1. business and industrial
2. energy
3. oil
4. diesel fuel

Jan. 26, 1965
J.‘ M. MALJANIAN ETAL
3,166,902
FUEL. CONTROL FOR A REGENERATIVE GAS TURBINE ENGINE
Filed Nov. 15, 1962
6 Sheets-Sheet l
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INVENTORS
JOHN
GENE.
BY
M. MALJANIAN
A.. MEYER
‘?
ATTORNEY
Jan. 26, 1965
J. M. MALJANIAN ETAL
3,166,902
FUEL CONTROL FOR A REGENERATIVE GAS TURBINE ENGINE
Filed Nov. 15, 1962
6 Sheets-Sheet 2
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IN
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JOHN 1 M.
MALJANIAN
GENE.
M
BY
A-
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ATTORNEY
Jan. 26, 1965
J. M. MALJANIAN ETAL
3,166,902
FUEL. CONTROL FOR A REGENERATIVE GAS TURBINE ENGINE
Filed Nov. 15, 1962
6 Sheets-Sheet 5
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INVENTORS
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JOHN
M-
GENE
A- MEYER
MALJANIAN
Jam 25, 1965
J. M. MALJANIAN ETAL
3,166,902
FUEL. CONTROL FOR A REGENERATIVE GAS TURBINE ENGINE
Filed Nov. 15. 1962
6 Sheets-Sheet 4
BYW
ATTORN
Y
Jan. 26, 1965
J. M. MALJANIAN ETAL
3,166,902
FUEL. CONTROL FOR A REGENERATIVE GAS TURBINE ENGINE
Filed Nov. 15, 1962
6 Sheets-Sheet 5
22
INVENTORS
JOHN
GENE
BY
'
MA‘
MALJANIAN
MEYER
'
ATTORNEY
Jan. 26, 1965
J. M. MALJANIAN ETAL
3,166,902
FUEL. CONTROL FOR ‘A REGENERATIVE GAS TURBINE ENGINE
6 Sheets-Sheet 6
Filed Nov. 15. 1962
FIC3-9
FIG--8
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76
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#2
INVENTORS
JOHN
GENE
MA-
MALJANIAN
MEYER
BYW
ATTORNEY
3,166,902
United States Patent
Patented .lan. 26, 1965
1
power controllever. More speci?cally, for each power
lever position, a given value of vhigh pressure rotor speed
is selected, along with a corresponding steady state dis
charge pressure (P2) of the low pressure compressor.
3,166,902
FUEL CONTROL FOR A REGENERATIVE GAS
TURBINE ENGINE
John M. Maljanian, 'Newington, and Gene A. Meyer,
Automatic compressor inlet temperature (T1) correc
2 Simsbury, Conn., assignors to Chandler Evans Corpo
ration, Hartford, Conn., a corporation of Delaware
Filed Nov. 15, 1962, Ser. No; 237,914
31 Claims. (Cl. 60-3916)
tion adjusts the absolute values of these settings for the
particular T1 condition, to provide the necessary steady
state settings which achieve optimum fuel consumption
rates, at optimum conditions of the recuperator, without
This invention pertains to a fuel control system for
compressor surge and turbine overtemperature.
Still another object of our invention is to provide a
operation of complex, multiple cycle, twin-spool, gas
fuel and speed control in which the torque output of the
free power turbine of the engine is controlled by con
trolling the “corrected” speed (N2/\/_T1) of the high pres
turbine engines which produce low speci?c fuel consump—
tions of orders of ‘magnitude that are comparable to com
pression ignition type (diesel) engines; and more par
ticularly has reference to such engines in which there is 15 sure compressor rotor, so that the torque exerted by the
incorporated a heat exchanger that may be of a recupera
power turbine is independent of the temperature (T1) of
.tive or regenerative type, for which corrections are made
the air entering the engine, as shown later in this speci
in the scheduled fuel flow to the engine, to compensate
?cation.
_
for the heat added to the fuel by the heat exchanger, in
Otheryobjects of our invention are to provide a fuel
order to prevent engine surge and/ or overtemperatures. 20 and speed control system embodying the following novel
As with all gas turbine engines, fuel is scheduled in
such a manner as to prevent engine surge and/or over
(1) A fuel control apparatus which is contained in a
temperature, which cause loss of performance and pos
single, unitary control package, with single lever for op
sible structural damage. Turbine overtemperature causes
eration under all conditions of environment, speed alti
damage by exceeding the temperature capability of its 25 tude, etc.
features:
materials which results in shorter engine life and possibly
'
'
(2) Means tohprovide for automatic starting of the
destruction of the engine during operation.
The required steady state operating fuel ?ow to the
engine.
’
,
(3) Means to automaticallyv provide for maximum ac
engine varies as a function of engine inlet temperature,
celeration of the engine from one power lever setting
altitude, compressor pressure ratio, engine speed, and en 30 to another, without causing‘engine (compressor) surge
gine inlet ram conditions; which entities constitute the,
and/ or engine overtemperature.
1
.
control parameters that determine the fuel ?ow to the
(4) Means to provide steady state operation of the
engine.
‘
'
, engine, with automatic compensation vforv variation in en
Acceleration fuel ?ow is scheduled to provide fast
' gine inlet conditions of, temperature and, pressure (alti
accelerations from one operating speed to another, as well 35 tude); and also changes of conditions in the recuperator. '
as rapid decelerations where the power demand is varied
(5) _ Means to automatically provide for maximum de
from one speed setting to another. .These changes in
, celeration of the engine from any‘given power lever
speed setting which produce a corresponding change in
power output must be accomplished without causing en
gine surge, overtemperature, or any other conditions
40
which, as a result of fuel ?ow variance from acceptable ‘
limits, could cause damage to the engine.
The general problem associated with the control of
gas turbine ‘engines with heat exchangers is the adjustment
in fuel flow to the engine which is required as a result of
conditions brought about by the recuperator, since heat
'
setting to any lower power leversetting, without causing
burner blowout.
(6) Means to provide automatic temperature compen
sation for high pressure rotor load torque, since provision
can be made on the engine for extraction of power from
the high pressure rotor;
-
'
>
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(7) A control system which is adaptable to gas tur
bines for either airborne or ground vehicles (trucks,
- tanks) .or power ‘stations (generator set, etc). How
added from the recuperative or regenerative type heat
_ ever, due :to weight and size problems associated with
exchanger (hereinafter referred to simply as the recuper
the aircraft-engine, the engines equipped with recupera
ator) must be compensated for by a corresponding cor
tors (heat exchangers) would be more ‘suitable to the
rection in fuel ?ow.
ground. applications—although the ‘principles of- control
Accordingly, one of the primary objects of our inven- , of our invention also apply to engines which could be A‘
tion is to provide a fuel and speed control system having
used in aircraft. ‘
'
"
~
means for making the necessary correction in fuel ?ow
Further objects of our‘ invention are to provide an
to the engine by sensing the temperature of the recupera
vimproved fuel and speedcontrol apparatus for a twin
tor and correcting the fuel ?ow in the fuel control as a 55 spool engine, equipped with a recuperator, which em
function of this temperature.
bodies the following noval features:
Due to the complex cycle of the engine being con
(8) A control apparatus comprising, in a single self
trolled, it is important that the ratio of selected corrected
oontained package, a primary fuel supply and control
speeds of the two component spools (i.e. high and low
system, and a secondary fuel supply and control system
pressure compressor rotors) be maintained at a de?nite 60 which supplements the primary system; each system
value for each particular selected position of the engine
comprising a series of component coordinated hydraulic
power control lever. Since no mechanical drive is availa
devices for regulating fuel delivery to'the engine; said
ble as a measure of low pressure rot-or speed, the low
pressure compressor discharge pressure is used as a meas
devices being collectively responsive to the control
parameters speci?ed hereinbelow, and subject to a single
ure of this speed. High pressure speed is mechanically 65. manual control power lever.‘
‘
available and is used directly.
(9) A control apparatus which comprises a series of
Accordingly, another primary object of our invention
devices that measure inlet air absolute temperature,'high
is to provide a fuel and speed control system having means
pressure compressor discharge pressure, recuperator tem
for maintaining the ratio of selected corrected speeds of
perature, and engine speed (rpm), and positions a pri—
the high and low pressure compressor rotors at a de?nite
mary fuel metering valve in accordance with a preselected
value, for each particular selected position of the engine
composite function of said temperature, said pressure and
3,166,902
,
4
3
speed; while the pressure differential (metering head)
to a secondary combustion chamber B2, to which addition
al fuel is supplied, at a rate WF2, from the fuel control
unit shown in FIGS. 2 and 3. The gases, generated by
the combustion of fuel in chamber B2, augment the gases
across said valve is maintained at a constant selected value.
(10) A fully automatic hydraulic control apparatus in
. which the primary fuel flow to the engine is compensated
for variations in absolute inlet air temperature, high pres
?owing into said chamber from turbine Th2, and both
?ow though the free power turbine PT and the secondary
turbine Th1 to a recuperator RC, from which they are
sure compressor discharge pressure, recuperator tempera
ture, and engine speed; and said compensation being in
herent in the operation, of the apparatus, so that addition
al correction factors for these variables are not required,
, in order to compensate for variations'in operating condi
tions due to“ said variables.
I
exhausted into the outside air. Compressed air ?owing
from compressor C2 to primary combustion chamber B1
10 also passes through the recuperator RC where it receives
heat from the exhaust gases ?owing therethrough.
interposed in air ?ow series relation between low-pres
(11)'IA, fully automatic, hydraulic control vapparatus
'which uses'as Icontrol “parametersf'jfor limiting the maxi
mum fuel ?oIw to the engine, the ‘quantities “corrected
sure compressor C1 and high-pressure compressor C2, is
an intercooler 1C, which receives cooling fluid from a
source (not shown), and cools the air ?owing from com
speed” ‘and “corrected; fuel new," as defined hereinbelow.
(12) A control apparatus which'produces a substan~
pressor C1 to compressor C2.
.
tially corrected constant engine‘ speed, (NZ/V11) corre
Air enters the engine from the circumambient atmos
” sponding‘to any selected position of asingle manual con
phere (station Q) through air ?ow silencer S and flows suc
cessively through compressor C1, intercooler IC, com
trol lever, under all engine operating conditions.
I
(13) A control apparatus which functions so that the 20 pressor C2, recuperator RIC, to primary combustion cham
engine can be accelerated at a maximum rate, correspond
ber 13,; and the gases generated, in chamber B1 ?ow
ing to the temperatureof theIair entering the engine (low
through primary turbine Th2 to secondary combustion
and decelerated at a maximum rate without causing burn
chamber, where they are augmented by the gases gen
erated in chamber B2; and both then ?ow successively
25 through power turbine PT, auxiliary turbine Th1, and re
pressure compressor), without causing compressor vstall
er .blowout.
.
I
,
(1I4)'A control apparatusvwherein the fuel ?ow regu
' cuperator RC, from which they are exhausted into the
circumambient atmosphere.
' lating mechanism operates 'in its‘own’?uid (whichmay'be
' either an: oil oi'fengine fuel), and acts directly on ‘thefuel
I supplied byIa constant delivery pump and regulates its
' ?ow to the engine by means of a plurality of suitable con
trol valves.
I
II
I
I
I
I
I
_
_
.
‘
The underscored numerals Q to lé indicate the succes
sive stations in the ?uid flow path from air inlet station
30
9 to exhaust gas outlet station l_§—as clearly indicated
I in FIG. 1.
‘
(15) A control apparatus "having overridespeedsv and
l temperature control devices which prevent the" engine
Broadly comprehended, the fuel supply and control
system of our invention, as herein disclosed, comprises
- from operating at'excessive speeds and temperatures.
the concept of .a hydromechanical fuel metering system
With these and other ‘objects in'view of which‘ may be 35 which schedules both primary and secondary engine
'~ incidentito our-improvements,Iour'invention consists in the
metered fuel ?ow in accordance with requirements for
satisfactory engine operation.
