A battery module, battery energy storage system and a related method

Abstract

The disclosure relates to a battery module (3) comprising a plurality of battery cells (4), and a casing (3a) housing said battery cells. Notably, the battery module (3) further comprises one or more igniters (5) provided within the casing (3a). The igniter (5) is configured to produce a spark when activated, so as to ignite a combustible gaseous mixture within the casing (3a), said gaseous mixture resulting from gas venting from one or more of the battery cells (4). The disclosure further concerns a battery energy storage system and a method of preventing build-up of a combustible gaseous mixture resulting from gas venting from one or more battery cells (4) in a battery energy storage system (1).

Description

[0001] A BATTERY MODULE, BATTERY ENERGY STORAGE SYSTEM AND A RELATED METHOD

[0002] FIELD OF THE DISCLOSURE

[0003] The present disclosure relates to battery energy storage systems, and more particularly to battery modules used in such systems. The present disclosure further concerns a method for preventing build-up of a combustible gaseous mixture resulting from gas venting.

[0004] BACKGROUND OF THE DISCLOSURE

[0005] In conventional battery energy storage systems, multiple battery cells are provided within a battery module for storing electrical power. A plurality of such modules are typically placed one above another as a rack, and multiple such racks are provided one next to another within a battery unit or enclosure. Furthermore, multiple such units or enclosures may be coupled to form the battery capacity of the system.

[0006] In case of a malfunction or damage, a battery cell may undergo gas venting, in which a flammable gaseous mixture is released from the battery cell. On rare occasion this gaseous mixture may ignite and cause a deflagration event. Uncontrolled, this deflagration may propagate to other battery cells, modules, racks or even units.

[0007] A conventional approach of preventing propagation of the deflagration has been e.g., to pre-emptively ventilate the gaseous mixture from the enclosure. Such ventilation both consumes energy and also requires periodic maintenance to ensure proper operation.

[0008] BRIEF DESCRIPTION OF THE DISCLOSURE

[0009] An object of the present disclosure is to provide a battery module, a battery energy storage system and a method achieving a simple and robust solution for preventing build-up of a combustible gaseous mixture resulting from gas venting.

[0010] The object of the disclosure is achieved by a battery module, a battery energy storage system and a method which are characterized by what is stated in the independent claims. The preferred embodiments of the disclosure are disclosed in the dependent claims.

[0011] The disclosure is based on the idea of providing a battery module with one or more igniters within a casing that houses a plurality of battery cells. The igniter is configured to produce a spark when activated, so as to ignite a combustible gaseous mixture within the casing. This allows an early, controlled ignition of the gaseous mixture before it accumulates in an amount sufficient to cause additional damage and propagation of the deflagration. An advantage of the solution proposed by the disclosure is that an arrangement with no moving parts and little energy consumption is achieved, while propagation of a deflagration is effectively prevented.

[0012] According to a first aspect of the present disclosure, a battery module is provided. The battery module comprises a plurality of battery cells and a casing housing said battery cells. Particularly, the battery module further comprises one or more igniters provided within the casing. The igniter is configured to produce a spark when activated, so as to ignite a combustible gaseous mixture within the casing. That is, the igniter is configured to produce sparking within the casing. For example, the igniter may be provided as a spark generator having a pair of electrodes closely spaced apart from each, such that a spark is generated between the electrodes when the electrodes are suspected to an electrical potential difference. Notably, in the context of this disclosure, the combustible gaseous mixture is used for describing a combustible gaseous mixture resulting from gas venting from one or more of the battery cells.

[0013] In an embodiment according to first aspect of the present disclosure, the battery module comprises a venting outlet. For example, such a venting outlet may be provided as a safety vent, a pressure relief valve, a flame arrester or any combination thereof. Suitably, at least one igniter is arranged between one or more battery cells and the venting outlet. Preferably at least one igniter is arranger between all of the battery cells and the venting outlet. As such a venting outlet allows communication between an inside and an outside of the casing, thereby allowing a gaseous mixture from within the battery module casing to flow out from the casing, a venting path is defined past the igniter. That is, a flow route of venting gas runs past the igniter. This, in turn, ensures that such a combustible gaseous mixture will indeed ignite before excessively building up.

