Abstract:
A system for the management of thermal transfer in a gas turbine engine includes a heat generating sub-system in operable communication with the engine, a fuel source to supply a fuel, a fuel stabilization unit to receive the fuel from the fuel source and to provide the fuel to the engine, and a heat exchanger in thermal communication with the fuel to transfer heat from the heat generating sub-system to the fuel. A method of managing thermal transfer in an aircraft includes removing oxygen from a stream of a fuel fed to an engine used to drive the aircraft, transferring heat from a heat generating sub-system of the aircraft to the fuel, and combusting the fuel. A system for the thermal management of an aircraft provides for powering the aircraft, supplying a fuel deoxygenating the fuel, and transferring heat between a heat generating sub-system of the aircraft and the fuel.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part application of U.S. patent application Ser. No. 10/407,004 entitled “Planar Membrane Deoxygenator” filed on Apr. 4, 2003, now U.S. Pat. No. 6,709,492, issued Mar. 23, 2004, the content of which is incorporated herein in its entirety. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to systems, methods, and devices for the management of heat transfer and, more particularly, to systems, methods, and devices for managing the transfer of heat between an energy conversion device and its adjacent environment. 
     BACKGROUND 
     Heat management systems for energy conversion devices oftentimes utilize fuels as cooling mediums, particularly on aircraft and other airborne systems where the use of ambient air as a heat sink results in significant performance penalties. In addition, the recovery of waste heat and its re-direction to the fuel stream to heat the fuel results in increased operating efficiency. One of the factors negatively affecting the usable cooling capacity of a particular fuel with regard to such a system is the rate of formation of undesirable oxidative reaction products and their deposit onto the surfaces of fuel system devices. The rate of formation of such products may be dependent at least in part on the amount of dissolved oxygen present within the fuel. The amount of dissolved oxygen present may be due to a variety of factors such as exposure of the fuel to air and more specifically the exposure of the fuel to air during fuel pumping operations. The presence of dissolved oxygen can result in the formation of hydroperoxides that, when heated, form free radicals that polymerize and form high molecular weight oxidative reaction products, which are typically insoluble in the fuel. Such products may be subsequently deposited within the fuel delivery and injection systems, as well as on the other surfaces, of the energy conversion device detrimentally affecting the performance and operation of the energy conversion device. Because the fuels used in energy conversion devices are typically hydrocarbon-based, the deposit comprises carbon and is generally referred to as “coke.” 
     Increasing the temperature of the fuel fed to the energy conversion device increases the rate of the oxidative reaction that occurs. Currently available fuels that have improved resistance to the formation of coke are generally more expensive or require additives. Fuel additives require additional hardware, on-board delivery systems, and costly supply infrastructure. Furthermore, such currently available fuels having improved resistance to the formation of coke are not always readily available. 
     SUMMARY OF THE INVENTION 
     The present invention is directed in one aspect to a system for the management of thermal transfer in a gas turbine engine. Such a system includes a heat generating sub-system (or multiple sub-systems) disposed in operable communication with the engine, a fuel source configured to supply a fuel, a fuel stabilization unit configured to receive the fuel from the fuel source and to provide the fuel to the engine, and a heat exchanger disposed in thermal communication with the fuel to effect the transfer of heat from the heat generating sub-system to the fuel. 
     In another aspect, a system for the management of heat transfer includes an energy conversion device and a fuel system configured to supply a fuel to the energy conversion device. The fuel system includes at least one heat generating sub-system disposed in thermal communication with the fuel from the fuel system to effect the transfer of heat from the heat generating sub-system to the fuel. The fuel is substantially coke-free and is heated to a temperature of greater than about 550 degrees F. 
     In another aspect, a method of managing thermal transfer in an aircraft includes removing oxygen from a stream of a fuel fed to an engine used to drive the aircraft, transferring heat from a heat generating sub-system of the aircraft to the fuel, and combusting the fuel. 
     In yet another aspect, a system for the thermal management of an aircraft includes means for powering the aircraft, means for supplying a fuel to the means for powering the aircraft, means for deoxygenating the fuel, and means for effecting the transfer of heat between a heat generating sub-system of the aircraft and the fuel. 
