Abstract:
A method for operating a gas turbine engine including a high pressure compressor, a variable inlet guide vane assembly and a water injection apparatus for injecting water into a flow of the engine is provided. The method comprises transmitting engine operating parameters including a temperature of the gas flow at an outlet of the high pressure compressor, T3, to an engine controller, using the controller to regulate a flow of water injected into the gas flow and to adjust a relative position of the inlet guide vane assembly until engine full power is about reached as determined by a pre-defined T3 operating parameter limit, and adjusting the controller to then facilitate operation of the engine with an increased output without exceeding the pre-defined T3 operating parameter limit.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to gas turbine engines and more particularly, to engine control systems used with gas turbine engines that include prebooster and precompressor water injection, and variable inlet guide vanes.  
           [0002]    Gas turbine engines typically include a compressor for compressing a working fluid, such as air. The compressed air is injected into a combustor which heats the fluid causing it to expand, and the expanded fluid is forced through a turbine. The compressor typically includes a plurality of compression stages sometimes contained in a separate low pressure compressor and a high pressure compressor.  
           [0003]    The output of known gas turbine engines may be limited by signals received by the engine controller indicative of the speed of the rotor shafts, sometimes referred to as XN2 for the speed of the low pressure rotor, and XN25 for the speed of the high speed rotor, as well as the temperature of the working fluid at the output of the high pressure compressor, sometimes referred to as temperature “T3”, and by the temperature of the working fluid in the combustor outlet, sometimes referred to as temperature “T41”. The indication of the temperature at the outlet of the combustor T41 is recorded by temperature sensors at a downstream location, such as the outlet of the high pressure turbine, which is sometimes referred to as “T 48 ”. To reduce both the T3 and T41 temperatures, while maintaining a constant flow of the working fluid, at least some known engines use an intercooler positioned in the fluid flow path between the low pressure compressor and the high pressure compressor. In steady state operation, the precooler or intercooler extracts heat from the air compressed in the compressor, which effectively reduces both the temperature and volume of air exiting the high pressure compressor. Such reduction in temperature reduces both the T3 and T41 temperatures. Increased power output therefore can be achieved by increasing flow through the compressor. However, such an intercooler may also reduce thermal efficiency of the engine.  
           [0004]    To facilitate reducing both the T3 and T41 temperatures for power augmentation, without sacrificing engine thermal efficiency, at least some known engines include prebooster or precompressor water injection. The water spray facilitates reducing both the T3 and T41 temperatures, and also reduces compressive engine horsepower. Because the T3 and T41 temperatures are reduced, the engine is not T3 and T41 constrained, the engine may operate at higher output levels below the T3 and T41 temperature limits.  
           [0005]    To facilitate optimizing power production from the gas turbine engine, at least some known engines that include water injection also employ variable inlet guide vane (VIGV) assemblies. The VIGV assemblies include a plurality of variably positioned inlet guide vanes that when rotated, facilitate changing the geometry of the gas turbine engines engine operation to facilitate improving engine performance over a wide range of engine operations. The combination of the water injection and the VIGV assemblies reduces an effective inlet flow temperature such that the gas turbine engine may be operated with increased power before being T3 and/or T41 temperature limited.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    In one aspect, a method for operating a gas turbine engine including a high pressure compressor, a variable inlet guide vane assembly and a water injection apparatus for injecting water into a flow of the engine is provided. The method comprises transmitting engine operating parameters including a temperature of the gas flow at an outlet of the high pressure compressor, T3, to an engine controller, using the controller to regulate a flow of water injected into the gas flow and to adjust a relative position of the inlet guide vane assembly until engine full power is about reached as determined by a pre-defined T3 operating parameter limit, and adjusting the controller to then facilitate operation of the engine with an increased output without exceeding the pre-defined T3 operating parameter limit.  
