for the emergency starting of a turbomachine
Field of the invention
The present invention relates to the field of rotary pyrotechnic actuators, in particular
5 for use in rotating machines, such as for starting up turbine engines. More particularly,
the invention relates to an emergency start system for bringing a turbine engine to its
nominal operating speed within a limited period of time.
Prior art
10 In the case of a multi-engined aircraft, for example, one or more engines can be shut
down during certain flight phases depending on the power requirements. They may then
need to be urgently restarted for an unplanned manoeuvre or because of an engine
fault.
15 Regarding turbine engines in particular, a main start-up system (often an electrical
starter) allows the engine to be activated during normal, routine operating conditions.
Generally, this main start-up system does not allow the nominal speed to be reached
within the space of time required during an emergency.
20 To gather the power required to rotate the turbine engine within a short time,
systems specifically for emergency starts can use pyrotechnic hot-gas generators. This
is the case in systems, as described in FR2862749, which inject the hot gases into the
primary circuit so that they expand in the high-pressure turbine that is rotating the entire
turbine engine. The end of the start-up sequence is equivalent to the ignition of the
25 combustion chamber, which is supplied with air and fuel, and this ignition allows the
turbine engine to take over at the desired power.
A pyrotechnic starter using this principle can be easy to design and is well suited to
single-use applications, like a missile for example. On the other hand, the hot gases
30 coming from the combustion of the propellant can have a detrimental effect on the
mechanical strength of the hot parts of the turbine engine downstream of their injection
apertures. Furthermore, these apertures have to be fitted with a stopper which closes at
the end of the emergency start if the starter is decoupled from the vehicle after use.
Other emergency start systems can use the high-energy gases coming from the
5 pyrotechnic gas generator to actuate a turbine or a displacement motor, as described in
FR299004, in order to rotate the turbine engine.
Generally, a transmission including a gear train adapts the rotational speed of the
starter to that of the turbine engine. In addition, idle rotation of the motor of the starter
10 has to be prevented during normal operating phases of the turbine engine on which said
starter is permanently installed. Indeed, constant rotation of the system would lead to
the starter aging despite not being in operation, and consumes energy owing to the
mechanical or aerodynamic friction in the motor of the starter running idle. Therefore,
this type of starter has to be decoupled from the turbine engine when not in operation,
15 by means of a declutching or freewheeling system in the case of a turbine. These
factors have a detrimental effect on the weight and complexity of the system.
The object of the invention is to propose a system for emergency starting a turbine
engine that makes use of the advantages of a pyrotechnic gas generator while avoiding
20 the drawbacks involved with the known solutions in terms of their size, their complexity,
or their impact on the wear of the turbine engine, in order to fit them permanently.
In addition, despite being discussed in relation to turbine engines, the problem of
causing rotating machines to rotate in order to quickly reach a nominal speed relates to
25 other applications: Therefore, the invention seeks a system for quick start-up that is
simple to incorporate on a rotating machine and is independent in terms of its mode of
operation. In this respect, other applications of this pyrotechnic rotary actuator that
require a high power density in a short period of time are also conceivable, for example,
a standby single-use traction system.
30
Disclosure of the invention
In this regard, the invention relates to a system for emergency starting a turbine
engine, characterised in that it comprises a flyer for driving the turbine engine, said flyer
comprising a drum rigidly connected to a rotary shaft, the axes of symmetry of the drum
5 and the shaft being coincident, the flyer further comprising at least one exhaust nozzle
for ejecting gas, which is positioned on the periphery of the drum and oriented
substantially tangentially to the rotation about said axis, and a pyrotechnic gas
generation device which is installed in the flyer and feeds said at least one exhaust
nozzle, said emergency start system further comprising a support in which the shaft of
10 the flyer rotates, and a volute for recovering the gases, which radially surrounds the flyer
and is rigidly connected to said support.
