NL2035489B1

NL2035489B1 - Efficient thermal protection for a gas generator

Info

Publication number: NL2035489B1
Application number: NL2035489A
Authority: NL
Inventors: Thea Hogedoorn Armanda; Marie Sanders Hubertus; Ravnan Sigurd
Original assignee: Hdes Service & Eng B V
Priority date: 2023-07-27
Filing date: 2023-07-27
Publication date: 2025-02-10
Also published as: WO2025023839A1

Abstract

Title: EFFICIENT THERMAL PROTECTION FOR A GAS GENERATOR Aspects of the present disclosure relate to a gas generator (1) comprising a housing (2) having an outlet (3) for releasing generated gas, and a main charge (4), contained in the housing, the charge comprising a mixture (m) that generates a target gas (G) upon thermal decomposition and that Will undergo a self-sustained exothermal decomposition reaction after ignition. The generator further comprises a thermal protection layer (5) that extends between the charge and the housing, whereby the thermal protection layer is comprised of a composition that generates target gas upon thermal decomposition by absorption of heat from the thermal decomposition reaction of the main charge. Further aspects relate to consumables for the generator. [FIG 2]

Description

Title: EFFICIENT THERMAL PROTECTION FOR A GAS

GENERATOR

TECHNICAL FIELD AND BACKGROUND

The present disclosure relates to a gas generator, typically a cool gas generator, configured for release of a target gas upon activation. The disclosure further relates to gas generating consumables for the generator.

Chemical gas generators are widely used. For example, in the field of pressurization, inflation of structures, and for emergency applications including but not limited to fire extinguishing, inflation of life vests, and to supply of oxygen/breathable air. Three types can be distinguished, gas generators that produce a hot mixture of gasses, gas generators that produce a hot near pure gas (e.g. oxygen, nitrogen etc.) and cool gas generators, which can produce a pure gas or mixture of gasses at or near ambient temperature.

Known hot and cool pure gas generating devices typically operate on the principle of activating a solid material comprising a mixture including a chemical compound that thermally degrades under release of a target gas, e.g. NaClO; for an oxygen generator.

To sustain an endothermic decomposition process, the mixture typically includes one or more constituents that generate heat by exothermic reaction with part of the generated gas, e.g. metal particles. Cool gas generators are able to release the gas as generated at or close to ambient temperature by providing internal heat dissipation.

Conversely, propellant gas generators operate with the aim of producing a maximum amount of gas using exothermally decomposing compositions.

EP1409082A1 discloses a chemical oxygen generator to produce cool oxygen gas comprising: a. a charge housing, b. a solid but porous charge contained in the said housing, the charge being made of a chemical mixture that generates oxygen upon decomposition and that will undergo a self- sustained exothermal decomposition after initiation, the said charge containing at most 3.0 wt.% of binder material.

In known configurations, hot remnants remain within the generator after firing. These remnants and/or the heat generated during operation induce a large thermal load onto the housing, which can heat up to 300 °C. To withstand the thermal load, temperature-resistant or insulating materials are added to the casing. These materials can be costly, heavy and/or bulky.

SUMMARY

Aspects of the present disclosure relate to a gas generator configured to mitigate one or more of the disadvantages associated with known gas generators.

The gas generator comprises at least a housing having an outlet for releasing generated gas. Situated within the housing is a main charge.

The charge comprises a mixture that generates a gas upon thermal decomposition. The mixture will undergo a self-sustained decomposition reaction after ignition whereby target gas is generated.

To mitigate heat transfer towards an exterior wall of the housing, the generator is further provided with a thermal protection layer that absorbs heat generated by decomposition of the main charge. The thermal protection layer extends between the charge and an inner face of the housing. Absorbing heat from the decomposition after ignition mitigates heat transfer to the generator wall.

The chemically decomposing thermal protection layer, as provided along the interior of the generator, absorbs heat by chemical decomposition.

