EP3835711A1 - Ignition system for a rocket propellant charge - Google Patents

Abstract

The invention relates to an ignition system (10) for a propellant charge comprising: an enclosure (101) in which the propellant charge (104) is present, the enclosure comprising a bottom (102) and an outlet for the propellant (104). 'exhaust (103) facing the bottom; and a pyrotechnic igniter (110) fixed to the bottom of the enclosure, the igniter comprising a body delimiting an initiation chamber in which are present a pyrotechnic charge, an initiator capable of initiating said charge and a wedging element to maintain the pyrotechnic charge in a predetermined position relative to the initiator, the igniter (110) being able to eject the gases resulting from the combustion of the pyrotechnic charge towards the propellant charge (104) in order to ignite it. The invention also relates to a system for controlling the combustion of a propellant charge.

Description

Technical area

The invention relates to the general field of systems for igniting a charge of propellant. It relates in particular to a system for controlling the combustion of such a charge.

Prior art

There are known systems for igniting a propellant charge which comprise an igniter in which is present a pyrotechnic powder which can be ignited by an initiator placed in the vicinity thereof. The initiation of the pyrotechnic powder generates hot gases which come into contact with the charge of propellant to ignite it.

As it is difficult to control the interaction between the initiator and the pyrotechnic powder, and the gases resulting from the combustion of the powder can transport particles, the known systems are difficult to model and do not allow ignition to be obtained. and therefore combustion of the charge which is repeatable. These drawbacks make it difficult to control the combustion of a propellant charge, for example to determine its combustion rate with precision.

There is therefore a need for an ignition system for a propellant charge which does not have the aforementioned drawbacks.

Disclosure of the invention

• une enceinte dans laquelle est présent le chargement de propergol, l'enceinte comprenant un fond et une sortie d'échappement en regard du fond ;
• un allumeur pyrotechnique fixé au fond de l'enceinte, l'allumeur comprenant un corps délimitant une chambre d'initiation dans laquelle sont présents un chargement pyrotechnique, un initiateur apte à initier ledit chargement et un élément de calage configuré pour maintenir le chargement pyrotechnique dans une position prédéterminée par rapport à l'initiateur, l'allumeur étant apte à éjecter les gaz issus de la combustion du chargement pyrotechnique vers le chargement de propergol afin de l'allumer.

To this end, the subject of the invention is a system for igniting a charge of propellant comprising:

• an enclosure in which the propellant charge is present, the enclosure comprising a bottom and an exhaust outlet facing the bottom;
• a pyrotechnic igniter fixed to the bottom of the enclosure, the igniter comprising a body delimiting an initiation chamber in which are present a pyrotechnic charge, an initiator capable of initiating said charge and a wedging element configured to hold the pyrotechnic charge in a predetermined position relative to the initiator, the igniter being able to eject the gases from from the combustion of the pyrotechnic charge to the propellant charge in order to ignite it.

The ignition system according to the invention comprises in particular a wedging element which makes it possible to maintain the pyrotechnic charge in position in the initiation chamber of the igniter, which ensures greater repeatability in the ignition of the propellant charge. . This ignition system is thus particularly advantageous for controlling the combustion of a charge of propellant.

In an exemplary embodiment, the pyrotechnic charge may comprise at least one pyrotechnic block in the form of a perforated disc centered on an axis of the pyrotechnic igniter and which defines a channel opening towards an outlet of the igniter. The use of at least one pyrotechnic block having the aforementioned form makes it possible to further improve the repeatability of the ignition. In particular, several blocks can be placed side by side centered on the same axis. The blocks can be obtained from a pyrotechnic powder which has been compacted.

In an exemplary embodiment, the wedging element may comprise an elastic return element, for example a spring. The use of an elastic return element makes it possible to have an igniter at low cost. Such a wedging element makes it possible to maintain a restoring force against the pyrotechnic charge during ignition. Alternatively, the wedge element may be a wedge.

In an exemplary embodiment, the pyrotechnic igniter may further comprise a cover between the pyrotechnic charge and an outlet of said igniter configured to break when the pressure in the initiation chamber reaches a predetermined threshold. The use of such a cap further improves the repeatability of the ignition of the propellant charge. In addition, the seal makes it possible to protect the pyrotechnic charge from the outside when the igniter is stored, which increases its lifespan.