           [0007]    In another aspect of the invention, a method for operating a gas turbine engine including a variable inlet guide vane assembly is provided. The method comprises adjusting a relative position of the variable guide vane assembly based on feedback to an engine controller, injecting water into the engine gas flow at a first flow rate until engine full power is about reached as determined by the engine controller, wherein at a specific effective engine inlet temperature, engine full power is limited by a pre-defined temperature of the gas flow at an outlet of the high pressure compressor, T3, adjusting pre-defined limits within the engine controller to enable the engine to operate with a reduced effective engine inlet temperature, and re-accelerating the engine to full power without exceeding the pre-defined T3 temperature. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is an exemplary schematic illustration of a gas turbine engine including compressor water injection;  
         [0009]    [0009]FIG. 2 is an exemplary schematic illustration of a gas turbine engine including compressor water injection and intercooling;  
         [0010]    [0010]FIG. 3 is an alternative exemplary embodiment of a schematic illustration of a gas turbine engine including booster water injection;  
         [0011]    [0011]FIG. 4 is another alternative exemplary embodiment of a schematic illustration of a single rotor gas turbine engine including compressor water injection;  
         [0012]    [0012]FIG. 5 is another alternative exemplary embodiment of a schematic illustration of a gas turbine engine including booster and compressor water injection;  
         [0013]    [0013]FIG. 6 is is another alternative exemplary embodiment of a schematic illustration of a gas turbine engine including compressor water injection;  
         [0014]    [0014]FIG. 7 is an exemplary schematic illustration of the gas turbine engine shown in FIG. 6 coupled to an electric generator;  
         [0015]    [0015]FIG. 8 is a side view of an LM6000 engine of General Electric Company modified to include spray injection;  
         [0016]    [0016]FIG. 9 is a cross sectional view of the engine shown in FIG. 8 and illustrating a nozzle configuration;  
         [0017]    [0017]FIG. 10 is a side view of an exemplary embodiment of a nozzle that may be used with any of the water injection systems illustrated;  
         [0018]    [0018]FIG. 11 is a top view of the nozzle shown in FIG. 11;  
         [0019]    [0019]FIG. 12 is an exemplary schematic diagram of a control circuit for controlling the supply of water and air to the nozzles in the engine shown in FIG. 8;  
         [0020]    [0020]FIG. 13 is a chart illustrating an exemplary water schedule for increasing power output from the engine arrangement shown in FIG. 8;  
         [0021]    [0021]FIG. 14 is a flow chart illustrating an exemplary method for operating any of the gas turbine engines shown in FIGS. 1-8;  
         [0022]    [0022]FIG. 15 is a table illustrating exemplary engine model predictions and results obtained using the method shown in FIG. 14; and  
         [0023]    [0023]FIG. 16 is a chart illustrating exemplary power curve results generated using the method shown in FIG. 14. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    Set forth below are exemplary configurations of turbine engines in accordance with various embodiments of the present invention. Initially, it should be understood that although specific implementations are illustrated and described, engine components of each embodiment can be practiced using many alternative structures and in a wide variety of engines. For example, and as described below in more detail, water spray injection can be performed at the inlet of a high pressure compressor, at an inlet of the booster, or at both locations.  
         [0025]    [0025]FIG. 1 is a schematic illustration of a gas turbine engine  10  which, as is well known, includes a controller  11 , a low pressure compressor  12 , a high pressure compressor  14 , and a combustor  16 . Engine  10  also includes a high pressure turbine  18 , a low pressure turbine  20 , a power turbine  22 , and a variable inlet guide vane assembly (VIGV)  23 . Engine  10  also includes a water injection apparatus  24  for injecting water into an inlet  26  of high pressure compressor  14 . Further details regarding water injection apparatus  22  are set forth below. For purposes of FIG. 1, however, it should be understood that apparatus  24  is in flow communication with a water supply (not shown) and water is delivered from the supply through apparatus  24  to compressor inlet  26 . Additionally, it should be understood that the operation of apparatus  24  is regulated by controller  11 . Apparatus  24  is air aspirated using a bleed source off compressor  14  to provide a finer spray mist. Waste heat boilers  28 ,  30 , and  32  are located downstream of power turbine  22 . As is known in the art, feed water is supplied to boilers  28 ,  30 , and  32  via a feedwater line  34 , and water in the form of steam is communicated from boilers  28 ,  30 , and  32  to various upstream components. More specifically, steam from boiler  28  is provided to an inlet  36  of combustor  16 , steam from boiler  30  is provided to an inlet of low pressure turbine  20  and an inlet of power turbine  22 , and steam from boiler  32  is provided to a last stage of power turbine  22 .  
