US 2974482 A
Description (OCR text may contain errors)
March '14, 1961 e. s. KELLEY COOLANT INJECTION SYSTEM FOR ENGINES Filed April 25, 1955 INVENTOR BEDREE El. KELLEY Ai'TORNEY a. N w A v 3 H w 2225.52 I I u mum United States 2,974,482 COOLANT INJECTION SYSTEM FOR ENGWES George S. Kelley, Ridgewood, N1, assignor to Guides- Wright Corporation, a corporation of Delaware Filed Apr. 25, 1955, Ser. No. 503,471 3 Claims. (Cl. 6ll-39.3)
This invention relates to jet engines and is particularly directed to a control system for jet engines which take in air from the surrounding atmosphere for combustion and *e ea'ire at supersonic flight speeds.
In a gas turbine'engine the performance of the com piessbrcomponent depends on the compressor speed and the temperature of the air entering the compressor. Because'of the ram effect of the entering air, at supersonic flight speeds the temperature of the air in the engine air inlet increases rapidly with increase in flight speed. In general, an increase in air inlet temperature has some what the same elfect on compressor performance as a decrease in compressor speed. Hence, control of the mannium compressor inlet air temperature is important from *the standpoint of the aerodynamic performance of the compressor. At the same time, any limit of the compressor inlet temperature may serve to limit other temperatures downstream therefrom.
Particularly *in the case of a twin-spool gas turbine e'gine, i.e. an engine having two independently rotatable and operable compressors disposed in tandem relation and delivering compressed air to a single combustion chamber, an increase in inlet air temperature may cause surging of at least the low pressure compressor to occur.
Consequently, as the inlet temperature increases with in creasing flight speed, the low pressure compressor operating point will move towards the surge region of said compressor and at some limiting air temperature will finally'surge.
An object of this invention is -'to provide novel means and method 'for reducing the temperature of the inlet air so as to prevent surging off the compressor. Specifically the invention comprises "the provision of means for iritroducing a liquid coolant such as water into the sen-- resser air-inlet when the inlet air temperature exceeds a redetermined value, said coolant being introduced "at a rate which inere'ase's in accordance with the increase said temperature above said value and which increases with increase in mass air flow rate through said inlet. liquid coolant injection system of the invention for keeping the temperature of the air entering the compressor below a predetermined value is particularly important at supersonic flight speeds where high air inlet temperatures are encountered. Hence the present invention permits large increase in the supersonic flight speeds of turbo jet engines.
Other objects of this invention will become apparent upon reading the annexed detailed description in connection with the drawing which illustrates schematically a twins'pool gas turhine engine incorporating the subject invention.
Referring to the drawing, 10 is a twin-spool turbo-jet engine having an inlet 12 which supplies air to a first stage or low pressure compressor 14 which compresses the air and then delivers said air at some intermediate pressure to a second stage or high pressure compressor 16 which further compresses the air to a still higher pressure. From the high pressure compressor 16 the air is delivered to a combustion chamber 20 where fuel is introduced and burned thereby increasing the air temperature. The hot gases from the combustion chamber then enter a first stage or high pressure turbine 22 which extracts energy from the hot gases and drives the high pressure compressor 16. From the turbine 22 the hot gases enter the second stage or low pressure turbine 24 which drives the low pressure compressor 14 and thence through the exhaust nozzle 26 finally discharging to the outside air to provide the engine with forward propulsive thrust. The two compressors 14 and'16 are independently rotatable there being no mechanical connection between the two. Similarly the two turbines are independently rotatable. The turbine 22 drives the compressor 16 through a shaft 28. The turbine '24 drives the compressor 14 through a shaft 30 which is co-axial with and disposed within the high pressure unit drive shaft 28. The structure described to this point comprises a conventional twin-spool turbo-jet engine.
