Patent Publication Number: US-2023145878-A1

Title: Methods for power transfer in cryogenic fuel applications

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of, and claims priority to and the benefit of, U.S. application Ser. No. 16/734,925, filed Jan. 6, 2020, and entitled “SYSTEMS AND METHODS FOR POWER TRANSFER IN CRYOGENIC FUEL APPLICATIONS,” which is incorporated by reference herein in its entirety for all purposes. 
    
    
     FIELD 
     The present disclosure relates generally to aircraft systems and, more particularly, to aircraft power plant and auxiliary systems. 
     BACKGROUND 
     It has been proposed to operate gas turbine engines, such as those used to propel aircraft, by using more than one type of fuel. Such fuels may be used together simultaneously or selectively during differing periods of operation. In such regimes, it is usual to use a conventional fuel such as, for example, kerosene as the primary fuel and a secondary fuel such as a cryogenic liquid fuel. The secondary fuel may be burned to power the engine either simultaneously with the primary fuel or as a substitute during certain periods of engine operation. Operating engines with blended traditional and cryogenic fuels may tend to enhance engine performance. 
     SUMMARY 
     In various embodiments, a fuel power transfer system for an engine comprises a cryogenic fuel supply, a fuel pump in fluid communication with the cryogenic fuel supply, a multi-position valve in fluid communication with the fuel pump and a combustion chamber of the engine, a fuel turbine operatively coupled to the fuel pump and having a primary discharge port in fluid communication with the combustion chamber, a primary heat exchanger in fluid communication between the multi-position valve and the fuel turbine, and a gearbox operatively coupled to the fuel turbine and the fuel pump and configured to transfer power from the fuel turbine to the engine. 
     In various embodiments, a motor-generator may be operatively coupled to the gearbox and selectively configurable to operate as a motor or a generator. In various embodiments, an auxiliary heat exchanger may be in fluid communication between the multi-position valve and the combustion chamber. In various embodiments, the fuel pump and the fuel turbine are operatively coupled via a common shaft. In various embodiments, the motor-generator is coupled to the gearbox via an accessory clutch and wherein the gearbox is configured to transfer power from the fuel turbine to the engine via a power transfer clutch. In various embodiments, the system further comprises a controller, a sensor in communication with the controller and configured to provide sensor feedback and a tangible, non-transitory memory configured to communicate with the controller, the tangible, non-transitory memory having instructions stored thereon that, in response to execution by the controller, cause the controller to perform operations comprising, determining a startup condition, controlling the motor-generator in response to the startup condition, controlling the multi-position valve in response to the startup condition, and controlling the accessory clutch in response to the startup condition. 
     In various embodiments, the operations further comprise determining an auxiliary heat condition and controlling the multi-position valve to direct a portion of the fuel to an auxiliary heat exchanger in fluid communication with the combustion chamber in response to the auxiliary heat condition. In various embodiments, the operations further comprise determining an operating power condition, controlling the multi-position valve in response to the operating power condition, and controlling at least one of the accessory clutch or the power transfer clutch in response to the operating power condition. 
     In various embodiments, the system comprises a primary turbine discharge valve configured to be controlled by the controller and in fluid communication between the combustion chamber and the primary discharge port, and a secondary turbine discharge valve configured to be controlled by the controller and in fluid communication between the combustion chamber and a secondary discharge port of the fuel turbine, wherein each of the primary turbine discharge valve and the secondary turbine discharge valve are configured to interrupt fluid communication with the combustion chamber. In various embodiments, the operations further comprise determining an intermediate operating power condition, controlling at least one of the accessory clutch or the power transfer clutch in response to the intermediate operating power condition, and controlling at least one of the primary turbine discharge valve or the secondary turbine discharge valve in response to the intermediate operating power condition. 
     In various embodiments, the operations further comprise selecting a motor mode of the motor generator in response to the startup condition, selecting a generator mode of the motor generator in response to the operating power condition, and controlling an electrical load disconnect relay in response to the operating power condition. In various embodiments, the sensor includes a first fuel pressure sensor in fluid communication with the primary discharge port and a second fuel pressure sensor in fluid communication with the secondary discharge port, wherein the operations further comprise receiving a primary discharge port pressure and a secondary discharge port pressure, and determining the operating power condition or the intermediate operating power condition based on the primary discharge port pressure and the secondary discharge port pressure. 