In an exemplary embodiment, the bottom of the enclosure may have a shoulder which defines a housing in which the igniter is tightly mounted. During ignition, the generation of gas in the igniter plates it at the bottom of the enclosure and it is held in place in the housing. This arrangement makes it possible to simply fix the igniter and also to allow easy replacement of the latter after use.

In an exemplary embodiment, a seal may be present between the bottom of the enclosure and the igniter. The seal between the igniter and the bottom makes it possible to further improve the repeatability of the ignition by preventing the gases from escaping through the bottom of the enclosure. The gasket also provides flexibility in fixing the igniter to the bottom to dampen vibrations.

In an exemplary embodiment, the igniter may further comprise a diffuser provided with vents for ejecting the gases resulting from the combustion of the pyrotechnic charge towards the propellant charge. The diffuser may have vents distributed circumferentially around the diffuser, the diffuser having for example a cylindrical shape. The use of such a diffuser makes it possible to direct the hot gases uniformly towards the propellant charge, and to further improve the repeatability of the ignition.

The invention also relates to a system for controlling the combustion of a propellant charge, comprising: a system for igniting a propellant charge such as that presented above, at least one pressure sensor present in the enclosure, and a processing unit configured to calculate a combustion rate of the propellant charge from the pressure measured by the pressure sensor. This control system takes advantage of the repeatability advantages of the ignition system to accurately calculate the burn rate of a propellant charge.

Brief description of the drawings

• [Fig. 1] La figure 1 est une vue schématique en coupe d'un système de contrôle de la combustion d'un chargement de propergol incorporant un système d'allumage selon un mode de réalisation de l'invention.
• [Fig. 2] La figure 2 montre une vue en perspective d'un allumeur selon un mode de réalisation de l'invention.
• [Fig. 3] La figure 3 est une vue éclatée de l'allumeur de la figure 2.
• [Fig. 4] La figure 4 est une vue en coupe de l'allumeur de la figure 2.
• [Fig. 5] La figure 5 est une vue similaire à celle de la figure 1, où l'allumeur a été déclenché.
• [Fig. 6] La figure 6 est une vue en perspective d'un bloc pyrotechnique selon un mode de réalisation.

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an exemplary embodiment thereof without any limiting nature. In the figures:

• [ Fig. 1 ] The figure 1 is a schematic sectional view of a system for controlling the combustion of a propellant charge incorporating an ignition system according to one embodiment of the invention.
• [ Fig. 2 ] The figure 2 shows a perspective view of an igniter according to one embodiment of the invention.
• [ Fig. 3 ] The figure 3 is an exploded view of the igniter of the figure 2 .
• [ Fig. 4 ] The figure 4 is a sectional view of the igniter of the figure 2 .
• [ Fig. 5 ] The figure 5 is a view similar to that of the figure 1 , where the igniter was triggered.
• [ Fig. 6 ] The figure 6 is a perspective view of a pyrotechnic block according to one embodiment.

Description of the embodiments

The figure 1 shows a schematic sectional view of a control system 1 of the combustion of a propellant charge, which comprises an ignition system 10 of a propellant charge, a pressure sensor 20 and a processing unit 30 connected in particular to the pressure sensor 20 by a cable 31.

The ignition system 10 comprises an enclosure 101, here of cylindrical shape around an axis A, having a bottom 102 and an exhaust outlet 103 facing the bottom 102. The exhaust outlet 103 is on the side opposite to the bottom 102. A charge of propellant 104 is present in the enclosure 101 on the wall thereof. The propellant charge 104 can for example be poured directly into the enclosure using known means or introduced in the form of one or more blocks. The propellant charge 104 here has a generally cylindrical shape.

