Document
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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON. D.C. 20546
TURBINE
N73-19793
(NASA) 12 p
CSCL 21E
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00/28 64781
KSt/Scientific & Technical Information Division
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Attention: Miss Winnie M. Morgan
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and Code KSI, the attached NASA-owned U.S. Patent is being
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an invention of . . ." X ^ ^ ^ T ^ K
y\V>- — -'-vx>
Elizabeth A. Carter
Enclosure
Copy of patent cited above
NASA-HQ
mi 3,713,290
United States Patent
[45] Jan. 30, 1973
Gold
|54| GAS TURBINE ENGINE FUEL 2,972,229 2/1961 Chandler et al 60/39.28 R 3,123,128 3/1964 Ziesloft 60/39.28 R CONTROL 3,511,047 5/1970 Yates 60/39.28 R | 75 | Inventor. Harold Gold, Shaker Heights, Ohio Primary Examiner—Carlton R. Croyle [73] Assignee: The United States of America as Assistant Examiner—Robert E. Garrett represented by the Administrator of Attorney—N. T. Musial, J. A. Mackin and John R.
the National Aeronautics and Space Manning Administration [22] Filed: May 28, 1971 [57] ABSTRACT | 2 1 ) Appl. No.: 147,922 A variable orifice system that is responsive to com- pressor inlet pressure and temperature, compressor discharge pressure and rotational speed of a gas-tur- [52| U.S. Cl 60/39.28 R bine engine is incorporated into a hydraulic circuit [51 | Int. Cl F02c9/04 that includes a zero gradient pump driven at a speed [58] Field of Search 60/39.28 R, 39.28 T proportional to the speed of the engine. The resulting system provides control of fuel rate for starting, steady (56] References Cited running, acceleration and deceleration under varying altitudes and flight speeds.
UNITED STATES PATENTS 2,947,141 8/1960 Russ 60/39.28 R 11 Claims, 7 Drawing Figures
i
PATENTEOJAK30I973
3.713,290
SHEET 1 OF 3
Y////////////////7/777A
INVENTOR HAROLD GOLD BY ATTORNEYS
PATENTED JAN 3 01973
3,713,290
SHEET 2 OF 3
FIG. 3 FIG. 4 FIG. 5 APPROXIMATE STEADY STATE NP, INVENTOR K 2a HAROLD GOLD K 2b~ BY P P / 2 FIG. 2 ATTORNEYS
PATENTED JAN 3 01973
3,713,290
SHEET 3 OF 3
104-x FIG. 6 I N V E N T O R HAROLD GOLD BY
wn*~-~* ~7
ATTORNEYS
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GAS TURBINE ENGINE FUEL CONTROL It is a further object to provide reduced fuel delivery during acceleration under high inlet air temperature ORIGIN OF THE INVENTION conditions.
ll is The invention described herein was made by an em- another object to provide fuel delivery during ployee of the United States Government and may be deceleration that is substantially a fixed fraction of the manufactured and used by or for the Government for steady running flow rate.
governmental purposes without the payment of any It is yet another object to provide fuel delivery during en ine royalties thereon or therefor. 8 starting that is proportional to engine speed and is enriched below idle speed to promote ignitiOn.
BACKGROUND OF THE INVENTION These and other objects and features of the invention „,. . . i . . L j r . i will be fully explained in the detailed description of the This invention relates to hydraulic control systems • »• . . . . , .. , , invention, that are used in aircraft gas-turbine-engine fuel con- trols. The fuel control described in the disclosure that BRIEF DESCRIPTION OF THE DRAWINGS follows utilizes a hydraulic control circuit that was 15 _. . . . , , , , , e 1 described in my U.S. Pat. No. 2,876,756 and a proper- ™ P"™? " of the structure and methods taught K ... . ,, . , ., . . ,. „ by the invention are disclosed in the following specifi- tional governor system that was described in my U.S. ' . ... , . , . , . . .
10 and Pat. No. 2,971,339. I have found that the hydraulic f " claims which is taken in conjunct.on with control circuit of U.S. Pat. No. 2,876,756 can be con- the accompanying drawings ,n which: ... .,, . , . . , . 7fi FIG. 1 is a schematic diagram of the fuel control figured to function precisely in accordance with a valid *" . .
f i i . - u • r in . .u . •_ system of the invention; law relating the maximum fuel flow rates that may be .,„-, - . .. . .. , . , , , ,. , ,. . . , . FIG. 2 is a graphic presentation showing the general K delivered to a gas-turbine engine during accelerator, , characteristics of tne a titude and fli ht d ind H H under varying altitude and flight speed conditions and , .„ * dem accordance with which the c ontrols s tem with a similar law defining the minimum fuel flow rate „ f tj .
unc ons that may be delivered during deceleration. The present , -, ' .