[0014] In an embodiment according to the first aspect present disclosure, the battery module comprises an ignition control unit operationally coupled to the one or more igniters. For example, the ignition control unit may be provided as a separate unit, or it may alternatively be integrated with the battery management system of the battery unit.

[0015] The ignition control unit may be configured to activate the igniter periodically, for example at pre-determined intervals. In another example, the ignition control unit may be configured to activate the igniter in response to manual input, i.e. upon operator input. In a further example, the ignition control unit may be configured to activate the igniter in response to a gas detector signal indicative of gas venting from one or more of the battery cells. Such a gas detector may produce a signal indicating a presence or concentration of a combustible gaseous mixture within the casing, resulting from gas venting from one or more battery cells.

[0016] The provision of a gas detector as discussed above can be carried out in a multitude of different ways. For example, the increase (within the casing) of one or more of temperature, light intensity, humidity, CO concentration, CO2concentration, H2concentration, heat flux, motion, acoustic signal(s) and pressure may be used for determining a presence or concentration of a combustible gaseous mixture within the casing, resulting from gas venting from one or more battery cells. Alternatively, or in addition, a decrease of 02 concentration or an optical signal(s) may be used for determining a presence or concentration of a combustible gaseous mixture within the casing, resulting from gas venting from one or more battery cells.

[0017] Moreover, the ignition control unit may be configured to operate according to more than one control mode, as discussed above, or even according to combinations thereof. For example, the ignition control unit may be configured to activate the igniter periodically in response to the gas detector signal indicative of gas venting from one or more of the battery cells, such that an interval between subsequent igniter activations is determined based on the gas detector signal. That is, the ignition frequency is higher when the presence of a gaseous combustible mixture is detected within the casing, and I or the ignition frequency is increased when the concentration of the combustible gaseous mixture increases (interval between subsequent igniter activations decreases).

[0018] Preferably, but not necessarily, the battery module comprises a humidity sensor provided within a casing of the battery module. The humidity sensor is operationally coupled to the ignition control unit and configured to produce a signal indicative of relative humidity prevailing within the casing. The ignition control unit may then be further configured to monitor relative humidity prevailing within the casing for detecting a peak increase in said relative humidity. For example, such a peak increase can be defined as either or both of a predetermined increase from a given base level, or a predetermined increase within a given time frame.

[0019] Upon detection of a peak increase in said relative humidity, the ignition control unit may further be configured to determine an occurrence of a combustion within the casing, and to generate a combustion alarm signal indicative of a combustion event within the casing. Such a combustion alarm may be relayed to a further control unit of an associated battery energy storage system and I or be used as a trigger for further measures (e.g. activating extinguishing equipment, decoupling the battery module or battery unit from the remaining system etc). Preferably, but not necessarily, the ignition control unit is coupled to one or more battery cells, so as to be powered therefrom.

[0020] Preferably, but not necessarily, the one or more igniters are coupled to one or more battery cells, so as to be powered therefrom.

[0021] It should be noted that the first aspect of the present disclosure encompasses any combination of two or more embodiments, or variants thereof, as discussed above.

[0022] According to a second aspect of the present disclosure, a battery energy storage system is provided. Notably, the battery energy storage system comprises multiple battery modules according to the first aspect of the disclosure, and an enclosure housing said battery modules. For example, the battery energy storage system may also comprise multiple such enclosures.

[0023] In an embodiment according to the first aspect, the battery modules are arranged as either or both of multiple battery modules superimposed one above another, and multiple battery modules positioned adjacent one next to another. For example, a plurality of battery modules may be superimposed one above another as racks, and multiple such racks may be provided one next another within the enclosure.

[0024] In an embodiment according to the second aspect, the system further comprises an ignition control unit operationally coupled to the igniters of the multiple battery modules. That is, the ignition control unit may additionally, or alternatively, be provided on the system level so as to control igniters of multiple battery modules (as opposed to the module specific ignition control units discussed above in connection with the first aspect). For example, the ignition control unit may be provided as a separate unit, or it may alternatively be integrated with the battery management system of the battery energy storage system.