As explained hereinbelow in more detail, this can advantageously produce an additional gas output which contributes to the overall output of the generator. This advantageously allows the use of comparatively less heat resistant outer walls and/or to reduce or even eliminate exterior thermal insulation, which in addition to cost, can advantageously reduce weight and/or volume of the generator. Note that the organic constituents (e.g. insulating rubber shells) in, for example, solid propellant gas generators generate gas but not under absorption of heat. On the contrary, the combustion is exothermic and generates additional heat.

In addition, the gas produced by the thermal protection layer can additionally contribute to an overall output volume or rate of the generator.

As explained in more detail below, the output gas can be a mixture or a single, pure gas composition. Accordingly, in addition to increased thermal protection, the present disclosure can provide one or more of increased output volume and/or rate, e.g. for actuation or inflation applications such as an inflation of a balloon or a life raft, or for increased output volume over an increased duration, such as for (medical/emergency) oxygen generators.

Typically, the thermal protection layer is comprised or essentially formed of a composition that generates gas upon thermal decomposition by absorption of heat from the thermal decomposition reaction of the main charge. Of course, the layer may comprise a mixture of gas generating compositions and/or additives including but not limited to binders.

The thermal protection layer acts as a consumable thermal protection shield that is activated by exposure to heat above a decomposition temperature, e.g. by contact with comparatively hot gas formed by the main charge and/or by absorption of (radiative or conductive) heat from slag remnants or from the main charge during gas generation.

Inventors found that forming the thermal protection layer of a composition that generates gas upon thermal decomposition by absorption of heat, e.g. residual heat from the main charge during decomposition or slag remnants thereof, advantageously allows the protection layer to be comparatively thin, especially as compared to conventional thermal insulation layers. For example, use of the thermal protection layer as disclosed herein can advantageously mitigate or even eliminate a need for conventional thermal insulation, e.g. refractory liners such as ceramic foams/fibers. Mitigating/eliminating a need for conventional thermal insulation can increase the performance of the gas generator as determined in amount of gas generated per overall generator volume or weight. At the same time, the thermal protection layer as disclosed herein can advantageously reduce the temperature of the generator housing to the point where it is safe to touch and/or where the housing itself can be formed of less resilient and/or thinner materials, e.g. aluminum, polymers, and/or polymer composites without degrading following generator ignition.

A number of different materials are known for use in the thermal protection layer that forms a gas upon absorption of heat. Suitable materials include materials that endothermically decompose with release of gaseous decomposition products. Preferably, target gaseous products. Compositions that undergo thermal decomposition resulting in the release of gas can provide a large heat sink per unit volume (as compared to a thermal mass per same unit volume) with an additional benefit of increased gas output of the generator.

In some preferred embodiments, the composition of the thermal protection layer and the mixture of the main charge generate the same gas or gas mixture upon thermal decomposition. The main charge and thermal protection layer can be selected independently, e.g. each generating a different type of gas. Alternatively, or in addition, the main composition and/or the thermal protection layer can comprise a mixture of materials or a gradient to release a mixed gas output, for example O2/N2, and/or a gas output with temporal variation in composition.

The output temperature of the gas generator can be tuned for a specific application. In some variations, the gas generator can be what is referred to as a cool gas generator. A cool gas generator can release gas at a temperature not exceeding ambient temperature plus a small margin,

typically < 30°C. For example, the temperature of the gas released can be < 50°C, preferably < 40°C, or even < 30°C (assuming ambient of 20-25°C). As such, a gas generated by the generator can be used in temperature-sensitive applications, e.g. as breathable gas (e.g. O2 or O2/Ns or other mixes) for 5 respirator/ventilator applications.

In general, an upper limit for the gas output temperature can be defined by an acceptable temperature for systems downstream of the gas generator. In practice, an upper limit can be about 100 degrees Celsius.