The ignition system 10 further comprises a pyrotechnic igniter 110 which is here mounted tightly in the bottom 102 of the enclosure 101. In particular, the bottom 102 here has a shoulder 102a defining a housing 102b in which the igniter 110 is located. mounted. During ignition, the igniter 110 is in abutment on the shoulder 102a allowing it to be held in place in the housing 102b. A seal 105 may be present around the igniter 110 between the bottom 102 and the igniter 110. The igniter 110 can alternatively be screwed directly into the bottom 102 of the enclosure 101.

The ignition system 10 may further include an axial locking element 106 of the igniter 110. For example, such an axial locking element of the igniter may include a nut and a wedge, able to exert pressure. on the initiator so as to keep it pressed against the bottom 102 of the enclosure 101. The axial locking element 106 is located on the side opposite the shoulder 102a and allows the igniter 110 to be pressed against the shoulder 102a.

The figures 2 to 4 show different views of the igniter 110 which will now be described in more detail.

The igniter 110 is here of cylindrical geometry around an axis B (which coincides with the axis A of the ignition system 10 when the igniter is mounted in said system). It comprises, in this example, a body 111 having a first part 111a which is intended to be mounted in the bottom 102, and a second part 111b which is mounted in the first part 111a, for example by crimping or screwing. In this example, the first part 111a thus has a maximum diameter greater than the maximum diameter of the second part 111b. This arrangement allows easy and inexpensive assembly, while ensuring greater reliability of the igniter 110.

The body 111 defines an initiation chamber 112 ( figure 4 ) in which are present a pyrotechnic charge 113 and an initiator 114. The pyrotechnic charge 113 is here composed of a plurality of pyrotechnic blocks 113a each taking the form of a perforated disc. The pyrotechnic blocks 113a are centered on the axis B of the igniter 110 and have an external diameter substantially equal to that of the initiation chamber 112. The openings of the pyrotechnic blocks 113a together define a channel 113b which opens towards an outlet of igniter 110. Channel 113b is centered on axis B and located opposite initiator 114.

In a variant, each pyrotechnic block 113a can have the shape of a solid disc (without central opening) and include grooves 121 which allow the passage of gases towards the periphery of the blocks, and a clearance between the blocks and the body 111 which allows the gases to reach the outlet of the igniter. The figure 6 represents a pyrotechnic block 113a according to this variant.

In this example, the body 111, and more precisely the second part 111b of the body, comprises a diffuser 115 in the form of a tube opening into the initiation chamber 112 at one end and which is closed at the other end. More precisely, in this example, the diffuser 115 is located in the extension of the channel 113b formed by the pyrotechnic blocks 113a. In the example illustrated, the internal diameter D1 of the diffuser 115 is substantially equal to the diameter D2 of the channel 113b. The diffuser 115 makes it possible to project the hot gases resulting from the combustion of the pyrotechnic charge 113 towards the propellant charge 104. The diffuser 115 here comprises vents 115a in the form of holes distributed circumferentially around the diffuser 115. The axis of each vent 115a is here perpendicular to the axis B. The axis of each vent may alternatively form an angle of between 0 ° and 90 ° with the axis B to project the gases resulting from the combustion of the pyrotechnic charge in a different direction towards the propellant charge 104. Preferably, the vents 115a are directed directly towards the propellant charge. The vents 115a allow a controlled diffusion of the hot gases towards the propellant charge, which allows even greater repeatability of the ignition of the charge.

According to the invention, the igniter 110 comprises a wedging element such as a spring 116 configured to maintain the pyrotechnic charge 113 in a predetermined position relative to the initiator 114. In the example illustrated, the spring 116 takes on bearing on the one hand on a bottom wall 117a of the igniter and on the other hand on the pyrotechnic charge 113 to press the latter against a wall 117b of the igniter 110 opposite to the bottom wall 117a. The wedging element (spring 116) is here arranged around the initiator 114, which allows it not to disturb the initiation and combustion of the pyrotechnic charge 113. Other configurations are possible, in particular the pyrotechnic charge. 113 may not be pressed directly against the wall 117b. It is also possible to use other types of wedging elements, for example a wedge.

The initiator 114 can be crimped directly into the bottom wall 117a, or else screwed into the latter. The initiator 114 here comprises two electrical conductors 114a to enable it to be triggered using an electric current. A centering element 114b is here provided to keep the initiator 114 in position in the igniter 110.

