United States Patent [191
`Burr et al.
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,696,156
`Sep. 29, 1987
`
`[54] FUEL AND OIL HEAT MANAGEMENT
`SYSTEM FOR A GAS TURBINE ENGINE
`
`[75] Inventors: Donald N. Burr, Glastonbury; Paul S.
`Danilowicz, Manchester; Thomas C.
`Franz; Thomas P. Mortimer, both of
`Bolton‘ Edward B‘ Pew Somers an
`of Con’n
`’
`’
`[73] Assignee: United Technologies Corporation,
`Hartford, Conn.
`21 A l‘ N _: .870 192
`[
`1
`PP o
`’
`[22] Flledi
`Jlllh 33 1986
`[51] int. Cl.‘ ........................ .. F02C 7/06; FOZC 7/224
`[52] us. (:1. ................................ .. 60/3908; 60/736
`[58] Field of Search ............... .. 60/3902, 39.08, 39.83,
`60/736; 184/611
`
`[56]
`
`.
`’
`References Clted
`U.S. PATENT DOCUMENTS
`3,300,965 I/ 1967 Sherlaw et al. .................. .. 60/3908
`3,382,672 5/ 1968 French ........................... .. 60/3928]
`
`3,779,007 12/1973 Lavash ........................... .. 60/3928]
`4,020,632 5/1977 Cof?nberry et al.
`.. 60/3903
`4,104,873 8/1978 Cof?nberry
`60/3908
`4,151,710 5/1979 Grif?n et a1.
`.. 60/3908
`4,354,345 10/1982 Dreisbach et a1. ............... .. 60/3908
`.
`.
`.
`Primary Exammer—l.ou1s J. Casaregola
`Attorney, Agent, or Ftrm-Tmxell K. Snyder
`[57]
`ABSTRACr
`A heat management system is provided for a gas turbine
`engine (10) having ?rst and second oil cooling loops
`(14, 16). The system distributes excess fuel ?ow from a
`main fuel pump (44) among a plurality of upstream
`locations (58, 6°, 68) for managing the transfer of heat
`between the Oil loops (14, 161mm! the ?owing fhel- A
`diverter valve (62) regulates the distribution of the by
`pass fuel responsive to engine heat generation, oil tem
`perature, and/or fuel temperature. A passive fuel distri
`bution con?guration using one or more fuel ?ow re
`strictors (72, 74, 76) is also disclosed.
`
`7 Claims, 2 Drawing Figures
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`34/
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`GE-1019.001
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`U. S. Patent Sep. 29, 1987
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`Sheetl of2
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`4,696,156
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`@MW
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`GE-1019.002
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`U. S. Patent Sep. 29, 1987
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`Shéet2 of2
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`4,696,156
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`GE-1019.003
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`1
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`FUEL AND OIL HEAT MANAGEMENT SYSTEM
`FOR A GAS TURBINE ENGINE
`
`FIELD OF THE INVENTION
`The present invention relates to a system for transfer
`ring heat energy between the fuel and lubricating oil of
`a gas turbine engine'or the like.
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`Against the heat production of the main engine lubri
`cation system and the accessory drive, the needs of the
`fuel stream must also be considered and balanced. It is
`typical in gas turbine engine installations to deliver the
`fuel to the engine combustor by a positive displacement
`pump connected mechanically to the rotating engine
`shaft. It will be appreciated by those skilled in the art ‘
`that a positive displacement pump, such as a gear pump
`or the like, delivers a volumetric ?ow rate directly
`proportional to the speed of the pump. As the flow rate
`from a pump turning proportional to engine shaft speed
`could never be made to match the fuel flow require
`ments of an aircraft gas turbine engine operating under
`a variety of power level demands and environmental
`conditions, it is common in the industry to size the posi
`tive displacement main fuel pump with an excess flow
`capacity under all engine operating conditions. The fuel
`system thus must include a fuel control valve and a
`bypass or return fuel line for routing the excess main
`fuel pump output back to the low pressure side of the
`pump.
`The use of a pump bypass, common in many ?uid
`?ow applications, normally does not impact the opera
`tion of the fuel supply subsystem in an aircraft applica
`tion. Under certain operating conditions, however, such
`as engine idling either in flight or on the ground, it will
`be nonetheless apparent that the amount of fresh fuel
`entering the fuel system is small while the relative vol
`ume of fuel being bypassed back to the pump inlet is
`quite large. The combination of pump inefficiency and
`recirculation of the excess main fuel pump output
`through the bypass line can heat the circulating fuel to
`an undesirably high temperature making it necessary to
`provide at least temporary cooling to the fuel supply
`system for idle operation.