‘ combination "and arrangement of elements hereinafter-de
scribed and illustrated inthe accompanying drawings, in
‘which
;
-
The inputs (i.e. control parameters) of our control
system are:
'
FIG. 1' is a schematic diagram of our ‘improved fuel 40
" supply and control system as applied to a twin spool tur
birie engine having an incorporated/‘recuperator.
FIG. 2 is a diagrammatic section of the engine of FIG.
(4) Compressor inlet temperature, T1.
1, ‘showing the connections-betweedthe‘ engine and other
elements of the -,fuel supply and control system of our 45
invention.
'
'
'
'
'
'
-'
-
I
FIG. 3 is a, schematic sectional-view of a fuel and speed
"edntrol apparatus embodying the principles and novel fea
tures of our invention.
,
' with engine performance requirements.
'(2) Secondary (or reheater fuel ?ow), WFZ, regulad
tion: in accordance with engine performance require‘
55
'
tion ‘in accordance with engine performance require
pressure compresSorCé,~ drivenby afprimary gas turbine
Th2. The rotor of the low-pressure ‘compressor C1, di
" ments.
In general, the primary acceleration fuel flow is sched
60 uled in accordance with high-pressure compressor dis
charge pressure, P.,, as biased by recuperator temperature,
connected to the primary turbine Th2; constitute respective
Ts. High-pressure compressor speed, N2, is controlled
lythe outer and inner spools of the engine.
'
. -A free power’ gas turbine PT, interposed-in ?uid flow
A primary combustion chamber B1, interposed in ?uid
ments.
(3) Secondary augmentation fuel flow, WFZL, regula
‘ turbine Th1, arrangedlin air ?ow seriestrelation-to a high
engine which may be used to propel a ground vehicle
(i.e.", truckor tank), or to‘rotate an aircraft-propeller.
‘I
(1) Primary fuel ?ow Wm, regulation in accordance
FIGS. 5-11 are diagrams of certain operating char
- acteristics of the engine’v and control'3shown in FIGS. 144.
series relation between the primary turbine Th2 and the
secondary turbine'TM, generates the power output of the
Cornbustor inlet (recuperator) temperature, T6.
Power turbine speed, NPT.
Power lever angle, PLA.
Primary fuel flow to the engine, Wm.
Secondary fuel How to the engine, WF2.
system are:
our invention, as hereinafterlmore, particularly described.
rectly connected to ft-lie'rotor ofauxiliary turbine Th1;
‘and the rotor? ofthehigh-pres‘sure compressor C2, directly
(5)
(6)
(7)
(8)
(9)
The outputs (i.e. controlled entities) of our control
' FIG.-4-is a schematic diagram of a simpli?ed version of
A's‘shown in FIG. 1, the‘ engine, to which our improved
.fuel supply and controli'syste'm' isapplied; comprises a
low-pressure air compressor C1, driven by a secondary gas
( l) High-pressure rotor speed, NZ.
(2) Low-pressure compressor pressure, P2.
(3) High-pressure compressor pressure, P4.
as a function of power lever angle, PLA, with compressor
inlet temperature, T1,. correction to maintain corrected
65
speed settings.
Secondary or reheater acceleration fuel flow, WFZ, is
scheduled in accordance with low-pressure compressor
pressure, P2. Low-pressure spool speed is maintained
?ow series relation between the high-pressure compressor
C2 and the primaryturbine~Tb2,~receives compressed air
by controlling P2 pressure as a function of set power lever‘
angle, PLA. As with speed, N2, set values of pressure,
P2, are corrected or reset with T1 temperature, to main-.
from compressor Cwand is supplied-with fuel (oil), at
tain essentially corrected N1 speed settings (since P2 is a
r a flow rate WFI', from the fuel control unit shown in
measure of N1, or low-pressure rotor speed).
The selected power lever angle, PLA, sets required cor-
FIGS. 2.and 3. Thegases generated by the combustion
:of fuel in chamber.B1.?owthroughprimarylturbine Th2
75 responding values of both speed N2 and pressure P2_simul—
5,166,902
5
6
.
taneously, theTl temperature correction being automatié
cally applied to both settings by a T1 transducer. An
Liquid and gas filled bulbs are not suitable, since it is
di?icult to prevent permeation of the bulb walls by the
adjustable hydraulic dashpot is provided on the throttle
fluid at such a high temperature, with a consequent error
shaft between the P2 and N2 setting to delay vreturn of
the
settingrinathe deceleration-direction, and tlfus pre
vent low-pressure compressor surge during decelerations.
The dashpot is-ineifectiveduring increased settings of the
power lever.
-
As is‘requi-red bytdesiredr engine performance, second
in- calibration. We therefore will use a differential metal
expansion device to respond to the recuperator temper
ature. The sensed expansion will be transduced to a hy
draulic pressure for use in the control.
Metering of acceleration limit fuel, both primary and
secondary, is accomplished by applying a ?xed metering
ary fuel ?ow WF2 is augmented by an increment of fuel 10 head to avalve whose port area is varied. in proportion to
the control parameters. Governing in steady state, for
?ow WFpwhich is proportional to the amount which the
both rotors, is done by a proportional closed loop error
N2 governor has cut in, or a ?xed value, whichever is the
sensing ‘control, in which the desired operating variable
least.
(rotor N2 for. the high-pressure rotor, and compressor dis
The power turbine (PT) governor. generates a pressure
signal (OS) as a_ function of power turbine speed, NPT. 15 charge pressure P2 for the low-pressure rotor), are biased
by inlet air temperature and areset by a manual power
At power turbine cut-in speed, this pressure acts to reduce
lever; and the governors act to vary fuel flow in propor
both primary and secondary fuel flow as a function of
tion to the error between the actual and desired values of
power turbine speed error to effectively serve the same
the variable.
function asretarding the throttle. The pressure gener
Means are provided, when the N2 governor cuts in, to
'atin‘g system is a part of the main control. Overspeed 20
augment the fuel flow to the low-pressure rotor by an
signal (OS) is available in the form of the generated pres
amount equal to the reduction of N2 rotor fuel. There is
sure. A pressure switch (not shown), set for the pres
sure corresponding to the shutdown speed, supplies an
electrical signal for shutting down the engine if required.
As shown in FIG. 3 the fuel and speed control package 25
contains the following main elements:_
,
(i) Positive displacement fuel pump integral with the
control package;
(ii) Primary fuel metering and speed control system
for the high pressure rotor;
(iii) Secondary fuel metering system and compressor
discharge pressure control system for the low-pressure
also a dashpot provision to delay deceleration of the N2
rotor after throttle “chop.”
_A power turbine governor will proportionally reduce
fuel ?ow to both combustors when a set speed is exceeded.
A hydraulic pressure signal will be available to actuate
an engine shut~down device when a set absolute maximum
speed is reached.
Referring now to FIG. 2 of the drawings, there are
shown, as principal elements of the engine mentioned
hereinabove: a supporting body 1, an air inlet 2 leading
to a low-pressure compressor G1, which is connected by a
shaft 3.to a low-pressure (secondary) gas turbine Th1.
rotor;
(iv) Single power lever mechanism to set the prescribed
combination of high-pressure rotor speed and low-pres 35 Compressed air is discharged from compressor C1 through
sure rotor pressure;
P
an intercooler 4, to a high-pressure compressor C2, where
its temperature is increased from T3 to T4, and its pressure
and secondary fuel flow to the engine as a function of
is increased from P3 to P4,. Intercooler 4 is provided with
a fan 5, driven. by countershafts _6--and 7 from shaft 3, to
power turbine speed error.
(vi) Modi?cation of fuel ?ow with variations of re 40 circulate cooling ?uid around theair passages through
cuperator gas temperature, soythat the primary acceler
said intercooler, and lowers the temperature T2 of the air
ation fuel flow will be proportional to the product of a
passing from compressorC1 to a temperature T3 of the air
function of high-pressure compressor discharge pressure
entering compressor C2.
(P4) and a function of recuperator temperature (T6).
Compressor C2 is connected by a shaft 8 to a high-pres
(vii) Compressor inlet temperature biasing of the high 45 sure gas turbine Th2, and dischargesits air through a
pressure rotor speed selector, so that the selected speed
recuperator RC, where the air isheated to a temperature
T6, by exhaust gases from low-pressure turbine Th1, ?ow
is essentially a “corrected” speed (N2/\/T1).
ing through a connecting conduit §. After passing
(viii) Time delay on deceleration of the high pressure
through recuperator RC, these gases are discharged
rotor.
(v) Power turbine governor to reduce, both primary
(ix) Compressor inlettemperature biasing of the low 50 through a passageway 10 into the outside air. A tempera
pressure rotor pressure selector.
The “two-spoo ” engine with which our invention oper
ture sensor 11 senses the temperature T6 in the recupen
\ator RC, as more fully described hereinbelow. Low-pres
sure compressor C1, turbine Th1 and connecting shaft 3
ates requires two separate but cooperating fuel control
constitute the outerspool of the engine; while high-pres
systems, one for each of the two rotors. Each system
must provide independent means for transient and steady 55 sure compressor C2, turbine Th2 and connecting shaft 8,
state control of the rotor with which it is associated, to
gether with certain additional coordinating functions;
constitute the inner spool of the engine.
.
The compressed air passing through recuperator RC
?ows into primarycombustion'chamber B1, which re
The, engine with which our invention operates is also
ceivesfuel oil, through a conduit 12 from a fuel control
distinguished from conventional aircraft gas turbines by
the presence of a recuperator, which introduces a special 60 unit 13, and the resulting combustion of said fuel in
chamber B1 generates gases that ?ow under increased
problem into the construction and functioning of the con
temperature and pressure, through high-pressure turbine
trol; in that-the control must modify the maximum limit
Th2, into secondary combustion chamber B2. Additional
ing, or acceleration, fuel schedule to compensate for the
fuel oil is fed into chamber B2, from control unit 13,
heatrecovered from the recuperator; and this is accom
plished by regulating the primary fuel flow in accordance 65 through a connecting conduit 14, and the additional corn
bustion- of this fuel in chamber B2 increases the pressure
with the equation:
and temperature of the gases therein. From chamber B2,
the combustion gases ?ow successively through a free
where A1, A2, and A3 are design constants.
The multiplication on the right-hand side ofth-is equa
tion may be carried out ‘by a combination of variable and
?xed ori?ces in series in certain fuel flow conduits.
The recuperator gas temperatures. (T5) of the order of
power gas turbine PT, low-pressure turbine Th1, and
recuperator RC. The free power turbine PT generates
the useful power of the engine 1 which is transmittedby a
shaft 15 to the driven load (e.g. wheels of a ground ve
hicle, or the propeller of a motor boat or aircraft).