F G js a f ntary tion of the hydraulic cir invention provides means for the utilization of this , cui{ of nG illustrating a variable oriflce structure hydraulic control circuit in gas turbine engine fuel con- employing a pressure motor; trols that function in accordance with these accelera- ti of the hydraulic cir- FIG 4 is a fragmentary por on tion and deceleration laws. , variable orifice structure 30 cujt of RG illustrating a SUMMARY OF THE INVENTION employing both a temperature and a pressure motor; FIG. 5 is a sectional view taken through the plane The fuel control of this invention utilizes a hydraulic 5—5 in FIG. 4; mechanism for controlling the flow of fuel to an aircraft FIG. 6 is a fragmentary portion of FIG. 1 illustrating gas-turbine-engine during the operational modes of: 35 the method of utilization of a hydraulic governor; and starting, acceleration, steady running, deceleration and FIG. 7 is a fragmentary portion of FIG. 1 illustrating stopping. The system provides a proportional, closed- the method of utilization of a fly-weight governor, loop governor for steady running operation, and an open-loop metering system for controlling fuel How DESCRIPTION OF THE PREFERRED rate during starting, acceleration and deceleration. . EMBODIMENTS In one embodiment of the invention, both the gover- Basic Hydraulic Control Circuit - As shown in the nor and the metering system derive their response to schematic diagram of the fuel control of FIG. 1, the engine speed from a positive displacement control system comprises the following components or pump that runs at a speed that is proportional to engine subsystems: the positive displacement pump 11, the speed, pressure regulator 12, the in-series pump orifice 13 and In a second embodiment the governor utilizes a bypass orifice network (enclosed by the dashed tne mechanical speed responsive device. As in U.S. Pat. ij ) 14. The direction of flow through the system is nes Nos. 2,876,756 and 2,971,339 the pressure gradient indicated by arrows.
across the control pump is maintained at substantially 50 Fuel enters the system upstream of pressure regula- zero by a pressure regulator to prevent pump slippage tor 12 through conduit 15. In this schematic diagram and to accomplish the metering functions. f | is considered to be being delivered from an engine ue The system provides: fuel delivery during accelera- driven, fixed displacement supply pump 10, hence tion that is in accordance with an altitude and flight regulator 12 is of the relief or return type. Regulator 12 speed independent law that defines the compressor 55 returns flow in excess of the system demand through surge limit; reduced fuel delivery during acceleration variable orifice 16 and through conduit 17 to the inlet under high inlet air temperatures to prevent turbine to pump 10. Movable wall 18 of regulator 12 commu- over-temperature; fuel delivery during deceleration nicates with the pressure in conduit 15 and hence with that is substantially a fixed fraction of the engine steady the pressure upstream of pump 11. On its opposite side running fuel flow rate; fuel delivery during starting that movable wall 18 communicates with the pressure is proportional to engine speed and is modified by com- downstream of pump 11 through passage 19. Movable pressor inlet air temperature and pressure. wall 18 is linked by suitable means to valve element 20 In accordance with the foregoing, it is a primary ob- and thereby varies the area of orifice 16. Movable wall jectof the invention to provide a fuel control system for 18 automatically varies the area of orifice 16 to hold aircraft gas-turbine engines that delivers fuel to the en- the pressure in conduit 15 equal to the pressure gine during acceleration in accordance with an altitude downstream of pump 11. By virtue of this pressure and flight speed independent law. regulation the pressure gradient across pump 11 is au-
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tomatically held at substantially zero. Pump 11 is imum value. Thus in the operating speed range orifice driven at a speed that is proportional to the speed of the 13 provides a fixed reference for metering and/or gas turbine engine (hereinafter referred to as engine governing. In the starting speed range the reduced area speed) through shaft 21. The flow discharged from of orifice 13 provides an enriched flow (as may be seen pump 11 flows through conduit 22 and orifice 13 and from equation (4)) to promote ignition, into manifold 23. Conduit 24 joins conduit 15 and Variable orifice network 14 comprises: variable ori- diverts flow to the bypass orifice network 14. In net- fices 30 and 31 which are actuated by common pres- work 14 conduit 24 divides into conduits 24a and 24fc sure motor 32; variable orifices 33 and 34 which are ac- and the network terminates at manifold 23. The flow tuated by common pressure motor 35; variable orifice from pump 11 and from orifice network 14 combine in 36 which is actuated by temperature motor 37; and manifold 23 and are conducted to the engine fuel-injec- variable orifice 38 which is actuated by governor tion system (not shown) through conduit 25. mechanism 39.
The pressure upstream of orifice network 14 is held Pressure motor 32 comprises movable wall 40, spring equal to the pressure upstream of pump 11 by the , 41, chambers 42 and 43 and output element 44.
passage junction and, as a consequence of the zero Chamber 42 is in pressure communication with the en- pressure gradient across pump 11, the pressure up- gine compressor discharge and chamber 43 is in pres- stream of orifice network 14 is held equal to the pres- sure communication with the compressor inlet. Mova- sure upstream of orifice 13. The pressure downstream ble wall 40 is suitably coupled by element 44 to varia- of orifice network 14 and orifice 13 are equalized by 20 ble orifices 30 and 31 to increase the area of orifices 30 manifold 23. As a consequence of the equalities of up- and 31 upon an increase in compressor discharge pres- stream and downstream pressures the flow through the sure and to decrease the area of orifices 30 and 31 orifice network 14 is made proportional to the flow upon an increase in compressor inlet pressure, through orifice 13. This proportionality can be ex- Pressure motor 35 comprises evacuated bellows or pressed by the following equation: 25 anneroid.element 45, one end of which is fastened in chamber 46, and output element 47. Chamber 46 is in = Gu MM' ^isl Gi3 ( ' ) . pressure communication with the compressor inlet.
Where: Bellows 45 is suitably coupled by element 47 to varia- C - volumetric flow rate through orifice network f 33 34 increase the area of these ori- H ble ori ices and to 14 30 fices upon an increase in compressor inlet pressure.