         [0026]    Variable inlet guide vane assembly  23  is known in the art and channels airflow entering turbine engine  10  downstream into the core engine. VIGV assembly  23  extends substantially circumferentially within engine  10  and includes a plurality of variable flaps (not shown) that are positionable during engine operation to facilitate improving engine performance over a wide range of engine operations. More specifically, as engine  10  is operated at design operating conditions, the flaps are generally axially aligned with respect to engine  10 . An orientation of the flaps is controlled by controller  11  based on the conditions at which the engine is operated.  
         [0027]    In addition to receiving the T3 and T41 temperatures, controller  11  receives a plurality of different engine operating parameters from a plurality of sensors coupled to engine  10 . For example, controller  11  receives values indicative of the core engine shaft speed, the engine inlet airflow, and the water flow injection rate. In one embodiment, controller  11  is a Mark VI Speedtronic™ Controller commercially available from General Electric Power Systems, Schenectady N.Y. Controller  11  is a processor-based system that includes engine control software that configures controller  11  to perform the below-described processes. As used herein, the term processor is not limited to just those integrated circuits referred to in the art as processors, but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits.  
         [0028]    [0028]FIG. 2 is a schematic illustration of another embodiment of a gas turbine engine  50  including water spray injection, controller  11 , and variable inlet guide vane assembly  23 . Engine  50  includes a low pressure compressor or booster  52 , a high pressure compressor  54 , and a combustor  56 . Engine  50  also includes a high pressure turbine  58 , a lower pressure turbine  60 , and a power turbine  62 . Engine  50  further includes a water injection apparatus  64  for injecting water into an inlet  66  of high pressure compressor  54 . For purposes of FIG. 2, it should be understood that apparatus  64  is in flow communication with a water supply (not shown) and water is delivered from such supply through apparatus  64  to inlet  66  of compressor  54 . An intercooler  68  also is positioned in series flow relationship with booster  52  to receive at least a portion or all of the air flow output by booster  52 , and the output of intercooler  68  is coupled to inlet  66  of compressor  54 . Of course, cooling water is supplied to intercooler  68  as illustrated or blower fans could be used for air cooling. Intercooler  68  could, for example, be one of the intercoolers described in U.S. Pat. No. 4,949,544.  
         [0029]    Waste heat boilers  70 ,  72 , and  74  are located downstream of power turbine  62 . As is known in the art, feed water is supplied to boilers  70 ,  72 , and  74  via a feedwater line  76  which extends through a first stage  78 A of intercooler  68 , and steam is communicated from boilers  70 ,  72 , and  74  to various upstream components. Particularly, steam from boiler  70  is provided to an inlet  80  of combustor  56 , steam from boiler  72  is provided to an inlet of low pressure turbine  60  and an inlet of power turbine  62 , and steam from boiler  74  is provided to a last stage of power turbine  62 .  
         [0030]    Although not shown in the exemplary configuration set forth in FIG. 2, it is contemplated that rather than, or in addition to, water spray injection at inlet  66  of high pressure compressor  54 , such injection can be performed at the inlet of low pressure compressor, or booster,  52  (booster water spray injection is illustrated in FIG. 3).  
         [0031]    An exemplary configuration of an engine  82  including booster water spray injection, controller  11 , and variable inlet guide vane assembly  23  is set forth in FIG. 3. The configuration of engine  82  is substantially similar to engine  10  shown in FIG. 1 with the exception that water spray injection apparatus  24  is located at an inlet  38  of low pressure compressor, or booster,  12 . In engine  82 , water is injected into booster  12  and cools the air flowing through booster  12 .  