In accordance with the invention a plurality of nozzles 32 are provided for introducing aliquid coolant, such as Water, into the air inlet passage 12. The nozzles 32 are connected to a manifold 34 to which the liquid coolant under pressure is supplied under control of a flow regulating mechanism 36. A pump 38 drivably connected to an electric motor 40 is arranged to supply coolant under pressure to the mechanism 36 through a passage '42, said pump having a conventional pressure relief valve 44 to limit its output pressure. The mechanism 36 has flow regulating means which control an internal passage 46, said latter passage connecting the coolant supply passage 42 to a passage 48 connected to the coolant manifold 34. V
Preferably, the mechanism 36 is substantially like the fluid flow regulating mechanism fully disclosed in copending application Serial No. 463,019 filed October 18, 1954, now Patent No. 2,834,375 and for a more complete description attention is directed thereto. Thus the mechanism 36 includes a main valve 50 and an auxiliary valve 52, said valve 52. being serially disposed in said passage 46 downstream of said main valve. The main valve Stl is supported by and is urged in a valve closing direction by a bellows 54- the interior of which communicates with the upstream side of the main valve through a restricted passage 56. A nozzle 58 communicates with the interior of the bellows 54 via a passage 60 whereby, when said nozzle 58 is open, a small quantity of coolant flows through the restriction 69 and discharges, through said nozzle, into the coolant passage 46 on the downstream side of the auxiliary valve 52. One end 0 a lever 62 overlies the discharge end of the nozzle 58 to function as a baflle member for said nozzle. A spring 64 is disposed between the lever 62 and the auxiliary valve 52 so as to urge the lever 62 in a nozzle closing direction and to urge the auxiliary valve 52 in a closing direction against the coolant pressure differential across said valve. The force of the spring 64 on the lever 62 is opposed by a second or control force transmitted thereagainst by a pin 66 from a lever 63. The lever '68 is pivoted at 69 and is disposed in a chamber 70 which is isolated or sealed from the coolant passage 46. A control pressure is supplied to the chamber 70 by a conduit 72. The pressure in the chamber '70 acts against a bellows 74 one end of which is secured to one end of an arm 76. The other end of the bellows 74 is connected to one end of a bell crank lever 78 which is pivotally mounted on the other end of said arm 76. The other end of said bell crank lever 78 engages a circular surface of the lever 68 at the point '79 for transmitting against the lever 78 the control fluid pressure force acting against the bellows 74. Intermediate its ends the arm 76 is mounted on a shaft 81 which projects from the housing Patented Mar. 14, 1961 of the mechanism 36, the axis of said shaft being substantially on the center of curvature of the circular surface of the lever 68. An arm 82 is connected to the outer end of said shaft so that upon rotative adjustment of the arm 82 the position of the point of engagement of the bell crank lever 78 with the lever 68 shifts along said latter lever. I
When the arm 82 is set so that the point of contact 79 of the bell crank lever 78 on the lever 68 is, as illustrated, above the pivot axis of the lever 68 the moment arm of the force exerted by the lever 78 on the lever 68 is considered positive. With such a positive moment arm the control pressure acting on the bellows 74 is transmitted against said lever 68 to exert a clockwise turning moment thereon and therefore the lever 68 through the pin 66 exerts a control force on the lever 62 which is proportional to the product of said control pressure force on the lever 68 and said positive moment arm. As fully explained in said copending application the mechanism 36 automatically operates to control the fluid flow therethrough in proportion to this control force and as already stated, in this case said fluid is a liquid coolant such as water. It is apparent therefore that the rate of coolant flow to the coolant nozzles 32 can be increased by increasing the control pressure in the chamber 70 and/or by moving the arm 82 in a counterclockwise direction so as to increase the positive moment arm of the force exerted by the bellows 74 through the bell crank lever 78 against the lever 68. Conversely the rate of coolant flow can be decreased by decreasing said control pressure and/ or moment arm. It is also apparent that if the arm 82 is adjusted so that said moment arm is zero or negative (opposite from that illustrated) then, regardless of the magnitude of the control pressure in the chamber 70, the control force exerted by the pin 66 on the lever 62 is zero and hence the rate of coolant fiow through the mechanism 36 to the nozzles 32 is zero.
In accordance with the invention the control pressure in the chamber 70 is regulated in proportion to the rate of mass air flow through the inlet 12. For this purpose a total head tube 90 directed upstream in the air inlet may be provided and connected to the conduit 72 so that the pressure in the chamber 70 is proportional to the impact pressure of said inlet air as measured by the tube 90. As also explained in said copending application at least in a predetermined high velocity range of the entering air flow this impact pressure is substantially proportional to the rate of mass air flow through said inlet. In the case of turbo-jet engines means are generally provided for controlling the compressor rotational speed and when, as here, the compressor inlet temperature is controlled, said impact pressure is a more accurate measure of the mass flow through said inlet. Also, the arm 82 of the mechanism 36 is connected to means for adjusting said arm with changes in the air inlet temperature. For this purpose a temperature responsive bulb 92 is disposed in the air inlet 12 and as is conventional said bulb is connected to a bellows 94 for producing expansion and contraction of one end of said bellows 94 with increase and decrease of said inlet temperature. The bellows 94 is operatively connected to the arm 82 sothat an increase in air inlet temperature produces a counterclockwise adjustment of said arm (as viewed on the drawing) so that when positive, the moment arm of the control pressure force on the lever 68 is increased by said adjustment. This connection may be direct or, as illustrated, preferably includes a servo mechanism, schematically indicated at 96, for amplifying the force and/or movement of the temperature responsive bellows 94. The connection between the temperature responsive bellows 94 and arm 82 is such that the moment arm of the control pressure force on the lever 68 is negative (opposite to that illustrated) when the air inlet temperature is below a predetermined value. Above said predetermined temperature value said moment arm becomes positive and has a magnitude which increases with increase in the air inlet 5 temperature above said predetermined value. Hence above said predetermined air inlet temperature and with the pump 38 operating to supply coolant to the regulating mechanism 36, coolant is supplied to the nozzles 32 and is discharged into the inlet 12 at a rate which is proportional to the product of the mass air flow through the inlet and the extent to which the inlet air temperature exceeds said predetermined value.