2,3 - volumetric flow rate through orifice 13 Temperature motor 37 comprises temperature AH — effective area of orifice network 14 responsive element 48 and output element 49. Element ^13 — effective area of orifice 13 4g ; j temperature communication with the compres- s n The flow rate Q is equal to the flow rate discharged | j bly coupled, by output element 49, 13 sor in et and is su ta by pump 11, which relationship is: 35 se the area of orifice 36 tQ variable orjflce 36 to decrea O — n \i upon an increase in compressor inlet temperature.
l3 ^ Governor mechanism 39 communicates with engine _ ' . . .. . . ... speed and is suitably coupled, by output element 50, to r D — volumetric displacement per engine revolution . ._ ' , . , ... _,„ v ., . , . , . ,. .„ variable orifice 38 to decrease the area of orifice 38 N— engine revolution rate (engine speed) 40 . .
e „, _ ... , ... upon an increase of engine speed above set speed.
r n • The flow rate deivered to the engine, 0 , is , . ,. . ° •, „ , .
6 < K m < 26 cl Lever 51 indicates the means for manually changing 226 = 0,3+6.4 (3) thesetspeed.
Combining equations ( 1 ) , (2) and (3) gives the The flow through orifice 38 discharges into manifold system flow equation- 45 ^2. From manifold 52 fuel flows into manifold 23 through parallel orifices 30 and 33 and series orifice 36 Qig= DyN [(A IA ) + 1] (4) and 34. Orifices 36 and 34 are connected by conduit 14 13 System Operation — Movable wall 26 of variable ori- 54. Fuel flowing in conduit 246 flows to manifold 23 fice 13 communicates directly with the pressure in con- through optional orifice 31a and fuel flowing in conduit duit 22 and hence with the pressure upstream of orifice 50 24c flows to manifold 23 through orifice 31. All con- 13. On its opposite side movable wall 26 communicates duits and manifolds are of sufficient cross-sectional with the pressure downstream of orifice 13 through area to make friction induced pressure gradients passage 27. Movable wall 26 is linked by suitable negligible. Orifice 31a provides an additional precise- means to valve element 28 and thereby varies the area ness of fuel control and may be disposed with if desired of orifice 13. Spring 29 urges movable wall 26 and 55 by blocking or eliminating the conduit in which it is valve element 28 in the direction to reduce the area of disposed.
orifice 13 and the pressure difference across orifice 13 Rotation of plug 53 to its closed position shuts off all urges the wall 26 and element 28 in the direction to in- flow to pump 11 and orifice network 14 as is required crease the area of orifice 13. The bias of spring 29 is for shutting down an operating engine. Upon such shut- preferably set to hold orifice 13 at its minimum area off the pressure in conduit 22 drops rapidly, allowing from zero engine speed to the cranking speed at which pressure regulator 12 to shunt back, at low pressure, ignition is initiated. As the ignited engine drives the en- the flow from the supply pump 10 during engine coast gine speed toward idle speed the increased pressure down.
drop across orifice 13 drives the orifice open reaching Under all modes of operation the fuel delivery to the its maximum area at an engine speed slightly below idle engine is in accordance with equation (4). From idle to speed. At all speeds from idle to maximum engine maximum engine speed, the fuel delivery is modulated speed the area of orifice 13 remains fixed at the max- by variations in N and A, , A remaining fixed. In 4 13
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steady running operation A is adjusted by the gover- the reduction in the value of K below K , in the cor- M t ta nor mechanism, through its variation of orifice 38, so relation given in equation (5). K represents the value tb that the fuel delivery equals the engine steady running of K at the highest compressor inlet temperature at t requirement. which the engine can be accelerated to maximum When the set speed is made substantially greater 5 design speed.
than the engine speed, such as occurs when lever 51 is FIG. 2 further illustrates the deceleration limit that is rapidly advanced to a higher speed setting, the gover- employed in the present invention and the approximate nor mechanism 39 drives orifice 38 to its maximum steady running line from which the limit is derived. As area. The resulting increase in A causes the fuel illustrated, the deceleration limit is substantially a fixed lu delivery to increase above the steady running require- fraction of the steady running fuel How rate and which ment and the engine accelerates. The increase in A is be expressed by the following relationship, 14 can limited by the other orifices of network 14. As will be demonstrated by the mathematical analysis that fol- (*>r)l(NP) = K (P IP ) (6) 4 3 t lows, the variation of orifices 30, 33, 36, 34 and 31 in , Where: response to engine and atmospheric parameters limits K = Constant the fuel delivery during the time that orifice 38 is at ,„ ^ ^ tenm Qf |he wgi h{ now m [Qn maximum area so that compressor surge and/or turbine • -. .• , A \ .
