US3024606A

US3024606A - Liquid cooling system for jet engines

Info

Publication number: US3024606A
Application number: US747608A
Authority: US
Inventors: Donald B Adams; Donald P Sullivan
Original assignee: Curtiss Wright Corp
Current assignee: Curtiss Wright Corp
Priority date: 1958-07-10
Filing date: 1958-07-10
Publication date: 1962-03-13
Anticipated expiration: 1979-03-13

Description

March 13, 1962 D. B. ADAMS ET AL LIQUID COOLING SYSTEM FOR JET ENGINES 2 Sheets-Sheet 1 Filed July 10, 1958 36 as zz HU U INVENTORS P. EULLIVA-N LD B. ADAMS- ATTORNEY March 13, 1962 D. B. ADAMS ET AL LIQUID COOLING SYSTEM FOR JET ENGINES 2 Sheets-Sheet 2 Filed July 10, 1958 INVENTORS D DNALD F. EIULLIVAN DEINALD ELADAME mww fl| ial ir|| -l illivlirsvfllv;

ATTORNEY 7 United Sates Patent 3,924,606 Patented Mar. 13, 1952 fifice 3,024,606 LIQUID COOLING SYSTEM FOR JET ENGINES Donald B. Adams, Wyoming, Ohio, and Donald P. Sullivan, Van Nuys, Califi, assignors to Curtiss-Wright Corporation, a corporation of Delaware Filed .iuly 1t), 1958, Ser. No. 747,608 3 Claims. (Cl. 6039.66)

This invention relates to jet engines and is particularly directed to an arrangement for cooling the walls of a hot gas or combustion chamber for such an engine.

In the case of a turbo-jet engine with an afterburner the Walls of the afterburner combustion chamber and exhaust duct and nozzle are subjected to extremely high temperature gases. This is particularly true when the turbojet engine is operating at high supersonic Mach numbers. Similarly the walls of the combustion chamber and exhaust passages of ramjet and rocket engines are also subjected to high temperatures. The use of a hollow wall structure for jet engines in which liquid fuel is circulated therethrough prior to combustion in the engine is a known expedient for maintaining the temperature of the wall structure within safe operating limits. When liquid hydrocarbon fuel is so used, the fuel vaporizes and as a consequence high pressures are required to keep the fuel volume within reasonable limits. This is particularly true at the high temperatures produced in the engine at high supersonic flight speeds. Furthermore, if a hydrocarbon fuel remains at too high a temperature for too long a period of time, it will crack, that is the more complex hydrocarbons of the fuel break up into hydrocarbons of less complex structure. Such fuel cracking is also objectionable because along with other factors such as fuel oxidation it tends to cause coking deposits to build up along the passage walls.

An object of the invention comprises the provision of an arrangement for cooling the wall structure of a jet engine by circulating a liquid through passages in said wall structure and also through a heat exchange structure for transferring heat to the jet engine fuel. This arrangement permits the use of a cooling liquid having relatively high thermal capacity, as for example a liquid metal such as sodium or a eutectic mixture of sodium and potassium. Also, with this arrangement, the heat from the cooling liquid can be rapidly transferred to the engine fuel in a heat exchange structure immediately prior to its discharge into the engine combustion chamber. This arrangement permits the use of hydrocarbon fuels which would crack if they were used directly for cooling said wall structure because of the relatively long length of time the fuel would require for circulation through said wall structure.

Other objects of the invention will become apparent upon reading the annexed detail description in connection with the drawing in which:

FIG. 1 is a schematic axial sectional view of a turbojet engine;

FIG. 2 is an enlarged schematic view of the afterburner and exhaust end of the turbojet engine of FIG. 1 and illustrating the invention;

FIG. 3 is an enlarged sectional view taken along line 33 of FIG. 2;

FIG. 4 is a view taken along line 4-4 of FIG. 3; and

FIGS. 5 and 6 are sectional views taken along the lines 5-5 and 66 of FIG. 4.

Referring first to FIG. 1 of the drawing, reference numeral ltl designates a turbojet engine having a compressor 12 supplying compressed air to a main combustion chamber 14 which in turn supplies combustion gases to the turbine 16 for driving said turbine. The combustion chamber fuel supply nozzles are shown at 18. The turbine 16 is drivably connected to the compressor 12 by the shaft Ztl.

