Abstract:
A fuel based thermal management system includes a fuel stabilization system which permits the fuel to exceed the traditional coking temperatures. High temperature components are arranged along the fuel flow path such that even at the higher operating temperatures the fuel operates as a heat sink to transfer heat from high temperature components to the fuel. An optimal high temperature ester-based oil permits an oil-loop to exceed current oil temperature limits and achieve a high temperature to permit efficient rejection of heat to the fuel late in the fuel flow path.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a thermal management system, and more particularly to a thermal management system which utilizes a fuel stabilization unit and isolates high temperature systems. 
   Modem aircraft utilize sophisticated Thermal Management Systems (TMS) for thermal management and cooling. In typical modes of operation of the aircraft, lubricating oil, hydraulic fluid, and accessory drives require cooling. At the same time, the avionic systems of the aircraft will require cooling during operation, some by a liquid coolant and others by air. Concurrently, it is generally desirable to heat the fuel delivered to the main propulsion engines to maximize the efficiency of the engine. 
   Typically, the fuel flow is utilized in combination with a fuel-oil heat exchanger. Although effective, the maximum operating temperature of aviation fuel is limited by a coking temperature limit. Coke deposits may result in a progressive degradation of engine performance. 
   To minimize this coking condition, the TMS often employs supplemental air-to-liquid heat exchangers that reject heat to either “ram air”, engine fan bypass air flow, and/or “bleed air”. 
   Ram air is air that is literally rammed into an inlet on the aircraft as a result of the aircraft&#39;s forward velocity. A penalty paid for the use of ram air includes system weight and aerodynamic drag. In addition, the installation of ram air circuits in an aircraft so as to convey the ram air to a point of use may be difficult. Moreover, in the case of aircraft intended for military use, ram air inlets may provide an undesirable aircraft radar return. 
   Fan bypass airflow is air drawn from the fan duct of a gas turbine engine. A penalty paid for the use of bypass airflow for thermal management is the reduction in operating efficiency of the engine. 
   Bleed air is air taken from the compressor section of the gas turbine engine, whether a main propulsion engine of the aircraft or an auxiliary power unit. A penalty paid for the use of bleed air is a reduction in operating efficiency of the engine from which the air is bled. 
   Accordingly, it is desirable to provide an effective, lightweight thermal management system which minimizes air-to-liquid heat exchangers. 
   SUMMARY OF THE INVENTION 
   The fuel based thermal management system according to the present invention includes a fuel stabilization system which permits the fuel to exceed the traditional coking temperatures. Air-to-liquid heat exchangers may be reduced and the heat generated by high temperature system components is rejected to the fuel which operates at a higher temperature due to the fuel stabilization system. High temperature components are arranged along the fuel flow path such that even at the higher operating temperatures the fuel operates as a heat sink to transfer heat from high temperature components to the fuel. 
   The present invention utilizes an optimal high temperature ester-based oil that permits an engine oil-loop which exceeds current oil temperature limits and achieves a high temperature which permits efficient rejection of heat to the fuel. 
   The present invention therefore provides an effective, lightweight thermal management system which minimizes air-to-liquid heat exchangers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
       FIG. 1  is a general block diagram of an integrated thermal management system according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates a general perspective view of a fuel based thermal management system (TMS)  10  for an energy conversion device (ECD)  12 . A fuel stabilization system (FSU)  14  receives a liquid fuel from a reservoir  16 . 
   Typically, the fuel serves as a coolant for one or more (three shown) liquid-to-liquid heat exchanger sub-systems  18 ,  20 , and  22 . The fuel becomes progressively heated along the fuel flow path as the fuel draws thermal energy from components arranged along the fuel flow path. The heated fuel is then delivered to the fuel injectors for combustion within the ECD  12 . 
   The ECD  12  may exist in a variety of forms in which the fuel, at some point prior to eventual use for processing, for combustion or for some form of energy release, acquires sufficient heat to support autoxidation reactions and coking if dissolved oxygen is present to any significant extent in the fuel. One form of the ECD  12  is a gas turbine engine, and particularly a geared turbofan engine which includes a turbofan  24  (illustrated schematically) which is speed reduced through a fan gear system  26  (illustrated schematically). 
   The fuel is typically a hydrocarbon such as a liquid jet fuel. The FSU  14  includes a deoxygenation system  28  which permits the fuel to remain stable at much higher temperatures without coking by removing dissolved oxygen from the liquid fuel which enables higher temperature loads to reject their heat to the fuel. It should be understood that various deoxygenation systems will benefit from the present invention. 