`Various methods have been proposed in the art for
`accommodating the widely varying needs of the fuel
`supply system, main engine lubrication system, and the
`accessory drive unit. U.S. Pat. No. 4,151,710 “Lubrica
`tion Cooling System for Aircraft Engine Accessory”
`issued May 1, 1979 to Griffin et a1, shows disposing the
`accessory drive fuel-oil heat exchanger downstream
`with respect to the engine fuel-oil heat exchanger in the
`fuel supply line. The circulating accessory oil is routed
`through or around the accessory fuel-oil heat exchanger
`and an air-oil cooler in order to manage the accessory
`drive heat rejection. The reference also discloses re
`moving heat energy from the fuel stream during periods
`of excessive fuel temperature, such as during ground
`idle. The total fuel flow passes through both the engine
`lubrication system fuel-oil cooler and the accessory
`drive fuel-oil cooler
`.
`Such prior art systems, while effective, lack the ?exi
`bility for ef?ciently accommodating the wide variations
`in heat generation occurring in the various systems
`described. In the subject reference, for example, by
`sizing the accessory fuel-oil cooler to accommodate the
`maximum mass ?ow of fuel in the fuel supply line, it is
`necessary to increase the size of the accessory fuel-oil
`heat exchanger so as to accommodate the higher fuel
`throughput. Additionally, by placing the accessory
`drive heat exchanger downstream of the engine lubrica
`tion system fuel-oil heat exchanger, the referenced ar
`rangement limits the fuel cooling available to the acces
`sory drive unit, requiring additional air-oil cooling ca
`pacity to achieve current stringent accessory drive oil
`temperature requirements.
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`
`BACKGROUND
`The cooling requirements of gas turbine engines are
`well known to the designers of today’s high perfor
`mance aircraft powerplants. Certain internal structures,
`such as bearings, are both cooled and lubricated by a
`circulating ?ow of oil which is distributed and collected
`throughout the main engine structure, returning to a
`central collection point after having absorbed signi?
`cant heat energy. Another source of heat is the acces
`sory drive system coupled to the main engine by a me
`chanical drive and clutch system. Such accessory
`drives, for example a constant speed drive for the air
`craft service electrical generator, are also provided with
`an independent circulating flow of oil for lubricating
`and cooling purposes.
`‘
`One method of cooling the circulating oil loops de
`scribed above is through the use of air-oil coolers and a
`flow of relatively cool compressor bleed air. Such cool
`ers, while effective, diminish the overall engine operat
`ing ef?ciency since the extraction of bleed air increases
`overall engine power demand for a given level of useful
`thrust. This power penalty results in an increase in en
`gine thrust speci?c fuel consumption.
`.
`Another method, often used in conjunction with air
`cooling, is to reject heat, from the circulating oil loops
`into the ?ow of fuel entering the engine combustion
`chamber. This method uses the fuel flow as a conve
`nient, recuperative heat sink and incurs few of the pen
`alties of air cooling, but is limited in effectiveness by the
`maximum temperature tolerable by the fuel.
`In order to appreciate the design problems associated
`with the management of heat generated in these sys
`tems, a brief discussion of the function and heat output
`of each is required. Cooling oil circulating through the
`main engine lubrication system receives heat energy at
`a rate related to the product of engine rotor speed and
`power output. The cooling needs of the main engine
`lubrication loop are thus at a minimum during periods
`of low power operation, such as idling, and at a maxi
`mum during high or full power operation, such as take
`off. Normal engine operation under cruise conditions
`would fall between the two ranges but closer to the
`higher power conditions.
`The lubricating and cooling oil of the accessory
`drive, and particularly for an accessory drive provided
`for the airframe electrical generator, does not receive
`heat energy proportional to the engine speed and power
`level but rather as a function of the electrical demand of
`the airframe. The accessory drive’s maximum heat re
`jection demand may therefore occur at nearly any time
`in the operation of the aircraft, depending on the num
`ber of ovens, coffee makers, reading lamps, electrical
`heaters, or other power consuming devices switched on
`in the airframe at any particular time. The accessory
`heat rejection demand also varies less overall than that
`of the engine lubrication system, with the minimum heat
`rate being about one-half of the maximum heat rejection
`rate.