To cool the outgoing gas, the generator can be provided with a filter and cooler assembly. The filter and cooler assembly (porous) can be advantageously positioned within the same housing as the main charge on a flow path towards the outlet. The filter and cooler have a mass to cool the generated gas passing towards the exit. Advantageously, the filter can also filter out unwanted gasses and particles. Optionally, the filter can be provided in a separate housing that is fluidly connectable to the outlet of the generator. Integrating the filter within same housing reduces the dimension/weight of the device and/or reduces a risk of user error (e.g. removing or connecting an incorrect filter).

It will be appreciated that the filter typically only needs to cool a minor fraction of the overall generated gas, as the majority of the gas output can already be cooled by passing through/by the remainder of the virgin (unreacted) main charge. Suitable compositions are known in the field, e.g. quartz/sand. In some variations, the filter additionally performs one or more of the following objectives: catching slag particles, which may be carried with the generated gas flow; scavenging other gas impurities that contaminate the target gas flow and that were not scavenged by special additives in the main charge; converting (e.g. catalytically) contaminating compounds to less harmful compounds, e. g conversion of CO to CO:.

In a preferred variation, the filter is at least in part comprised of a composition that generates gas upon thermal decomposition due to absorption of heat from the thermal decomposition reaction of the main charge. It will be appreciated that the composition may be the same as in the thermal protection layer. Accordingly, in some variations, the thermal protection layer can be understood as extending between the main charge and the outlet.

Conceptually, the housing of the generator can be understood as a reactor having an internal volume bound by external walls. Within the housing, there is provided the gas generating charge and the thermal protection as disclosed herein. Optionally but preferably, the housing further comprises a filter assembly, which may at least in part be formed of a composition that generates gas upon thermal decomposition due to absorption of heat from the thermal decomposition reaction of the main charge.

In some variations, the thermal protection layer and the main charge are formed as an integrally formed part or set of parts for inserting into the housing. This can reduce the complexity of generator (re)filling. The parts can be pressed-formed into a desired shape.

As detailed further hereinbelow, the main charge, protective layer, and optional additional layers, such as the filter, can be understood as forming one or more cartridges configured to be inserted into the generator prior to use. After use, the remnants (e.g. burnt slag) can be removed and replaced with fresh cartridges.

It will be appreciated that the main charge is preferably a porous grain structure, as known in the field. The grain structures may comprise additives including but not limited to catalysts to convert undesired gaseous products. For examples, reference is made to EP1409082A1, which is hereby incorporated by reference.

To increase mechanical integrity, a binder can be added to the main charge, the thermal protection layer, or both. The binder is preferably from the following group: inorganic binders: particularly sodium silicate

(Na:Si03) or potassium silicate (K2S103) or a mixture thereof. In contrast to

EP1409082A1 an amount of binder can be > 3.0 wt% e.g. about 5 wt% or > 5 wt% (as respectively based on a mass of the main charge / the thermal protection layer). To minimize the amount of dead material within the system, the amount of binder is typically as low as possible. An upper limit can be < 10 wt%. A lower limit can be 1 wt%. In some embodiments, binder can he absent.

In another or further embodiment, a liner can be provided that extends between the main charge and the thermal protection layer. The liner can mitigate contact between the main charge/ thermal protection layer, e.g. prior to and during press forming. The liner can be made of a non- reactive metal.

Typically the mixture of the main charge includes granules with at least a first constituent thermally decomposing resulting in the release of the target gas and a second constituent (e.g. a metal particle) reacting with part of released gas under generation of heat.

To allow passage of formed gas towards the outlet, the main charge has a porosity towards the outlet. The porosity provides further heat exchange between formed gas and virgin portions of the main charge, which cools the gas and pre-heats the main charge.

The thermal protection layer is preferably a continuous layer, e.g. a non-porous or comparatively less porous layer, that extends alongside the walls of the generator up to the filter or the outlet. The thickness of the thermal protection layer can increase with increasing amount of the main charge. Preferably the thermal protection layer is as thin as functionally possible. Typically, the thermal protection layer has a thickness > 1.0 mm.