In this example, a cover 118 is positioned between the pyrotechnic charge 113 and the diffuser 115 which is configured to rupture when the pressure in the initiation chamber 112 reaches a predetermined threshold. The cover 118 can be metallic, for example aluminum, brass, copper or stainless steel. The cover 118 may have a thickness of between 50 μm and 500 μm depending on the material and the predetermined pressure threshold chosen.

The igniter 110 is, in this example, connected to the processing unit 30 by a cable 32 connected to the conductors 114a. The processing unit 30 can then also play the role of control unit for the igniter 110 and make it possible to trigger the latter. Alternatively, a separate control unit may be employed to control the ignition of the igniter 110.

The pressure sensor 20 is here fixed in the bottom of the enclosure 102 and opens out inside the enclosure 102 in order to measure the pressure there. The processing unit 30 can thus calculate the combustion rate of the propellant charge 104 from the pressure measurement.

The figure 5 illustrates an ignition sequence of the control system 1. First of all, the processing unit 30 circulates an electric current via the cable 32 in the initiator 114, which has the effect of triggering the initiator 114 which will igniting the pyrotechnic charge 113. The hot gases resulting from the combustion of the pyrotechnic charge 113 increase the pressure in the initiation chamber 112 up to the pressure threshold at which the cap 118 is broken. The hot pressurized gases can then enter the diffuser 115 and be ejected through the vents 115a in the direction of the propellant charge 104 to ignite it. Once ignited, the charge of propellant 104 is consumed and the gases escape through the exhaust outlet 103 of the ignition system 10. Throughout the ignition sequence and afterwards, the pressure sensor 20 records the variations in pressure. the pressure in the enclosure 102 as a function of time and transmits them to the processing unit 30 which can calculate the combustion rate of the propellant charge 104 accurately and repeatably.

It will be noted that in order to control a loading of propellant, the ignition system can be positioned vertically with the exhaust outlet 103 directed upwards as illustrated on the diagrams. figures 1 and 4 , or even horizontally.

Claims (8)

Ignition system (10) of a propellant charge comprising: - an enclosure (101) in which the propellant charge (104) is present, the enclosure comprising a bottom (102) and an exhaust outlet (103) facing the bottom; and - a pyrotechnic igniter (110) fixed to the bottom of the enclosure, the igniter comprising a body (111) delimiting an initiation chamber (112) in which are present a pyrotechnic charge (113), an initiator (114) suitable to initiate said charge and a wedging element (116) configured to maintain the pyrotechnic charge in a predetermined position relative to the initiator, the igniter being able to eject the gases resulting from the combustion of the pyrotechnic charge (113) towards the charging of propellant (104) in order to ignite it. System according to Claim 1, in which the pyrotechnic charge (113) comprises at least one pyrotechnic block (113a) in the form of a perforated disc centered on an axis (B) of the pyrotechnic igniter and which defines a channel (113b ) leading to an outlet of the igniter. A system according to claim 1 or claim 2, wherein the wedge member (116) comprises an elastic return member. A system according to any one of claims 1 to 3, wherein the pyrotechnic igniter (110) further comprises a seal (118) between the pyrotechnic charge (113) and an outlet of said igniter configured to rupture when pressure in the igniter. initiation chamber reaches a predetermined threshold. A system according to any one of claims 1 to 4, wherein the bottom (102) of the enclosure has a shoulder (102a) which defines a housing (102b) in which the igniter (110) is clamped. System according to any one of claims 1 to 5, in which a seal (105) is present between the bottom (102) of the enclosure (101) and the igniter (110). A system according to any one of claims 1 to 6, wherein the igniter (110) further comprises a diffuser (115) provided with vents (115a) to eject the gases resulting from the combustion of the pyrotechnic charge (113) towards the propellant charge (104). System (1) for controlling the combustion of a propellant charge (104), comprising: an ignition system (10) of a propellant charge according to any one of claims 1 to 7, at least one sensor pressure (20) present in the enclosure (101), and a processing unit (30) configured to calculate a combustion rate of the propellant charge (104) from the pressure measured by the pressure sensor (20) .

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