Abstract:
A combustor for a gas turbine engine includes a fuel delivery system that uses circumferential fuel staging. The fuel delivery system includes a plurality of fuel supply rings and a backpurge sub-system. The fuel supply rings are arranged concentrically at various radial distances to supply fuel to a combustor through a plurality of combustor manifolds and pigtails. The backpurge system uses high temperature and high pressure combustor air to purge fuel from non-flowing fuel supply rings, combustor pigtails, and combustor manifolds. Additionally, the fuel delivery system includes at least two orifices to minimize pressure decays during filling stages.

Description:
This is a Division of application Ser. No. 09/640,356 filed Aug. 16, 2000 (U.S. Pat. No. 6,405,524). 
    
    
     BACKGROUND OF THE INVENTION 
     This application relates generally to combustors and, more particularly, to fuel delivery systems for gas turbine engine combustors. 
     Air pollution concerns worldwide have led to stricter emissions standards both domestically and internationally. Aircraft are governed by both Environmental Protection Agency (EPA) and International Civil Aviation Organization (ICAO) standards. These standards regulate the emission of oxides of nitrogen (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO) from aircraft in the vicinity of airports, where they contribute to urban photochemical smog problems. Most aircraft engines are able to meet current emission standards using combustor technologies and theories proven over the past 50 years of engine development. However, with the advent of greater environmental concern worldwide, there is no guarantee that future emissions standards will be within the capability of current combustor technologies. 
     In general, one class of engine emissions (NOx) are formed because of high flame temperatures within a combustor. Combustor flame temperature is controlled by increasing airflow during periods of increased fuel flow in an effort to evenly meter combustor flame temperature across the combustor. Known combustors inject fuel through a plurality of premixers that are arranged circumferentially at various radial distances from a center axis of symmetry for the combustor. To achieve a full range of engine operability, such combustors include fuel delivery systems that circumferentially stage fuel flows through the premixers to evenly disperse fuel throughout the combustor. 
     Such combustors are in flow communication with external boost air systems. As engine power is increased, fuel is injected through premixers at different radial distances. To reduce auto-ignition of fuel, residual fuel is purged from non-flowing premixers with the external boost air system. Because of the various fuel supply and premixer configurations that are used during fuel staging, such external boost air systems are often elaborate and complex. However, despite such complex boost air systems, during fuel stage transitions, pressure decays may occur as a result of the purging. Such pressure decays may cause an overtemperature or overspeed within the turbine. 
     BRIEF SUMMARY OF THE INVENTION 
     In an exemplary embodiment, a combustor for a gas turbine engine includes a fuel delivery system that uses circumferential fuel staging and combustor air pressure for purging residual fuel from non-flowing engine components. The fuel delivery system includes a plurality of fuel supply rings and a backpurge sub-system. The plurality of fuel supply rings arc arranged concentrically at various radial distances to supply fuel to a turbine engine combustor through a plurality of combustor manifolds and pigtails. The backpurge system uses combustor air to purge fuel from non-flowing fuel supply rings, combustor pigtails, and combustor manifolds. Additionally, the fuel delivery system includes at least two orifices to minimize pressure decays during filling stages. 
     During engine operation, as power is adjusted, fuel delivery system fuel stages supply fuel to the combustor through various combinations of fuel supply rings. The backpurge system drains and dries residual fuel from the non-flowing fuel supply rings and any associated combustor components. Because the backpurge system uses combustor air at a high pressure and temperature, residual fuel is easily removed and auto-ignition of the residual fuel is reduced. As a result, a combustor is provided that is cost-effective and highly reliable, 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is schematic illustration of a gas turbine engine including a combustor; and 
     FIG. 2 is a schematic illustration of a fuel delivery system used with the gas turbine engine shown in FIG.  1   
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a schematic illustration of a gas turbine engine  10  including a low pressure compressor  12 , a high pressure compressor  14 , and a combustor  16 . Engine  10  also includes a high pressure turbine  18  and a low pressure turbine  20 . 
     In operation, air flows through low pressure compressor  12  and compressed air is supplied from low pressure compressor  12  to high pressure compressor  14 . The highly compressed air is delivered to combustor  16 . Airflow (not shown in FIG. 1) from combustor  16  drives turbines  18  and  20 . 
     FIG. 2 is a schematic illustration of a fuel delivery system  50  for use with a gas turbine engine, similar to engine  10  shown in FIG.  1 . In one embodiment, the gas turbine engine is an LM6000 engine available from General Electric Company, Cincinnati, Ohio. In an exemplary embodiment, fuel delivery system  50  includes a backpurge sub-system  51  to purge and drain liquid from non-flowing portions of fuel delivery system  50  to meet load and speed variations during engine accelerations and decelerations or fuel transfers. Backpurge subsystem  51 , described in more detail below, uses high temperature and pressurized combustor air pressure to drain and purge fuel from non-flowing portions of fuel delivery system  50 . 