     In still another aspect, a system for the management of thermal transfer in an aircraft includes an aircraft engine, a heat generating sub-system (or multiple sub-systems) disposed in operable communication with the aircraft engine, a fuel source configured to supply a fuel, a fuel stabilization unit configured to receive the fuel from the fuel source and to provide an effluent fuel stream to the aircraft engine, and a heat exchanger disposed in thermal communication with the effluent fuel stream from the fuel stabilization unit and the heat generating sub-system to effect the transfer of heat from the heat generating sub-system to the effluent fuel stream. 
     One advantage of the above systems and method is an increase in the exploitable cooling capacity of the fuel. By increasing the exploitable cooling capacity, energy conversion devices are able to operate at increased temperatures while utilizing fuels of lower grades. Operation of the devices at increased temperatures provides a greater opportunity for the recovery of waste heat from heat generating components of the system. The recovery of waste heat, in turn, reduces fuel consumption costs associated with operation of the device because combustion of pre-heated fuel requires less energy input than combustion of unheated fuel. Increased cooling capacity (and thus high operating temperatures, recovery of waste heat, and reduced fuel consumption) also increases the overall efficiency of operating the device. 
     Another advantage is a reduction in coke formation within the energy conversion device. Decreasing the amount of dissolved oxygen present within the fuel as the temperature is increased retards the rate of oxidative reaction, which in turn reduces the formation of coke and its deposition on the surfaces of the energy conversion device, thereby reducing the maintenance requirements. Complete or partial deoxygenation of the fuel suppresses the coke formation across various aircraft fuel grades. A reduction in the amount of oxygen dissolved within the fuel decreases the rate of coke deposition and correspondingly increases the maximum allowable temperature sustainable by the fuel during operation of the energy conversion device. In other words, when lower amounts of dissolved oxygen are present within a fuel, more thermal energy can be absorbed by the fuel, thereby resulting in operations of the energy conversion device at higher fuel temperatures before coke deposition in the energy conversion device becomes undesirable. 
     Operational advantages to pre-heating the fuel to temperatures that prevent, limit, or minimize coke formation prior to entry of the fuel into the FSU also exist. In particular, oxygen solubility in the fuel, diffusivity of oxygen in the fuel, and diffusivity of oxygen through the membrane increase with increasing temperature. Thus, FSU performance may be increased by pre-heating the fuel. This may result in either a reduction in FSU volume (size and weight reductions) or increased FSU performance, which may result in further reductions in the fuel oxygen levels exiting the FSU. Furthermore, the reduction in FSU volume may further allow system design freedom in placement of the FSU within the fuel system (either upstream- or downstream of low-grade heat loads) and in the ability to cascade the heat loads and fuel system heat transfer hardware. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a system for the management of heat transfer between an energy conversion device and a fuel system. 
         FIG. 2  is a schematic representation of a fuel stabilization unit showing a fuel inlet. 
         FIG. 3  is a schematic representation of the fuel stabilization unit showing a fuel outlet and an oxygen outlet. 
         FIG. 4  is a cross sectional view of an assembly of a flow plate, permeable composite membranes, and porous substrates that comprise the fuel stabilization unit. 
         FIG. 5  is a schematic representation of a fuel passage defined by the flow plate. 
         FIG. 6  is an alternate embodiment of a fuel passage defined by the flow plate. 
         FIG. 7  is an exploded view of a flow plate/membrane/substrate assembly. 
         FIG. 8  is a system for the management of heat transfer in which a high temperature heat source is a high temperature oil system. 
         FIG. 9  is a system for the management of heat transfer in which a high temperature heat source is a cooled turbine cooling air unit. 
         FIG. 10  is a system for the management of heat transfer in which a high temperature heat source is a turbine exhaust recuperator. 
         FIG. 11  is a system for the management of heat transfer in which a high temperature heat source is a fuel-cooled environmental control system precooler. 
         FIG. 12  is a system for the management of heat transfer in which a high temperature heat source is an integrated air cycle environmental control system. 
         FIG. 13  is a system for the management of heat transfer in which a high temperature heat source is a heat pump. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a system for the management of heat transfer is shown generally at  10  and is hereinafter referred to as “system  10 .” As used herein, the term “management of heat transfer” is intended to indicate the control of heat transfer by regulation of various chemical- and physical parameters of associated sub-systems and work cycles. The sub-systems include, but are not limited to, fuel systems that provide a hydrocarbon-based fuel to the work cycle. The work cycle may be an energy conversion device. Although the system  10  is hereinafter described as being a component of an aircraft, it should be understood that the system  10  has relevance to other applications, e.g., utility power generation, land-based transport systems, marine- and fresh-water based transport systems, industrial equipment systems, and the like. Furthermore, it should be understood that the term “aircraft” includes all types of winged aircraft, rotorcraft, winged- and rotor hybrids, spacecraft, drones and other unmanned craft, weapons delivery systems, and the like. 