Inventors found that a layer > 1 mm can effectively reduce wall temperature to a point allowing use of single-walled Al, plastic or composite walls as opposed to conventional titanium-based walls, multi-layered walls, and/or thermally insulated walls. Typically, the thermal protection layer has a thickness not exceeding 20 mm, but more than 0.2 mm, for example, in a range of 0.5-10 mm, 1-6 mm, or 2-4 mm.

Advantageously, portions of the housing bordering the main charge can be a single-walled structure. The walls can be formed of a plastic composition or plastic composite. Alternatively, or in addition, the walls can be formed of aluminum, e.g. thin walls (< 2 mm). Advantageously the disclosure can provide a gas generator having a wall structure that can be without additional thermal insulation (refractory, aerogel, fibrous insulation, etc.).

In some embodiments, the main charge and the thermal protection layer are configured to generate: a) oxygen gas; b) carbon dioxide gas; c) nitrogen gas; and/or d) hydrogen gas. Optionally the gas generator can be configured to generate a mixture of two or more of a) oxygen gas; b) carbon dioxide gas; c) nitrogen gas; d) hydrogen gas. For example, an N»2/0»> mixture.

In some embodiments, the gas generator can further comprise an inert thermal insulation sheet extending between the housing and the thermal protection layer. Said insulation can have a thickness < 20 mm, preferably not exceeding 5 mm. While the insulation need not be needed to protect the walls from excessive heat, inventors found that addition of a thin layer of thermal insulation can provide improved performance, e.g. overall gas output, of the generator for a given overall dimensioning. Without wishing to be bound by theory, it is believed that the insulation can increase gas generation efficacity by the thermal protection layer by mitigating heat loss towards the exterior wall.

According to a further aspect, there is provided a cartridge for use with a housing having an outlet for releasing generated gas to form the gas generator as disclosed herein. The cartridge comprises a charge comprising a mixture that generates a target gas upon thermal decomposition and that will undergo a self-sustained exothermal decomposition reaction after ignition, and a thermal protection layer that circumferentially extends around the charge, whereby the thermal protection layer is comprised of a composition that generates gas upon thermal decomposition by absorption of heat from the thermal decomposition reaction of the main charge.

The protective layer and the charge are an integrally formed part or set of parts. This can ease assembly into the housing. To facilitate storage/transport of individual cartridges, the cartridge can be hermetically sealed by a consumable packing sheet, e.g. a plastic sheet, for loading the housing with a charge while packaged. This will also make it possible to replace the cartridge by the user without having to replace the whole cool gas generator. This can reduce costs for the user and will make the whole device more sustainable.

The disclosure further provides a kit of parts for forming a gas generator as disclosed herein. The kit comprises at least the cartridge according to any of claims 12-14, and a generator housing to receive the cartridge and having an outlet for releasing generated gas.

BRIEF DESCRIPTION OF DRAWINGS

These and other features, aspects, and advantages of the apparatus, systems and methods of the present disclosure will become better understood from the following description, appended claims, and accompanying drawing wherein:

FIG 1 illustrates a conventional Cool gas generator during operation;

FIG 2 provides a cross-section side view of an embodiment of a gas generator;

FIG 3 provides a cross-section side view of an embodiment of a gas generator during operation;

FIG 4 provides a cross-section side view of an embodiment of a gas generator;

FIG 5 provides a cross-section side view of an embodiment of a gas generator;

FIG 6 provides a cross-section side view of an embodiment of a gas generator;

FIG 7 provides a partial cross-section side view of a gas generator;

FIG 8 provides a cross-section side view of a cartridge for use with a housing to form a generator; and

FIG 9 illustrates a conventional hot gas generator.