     In various embodiments, a method of controlling a fuel power transfer system for an engine comprises determining a startup condition, controlling a motor-generator in response to the startup condition, controlling a multi-position valve in response to the startup condition, and controlling an accessory clutch in response to the startup condition. 
     In various embodiments, the method includes determining an auxiliary heat condition and controlling the multi-position valve to direct a portion of a fuel to an auxiliary heat exchanger in fluid communication with a combustion chamber of the engine in response to the auxiliary heat condition. In various embodiments, the method includes determining an operating power condition, controlling the multi-position valve in response to the operating power condition, and controlling at least one of the accessory clutch or the power transfer clutch in response to the operating power condition. In various embodiments, the method includes determining an intermediate operating power condition, controlling at least one of the accessory clutch or the power transfer clutch in response to the intermediate operating power condition, and controlling at least one of the primary turbine discharge valve or the secondary turbine discharge valve in response to the intermediate operating power condition. 
     In various embodiments, an article of manufacture is provided. The article of manufacture may include a tangible, non-transitory computer-readable storage medium having instructions stored thereon that, in response to execution by a processor, cause the processor to perform operations comprising determining a startup condition, controlling a motor-generator in response to the startup condition, controlling a multi-position valve in response to the startup condition, and controlling an accessory clutch in response to the startup condition. 
     In various embodiments, the operations include determining an operating power condition, controlling the multi-position valve in response to the operating power condition, and controlling at least one of the accessory clutch or the power transfer clutch in response to the operating power condition. In various embodiments, the operations include determining an intermediate operating power condition, controlling at least one of the accessory clutch or the power transfer clutch in response to the intermediate operating power condition, and controlling at least one of the primary turbine discharge valve or the secondary turbine discharge valve in response to the intermediate operating power condition. In various embodiments, the operation further comprise operations further comprise selecting a motor mode of the motor generator in response to the startup condition, selecting a generator mode of the motor generator in response to the operating power condition, and controlling an electrical load disconnect relay in response to the operating power condition. 
     The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be exemplary in nature and non-limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the detailed description and claims when considered in connection with the figures, wherein like numerals denote like elements. 
         FIG.  1 A  illustrates an exemplary aircraft, in accordance with various embodiments; 
         FIG.  1 B  illustrates an exemplary gas turbine engine, in accordance with various embodiments; 
         FIG.  2    illustrates a fuel and power transfer system, in accordance with various embodiments; and 
         FIG.  3    illustrates a method of controlling a fuel power transfer system. 
     
    
    
     DETAILED DESCRIPTION 
     All ranges and ratio limits disclosed herein may be combined. It is to be understood that unless specifically stated otherwise, references to “a,” “an,” and/or “the” may include one or more than one and that reference to an item in the singular may also include the item in the plural. 
     The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the exemplary embodiments of the disclosure, it should be understood that other embodiments may be realized and that logical changes and adaptations in design and construction may be made in accordance with this disclosure and the teachings herein. Thus, the detailed description herein is presented for purposes of illustration only and not limitation. 
     The scope of the disclosure is defined by the appended claims and their legal equivalents rather than by merely the examples described. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, coupled, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact. Surface shading lines may be used throughout the figures to denote different parts but not necessarily to denote the same or different materials. 
     With reference to  FIG.  1 A , an aircraft  10  is illustrated in accordance with various embodiments. Aircraft  10  comprises a fuselage  12 , wings  14 , cockpit controls  16 , landing gear  18 , and a propulsion system, such as gas turbine engines  20 . In various embodiments, aircraft  10  may include a fuel and power transfer system  200 . 
     In various embodiments and with reference to  FIG.  1 B , a gas turbine engine  20  is provided. Gas turbine engine  20  may be a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . In operation, fan section  22  can drive air along a bypass flow-path B while compressor section  24  can drive air through a core flow-path C for compression and communication into combustor section  26  then expansion through turbine section  28 . In various embodiments, gas turbine engine  20  may incorporate a plurality of engine accessories such as, for example, components of power transfer system  200 . Although depicted as a turbofan gas turbine engine  20  herein, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of engines including turbojet engines, a low-bypass turbofans, a high bypass turbofans, reciprocating engines, or any other internal combustion engine known to those skilled in the art. 