In other words, the exhaust nozzles produce tangential gas ejection jets that make it
possible to produce a torque on the flyer shaft. The system can thus be used to drive a
15 turbine engine by the shaft of the system being coupled to the input gearing of said
turbine engine. With regard to a single usage, the pyrotechnic device allows gases to be
generated in a chamber upstream of the exhaust nozzles at a high pressure and
temperature, thus creating thrust and therefore the torques required for driving a turbine
engine up to the speeds corresponding to its nominal operating speed. The fact that this
20 pyrotechnic device is installed in the flyer reduces the transfer problems and the losses
during the operation thereof. Moreover, the principle of the flyer means that it can be
positioned on the turbine engine and said turbine engine can drive the flyer during
normal operation, i.e. when the emergency start system is not operating. Indeed, the
flyer creates few friction losses and is not at risk of being used prematurely.
25
Preferably, the gas generation device comprises a solid propellant block. This makes
it simpler to maintain the device. It is thus conceivable to replace the pyrotechnic device
in a simple manner after use.
30 Advantageously, the gas generation device comprises a combustion chamber which
feeds said at least one exhaust nozzle and is formed within the solid propellant block.
In addition, said at least one exhaust nozzle can be a two-dimensional exhaust
nozzle. This allows the flyer to have a more compact design and to be simpler to
produce.
5
Preferably, since the flyer has a direction of rotation defined by the orientation of the
exhaust nozzles, the volute has an opening at one angular sector around the axis of
rotation of the flyer, and the cross section of the stream from the volute changes, by
rotating in the direction of rotation of the flyer, from one edge to the other of the angular
10 sector that is complementary to the angular sector of the opening. Indeed, the shape of
the volute helps to expand the gases exiting the exhaust nozzles, and thus, by means of
the thrust from said nozzles, contributes to the torque provided by the flyer. It is
therefore important to optimise the shape of the volute. In addition, this shape allows the
hot gases that exit the exhaust nozzles to be discharged radially in relation to the axis,
15 thus limiting the extent to which the equipment around the flyer heats up.
Advantageously, the emergency start system comprises a means for igniting the
pyrotechnic gas generation device, which means can be placed in armed or disarmed
mode. In particular, this prevents the system from being ignited at the incorrect time.
20
The invention also relates to a turbine engine comprising a system according to the
invention and a shafl and a transmission means which couples the shaft of the flyer to
the shaft of the turbine engine, the support being held in a stationary manner relative to
a casing of the transmission means. Since the flyer operates independently of the
25 turbine engine, it can be positioned externally, for example attached to the casing of the
auxiliary gearbox, and the turbine engine can be protected from the effect of the ejection
gases. For example, since the turbine engine further comprises an outlet exhaust
nozzle, the volute can open into a pipe that supplies the expanded gases into said outlet
exhaust nozzle of the turbine engine. The pyrotechnic starter can also be mechanically
30 coupled to a main start-up system of said turbine engine.
Brlef description of the drawings
The present invention will be better understood, and other details, features and
advantages of the present invention will become clearer upon reading the following
description, given with reference to the accompanying drawings, in which:
5 Fig. 1 is a perspective view of a flyer of a start-up system according to the
invention.
Fig. 2 is a section through half a flyer of a start-up system according to the
invention, in a plane perpendicular to the axis of rotation and passing through the
exhaust nozzles.
10 Fig. 3 is a longitudinal section through an emergency start system according to
the invention prior to use.
Fig. 4 is a schematic perspective view of one arrangement of the means for
discharging the gases on an emergency start system according to the invention.
Fig. 5 is a schematic section, in a plane perpendicular to the axis of rotation,
15 through the volute for discharging the gases and through the flyer of a system according
to the invention.
Fig. 6 is a longitudinal section through an emergency start system according to
the invention at the start of the ignition thereof.
Fig. 7 is a longitudinal section through an emergency start system according to
20 the invention towards the end of its ignition.
Fig. 8 is a diagram showing how an emergency start system according to the
invention is installed on a turbine engine.
Detailed description of the invention
25 With reference to Fig. 1 to 3, the invention relates to a system capable of rotating a
shaft by producing a torque that is sufficient to start up a turbine engine. This system
comprises a flyer 1 consisting of a cylindrical drum 2 and a rotary shafl 3, which are
rigidly interconnected and have the same axis LL.