DESCRIPTION OF EMBODIMENTS

Terminology used for describing particular embodiments is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term "and/or" includes any and all combinations of one or more of the associated listed items. It will be understood that the terms "comprises" and/or "comprising" specify the presence of stated features but do not preclude the presence or addition of one or more other features. It will be further understood that when a particular step of a method is referred to as subsequent to another step, it can directly follow said other step or one or more intermediate steps may be carried out before carrying out the particular step, unless specified otherwise. Likewise, it will be understood that when a connection between structures or components is described, this connection may be established directly or through intermediate structures or components unless specified otherwise.

The invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. In the drawings, the absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity.

Embodiments may be described with reference to schematic and/or cross-

section illustrations of possibly idealized embodiments and intermediate structures of the invention. In the description and drawings, like numbers refer to like elements throughout. Relative terms as well as derivatives thereof, should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the system be constructed or operated in a particular orientation unless stated otherwise.

FIG 1 provides a cross-section side view of a conventional type cool gas generator 1 during operation. The gas generator 1 comprises a housing 2 having an outlet 3 on one end to release generated gas G. The housing contains, at least initially, a main charge 4 and a filter assembly 7.

The main charge comprises a mixture that generates a target gas G upon thermal decomposition and that will undergo a self-sustained exothermal decomposition reaction after ignition by igniter 8, which is positioned on a side of the housing 2 opposite the outlet. The embodiment, as shown, is depicted in a working condition following initial ignition by the igniter 8, which sets of the main charge 4, resulting in a burning front 4c which progressively moves down the length of the main charge 4, somewhat similar to a cigarette. The heat generated upon the self-sustained thermal decomposition of part of the mixture releases gas a G which travels down the remainder of the virgin (unburnt) portion 4a main charge and through the filter towards the outlet 3. Hot remnants 4b of the main charge 4 remain after combustion. To sustain heat from the combustion and hot remnants, the walls of the housing are formed of a thick high-temperature resistant material, such as titanium. Optionally one or more external thermal insulation layers can be provided.

FIG 9 illustrates a conventional type hot gas generator. The generator comprises a housing holding a main charge configured for generating gas by a self-sustaining exothermal decomposition. The charge is typically non-porous. An igniter is provided to initiate thermal decomposition of the main charge. An outlet is provided opposite the outlet to release generated hot gas. A thermal protection, typically formed of a rubber, extends along an inner face of the wall. Upon ignition, gas generated by thermal decomposition flows via a central passage (hole) to be released at the outlet. The protection layer decomposes in the process.

FIGs 2-7 detail aspects of the gas generator 1 as disclosed herein.

The gas generators differ from known generators already in the provision of at least a thermal protection layer 5.

FIG 2 illustrates an embodiment in cross-section side view. The gas generator 1 comprises a housing 2 having an outlet 3 for releasing generated gas. Contained within the housing is a main charge 4. The embodiment, as illustrated further, comprises a filter assembly 7. The filter assembly 7 is contained within the same housing at a position between the main charge and the outlet.

The main charge can be ignited by an igniter 8. The igniter can be an electric igniter, or a chemical igniter as known in the field. In some embodiments, e.g. as shown, the igniter is positioned on an opposite end of the housing opposite the outlet 3. One or more lid sections 2t can be provided to seal the housing during storage. A lid for sealing the outlet may also be provided (not shown). Note that one or more of the lids may be configured such as to provide free access to the interior of the housing, e.g. for inserting (e.g. shdingly) active components of the gas generator 1 into the housing, including but not limited to filter assembly 7, the main charge 4, and/or a pre-formed cartridge comprising a main charge 4 (as discussed with more detail with reference to FIG 8).

The thermal protection layer 5 is formed of a composition that generates gas upon thermal decomposition by absorption of heat from the thermal decomposition reaction of the main charge. The thermal protection layer extends between the main charge 4 and sidewalls of the housing 2. As such, the thermal protection layer 5 shields the housing wall(s) from residual heat from the combustion. In some variations, the thermal protection layer 5 can also extend between end faces of the housing 2 and the main charge 4, e.g. along the lid to protect the lid from excessive heating. Note that a lid can alternatively or additionally be provided at the sidewall or a bottom of the housing, cf. FIG 3.