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`GE-1019.004
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`3
`SUMMARY OF THE INVENTION
`It is an object of the present invention to provide a
`system for transferring heat energy generated in a gas
`turbine engine among a ?rst oil loop for cooling an
`engine accessory drive, a second oil loop for cooling
`and lubricating the engine bearings and other internal
`structures, and the fuel stream supplied to-the engine for
`combustion therein.
`It is further an object of the present invention to
`distribute said heat energy responsive to the current
`rate of heat generation occurring within the accessory
`drive, engine, and fuel stream for achieving ef?cient
`and reliable operation over the engine power output
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`range.
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`It is further an object of the present invention to
`provide a heat transfer system able to cool the fuel
`stream by one or more oil loops during low power
`engine operation, and to cool the oil loops with the fuel
`stream during high power engine operation.
`It is still further an object of the present invention to
`accomplish the distribution of heat energy by directing
`a bypass ?ow of fuel among a plurality of return loca
`tions in the fuel stream responsive to the desired heat
`transfer performance.
`According to the present invention, heat is trans
`ferred between each oil loop and a ?owing fuel stream
`by a pair of fuel-oil heat exchangers receiving the fuel
`‘ stream in series. The fuel stream passing through the
`fuel-oil heat exchangers includes at least a portion of the
`30
`' fuel supplied from the aircraft fuel tank by a boost pump
`7 at a metered rate equal to that currently being delivered
`to the gas turbine engine combustor.
`The fuel stream enters a main fuel pump operating at
`a fuel ?ow rate in excess of the metered rate, hence
`requiring a portion of the fuel ?owing therefrom to be
`~ returned to the fuel stream prior to the main fuel pump.
`This diversion of the main pump outlet ?ow is accom
`'~ plished by a fuel controller which determines the me
`‘2 tered fuel flow rate responsive to the demanded engine
`power level.
`According to the present invention, a bypass conduit
`having at least two branches is provided for returning
`the bypass ?ow to two or more locations in the stream
`?owing to the main fuel pump, thus altering the fuel
`?ow rate and effectiveness of one or both of the fuel-oil
`heat exchangers.
`The bypass fuel is allocated among the return loca
`tions responsive to the engine power level. Speci?cally,
`one embodiment of a system according to the present
`invention returns the bypass fuel to ?rst and second
`locations disposed respectively upstream of the ?rst
`loop fuel-oil heat exchanger and intermediate the ?rst
`and second loop fuel-oil heat exchangers. Allocation of
`the bypass fuel ?ow between the ?rst and second loca
`55
`tions is accomplished by a diverter valve manipulated
`responsive to the engine power level.
`A second embodiment according to the present in
`vention returns the bypass fuel ?ow to ?rst and third
`locations disposed respectively upstream of the ?rst
`loop fuel-oil cooler and downstream of the second fuel
`oil cooler prior to the main fuel pump. Allocation of the
`bypass fuel between the ?rst and third locations is ac
`complished passively by the effect of one or more ?ow
`restrictors placed in the bypass return line. It is an addi
`65
`tional feature of this second embodiment that the fresh
`metered fuel entering the system from the boost pump
`may bypass the fuel-oil heat exchangers at high metered
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`4,696,156
`4
`fuel ?ow rates reducing the total fuel pressure drop
`between the boost pump and the main fuel pump.
`The present invention thus optimally matches ?uid
`temperatures and heat exchange rates between the fuel
`supplied to the engine and the oil loops under all engine
`operating conditions, thereby reducing the requirement
`for auxiliary oil cooling with compressed engine air or
`the like. The invention further provides, for those situa
`tions wherein the rate of heat buildup in the fuel stream
`is excessive due to a high bypass ?ow as compared to
`the metered ?ow, a means for cooling the recirculating
`fuel through a reverse transfer of heat energy from the
`fuel into the circulating oil loops.
`Still another advantage of the allocating function
`according to the present invention is a reduction in the
`maximum rate of fuel ?owing through an individual
`fuel-oil heat exchanger relative to the minimum rate,
`thus reducing exchanger size while providing suf?cient
`heat transfer capacity under all cooling conditions.