     Flame temperatures within combustor  16  (shown in FIG. 1) control liquid fuel emissions and as a result, combustor  16  uses circumferential staging to achieve full engine operability. Fuel delivery system  50  includes a plurality of fuel supply manifold rings  52  arranged concentrically with respect to each other. In one embodiment, rings  52  are fabricated from metal. Specifically, fuel supply manifold rings  52  include an “A” ring group or radially outer group  54 , a “B” ring group or intermediate group  56 , and a “C” ring group or radially inner group  58 . In one embodiment, rings  52  are approximately 0.5″ diameter stainless steel tubes. In another embodiment, rings  52  are approximately 0.625″ diameter stainless steel tubes. In a further embodiment, rings  52  are approximately 0.375″ diameter stainless steel rings. Each group  54 ,  56 , and  58  is connected to a plurality of manifolds (not shown). Each combustor manifold includes a plurality of pigtails (not shown) that connect each manifold to a combustor premixer (not shown). In one embodiment, fuel delivery system  50  is a liquid fuel system for a dual fuel engine. In another embodiment, fuel delivery system  50  is a dry low emission (DRE) liquid fuel system. 
     “A” ring group  54  includes four fuel supply manifold rings  52  for supplying fuel to combustor manifolds. Fuel supply manifold rings  52  are concentrically aligned with respect to each other and are positioned substantially coplanar with respect to each other. A smallest diameter manifold ring  62  is known as an A 1  ring and is radially inward from a second fuel supply ring  64  known as an A 2  ring. A third fuel supply ring  66  is known as an A 3  ring and is radially outward from A 2  ring  64  and is radially inward from a fourth supply ring  68  known as an A 4  ring. 
     Each fuel supply ring  62 ,  64 ,  66 , and  68  includes a temperature/pressure sensor  70 ,  72 ,  74 , and  76 , respectively, connected between each respective manifold ring  60  and a respective purge valve  80 ,  82 ,  84 , and  86 . Purge valves  80 ,  82 ,  84 , and  86  are commonly connected with piping  88  extending between purge valves  80 ,  82 ,  84 , and  86 , and a heat exchanger  90 . A temperature sensor  91  monitors a temperature of combustor air flowing through heat exchanger  90 . 
     Each fuel supply ring  62 ,  64 ,  66 , and  68  also includes a staging valve  100 ,  102 ,  104 , and  106 , respectively. Common piping  110 ,  112 ,  114 , and  116  connect each staging valve  100 ,  102 ,  104 , and  106 , and each respective purge valve  80 ,  82 ,  84 , and  86 , to each “A” group fuel supply ring  62 ,  64 ,  66 , and  68 , respectively. Each staging valve  100 ,  102 ,  104 , and  106  are commonly connected with piping  120  extending between staging valves  100 ,  102 ,  104 , and  106  and an “A” group shut-off valve  122 . 
     “A” group shut-off valve  122  controls a flow of fuel to staging valves  100 ,  102 ,  104 , and  106  and is between staging valves  100 ,  102 ,  104 , and  106  and an “A” group fuel metering valve  124 . An “A” drain valve  126  is connected to piping  120  between “A” group shut-off valve  122  and staging valves  100 ,  102 ,  104 , and  106 , and extends to connect with piping  88  between heat exchanger  90  and purge valves  80 ,  82 ,  84 , and  86 . In the exemplary embodiment, back purge sub-system  51  includes “A” drain valve  126 , purge valves  80 ,  82 ,  84 , and  86 , and staging valves  100 ,  102 ,  104 , and  106 . 
     “B” ring group  56  includes one fuel supply manifold ring  52  for supplying fuel to combustor manifolds. Specifically, a fuel supply manifold ring  162  is known as a “B” ring and is radially inward from “A” group rings  60 . Fuel supply ring  162  is connected with piping  164  to a “B” group fuel shut-off valve  166 . “B” group fuel shut-off valve  166  controls a flow of fuel to “B” ring group  56  and is between manifold ring  162  and a “B” group fuel metering valve  168 . A temperature/pressure sensor  170  is connected between manifold ring  162  and “B” group shut-off valve  166 . 
     A purge valve  174  is connected with piping  178  to piping  164  between temperature/pressure sensor  170  and “B” group shut-off valve  166 . Piping  178  extends from purge valve  174  to a heat exchanger  179 . A “B” group drain valve  180  is connected with piping  182  to piping  164  between purge valve piping  178  and heat exchanger  179 . Drain valve piping  182  is also connected to purge valve piping  178  between purge valve  174  and heat exchanger  179 . A temperature of combustor air flowing through heat exchanger  179  is monitored with a temperature sensor  184 . In the exemplary embodiment, back purge sub-system  51  also includes drain valve  180  and purge valve  174 . 