     Gas turbine engine  20  may generally comprise a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A-A′ relative to an engine static structure  36  via one or more bearing systems  38  (shown as bearing system  38 - 1  and bearing system  38 - 2 ). It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided, including for example, bearing system  38 , bearing system  38 - 1 , and bearing system  38 - 2 . 
     Low speed spool  30  may generally comprise an inner shaft  40  that interconnects a fan  42 , a low pressure (or first) compressor section  44  (also referred to a low pressure compressor) and a low pressure (or first) turbine section  46 . Inner shaft  40  may be connected to fan  42  through a geared architecture  48  that can drive fan  42  at a lower speed than low speed spool  30 . Geared architecture  48  may comprise a gear assembly  60  enclosed within a gear housing  62 . Gear assembly  60  couples inner shaft  40  to a rotating fan structure. High speed spool  32  may comprise an outer shaft  50  that interconnects a high pressure compressor (“HPC”)  52  (e.g., a second compressor section) and high pressure (or second) turbine section  54 . A combustor  56  may be located between HPC  52  and high pressure turbine  54 . A mid-turbine frame  57  of engine static structure  36  may be located generally between high pressure turbine  54  and low pressure turbine  46 . Mid-turbine frame  57  may support one or more bearing systems  38  in turbine section  28 . Inner shaft  40  and outer shaft  50  may be concentric and rotate via bearing systems  38  about the engine central longitudinal axis A-A′, which is collinear with their longitudinal axes. As used herein, a “high pressure” compressor or turbine experiences a higher pressure than a corresponding “low pressure” compressor or turbine. 
     The core airflow C may be compressed by low pressure compressor  44  then HPC  52 , mixed and burned with fuel in combustor  56 , then expanded over high pressure turbine  54  and low pressure turbine  46 . Mid-turbine frame  57  includes airfoils  59  which are in the core airflow path. Low pressure turbine  46 , and high pressure turbine  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. 
     Gas turbine engine  20  may be, for example, a high-bypass geared aircraft engine. In various embodiments, the bypass ratio of gas turbine engine  20  may be greater than about six (6). In various embodiments, the bypass ratio of gas turbine engine  20  may be greater than ten (10). In various embodiments, geared architecture  48  may be an epicyclic gear train, such as a star gear system (sun gear in meshing engagement with a plurality of star gears supported by a carrier and in meshing engagement with a ring gear) or other gear system. Geared architecture  48  may have a gear reduction ratio of greater than about 2.3 and low pressure turbine  46  may have a pressure ratio that is greater than about  5 . In various embodiments, the bypass ratio of gas turbine engine  20  is greater than about ten (10:1). In various embodiments, the diameter of fan  42  may be significantly larger than that of the low pressure compressor  44 , and the low pressure turbine  46  may have a pressure ratio that is greater than about (5:1). Low pressure turbine  46  pressure ratio may be measured prior to inlet of low pressure turbine  46  as related to the pressure at the outlet of low pressure turbine  46  prior to an exhaust nozzle. It should be understood, however, that the above parameters are exemplary of various embodiments of a suitable geared architecture engine and that the present disclosure contemplates other gas turbine engines including direct drive turbofans. 
     In various embodiments, the next generation of turbofan engines may be designed for higher efficiency which is associated with higher pressure ratios and higher temperatures in the HPC  52 . These higher operating temperatures and pressure ratios may create operating environments that may cause thermal loads that are higher than the thermal loads encountered in conventional turbofan engines, which may shorten the operational life of current components. 
     In various embodiments, HPC  52  may comprise alternating rows of rotating rotors and stationary stators. Stators may have a cantilevered configuration or a shrouded configuration. More specifically, a stator may comprise a stator vane, a casing support and a hub support. In this regard, a stator vane may be supported along an outer diameter by a casing support and along an inner diameter by a hub support. In contrast, a cantilevered stator may comprise a stator vane that is only retained and/or supported at the casing (e.g., along an outer diameter). 