A thickness ‘t5 of the thermal protection layer 5, as illustrated in

FIG 7, is preferably as thin as functionally possible. A minimum can be determined experimentally for a given load shape, size, and composition, e.g. by thermal imaging of the housing.

The composition of the main charge, the filer, and the igniter are known in the field. For examples, reference can be made to EP1409082A1, which is hereby incorporated in full.

The composition of the main charge, the thermal protection layer 5, and the filter (if present) can depend on an intended application, e.g. composition of the gas to generate.

For gas generators configured to generate carbon dioxide (CO:), carbonates, formats and oxalates were found suitable as thermally decomposable constituent of the thermal protection layer. Particularly suitable are compounds having a metal cation, as these can offer a clean decomposition with a solid residue and/or limited or no side-reactions.

For gas generators configured to generate oxygen (O2), chlorates represent a suitable choice. Alternatively, compositions, such as other halogen-oxygen compounds, can be used as well, provided these decompose chemically under absorption of heat. Similarly, compounds having a metal cation can be particularly preferred.

For dinitrogen (N2) generators, nitrides can be selected, particularly metal nitrides. Again, provided these such compounds decompose chemically under absorption of heat.

For hydrogen generators (Hz), metal hydrides can present good results. Other materials that can be used are metal alanates.

Examples of carbonates include: MgCOs, CaCO:3, Cu2(0H):C03,

FeCO;3, MnCO:3, and ZnCO:3. Examples of formates include: HCOsNa,

HCO:K and HCO:Mg. Examples of oxalates include: MgC204, CaC204,

Na2C204, K2C204, FeC204 and SnC204. Accordingly, in some embodiments, the thermal protection layer comprises one or more compounds selected from the above carbonates, oxalates, and/or formates.

Examples of metal nitrides include LisN and MgsN:. Li;N decomposes at 300 - 500 degrees Celsius into lithium and Ns, Mg;N: decomposes from about 700 °C in magnesium and Ng. Both under the uptake of heat and under release of nitrogen which is added to the production of the main charge. Accordingly, in some embodiments, the thermal protection layer comprises one or more compounds selected from the above nitrides or further nitrates, provided that such compounds decompose chemically under absorption of heat.

Examples of metal hydrides include titanium hydride (TiH>) and magnesium hydride (MgH:>). Titanium hydride was found to decompose at 450-500 °C. Magnesium hydride decomposes at about 327 °C. Examples of metal alanates include: lithium alanate (LiAlH4), magnesium alanate (Mg(AlH4)2), and calcium alanate Ca(AlH4)2. Accordingly, in some embodiments, the thermal protection layer comprises one or more compounds selected from the above metal hydrides or further hydrides, provided such compounds decompose chemically under absorption of heat.

In some embodiments, the thermal protection layer 5 may comprise a composition gradient. For example, a radial gradient whereby decomposition temperature decreases towards the generator wall to increase thermal protection and overall gas output of the device.

FIG 3 illustrates a variation during use which differs from the embodiment described in relation to FIG 2 primarily in that the thermal protection layer 5 extends between the main charge and the filter assembly 7. Extending the thermal protection layer 5 between the filter and the main charge can advantageously maintain an overall function of cooling the outflow of generating gas while reducing an overall content of dead material within the system. Alternatively, or in addition, thermoregulating constituent can be comprised in the filter or filter, e.g. a mixture of sand and metal carbonate.