30 With the drum 2 having a given width D along the axis of rotation LL, a plurality of
exhaust nozzles 4 are arranged on a narrower strip, of width d, of the peripheral
cylindrical wall 5 of said drum. This strip is located at one side of the cyl~ndricawl all 5 of
the drum 2. With reference to Fig. 1 and 2, if, for example, the lefl transverse surface is
denoted the upper surface 6 of the drum 2 and the right transverse surface is denoted
the lower surface 7 of the drum, the strip in which the exhaust nozzles 4 are located can,
for example, be off-centre as shown, and close to the upper surface 6. The exhaust
nozzles 4 are oriented tangentially to the cylindrical wall 5, all facing the same direction.
This direction is the same as that of the gas jet that should exit said nozzles, and
therefore, by way of reaction, it causes the flyer 1 to rotate during operation in the
opposite direction to that of the gas jet. In the example, the exhaust nozzles 4 are
distributed evenly in azimuth, and there are three of them, with two being visible in Fig.
1.
Still referring to the example, the exhaust nozzles 4 are two-dimensional. This means
that they are defined by their shape in a sectional plane transverse to the axis of rotation
LL. With reference to Fig. 2, the exhaust nozzle 4 forms a duct of length dz that diverges
starting from a neck 8, which has the minimum cross section. This neck 8 is located on a
radius R of the axis LL of the flyer 1, and the exhaust nozzle 4 is oriented along an axis
ZZ that is substantially perpendicular to the radius passing through the neck 8.
Alternatively, it is possible, for example, to design the exhaust nozzles 4 to have an
asymmetric shape, depending on the required ease of design and production. In this
case, said exhaust nozzles are still defined as a diverging duct oriented along an axis
zz.
Via the neck 8, the exhaust nozzle 4 is in communication with a combustion chamber
9, whikh should contain pressurised gas when the flyer 1 is in operation. In the example
shown, this combustion chamber 9 is shared by the three exhaust nozzles 4 positioned
on the cylindrical wall 5 of the drum 2.
seen that the drum 2 forms a cavity between its cylindrical wall 5 and its upper surface 6
and lower surface 7. The internal cavity in the drum 2 is filled by a solid block 10 of a
material designed to produce hot gases when set alight by an ignition device, which is
positioned in the region of the combustion chamber 9 but not shown in the drawings.
5 This material is generally made of solid propellant. The space left free in the drum 2
between the strip occupied by the nozzles 4 and the lower surface 7 is of such a size as
to form a sufficient store of propellant, the combustion of which will generate gases for
the necessary period of time to start up the turbine engine.
10 In the flyer 1, before use, the combustion chamber 9, which feeds the exhaust
nozzles 4 and is intended for receiving the gases produced by the combustion of the
propellant, is dug out of the propellant block 10 and occupies less space in the region of
the exhaust nozzles. Preferably, the exhaust nozzles 4 are sealed by a membrane 11,
which is ejected by the pressure during ignition, thus preventing dust and moisture from
15 entering the combustion chamber 9.
To form an emergency start system of a turbine engine, the flyer 1 is incorporated on
a support 12 comprising bearings 13, 14, in which the shaft 3 rotates. As shown, the
shaft 3 is intended to be coupled to a shaft 15 that drives the turbine engine. In the
20 solution shown, this shaft 15 drives the turbine engine by means of a system of gears
(not shown) to multiply/reduce the correct rotational speed. On the other hand, said
shaft is coupled, for example by means of splines, on the shaft 3 of the flyer 1, and is
designed to breakif the transmitted torque accidentally exceeds a maximum permissible
value.
25
As shown in Fig. 3 to 5, the support 12 includes a volute 16. This volute 16 radially
surrounds the flyer 1. The volute is designed to allow the gases exiting the nozzles 4 to
expand before discharging them. Together with the portion of the support 12 that
surrounds the drum 2, the volute forms a duct 16 which winds around the flyer 1. The
30 internal wall of this duct 16 is open opposite the passage for the exhaust nozzles 4 in
order to collect the gases exiting said nozzles. In the example shown, the radial cross
section of the duct formed by the volute 16 is substantially rectangular.