     In various embodiments, rotors may be configured to compress and spin a fluid flow. Stators may be configured to receive and straighten the fluid flow. In operation, the fluid flow discharged from the trailing edge of stators may be straightened (e.g., the flow may be directed in a substantially parallel path to the centerline of the engine and/or HPC) to increase and/or improve the efficiency of the engine and, more specifically, to achieve maximum and/or near maximum compression and efficiency when the straightened air is compressed and spun by rotor  64 . 
     With additional reference to  FIG.  2   , system  200  is shown integrated with the gas turbine engine  20  of aircraft  10  according to various embodiments. System  200  includes a controller  202  which may be integrated into computer systems onboard aircraft  10 . In various embodiments, controller  202  may be configured as a central network element or hub to access various systems, engines, and components of system  200 . Controller  202  may comprise a network, computer-based system, and/or software components configured to provide an access point to various systems, engines, and components of system  200 . In various embodiments, controller  202  may comprise a processor. In various embodiments, controller  202  may be implemented in a single processor. In various embodiments, controller  202  may be implemented as and may include one or more processors and/or one or more tangible, non-transitory memories and be capable of implementing logic. Each processor can be a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof. Controller  202  may comprise a processor configured to implement various logical operations in response to execution of instructions, for example, instructions stored on a non-transitory, tangible, computer-readable medium configured to communicate with controller  202 . In this regard, controller  202  may be configured to control various components of system  200  via control signals  208 . 
     System program instructions and/or controller instructions may be loaded onto a non-transitory, tangible computer-readable medium having instructions stored thereon that, in response to execution by a controller, cause the controller to perform various operations. The term “non-transitory” is to be understood to remove only propagating transitory signals per se and includes all standard computer-readable media that are not only propagating transitory signals per se. 
     In various embodiments, controller  202  may be in electronic communication with a pilot through a control interface  204  of cockpit controls  16 , for example, a multifunction display, a switch panel, and/or the like which an operator can operate. The control interface  204  may enable the operator to interact with system  200  for example, to issue commands, display information such as, for example, warnings, or receive outputs. Control interface  204  may comprise any suitable combination of hardware, software, and/or database components. 
     System  200  comprises one or more feedback elements to monitor and measure aircraft  10  and gas turbine engine  20  characteristics. For example, controller  202  is in electronic communication with sensors  206  that may be coupled to or in direct electronic communication with aircraft systems such as, for example, propulsion systems, fuel systems (e.g., primary and secondary fuel systems), and/or the like. Controller  202  may be in electronic communication with the full suite of aircraft sensors and other data sources available within and without the aircraft  10 . Sensors  206  may comprise a temperature sensor, a torque sensor, a speed sensor, a pressure sensor, a position sensor, an accelerometer, a voltmeter, an ammeter, a wattmeter, an optical sensor, or any other suitable measuring device known to those skilled in the art. Sensors  206  may be configured to transmit measurements to controller  202 , thereby providing sensor feedback about the measured system. The sensor feedback may be, for example, a speed signal, or may be position feedback, temperature feedback, pressure feedback or other data. 
     System  200  includes a cryogenic fuel supply  210  which may be configured to store a fuel such as a cryogenic liquid fuel. In various embodiments, the fuel may be one of molecular hydrogen, methane, ethane, propane, butane, natural gas and/or the like. The cryogenic fuel supply  210  is in fluid communication with a fuel pump  212  via supply line  214 . The fuel pump  212  is configured to increase the pressure of the fuel (such as, for example, above a critical pressure of the fuel) and supply the fuel at an increased pressure to a multi-position valve  216 . In various embodiments, the fuel pump  212  is coupled to a gearbox  218  and receives operative power therefrom such as, for example, via a pump shaft. 
     In various embodiments, gearbox  218  may receive operative power from the gas turbine engine  20 . For example, in various embodiments, gearbox  218  may be coupled to any of the spools (e.g.,  30 ,  32 ) and/or shafts (e.g.,  40 ,  50 ) of gas turbine engine  20  by a power transfer shaft  220 . The power transfer shaft  220  may be coupled to the gearbox  218  through a power transfer clutch  222 . In this regard, the gearbox  218  may be selectively mechanically coupled to the gas turbine engine  20  and thereby configured to transmit to or receive power from the gas turbine engine  20 . 