`Both these and other advantages will be apparent to
`those skilled in the art upon careful inspection of the
`following description and the appended claims and
`drawing ?gures.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 shows a ?ow schematic of a ?rst embodiment
`of a fuel and oil heat management system according to
`the present invention.
`FIG. 2 shows a ?ow schematic of a second embodi
`ment of a fuel and oil heat management system accord
`ing to the present invention.
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`DETAILED DESCRIPTION OF THE
`PREFERRED AND ALTERNATIVE
`EMBODIMENTS
`FIG. 1 shows a schematic representation of the fuel
`and oil ?ow systems for a gas turbine engine 10. An
`accessory drive 12 is mechanically linked (not shown)
`to the engine 10 and is cooled by a ?rst oil loop 14
`wherein oil ?owing from the accessory drive 12 passes
`in sequence through a ?rst air-oil cooler 18 and a ?rst
`fuel-oil heat exchanger 20 before being returned to the
`accessory drive unit 12. Cooling air 22, extracted from
`the compressor or fan section of the engine 10, passes
`through the air-oil cooler 18 and is regulated by a ?rst
`air control valve 24.
`Lubricating and cooling oil for the main engine bear
`ings and other internal components circulates in a
`wholly separate oil loop 16, passing in sequence
`through a second air-oil cooler 26 and a second fuel-oil
`heat exchanger 28 before returning to the engine 10.
`Cooling air 30 for the second air-oil cooler 26 is also
`extracted from the engine fan or compressor and is
`regulated by a second air control valve 32.
`Combustion fuel is supplied to the engine from the
`main fuel tank 34 by a fuel system including an engine
`driven boost pump 36. Boost pumps are typically cen
`trifugal pumps designed to operate at an essentially
`constant pressure for a given engine speed, independent
`of the volumetric ?ow rate of fuel therethrough. Boost
`pump 36 supplies fuel to a fuel conduit 38 at a ?ow rate
`equivalent to the current fuel demand of the gas turbine
`engine 10. This ?ow rate, termed the “metered fuel ?ow
`rate”, is determined by the main engine fuel control 40
`as discussed hereinbelow.
`The metered fuel ?ow enters the ?rst fuel oil heat
`exchanger 20, passing therethrough and ?owing subse
`quently through the second fuel-oil exchanger 28, a fuel
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`?lter 42, and a positive displacement main fuel pump 44,
`ing fuel is rejected from the system through the air-oil
`?nally entering the fuel controller 40. It should be noted
`coolers 18, 26.
`that the main fuel pump 44 is driven by the engine 10
`During periods of full power or cruise engine opera
`and thus has a pump speed proportional to the engine
`tion, the diverter valve 62 is moved to the second posi
`speed.
`tion wherein the entire ?ow of bypass fuel is returned to
`As discussed in the preceding section, the main fuel
`the second return location 60 through the branch 56. In
`pump 44 develops a volumetric ?ow rate dependent
`this con?guration, the fresh supply of fuel from the fuel
`upon the pump shaft speed and is therefore sized to
`tank 34 forms the entire fuel ?ow through the ?rst
`provide a fuel ?ow at the pump outlet 46 in excess of the
`fuel-oil heat exchanger 20 wherein the fuel absorbs heat
`metered fuel ?ow rate. The fuel controller 40 accepts
`from the circulating oil in the ?rst loop 14. The second
`the fuel from the pump outlet 46 and divides the ?ow
`fuel-oi] heat exchanger 28 receives both the bypass fuel
`stream between a supply line 48 which is routed to the
`returned by the controller 40 as well as the fuel ?owing
`combustion section 50 of the gas turbine engine 10, and
`from the ?rst fuel-oil heat exchanger 20. This combined
`a bypass line 52. The fuel ?ow rate in the supply line 48
`fuel ?ow passes through the second fuel-oil heat ex
`changer 28, cooling the oil circulating in the second oil
`is the metered fuel ?ow rate as determined by the fuel
`controller 40 while the fuel ?ow in the bypass line 52 is
`loop 16, and passing subsequently through the ?lter 42
`equal to the excess main pump fuel delivery.
`and main fuel pump 44.