With reference to Fig. 5, the cross section of the external wall of the volute 16 has a
5 spiral shape around the axis LL of the flyer 1. If cp denotes the azimuth around the axis
LL, the distance from the external wall of the volute 16 to the axis follows a law S(cp),
which increases steadily in this example, as a function of cp between a point A and a
point B in the direction of rotation corresponding to that of the flyer 1 during operation. In
Fig. 5, the direction of rotation is anticlockwise and corresponds to nozzles 4 oriented as
10 in Fig. 2.
In addition, the width of the volute 16 along the axis LL increases in this example
from A to B. This is shown by the sections shown in Fig. 3, 6 and 7, which show the
cross section of the volute 16 in the longitudinal sectional half-planes passing through
15 point A (at the top) and point C (at the bottom), which is an intermediate point between A
and B and shown in Fig. 5. The cross section of the duct formed by the volute 16 thus
changes (increases in the example given here) steadily, according to a law S(cp),
between the points A and B in azimuth cp to guide the expansion of the gases.
20 By means of the opening 17a defined in azimuth between the points B and A, the
volute 16 opens into a conduit 17 for discharging the gases, as shown in Fig. 4 and 5.
Depending on the type of setup, these gases can be discharged directly into the
atmosphere. With reference to Fig. 8, when the system is fitted. on a turbine engine 20,
the conduit 17 can open into the outlet exhaust nozzle 21. This allows the hot gases
25 exiting the flyer 1 to be ejected into an environment already provided to withstand the
temperature conditions of the gases, and also makes it possible to protect the turbine
engine andto take.advantage of pressure conditions that pramote the ejection of said
gases.
30 With reference to Fig 6, when the propellant block 10 is ignited, the combustion
starts in the combustion chamber 9, which is in its initial shape as shown in Fig. 3. The
combustion chamber 9 fills with pressurised gas and is used as a chamber for supplying
the exhaust nozzles 4 with high-energy gas at specified temperature conditions Ti and
pressure conditions Pi. This gas exits through the exhaust nozzles 4, thus generating
thrust and producing a torque that causes the flyer 1 to rotate at a speed w. With
5 reference to Fig. 5, as the combustion progresses, the propellant is used up and the
volume of the combustion chamber 9 of the exhaust nozzles 4 changes in the block 10
until all the propellant has been used. It is routine practice for a person skilled in the art
to determine the initial shape of the combustion chamber 9 and the initial weight of the
propellant block 10 so that the pressure conditions Pi and temperature conditions Ti of
10 the gases in the combustion chamber 9 change during this process to provide the torque
according to a desired variation over the required time.
During the propellant combustion phase, the pressure Pi is sufficiently high for each
of the exhaust nozzles 4 to be primed by a sonic flow to the neck 8. At its outlet cross
15 section, each exhaust nozzle 4 thus creates a gas jet in the direction ZZ tangential to the
neck 8. At the outlet cross section Se of the exhaust nozzle 4, this jet reaches a high
speed Ve, whereas the pressure Pe and the temperature Te of the gases have reduced
compared with those of the gases in the combustion chamber 9. This produces a
tangential force F, also referred to as thrust, in the opposite direction to the speed Ve,
20 which is dependent on the mass flow rate, on the speed of the jet passing therethrough
and on the difference between this outlet pressure Pe of the jet and a static pressure
around the flyer 1 in the volute 16. The torque provided by the flyer 1 on the rotary shaft
3 is the sum of the torques, which, for each exhaust nozzle 4, is this force F multiplied
by the radius R of the neck 8.
25
In a suitable embodiment, the neck 8 is made in and formed, for example, of an
abrad.able, woven and stamped material, such as carbonlceramics or any other device,
so as to reduce as much as possible the transfer of heat by conduction and radiation
from the hot gases to the drum 2 when the propellant is combusted. It goes without
30 saying that the configuration shown in the drawings is just one example. A person skilled
in the art will adapt the number of exhaust nozzles 4, the size thereof and the
distribution thereof in azimuth depending on the torque to be provided and the gas
pressure available in the combustion chamber 9. In addition, although the twodimensional
shape of the exhaust nozzles 4 is advantageous in terms of size for the
system, it is conceivable to use other shapes, in particular an axisymmetric shape.
