The present invention relates to the field of rotary pyrotechnic actuators, in particular 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.
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.
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.
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 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 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 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 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, 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 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 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.
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 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 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 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 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.
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.
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.
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 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, 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.
The invention also relates to a turbine engine comprising a system according to the invention and a shaft 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 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 coupled to a main start-up system of said turbine engine.
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:
With reference to
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 cylindrical wall 5 of the drum 2. With reference to
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
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, which 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.
Therefore, a gas generator is required in order to fill the combustion chamber 9 with pressurised gas. With reference to
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 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 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 break if the transmitted torque accidentally exceeds a maximum permissible value.
As shown in
With reference to
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
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
With reference to
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 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, 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.
In a suitable embodiment, the neck 8 is made in and formed, for example, of an abradable, woven and stamped material, such as carbon/ceramics 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 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 two-dimensional 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.
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, and are then discharged to the outside via the exit conduit 17.
With reference to
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 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 are thus discharged naturally with the gases when the flyer 1 starts up.
With reference to
Preferably, the system for controlling the ignition device is designed to be armed, i.e. 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 block 10, for example a wireless connection using optical or laser means.
With reference to
It should be noted that the flyer 1 does not introduce extra gearing. Moreover, said 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.
Owing to these different features, the operating principle of the flyer 1 as a means for emergency starting an aircraft turbine engine 20, in a setup as shown in
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 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 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 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
The described emergency start system is not limited to the configuration shown in
Number | Date | Country | Kind |
---|---|---|---|
1451020 | Feb 2014 | FR | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/FR2015/050290 | 2/6/2015 | WO | 00 |