'
The fuel control unit 13 is connected to a fuel supply
as ‘high as 1400" F. must be sensed'for usein the control. 75 tank 16, by a‘supply conduit 17, andan excess fuel return
3,166,902
7
8
conduit 18. Unit 13 is also connected to the engine by:
a conduit 19, which communicates with the discharge pas~
sage 20 of high-pressure compressor C2; by a conduit 21,
which communicates with a temperature bulb 22 located
Structural and metallurgical limitations impose a top
limit on the temperature of the gas entering the turbine
at station g, and this temperature is attained in three steps,
starting with the inlet air at station 1, namely
(1) The temperature rise (T2-—T1) due to compression of
in air inlet 2; and ‘by a conduit 23 which communicates
with- the discharge passage 24 of low-pressure compressor
the air,
C1. Shafts 25 and 26, connected to the shaft 8, drive a
(2) The rise (113-112) due to heat absorbed from the
high-pressure rotor speed governor in control unit 13, and
recuperator, and
shafts 27, 28 and 29, connected to the power turbine
(3) The rise (Tr-T3) due to combustion of fuel.
shaft '15, drive a power turbine speed governor, also in 10
‘control unit 13. Temperature sensor 11 is connected to
So that the permissible top limit of the temperature T;
control unit 13,- by conduits 43 and 78, which transmit the
control pressure (P,,) in unit 13 to said sensor.
shall not be exceeded it is therefore necessary that the
control modify the fuel ?ow according to recuperator gas
SIMPLIFIED VERSION OF ENGINE
temperature T3. This could be achieved quite well if the
15 temperature T 4 could be measured directly, and the fuel
flow WF1 controlled so that the allowable maximum of T4
is never exceeded. This, however, is impractical, since
In order to facilitate an understanding of one of the
‘principal problems solved by our invention, we have
depicted in FIG. 4 a simpli?ed version of a free power gas
turbine engine equipped with a recuperator. From a com
parison of FIGS. 1 and 4, it will be noted that, in the sim
for one reason, T, is of the order of 1800" F. or more,
and most measuring devices are not very reliable at such
20 temperatures. A more important reason is that the char
acteristics of the engine are such that almost instantaneous
response of the fuel ?ow is needed when T, is used as a
measured control parameter, and all temperature meas
pli?ed engine of FIG. 4, the low-pressure compressor C1
and its driving turbine Th1, as well as the secondary com
bustion chamber B2 (of FIG. 1) have been eliminated,
and the exhaust gases from the high-pressure turbine Tb,
uring devices have time lags that are intolerably long.
pass directly to the free power turbine PT and are then 25
However, we have discovered that the turbine Th2 can
be protected against overtemperature without measuring
returned directly to the recuperator RC.
T4. As disclosed hereinbelow, a method is disclosed
Accordingly, only the following stations in the ?uid
whereby a measurement of the lower temperature T3 can
?ow path are considered, in FIG. 4: Stations 1 and g at
be used, along with other control parameters, to control
the entrance and exit of the high-pressure compressor C2;
the fuel ?ow Wm in such a way that the turbine gas tem
30
station § at the junction of the recuperator RC and com
perature T4 is limited to a maximum permissible value.
bustion chamber B1; station 2 at the junction of chamber
Our method also avoids the need for very rapid response
B1 and the high-pressure turbine Th2; station E between
in the temperature measuring device, since the recupera
turbine Th2 and the free power turbine PT; station Q be
tor itself has a rather long time constant. Our tempera
tween turbine PT and reouperator RC; and station _'i_' at the
ture measuring device, as described hereinbelow, has an
exit of the recuperator.
“anticipating” characteristic, so that the effect of time lags
On the simpli?ed basis of FIG. 4 just indicated, the fol
is even further minimized.
lowing is an analysis of the functions and operation of the
The second problem referred to above has to do with
elements involved.
the torque output of the free power turbine PT. As shown
Air is drawn into the compressor at station _1_, at pres 40 hereinafter, when the gas generator portion of the engine
sure P1 and temperature T1, and leaves the compressor
is rotating at a speed N1 r.p.m., and the temperature of
rotor at station 2 at a higher pressure and temperature P2
the incoming air is T1 degrees Rankine, and if the free
and T2; and the air from station 3 passes through the re
power turbine is locked at standstill, the torque Q exerted
cuperator RC to station ‘it. In the recupcrator RC, it re
by the free power turbine is a function of the “corrected”
ceives heat from counter-?owing hot gas from the power
speed (NI/Vi).
turbine PT exhaust.
As the temperature of the incoming air may vary from
At station :33 the air, which has now been heated to tem
—65 degrees F. to +150 degrees F., the “corrected” speed
perature T3, enters the combustion chamber 3;, where
(for variations in T1) of the gas generator will vary by
additional heat is added by burning fuel, (WE-1). In the
combustion chamber the air reaches a temperature T, at 50 approximately 25%, when its actual speed is held con
stant. Unless precautions are taken, it is therefore likely
station Q, where it enters primary turbine Th2. The heated
that the output gearing from the free power turbine may
air expands through this turbine, doing work thereon, and
be overstressed when the engine is running in a very cold
leaves it at station _5_ with the pressure and temperature P5
environment. But if, instead of imposing a top limit on
and T5.
The primary turbine Th2 is coupled to the compressor, 55 the actual speed N1, we control the “corrected” speed
(N 1/\/ T1) of the gas generator, the torque Q exerted by
and the combination of these two, with the recuperator
the power turbine becomes independent of the incoming
RC and combustion chamber B1, is referred to as the “gas
air temperature T1, as will be shown hereinbelow, where
generator” portion of the engine.
we disclose a simple governor which achieves proper con
The gas from the gas generator, at pressure P5 and tem
perature T5, enters a second and independent power tur 60 trol of the “corrected” speed.
We now proceed to consider how the fuel ?ow Wpl
bine PT at station Q and expands to an exhaust pressure
to the gas generator turbine Tb2 is related to the turbine
and temperature P6 and T6, at station
During expansion through the free turbine PT, usually
referred to as a “free power turbine,” useful work is done,
and this work may be extracted through a reduction gear
coupled to the power output shaft.
The exhaust gas from station _6 is now passed through
the recuperator RC, where it gives up heat to the counter
?owing compressed air from the compressor. The spent
gas is ?nally exhausted from the engine at station 2.
There are two particular problems that arise in the con
trol of such a recuperativc gas turbine engine.
The ?rst problem is this: the fuel ?ow to the combus
tion chamber must be modi?ed according to the tempera
ture of the air leaving the recuperator at station 3.
inlet gas temperature T, and other engine operating param
eters. This analysis is given to facilitate an understanding
of the problem solved by our invention, and is therefore
somewhat simpli?ed. Thus, we have neglected all second
ary effects due to engine efficiency, heat losses due to
radiation, etc., but the basic conclusions are not thereby
affected.
The discussion of this section is con?ned to the gas gen
erator (Th2, C2 and RC), of FIG. 4, and in Equations
l—24 hereinbelow
Cp denotes speci?c heat at constant pressure, B.t.u./lb.—°R.
C, denotes speci?c heat at constant volume, B.t.u./lb.-°R.
75 g denotes acceleration of gravity
‘3,166,902
9
10,
-
H denotes heating value of fuel, B.t.u./ lb.
H
J denotes energy conversion factor, 778 ft.—lb./B.t.u.
closed hereinbelow, the output ‘is used to vary the position
7 denotes ratio of speci?c heats, Cp/Cv
pressure dropis maintained,..and thus 'the'fuel ?ow WF1
of a primary fuel metering valve across which a constant
is limited in accordance with Equation 5, and the turbine
is protected from damage due to overtemperature.
As described hereinafter, while the control is limiting
The turbine inlet gas temperature T; is the sum of the
temperature T3 at the exit of the recuperator and the
temperature rise (Tr-T3) in the combustion chamber.
T4:
fuel ?ow W‘Fl in accord with Equation 5, the speed gov
ernor is inoperative. But when the “corrected speed”
is attained for which the manual lever is set, the governor
will cut in to reduce the fuel flow below the value allowed
1
by Equation 5, in such away that theset speed will be
Where CI) and H are as indicated in the example follow
maintained.
Turning now» to the free power turbine PT, we shall
ing Equation 5, and WEI/WA1 is the fuel/ air ratio in the
combuster.
To prevent T4 from exceeding a speci?ed limit, sayTi’l‘,
the fuel ?ow WF1 admitted must not exceed
justify‘ the statement previously made, that the ‘torque Q
15 exerted by the power turbine PT isv a single-valued func
tion‘ of the “corrected” 'speediof'the gas generator portion
of the engine.
(2)
The" hot . gas from the gas generator enters the‘ free
power turbine PT at station 5, and expands down to the
When the turbine ?ow is “choked,” or super-critical, 20 pressure P5, prior to ?owing. into the recuperator RC,
which occurs whenever the pressure ratio across the tur
which'is designed so that ‘the gas passing through it has
bine exceeds about 1.89, the following relation is known
a very small pressure drop, and the pressure P6 will be
to apply.
substantially equal to the atmospheric~ pressure.
In this analysis, we again neglect secondary effects such
askef?ciency and heat loss, so that the, basic conclusions
may be clearly established.
W-henthe exhaust gas fromthe gas generator portion
a constant; or
of‘ the engine, at temperature T5 and pressure P5, is
k'r'pz I
W =——
(4)
allowed to expand'freely through a nozzle downv to pres
sure P1, the kinetic energy acquired by each pound of
exhaustv gas is given by the expression
Substituting (4) in (2), and letting T4=T4*
Win/r.
7-1
WF,= '“TP2><%’>< <T.*—T3>
(5)
35
If this rate of fuel ?ow is admitted to the engine, the
turbine inlet temperature T; will be maintained at its
desired maximum, T4*.
For example, assume a gas/generator consuming 3 lbs.
of air per second at a turbine inlet temperature of 2400°
R. and a compressor- discharge pressure P2=20O'p.s.i.a.
Then
From (6). we conclude that the_velocity acquired by
the gas is
u=
2gJcpT5[<F‘:) “1 — 1] inches per second
'
'
(7)
If this high velocity gas is‘ directed peripherally against
a turbine wheel, and directed through the turbine wheel
in: =—VY% X ?gTkég = .735
and if
Up: .24 B.t.u./lb./° F, and
H: 17,000 -B.t.u./lb. of fuel,
= .000000212 P2(T4*— T3) lb/see.
= .000763 P2(T4*— T3) lb./hour
If the maximum permissible turbine gas temperature is
set at T4*=2400° R- then the maximum limiting fuel
?ow that may be permitted to enter the engine is given
by the equation
'
and the control system of our invention, as disclosed
herein, produces a relationship such as the above.
so that its peripheral component of momentum is re
versed (as is the case when the high velocity gas impinges
on the blades of. a stationary impulse turbine wheel), the
torque exerted on the Wheel is
where. r isthe radius at which. the gas impinges.
torque-Qis then, using (.7)-and (8)’: '
II
The
7 *1] (9)
The curve in FIG. 5 shows a portioniof av“performance
map” of a simple gas turbine, or of the gas generator
portion of a free-power turbine engine:
In steady operation at a constant corrected speed
We set a value for T4*, which will be the greatest gas 65 IVA/T1, the compressor map gives a steady operating
temperature allowed. by engine limitations. We then
point as at A (in FIG. 5), where it is well known that the
measure the temperature T3‘ at the recuperator outlet, and
following quantities are ?xed:
provide means to subtract this measured temperature
from T41‘.
Table l'
We also measure the compressor discharge air pressure
‘ Corrected speed ________ __~.. _____________ __ N/VTI
The general principle is as follows:
P2, and provide means to mechanically multiply this by
the quantity just obtained, as described hereinbelow.
The output of this mechanical computer then repre
sents the permissible primary maximum fuel ?ow WI‘1L to
the engine.
Compressor pressure ratio _________________ __ P2/P1
Corrected" air ?ow ___________________ _. WA/vTl/Pl
Corrected fuel ?ow __________________ __ WFP1/\/T—1
In the embodiment of our invention dis 75 Corrected turbine inlet temperature __________ __ T4/T1
3,166,902
11
12
’ From thermodynamics,’ and the equality of turbine
work and compressor work
We have already stated in Table I that if (Nl/VTTF is
kept constant, then (WAx/Tl/ P1) is also constant, so that
Equation 17 may now be written as
Q
_T‘ilPi) 1]
P L1
_
_2
.