     In one embodiment of the system  10 , a fuel system  12  includes a fuel stabilization unit (FSU)  16  that receives fuel from a fuel source  18  and provides the fuel to the energy conversion device (hereinafter “engine  14 ”). Various heat generating sub-systems (e.g., low temperature heat sources  24 , pumps and metering systems  20 , high temperature heat sources  22 , combinations of the foregoing sources and systems, and the like), which effect the thermal communication between various components of the system  10  during operation, are integrated into the fuel system  12  by being disposed in thermal communication with the fuel either upstream or downstream from the FSU  16 . A fuel pre-heater  13  may further be disposed in the fuel system  12  prior to the FSU  16  to increase the temperature of the fuel received into the FSU  16 . Selectively-actuatable fuel line bypasses  23  having valves  25  are preferably disposed in the fuel system  12  to provide for the bypass of fuel around the various sub-systems and particularly the high temperature heat sources  22 . 
     The engine  14  is disposed in operable communication with the various heat generating sub-systems and preferably comprises a gas turbine engine having a compressor  30 , a combustor  32 , and a turbine  34 . Fuel from the fuel system  12  is injected into the combustor  32  through fuel injection nozzles  36  and ignited. An output shaft  38  of the engine  14  provides output power that drives a plurality of blades that propel the aircraft. 
     Operation of the system  10  with the FSU  16  allows for the control of heat generated by the various sources and systems to provide benefits and advantages as described above. The temperature at which coke begins to form in the fuel is about 260 degrees F. Operation of the engine  14  (e.g., a gas turbine engine) at fuel temperatures of up to about 325 degrees F. generally produces an amount of coke buildup that is acceptable for most military applications. Operation of the system  10  with the FSU  16  to obtain a reduction in oxygen content of the fuel, however, enables the engine  14  to be operated at fuel temperatures greater than about 325 degrees F., preferably greater than about 550 degrees F., and more preferably about 700 degrees F. to about 800 degrees F. with no significant coking effects. The upper limit of operation is about 900 degrees F., which is approximately the temperature at which the fuel pyrolizes. 
     Referring now to  FIGS. 2-7 , the FSU  16  is shown. The FSU  16  is a fuel deoxygenating device that receives fuel either directly or indirectly from the fuel source. Upon operation of the FSU  16 , the amount of dissolved oxygen in the fuel is reduced to provide deoxygenated fuel. As used herein, the term “deoxygenated fuel” is intended to indicate fuel having reduced oxygen content relative to that of fuel in equilibrium with ambient air. The oxygen content of fuel in equilibrium with ambient air is about 70 parts per million (ppm). Depending upon the specific application of the FSU  16  (e.g., the operating temperatures of the system  10  of FIG.  1 ), the oxygen content of deoxygenated fuel may be about 5 ppm or, for applications in which operating temperatures approach about 900 degrees F., less than about 5 ppm. A reduction in the amount of dissolved oxygen in the fuel enables the fuel to absorb an increased amount of thermal energy while reducing the propagation of free radicals that form insoluble reaction products, thereby allowing the fuel to be substantially coke-free. As used herein, the term “substantially coke-free” is intended to indicate a fuel that, when used to operate an engine at elevated temperatures, deposits coke at a rate that enables the maintenance and/or overhaul schedules of the various apparatuses into which the FSU  16  is incorporated to be extended. 
     The FSU  16  includes an assembly of flow plates  27 , permeable composite membranes  42 , and porous substrates  39 . The flow plates  27 , the permeable composite membranes  42 , and the porous substrates  39  are preferably arranged in a stack such that the permeable composite membranes  42  are disposed in interfacial engagement with the flow plates  27  and such that the porous substrates  39  are disposed in interfacial engagement with the permeable composite membranes  42 . The flow plates  27  are structured to define passages  50  through which the fuel flows. 