         [0032]    [0032]FIG. 4 is an exemplary schematic illustration of a single rotor gas turbine engine  84  including compressor water injection, controller  11 , and variable inlet guide vane assembly  23 . Engine  84  includes a high pressure compressor  86 , a combustor  88 , and a high pressure turbine  90 . A shaft  92  coupled high pressure compressor  86  and high pressure turbine  90 . A power turbine  94  is downstream from high pressure turbine  90 , and a shaft  96  is coupled to and extends from power turbine  94 . Water spray injection apparatus  98  is located at an inlet  100  of high pressure compressor  86 .  
         [0033]    A dual rotor gas turbine engine  10  is shown schematically in FIG. 5. Engine  160  includes a booster  162  and a power turbine  164  connected by a first shaft  166 , a high pressure compressor  168  and a high pressure turbine  170  connected by a second shaft  172 , and a combustor  174 . Engine  160  also includes pre-booster water spray injection apparatus  176 , pre-compressor water spray injection apparatus  178 , controller  11 , and variable inlet guide vane assembly  23 .  
         [0034]    [0034]FIG. 6 is an exemplary schematic illustration of a gas turbine engine  200  including compressor water injection, controller  11 , and variable inlet guide vane assembly  23  (not shown in FIG. 6). Engine  200  includes a low pressure compressor  202  and a high pressure compressor  204 . In this embodiment, low pressure compressor  202  is a five stage compressor, and high pressure compressor  204  is a fourteen stage compressor. A combustor (not shown) is downstream from compressor  204 . Engine  200  also includes a high pressure turbine (not shown) and a low pressure turbine (not shown). The high pressure turbine is a two stage turbine, and the low pressure turbine is a five stage turbine.  
         [0035]    Engine  200  also includes a water injection apparatus  206  for injecting water into an inlet  208  of high pressure compressor  204 . Water injection apparatus  206  is controlled by controller  11  and includes a water metering valve  210  in flow communication with a water manifold  212 . Water is supplied to metering valve  210  from a water source or reservoir. Air is supplied to an air manifold  213  from an eight stage bleed  214  of high pressure compressor  204 . Bleed  214  serves as a source of heated air. A heat exchanger  216  is coupled to flow pipe or tube  218  which extends from eight stage bleed  214  to air manifold  213 . Feeder tubes  220  and  221  extend from air manifold  213  and water manifold  212  to twenty four spray nozzles  222  and  223  radially spaced and extending through outer casing  224 . Nozzles  222  are sometimes referred to herein as short nozzles  222 , and nozzles  223  are sometimes referred to herein as long nozzles  223 . Nozzles  222  and  223  are radially spaced around the circumference of casing  224  in an alternating arrangement as described below in more detail.  
         [0036]    Twenty four water feeder tubes  221  extend from water manifold  212 , and twenty four air feeder tubes  220  extend from air manifold  213 . Each nozzle  222  is coupled to one water feeder tube  221  from water manifold  212  and to one air feeder tube  220  from air manifold  213 . Generally, water flowing to each nozzle  222  and  223  is atomized using the high pressure air (e.g., at about 150 psi) taken off eight stage bleed  214  of high pressure compressor  204 . The droplet diameter, in this embodiment, should be maintained at about 20 microns. Such droplet diameter is maintained by controlling the rate of flow of water through valve  210  using the water schedule described below in more detail and utilizing the high pressure air from bleed  214 .  
         [0037]    The above described water injection apparatus  206  may also be utilized in connection with pre-low pressure compressor water spray injection. For example, water injection apparatus  206  may also be utilized with engine  10  (shown in FIG. 1), engine  50  (shown in FIG. 2), engine  82  (shown in FIG. 3), engine  84  (shown in FIG. 4), or engine  160  (shown in FIG. 5). It is believed that such pre-low pressure compressor water spray injection provides at least many of the same advantages as the intermediate, or pre-high pressure compressor described in more detail below.  