over-temperature are prevented. ^ When the set speed is made substantially less than 20 *f= P fDyN [(A /A ) + 1] (7) 1 4 I 3 the engine speed, such as occurs when lever 51 is Where: rapidly withdrawn to a lower speed setting, governor p,= fuel density mechanism 39 drives orifice 38 to zero area. The Rearranging equation (7) in terms of the left hand resulting decrease in A causes the fuel delivery to , , 14 tefm m tions (5) and (6) obtain for the contro decrease below the steady running requirement and the 25 svstenv engine decelerates. The decrease in A is limited by H orifice 31. As will be demonstrated by the mathemati- wJNP = p D )/P [(A JA ) + 1 ] (g) t f v 2 t a cal analysis that follows, the variation of orifice 31 in Letting p,D = D, equation (8) becomes v response to engine and atmospheric parameters limits ,JMP — n / p KIA IA •v-u 11 the fuel delivery during the time that orifice 38 is at 30 ^'nTd ^'equations (5) and zero area so that combustor blow-out does not occur. , . . . . . • .. c * • j n r t „ . . , „ . , . . . (9) and solving for/4, gives the value of-4,4 required 4 6 Correlation of System with Acceleration and . . . . . . r» • • ._• -. , .. . _, , • , , «• . _, • during maximum engine acceleration. Designating this Deceleration Laws — The altitude and flight speed in- , e A A .t c \\ • • • i j j , , , , - , . , , „ value of AH as A, , the following expression is yielded: 4a dependent law, relating t h e maximum fuel flow rates . 1 1 0 o r j that may be delivered to a gas turbine engine during ac- A =A [(K /> )/D - 1 ] + [A K )/D] P ( 10) l4a l3 2 2 13 3 3 celeration, that is employed in this invention, is ex- pressed in the following relationship: Equation (10) expresses the required variation of A with the absolute pressures PI and P . Because P l 4 a 3 3 (w )/(NPi) = K + K (P /P^) (5) varies over a much larger increment of pressure than f 2 3 3 Where: does P it is desirable to utilize the pressure difference w — Weight flow rate of fuel to engine (P -P^) rather than P absolute. For this purpose, f 3 3 PI — Compressor inlet total pressure equation (10) can be rewritten as follows: /> - Compressor discharge total pressure UK +K \ m < P m K -Constant .. ^^--•4M^ +K )/D(P,-l)^ 2 3 K,-Constant +[(A, K )ID](P -P,) (11) 3 3 3 FIG. 2 which presents equation (5) graphically illus- Equation ( I I ) establishes that A is a linear func- l 4 a trates typical relative magnitudes of the parameters. In tion of (P — P ) which has a slope equal to 1(A K )ID] 3 2 13 3 FIG. 2, K is shown to lie between an upper value, K and an intercept equal to [A [(K +K )/D(P - 1]}.
2 2a 13 1 3 t and a lower value, K . The fuel flow rate given by the 50 Equating the right hand terms of equations (6) and u correlation of equation (5) for K equal to K (9) and solving for A gives the value of A required 2 ta 14 lt represents the maximum allowable acceleration flow during maximum deceleration. Designating this value rate at compressor inlet temperatures which are below of A as A the following expression is yielded: I4 l4<t< a fixed temperature. This fixed temperature, which I _ will refer to as the design temperature, is the inlet tem- 55 ^ud= [(A K, )/D P - A ( 1 2 ) 1 3 4 3 t3 perature at or below which the compressor surge In terms of the pressure difference (P -P ) equation 3 2 limited acceleration fuel flow is less than the turbine (12) is inlet temperature limited acceleration fuel flow. At Ai4d = A, [(KilD(P-> — 1)] compressor inlet temperatures above the design tem- -I- [(A K )ID](P — P ) (13) l3 t 3 2 perature the compressor surge limited fuel flow causes Referring to FIG. 1, it can be seen that when orifice the turbine inlet temperature limit to be exceeded. , , .
38 is at zero area the va ue of AH is equa to the effec Therefore, the maximum fuel flow rate that may be , gi maximum tive area of orifice 3 Accordin Vi at delivered during acceleration is less than the surge deceleration: limited value at compressor inlet temperatures above the design temperature. The reduction in maximum ac- A = A ( 1 4 ) ltd 3l celeration fuel flow that accompanies compressor inlet Where: temperature above the design temperature appears in A,, — Effective area of orifice 31
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Variable orifice 31 is actuated by pressure motor 32. /4 _, = ^ ( 2 1 ) C Motor 32 is responsive to (P —Pi) and accordingly 1 Orifice 30 is in parallel with the sub-network A _,. I 3 c set: now designate a second sub-network: A = ((A K )/D](P -P ) ( 1 5 ) 5 A -* = A» + Ac-i ( 2 2 ) 3i l 3 t 3 I c By making A, vary in accordance with equation Where: M (15) 1 neglect the term A [(KJD(P - 1)] in the A . — effective area of network of orifices 30, 33, 13 t c t system requirement equation, equation (13). This 36 and 34 neglected term could be taken into account through X —effective area of orifice 30 3 0 the use of an additional variable orifice 31a which is in 10 Noting that A _ is in series with orifice 38 and that c 2 parallel with orifice 31 and is made responsive to P by orifice 31 is in parallel with that series pair, the effec- tive ar being linked to motor 35 as shown in phantom in FIG. ea network 14 is 2. Accordingly I may set: - - --. - - i * I ^o—2 A = A [ ( K / D P - l ] ( 1 6 ) 1 5 '"~ " L , (A~*\> 3 I a t 3 4 2 A — Effective area of orifice in parallel with ori- V \ A ) (23) 3ta 3S fice31 When orifice 3la is utilized: During maximum acceleration orifice 38 is driven to _ . maximum area. I rnake the maximum value of A^ much A = A + A t*<i ai at« (17) 20 larger than A . , in which case the value of A set by e t l4a It may be seen by substituting equations ( 1 5 ) and the control system is,from equation (23).