     The assembly of flow plates  27  is mounted within a vacuum housing  60 . Vacuum is applied to the vacuum housing  60  to create an oxygen partial pressure differential across the permeable composite membranes  42 , thereby causing the migration of dissolved oxygen from the fuel flowing through the assembly of flow plates  27  and to an oxygen outlet  35 . The source of the partial pressure differential vacuum may be a vacuum pump, an oxygen-free circulating gas, or the like. In the case of an oxygen-free circulating gas, a strip gas (e.g., nitrogen) is circulated through the FSU  16  to create the oxygen pressure differential to aspirate the oxygen from the fuel, and a sorbent or filter or the like is disposed within the circuit to remove the oxygen from the strip gas. 
     Referring specifically to  FIG. 2 , an inlet  57  of the FSU  16  is shown. Fuel entering the FSU  16  flows from the inlet  57  in the direction indicated by an arrow  47  and is dispersed into each of the passages  50 . Seals  45  between the stacked flow plates  27  prevent the fuel from contacting and flowing into the porous substrates  39 . 
     Referring specifically to  FIG. 3 , outlets of the FSU  16  are shown. Oxygen removed through the porous substrates  39  is removed through an oxygen outlet  35  via the vacuum source, as is indicated by an arrow  51 . Deoxygenated fuel flowing through the flow plates  27  is removed through a fuel outlet  59 , as is indicated by an arrow  49 , and directed to one or several downstream sub-systems (e.g., pumps and metering systems, high temperature heat sources, and the like) and to the engine. 
     Referring now to  FIG. 4 , the assembly of flow plates  27 , permeable composite membranes  42 , and porous substrates  39  is shown. As stated above, the FSU  16  comprises an assembly of interfacially-engaged flow plates  27 , permeable composite membranes  42 , and porous substrates  39 . The flow plates  27 , described below with reference to  FIG. 5 , comprise planar structures that define the passages  50  through which the fuel is made to flow. The permeable composite membranes  42  preferably comprise fluoropolymer coatings  48  supported by porous backings  43 , which are in turn supported against the flow plates  27  by the porous substrates  39 . The application of vacuum to the assembly creates the partial pressure gradient that draws dissolved oxygen from the fuel in passages  50  through the permeable composite membranes  42  (in particular, through the fluoropolymer coatings  48 , through the porous backings  43 , and through the porous substrates  39 ) and out to the oxygen outlet  35 . 
     The permeable composite membrane  42  is defined by an amorphous fluoropolymer coating  48  supported on the porous backing  43 . The fluoropolymer coating  48  preferably derives from a polytetrafluoroethylene (PTFE) family of coatings and is deposited on the porous backing  43  to a thickness of about 0.5 micrometers to about 20 micrometers, preferably about 2 micrometers to about 10 micrometers, and more preferably about 2 micrometers to about 5 micrometers. The porous backing  43  preferably comprises a polyvinylidene difluoride (PVDF) or polyetherimide (PEI) substrate having a thickness of about 0.001 inches to about 0.02 inches, preferably about 0.002 inches to about 0.01 inches, and more preferably about 0.005 inches. The porosity of the porous backing  43  is greater than about 40% open space and preferably greater than about 50% open space. The nominal pore size of the pores of the porous backing  43  is less than about 0.25 micrometers, preferably less than about 0.2 micrometers, and more preferably less than about 0.1 micrometers. Amorphous polytetrafluoroethylene is available under the trade name Teflon AF® from DuPont located in Wilmington, Del. Other fluoropolymers usable as the fluoropolymer coating  48  include, but are not limited to, perfluorinated glassy polymers and polyperfluorobutenyl vinyl ether. Polyvinylidene difluoride is available under the trade name Kynar® from Atofina Chemicals, Inc. located in Philadelphia, Pa. 
     The porous substrate  39  comprises a lightweight plastic material (e.g., PVDF PEI polyethylene or the like) that is compatible with hydrocarbon-based fuel. Such material is of a selected porosity that enables the applied vacuum to create a suitable oxygen partial pressure differential across the permeable composite membrane  42 . The pore size, porosity, and thickness of the porous substrate  39  are determined by the oxygen mass flux requirement, which is a function of the mass flow rate of fuel. In a porous substrate  39  fabricated from polyethylene, the substrate is about 0.03 inches to about 0.09 inches in thickness, preferably about 0.04 inches to about 0.085 inches in thickness, and more preferably about 0.070 inches to about 0.080 inches in thickness. Alternatively, the porous substrate may comprise a woven plastic mesh or screen. a thinner and lighter vacuum permeate having a thickness of about 0.01 inches to about 0.03 inches. 