"r
10
Q
_=
T
_s==_i__'
P “L1
.2
‘Tr T1 [1%)
1 __
1]
11
< )
-
7)
A71
.? fig, T1)
*_
( >
18
or using the alternative notation
(10)
so that
T
N1
P1 f<51
Q:
_
1V1
__
i1
___
AI]
-_,_
5 KW?) v/5f1<v@)
19
( )
In Equations 18 and 19, the quantities Q/Pl and Q/‘a‘
*Hence, T5/T1 is constant, as well as the quantities 15 are referred to as the “corrected torque.” These equa
tions are interpreted to mean that when the corrected
tabulated in Table I above.
speeds of both the gas generator and the free power tur
Now consider the quantity P5/P1. From adiabatic ex
bine portions of the engine are kept constant, then the cor
pansion through the turbine, and assuming no pressure
rected torque output of the gas turbine is also constant.
drop from station 2 to station 4, so that P4=P2:
If the engine is operating in an environment where the
7-1
inlet air pressure does not vary appreciably, as in the
case of ground vehicle propulsion, for example, where
P1
P 2 P1
T4
P1
the engine is nearly always close to sea level, the quantity
_ 215.11 E2
6 is constant, and Equation 19 shows that in this case
(12)
_ T1 T4 P,
25 the actual output torque Q is a function of the corrected
So that P5/P1 is constant as well as the quanti?es
speeds, Nl/i/? of the gas generator and v/Vi; of the free
tabulated in Table 1.
power turbine.
Looking again at Equation 9, we now see that every
Equation 19 shows that maximum torque is exerted by
thing on the right hand side is constant when the corrected
the power turbine when it is at standstill-that is, when
speed is constant, with the exception of P1. So Q in
v=0, and it is in this case that the greatest load is ap
' (8) may be rewritten as a function of any of these inter
plied to the output shaft gearing.
115: Ei.Z2)=(B)TXZiZ
dependent constant quantities, like the corrected speed.
Thus
The foregoing analysis shows that for a constant com
pressor inlet pressure P1, the corrected speed function
N1
N/\/T1
is solely a function of compressor inlet tempera
__=
(13)
P1 f
ture T1. Also, the corrected speed function (NA/T1) is
a function of the actual output torque (Q) such that there
Frequently the compressor inlet pressure is expressed
is a single value of output torque Q for each value of
in units of one standard atmosphere, using the notation
corrected speed N/\/T1. The de?nition of corrected
P, __
speed “NA/T1” shows that a variation in compressor in
let temperature T, will result in a variation of corrected
and the inlet air ‘temperature is expressed in units of
speed N/\/T1. Since it is desired to maintain the actual
518.4 degrees F., using the notation
output torque Q as nearly constant as possible, it is nec
essary to change the value of N when the value of T1
45 changes in order to maintain the corrected speed (N / \/T1)
constant. The value of N is changed by modifying the
14159-5
Using this notation Equation 13 becomes
fuel flow to the gas generator so that a new value of N
a: , 5h
5
(14)
w/E
.The above. analysis was limited to the case of a free
power turbine wheel at rest. If the wheel is rotating so
that its peripheral velocity is v, then the gas from the
is established such that the N/\/T1 relationship is main
tained unchanged. Thus, the fuel ?ow to the gas gen
50 erator is regulated as a function of corrected speed which
in turn is a function of compressor inlet temperature T1.
It is also plain from (19) that this maximum torque can
be limited by placing a maximum limit on the gas gen
nozzles approaches the wheel peripherally with the rela 55 erator corrected speed NILA/T; or N1/ {5:
Our invention includes a governor in which the cor
tive velocityv (u-v), and its direction is reversed so that
rected speed of the gas generator may be set by a manual
it leaves the wheel with equal relative velocity"(u—v).
lever and automatically maintained by a simple governor,
The torque exerted on the wheel is in this case
and the operation of this device is also disclosed herein.
The foregoing discussion dealt with the speed of the
gas generator and with the fuel ?ow to the combustion
chamber in the gas generator portion of the engine.
Using a from Equation 7, we have
In an actual free power turbine engine, means must be
included for limiting the speed of the free power turbine.
In some applications, such as in ground vehicle propul
65
sion, it may be safe to assume that the power turbine,
directly coupled to the driving wheels, will never over~
(16)
speed except at a dangerously high velocity of the vehicle.
The ?rst term on the right of (16) is the same as the
In other applications, a separate governor, arranged to
right side of (9), and we have already shown that this is
override the gas generator governor, may be included, as
equal to. f(N/x/IT. It is then obvious from (16) and
(13) that
disclosed in co-pending patent application of Chandler
(17)
now Patent No, 3,108,435, issued October 29, 1963, and
assigned to the same assignee as this application; and does
75 not form part of the present invention.
Q I
if
T1
g VT!
1
PX
and Wright, Serial Number 494,055, ?led March 4, 1955 ,
w
3,166,902
13
.
P4 is the compressor discharge‘ pressure,
Returning to FIG. 3, it will be noted that the fuel and
speed control apparatus of our invention, shown in FIG.
2 as control unit 13, comprises a ?uid-tight case 40, which
AD is the area of the ?exible diaphragm 72,
several control elements contained within case 40 pro
vides a ?ow of su?icient magnitude to ?ll and pressurize
the case 40.
_
Fs is the downward force oflthe spring 73, and
PR4 is the “regulated pressure”
houses all of the operating mechanisms of they control
system. Fuel taken from tank 16 is conveyed through
line 17 and pumped to a comparatively high pressure by
pump 42 and then directed to the several control ele
ments contained within case 40. Leakage ?ow from the
14
Expressed mathematically, if
PRIMARY FUEL FLOW CONTROL
then
P4+A_=PR4
D
10
(20)
Denote the pressure in the case 40 by P,,.
Then sub
tracting Uc from both sides of (20):
The pressure in case 40 is maintained at
a substantially constant control pressure Pc somewhat
less than the discharge pressure of pump 42, by a spring
biased ball check valve 41, through which excess fuel in
case 40 is returned (by conduit 18) to fuel tank 16.
Conduit 17 is connected to the inlet side of a high-pres
sure, positive-displacement pump 42 (preferably of the
.
F5
(P4_'Pc)=(PR4_Pe)_“Id
(21)
At the top of FIG. 3 isshowna T6 sensor-11, which is
responsive to the temperature T6 of the air at the exit of
the recuperator RC.
The sensor 11 comprises an outer tube 75 of material
gear type), which is driven by the engine (1), through 20 having a high coe?icient of expansion, surrounding an
shafts 43 and 44, connected to shafts 26 and 25 (FIG.
inner rod 76 of material having a low coefficient of ex
2). Fuel discharged by pump 42 ?ows through conduits
pansion. When the sensor is exposed to a stream of gas
45 and 46 to a primary metering valve 47, and thence
at a high temperature, the tube, being ?xed at its left
hand end, will expand so that its free right hand end is
surizing check valve 50, and a conduit 51, which connects 25 appreciably displaced to the right. The inner rod 76, on
with conduit 12, leading to the primary combustion cham
the other hand, will remain at substantially its initial
through a conduit 48, a solenoid shut-off valve 49, a pres
ber B1 of the engine.
'
Conduit 46 is connected by a conduit 52 to a primary
length (because of its low expansion coefficient). The
metering head regulator 53, which is in turn connected
result is that the left hand end of the inner rod 76 experi
ences a displacement to the right when the temperature
by a conduit 54 to the inlet conduit 17 of pump 42,
T6 increases.
whereby a portion of the fuel discharged by pump 42
The left hand end of the inner rod abuts a pivoted lever
may be returned to the inlet side of the pump, Whenever
77, with which is associated an ori?ce 78a, in such a way
the pressure in chamber 55a, acting on a diaphragm 55
that when the inner rod 76 is displacedtowards the right,
in regulator 53, is high enough to overcome the opposing
because of an increase in T6, the ori?ce 78a opens up,
force of a spring 56, plus the fuel pressure in chamber 35 and vice versa.
57, and open a valve 58. The chamber 57 is connected,
A fuel line, comprising conduits 78, 79 and'80, connects
by a conduit 59 and a chamber 60, to conduit 48; so that
the temperature sensor 11 to the transducer 68, and con
the pressure differential acting on diaphragm 55, equals
sequently the chamber 81 of the sensor 11 is normally
the pressure drop (metering head) across valve 47, and
?lled with fuel from chamber 69 of transducer 68. To
said metering head is thus maintained at a substantially 40 prevent this fuel from penetrating into the engine case, a
constant value, as determined by the spring 56.
Conduit 45 is also connected to conduit 17, through
conduit 61, relief valve 62 and conduit 63, so that the
?exible sealing bellows 82 is provided. The chamber 81
fuel pressure in conduit 45 can never exceed a safe, maxi
pressure PC.
of the sensor 11 is vented to the case 40 of the control by
a connecting conduit 43, and is thus subject to the case
mum value, as determined by a spring 64, which biases 45
The pressure PM in chamber 69 of the transducer 68 is
check valve 62 towards closed position.
equal to the-compressor discharge pressure P4+a constant
The metering valve 47 is of the spool type, the upper
C1 which is determined by preload on spring 73. When
end of which is attached to a diaphragm 65, between
ori?ce 78a is closed by lever 77 (and there is no ?ow
which and a stationary sleeve 66, in which the spool valve
through restrictions'79a and 141), the pressure in con
47 moves, is a spring 67, so disposed as to urge the 50 duit 79 is equal to pressure PM in chamber 69; however,
diaphgram upwards. As shown in FIG. 3, the lower side
when ori?ce 78a is opened by lever 77 , in response to tem
of diaphragm 65 is subject to the case fuel pressure Pc,
perature T6, ‘fuel ?ows through ‘restriction 86a, conduit
and the upper side of the diaphragm is subjected to a pres
78, chamber 81 and conduit 43 into case 40. This reduces
sure (Pmn) so that the ?ow area through the metering >
the pressure in conduit 79 from PM to a lower pressure
valve 47 is due to a balance between the upward force of 55 PR4’, which re?ects the effect of change in temperatureiTs.
the spring and case pressure Pc and the downward force
A restriction 79a in conduit 79 still further lowers the
due to the pressure PR4", acting on the diaphragm.
pressure PR4, to PM», when'there is any fuel ?ow through
branch conduit 84, as hereinafter described. The modi
At the top left of the schematic diagram of FIG. 3 is
‘?ed pressure PR4” acting on diaphragm 65, in opposi
shown a P4 transducer 68 which'converts the pneumatic
discharge pressure (P4), of the high-pressure compressor 60 tion to the case:pressure Pc and the force of spring 67,
actuates the primary metering valve 47 in accordance
C2, ‘into a hydraulic ‘pressure (PR4) that is used to actuate
with the value of pressure PR4”;
the primary metering valve 47. Fuel at pump pressure
At the center right, of FIG. 3 is shown a speed gov
(PF) is admitted to the lower chamber 69 of the trans
ernor 85, which will be described below. Associated
ducer 68 through a conduit 70 and restricting ori?ce
with the speed governor 85‘is an ori?ce 84a, closed when
70a. The upper chamber 71 of the transducer is con
the governor is not operating, which is the state during
nected by pipe 19 to the discharge passage 20 of the high
acceleration of the engine.
pressure compressor, C2, and the upper and lower cham
We now describe the situation during acceleration of
bers are separated by a ?exible diaphragm 72 which is
the gas generator portion (C2, RC, B1 and T;,,), of the
biased downwardly by a spring 73. Accordingly, the 70 engine.
transducer 68 acts as a pressure regulator,,such that the
pressure PR4 acting upwards on the diaphragm 72 will bal
ance the downward force of the spring 73, plus the down
ward force on the diaphragm due to the compressor dis
charge pressure P4.
The primary metering valve 47, transducer 68, and T6
sensor 11, with theirsassociated elements, determine the
primary fuel flow tothe engine during acceleration, since
the ori?ce 84a'is closed because when the speed'governor
75 is inoperative, lever 86 closes said'ori?ce.