5
Moreover, the shape of the volute 16 contributes to the output of the exhaust nozzles
4 and thus to the performance of the flyer 1 when ignited. The combustion gases ejected
at the speed Ve, pressure Pe and temperature Te from each of the exhaust nozzles 4
continue to expand in the volute 16 as the exhaust nozzle 4 rotates inside the volute 16,
10 and are then discharged to the outside via the exit conduit 17.
With reference to Fig. 5, the distribution of the cross section of the volute 16
according to the azimuth cp between points A and B is optimised to achieve a good
balance between the level of expansion, which determines the torque provided by the
15 flyer 1, and a gas ejection temperature Te that is compatible with the area surrounding
the system. In particular, this balance takes account of the forced-convection
phenomena in the volute 16, the conduction by the means for fastening the device, and
the thermal radiation from the assembly.
20 In addition, the volute 16 contributes to protecting the equipment surrounding the
flyer 1 by guiding the gases ejected through the exhaust nozzles 4 towards the conduit
17.
Moreover, the protective membrane 11 that seals each exhaust nozzle 4 while the
25 flyer 1 is not in use is designed to be disintegrated upon ignition under the combined
effect of the pressure and the temperature of the gases coming from the combustion of
.%the propellant. The remains of said membrane aw thus discharged naturally with the
gases when the flyer 1 starts up.
30 With reference to Fig. 1 and 3, to trigger the combustion of the propellant block 10,
the start-up system uses an electrical control in the example shown. In the flyer 1, the
device (not shown in the drawings) for igniting the aforementioned propellant block 10 is
connected to a circular contact track 18 flush with the surface of the cylindrical wall 5 of
the drum 2. An electric sliding contact breaker 19 is positioned in contact with the
contact track 18 on the support 12 to send an electric current to the ignition device. The
5 contact breaker 19 is in turn connected to a control system (not shown) that sends the
current, via said ignition device, to set the propellant alight in the event of an emergency
start.
Preferably, the system for controlling the ignition device is designed to be armed, i.e.
10 ready to transmit a sufficient current to trigger the combustion, or disarmed, i.e.
prevented from doing so. The disarmed position is advantageous in that it avoids
accidental ignitions.
The invention also covers the possibility of using other ways of igniting the propellant
15 block 10, for example a wireless connection using optical or laser means.
With reference to Fig. 8, an advantageous setup for a turbine engine 20 involves
attaching the support 12 on the auxiliary gearbox casing 22, shown here upstream of the
turbine engine 20. As shown in Fig. 8, this optionally allows the pyrotechnic emergency
20 starter to be connected in series, at its other end, to the main starter 23 of the turbine
engine. This main, generally electrical starter 23 is typically used to start up the turbine
engine 20 normally.
It should be noted that the flyer 1 does not introduce extra gearing. Moreover, said
25 flyer is a small rotary part having low inertia and low aerodynamic drag. Therefore, it can
be positioned easily in series between the main starter 23 and the turbine engine 20,
. . ready for possible emergency use without creating significant performance losses. YU
Owing to these different features, the operating principle of the flyer 1 as a means for
30 emergency starting an aircraft turbine engine 20, in a setup as shown in Fig. 8,
corresponds to the choice between three states described below.
A first, disarmed state corresponds to the case in which the turbine engine 20 is
operating normally. The engine is used, for example, together with the other turbine
engines of the aircraft to provide the nominal power for the current flight conditions. In
this case, the shaft 15 rotates the flyer 1. For its part, the system for controlling the
device for igniting the propellant block 10 is disarmed. Optionally, the control system
either continuously sends or intermittently sends upon request a weak electrical signal to
the device for igniting the propellant block 10 in order to detect possible interruptions in
the control chain. If a fault is confirmed by the logic of this system, the fault is processed
accordingly and a suitable signal is generated.
This first disarmed state corresponds exactly to the case in which the turbine engine
is starting up normally. In this case, it is the main starter that rotates the flyer 1 at the
same time as the turbine engine 20.
The second, armed state corresponds to the flight conditions in which the turbine
engine 20 is put on standby compared with the other turbine engines of the aircraft. In
this case, either the turbine engine 20 is idling and rotating the flyer 1, or it is simply
stopped. The system for controlling the device for igniting the propellant block 10 is
20 armed in this case. The electrical connection between the contact breaker 19 and the
contact track 18 still allows potential anomalies to be detected on the emergency start
system, and for the fault to be processed accordingly and suitable signals generated.