(16) in equation ( 1 7 ) that the system requirement equation, equation ( 1 3 ) is mathematically satisfied. A = A + A _ (24) l4a 3l e 2 However, I find in practice that to hold /4 greater A was previously defined by equation (15). Sub- 310 3l than zero at moderately low values of P , the pump dis- 25 stituting equation (15) inequation (24) gives: placement D must be impractically small (as may be in- _ \ i n i p P\ A A K D p p + A 2 5 ferred from equation (16)). Therefore,! find it prefera- _ . "'-( i* *>l <- *~ *> <-? < > ble not to utilize orifice 31a Equating the right hand terms of equat.ons (25) and ( ields the re uired value of A : The effect on the system output of the absence of ori- '' > * 1 ^ fice 31a can be observed by substituting equations (14) 30 rfKi+Kt\ and ( 1 5 ) in the system equation, equation (9). This A - =A |_^ Q J Pj- C 2 U gives: . . -*<] ( 1 8 ) Comparison of equation (18) with equation (6) 35 (26) shows that the absence of orifice 31* causes the in- . , Orifice 3fl res jve to (p p } therefore> set F 3 2 troduction of the altitude dependent term [(D/P ) - " K ] in the system output. A = [A (K -K )/D] (P ~P^ (21) 4 30 1 3 3 4 3 This effect results in an increase in the deceleration And it follows from equation (22) that /4 _, is C limit as the altitude is increased (P decreased). An in- 40 required to vary in accordance with the relationship: crease in the deceleration limit with altitude is desira- A = A ble because the susceptibility of the engine combustor e-i \3[(Kt+K )/D(P — 1) ] ( 2 8 ) 3 t At to blow-out during deceleration increases with altitude. maximum compressor inlet temperature the con- tro1 s stem During steady running or acceleration, orifice 38 is y establishes A,,, in accordance with equation 45 2 1 At this open and fuel flows through the network of orifices that < ) - temperature the engine parameter K is e ual to Settm K K in are in series with orifice 38 as well as through orifice 1 *»• 8 * = » equation (28) and 31. The effective area of the sub-network of orifices equating the right hand terms of equations (28) and lves comprising orifices 33, 36 and 34 is given by: *• ' 8 50 / j 3 = | 3 | -ft A -I = AK+ C /AyV At design temperature and below the control system
V VAjs/ ( ) establishes A ., in accordance with equation (20). In
e this temperature range the engine parameter K is " z y Where: equal to K . Setting K = K in equation (28) and 55 ta t 2o A _, — effective area of network of orifices 33, 34 equating the right hand terms of equations (28) and c and 36 (20) gives: /Isj-effective area of orifice 33 _ r/K* + K \ ,1 ' 3 D 31 13 A — effective area of orifice 34 |_ \~~~D / / z - i j - 3t A se — effective area of orifice 36 50 For values of compressor inlet temperature at or It now follows from equations (30) and (29) that: below the design temperature I set A much larger than _ A , in which case equation (19) reduces to: A = A 34 3t L D J (31)
AC-I^AU + AM (20)
At the maximum compressor inlet temperature X is The four variable orifices: 30, 33, 34 and 31; as J8 reduced to zero, in which case equation (19) reduces defined by equations (27), (29), (31) and (15), respec- to: • lively, exactly match the orifice network 14 to a given
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set of engine coefficients (K , K , K and K ) and a set and described in the following section of the specifica- 2a u 3 4 of control system coefficients (D and A ). This may be tion.
I 3 Substituting equation (20) in equation (22) yields: VARIABLE ORIFICE STRUCTURES _ . . FIG. 3 illustrates a n orifice structure that m a y b e e m - e xt < 3 2 > ... . -*.~"** *. ,-., - , . ployed to control the variable orifice pair 30 and 3 lor Substituting equation (32) in equat.on (24) y.elds: ^^ , 33 * .
of varjab e orifices and M la the configura tion of FIG 3 a A ,40 = ^3. + ^30 + ^33 + ^ ( 3 3 ) Fissure motor of the type indicated at Now substituting equations ( 2 7 ) , (29), ( 3 1 ) , and 32 in FIG. 1 is employed and in consonance with that |0 (15) in equation (33) yields equation ( 1 1 ) where K = numerals identifying orifices 30 and 31 are employed.
t K However, it may be readily seen that by the substitution 2n And substituting equation ( 2 1 ) in equation ( 2 2 ) of a pressure motor of the type indicated at 35 in FIG.
yields: • 1 > t h e structure would be equally functional for the ori- ! fice pair 33 and 34.
A ,i= A A ( 3 4 ) In FIG. 3 movable wall 40 comprises piston 55 which c 3 a 3 3 Substituting equation (34) in equation (24) yields: mates slidably with bore 56 of housing body 3.
_ Chamber 43 which communicates with P is formed by t A 4a A + A A ' ~~ *\ M+ 33 ( 3 5 ) Element 44 is a cylinder that is bore 56 and end S7 Now substituting equat.ons (27), (29), and (15) in , , „ , c ed {o and js coaxia with iston c inder 44 equation (35) yields equation ( 1 1 ) where K = K . , , „ f t6 mates s idab with bore 5g and extends th bore In circumstances of engine use in which the accelera- • < Chamber 42b commu- 58 to pr jnto chamber 42b tion rate that can be obtained under the limit defined through passage 59. Cham- nicates with chamber 42fl by K» is acceptable at low compressor inlet tempera- p .