`In this ?rst embodiment of the present invention, the
`It will be appreciated that during operation at these
`bypass line 52 includes two branches, a ?rst branch 54
`higher power levels, both the metered fuel flow rate
`and a second branch 56 together providing a means for
`and the main fuel pump delivery rate are considerably
`20
`returning and distributing the bypass ?ow between two
`higher than those under idle conditions. The high me
`return locations 58, 60, respectively. The ?rst and sec
`tered fuel ?ow rate provides adequate total heat capac
`ond return locations 58, 60 are disposed respectively
`ity in the supplied fuel stream for absorbing all the heat
`upstream of the ?rst fuel-oil heat exchanger 20, and
`energy generated by the accessory drive 12 and the
`intermediate the ?rst and second fuel-oil heat exchang
`engine 10 thus allowing closure of the ?rst and second
`ers 20, 28. The ?ow of bypass fuel is allocated between
`air?ow regulating valves 24, 32 improving overall en
`gine ef?ciency.
`the locations 58, 60 by a diverter valve 62 operable
`between a ?rst position wherein the entire ?ow of by
`Additionally, by redirecting the bypass fuel return
`pass fuel in the bypass line 52 is directed to the ?rst
`?ow from the ?rst location 58 to the second location 60
`return location 58, and a second position (not shown)
`downstream of the ?rst'fuel-oil heat exchanger 20 in
`wherein the entire bypass fuel ?ow is directed to the
`creases the temperature effectiveness of the ?rst fuel-oil
`second location 60. It should be noted at this time that
`heat exchanger 20 which receives only fresh fuel from
`although the diverter valve 62 is disclosed as operating
`the fuel tank 34, unmixed with the warmer bypass fuel
`in an either/or fashion for diverting the entire bypass
`stream. This ?ow con?guration insures that the maxi
`fuel stream, it may be useful under some circumstances
`mum cooling capacity of the fresh fuel stream is avail~
`to employ a partial diverter valve operable for dividing
`able to the accessory drive unit 12 through the ?rst oil
`the bypass fuel between the ?rst and second branches
`cooling loop 14 when the engine operates at full or
`cruising power
`54, 56 in a proportional manner.
`It is preferable to operate the diverter valve 62 re
`One ?nal feature of the embodiment of FIG. 1 are oil
`sponsive to an engine operating parameter related to the
`bypass lines 64, 65 disposed in the oil loops 14, 16 for
`rate of heat rejection to the oil loops 14, 16. One such
`directing oil around the respective fuel-oil heat ex
`parameter is the fuel pressure rise across the engine
`changers 20, 28. The bypass ?ows are regulated by
`driven boost pump 36 which is related to engine speed.
`control valves 66, 67 which are opened responsive to
`In operation, fuel and oil ?ow in the above~described
`fuel and oil temperature during periods, such as at idle,
`systems with heat exchange therebetween accom
`wherein the fuel is too hot to absorb additional heat
`45
`plished in the fuel-oil heat exchangers 20, 28. Under
`energy, thereby allowing the system to more ?exibly
`conditions of low engine power, such as idling either on
`accommodate the needs of the various systems.
`the ground or in flight, the metered fuel ?ow rate is
`By placing the fuel-oil heat exchangers 20, 28 up
`relatively low, matching the fuel demand of the engine
`stream of the main fuel pump 44 and the fuel ?lter 42,
`10. As the engine shaft speed at idle is also relatively
`the heat management system according to the present
`low as compared to cruise or full power levels, the
`invention also reduces or eliminates the need for auxil
`output of the positive displacement main fuel pump 44,
`iary fuel heating to avoid icing up of the fuel ?lter 42
`although much greater than the metered fuel ?ow rate,
`under extremely cold operating conditions.
`is also reduced. The diverter valve 62 is positioned
`FIG. 2 shows a schematic representation of a second
`during these periods to direct the entire bypass fuel ?ow
`embodiment of the heat management system according
`55
`to the ?rst return location 58 through the ?rst return
`to the present invention wherein like reference numer
`branch 54. In this con?guration, the entire bypass fuel
`als are used to denote elements in common with the
`?ow and metered fuel ?ow pass sequentially through
`embodiment shown in FIG. 1. The second embodiment
`the ?rst and second fuel-oil heat exchangers 20, 28.