The third, ignited state corresponds to the case in which an emergency start
I
I
25 command is sent. The ignition command can only be effective if the system for
controlling the device for igniting the propellant block 10 is armed. The design of the
h installed system does not allow the state to change directly from the first to the third. .*
By following the ignition phases of the flyer 1 as described with reference to Fig. 6
30 and 7, it is now the flyer 1 that produces a torque and drives the turbine engine 20. The
entire system is designed to allow the rotational speed w of the flyer 1 to quickly reach
I
the necessary speed for the turbine engine to provide the expected power. In addition,
the main starter is also activated, as are the ignition system and fuel metering system of
the turbine engine, according to the established laws to ensure said turbine engine is
brought to speed once the flyer 1 has finished operating.
5
The described emergency start system is not limited to the configuration shown in
Fig. 8 or even to the emergency starting of a turbine engine. As set out at the outset, it
can for example be used as, a standby single-use traction system to provide a high
power density in a short period of time. It is also conceivable to design a setup using
10 several systems according to the invention coupled to the same shaft. It may thus be
advantageous to produce just one type of system and to adjust how many of them are
fitted depending on the required power.

Claims
1. System for emergency starting a turbine engine, characterised in that it comprises
a flyer (I) for driving the turbine engine (20), said flyer comprising a drum (2)
5 rigidly connected to a rotary shaft (3), the axes of symmetry (LL) of the drum (2)
and of the shaft (3) being coincident, the flyer further comprising at least one
exhaust nozzle (4) for ejecting gas, which is positioned on the periphery of the
drum (2) and oriented substantially tangentially to the rotation about said axis
(LL), and a pyrotechnic gas generation device (10, 9 18) which is installed in the
10 flyer (1) and feeds said at least one exhaust nozzle (4), said emergency start
system further comprising a support (12) in which the shaft (3) of the flyer rotates,
and a volute (16) for recovering the gases, which radially surrounds the flyer (1)
and is rigidly connected to said support (12).
15 2. System according to the preceding claim, wherein the gas generation device (10,
9, 18) comprises a solid propellant block (10).
3. System according to the preceding claim, wherein a combustion chamber (9)
feeding said at least one exhaust nozzle (4) is formed in the solid propellant block
20 (10).
4. System according to any of the preceding claims, wherein said at least one
exhaust nozzle (4) is a two-dimensional exhaust nozzle.
25 5. System according to any of the preceding claims, wherein, since the flyer (I) has
a direction of rotation def~ned by the orientation of the exhaust nozzles (4), the
volute (16) has an opening (17a) at one angular sector (B-A) around the axis of
rotation (LL) of the flyer (I)an,d the cross section (Sv(cp)) of the stream from the
volute (16) changes steadily, by rotating in the direction of rotation of the flyer (I),
30 from one edge to the other of the angular sector (A-B) that is complementary to
the angular sector of the opening (17a).
6. sydcrr) according '3
igniting 111- pyroiichiiic gas ge?,eiaiiciril c!evicc: (101, it beirizy lonssibie io p!ace fait1
ig~-~iiiorin?e ails in armed mode or cii-acitv;ieri rriotie.
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. .
7 . ileabi12e engine (:ompr!f:flg a s!/ster;-I %(:i:~Tdir~icg all\! 0":1-1c: precer!ii:c!- . riairrrc-,
. , said iiirbine el.\gille (20)c o!n\:,risir.irj 2, ;l-,z:H ;;nc! a transii-!isslo~-;n~e an:; (15) vvhic:h,
cailpies :;haft (3)o f ii,[e jlyer (?)i o the sY.iaii cf ike i~srbiiiee iigirie, lkie si.!ppor'i
(12) being heid in a s(atior~ar)i n-fanner rektive lo a casing (22) of the iransirfiission
1 0 rnearis.
. .
8, l - ~ - !el~~gil~n~e~.~ c r~;~~ j~~i" ~i~~k!;?i rp~i,ec~;c~jdi t,ig c;!ainr], .f~~rtl.~ce~a> i~~t~:~ii?d.?~ i