bers 42fl and 42fc comtnunicate with 3 By virtue of the tures orifices 34 and 36 may be eliminated, in which communications the area of the assembly 25 foregoing case the sub-network comprising orifices 33,34 and 36 p , ^ acted upon by 3js equa to the area acted upon by p is reduced to orifice 33 alone. j Spring 41 of FIG is divided into two parts 41fl and Operation Under Intermediate Compressor Inlet i j the configuration of FIG. 3. Adjustable spring 4 f c n Temperatures - The-effective-area A is reduced, by _ engages spring 41fr and provides a means for 3e base 60 the action of motor 37, from a maximum value at the 30 | adjustment of the assembly. Spring base 60 corn- axia design temperature to zero at the maximum inlet tern- , prises screw 6 bead 62 and lock nut 63 Head 62 is perature at which the engine can be accelerated to ably coupled to screw 61. Screw 61 engages rotat maximum design corrected speed. As stated prev.ously, threaded hole 64 of end cap 65. Variable orifice 30 is the value of A is made much larger than A at the formed by the cooperative action of rectangular slot 66 M M design temperature and below. The reduction of A^ as 35 of cylinder 44 and surface 67 of annulus 68 slot 66 inlet temperature rises above design temperature is chamber 69 of cylinder 44 and chamber 69 opens into such that the sub-network area A _i, as defined by communicates with annulus 70 through holes 71. An- ( equation (19), reduces linearly with temperatures from | communicates with manifold 52. Rectangular nu us 70 A + A to A . The reduction in the acceleration fuel ] 56 provides the linear variation of Ay, with (P -P ) 33 3t 33 s ot 3 2 delivery by the system resulting from this reduction in specified by equation (27). Variable orifice 31 is as A _, corresponds to the linear variation of the parame- formed by the cooperative action of rectangular slot 72 e ter K from K to K over the temperature range. of cylinder 44 and the surface 73 of annulus 74. Slot 72 2 la 26 A is made to vary with inlet temperature to achieve s into chamber 75 of cylinder 44 and chamber 75 36 open the above specified variation of A^ at sea level stan- communicates with annulus 74 through holes 76. An- dard inlet pressure. This is accomplished by varying A i communicates with conduit 24b. Rectangular 3t nu us 74 with temperature such that the value of A at each | 72 provides the linear variation of A with (P -P ) M s ot 3l 3 t value of temperature is equal to the value computed as specified by equation (15).
from equation (19) utilizing the required value of A _ The variable orifice structure illustrated in FIG. 4 c t and the values of A and A given by equations (29) 50 performs the function of the network of orifices com- 33 34 and (30), respectively, for PI equal to sea level stan- prising orifices 33, 34 and 36. Accordingly, the up- dard pressure. Under altitude conditions where P is stream annulus 76 in housing body 4 communicates t reduced and correspondingly the value of A reduces, with manifold 52 and the downstream annulus 77 com- M the attenuation of A by /4 (see equation (19)) municates with manifold 23. Evacuated bellows 45 of 3t M becomes less than at sea level. However, this effect is 55 pressure motor 35 is coupled to end cap 78 of chamber very small up to altitudes at and beyond which air tem- 46a. Element 47 is a cylinder that is coupled to and is peratures above the design temperature (typically 59° coaxial with bellows 45. Cylinder 47 mates slidably F) do not occur. with bore 79 of sleeve 80 and extends through bore 79 Gas turbine engines that utilize regenerators may be to project into chamber 46fc of sleeve 80. Chamber 46a employed on helicopters and turbo-propeller aircraft. communicates with chamber 46a through passage 81.
Under these circumstances, compressor inlet tempera- Chambers 46a and 46fc communicate with P . By virtue t tures above the design temperature could be encoun- of the foregoing communications, P acts on the entire t tered at low values of P . In this case the linear varia- pressure area of bellows 45. Spring 82 coacts with the t tion of the value of A _, with inlet temperature in a spring characteristics of bellows 45 and its rate is c manner that is independent of P may be required. This selected to provide the assembly with the desired axial- t manner of variation of A _ can be accomplished by displacement to pressure-increment response. Adjusta- c t means of the orifice structure shown in FIGS. 4 and 5 ble spring base 83 engages spring 82 and provides a
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means for axial adjustment of the assembly. Spring base ference is equal to the pressure drop across orifice 13.
83 comprises screw 84, head 85 and lockout 86. Head From idle speed and above the area of orifice 13 is 85 is rotatably coupled to screw 83. Screw 84 engages fixed and thereby provides an accurate speed threaded hole 87 of sleeve 80. Variable orifice A _ is reference. From equation (2) the pressure drop across e l formed by the cooperative action of rectangular slot 88 orifice 13 is of cylinder 47 and rectangular slot 89 of sleeve 80. Slot AP — m MI t 88 opens into chamber 90 of cylinder 47 and chamber LP - (D p,Nl)l(2g A ) (36) K v 13 90 communicates with annulus 76 through holes 91 in Where: AP ressure dr across oriflce 13 cylinder 47 and holes 92 in sleeve 80. Sleeve 80 is ex- " ~ P °P ternally a cylinder that is coaxial with bore 79 and P/ - fuel density mates rotatably with bore 93. Shaft 94 of sleeve 80 pro- * ~ acceleration of gravity jects out of housing body 4 where it is engaged by level Equating the net spring force to the net pressure force the 95. Snap ring 96 engages bore 93 and shoulder 97 of equilibrium speed is P Vent aXia m V emem C0lla , °. « ? iTo? ' ° , ' r '5 N= A /D \l(2 F.)l(A p ) (37, 13 y S lol f 98 of level 95 clamps shaft 94 to provide for rotation of where- sleeve 80 and collar 98 projects beyond bore 93 to axi- p _ .j f net spI nR orce ally lock sleeve 80 against snap ring 96. Arm 99 of lever " _ A area of jston 101 95 is coupled to temperature motor 48 by element 49. , governor gain S|ot 07 js contoured to provide the As may be observed in FIG. 4, A*., varies linearly with essary for system stability over the 20 variation that is nec P through the axial movement of cylinder 47 and as , . , .