     Referring now to  FIGS. 5 and 6 , the flow plates  27  comprise planar structures having channels, one of which is shown at  31 , and ribs or baffles  52  arranged in the channels  31  to form a structure that, when assembled with the permeable composite membranes  42 , define the passages  50 . The baffles  52  are disposed across the channels  31 . The passages  50  are in fluid communication with the inlet  57  and the outlet  59 . The vacuum is in communication with the porous substrates  39  through the oxygen outlet  35  (FIG.  3 ). 
     The baffles  52  disposed within the passages  50  promote mixing of the fuel such that significant portions of the fuel contact the fluoropolymer coating  48  during passage through the FSU  16  to allow for diffusion of dissolved oxygen from the fuel. Because increased pressure differentials across the passages are generally less advantageous than lower pressure differentials, the baffles  52  are preferably configured to provide laminar flow and, consequently, lower levels of mixing (as opposed to turbulent flow) through the passages  50 . Turbulent flow may, on the other hand, be preferred in spite of its attendant pressure drop when it provides the desired level of mixing and an acceptable pressure loss. Turbulent channel flow, although possessing a higher pressure drop than laminar flow, may promote sufficient mixing and enhanced oxygen transport such that the baffles may be reduced in size or number or eliminated altogether. The baffles  52  extend at least partially across the passages  50  relative to the direction of fuel flow to cause the fuel to mix and to contact the fluoropolymer coating  48  in a uniform manner while flowing through the flow plates  27 . 
     Referring to  FIG. 5 , in operation, fuel flowing through the passages  50  of the flow plate in the direction of the arrow  47  is caused to mix by the baffles  52  and contact the fluoropolymer coating  48 . As shown, the baffles  52  are alternately disposed at the upper and lower faces of the flow plate. In this embodiment, the baffles  52  induce vertical (upwards and downwards) velocity components that enhance mass transport and effectively increase the oxygen diffusivity in the fuel. This increases the oxygen/fluoropolymer contact, and thus the amount of oxygen removed from the FSU. Fuel flowing over the baffles  52  is encouraged to mix such that the fuel more uniformly contacts the fluoropolymer coating  48  to provide for a more uniform diffusion through the porous backing  43  and into the porous substrate  39  and out of the FSU. Referring to  FIG. 6 , another embodiment of the flow plate is shown including baffles  52  arranged at one side of the flow plate. It should be understood that it is within the contemplation of this invention to include any configuration of baffles  52  or mixing enhancers, including, but not limited to, inertial devices, mechanical devices, acoustic devices, or the like, to induce either a turbulent flow regime or a laminar flow regime to attain the desired amount of mixing and/or mass transport according to application-specific parameters. 
     Referring to  FIG. 7 , one exemplary embodiment of a stack of flow plates  27  is shown. The flow plates  27  are preferably rectangularly-shaped to facilitate the scaling of the FSU for various applications by the adjustment of the number of flow plates  27 . Alternately, the flow plates  27  may also be circular in structure, thereby providing increased structural integrity to the stacked arrangement. Regardless of the shape of the flow plates  27 , the stack is supported within the vacuum frame  60  that includes an inlet  62  that defines the vacuum opening to provide vacuum communication with the porous substrates  39 . 
     Referring now to  FIGS. 2-7 , the specific quantity of flow plates  27 , permeable composite membranes  42 , and porous substrates  39  for use with the FSU  16  are determined by the application-specific requirements of the system  10 , such as fuel type, fuel temperature, and mass flow demand from the engine. Further, different fuels containing differing amounts of dissolved oxygen may require differing amounts of filtering to remove a desired amount of dissolved oxygen to provide for optimization of the operation of the system  10  and for optimum thermal management of the system  10 . 
     Performance of the FSU  16  is related to permeability of the permeable composite membrane  42  and the rate of diffusion of oxygen therethrough. The permeability of the permeable composite membrane  42  is a function of the solubility of oxygen in the fluoropolymer coating  48  and the transfer of the oxygen through the porous backing  43 . The permeable composite membrane  42  (the combination of the fluoropolymer coating  48  and the porous backing  43 ) is of a selected thickness to allow for the desired diffusion of dissolved oxygen from the fuel to the porous substrate  39  for specific applications of vacuum or strip gas (e.g., nitrogen). 