     “C” ring group  58  includes two fuel supply manifold rings  52  for supplying fuel to combustor manifolds. Manifold rings  52  within “C” ring group  58  are concentrically aligned with respect to each other and are radially inward from “B” ring group manifold ring  162 . A smallest diameter manifold ring  202  is known as a C 1  ring and is radially inward from a second fuel supply ring  204  known as a C 2  ring. 
     Each fuel supply ring  202  and  204  includes a temperature/pressure sensor  206  and  208  respectively, connected between each respective manifold ring  52  and a respective purge valve  220  and  222 . Purge valves  220  and  222  are commonly connected with piping  224  extending between purge valves  220  and  222 , and a heat exchanger  230 . A temperature sensor  232  monitors a temperature of combustor air flowing through heat exchanger  230 . 
     Each fuel supply ring  202  and  204  also includes a staging valve  234  and  236 , respectively. Common piping  238  and  240  connect each staging valve  234  and  236 , and each respective purge valve  220  and  222  to each “C” group fuel supply ring  202  and  204 , respectively. Each staging valve  234  and  236  are commonly connected with piping  241  extending between staging valves  234  and  236  and a “C” group shut-off valve  242 . A pair of orifices  244  and  245  are between each staging valve  234  and  236  and “C” group shut-off valve  242 . 
     “C” group shut-off valve  242  controls a flow of fuel to staging valves  234  and  236  and is between staging valves  234  and  236  and a “C” group fuel metering valve  246 . A drain valve  248  is connected to piping  240  between “C” group shut-off valve  242  and staging valves  234  and  236 , and extends to connect with piping  224  between heat exchanger  230  and purge valves  220  and  222 . In the exemplary embodiment, back purge sub-system  51  also includes drain valve  248 , purge valves  220  and  222 , and staging valves  234  and  236 . 
     Each group fuel metering valve  124 ,  168 , and  246  is commonly connected with piping  250  to a fuel delivery system main shut-off valve  252 . A temperature/pressure sensor  253  is connected to piping  250  between fuel metering valves  124 ,  168 , and  246  and fuel delivery system main shut-off valve  252 . Fuel delivery system main shut-off  252  is in flow communication with a liquid fuel source  256  and controls a flow of fuel to fuel delivery system supply ring groups  54 ,  56 , and  58 . 
     Each group heat exchanger  90 ,  179 , and  230  is commonly connected with piping  260  to a fuel/air separator  262  that is in flow communication with a drain tank  264 . A temperature sensor  266  is connected to drain tank  264  and monitors a temperature of fluid entering drain tank  264 . Drain tank  264  is at ambient pressure. The combination of fuel/air separator  262  and heat exchangers  90 ,  179 , and  230  control a temperature of purge air entering drain tank  264 . In one embodiment, purge air temperature entering drain tank  264  is less than approximately 100° F. 
     During engine operation, fuel delivery system  50  operates with circumferential staging. Initially when engine  10  is being started and increased in power, fuel is supplied to combustor  16  through “B” ring group  56  and A 1  ring  62 . As power is increased, a next fuel stage supplies fuel to only “B” ring group  56 . During engine operations as a fuel flow to various fuel supply rings  52  is shutoff, backpurge sub-system  51  uses combustor air to remove residual liquid fuel from non-flowing supply rings  52  to prevent auto-ignition of the fuel. Because combustor air is provided internally at a higher temperature and pressure than air provided with known purge systems, overtemperatures and overspeeds of turbine  10  are reduced during purging. 
     Specifically, during engine start, as fuel staging is changed from supplying fuel to “B” ring group  56  and A 1  ring  62  to only supplying fuel to “B” ring group  56 , fuel flow to A 1  ring group  56  is shut-off and backpurge sub-system  51  removes fuel from A 1  premixers, pigtails, and A 1  ring  62  by sequencing valves. Initially “A” ring group fuel shutoff valve  122  is closed, and A 1  purge valve  80  and “A” drain valve  126  are opened. After approximately two minutes, and A 1  purge valve  80 , “A” drain valve  126 , and A 1  staging valve  100  are closed to complete a purging cycle. 
     As engine power is further increased, another fuel stage permits fuel is be supplied to “B” ring group  56  and “C” ring  202 . During such a fuel stage, fuel is supplied to C 1  ring  202  after “C” group shutoff valve  242  and C 1  staging valve  234  are opened. As power is further increased, fuel is then supplied to “B” ring group  56  and “C” ring group  58  and C 2  ring  204  is filled after C 2  staging valve  236  is opened. Because fuel flows through orifices  244  and  245  prior to entering staging valves  234  and  236 , respectively, load variations and manifold pressure decay are reduced during such the fuel stage transition. 