From the turbine 16 the exhaust gases discharge through an exhaust duct 22 and thence through a nozzle 24 into the surrounding atmosphere. The nozzle 24 is formed by a rigid centerbody structure 26 having an enlarged plug-type end 28 and by an axially movable wall structure 30. The wall structure 30 forms a continuation of the exhaust duct 22 and has a flared end 32 so that axial adjustment of the wall structure 30 is effective to vary the nozzle area.

Fuel nozzles

34 and 36 are provided for supplying fuel to the exhaust duct 22 for combustion therein downstream of the fiameholder structure 38 so that the space 40 downstream of said flameholder structure forms the combustion chamber for the engine afterburner.

The details of the afterburner and nozzle end of the engine are more clearly shown in FIGS. 2-6 together with the arrangement of the invention for cooling the wall structure of said afterburner and nozzle.

Referring now to FIGS. 2-6 the wall structure for the outer portion of the afterburner chamber 40 forms a continuation of the exhaust duct 22. This wall structure comprises a hollow outer wall 42 formed by radially spaced

annular layers

44 and 46 of sheet metal secured together by a corrugated sheet-metal member 48 disposed between said layers to form a hollow rigid wall 42. The corrugations of the member 48 are secured to and run axially between the

layers

44 and 46 to form longitudinally extending passages 50 therebetween.

The corrugated member 48 terminates short of the downstream end of the hollow wall 42 to leave an annular space 52 between its

layers

44 and 46 at said downstream end. An annular manifold structure 54 is provided at the upstream end of the hollow wall 42 for supplying a liquid coolant thereto for flow through the passages 50.

The manifold structure 54 has a pair of annular inlet and

outlet parts

56 and 58 separated by partition means 55 such that the annular inlet port 56 is in communication with only alternate passages 50 and the outlet part 58 is in communication with only the remaining passages 59. With this construction of the manifold 54, a liquid supplied to the inlet port 56 will flow through half the passages 50 to the annular space 52 at the downstream end of the hollow wall 42 and then flow back upstream through the remaining passages 56 to the annular outlet port 58 in the manifold 54.

A pump 60 is provided for circulating a suitable cooling liquid through the passages 50 of the hollow wall 42. For this purpose the pump 60 has a supply line 62 connected to the inlet port 56 of the annular manifold 54. From the outlet port 58 of the manifold 54 the liquid coolant is returned to the pump 6% through the line 64 and a heat exchange structure 66 and thence through a line 68 back to the pump whereby said passages and heat exchanger from a loop passageway for circulation of said liquid therearound by the pump 60. A suitable expansion chamber '70 is connected to the outlet side of the pump 69 to accommodate expansion and contraction of the liquid coolant so that the hollow wall passages 50 can at all times remain full of said liquid.

The afterburner fuel is supplied by a pump under control of a main fuel regulating valve 82. From the main fuel valve 82 a portion of the fuel is supplied direct to the fuel nozzles 34 via the fuel line 84. The remaining portion of the fuel is supplied to the fuel nozzles 46 through the heat exchange structure 66, valve 86 and fuel line 88. The afterburner fuel nozzles 3.6 aredisposed but a short distance upstream of the flameholder structure 38. The afterburner fuel nozzles 34, however, are disposed a substantial distance upstream of the fuel nozzles 36 and the afterburner flameholderstructure 38.

The valve 82 regulates the total fuel supply to the

afterburner fuel nozzles

34 and 36 while the valve 86 regulates the division of fuel flow between said nozzles. The valve 86 preferably is automatically controlled by the temperature of the fuel as it leaves the heat exchanger 66 such that during operation the temperature of the fuel, as it leaves the heat exchanger 66, is maintained at least approximately at a predetermined value, for example 900 F. Thus any increase in said temperature above 900 F. results in opening adjustment of the valve 86 so that a larger percentage of the fuel is diverted through the heat exchanger 66. In this way the valve 86 is automatically operative to prevent the temperature of the fuel supplied thru the heat exchanger 66 from exceeding a predetermined value. Temperature control of the valve 86 is schematically indicated as comprising a conventional fluid filled temperature responsive bulb 90 in the fuel line 38 at the heat exchanger 66. The bulb 90 is connected to a bellows 92 which in turn is mechanically connected to the valve 86 so that an increase in fuel temperature at the bulb 90 results on opening adjustment of said valve against the spring 94.