[0025] The ignition control unit may be configured to activate the igniter periodically, for example at pre-determined intervals. In another example, the ignition control unit may be configured to activate the igniter in response to manual input, i.e. upon operator input. In a further example, the ignition control unit may be configured to activate the igniter in response to a gas detector signal indicative of gas venting from one or more of the battery cells. Such a gas detector may produce a signal indicating a presence or concentration of a combustible gaseous mixture within the casing, resulting from gas venting from one or more battery cells.

[0026] The provision of a gas detector as discussed above can be carried out in a multitude of different ways. For example, the increase (within the casing) of one or more of temperature, light intensity, humidity, CO concentration, CO2concentration, H2 concentration, heat flux, motion, acoustic signal(s) and pressure may be used for determining a presence or concentration of a combustible gaseous mixture within the casing, resulting from gas venting from one or more battery cells. Alternatively, or in addition, a decrease of 02 concentration or an optical signal(s) may be used for determining a presence or concentration of a combustible gaseous mixture within the casing, resulting from gas venting from one or more battery cells.

[0027] Moreover, the ignition control unit may be configured to operate according to more than one control mode, as discussed above, or even according to combinations thereof. For example, the ignition control unit may be configured to activate the igniter periodically in response to the gas detector signal indicative of gas venting from one or more of the battery cells, such that an interval between subsequent igniter activations is determined based on the gas detector signal. That is, the ignition frequency is higher when the presence of a gaseous combustible mixture is detected within the casing, and I or the ignition frequency is increased when the concentration of the combustible gaseous mixture increases (interval between subsequent igniter activations decreases).

[0028] Preferably, but not necessarily, the battery energy storage system comprises a humidity sensor provided within a casing of one or more battery modules. The humidity sensor is operationally coupled to the ignition control unit and configured to produce a signal indicative of relative humidity prevailing within the casing. The ignition control unit may then be further configured to monitor relative humidity prevailing within the casing for detecting a peak increase in said relative humidity. For example, such a peak increase can be defined as either or both of a predetermined increase from a given base level, or a predetermined increase within a given time frame.

[0029] Upon detection of a peak increase in said relative humidity, the ignition control unit may further be configured to determine an occurrence of a combustion within the casing, and to generate a combustion alarm signal indicative of a combustion event within the casing. Such a combustion alarm may be used as a trigger for further measures (e.g. activating extinguishing equipment, decoupling the battery module or battery unit from the remaining system etc).

[0030] In an embodiment according to the second aspect of the disclosure, either or both of the ignition control unit and the one or more igniters are coupled to at least one battery module, so as to be powered therefrom.

[0031] In an embodiment according to the second aspect of the disclosure, the battery energy storage system comprises a primary power interface for coupling the energy storage system to an electrical network. The primary power interface may be configured such that the battery cells can be charged from and discharged to said electrical network. Suitably, either or both of the ignition control unit and the one or more igniters are coupled to the primary power interface so as to be powered therefrom.

[0032] In an embodiment according to the second aspect of the disclosure, the battery energy storage system comprises a secondary power interface for coupling an UPS (uninterrupted power supply) -system. Suitably, the ignition control unit and I or the one or more igniters are coupled to the secondary power interface so as to be powered therefrom.

[0033] It should be noted that the second aspect of the disclosure encompasses any combination of two or more embodiments, or variants thereof, as discussed above.

[0034] In a third aspect of the present disclosure, a method is provided for preventing build-up of a combustible gaseous mixture resulting from gas venting from one or more battery cells in a battery energy storage system.

[0035] In the method multiple battery modules are provided, each module having a casing holding a plurality of battery cells. An enclosure housing said battery modules is also provided.

[0036] Moreover, one or more igniters within a casing of at least one battery module is provided. The igniter is configured to produce a spark when activated so as to ignite a combustible mixture of fumes within the casing, said fumes resulting from gas venting from one or more of the battery cells.

[0037] For example, the igniter may be activated periodically, in response to manual input, or in response to a gas detector signal indicative of gas venting from one or more of the battery cells.