3,166,902
15
16
The fuel ?ow to the engine for proper acceleration is,
from Equation 5
i
'
to its downward displacement, then the ?ow of fuel
through the valve is also proportional to (FEW-PC), i.e.,
'
Wr'1=C(PR4'-"Pc)
Where k is a constant, T4* is the desired maximum allow
able turbine inlet temperature, and T6 is the measured
temperature of the air leaving the recuperator.
Fuel from the fuel pump 42 is supplied to the P4 trans
ducer assembly through the ori?ce 70a, at some pres
or substituting Equation 24
the compressor discharge chamber 20 of the engine, and
is therefore subjected to the pressure P4.
Let PM be the fuel pressure in the lower part of the
produce the correct fuel ?ow provided
A,
1+ AF)
2
1O Comparing this last equation with (5), it will be readily
sure PF.
seen that the control shown schematically in FIG. 3 will
The upper chamber of the transducer is connected to
transducer.
1
Ac
2
'
Then the downward force on the diaphragm is (P4AD),
The ori?ce 80a of FIG. 3 being assumed ?xed, it is read
ily apparent that as T6 increases, the opening of ori?ce
78:: increases, and the quantity on the left hand side of
(26) decreases. The manner in which this quantity de
creases with increasing AG in a somewhat non-linear way,
is shown in FIG. 6.
At the right end, the ?oating lever 86 is subject 'to the
upward force from a spring 89 that tends to rotate the
?oating lever counter-clockwise about the movable ful
crum. The lower end of this spring is urged upward
' where AD is the e?ective area of the diaphragm 72 that
separates the upper‘ and lower chambers 71 and 62 of
the transducer, plus the force Fs of spring 73. The up
' ward force on this diaphragm is (PMAD). When these
forces are in equilibrium, we have already shown (Equa
' tion‘ 20) ' that
Fe
An
and the valve 72a attached to the diaphragm 72 will open
by a bellows 90 as shown.
'or close to pass more or less fuel to the case 40 of the
law of pressure drop through ori?ces
. <PRi'—P.,>=<PRr-P°);A,
0
AF
1+(—)
<22)
lows 90 by a conduit 92, are ?lled with an incompressible
?uid, and exposed to the compressor inlet air stream.
The upward expansion of the bellows 9t), and therewith
the upward displacement of the bottom of the spring 89,
is therefore proportional to the air stream temperature
(T1).
When the upward force of ?yweights 87 is low enough,
the spring 89 and temperature bellows 90 will rotate
the lever 86 about the movable fulcrum 88 until the lever
bottoms on the ori?ce 34a, closing it effectively against
leakage of fuel, and when this is the case, the upward
40 force exerted by the spring 89 is proportional to the
temperature T1, say kTTl.
where AC and AF below denote the areas of ori?ces 78a
The distance between the point of application of the
upward force of ?yweights 87 and the spring 89 being
I, and the movable fulcrum being positioned by the
and 80a respectively, and substituting (21) in (22)
(23)
manual lever at a distance x from the spring 89, we ob
The case pressure Pc may be regulated to any value
we please; in particular, we may make Pc=Fs/AD, and 50
in that case
The bellows 9t), and a tem
perature-responsive bulb g1, which is connected to bel
"control at pressure PC, to maintain the pressure PR4 at
the value given above. The manner in which such a
jpressure vregulator works is well known.
Because the ori?ces 80a and 78a are in series between
‘a region where the pressure is PR4 to a region of lower
pressure PC, there is a continuous flow of ?uid through
‘80a and 78a, and the ?uid pressure in the line between
80a and 78a is denoted by PM’ in FIG. 3. From the
serve that the force kNN2 exerted by the ?yweights 87
will overcome the force kTT exerted by the temperature
bellows 90 and spring 89, whenever
kNN2 (l—x)>kTT1x
or when
.
N2
low
ii
an
a:
55 or when
A?’
&
AD
' may be made any other value necessary to produce the
desired engine acceleration schedule by biasing PR4 -
above P4.
Primary metering valve 47 receives fuel from the main
pump 42 at pressure PF, and delivers it to the engine at
pressure PM. The pressure di?erence (Pg-PM) is main
tained at a constant value by the by-pass pressure regu
lating valve 53.
That is, whenever the “corrected speed" (HA/T1) of
the engine exceeds some value corresponding to a manu
ally selected magnitude of x, the ?yweight force will
overcome the temperature spring force, and rotate the
?oating lever 86 in the clockwise direction. This causes
the lever to separate from its resting place on ori?ce 84a,
and the ori?ce will open.
From FIG. 3, it will be seen that the opening ori?ce
84a will cause the pressure PR4! to drop to a lower value
It will be seen in FIG. 3 that diaphragm 65 to which is
PM’, because of the pressure drop across ori?ce 79a, and
attached the spool of the metering valve 47 is urged
the result of this is a closing down of the main metering
‘downward by the pressure di?erence (PR4I—PC), when 70 valve 47 with a consequent reduction in fuel ?ow WFl to
‘there is no fuel ?ow through ori?ce 7&1, and is urged
the engine. This reduction in fuel flow will prevent the
upward by spring 67 whose rate is ks.
engine from continuing its previous acceleration, and the
The downward displacement of the metering valve is
speed of the engine will be held constant at the selected
therefore proportional to the pressure (PMI—PC), and
“corrected” value.
if the port are? of the mete?tug valve 47 is proportional
The tube 75 of the T6 temperature sensor 11 is im
3,166,902
17
18
mersed in the gas stream at the exit from the recuperator
vents escape of fuel from chamber 60, when valve 49 ‘is
closed.
SECONDARY FUEL FLOW CONTROL
(station 6 in FIG. 1).
We stated previously that the sensor 11 consists of
an outer tube 75 of highly expandible metal, the tube
being ?xed at its left hand extremity to the case 74 and
incloses a rod 76 of low coe?icient of temperature ex
pansion, the rod being attached to the tube 75 at its right
So far, we have considered those elements of our fuel ~
control apparatus, depicted in the upper part of FIG. 3,
that regulate the primary fuel flow to the engine. We
will now describe the elements in the lower part of FIG.
3 which control the secondary fuel flow to the engine.
it will be plain that this point will be displaced towards 10 A conduit 1-10 connects conduit 61 with branch con
duits 111 and 112. Fuel from 111D flows through a re
the right as the temperature of the whole assembly is
striction 1&3 in conduit 112, under a reduced pressure
raised, and vice versa, due to the relative differential
PR2 into the lower chamber "114 of a transducer 115,
expansion of the tube 75 and the rod 76, so that an
and ‘from thence through a restriction 1.16 in aconduit
increase in the temperature T6 results in a proportionate
opening of the ori?ce 78a.
15 1-17, under a reduced pressure PR2’, into a chamber 118
of a secondary fuel metering valve 119. A ?exible dia
We mentioned above the “anticipating” effect of the
phragm 120 separates chamber 118 from a chamber 121,
T6 sensor. Suppose the temperature T6 suffers a sudden
into which fuel enters from case 40 through a port 122
change (say an increase) from a previously existing
at case pressure PC, so that said diaphragm is subject to
steady value. This increase will be immediately detected
by the highly expansive outer tube ‘75, the free end of 20 the pressure differential (PR2'—- c). Diaphragm 120 is
attached to valve 119 and a spring 123 biases said dia—
which will at once begin to move to the right, pulling
phragm to the left, whereby the fuel flow area through
the inner rod 76 with it and opening the ori?ce 78a.
valve 119 is varied in accordance with the fuel pressure
Some appreciable time later, heat due to the increase in
hand end.
Now ?xing attention on the left hand end of rod 76,
T5 will penetrate into the low coel?cient of expansion
inner rod 76, which will then move in a direction tending
to close the ori?ce 78a. By suitable matching of the
time delays in the temperature response of the two ele
ments 75 and 7 6 of the sensor 11, the net over-all response
can be matched to the response of the recuperator RC
itself, so that transient effects of changes in T6 can be 30
differential (PR21-Pc) and the rate of spring 1123.
Fuel ?ows through conduits 110 and 111, a chamber
124 (of a throttling metering head regulator 125), a valve
126, a chamber 127, conduits 12$, r129, 13% and 131, a
solenoid shut-off valve ‘132, a check valve 133, and con—
duit 14 (of FIG. 2) to the secondary combustion cham
ber B2 of the engine 11.
'
In the metering head regulator 125, a diaphragm 134
compensated for.
The operator’s control of the speed and power of the
engine 1 is effected by a manual control lever 93, which
separates chamber 127 from a chamber 135, connected by
conduits V131’: and 137 to conduit 131, and houses a spring
is ?xed to a shaft 94, journalled in the case 46 and ex
tending into control unit 13, as shown in the upper right ‘
138 that biases valve 126 (attached to diaphragm 134) to
wards the open position. Valve 126 reduces the fuel
vcorner of FIG. ‘3.
pressure from a value PF in chamber 124, to a value PS
in conduits 128 and 1129, and valve 119 reduces the pres
sure PS to a value Pm in conduits 130 and 131. Con~
duit 136 transmits the pressure Pm to chamber 135, so
Also ?xed ‘on shaft 94 is a cam 95,
on which rides a follower \% whose other end is attached
'to a piston 97, so that when cam 95 is rotated through
an angle .PLA which increases its pitch radius, piston 97
is moved to the left in a cylinder g8, against the force 40 that the valve 126 responds to the pressure differential
(PS—PM2) and the force of spring 133.
of an opposing spring 99. A rod 100 connects piston
A conduit @1443, having a restriction 1141, connects con
97 with roller 88 and piston 97 is provided with a passage
duit 79 to a chamber 142 of a secondary fuel ?ow aug
‘1011 through which liquid may pass only from left to right
mentation valve 143, which comprises a spool valve 144
by virtue of check valve 191a. Motion of piston 97 is
not therefore effected to the left, however motion to the 45 attached to a ?exible diaphragm 145, separating chamber I
right is at a retarded rate determined by the size of the
opening of passage H52, as determined by adjusting needle
valve 193 into case pressure P(, so that cylinder 98 and
piston 97 function as a dash-pot, to'retard the rate at
which a movement of lever 93 may move the roller 83
to the right only, and thereby change the rate of retard
ing the N2 throttle setting of the engine. The retarding
dashvpot action of cylinder 93 and piston 97 is required to
prevent such sudden changes in ‘fuel flow WF1 (upon
.quick movements on lever 97) as may cause compressor
and engine stall or burner blow-out.
Liquid :fuel is displaced from cylinder 98 through a.
142 from a chamber 14-6 that is connected by a conduit
147 with conduit 84. A spring 148, attached to dia
phragm 14-5 biases valve 144 towards closed position, in
opposition to the fuel pressure differential between cham
bers ‘142. and 1146 acting on diaphragm I145. The ?ow
area through valve 144 establishes an additional fuel ilow
path ‘from conduit 12-? to conduit 137, which augments
the fuel ?ow through secondary metering valve 1-19.
A conduit 15% connects conduit v1117 (upstream of re
striction 116) with a chamber [151 which is closed, by a
flexible diaphragm 152, having an attached ?xed pivot ‘153,
that contacts a floating lever 1154. The right end of le
passage 1532 which communicates with the interior of case
40, and such admission of fuel is controlled by an ad
ver 154 is biased upwardly by a spring» 155, so as to
rock in a counterclockwise direction about a movable roll
by the valve 193 can be adjusted from the outside of
end portion of lever 1154 varies the flow area through
justable needle valve 1433, which is screw-threaded through 60 er pivot ‘156, in opposition to the upward thrust of ?xed
pivot 153 by diaphragm .152. The movement of the left
the wall of case 40 and provided with a slot 104, where
nozzles 157 and ‘153 at the upper ends of conduits 159
and use. Conduit v159 is connected to conduit 140 by a
Solenoid valve 49 is adapted to open and close com
munication between conduit 48 and chamber d4), upon 65 conduit 161, so that variations in the ?ow area of nozzle
157, by movement of lever 154, cause-s variations in the
energizing or deenergizing of a solenoid 195, which is
pressure in conduit 14% and chamber ‘142.
accomplished by manually closing or opening a switch
Roller pivot 15% is connected by a link 162 to a roller
196, in an electric circuit 197 to which current is sup
case 49.