     The rate of diffusion of oxygen from the fuel through the surface of the permeable composite membrane  42  is affected by the duration of contact of fuel with the permeable composite membrane  42  and the partial pressure differential across the permeable composite membrane  42 . It is desirable to maintain a steady application of vacuum on the FSU  16  and constant contact between the permeable composite membrane  42  and fuel in order to maximize the amount of oxygen removed from the fuel. Optimizing the diffusion of dissolved oxygen involves balancing the fuel flow, fuel temperature, vacuum level, and the amount of mixing/transport, as well as accounting for minimizing pressure loss and accounting for manufacturing tolerances and operating costs. 
     Referring back to  FIG. 1 , the fuel source  18  may comprise a plurality of vessels from which the fuel can be selectively drawn. In winged aircraft, such vessels may be irregularly-shaped so as to be accommodated in the wings of the aircraft. Each vessel is disposed in fluid communication with a pump, which may be manually or automatically controlled to selectively draw fuel from either or both of the vessels and to pump the fuel to the FSU  16 . 
     Still referring back to  FIG. 1 , one aspect of the thermal management of the system  10  may be embodied in the transfer of heat between fuel stored in the fuel source  18  and at least one of the low temperature heat sources  24 . In particular, because the low temperature heat sources  24  are below the coking limit of the fuel, the fuel flowing from the fuel source  18  may function as a low-grade heat sink to absorb heat from some or all of the low temperature heat sources  24 . Such low temperature heat sources  24  include, but are not limited to, hydraulic heat loads, generator heat loads, engine accessory gear box heat loads, fuel pump heat loads, fan drive gear system heat loads, and engine oil system loads. The fuel flowing from the fuel source  18  may be circulated to any one or a combination of such loads for the exchange of heat therewith. The amount of heat absorbable by the fuel is such that the temperature of the fuel therein is maintained at less than the temperature limit at which fuel can be received into the FSU  16 . 
     Referring now to FIGS.  1  and  8 - 13 , the management of heat transfer between the fuel and the various high temperature heat sources  22  is shown. In  FIG. 8 , the high temperature heat source  22  may comprise a high temperature oil system  76 . The high temperature oil system  76  includes a heat exchanger  77  configured to transfer heat from an oil stream  73  received from at least one bearing and/or gearing arrangement  78  to the deoxygenated fuel from the FSU  16 . Accordingly, the temperature of the bearing and/or gearing arrangement  78  is reduced considerably, and the temperature of the fuel stream from the heat exchanger  77  is increased to a temperature near that of the maximum oil temperature and greater than the coking limit of about 325 degrees F. but less than the temperature at which pyrolysis occurs (about 900 degrees F.). 
     The high temperature heat source  22  may further comprise a cooled turbine cooling air unit  80 , as is shown with reference to FIG.  9 . The cooled turbine cooling air unit  80 , including heat exchanger  82 , effects the heat transfer between the deoxygenated fuel from the FSU  16  and the engine  14  by receiving an air stream at a temperature of about 1,200 degrees F. from the compressor  30  of the engine  14  and the deoxygenated fuel stream from the FSU  16 . Heat is transferred between the received air stream and the fuel stream, thus heating the deoxygenated fuel and cooling the air. The heated fuel is directed to the combustor  32 , and the cooled air is directed to a compressor  39 . The outlet stream from the compressor  39  is split into three streams and directed back to the compressor  30 , the combustor  32 , and the turbine  34 . The temperature of the heated fuel is greater than the coking limit of about 325 degrees F. and less than the temperature at which pyrolysis occurs (about 900 degrees F.). In particular, the temperature of the heated fuel is preferably about 700 degrees F. to about 800 degrees F. Upon directing the cooled air to the turbine  34 , a buffer layer of cool air is received at the surfaces of the turbine, thereby allowing the combustion gases received from the combustor  32  to be of higher temperatures. 