With the structure described, circulation of the liquid coolant through the passages 50 of the afterburner hollow wall 42 serves to keep the temperature of said wall below a maximum safe value. The heat absorbed by the liquid coolant is extracted in the heat exchanger 66 by the fuel flowing therethrough in heat exchange relation to said coolant. This fuel is heated to a sutficiently high temperature in the heat exchanger 66 so that it vaporizes therein or it at least vaporizes promptly upon being discharged into the afterburner from the downstream fuel nozzle 36. The fuel nozzles 34 are disposed a substantial distance upstream of the flameholder structure 38 so as to give this unheated portion of the fuel time to vaporize and mix with the turbine exhaust gases before reaching the fiameholder.

The cooling liquid circulated through the passages 50 of the hollow afterburner wall 42 preferably is a metal which is in the liquid state at the temperatures of the turbine exhaust. Hence the coolant metal will become a liquid before the engine after-burner is started. A suitable metal for this purpose is an eutectic mixture of sodium and potassium. Other metals such as pure sodium may also be used. Such a liquid coolant has the advantage of a high thermal capacity so that it will absorb a large amount of heat with a relatively small temperature rise.

If a hydrocarbon fuel were used directly as the fluid coolant in the passages 50 it would vaporize therein and would require large pressures to keep the volume of the fuel required for cooling within reason. This would mean that with a hydrocarbon fuel as the coolant for the passages 50, the walls of said passages would have to be strong enough to withstand much higher pressures than is required when a liquid metallic coolant is so used. Also because of the large surface area of the hollow wall structure 42 required to be cooled a substantial time is required for circulation of the coolant thru its passages 50. Hence if a hydrocarbon fuel were used as a coolant in these passages the fuel would tend to crack because of the temperature the fuel would attain and because of the length of time the fuel would be at this temperature. Such cracking is objectionable because it changes the structure of the fuel and in addition fuel cracking along with other factors such as fuel oxidation in the passages 50 would tend to cause coking deposits to build up along the walls of said passages.

By using a liquid metal coolant to cool the hollow wall 42 and then transferring the heat from the liquid coolant to the fuel in the heat exchanger 66, the heat can be transferred rapidly to the fuel so that the fuel is at a high temperature for only a short period of time before it is discharged into the engine afterburner at the fuel nozzles 36. With this arrangement the length of time the fuel is at the high temperature before burning in the afterburner can be kept sufiiciently short to minimize cracking of the fuel.

In order to minimize the heat transfer from the afterburner combustion gases to the liquid coolant in the hollow wall passages 50, the wall structure for the outer portion of the afterburner chamber 40 also includes a heat barrier or insulating layer disposed over the inner surface of the hollow wall 42. The heat insulating layer preferably is of a sheet metal honeycomb construction having an inner cylindrical shell 102 with a honeycomb structure 104 disposed between said shell and the hollow wall 42. The inner shell 102 has longitudinally extending corrugations 106 to facilitate expansion and contraction of said shell. The walls of the honeycomb structure 104 have openings 108 so that the cells of said structure are interconnected. These interconnected cells are vented to the surrounding atmosphere for example by the passage indicated at 110.

The honeycomb layer 100 prevents the heat loss from the afterburner gases to the liquid coolant in the passage 50 of the hollow wall 42 from becoming excessive. Also because of the corrugations 106 the layer 100 will tend to expand with internal pressure so that it transmits the internal pressure to the liquid cooled hollow wall 42. With this arrangement the relatively cool outer wall 42 carries all the structural loads while the inner wall or layer 100 not only acts as a heat barrier but, because of its resiliency, also acts to transfer the internal gas pressure loads to the cool outer wall. Having the loads all carried by the relatively cool wall 42 minimizes the required weight of the afterburner wall structure.

The wall structure of the centerbody 26 and plug 28 and that of the axially movable wall 30 are all subjected to the hot afterburner gases. Each of these wall structures, like that for the outer portion of the afterburner combustion chamber 40, includes a hollow liquid cooled wall together with a honey-comb layer disposed over said hollow wall to function as a heat barrier.

In the case of the centerbody 26, the hollow wall of said centerbody has an outlet annular manifold 122 at one end and an inlet annular manifold 124 adjacent the maximum diameter portion of the plug 28. The pump 60 is connected to the inlet manifold 124 by a line 126 and a line 128 returns the coolant from the outlet manifold 122 to the return line 64. In this way all the liquid coolant supplied to the manifold 124 flows longitudinally through passages (similar to the passages 50) in the hollow wall 120 to its outlet manifold 122 to cool said well.