.
cam follower 163 which rides upon a'cam 164 to which
plied by a battery 1% (as shown in FIG, 2). When the
operator desires to stop the engine 1, he opens switch 70 it is held in contact by a spring 165. Cam 164 is pivoted
166, which deenergizes solenoid 1G5, and closes valve
49, whereupon the ‘fuel flow WFl to the engine is shut
off.
The ball check valve 59 maintains a desired fuel pres
sure in the fuel control apparatus at all times, and pre
at 166 and is connected by a link 1&7 with cam 95, so
that as cam 515 is rotated. by lever 93, earn 164 is also
correspondingly rotated, about its pivot 166. Spring 155
seats in a movable abutment 168, supported by the left
end of a lever 169, which is pivoted alt-170, and whose
3,166,902
T9
'
right end is interposed between spring 8b and bellows
and
550, so that expansion or contraction of said bellows (re—
WF2=secondary fuel flow
P2=l0W-pressure compressor discharge pressure
A4, A5=design constants
WF2,'=secondary augmentation flow and is proportional
sponsive to air inlet temperature T1 in tube 91) varies
the tension of spring 155 and the loading of lever 154.
The lower end of conduit lid has a restriction 171,
and is connected by a conduit 172 to a chamber TF3,
to the amount of cut in of the primary fuel flow gov
which is closed by a ?exible diaphragm 174. A link
‘175 connects diaphragm 174 with a lever 376, which is
pivoted at 177 and biased in a clockwise direction by
a spring 178. Movement of the right end portion of
lever 175 varies the flow areas through nozzles 179, 18%
and 181, into a chamber 182 which communicates through
ernor (the N2 governor).
Both primary and secondary fuel flows WFl and WFZ are
scheduled as a function of the positions of a primary
metering valve 47, and a secondary metering valve 119, in
a system where the metering heads, or pressure drops
a port 183 with case 4%, whereby the pressure in chamber
across these valves are held constant.
182 is case pressure PC.
The primary metering head regulator 53 bypasses fuel
A conduit 184 connects conduits 117 and 166, so that 15 flow around the fuel pump 4&2 and the secondary meter
the pressure (PR?) in 117 is varied by variations in
the ?owrarea through nozzles 158 and 179. Nozzle 253i?
is connected by a conduit 185 with conduit lei, so that
the pressure in chamber 142 is varied by variations in the
?ow areas through nozzles ‘15? and 18d. Nozzle 1.82
both circuits. The magnitude of metering head is deter
mined by the area of the diaphragm in each regulator,
divided into the preload of its spring.
is connected by a conduit 186 with chamber 1% pressure
Identical pressure transducers 6S and M5 are used in
ing head regulator 125 throttles the fuel flow, as required
to hold a constant drop across the metering valves of
from conduit 147 may be discharged through conduit 186
the primary and secondary fuel circuits to convert pneu
and nozzle 18!, so that the pressure in chamber 14s is
matic engine signal pressures to hydraulic pressures. The
varied by variations in the ?ow area through nozzle lltil.
pressure transducers throttle incoming pump discharge
Returning to the ‘low-pressure compressor discharge 25 pressure to scheduled levels above the pneumatic P4 and
pressure (P2) transducer 115, it will be noted that the
P2 engine pressures. These scheduled pressures being
pressure P2 isrtransmitted from discharge chamber Ed in
engine 1 to the fuel control unit 13 by conduit 23, which
PM and PR2 respectively, as expressed by:
is connected to a chamber 1%“, and said pressure and a
spring 1% act on a diaphragm £92, attached to a valve 393,
which controls the fuel ?ow from chamber 114 into case
40, whereby transducer 115 converts the pressure P2 to
The values of C1 and C2 are determined by the spring
a control pressure PR2.
preload on the transducer diaphragm.
'Conduit 1'72 connects conduit 11%} (downstream of re
The variable bleed circuits in both the primary and
striction 1'71) with an annular groove 21a in a power 35 secondary fuel systems serve to modulate the transduccd
turbine speed governor 211‘, which is driven by the engine
l, through connected shafts 29, 28, 27 and 15 (PEG. 2).
pressures PM and l’m for acceleration fuel scheduling.
These circuits are as shown in the upper and lower parts
Drive shaft 29 is connected to a spindle 212 which ter
of FIG. 3, respectively.
minates at its upper end in a horizontal cylinder 2R3, hav
acceleration, bleeds 34a, 157, 153 are closed,
ing at its opposite ends case pressure port 214 and outlet 40 as During
well as 179, 180 and 181 which open only during
port 21d. Cylinder 213 rotates in a chamber 215 which
power turbine governor operation. The power turbine
communicates through a port 217 with case 4%. A pas
PT acts only as a topping governor to prevent overspeed
‘ sageway 218 and 21% connects conduit 172 with the in
of the output shaft 15. Therefore, the modulated pres
sure PM” and PR2, establish the respective primary and
secondary acceleration ?ows as follows:
terior of cylinder 213, in which is mounted a slidable spool
valve 219 that is biased toward port 215 by a spring 22%.
Valve 219 has a passage 221 through which liquid fuel
?owing through conduit 172 and passageway 218 escapes
into the right end of cylinder 213 and from thence through
_port 215 into, chamber are to the case via opening 27. .
With ori?ces closed as noted above, PR4'ZPR4H, and
By virtue of the foregoing arrangement of the elements 50
for a ?xed value of T6, acceleration flow would be propor
tional to P4+a constant. However, by bleeding off
through variation in T6 which varies ori?ce 78a, the
of speed governor Zlll, said governor generates in con
duit 172 a pressure (PRPT) which is proportional to
the speed (NPT) of the power turbine PT. A conduit
222 connects conduit 172 with a speed (r.p.m.) guage
schedule can be proportionally changed as ‘a function of
223 which is located so that the engine operator may '
know the speed (r.p.m.) of the power turbine at all
times.
T
(Ag-T5) to meet the schedule dictated by the equation
(A) above.
With ori?ces closed, as noted above, PR2I:PR2, and
the schedule noted above can be achieved, since
Ignition fuel ?ow required to start the engine 1 is pro
vided through a conduit 187, having a manually
adjustable needle valve 188, which is connected to primary (it)
fuel conduit 12, whereby fuel is fed into combustion
and since metering head is constant and fuel flow is a
chamber B1.
function of PR2. As the (N2) speed governor 85 cuts in,
a pressure drop occurs across ori?ce 79a, with the com
OPERATION OF CONTROL SYSTEM
mencing of ?ow through ori?ce 84a. This pressure drop
The fuel control system of our invention determines two
is a function of the opening of ori?ce 84a, which deter
fuel flows to the engine, viz.: a primary fuel ?ow and 65
mines the ?ow and hence, this drop (PR4,—PR4~) across
a secondary fuel flow, as follows:
‘79a. This pressure drop across the augmentation valve
343 will produce a stroke of this valve proportional to
(A)
(PRy—PBA~), since stroke is determined by the area of
(B l
valve diaphragm 14S, and the preload and rate of spring
where
MS. Increasing the governor 85 cut-in increases
WFl‘iprimary fuel ?ow
P4=high-pressure compressor discharge pressure
T6=recuperator temperature
A1, A2, A3=design constants
(PR4'—P¢"), which produces increasing stroke and hence,
increasing fuel flow. The secondary system fuel meter
ing head is maintained across the augmentation valve
75 144, hence making change in fuel ?ow a function of stroke.
3,166,902
21
Maximum augmentation fuel flow can be limited by a
maximum ?ow stop on this valve.
Therefore WFZ, is de?ned as follows:
22
P2 pressure is approached, the P2 governor cuts in, there
by opening bleed 158, and causing secondary fuel ?ow
(WF2) to be reduced in accordance with the control
determined droop gain (Wm/P2 error). Secondary fuel
where
?ow (WFZ) will continue to be reduced after governor
cut-in as the P2 pressure increases, until the required sec
ondary steady state fuel ?ow is achieved. The P2 pressure
N2A= (N2) governor 85 cut in speed
will then be controlled at a predetermined pressure above
N23: (N2) actual speed after cut-in.
P2 governor cut-in. The supplementary ignition ?ow
will be turned off at a predetermined N2 speed or F2
10
Primary and secondary steady state fuel ?ows, WM
pressure.
and WF2, are achieved by modulating PR4,» and PR2, pres
‘ Subsequent increasing of the power lever angle will in
sures. In the primary circuit, PR4” pressure is modulated
crease N2 speed and P2 pressure to prescheduled levels as
by the N2 governor 85, via bleed 84a. In the secondary
a function of power lever angle.
circuit, PR2, pressure is modulated by the P2 governor, via
Engine deceleration is achieved by retarding the rate
bleed 158. Primary and secondary fuel flows are thereby 15
of change in the power lever angle PLA. A direct reduc
established in accordance with the error in set (N2) speed
tion of secondary fuel ?ow (WFZ) will result in a flow
and (P2) pressure parameters.
level which is set, either as a function of the secondary
Governor droop rates may be varied by changing bleed
circuit bleed sizes, or to the minimum flow established
79a in the primary circuit, and by changing bleed 116 20 by
an adjustable ?ow stop, whichever limits the higher
in the secondary circuit. Reducing the flow areas for
level.
Although the N2 governor lever has been retarded,
each bleed will respectively increase droop rates. This
which would normally result in a direct ?ow reduction
adjustment may also be made by changing the rate of
as in the secondary system, dash pot 97~99 limits the re~
spring 89 of governor 85, or the rate of spring 155 of the
tardation of the lever cam follower 96 of the N2 governor.
P2 governor.
'
25 N2 speed is reduced, therefore, as a function of time.
The change in T1 temperature, as sensed by the T1
This action prevents an undesirable mismatch in speed
sensor 91, produces a change in length of the T1 motor
of the two engine spools during deceleration. Fuel flows
bellows 90, which varies the set preload on spring 89
in both circuits is reduced until the new desired steady
of the governor 85. Increasing T1 temperature increases
state parameters are achieved.
.
the bellows 90 length, which in turn increases the preload
Normal engine shut down may be effected by retarding
of the governor spring 89, and reduces the preload of the
the power lever 93 to the idle speed position, and then
P2 governor spring, to correct set speed conditions, as a
shutting off fuel flow in both fuel circuits by operation
function of T1 temperature, in order to meet the T1 cor
of solenoid valves 49 and 132.
rection requirements.
If, during operation of the engine, the power turbine
The selection of pressure (P2) and speed (N2), as a
speed (NPT) exceeds a preset value, as determined by the
function of throttle angle PLA, is determined by ‘the N2
spring preload setting on the power turbine governor
and P2 governor cams 95 and 164 respectively, which
diaphragm 151, the power turbine governor will operate
set the lever arm ratio between spring preload and set
reference forces on the respective governors.
to open ori?ces 179, 189 and 181, which in effect cause
cut-in of the P2 and N2‘ governor circuits, and bleed off
A spring loaded dash pot, 97-99, with provision for a 40 of the high-pressure side of the augmentation valve
variable ?ow rate, limits the deceleration time of the
diaphragm 145, to effect closing down of the three meter
high-pressure compressor (C2) spool. In the increasing
ing valves 4-7, 119 and 144 in the control. The closing
speed direction, the dash pot 97-99 has no effect and,
down of these valves is proportional to power turbine
therefore, a set speed is established directly by power
governor 211 set speed error, and the respective gains are
lever angle PLA. A screw adjustment 103 is provided to 45 determined by the combinations of sizes of ori?ces used
vary the area of port 102 which bleeds ?ow from the dash
in the respective circuits.
pot during deceleration of the N2 spool (C2——Tb2). This
area may be adjusted to permit decelerations of the order
of less than 1.0 second to more than 15 seconds.