2 d and a titude of o eration flnd that a con may be observed ,n FIGS. 4 and 5 vanes linearly with i rithmic variation touf that jdes a substantially oga the rotation of sleeve 80 with respect to cylinder 47 at , p e t of of orifice 36 area with the axia dis lac men all axial position of cylinder 47. Cylinder 47 is r 50 is satisfactory for stability.
cylinde prevented from rotating by its engagement to bellows 25 utilization of a fly-weight type speed-responsive The motor is illustrated in FIG. 7. The variable orifice struc- ture and the loadin SPEED RESPONSIVE MOTOR AND GOVERNOR g spring base mechanism illustrated n are ACTION ' FIG. 1 identical to that illustrated in FIG. 6 and therefore the identical parts bear the same numerals in FIG. 6 illustrates the principal elements of a speed 30 . in FIG. 7 cylinder 50 projects out of hous- both flgures responsive variable orifice of the type described in U.S. extremity with thrust bear- ing body 7 and is fitted at its Pat. No. 2,971,339. Element 50 is a cylinder that mates 121. Fly-weight assembly 122 comprises carrier ing slidably with bore 100 of housing body 6 and is integral weight 125 and weight arms 126. Shaft 123 shaft m> with coaxial cylinder 101. Cylinder 101 mates slidably | bearings (not shown) and is I25 is carried in suitab y with bore 102. Chamber 103 which communicates with d to the engine shaft by suitable means, (not couple condu.ts 24a is formed by bore 102 and end cap 104. . Q equalizes the pressure in chamber shown) Passage 12 Chamber 105 communicates with chamber 106 . ber. The action of fly- 106 and the fly weight cham through passage 120 and chambers 105 and 106 com- t be wdght governors is well known and need no municate with manifold 23. By virtue of the foregoing . However, it is noteworthy that feed back 4Q described communications the area of the assembly acted upon d as is the force Jg proportional to the square of spee by the pressure ,n man.fold 23 is equal to the area acted hanism of FIG. 6. Therefore case of the governor mec upon by the pressure in condu.t 24a. Variable orifice may be the same for the stabilizing shape of slot 107 38 is formed by the cooperative action of contoured , . Furthermore, any governor bo h governors slot 107 in cylinder 50 and the surface 108 of annulus 45 mechanism can be utilized to va the area of orifice 109. Slot 107 opens into chamber 110 of cylinder 50 i 3g ovided its in and d namic character stics are and chamber 110 communicates with annulus 111 , suitab e for the ticular en ine and the maximunl through holes 112. Annulus 111 communicates with i nts area tne associated orifice 38 meets the requ reme conduit 24a and annulus 109 communicates with of network 14 manifold 52. Loading spring 113 engages the end of 50 ct to the requirement of network 14, it with respe cylinder 50 in chamber 106 and adjustable spring base ) that for a maximum can be seen from equation ( 2 3 114. Bias spring 115 engages piston 101 and end cap value of /4 that provides: J8 104. Bias spring 1 15 is not essential to the operation of the speed responsive variable orifice but provides Mas/^c-z) > (4) the attenuation of A . , as it appears in e t mechanical advantages that are well known to those 55 equation (23), is 3 percent. For a given maximum value skilled in the art. In all conditions of operation the net of A the greatest attenuation of /4 _ will occur during 3S C 2 spring force is in the direction of the force exerted by sea level operation near 1 00 percent design speed, at spring 113. Lever 51 is coupled by shaft 116 to gear which condition A^ is at its greatest value. The 117. Gear 117 engages rack 118 in spring base 114. attenuation of /4 _ by as great as 10 percent undersea r 2 Spring base 114 is cylindrical and slidably mates with level operation near 100 percent design speed bore 118. Passage 1 19 in spring base 1 14 equalizes the produces only a negligible decrease in the acceleration pressures on opposite ends of the spring base. Under rate of the engine.
steady running of the engine the net spring force is in mMPFNCATinw pnu PIICI nuwsn-v equilibrium with the net pressure force. The pressure COMPENSATION FOR FUEL DENSITY force is equal to the product of the area of piston 101 VAKIA 1 lONb and the difference in pressure between passage 24a and As shown by equation (7) the weight flow rate manifold 23. As previously explained, this pressure dif- delivered by the system is directly proportional to the
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fuel density. This effect of fuel density on the accelera- delivery to the engine during steady running, the first tion and deceleration limits can be eliminated by mentioned parallel array and said second variable ori- -* providing a means by which the displacement of pump fice being operable to limit the maximum rate of fuel 11 per revolution of the engine (D ) can be varied to delivery during engine acceleration and said second y hold the product (D p,) constant. Because the range of variable orifice being operable to limit the minimum v -' deviation of fuel density from the mean normally en- rate of delivery of fuel to the engine during engine countered is less than 5 percent, the range of pump dis- deceleration.
placement variation required is small. Because of this 2. In the system of claim 1, said first mentioned flow small requirement and because the pump operates in restriction means being a spring biased, pressure zero pressure gradient, the adjustability is readily found responsive variable orifice, said variable orifice being in any of several positive displacement pump types, in- responsive to said spring bias and the pressure dif- cluding gear pumps. Knob 127 shown on pump 11 in ference across said variable orifice, said variable orifice FIG. 1 and the density scale indicated at 128 shows the being thereby responsive to the rate of flow from said manner in which the operator may adjust the system to ,e pump, and being so disposed to open gradually from a known fuel density. cranking speed to idle speed and to remain at fixed When the product D p is held constant the . opening above idle speed.