Similar as for conventional cool gas generators (cf. FIG 1), the main charge decomposes gradually downward from the igniter towards the outlet at a burning front 4c under release of a target gas (indicated as gas

G4) e.g. Oz. Different to conventional generators (for example FIG 9), heat from the hot remnants (slag) 4b is absorbed by the thermal protection layer 5, resulting in the formation of a further gas (indicated G5), e.g. Ne, which also diffuses towards the outlet 3, through virgin charge 4a, thermal protection layer 5 and filter 7. A thin layer of virgin 5 can remain between decomposed remnants 5b of thermal protection layer 5 and the generator wall

FIG 4 illustrates a variation wherein the amount of filter assembly 7 is reduced. In some embodiments, a convention filter can be completely omitted, i.e. replaced by the thermal protection layer, to further increase an overall output of the cool gas generator per unit volume.

FIG 5 illustrates a variation wherein a liner 6 is added that extends between the main charge 4 and the thermal protection layer 5. The liner can advantageously stabilize the generator contents during assembly.

The Liner can be formed of a thin layer, e.g. a thin metal or ceramic sheet. It will be appreciated that provision of the liner is not limited to the configurations as illustrated. The liner can equally be combined with other variations. For example, as illustrated in FIG 6, the liner 6 can also be applied in configurations wherein the thermal protection layer 5 extends between the mains charge and the filter assembly 7.

Alternatively, or in addition, a liner may be provided between the rector wall and the thermal protection layer 5 to facilitate smooth filling of the generator, e.g. by inserting the contents as one or more pre-formed pieces having a cross-section matching a cross-section of the generator.

In yet other or further variations, a thermal insulation layer may be provided between the generator wall, e.g. the side walls, and the generator contents. FIG 7 provides a partial view of a gas generator, whereby starting from the side wall 2 of the generator, there is provided an inert thermal insulation sheet 9, a thermal protection layer 5, and a main charge 4. The variation, as depicted, also includes a liner 6 between the thermal protection layer 5 and the main charge 4. The inert thermal insulation sheet preferably has a thickness ‘t9’ < 20 mm. Preferably the layer is as thin as functionally possible to reduce and minimize a dead volume within the generator associated to the insulation. Inventors surprisingly found that the insulation, despite adding unreactive content, can increase overall performance of the gas generator 1 in terms of overall gas output. As mentioned, this is believed to relate to an increased effectivity of the thermal protection layer 5 in generating gas by reducing heat losses to ambient. Inventors confirmed that layers of 3 or even 1 mm already resulted in an increased performance.

As for the other variations, according to the invention, the generator wall 2 can be thinner and/or formed of materials having lower temperature resistance than conventional generators having no thermal protection layer as disclosed herein.

In a preferred embodiment, e.g. of one or more of the thermal protection layer 5 and the main charge 4 are an integrally formed part or set of parts. The part (or set of parts) being dimensioned to fit in the interior of a generator. As such, the parts form one or more cartridges 10, which can be used to fill or re-fill a generator housing with a charge selected for an intended purpose, e.g. Hs generation.

FIG 8 illustrates a cartridge 10 for use with a housing as disclosed herein to form the gas generator according to any of the appended claims.

The cartridge comprises a charge 4 comprising a mixture that generates a target gas upon thermal decomposition and that will undergo a self- sustained exothermal decomposition reaction after ignition, and a thermal protection layer 5 that extends, typically circumferentially, around the charge, whereby the thermal protection layer is comprised of a composition that generates gas upon thermal decomposition by absorption of heat from the thermal decomposition reaction of the main charge.

In a preferred embodiment, the protective layer and the charge are an integrally formed part (e.g. by press forming). The cartridge may include one or more of a liner 6, an inert thermal insulation sheet, a filter assembly 7. Alternatively, or in addition, the cartridge may be pre-fitted with an igniter 8, e.g. as shown.

In a preferred variation, e.g. as shown, the cartridge 10 can be hermetically sealed from ambient by a packaging sheet 11, e.g. a plastic packing sheet, to enable long-term storage of the active contents prior to usage. Upon usage, the package can be removed. Alternatively, or in addition, one or more openings can be provided to allow an outward flow of formed gas, e.g. by punctuating or a thermo or pressure-activated degradation of the packaging.

For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.