The delaying of (N2) deceleration prevents the low
pressure compressor C1 from going into surge, by equaliz
‘ A pressure signal is generated by the power turbine
governor system to provide a guage 223 indication of
power turbine speed. This pressure may also, if desired,
be used to operate a preset pressure switch which would
ing the deceleration rates of the two rotor spools,
deenergize the solenoids and shut down the engine.
Ignition fuel ?ow to start the engine is provided from
(Cl-Th1) and (C2—Tb2). The (Cr-Th1) spool has a
conduit 111) through an adjustable needle valve 188 in
much lower inertia hence, tends to decelerate faster than
the (CZ-Th2) spool.
branch conduit 187, of the engine primary fuel circuit; and
an engine solenoid actuated valve 189 is used to initiate
The power lever 93. may be set in any position from
idle to maximum power before the’ engine is cranked.
and turn off ignition ?ow.
Minimum primary acceleration fuel flow is supplemented
with the preselected ignition ?ow for proper ignition.
Secondary flow is shut off by solenoid-operated valve 132
in the secondary fuel line until primary ignition occurs.
starting motor (not shown), the primary ignition switched
’
The high-pressure spool (C2-—Tb2) is cranked by a
on, and solenoid valve 49 is opened by closing switch
1%, to start primary fuel ?ow WFP which is supple
mented by ignition fuel ?ow through valve 138. The
primary flow WFI will be metered in accordance with T6
temperature and 1’, pressure, as speci?ed by the primary
acceleration schedule (FIG. 7). The ignition ?ow will
After primary ignition, secondary fuel ?ow is turned on,
providing acceleration flow for secondary ignition. As
the engine accelerates, acceleration ?ow is metered in
both fuel circuits until the preselected steady state speed 65 be provided by a parallel path through the adjustable
(N2) or pressure (P2) is approached. Since the N2
fuel flow valve 188, and solenoid valve 189, in the control
spool accelerates much faster than the P2 pressure spool,
unit 13; and this ignition ?ow is added to the control
'the N2 governor will cut in ?rst, thereby opening bleed
primary fuel ?ow. The amount of ignition flow may be
84a and reducing primary fuel ?ow, in accordance with
trimmed as required to individual engine requirements.
the control-determined droop gain (WF1/ N2 error). Flow 70
will continue to be reduced from the acceleration value
as speed (N2) increases until the required steady state
speed is achieved. As the engine continues to accelerate
When ignition occurs and the temperature sensor 11
senses the temperature in the primary combustion in
chamber B1, switch 190 (FIG. 2) is closed. This will
shut off ignition ?ow, ‘and energize the secondary fuel
(due'to increasing P2 pressure), the speed (N2) is held
flow solenoid valve 132. The fuel flow, scheduled with
constant. As the (power-lever determined) steady state 75 low-pressure compressor delivery pressure (P2), (FIG. 7),
3,166,902
will determine the star-ting ?ow to the secondary com
PLA), the governor d5 cut~in begins. The ?yweight 37
bustor B2.
Upon ignition, the engine will accelerate to slow idle
speed, it the power lever has not been advanced to any
toes lift lever 86 and uncover ori?ce 184a, reducing PR4’,
and hence, WFI. The rate of cut-in with speed error
is determined by the net governor spring 59 rate, ?y
other position that may be required by an arbitrarily
selected power lever setting. The engine is accelerated
weight 87 design, and the selected ori?ces of the primary
me ering computing system. During governor cut-in, a
by advancing the power lever 93 from any power lever
setting to a higher power lever setting. The primary
system acceleration schedule is de?ned by P4 pressure,
modi?ed as a function of recuperator temperature T6, 10
pressure drop, as a function of the amount of cut~in, will
appear across ori?ce ‘79a. This pressure drop is used
to position the augmentation ?ow valve 144 in the sec
as shown in FIG. 8.
Engine compressor pressure P4 is sensed by the control
P4 hydraulic transducer 68, which produces the equivalent
hydraulic pressure PR4. PM is maintained at a constant
value above R, by the selected preload on spring 73, to
produce the required schedule as de?ned in FIGURE 7,
‘and allows the control to reduce fuel flow below the
ondary ?ow system.
The P2 governor cut-in point is determined by the
sp
F55 preload, acting against the diaphragm 152.
The opposing force is set, in the increasing direction with
increasing power lever angle FLA, by the P2 governor
cam 1642. This opposing force is also biased to decrease,
with increasing T1 temperature, through a linkage 169
starting value during governing. The P4 transducer 73
from the T1 sensor bellows 39'“, to maintain a value of
corrected N1 setting at any selected value of FLA.
operates on pump pressure PF, as supplied through ori?ce
As N1 speed increases, increasing the corresponding
'7‘Ja and bypassed through regulated ori?ce 68a.
PR4 is supplied to the WFl metering valve diaphragm
P2 and PM pressures, the diaphragm 15?.- force will over
come the opposing preload from spring 155, and uncover
édthrough ori?ces Mia and 79a. The pressure between
ori?ce 153, effecting cut-in of the P2 governor by bleed
these two ori?ces (PR4)) is varied by the T6 temperature
ing off pressure
The rate of cut-in, with pressure
sensor 11 which in effect reduces PR4 to a value (PRp),
error signal, is a function of the diaphragm 152. size,
lower than PM by the amount of increase in T6 tempera 25 net governor spring 15% rate, and the selected ori?ces of
ture or bleed oil0 through ori?ce 73a. The T6 sensor 11
the secondary metering system.
operates on di?erential expansion between the tube 75
The pressure drop across ori?ce We, applied across
vand contained rod 76, to uncover ori?ce 78a as a function
the diaphragm T45, acting on the augmentation valve
of T6. , With ori?ce 34a closed, and no ?ow through
Md, will add fuel flow to the secondary system in parallel
ori?ce 141, the pressure PR4, (equal to PR4”) positions
the ‘WP, metering valve 47 against its loading spring 67.
with the secondary metering valve 114, proportional to
the amount of N2 governor cut-in. This augmentation
Fuel ?ow WFl through the metering valve 47 is a func_
fuel ?ow ‘NF? will be zero at zero cut-in and rise to a
tion of valve position only, since the primary ?ow meter
maximum preset value at some percentage of cut-in.
ing head regulator 53, operates to maintain a constant
Since the augmentation ?ow Wm, is desired only dur
pressure drop across the metering valve 47. The metering 35 ing acceleration of the engine, means is provided to shut
head regulator 53 senses'this differential pressure and
off augmentation ?ow during deceleration. This will be
bypasses pump output ?ow to pump inlet 17, as required
discussed below. With decreasing N2 shaft horsepower
to regulate the metering head.
load, augmentation flow to the secondary is increased
The control pressure P2 is sensed by transducer 125
to optimize performance.
and converted to the required biased PR2 pressure, by the 40
The engine is decelerated by retarding the power lever
same method that was utilized by the P4 transducer 68.
The pressure PR2, equal to PR2 (when there is no
?ow through ori?ce 116), positions the W512 metering
valve 114- in accordance with the requirements of the
engine, as shown in FIGURE 7. The position of the
metering valve 119, as with valve 47 in the primary
system, determines the secondary fuel flow, (WFZ), since
93 from any higher power lever setting to a lower lever
setting.
Retarding the power lever angle will unload the gov
ernor ?yweignts 37, causing the tees to rise to a high
position and completely uncover ori?ce 84a. This re
duces PR4” pressure to a lower value, causing the meter
ing valve 127 to close off toward a minimum value, and
the pressure differential across valve 119 is maintained
reducing the primary metered flow ‘N11 to the engine.
constant by the secondary metering head regulator 125.
The secondary ?ow metering head regulator 125 senses
The engine will then decelerate to a new steady state
the pressure differential across metering valve 119 and
throttles the pump output pressure PF, which is estab
lished by the primary flow system, to maintain a ?xed
head across the secondary metering valve 119 (and, as
will be discussed later, the augmentation ?ow valve 144) .
power lever angle.
The fuel control system will accelerate the engine until
steady state conditions (as dictated by the power lever
setting) are achieved. Steady state control is maintained
by the N2 governor 85 and P2 governor, respectively, for
the primary and secondary systems. General governor
operation is indicated in FIGURE 9 for‘ both the N2
operating point, corresponding to the newly selected
The NZ governor dashpot 97-99 will retard, or cause
a time delay, in the rate of reset of the N2 speed, in the
decelerating direction, to equalize the deceleration times
of the two engine rotors and prevent low-pressure com
pressor surge, as indicated in FIGURE 11.
Retarding of the throttle 93 will, (as in the primary
system) uncover bleed 15$, reducing pressure PR2’, and
hence secondary fuel ?ow WFZ. The N1 speed will reset
at a lower value, corresponding to the new lower selected
throttle position, as dictated by the P2 pressure.
and P2 system.
As previously mentioned, the augmentation ?ow is not
The N2 governor 85 setting is established by the pre
desired during engine deceleration because deceleration
load force in the spring 89 loading the governor ?y
time will be increased. In accordance with this require
weight 37 toes. The preload of the spring 89 is in 65 ment, reduction of the throttle angle FLA will produce
creased with increasing power lever angle PLA through
simultaneous opening of ori?ce 157, causing the high
the cam 95, roller 88, and lever 86 arrangement to
increase set speed with power lever angle. The T1
temperature sensor also increases this preload, with in
pressure signal to the augmentation valve 144 to be
reduced (note ori?ce lldl in the line 14d to the augmenta
tion valve). The augmentation valve 1-434} will then close
creasing Tl temperature, to maintain set values of cor
rected speed. The governor S5 setting, as a function of
and open only during N2 governor cut-in.
during decelerations, remain closed during accelerations,
T1 and PLA, is indicated by FIGURE 10.
As the N2 governor ,?yweight 87 centrifugal force in
creases with N2 speed, and at the point where said force
instant that power tur ine set speed is exceeded.
equals the spring $5? prcload (as determined by T1 and
centrifugal force generated by the spinning valve 219 is
The power turbine speed governor 21}. operates to cut
in and reduce N2 and P2 settings sinultaneously at the
1
The
3,186,902
26
25
balanced by the pressure PRPT developed between ori?ces
171 and 173, The pressure PRPT, acting on the diameter
of the valve 219 in the control will, at the overspeed con~
dition, cause an unbalance condition between the dia
phragm spring 178 load and the pressure generated dia
phragm 174 force. This unbalance will simultaneously
uncover ori?ces 178, 18th and 181 to reduce primary and
secondary metered fuel flows, and shut off the augmenta
tion fuel ?ow. The relative rates of cutback of the pri
mary and secondary fuel ?ows will be determined by selec
tion of the diaphragm loading spring 178, diaphragm 17d
size, and relative sizes of ori?ces 179, and 181. The load
ing spring 220 on the rotating valve 219 in the power
turbine control has been included to insure that no leak
ing the maximum fuel ?ow to said combustion chamber
in accordance with the equation:
wherein (W311) is the rate of said fuel flow, (K) is a pre
selected constant, (P2) is the discharge pressure of said
compressor, (T,;*) is the preselected maximum per
missible temperature of gases entering said turbine, and
(T3) is the temperature of the air leaving said recupera
tor.