         [0038]    [0038]FIG. 7 is a schematic illustration of gas turbine engine  200  coupled to an electric generator  228 . As shown in FIG. 10, engine  200  includes a high pressure turbine  230  and a low pressure turbine  232  downstream from high pressure compressor  204 . High pressure compressor  204  and high pressure turbine  230  are coupled via a first shaft  234 , and low pressure compressor  202  and low pressure turbine are coupled via a second shaft  236 . Second shaft  236  also is coupled to generator  228 . A combustor  238  is between compressor  204  and turbine  230 . Engine  200  may be, for example, an LM6000 Gas Turbine Engine commercially available from General Electric Company, Cincinnati, Ohio.  
         [0039]    Rather than being originally manufactured to include injection apparatus  206 , it is possible that apparatus  206  is retrofitted into existing engines. Injection apparatus  206  would be provided in kit form and include tubing  218  and  220 , along with water and air manifolds  212  and  213  and water metering valve  210 . Nozzles  222  and  223  also would be provided. When it is desired to provide water spray injection, nozzles  222  and  223  are installed in outer casing  224  and flow tube  218  is installed and extends from eighth stage bleed  214  to air manifold  213 . Valve  210  is coupled between a water source and water manifold  212 , and water manifold  212  is coupled to air manifold  213 .  
         [0040]    [0040]FIG. 8 is a side view of an LM6000 engine  250  of General Electric Company including a controller  11  and a variable inlet guide vane assembly  23 . Engine  250  includes an inlet  252 , a low pressure compressor  254 , and front frame  256 , and a high pressure compressor  258 . Engine  250  is modified to include water spray injection apparatus  260 , which includes an air manifold  262  and a water manifold  264  coupled to twenty four radially spaced nozzles  266  mounted to an engine outer casing  268 . Nozzles  266  spray water into engine  250  at a location between low pressure compressor  254  and high pressure compressor  258 . Injection apparatus  260  also includes a connector  270  for connecting to an eight stage bleed  272  of high pressure compressor  258 , and a pipe  274  extending from connector  270  to air manifold  262 . Although not shown in FIG. 8, a heat exchanger (air to air or water to air) may be coupled to pipe  274  to reduce the temperature of the air supplied to air manifold  262 . For illustration purposes, nozzles  276  are shown secured to inlet  252  of low pressure compressor  254 . Air and water manifolds also could be coupled to nozzles  276  to provide pre-low pressure compressor water spray injection. The components of injection apparatus  260  described above are fabricated from stainless steel.  
         [0041]    High pressure compressor  258  includes stator vanes which typically are not grounded to case  268 . When used in combination with water spray injection, it has been found that grounding at least some of such vanes which come into contact with the water spray may be necessary. To the extent required, and using for example, graphite grease, such vanes can be grounded to case  268 . That is, graphite grease may be applied to the bearing area of such vanes. For example, such graphite grease can be used at the inlet guide vane and for each down stream vane through the second stage. In operation, a portion of the grease heats and dissipates, and the graphite remains to provide a conductive path from the vane to case  268 .  
         [0042]    It also should be understood if the water can be supplied to the water spray injection nozzles under sufficient pressure, it may not be necessary to supply high pressure air to nozzles. Therefore, it is contemplated that the eight stage bleed could be eliminated if such high pressure water is available.  
         [0043]    [0043]FIG. 9 is a cross sectional view of engine  250  and illustrating nozzles  266 . Nozzles  266  are configured so that water injected into the gas flow to high pressure compressor  258  provides substantially uniform radial and circumferential temperature reductions at the outlet of high pressure compressor  258 . Nozzles  266  include a set  282  of long nozzles and a set  284  of short nozzles. In the configuration shown in FIG. 10, at least one short nozzle  284  is located at a radially intermediate location between two radially aligned long nozzles  282 . Short nozzles  284  are about flush with the circumference of the flow path and long nozzles  282  extend about four inches into the flow path. Of course, other lengths nozzles may be utilized depending upon the desired operation results. In one specific implementation, nozzle  284  extends about 0.436 inches into the flow path, and nozzle  282  extends 3.686 inches into the flow path. The water ratio between short nozzles  284  and long nozzles  282  (e.g., 50/50) may also be selected to control the resulting coding at the compressor outlet.  