Liquid coolant is also supplied by the line 126 to an inlet manifold 130 at the rear end of the plug 28 from which it flows through passages (similar to the passages 50) in its hollow wall 132 to an outlet manifold 134 which is connected to the return line 128.

Likewise liquid coolant is supplied by the pump 60 and supply line 142 to an annular inlet manifold 144 disposed at a mid or intermediate point along the hollow wall 146 of the movable wall structure 30. The inlet manifold 144 communicates with only alternate passages (similar to the passages 50) in the hollow wall 146 and only with the portion of said passages along the upstream portion of said wall. A partition 148 is disposed across only these alternate passages at said mid or intermediate point. An annular outlet manifold 150 is disposed adjacent to the inlet manifold and communicates with only the same alternate passages as the inlet manifold but on the other side of the partition 148. Liquid supplied to the inlet manifold 144 flows through said alternate passages to an annulus 152 at the upstream end of the hollow wall 146 and thence through the other passages in the hollow wall 146 to an annulus 154 at its downstream end and then through the first mentioned alternate passages to the outlet manifold 150 which in turn communicates with the return line 64.

Since the wall 30 is axially movable the connections to the

manifolds

144 and 150 are flexible as schematically indicated on the drawing at 160 and 162 respectively. Linkage 164 is connected to the wall 38 for axially adjusting its position to vary the nozzle area.

The hollow walls 120, 132, and 146 are provided with heat barrier layers 166, 168, and 170 respectively of honeycomb construction similar to layer 101 of the hollow wall 42. Actually the outer wall structure of the afterburner chamber 40, the wall structure of the centerbody 26, plug 28, and movable wall 38 essentially are all the same. The only diiferences lie in the various manifold arrangements described for circulating the liquid coolant through their hollow walls.

While we have described our invention in detail in its present preferred embodiment it will be obvious to those skilled in the art after understanding our invention that various changes and modifications may be made therein without departing from the spirit or scope thereof.

We claim as our invention:

1. In combination with a jet engine having a chamber thru which the engine combustion gases flow at substantial velocity, said chamber having a hollow wall providing a rigid wall structure with a plurality of passages therethru; means providing a loop passageway including said hollow wall passages; a coolant within said loop passageway for circulation therearound for cooling said hollow wall, said coolant being a metal which is in the liquid state during engine operation; two nozzle structures for discharging fuel into said engine for combustion therein and flow of the combustion gases thru said chamber, said two nozzle structures being spaced so that one is disposed a substantial distance downstream of the other; a common source of fuel having passage connections to both said nozzle structures; a heat exchange structure interposed in the flow path of said liquid coolant to and from said chamber Wall and in the flow path of fuel flow from said common source only to the downstream one of said two nozzle structures for flow of said latter fuel and liquid coolant thru said heat exchanger in heat exchange relation for transferring heat from said liquid coolant to the fuel supplied to the downstream nozzle structure; and

means for regulating the division of fuel flow from said common source to said two nozzle structures.

2. The combination claimed in claim 1 and in which said last mentioned means comprises valve means; and means responsive to the temperature of the fuel leaving said heat exchange structure and operatively connected to said valve means for increasing the fuel flow thru said heat exchange structure should said temperature exceed a predetermined value.

3. The combination recited in claim 2 in which said wall construction has an inner layer providing a heat barrier between said hot gases and said rigid hollow wall, said inner layer having a honeycomb construction with an inner shell closing the cells of said honeycomb to the hot gases, said inner shell having corrugation to permit outward expansion thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,563,608 Wood Dec. 1, 1925 1,870,809 Handy Aug. 9, 1932 2,104,974 Dawes Jan. 11, 1938 2,512,875 Reynolds June 27, 1950 2,548,092 Bartlett et al Apr. 10, 1951 2,586,025 Godfrey Feb. 19, 1952 2,718,753 Bridgeman Sept. 27, 1955 2,720,753 Sharpe Oct. 18, 1955 2,776,092 Collins Jan. 1, 1957 2,780,915 Karen Feb. 12, 1957 2,793,496 Mortimer May 28, 1957 2,794,319 Stockdale June 4, 1957 2,880,577 Halford et a1. Apr. 7, 1959 2,925,712 Johnson et a1 Feb. 23, 1960 FOREIGN PATENTS 489,052 Canada Dec. 23, 1952 102,388 Great Britain Jan. 4, 1917 618,846 Great Britain Feb. 28, 1949 760,243 Great Britain Oct. 31, 1956