3. A fuel control according to claim 2, having means
for measuring the recuperator outlet air temperature (T3),
means for automatically substracting said temperature
(T3) from said maximum temperature T?‘, means for
age occurs during the cranking and starting of the engine. 15 automatically measuring said compressor discharge pres
sure (P2), and computer means for mechanically multi
The engine will be shutdown by turning off the ignition
plying the dilference between said temperatures
switch on valve 189 to simultaneously close both primary
and secondary solenoid valves 49 and 132 and stop all fuel
?ow to. the engine.
Both circuit pressurizing and check valves 59 and 133, 20 by said measured pressure (P2).
4. A fuel control according to claim 3, having a posi
tionable fuel metering valve for regulating the fuel ?ow
zles, will prevent undue dribbling of fuel into the com
(W511), means for maintaining a constant pressure drop
bustion chambers B1 and B2, and minimize coking of the
across said valve, means to vary the position ‘of said
nozzles therein. This might otherwise be a problem
valve, in accordance with the output of said computer
caused by long fuel lines slowly emptying into hot com
means, and means to limit said fuel ?ow, in accordance
bustion chambers.
with said equation, so that said turbine is protected from
The'control system case pressure (PC) is maintained at
damage due to overtemperature.
essentially ambient pressure by connecting case 4% to the
5. A fuel control according to claim 4, wherein said
fuel tank 15 through a check valve 41. With the control
case pressure P,c ?xed at an ambient reference, all hy 30 engine comprises a first and a second gas turbine, said
?rst turbine drives said compressor, and said second tur
draulic pressures computed in the control refer to this
which are mounted as close as possible to the engine noz
?xed reference, eliminating the need for balancing dia
phragms.
.
i
The requirement of control operation submerged in
bine is a free power turbine which delivers the power
output of said engine; and means for passing the gases
discharged by said ?rst turbine successively through said
deep water, such as may be called for in a tank type 35 second turbine and said recuperator, so that the heat of
the gases passing through said recuperator is utilized to
vehicle, will present no problem, since all ambient refer
heat the compressed air passing through said recuperator.
ences, such as exposed bellows and/ or diaphragms, have
6. A fuel control according to claim 5, having a posi
been eliminated. The only required ambient reference
tionable manual power control lever, and a speed gover—
of the control will be a single line back to the fuel
nor driven by said ?rst turbine, for regulating the speed
tank.
(N2) of said ?rst turbine, means for modifying the ac
While we have shown and described the preferred em
tion of said governor in accordance with the temperature
bodiznent of our invention, we desire it to be understood
(T1) of the air entering said compressor and the angular
that we do not limit the invention to the precise con
position of said manual control lever; means for render
struction and arrangement of elements disclosed by way
of illustration, since these may be changed and modi?ed 45 ing said governor inoperative when the control is limiting
said fuel flow (WF1) in accordance with said equation;
by those skilled in the art without departing from the
and means for cutting in said governor when the cor
spirit of our invention or exceeding the scope of the ap
pended claims.
rected speed (Nz/x/Tl) of said ?rst turbine attains a
value for which said manual lever is set, so that said set
Vvle claim:
1. In operative association with a gas turbine engine, 50 speed‘is maintained under varying operating conditions.
7. A control according to claim 6, having means for
having a compressor supplying compressed air through
a heat recuperator to a fuel combustion chamber, a fuel
- control comprising: means supplying fuel to said com
controlling the corrected speed (N2/\/T1) of said ?rst
turbine, so that the torque (Q) exerted by said second
turbine is a single-valued function of said corrected speed,
bustion chamber, at a rate varying in accordance with the
mass rate of air flow thereto, and means for automatically 55 whereby the maximum value of said torque (Q) is limited
modifying the rate of ‘said fuel supply, in accordance with
by a selected maximum value of said corrected speed.
a function of the product of the compressor discharge
8. In operative association with a gas turbine engine,
ressure and the temperature of the air leaving said
comprising: a ?rst, low-pressure air compressor driven by
recuperator, so that the temperature of the gases leaving
a ?rst gas turbine, a second, high-pressure air compressor,
said combustion chamber never exceeds a preselected
divert by a second gas turbine, for supplying compressed
maximum limit.
air through a heat recuperator to a ?rst fuel combustion
2. In operative association with a gas turbine engine,
chamber, a third, free-power turbine, interposed in gas'
having a compressor supplying compressed air through a
flow series relation between said ?rst and second turbines,
for generating the power output of said engine, and a
for discharging combustion gases generated in said cham 65 second fuel combustion chamber, interposed in gas flow
ber successively through said turbine and recuperator; a
series relation between said second andthird turbines; a
fuel control comprising: means supplying fuel to said
single-unit fuel control comprising: means for coordinate
combustion chamber, in accordance with the mass rate of
ly regulating fuel ?ow from a common supply source to
air flow therethrough, and means for automatically modi
said ?rst and second combustion chambers, in accordance
fying the rate of said fuel supply in accordance with the
with the rate of‘ mass air ?ow through said engine, and
temperature of the air leaving said recuperator so as to
means for automatically modifying the fuel flow to said
compensate for the heat added to said air by said recupera
?rst combustion chamber, in accordance with the tem
tor, whereby the temperature of the gases discharged from
perature of the air leaving said recuperator, so that the
said combustion chamber into said turbine never exceeds
temperature of the gases leaving said ?rst combustion
heat recuperator to a fuel combustion chamber, means
a preselected maximum limit, including means for limit- > - chamber never exceeds a preselected maximum limit, in_
3,1 ease-e
c‘;
.
v
mm
a?
eluding means for limiting the maximum fuel ?ow to said
?rst combustion chamber in accordance with the equation:
wherein (WF1) is the rate of said fuel flow, (K) is a
preselected constant, (P2) is the discharge pressure of
said second compressor, (T,,*) is the preselected maxi
mum permissible temperature of gases entering said sec
ond gas turbine, and (T3) is the temperature of the air
leaving said recuperator.
9. A control according to claim 8, including means, re-
sponsive to the temperature (T1) of the air entering said
?rst compressor,'for automatically correcting said fuel
operating conditions; the correcte' speed of each of said
rotors being de?ned as its actual speed (N), divided by
the square root of the temperature (T1) of the air enter
ing its compressor,
ii. A fuel control as in claim 14, wherein said control
includes means for modifying
fuel flow to said first
combustion chamber, in accordance with the temperature
of the air leaving said recuperator, so as to achieve opti
mum fuel consumption rates, during engine steady-state
10 operation, Without encountering compressor surge and tur
overtemperature.
16. A fuel control as in claim 15, wherein said engine
also comprises a free power turbine for delivering the
flow to the ?rst combustion chamber for each particular
power output of said engine, and said control comprises
(T1) temperature condition, so as to provide the desired 15 means, responsive to the temperature ("51) of the air
steady-state operation of the engine, at optimum fuel con»
entering said first compressor, for automatically con
sumption rates and optimum temperature condition in
trolling the corrected peed of said second gas turbine,
said recuperator, without encounting compressor surge
so that the torque exerted by said free power turbine is
and turbine overternperature.
independent of said (T1) temperature.
10. A fuel control according to claim 9, having means 20
17. A fuel control as in claim 15, wherein said control
for measuring the recuperator outlet air temperature (T3) ,
means for automatically substracting said temperature
(T3) from said maximum temperature T51‘, means for
automatically measuring said compressor discharge pres
sure (P2), and computer means for mechanically multi
plying the difference between said temperatures,
include means for obtaining maximum acceleration of the
engine from one manual power lever setting to another,
without causing compressor surge and engine vertem
perature.
18. A fuel control as in claim 15, wherein said fuel
control comprises means for modifying the fuel flow to
said ?rst combustion chamber, so as to obtain maximum
(Til-Ts).
engine deceleration from any manual power lever setting
by said measured pressure (P2).
to any lower setting, without causing burner blowout.
11. A fuel control according to claim 10, having a posi
19. A fuel control as in claim 15, wherein said control
tionable fuel metering valve for regulating the fuel flow
comprises means to automatically compensate the fuel
(Wm) to said first combustion chamber, means for main
flow to said ?rst combustion chamber, for variations in
taining a constant pressure drop across said valve, means
the temperature and pressure of the air entering said
to vary the position of said valve in accordance with the
?rst compressor, and for changes in temperature condi
output of said computer means, and means to limit Said 35 tions in said recuperator.
fuel ?ow, in accordance with said equation, so that said
20. A fuel control as in claim 15, wherein the fuel
gas turbine is protected from damage due to overternpera
supply to the engine comprises a primary fuel supply
system for supplying fuel to the ?rst combustion chamber,
12. A fuel control according to claim 11, having a po
and a secondary fuel supply system for supplying fuel to
sitionable, manual power control lever, and a speed gov
the second combustion chamber to supplement said
ernor driven by said second turbine, for regulating the
primary fuel supply; each system comprising a plurality
speed (N2) of said second turbine, means for modifying
of component, coordinated hydraulic devices, arranged
the action of said governor in accordance with the tem
therein in fuel ?ow series relation, and subject to the
perature (T1) of the air entering said ?rst compressor
manual power control lever, for regulatin<7 the fuel flow
and the angular position of said manual control lever;
therethrough to the engine; said devices in each system
means for rendering said governor inoperative when the 45 being collectively responsive respectively to the corrected
control is limting said fuel flow (W511) in accordance with
speed and corrected fuel flow through its system; cor
said equation; and means for cutting in said governor
rected speed being the actual speed of a compressor rotor
when the corrected speed (NZ/Vi) of said second tur
divided by the square root of the temperature of the air
bine attains a value for which said manual lever is set, so 50 entering said compressor; and corrected fuel flow being
that said set speed is maintained under varying operating
the actual r1161 flow to the related combustion chamber,
conditions.
multiplied by the pressure of the air entering the com
13. A control according to claim 12, having means for
pressor supplying air to said chamber, and divided by
controlling the corrected speed (NZ/V11) of said second
the square root of the temperature of said air.
turbine so that thetorque (Q) exerted by said free power
21. A fuel control as in claim 29, wherein the primary
turbine is a single-valued function of said corrected speed,
fuel system comprises a series of coordinated devices that
whereby the maximum value of said torque (Q) is limited
collectively measure low-pressure compressor inlet air
by a selected maximum value of said corrected speed.
absolute temperature, high-pressure compressor discharge
pressure, recuperator discharge temperature, and engine
14. in operative association with a gas turbine engine,
ture.
.
.
comprising: a ?rst, low-pressure air compressor, driven by 60 speed (rpm); and position a primary fuel metering
a ?rst gas turbine; a second, high-pressure air compressor,
valve, in accordance with a preselected, composite func
driven by a second gas turbine; for supplying compressed
tion of said temperatures, pressure and speed, while the
air through a heat recuperator to a ?rst fuel combustion
pressure drop across said valve is maintained at a con
stant selected value.
chamber; and a second fuel combustion chamber, inter
posed in gas flow series relation between said ?rst and 65
22. A fuel control as in claim 21, including override
second turbines; a single-unit fuel control, comprising: a
engine speed and temperature control devices, which
manual power control lever, means for coordinately regu—
modify the fuel flow to the engine, so as to prevent the
lating fuel flow from a common supply source to said
?rst and second combustion chambers, so as to maintain
the ratio between the corrected speeds of said first and
second compressor rotors at a selected de?nite value, for
each particular position of said lever, so that for each
, lever position a selected value of second compressor rotor
speed, and a corresponding steady-state discharge pres
sure of said ?rst com ressor is obtained, under varvin
,
,
7
.
c
engine operatinw at excessive speeds and temperature.
23. In operative association with a two-spool, gas tur
bine engine, comprising: a ?rst rotor, consisting of a low
pressure air compressor driven by a ?rst gas turbine; at
second rotor, consisting of a high pressure air compressor
driven by a second gas turbine; said compressors supply
ing compressed air through a heat recuperator to a ?rst
fuel combustion chamber; and a second fuel combustion