`according to the present invention distributes the by
`During extended periods of idling resulting in exces
`pass fuel ?owing in bypass line 52 between two return
`sive heat buildup in therecirculating fuel, the ?rst fuel
`locations on the low pressure side of the main fuel pump
`oil heat exchanger 20 acts to remove heat from the fuel
`44, a ?rst location 58 via a ?rst branch 54, and a third
`by transferring heat in the reverse direction into the ?rst
`location 68, via a third branch 70. It will be appreciated
`oil loop 14. This heat is removed from the loop 14 by
`that the return location and branch denoted by refer
`opening the valve 24 to admit a flow of cooling air 22
`ence numerals 68 and 70, while forming the only other
`65
`through the ?rst air-oil cooler 18. Similarly, during
`location and branch in the disclosed second embodi
`periods of in?ight engine shutdown, heat removed from
`ment according to the present invention, are termed the
`the windmilling engine, accessory drive, and recirculat
`third -location and third branch to distinguish from the
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`second location and second branch discussed herein
`above with respect to the ?rst embodiment.
`The second embodiment uses passive means for allo
`cating the bypass fuel ?ow between the ?rst and third
`locations 58, 68 comprising one or more ?ow restrictors
`72, 74, 76, disposed respectively in the ?rst branch 54,
`the fuel inlet of the ?rst fuel-oil heat exchanger 20,
`and/or the third branch 70. Based on differential pres
`sures and fuel ?ow rates at different points in the vari
`ous fuel lines, the ?ow restrictors 72, 74, 76 allocate not
`only the bypass fuel ?owing in bypass line 52 between
`the ?rst location 58 and the second location 68, but may
`additionally allocate the ?ow of fresh fuel from the fuel
`tank 34 between the inlet of the ?rst fuel-oil heat ex~
`changer 20 and the second return location 68 as dis
`cussed hereinbelow.
`During periods of low power or idle engine operation
`when the metered fuel ?ow rate is low, bypass fuel in
`the bypass line 52 flows into branches 54, 70 and is
`returned to the supply side of the main fuel pump 44 at
`return locations 58 and 68. During such periods of oper
`ation, suf?cient ?ow of recirculating bypass fuel is pres
`ent through the ?rst fuel-oil heat exchanger 20 to permit
`cooling of the fuel by the ?rst oil loop 14 and the ?rst
`air-oil cooler 18. The exact distribution of the bypass
`fuel between the ?rst and second locations 58, 68 are
`determined by the needs of the individual systems, and
`effected by sizing the flow restrictors 72, 74, 76 appro
`priately.
`During periods of high engine power operation, such
`as while cruising or during takeoff, fresh fuel supplied
`from the fuel tank 34 is split at location 58 between the
`?rst fuel-oil heat exchanger 20 and the ?rst branch 54.
`The fresh unmixed fuel bypasses the exchangers 20, 28,
`joining the bypass fuel in the third branch 70, entering
`the main fuel pump supply at the third return location
`68. The ?ow restrictors 72, 74, 76 are again used to
`insure a proper distribution of fresh fuel between the
`fuel-oil heat exchangers 20, 28 and the ?rst branch 54
`according to the heat transfer needs of the joined loops.
`It should be noted that although the second embodi
`ment is shown in FIG. 2 as utilizing ?xed ori?ce type
`?ow restrictors, it is within the scope of the present
`invention to utilize ?ow restrictors having different
`?ow coef?cients depending on the direction of the fuel
`flowing therethrough as well as active fuel ?ow di
`verter means such as flow control valves or the like.
`Since the actual sizing and distribution of the recycle
`and fresh fuel between the ?rst and third locations 58,
`68 is dependent upon the heat transfer needs of the
`engine 10 and the accessory drive 12 over the entire
`engine and drive operating envelope, no speci?c restric
`tor sizes or ?ow proportions are disclosed herein. Such
`parameters would be developed for each individual
`engine application based on test results, predicted heat
`generation rates, required operating environments, and
`the speci?cations of the individual engine manufacturer.
`The second embodiment according to the present
`invention thus reduces the proportional range of fuel
`flow rate in both the ?rst fuel-oil heat exchanger 20 and
`the second fuel-oil heat exchanger 28 by diverting a
`portion of the fresh fuel from the tank 34 through the
`?rst branch 54 and third branch 70. The use of ?ow
`restrictors 72, 74, 76 to effect the reversing ?ow 73 in
`the ?rst branch 54 provides a passive means for allocat
`ing the ?ow of both fresh and bypass fuel between the
`?rst and third return locations 58, 68 over the range of
`engine operation.