         [0044]    The temperature sensor for obtaining the temperature at the inlet of the high pressure compressor (i.e., temperature T 25 ), is aligned with a long nozzle  282 . By aligning such temperature sensor with a long nozzle  282 , a more accurate temperature measurement is obtained rather than having such sensor aligned with a short nozzle  284 .  
         [0045]    [0045]FIGS. 10 and 11 illustrate one of nozzles  266 . Long and short nozzles  282  and  284  differ only in length. Nozzle  266  includes a head  286  having an air nozzle  288  and a water nozzle  290 . Air nozzle  288  couples to an air pipe (not shown) which extends from nozzle  288  to air manifold  262 . Water nozzle  290  couples to a water pipe (not shown) which extends from nozzle  290  to water manifold  264 . Nozzle  266  also includes a stem  292  and a mounting flange  294  for mounting nozzle  266  to case  262 . A mounting portion  296  of stem  292  facilitates engagement of nozzle  266  to case  262 .  
         [0046]    Stem  292  is formed by an outer tubular conduit  298  and an inner tubular conduit  300  located within conduit  298 . Air flows into nozzle  288  and through the annulus between outer conduit  298  and inner conduit  300 . Water flows into nozzle  290  and through inner conduit  300 . Mixing of the air and water occurs in stem portion  302  formed by a single conduit  304 . An end  306  of nozzle  266  is open so that the water and air mixture can flow out from such end  306  and into the flow path.  
         [0047]    [0047]FIG. 12 is a schematic diagram of a control circuit  350  for controlling the supply of water and air to nozzles  282  and  284  in engine  250  for both frame water injection (aft looking forward) and inlet water injection (aft looking forward). Control circuit  350  is implemented by controller  11 . As shown in FIG. 12, demineralized water is pumped through a motor driven water pump  352 . Sensors  354  are coupled to the water delivery line such as a linear variable differential transformer, a pressure sensor, and a water meter valve. A relief valve  356  is connected in parallel with pump  352 , and a flow meter  358  is coupled in series with pump  352 . An air purge line  360  also is coupled to the water delivery line. Controls  362  for a normally closed solenoid valve control  364  air purge operations. A filter  366  also is provided in the water delivery line, and sensors  368  with valves  370  (manual hand valve-locking flag feature (normally open)) are coupled in parallel with filter  366 .  
         [0048]    Normally open valves  372 , coupled to controls  374 , are provided to enable water to drain from the water delivery line into a water drain system. Water in the water delivery line flows through a heat exchanger  376  which receives air from the eight stage bleed of high pressure compressor  258 .  
         [0049]    For frame water injection, multiple sensors  378  and control valves  380  control the supply of water to nozzles  282  and  284 . Circuit  350  also includes a water accumulator  382 . For inlet water injection, sensors  378  and control valve  384  control the supply of water to nozzles  282 .  
         [0050]    Letter designations in FIG. 12 have the following meanings.  
         [0051]    T—temperature measurement location  
         [0052]    P—pressure measurement location  
         [0053]    PI—pressure indicator  
         [0054]    N/C—normally closed  
         [0055]    N/O—normally open  
         [0056]    PDSW—pressure differential switch  
         [0057]    PDI—pressure differential indicator  
         [0058]    DRN—drain  
         [0059]    ZS—position switch  
         [0060]    WMV—water metering valve  
         [0061]    PRG—purge  
         [0062]    LVDT—linear variable differential transformer  
         [0063]    In FIG. 13, a solid line is a water supply line, a double dash line is a drain line, and a solid line with hash marks is an electrical line. Boxes identify interfaces between the water supply system and the engine. Water metering valves  286  and other control/measurement valves  288 , and an orifice  290  (for inlet water injection) are utilized in connection with the control of water flow through circuit  350 .  