     The high temperature heat source  22  may comprise a turbine exhaust recuperator  86 , as is shown with reference to FIG.  10 . The turbine exhaust recuperator  86  provides for the management of heat transfer by utilizing hot gases exhausted from the turbine  34  to heat the fuel directed to the combustor  32 . Upon operation of the turbine exhaust recuperator  86 , turbine exhaust at about 1,200 degrees F. is directed to a heat exchanger  88  and used to heat the deoxygenated fuel received from the FSU  16 . Upon such a heat exchange, cooled exhaust is ejected from the heat exchanger  88 . The heated fuel is directed to the combustor  32 . The temperature of the fuel directed to the combustor  32  is at least about 550 degrees F., preferably about 550 degrees F. to about 900 degrees F., and more preferably about 700 degrees F. to about 800 degrees F. 
     Two similar applications to the turbine exhaust recuperator are a fuel-cooled engine case and a fuel-cooled engine exhaust nozzle. Both of these represent high temperature heat sources similar to the turbine exhaust recuperator. In these applications, compact fuel heat exchangers, coils, or jackets are wrapped around either the engine case or the exhaust nozzle to transfer heat from these sources either directly to the fuel or first to an intermediate coolant and then from the intermediate coolant to the fuel. The heated fuel is then directed to the combustor  32 . 
     In  FIG. 11 , the high temperature heat source may be a fuel-cooled precooler  70 , which is most often incorporated into an aircraft, and which is hereinafter referred to as “precooler  70 .” The precooler  70  comprises a heat exchanger  72  that receives an air stream at a temperature of about 1,000 degrees F. from the compressor  30  of the engine  14  and fuel from the FSU  16 . Heat is transferred between the incoming air streams and fuel streams to provide an outlet air stream at a temperature of about 450 degrees F. and an outlet fuel stream at a temperature of up to about 900 degrees F. and preferably about 400 degrees F. to about 800 degrees F. The outlet air stream is directed onto the aircraft to provide one or more pneumatic services. The outlet air stream may be utilized to power an environmental control system to provide pressurized cooling air to a cabin  74  of the aircraft. Alternately, or additionally, the air stream may be routed through various airframe structures (e.g., wings and fuselage walls) to provide one or more thermal functions such as de-icing operations and the like. The outlet fuel stream is directed to the combustor  32 . 
     Referring to  FIG. 12 , the high temperature heat source  22  may comprise an integrated air cycle environmental control system  94  (hereinafter referred to as IACECS  94 ″). The IACECS  94 , which is a variation of the fuel-cooled ECS precooler  70  described above with reference to  FIG. 11 , functions as a heat sink to the aircraft cabin ECS. The IACECS  94  includes a first fuel/air heat exchanger  96  disposed in serial fluid communication with a second fuel/air heat exchanger  98 . The first fuel/air heat exchanger  96  receives a high temperature (about 1,000 degrees F.) air stream  101  bled from the compressor  30  of the engine  14  and the fuel stream from the FSU  16 . Upon the exchange of heat, fuel at at least about 325 degrees F., preferably about 550 degrees F. to about 900 degrees F., and more preferably about 700 degrees F. to about 800 degrees F. is directed to the combustor  32 . Cooled air ejected from the first fuel/air heat exchanger  96  is directed to a compressor  95  of the IACECS  94 . Heat from an air bleed stream  103  from the compressor  95  is then exchanged with the fuel stream from the FSU  16 , and heated fuel is directed to the first fuel/air heat exchanger  96  while cooled air is directed to a turbine  105  of the IACECS  94  where it is expanded resulting in low temperature air at the desired cabin pressure. The low temperature air is then received from the turbine  105  and directed to the cabin. 
     Referring now to  FIG. 13 , another high temperature heat source  22  for an aircraft application may comprise a heat pump  100 . The heat pump  100  transfers heat from a low temperature source to the deoxygenated fuel that acts as a high temperature heat sink. Because the heat transfer occurs from the low temperature source to the deoxygenated fuel, the heat pump  100  enables the transfer of heat to the deoxygenated fuel from a heat source at a lower temperature to the fuel heat sink at a higher temperature. The fuel discharged from the heat pump  100 , which is at a temperature of up to about 900 degrees F., is directed to the combustor  32 . 
     Referring now to all of the Figures, as indicated from the above disclosure, the system  10  provides for the management of heat transfer between the engine  14  and various other associated components of the system  10  via the regulation of various parameters, namely, the oxygen content of the fuel fed to the engine  14  and the temperature of the fuel into the engine  14 . Regulation of such parameters results in improved thermodynamic efficiency of the engine. 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.