     As engine power is further increased, a next fuel stage shuts-off fuel flow to “C” ring group  58  and supplies fuel to “A” ring group  54  and “B” ring group  56 . During such a fuel stage, “A” group shut-off valve  122  and “A” staging valves  100 ,  102 ,  104 , and  106  are opened. “C” ring group shut-off valve  242  is then closed, and C 1  and C 2  purge valves  220  and  222 , respectively, and “C” ring group drain valves  248  are opened. Approximately two minutes later, C 1  and C 2  staging valves  234  and  236 , respectively, C 1  and C 2  purge valves  220  and  222 , respectively, and “C” ring group drain valve  248  are closed and purging is complete. 
     As power is further increased, fuel is supplied to “A”, “B”, and “C” ring groups  54 ,  56 , and  58 , respectively. During such fuel staging, fuel is supplied to “C” rings  202  and  204  after “C” ring group shutoff valve  242 , and C 1  and C 2  staging valves  234  and  236 , respectively, are opened. 
     Engine  10  is also operated with circumferential staging as power is decreased from high power operations. Prior to reductions in power, engine  10  operates with fuel supplied to “A”, “B”, and “C” ring groups  54 ,  56 , and  58 , respectively. Depending on particular a particular engine  10 , flow rates to “A”, “B”, and “C” ring groups  54 ,  56 , and  58 , respectively, will change depending upon power operating levels of engine  10 . As power is decreased, fuel is then initially supplied to only “A” ring group  54  and “B” ring group  56 , and fuel is purged from “C” ring group premixers, pigtails, and manifolds  202  and  204  after “C” ring group shut-off valve  242  is closed. C 1  and C 2  purge valves  220  and  222 , respectively, and “C” group drain valve  248  are then opened. Approximately two minutes later, C 1  and C 2  staging valves  234  and  236 , respectively, C 1  and C 2  purge valves  220  and  222 , respectively, and “C” ring group drain valve  248  are closed and purging is complete. 
     As power is further decreased, fuel is then supplied through another fuel stage to only “B” ring group  56  and “C” ring group  58 . “C” ring group  58  is filled after “C” ring group shut-off valve  242  and C 1  and C 2  staging valves  234  and  236 , respectively, are opened. After “C” ring group  58  is filled, “A” ring group shut-off valve  122  is closed and A 1 , A 2 , A 3 , and A 4  purge valves  80 ,  82 ,  84 , and  86 , and “A” ring group drain valve  126  are opened. After approximately two minutes purging is complete, and “A” ring group drain valve  122  and A 1 , A 2 , A 3 , and A 4  staging and purge valves  100 ,  102 ,  104 , and  106 , and  80 ,  82 ,  84 , and  86 , respectively, are closed. 
     As engine power is further decreased, fuel is supplied to “B” ring group  56  and “C” ring  202  and fuel flow to “C” ring  204  is decreased. During this fuel stage, C 2  staging valve  236  is closed and C 2  purge valve  222  is opened. After approximately two minutes, purging of C 2  ring  204  is complete, and C 2  purge valve  222  is closed. 
     As power is further decreased, fuel is supplied to only “B” ring group  56  and fuel is purged from C 1  ring  202 . Initially “C” ring group shut-off valve  242  is closed and C 1  and C 2  purge valves  220  and  222 , C 2  staging valve  236 , and “C” ring group drain valve  248  are opened for approximately two minutes to complete the purging. After the purging is complete, C 1  and C 2  staging valves  234  and  236 , C 1  and C 2  purge valves  220  and  222 , and “C” ring group drain valve  248  are closed. 
     Whenever fuel flow to “B” ring group  56  is shut-off, “B” ring group  56  is purged after “B” ring group shut-off valve  166  is closed. “B” ring group drain valve  180  and “B” purge valve  174  are opened for purging. After approximately two minutes, “B” ring group  56  is purged, and “B” ring group drain valve  180  and “B” purge valve  174  are closed. 
     The above-described combustor is cost-effective and highly reliable. The combustor includes a fuel delivery system that effectively purges residual fuel from fuel supply rings and combustor pigtails and premixers that are not in use during a particular fuel stage. Because the backpurge system uses high temperature and high pressure combustor air, walls within non-flowing components are effectively drained and dried. As a result, auto-ignition of residual fuel is reduced. Furthermore, because the fuel delivery system includes a pair of orifices, load variations during fuel stage transitions are reduced. Thus, a combustor is provided which may be effectively purged at part power operations. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.