     In various embodiments and in like regard, gearbox  218  may be mechanically coupled to a motor-generator  224  via accessory shaft  226  and accessory clutch  228 . Motor-generator  224  may be selectively operable as a motor or as a generator. In this regard, in motor operation, motor-generator  224  may be configured to provide operative power to the fuel pump  212  via the gearbox  218  by engaging the accessory clutch  228 . Similarly, motor-generator  224  may be configured to provide operative power to the gas turbine engine  20  via the gearbox  218  by engaging the accessory clutch  228  and the power transfer clutch  222 . Motor-generator  224  may be coupled to an electrical load  230  such as, for example, an electrical power system of aircraft  10 . When configured to operate as a generator, motor-generator  224  may supply electrical power to the electrical load  230  in response to receiving operative power from the gearbox  218 . In various embodiments, the electrical load  230  may be disconnected from the motor-generator  224  by, for example, an electrical load disconnect relay  232 . 
     In various embodiments, a fuel turbine  234  may be operatively coupled to the fuel pump  212  and/or the gearbox  218  such as, for example, via a common shaft  237 . In various embodiments, the fuel turbine  234  may provide input to the gearbox  218  and subsequently drive the fuel pump  212  and motor-generator  224  via geared shafting configured to provide desired rotational speeds for each component. The fuel turbine  234  may be a variable pressure discharge turbine and may include a primary discharge port  236  (i.e., a first discharge port) and a secondary discharge port  238  (i.e., a second discharge port) in fluid communication with a combustion chamber of the gas turbine engine  20  (e.g., combustor  56 ). In various embodiments, each discharge port of the fuel turbine  234  may be in fluid communication with a respective control valve configured to regulate and/or interrupt fluid communication with the combustion chamber. For example, a primary turbine discharge valve  240  and a secondary turbine discharge valve  242  (i.e., a first valve and a second valve) may be coupled to the respective discharge port of the fuel turbine  234 . In various embodiments, sensors  206  may include a first fuel pressure sensor  244  may be in fluid communication with the primary discharge port  236  and a second fuel pressure sensor  246  may be in fluid communication with the secondary discharge port  238 . 
     In various embodiments, multi-position valve  216  may be in fluid communication with a primary heat exchanger  248 . The multi-position valve  216  may be configured to send a portion of the fuel from fuel pump  212  through the primary heat exchanger  248 . The primary heat exchanger  248  may extract heat from the gas turbine engine  20  and impart heat energy to the fuel. In this regard, the primary heat exchanger  248  may be configured to vaporize and expand the fuel and deliver heated gaseous fuel to the inlet  250  of the fuel turbine  234 . It will be appreciated that fuel serves as a working fluid for the fuel turbine  234  which may thereby extract energy from the working fluid to drive loads such as the fuel pump  212 , gearbox  218 , motor-generator  224 , and power transfer shaft  220  and that these loads may be modulated (e.g., by commands from controller  202 ) via clutches  222  and  228 . The heated gaseous fuel may be further expanded by the fuel turbine  234  and may be directed to the combustion chamber via the primary discharge port  236  and/or the secondary discharge port  238 . 
     In various embodiments, multi-position valve  216  may be in fluid communication with an auxiliary heat exchanger  252  in fluid communication with the combustion chamber. The multi-position valve  216  may be selectively configurable to direct a portion or an entirety of the fuel pump  212  fuel output directly to any of the combustion chamber, the auxiliary heat exchanger  252 , or the primary heat exchanger  248 . In various embodiments, the auxiliary heat exchanger  252  may be in fluid communication with the primary turbine discharge valve  240  and/or the secondary turbine discharge valve  242 . In this regard, by selecting a position of the multi-position valve in response to a startup condition, the auxiliary heat exchanger  252  may be configured to preheat fuel from the fuel pump  212  to a gaseous state during the startup condition prior to introduction to the combustion chamber. In like regard, by selecting a position of the multi-position valve in response to an operating power condition, the auxiliary heat exchanger  252  may be configured to reheat the expanded gaseous fuel from either of the primary discharge port  236  and/or the secondary discharge port  238  prior to introduction to the combustion chamber during the operating power condition. 