[0038] The igniter may be activated periodically, for example at pre-determined intervals. In another example, the igniter may be activated in response to manual input, i.e. upon operator input. In a further example, the igniter may be activated response to a gas detector signal indicative of gas venting from one or more of the battery cells. Such a gas detector may produce a signal indicating a presence or concentration of a combustible gaseous mixture within the casing, resulting from gas venting from one or more battery cells.

[0039] Moreover, the igniter may be activated in accordance to more than one control mode, as discussed above, or even according to combinations thereof. For example, the igniter may be activated periodically in response to the gas detector signal indicative of gas venting from one or more of the battery cells, such that an interval between subsequent igniter activations is determined based on the gas detector signal. That is, the ignition frequency is higher when the presence of a gaseous combustible mixture is detected within the casing, and I or the ignition frequency is increased when the concentration of the combustible gaseous mixture increases (interval between subsequent igniter activations decreases).

[0040] Preferably, but not necessarily, the battery module comprises a humidity sensor provided within a casing of the battery module. The humidity sensor is operationally coupled to the ignition control unit and configured to produce a signal indicative of relative humidity prevailing within the casing. The ignition control unit may then be further configured to monitor relative humidity prevailing within the casing for detecting a peak increase in said relative humidity. For example, such a peak increase can be defined as either or both of a predetermined increase from a given base level, or a predetermined increase within a given time frame.

[0041] Upon detection of a peak increase in said relative humidity, the ignition control unit may further be configured to determine an occurrence of a combustion within the casing, and to generate a combustion alarm signal indicative of a combustion event within the casing. Such a combustion alarm may be relayed to a further control unit of an associated battery energy storage system and I or be used as a trigger for further measures (e.g. activating extinguishing equipment, decoupling the battery module or battery unit from the remaining system etc).

[0042] In an embodiment according to the third aspect of the present disclosure, a humidity sensor may be provided. Suitably, such a humidity sensor is configured to produce a signal indicative of relative humidity prevailing within a casing of at least one battery module.

[0043] Moreover, relative humidity prevailing within the casing is monitored. Upon detection of a peak increase in said relative humidity, an occurrence of a combustion within the casing is determined. Furthermore, upon determination of a combustion within the casing, a combustion alarm signal indicative of a combustion event within the casing is produced.

[0044] Such a combustion alarm may be used as a trigger for further measures (e.g. activating extinguishing equipment, decoupling the battery module or battery unit from the remaining system etc).

[0045] It should be noted that the second aspect of the disclosure encompasses any combination of two or more embodiments, or variants thereof, as discussed above. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In the following, the disclosure will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which:

[0047] Fig. 1 schematically illustrates a battery module according to an embodiment of the present disclosure, and

[0048] Fig. 2 schematically illustrates battery energy storage system according to an embodiment of the present disclosure.

[0049] DETAILED DESCRIPTION OF THE DISCLOSURE

[0050] Fig. 1 schematically illustrates a battery module 3 according to an embodiment of the present disclosure. Notably, multiple battery cells 4 are housed within a casing 3a of the battery module 3. Although not explicitly depicted in Fig. 1 the battery cells are electronically couplable to a battery energy storage system so as to be charged from and discharged from an electrical network.

[0051] The battery module 3 additionally comprises a venting outlet 3b. The venting outlet is configured such that, in the event of gas venting from one of the battery cells 4, the resulting combustible gashouse mixture can be vented to a surrounding environment through the venting outlet 3b.

[0052] The battery module 3 further comprises an igniter 5 configured to, upon activation, produce a spark which can ignite a gaseous combustible mixture resulting from gas venting. Notably, the igniter 5 is positioned between the venting outlet 3b and the battery cells 4, i.e., on the venting path. Moreover, the igniter 5 is operationally coupled to an ignition control unit 6, which is configured to activate the igniter 5.