v f equilibrium speed provided by the hydraulic governor 3. In the orifice network of claim 1, a fifth variable of FIG. 6 is orifice responsive to compressor inlet absolute pressure ano< a 1 1 , 20 si" * variable orifice responsive to compressor N = A ID \2gF,p )/A (38) inlet temperature, said fifth and said sixth variable ori- I3 f l a i It is observable from comparison of equations (37) ond series pair, said second series pair fice forming a sec and (38) that the adjustment of D \o eliminate the ef- ie orifice forming a parallel array, v and said fourth variab feet of fuel density on the acceleration and decelera- being operable above a said sixth variable oriflce tion limits does not eliminate or magnify the effect of specified temperature to reduce the limit of maximum fuel density on the equilibrium speed of the hydraulic | delivery during engine acceleration, rate of fue governor, but changes the direction of the effect. In 4 [ j network of claim 1, said fourth varia- n the or fice either event a change of fuel density of 5 percent ble orifice being responsive to compressor absolute results in only a-2% percent change in equilibrium inlet pressure and to compressor inlet temperature, speed. This effect is observable only at the 100 percent 30 5. In claim 4, said fourth variable orifice comprising and idle speed stops provided for lever 51, and may be an orifice structure, said structure comprising a cylin- compensated for by adjustment of these stops. There- drical sleeve and a mating cylindrical piston, said piston fore, through the use of cams and the like, the fuel den- having an axial bore, a slot being through the wall of sity adjustment and the speed stop adjustment can be said piston and opening into said bore, a second slot made from a single input. 35 gh the wall of said sleeve, said piston being being tnrou What is claimed is: coupled to a linear actuator, said linear actuator being 1. A fuel control for a gas-turbine engine comprising responsive to compressor inlet pressure, said sleeve a liquid fuel supply means, means for pressurizing the coupled to a rotary actuator, said rotary actuator being liquid, a positive displacement pump operating at a being responsive to compressor inlet temperature, said speed proportional to the speed of the engine, pressure i being overlapped to form said variable orifice, the s ots responsive means operating in conjunction with said area of said orifice being variable through the axial dis- pressurizing means to maintain the pressure gradient placement of said piston and/or the rotary displace- across said pump at zero, a conduit for receiving the t of said sleeve, the interior of said piston being in m e n flow from said pump, flow restriction means in said communication with a point between said first and conduit, a branch conduit for diverting flow from the third orifices and said second slot being in communica- upstream side of said pump, second flow restriction tion with said third conduit.
means in said branch conduit, said conduits being 6. In the orifice network of claim 1, said third varia- joined downstream of said first mentioned flow restric- ble orifice comprising an orifice structure, said struc- tions means, whereby the pressure difference across 50 ture being actuated by a pressure responsive, spring , said second flow restriction means is made equal to the biased movable wall, said wall being between a first and pressure difference across said first mentioned flow second pressure chamber, said first chamber being in a restriction means and said flows are combined, a third communication with the pressure upstream of said net- conduit for delivering said combined flow to the en- work, said second chamber being in communication gine; the second mentioned flow restriction means 55 with the pressure downstream of said orifice network, being a network of variable orifices, said network com- 7. In the orifice network of claim 1, said third varia- prising: a first variable orifice and a second variable ori- ble orifice comprising an orifice structure, said struc- fice responsive to the difference between compressor ture being actuated by a spring biased fly-weight discharge pressure and compressor inlet pressure, a mechanism, said mechanism being driven at a speed third variable orifice responsive to engine speed and a proportional to the speed of said engine, fourth variable orifice responsive to compressor inlet 8. In claim 1, said positive displacement pump being absolute pressure; said first variable orifice and said of the adjustable displacement type, fourth variable orifice forming a parallel array, said 9. In the orifice network of claim 1, said first and said parallel array and said third variable orifice forming a second variable orifices comprising a multi-orifice series pair, said series pair and said second variable ori- structure, said structure comprising a cylindrical valve fice forming a second parallel array; said third variable spool and a mating valve sleeve, a pair of separate orifice being operable to regulate the rate of fuel chambers in said spool, each chamber being provided
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with an inlet opening and an outlet opening in the wall fuel supply pump and said conduit, said second flow of said spool, an inlet annulus in said sleeve at each control means comprising first and second variable ori- inlet opening, an outlet annulus in said sleeve at each fices connected serially between the output of said fuel outlet opening, said outlet annuluses communicating supply pump and said conduit, a third variable orifice with said third conduit, said inlet annulus of one 5 connected in parallel with said second orifice, fourth chamber communicating with the upstream side of said and fifth variable orifices connected in series relation- third orifice, said inlet annulus of the other chamber ship to each other and in parallel with said third orifice, communicating with the downstream side of said third a sixth variable orifice connected between the output orifice, said outlet annuluses being axially positioned of said fuel supply pump and said conduit, means for such that .axial movement of said spool varies the area varying the area of said first variable orifice in propor- of each outlet exposed to respective outlet annuluses to tion to engine speed, means for varying the area of said provide variable orifices, a coaxial cylindrical piston third and fifth variable orifices in accordance with coupled to said spool, said spool and said piston defin- compressor inlet pressure, means for varying the area ing a spool assembly, a pair of opposing springs axially of said fourth variable orifice inversely with inlet tem- restraining said spool assembly and passage means 15 perature, and, means for varying the area of said communicating compressor inlet pressure to the piston second and sixth variable orifices in accordance with end of said spool assembly and compressor discharge compressor discharge pressure and inversely to com- pressure to the opposite side of said piston and opposite pressor inlet pressure.
end of said spool.
11. The fuel control system of claim 10 and includ- 10. In a gas-turbine engine fuel control system of the 20 .
ing: a seventh variable orifice connected in parallel type utilizing a zero-gradient pump and a flow control with said sixth variable orifice, the area of said seventh means connected serially between a fuel supply pump variable orifice being controlled by said means for and a conduit which delivers fuel to a fuel injection varying the area of said third and fifth variable orifices.
system, the improvement comprising; a second flow control means connected between the output of said 25 * * * * *