     With additional reference to  FIG.  3   , a method  300  of controlling a fuel and power transfer system is illustrated according to various embodiments. Method  300  comprises determining a startup condition, controlling a motor-generator in response to the startup condition, controlling a multi-position valve in response to the startup condition, and controlling an accessory clutch in response to the startup condition (step  302 ). For example, controller  202  may determine a startup condition in response to an input from control interface  204  such as an engine start command. The controller  202  may command the accessory clutch  228  to engage and may select a motor mode of the motor-generator  224 . In this regard, controller  202  may provide operative force to the fuel pump  212  via gearbox  218 . Stated another way, the controller  202  may control and/or configure the multi-position valve  216  to enable fluid communication between the fuel pump  212  and the combustion chamber but bypass the primary heat exchanger  248  in response to the startup condition. 
     In various embodiments, method  300  includes controller  202  determining an auxiliary heat condition and controlling the multi-position valve  216  to direct a portion of a fuel to the auxiliary heat exchanger  252  (step  304 ). Method  300  includes determining an operating power condition, controlling the multi-position valve in response to the operating power condition, and controlling at least one of the accessory clutch or the power transfer clutch in response to the operating power condition (step  306 ). In various embodiments, method  300  includes determining an intermediate operating power condition, controlling at least one of the accessory clutch or the power transfer clutch in response to the intermediate operating power condition, and controlling at least one of the primary turbine discharge valve or the secondary turbine discharge valve in response to the intermediate operating power condition (step  308 ). In various embodiments, the controller  202  may determine the intermediate operating condition based on a power setting of the turbine engine  20  such as, for example, a cruise power setting which may be entered via the control interface  204 . The intermediate operating condition may be determined based on sensors  206  measurements such as, for example, measurements at a P 3  (e.g., a combustor inlet pressure) station of the turbine engine  20  or a fuel pressure measurement. In like regard, an operating power condition may be determined where the measurements are relatively greater than that of the intermediate operating condition such as, for example, a full power setting which may be entered via the control interface  204 . In various embodiments, method  300  includes comprise selecting a motor mode of the motor generator in response to the startup condition, selecting a generator mode of the motor generator in response to the operating power condition, and controlling an electrical load disconnect relay in response to the operating power condition (step  310 ). 
     For example, controller  202  may determine an operating power condition or an intermediate operating power condition of gas turbine engine  20  such as, for example, based on sensor data from sensors  206  or in response to a power setting command from control interface  204 . The controller  202  may receive a primary discharge port pressure from the first fuel pressure sensor  244  may a secondary discharge port pressure from the second fuel pressure sensor  246 . In this regard, the controller  202  may determine the operating power condition or the intermediate operating power condition based on the primary discharge port pressure and the secondary discharge port pressure. 
     Controller  202  may control the multi-position valve  216  to enable fluid communication between the fuel pump  212 , the primary heat exchanger  248 , and the inlet  250  of the fuel turbine  234 . The controller  202  may command accessory clutch  228  to engage and may command the power transfer clutch  222  to engage. The controller  202  may select a generator mode of the motor-generator  224  and may command the electrical load disconnect relay  232  to close and thereby enable electronic communication between the electrical load  230  and the motor-generator  224 . In this regard, the controller  202  may configure the fuel turbine  234  to transmit power to the gearbox  218  and thereby transfer power between the gas turbine engine  20  and the electrical load  230 . 
     In various embodiments controller  202  may determine an intermediate operating power condition in response to an intermediate power setting from the control interface  204  or in response to sensor  206  data such as gas turbine engine  20  station temperatures, rotor speeds, internal pressures, inlet  250  temperature, the fuel turbine discharge port pressures and/or the like. The controller  202  may control or module each of the primary turbine discharge valve  240  and a secondary turbine discharge valve  242  in response to the intermediate power condition. The controller  202  may command the power transfer clutch to disengage. In this regard, controller  202  may control the fuel turbine  234  discharge pressure to remain above the combustion chamber operating pressure and thereby tend to inhibit back driving of the fuel turbine  234  by the gas turbine engine  20 . 
     Benefits and other advantages have been described herein with regard to specific embodiments. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system. However, the benefits, advantages, and any elements that may cause any benefit or advantage to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the disclosure. The scope of the disclosure is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B and C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C. 
     Systems, methods and apparatus are provided herein. In the detailed description herein, references to “various embodiments,” “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments. 
     Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is invoke 35 U.S.C. 112(f) unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.