   From the reservoir  16  the fuel serves as a coolant for a hydraulics subsystem  30  as the fuel is communicated to the fuel stabilization system (FSU)  14  through a fuel boost pump  32 . From the fuel boost pump  32  the fuel serves as a coolant for the first and second liquid-to-liquid heat exchanger sub-systems  18 ,  20 . The first liquid-to-liquid heat exchanger sub-system  18  includes a generator oil loop  34 . From the first liquid-to-liquid heat exchanger sub-system  18  fuel is communicated to the second liquid-to-liquid heat exchanger sub-system  20  that includes a fan gear oil loop  36  prior to the fuel being communicated to a main fuel pump  38 . 
   The first and second liquid-to-liquid heat exchanger sub-systems  18 ,  20  preferably operate at conventional aircraft oil temperatures which are typically less than approximately 325 degrees Fahrenheit. That is, the components which are cooled by the generator oil loop  34  and the fan gear oil loop  36  are preferably operated below approximately 325 degrees Fahrenheit. Concurrently, the fuel flow prior to the main fuel pump  38  receives thermal energy from the oil loops  34 ,  36  and will thereby remain below approximately 325 degrees Fahrenheit. It is preferred that the fuel remain below approximately 325 degrees Fahrenheit prior to the main fuel pump  38  to minimize cavitations within the main fuel pump  38 . 
   The temperature of the fuel increases as the fuel is communicated from the first liquid-to-liquid heat exchanger subsystem  18  to the second liquid-to-liquid heat exchanger sub-system  20 . Preferably, the most temperature sensitive components are located furthest up stream of the ECD  12 . That is, the fuel is lower in temperature the further the fuel is from the ECD  12 . It should be understood, however, that should the main fuel pump  38  be capable of operating at fuel temperatures above approximately 325 degrees Fahrenheit, the fuel temperature may be permitted to exceed approximately 325 degrees Fahrenheit as the deoxygenated fuel from the FSU  14  will accept thermal energy in the range of 600 to 800 degrees Fahrenheit. 
   From the main fuel pump  38 , the fuel serves as a coolant for the third liquid-to-liquid heat exchanger sub-systems  22 . The third liquid-to-liquid heat exchanger sub-system  22  includes an engine oil loop  40 . The components cooled by the engine oil loop  40  are the most resistant to temperature and are permitted to exceed approximately 325 degrees Fahrenheit. Preferably, the components cooled by the engine oil loop  40  utilize an optimized high temperature ester-based oil which operates at temperatures in excess of approximately 325 degrees Fahrenheit. Such an optimized high temperature ester-based oil is produced by NYCO S.A. Paris France under the trade name of GTO7. The optimized high temperature ester-based oil combined with the deoxygenated fuel temperature thermal retention capabilities permits associated components to operate above the conventional 325 degrees Fahrenheit temperature limit. 
   In combination with the deoxygenated fuel, the components cooled by the fuel flow are preferably separately distributed along the fuel flow path to advantageously utilize the increased temperature capabilities of the high temperature oil and higher temperature deoxygenated fuel. That is, although the fuel temperature is much higher after being utilized to previously cool the earlier oil loops  34 ,  36 , the higher temperature fuel still operates as a heat sink for the still higher temperature engine oil loop  40  which includes components which are permitted to operate at the higher temperatures. Requirements for supplemental air-to-liquid heat exchangers are thereby minimized or eliminated. 
   The optimized high temperature ester-based oil are also preferably utilized with the first and second liquid-to-liquid heat exchanger sub-systems  18 ,  20  even though full advantage of the increased temperature capabilities may not be utilized. Moreover, separation of the oil loops in response to temperature capabilities permits components which may operate at higher temperatures to more fully utilize the capabilities of the high temperature oil and the deoxygenated fuel which, although at an elevated temperature later in the fuel flow path, operates as a heat sink to the still higher temperature components such as those in the engine oil loop  40 . 
   It should be understood that the location of the FSU  14  represents only one of many possible locations, and that the FSU may alternatively be located between the first and second liquid-to-liquid heat exchanger sub-systems  18 ,  20  or downstream of the main fuel pump  38  while still deoxygenating the fuel to be advantageously utilized at higher temperatures with high temperature resistant components. 
   It should be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit from the instant invention. 
   Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention. 
   The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.