Of course, it 1s to be appreciated that any one of the above embodiments or processes may be combined with one or more other embodiments or processes to provide even further improvements in finding and matching designs and advantages.

In interpreting the appended claims, it should be understood that the word "comprising" does not exclude the presence of other elements or acts than those listed in a given claim; the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements; any reference signs in the claims do not limit their scope; several "means" may be represented by the same or different item(s) or implemented structure or function; any of the disclosed devices or portions thereof may be combined together or separated into further portions unless specifically stated otherwise.

Where one claim refers to another claim, this may indicate synergetic advantage achieved by the combination of their respective features.

But the mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot also be used to advantage.

The present embodiments may thus include all working combinations of the claims wherein each claim can in principle refer to any preceding claim unless clearly excluded by context.

Claims

CONCLUSIONS

1. A gas generator (1) comprising a housing (2) having an outlet (3) for release of generated gas, and a main charge (4) contained in the housing, the charge comprising a mixture which upon thermal decomposition generates a target gas (G) and which, upon ignition, will undergo a self-sustaining decomposition reaction, wherein the generator further comprises a thermally protective layer (5) extending between the charge and the housing, the thermally protective layer comprising a composition which generates additional gas upon thermal decomposition while absorbing heat from the thermal decomposition reaction of the main charge.

2. The gas according to claim 1, wherein the composition (c) of the thermally protective layer and the mixture (m) of the main charge generate the same gas upon thermal decomposition.

3. The gas generator according to claim 1 or 2, further comprising a filter assembly (7) provided within the housing at a position between the charge and the outlet (3) and having a mass for cooling the generated gas and wherein the filter is at least partly comprised of the same or a further composition (c2) which generates gas upon thermal decomposition after absorption of heat from the thermal decomposition reaction of the main charge.

4. The gas generator according to any one of the preceding claims, wherein the thermal protective layer (5) and the main charge (4) are an integrally formed part.

5. The gas generator according to any of the preceding claims, further comprising a liner (6) extending between the main charge (4) and the thermal protective layer (5).

6. The gas generator according to any of the preceding claims, wherein the thermally protective layer (5) has a thickness in a range of 0.5 to 20.0 mm, preferably not more than 4.0 mm.

7. The gas generator according to any one of the preceding claims, wherein portions of the housing adjacent to the thermally protective layer and the main charge have a single-walled structure.

8. The gas generator of any preceding claim, wherein portions of the housing adjacent the main charge are formed from a plastics composition or a plastics composite.

9. The gas generator of any preceding claim, wherein the main charge (4) and the thermally protective layer (5) are configured to generate: a) oxygen gas; b) carbon dioxide gas; c) nitrogen gas; d) hydrogen gas.

10. The gas generator of any preceding claim, configured to generate a mixture of two or more of a) oxygen gas; b) carbon dioxide gas; c) nitrogen gas; d) hydrogen gas.

11. The gas generator according to any of the preceding claims, further comprising an inert thermal insulation layer (9) extending between the housing (2) and the thermal protective layer (5), said insulation having a thickness < 20 mm, preferably not more than 5 mm.

12. A cartridge (10) for use with a housing (2) having an outlet (3) for released generated gas to form the gas generator (1) according to any preceding claim, said cartridge comprising a charge comprising a mixture (m) which generates a target gas (G) upon thermal decomposition and which, upon ignition, will undergo a self-sustaining exothermic decomposition reaction, and a thermally protective layer (5) extending around the periphery of the charge, the thermally protective layer being comprised of a composition (c1) which generates gas upon thermal decomposition after absorption of heat from the thermal decomposition reaction of the main charge.

13. The cartridge of claim 12, wherein the protective layer and the charge are an integrally formed part.

14. The cartridge according to any one of claims 12 to 13, hermetically sealed by a packaging film (11).

15. A kit of parts comprising the cartridge according to any one of claims 12 to 14, and a generator to receive the cartridge and having an outlet (3) for released generated gas.