power unit. Air intake into the engine passes over fan blades  1  in a fan case  2  and is then split into an outer annular flow through the bypass duct  3  and an inner flow through the low-pressure axial compressor  4  and high-pressure centrifugal compressor  5 . Compressed air exits the compressor  5  through a diffuser  6  and is contained within a plenum  7  that surrounds the combustor  8 . Fuel is supplied to the combustor  8  through fuel supply tubes  9  which is mixed with air from the plenum  7  when sprayed through nozzles into the combustor  8  as a fuel-air mixture that is ignited. A portion of the compressed air within the plenum  7  is admitted into the combustor  8  through orifices in the side walls to create a cooling air curtain along the combustor walls or is used for cooling to eventually mix with the hot gases from the combustor and pass over the nozzle guide vane  10  and turbines  11  before exiting the tail of the engine as exhaust. 
       FIGS. 2 and 3  show first and second embodiments of a fuel nozzle  12  located in a reverse flow combustor. It will be understood however that a fuel nozzle  12  can be installed in a straight flow combustor or any other combustor configuration. As indicated in  FIGS. 2 and 3 , compressed air from the diffuser  6  is contained within the plenum  7  and enters through air inlet openings  13  in the nozzle  12  to be mixed with fuel and then to be propelled under pressure into the combustor  8  for ignition.  FIG. 2  shows a separate igniter  14  whereas  FIG. 3  indicates that the igniter  14  may be housed within the centre of the nozzle  12  in a compact fuel nozzle-igniter unit. A centrally placed igniter provides the possibility for eliminating primary fuel injection during the start up conditions. 
       FIGS. 4 and 5  show details of the fuel nozzle  12  construction. Fuel is conveyed through the fuel supply tube  9  and enters a fuel inlet  15  which is in communication with a plurality of fuel spray orifices  16  via a cylindrical shape fuel distribution gallery  17 . The fuel gallery  17  includes cylindrical side walls and disc shaped top and bottom walls. The top wall supports a plurality of fuel spray tubes  18  having a lower end in communication with the fuel gallery  17 . The fuel spray tubes  18  have a distal end with fuel spray orifices  16  directed towards a generally annular fuel vortex generator  19  having a scalloped fuel deflecting surface  20  disposed downstream a distance from each fuel spray orifices  16 . 
     A central mixing chamber  21  is defined between the fuel spray orifices  16  and the contoured or scalloped fuel deflecting surface  20 . As best seen in  FIG. 6 , the fuel deflecting surface  20  has a surface contour oriented to deflect fuel jets sprayed from the fuel orifices  16  into the mixing chamber  21  in a plurality of counter rotating adjacent pairs of fuel laden vortices  22 . 
     As seen in  FIGS. 4 and 5 , the fuel nozzle  12  in the embodiment illustrated also includes an external shield  23  into which compressed air flows from the plenum  7  through air inlet openings  13 , flows downstream to mix with fuel in the mixing chamber  21  and then exits through the annular airflow outlet  24  that surrounds the fuel-air mixture outlet  25  from the mixing chamber  21 . The external shield  23  defines an annular air supply passage  26 . The external shield  23  also internally houses and supports the fuel gallery  17 , fuel vortex generators  19 , air assist gallery  27  and airflow vortex generator  28  which will be described below. 
     The air supply passage  26  provides air flow to the mixing chamber  22  by two paths. Firstly air flows through inlet openings  29  into the air assist gallery  27  which surrounds each fuel spray tube  18 . The air assist gallery  27  includes a cover plate  30  through which the fuel tubes  18  extend. Each fuel tube  18  is surrounded by an annular air assist opening in the cover plate  30  to provide an annular flow of air directed parallel to the fuel jet ejected through the fuel spray orifices  16  as indicated by arrows in  FIG. 5 . 
     It will be understood that the fuel jets emitted through the fuel spray orifices  16  are surrounded by an annular flow of air traveling parallel and impinging on the fuel deflecting surface  20  of the fuel vortex generator  19  to create (as shown in  FIG. 6 ) pairs of counter rotating fuel vortices  22 . 
     As shown in  FIG. 5 , the air conveyed through the annular air supply passage  26  also supplies air that flows into the mixing chamber  21 , via an air inlet  29   a  defined between the fuel vortex generator  19  and the airflow vortex generator  28 , in a direction generally transverse to the direction of fuel jets emitted from the fuel spray orifices  16  into the mixing chamber  21 . The resulting fuel-air mixture proceeds to the fuel-air outlet  25  downstream from the mixing chamber  21 . 
     As seen in  FIGS. 5 and 7 , the fuel nozzle  12  also includes an air flow vortex generator  28  which is disposed between the air supply passage  26  and the mixing chamber  21 . The air flow vortex generator  28  has an air flow deflecting surface  31  with a surface contour oriented to deflect air flow into the mixing chamber  21  in a plurality of counter rotating adjacent pair of airflow vortices  32  as illustrated in  FIG. 7 . It will be understood from  FIG. 5  that the counter rotating pairs of airflow vortices  32  are deflected into a transverse direction relative to the fuel jets emitted through the fuel spray orifices  16 . The fuel jets impinge on the fuel deflecting surface  20  and the resulting fuel vortices  22  are swept downstream by the airflow vortices  32  into the mixing chamber  21 . The nozzle  12  as illustrated is symmetric about a central axis and the fuel jets are directed axially downstream whereas the counter rotating pairs of airflow vortices  32  are directed radially inwardly towards the mixing chamber  21 . 
     As shown in  FIG. 6 , the fuel deflecting surface  20  of the fuel vortex generator  19  includes cusps  33  pointed towards each fuel spray orifice  16  with a concave arc extending adjacent cusp  33 . The fuel jet is therefore separated and guided by the fuel deflecting surface  20  to create counter rotating pairs of fuel laden vortices  22  as indicated in  FIG. 6 . As shown in  FIG. 7 , the airflow deflecting surface  31  of the airflow vortex generator  28  includes a flow separation edge  34  disposed between adjacent fuel spray orifices  16  and a concave arch extends between separation edges  34 . 
     The fuel nozzle  12  therefore utilizes the phenomenon of counter rotating stream wise vorticity to eliminate or reduce the coupling effect on the fuel-air mixture before combustion takes place. One set of counter rotating vortices  22  is generated by the pressurized fuel jets impinging on the deflecting surface  20  of the fuel vortex generator  19 . Airflow vortices  32  are generated as airflow goes through flow separation over separation edges  34 . The superposition of two counter rotating vortices  22 ,  32  further benefits mixing for improving efficiency and reducing emissions from the combustion process due to an increase in shear contact area between turbulent air/fuel, air/air, and fuel/fuel layers. 
     Although the above description relates to a specific preferred embodiment as presently contemplated by the inventor, it will be understood that the invention in its broad aspect includes mechanical and functional equivalents of the elements described herein.