         [0064]    [0064]FIG. 13 is a chart illustrating an exemplary water schedule for power augmentation of engine  250 . The amount of water supplied to the nozzles for power augmentation varies depending, for example, on the ambient temperature as well as the size of the desired droplets. Accordingly, amount of percent increase of water supplied to the nozzles for evaporative cooling also varies. A droplet size of 20 microns has been found, in at least one application, to provide the acceptable results. Of course, the operating parameters of the engine in which water spray injection is utilized, the desired operating parameters, and other factors known to those skilled in the art affect the amount of water spray injection.  
         [0065]    [0065]FIG. 14 is a flow chart  500  illustrating an exemplary method for operating a gas turbine engine, such as any of engines  10 ,  50 ,  82 ,  84 ,  160 ,  200 , or  250  (shown above in FIGS. 1-8). FIG. 15 is a table  502  illustrating exemplary test results obtained using the method illustrated in FIG. 14. FIG. 16 is a chart  504  illustrating exemplary power curve results generated using the method shown in FIG. 14. Specifically, flow chart  500  illustrates an exemplary method that may be employed on any gas turbine engine that includes water injection system, such as apparatus  24  (shown in FIG. 1), an engine controller, such as controller  11  (shown in FIG. 1) and a variable inlet guide vane (VIGV) assembly, such as assembly  23  (shown in FIG. 1). More specifically, the exemplary results illustrated in FIGS. 15 and 16 were obtained following engine cycle model predictions and engine testing on an LM6000 PC SPRINT™ Gas Turbine Engine commercially available from General Electric Company, Cincinnati, Ohio, and modified to include a VIGV assembly.  
         [0066]    Initially, before the engine is operated, the engine controller is reconfigured  510  to facilitate changing specific turbine operational parameters. Reconfiguring  510  the engine controller facilitates optimizing gas turbine output and efficiency. Specifically, controller adjustments for parameters representing corrected core engine shaft speed, XN25R3, injected inter-cooling water flow, and engine inlet air flow are reconfigured  510 . More specifically, the modifications to core engine shaft speed facilitate enabling a nominal speed increase of up to approximately two percent based on the inlet temperature during engine operation, and the modifications to injected inter-cooling water flow facilitate enabling a nominal flow rate increase of up to approximately two hundred percent based on the inlet temperature during engine operation. Furthermore, altering the operational schedule for the VIGV assembly to respond in light of the aforementioned engine control software changes, facilitates enabling a nominal air flow increase of approximately two percent based on the inlet temperature during engine operation.  
         [0067]    In particular, these operating parameters are influenced by the application of turbine variable inlet geometry and as shown in the exemplary test results, operating an engine using these engine control software changes in combination with the VIGV assembly facilitates enhanced engine efficiency and performance. More specifically, as described in more detail below, the engine cycle model predictions, shown in FIG. 15, also have shown an approximate four percent increased gas output and a gas turbine efficiency (heat rate) improvement of approximately one-half percent. The exemplary results were obtainable over a normal ambient operating range.  
         [0068]    During operation, the engine is initially operated  520  to its maximum power output without spray injection. A working fluid, such as air, is compressed while flowing through a low pressure compressor, and compressed air is supplied from the low pressure compressor to a high pressure compressor. The output of the gas turbine engine is limited by signals received by the engine controller indicative of a temperature T3 of the working fluid at the output of the high pressure compressor. When a predefined T3 temperature limit is reached, engine maximum power output is achieved based on the predefined T3 temperature limit for a specific inlet temperature. This is illustrated in FIG. 16 using power curve  526 . For example, with the engine operating with an inlet temperature of approximately 70° F. (point a in FIG. 16), the engine produces an output of approximately 37.9 MW, when limited by the compressor discharge temperature T3.  