As illustrated, the temperature responsive bellows 94 and total head tube 90 are both preferably disposed upstream of the point of introduction of the coolant into the inlet 12 from the nozzles 32.
The temperature responsive bellows may also control a switch for closing said switch when the .air inlet temperature excecds a predetermined value. The switch when closed completes an electric circuit to the motor 40 for energizing said motor to drive the coolant pump 38. Preferably the switch 190 closes at an air inlet temperature below that at which the moment arm of the control pressure force on the lever 68 becomes positive. With such an arrangement coolant is introduced into the inlet as soon as the moment arm of the control pressure force on the lever 68 becomes positive. Obviously, however, the switch 100 may control the initiation of coolant introduction into the inlet by having it set to close at an inlet temperature higher than that at which said moment arm becomes positive. In either case however, whenever the air inlet temperature exceeds some predetermined value, coolant is introduced into the inlet to cool the air entering the compressor 14 and the rate at which the coolant is introduced into the inlet depends on the extent to which the temperature of the entering air exceeds said value and on the mass air flow rate into the inlet. Hence the mechanism 36 may be calibrated so that whenever the temperature of the air entering the inlet exceeds a predetermined value the liquid coolant is introduced into the inlet at a rate which is sufficient to cool the air so that the temperature of the air entering the compressor is maintained substantially at said predetermined value. With such an arrangement surging of the compressor 14 which might otherwise occur at high flight speeds because of the resulting high inlet temperatures is prevented. In addition by keeping the temperature of the air entering the compressor below a predetermined value the danger of excessive temperatures occurring in the engine downstream therefrom is greatly minimized.
The particular temperature at which the liquid coolant is introduced into the inlet obviously is subject to con siderable variation. If prevention of surging of the comp essor is the primary consideration this predetermined temperature will depend on the compressor and engine design. For example in the case of a particular compressor this temperature may be of the order of 275 F. and in other designs may be much lower or higher. Also the particular liquid coolant used will depend on this temperature because in order to obtain the maximum cooling effect from the coolant its physical characteristics preferably should be such that it evaporates rapidly at the temperature and pressure conditions existing in the inlet upon introduction therein.
While I have described my invention in detail in its present preferred embodiment, it will be obvious to those skilled in the art, after understanding my invention, that various changes and modifications may be made therein without departing from the spirit or scope thereof. I aim in the appended claims to cover all such modifications.
I claim as my invention:
1. In a gas turbine engine having an air compressor and an air inlet passageway for supplying air to said compressor; in combination therewith means responsive to the temperature of the air within said inlet passageway upstream of said compressor; means controlled by said responsive means and operable for initiating the introduction of a liquid coolant into said passageway upstream of said compressor only when the air temperature within said inlet exceeds a predetermined value; and means for measuring the rate of mass air flow through said inlet and including means responsive to said air flow measurement for controlling the rate of said coolant introduction so that at air inlet temperatures above said predetermined value an increase in said air flow rate by itself results in an increase in the rate of said coolant introduction.
2. The combination recited in claiml in which the point of coolant introduction into the compressor inlet passageway being between the point of inlet temperature measurement and the compressor.
3. The combination recited in claim 1 in which said liquid coolant introducing means includes means for varying the rate of introduction of said liquid coolant so that at a given rate of air mass flow through said inlet the rate of said-liquid coolant introduction increases with increase in said air inlet temperature above said predetermined value.
References Cited in the file of this patent UNITED STATES PATENTS 2,438,998 Halford Apr. 6, 1948 2,657,530 Lee Nov. 3, 1953 2,628,472 Dray et al. Feb. 17, 1953 2,689,452 Jordan Sept. 21, 1954 2,863,282 Torell Dec. 9, 1958 FOREIGN PATENTS 614,106 Great Britain Dec. 9, 1948 703,619 Great Britain Feb. 10, 1954