`
`8
`As discussed above with respect to the ?rst embodi
`ment, the higher metered fuel ?ow rate present at nor
`mal engine power levels is more than sufficient to cool
`the accessory drive 12 and the engine 10 without the
`need for diverting cooling air 22, 30 from the engine fan
`or compressor sections and thereby avoiding any loss of
`ef?ciency resulting therefrom. It will be appreciated,
`however, that the cooling air regulating valves 24, 32
`may be controlled responsive to the fuel and/or oil
`temperatures in the respective loops 14, 16 as necessary
`to optimize system performance over the entire range of
`engine operation.
`The present invention thus provides a heat manage
`ment system for bene?cally distributing fuel in the fuel
`supply system of a gas turbine engine among various
`locations with respect to ?rst and second fuel-oil heat
`exchangers disposed in a heat transfer relationship with
`the fresh and bypass fuel streams for the purpose of
`maximizing the internal heat transfer between the circu
`lating cooling oil and the fuel. The foregoing discussion,
`while attempting to disclose the invention in broad
`terms commensurate with the scope thereof, nonethe
`less has been directed to an explanation of only two
`embodiments thereof and should therefore not be inter
`preted as limiting, but rather as an illustration of what
`applicants believe is the best mode for carrying out the
`invention.
`We claim:
`1. A system for transferring heat energy among a heat
`generating gas turbine engine, a heat generating acces
`sory drive coupled to the gas turbine engine, a stream of
`fuel ?owing at a metered ?ow rate, and a stream of
`cooling air, comprising:
`a ?rst oil circulation loop wherein a ?rst flow of oil
`circulates through the accessory drive, a ?rst air
`oil cooler having a ?rst, regulated portion of the
`cooling air stream also passing therethrough, and a
`?rst fuel-oil heat exchanger;
`a second oil circulation loop wherein a second ?ow
`of oil circulates through the gas turbine engine, a
`second air-oil cooler having a second, regulated
`portion of the cooling air stream also passing there
`through, and a second fuel-oil heat exchanger;
`means for conducting at least a portion of the metered
`fuel stream, in sequence, through the ?rst fuel-oil
`heat exchanger, the second fuel-oil heat exchanger,
`and a main fuel pump, the main fuel pump operat
`ing at a fuel delivery rate in excess of the metered
`fuel ?ow rate;
`a fuel controller for receiving the fuel ?owing from
`the main fuel pump and dividing the received fuel
`between a supply stream having a ?ow rate equal
`to the metered ?ow rate, and a bypass stream hav
`ing a ?ow rate equal to the excess of the main pump
`delivery rate over the metered ?ow rate; and
`means, in ?uid communication with the fuel control
`ler and the conducting means, for returning the
`bypass fuel stream into the fuel conducting means
`upstream of the main fuel pump at a plurality of
`distinct locations.
`2. The system for transferring heat energy as recited
`in claim 1, further comprising
`means, responsive to an operating parameter of the
`gas turbine engine, for apportioning the bypass
`?ow stream among each of the distinct locations in
`the fuel conducting means.
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`GE-1019.007
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`4,696,156
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`3. The system for transferring heat energy as recited
`a ?rst location disposed upstream of the ?rst fuel-Oil
`in claim 1, wherein the plurality of distinct locations
`heat exchanger’ and
`a second location disposed intermediate the second
`includes
`fuel-oil heat exchanger and the main fuel pump.
`a ?rst ‘location disposed upstream of the ?rst fuel-oil 5
`6. The system for transferring heat energy as recited
`in claim 5, wherein the apportioning means includes
`heat exchang?r» and
`a second location disposed intermediate the ?rst and
`a ?ow restrictor disposed in the returning means
`second fuel-oil heat exchangers.
`intermediate the ?rst and second locations.
`4. The system for transferring heat energy as recited
`7- The system for transferring heat energy as recited
`in claim 2, wherein the apportioning means comprises 10 m clam‘ 6’ wherem
`a diverter valve for actively directing the bypass fuel
`th? ?ow refsmctor dlsposed m the returpmg means
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`intermediate the ?rst and second locations further
`stream among the plurality of distinct locations.
`_
`provides a different coef?cient of ?uid ?ow depen
`'
`5. The system for transferring heat energy as recited
`dent upon the direction of fuel ?owing there_
`in claim 2, wherein the plurality of distinct locations 15
`through
`includes
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`GE-1019.008