         [0069]    Once maximum power output is achieved, water injection apparatus is initiated  532  and water is injected into the engine. Due to the higher temperature environment at the location at which the water spray is injected, the water spray partially evaporates before entering the high pressure compressor. The water spray cools the air flow in the high pressure compressor for at least each stage of the compressor through which such spray flows, i.e., until it evaporates. Usually by the sixth stage of the compressor, the water spray is evaporated. The air is further compressed by the high pressure compressor, and highly compressed air is delivered to the combustor. Airflow from the combustor drives the high pressure turbine and the low pressure turbine.  
         [0070]    The water particles from the water spray apparatus provide the advantage that the temperature of the airflow at the outlet of the high pressure compressor (temperature T3) and the temperature of the airflow at the outlet of the combustor (temperature T41) are reduced as compared to such temperatures without the spray. Specifically, the water spray extracts heat from the hot air flowing into and through the compressor, and by extracting such heat from the air flow, the T3 and T41 temperatures are reduced along with the required compressor power.  
         [0071]    More specifically, the water injection has the effect of reducing the compressor outlet temperature T3, such that in effect, the turbine is operated as if it were at a lower inlet temperature. This is illustrated in FIG. 16. Starting from power curve  526 , at point (a) and injecting water, the engine power is then increased  542  as the T3 temperature remains the limiting control parameter, until it reaches point (b) on power curve  540 . This power level illustrated on power curve  540 , is substantially the equivalent of power settings available at point (c) on original power curve  526 . For example, with the engine operating with an inlet temperature of approximately 70° F. and 37.9 MW point (a), after water injection is applied and the engine is re-accelerated  542 , the engine produces a power output of approximately 45.2 MW at point (b), when limited by the same predefined compressor discharge temperature T3 limit. This is substantially equivalent to operating on power curve  526  at point (c), which is more than 15° F. cooler in inlet temperature.  
         [0072]    Applying the same principle, when the engine is operated with an increased water schedule, speed limit, and active VIGV, the engine controller modifications enable the turbine to operate at an even higher power level, illustrated at point (d) on power curve  550 . This is substantially equivalent to an even lower inlet temperature, illustrated at point (e) on original power curve  526 . Specifically, the engine controller modifications impact the operating parameters that limit the operation of the water-injected engine: core airflow, core speed, and water-injection flow rate. More specifically, when demonstrated using a Brayton Cycle, the management of the inlet air by the VIGV system allows a cycle volume increase, and the core speed increase effectively increases the pressure ratio of the turbine, thus allowing a cycle pressure and mass flow increase. As a result, the area enclosed in a continuous Braton Cycle pressure versus volume, which represents the work output of the system, is increased.  
         [0073]    As shown in FIG. 15, the modeling was completed using various combinations (+1 representing inclusion of the parameter, −1 representing exclusion of the parameter) of water injection (SPRINT), core engine shaft speed, variable inlet guide vane operation, and a passive clearance control (PCC) system, which was weighted to be a less significant factor during modeling. Modeling cycles were performed at an inlet temperature of 50° F. and at an inlet temperature of 80° F. As shown in the results, in each model cycle, the engine operating with the water injection, the VIGV, and the software modifications (represented by line  7  of each model cycle) produced a higher output.  
         [0074]    The above-described methods provide a cost-effective and highly reliable means for enhancing gas turbine engine operation. The method includes modifying the gas turbine engine controller software to impact several operational predefined parameter limits such that enhanced turbine performance is facilitated. Specifically, operational parameter changes are made to the controller of an engine that includes water injection and variable inlet guide vanes, such that the engine is capable of operating with an increased water injection flow rate, an increased core engine speed, and with an increased inlet air flow. Accordingly, the turbine is operable with a reduced effective inlet temperature over a range of normal inlet temperatures. As a result, the combination of the VIGV and the controller modifications enables the turbine to operate with enhanced performance and output in a cost-effective and reliable manner.  
         [0075]    Exemplary embodiments of turbines and engine controllers are described above in detail. The methods described are not limited to the specific turbine embodiments described herein, but rather, components of each method may be utilized independently and separately from other components described herein. Furthermore, components of each gas turbine engine may also be used in combination with other turbine components.  
         [0076]    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.