[0053] The battery module of Fig. 1 also comprises a gas detector 7a and a humidity sensor 7b, both operationally coupled to the ignition control unit 6. For example, the gas detector 7a can detect the presences and / or concentration of a combustible gaseous mixture within the casing 3a, and produce a corresponding signal. Based on this signal, the ignition control unit 6 can initiate a periodical ignition sequence of the igniter 6, or modify the interval of subsequent igniter activations. If a combustion is induced, it has been discovered to result in a peak increase of humidity within the casing 3a. This can then be detected by the ignition control unit from a corresponding signal produced by the humidity sensor.

[0054] While Fig. 1 depicts an illustrative embodiment of the present disclosure with reference to a single igniter 5, gas detector 7a and humidity sensor 7b, it should be noted that the battery module 3 can be implemented with multiple such igniters, gas detectors and humidity sensors. Moreover, the battery module 3 can be provided with a number of battery cells differing from that illustrated in Fig. 1

[0055] Fig. 2 schematically illustrates battery energy storage system 1 according to an embodiment of the present disclosure. Notably, the battery energy storage system 1 comprises multiple battery modules 3 housed within an enclosure 2. While the battery modules 3 in Fig. 2 are depicted with different configurations for illustrative purposes, they may suitably be of similar configurations, e.g., such as the configuration depicted in Fig. 1 .

[0056] In a similar manner to those of Fig.1 , the battery modules 3 of Fig. 2 also have a casing 3a housing a plurality of battery cells 4. Arranged within the casings 3a of the battery modules 3, an igniter 5, a gas detector 7a and a humidity sensor 7b are provided.

[0057] Notably, battery energy storage system 1 of Fig.2 illustrates a centralised ignition control unit 6, which is operationally coupled to the igniters 5, gas detectors 7a, and humidity sensors 7b of multiple battery modules 3.

[0058] The battery energy storage system 1 of Fig. 2 also comprises a primary power interface 8 through which the battery cells 4 of the battery modules 3 can be coupled to an electrical network 10, so as to charge and discharge the battery cells 4 therefrom. Moreover, the ignition control unit 6 is also coupled to the primary power interface 8, such that the ignition control unit 6 (and possibly also the igniters 7, gas detectors 7a and humidity sensors 7b) can be powered by the electrical network 10.

[0059] Furthermore, the battery energy storage system 1 of Fig. 2 also comprises a secondary power interface 9. The ignition control unit 6 is also coupled to the secondary power interface 9, such that the ignition control unit 6 (and possibly also the igniters 7, gas detectors 7a and humidity sensors 7b) can be powered by an UPS (uninterrupted power supply) system via the secondary power interface.

[0060] LIST OF REFERENCE NUMERALS

[0061] 1 battery energy storage system

[0062] 2 enclosure

[0063] 3 battery module

[0064] 3a casing

[0065] 3b venting outlet

[0066] 4 battery cell 5 igniter

[0067] 6 ignition control unit

[0068] 7a gas detector

[0069] 7b humidity sensor 8 primary power interface

[0070] 9 secondary power interface

[0071] 10 electrical network

[0072] 11 UPS system

Claims

CLAIMS1. A battery module (3), comprising: a plurality of battery cells (4), and a casing (3a) housing said battery cells, characterized in that the battery module (3) further comprises one or more igniters (5) provided within the casing (3a), the igniter (5) being configured to produce a spark when activated, so as to ignite a combustible gaseous mixture within the casing (3a), said gaseous mixture resulting from gas venting from one or more of the battery cells (4).

2. The battery module according to claim 1 , characterized by comprising a venting outlet (3b), wherein at least one igniter (5) is arranged between one or more battery cells (4) and the venting outlet (3b).

3. The battery module according to claim 1 or 2, characterized by comprising a control unit (6) operationally coupled to the one or more igniters (5), where in the ignition control unit (6) is configured to one or more of the following: activate the igniter (5) periodically; activate the igniter (5) in response to manual input, and activate the igniter (5) in response to a gas detector (7a) signal indicative of gas venting from one or more of the battery cells (4).

4. The battery module according to claim 3, characterized in that the ignition control unit (6) is configured to activate the igniter (5) periodically in response to the gas detector (7a) signal indicative of gas venting from one or more of the battery cells (4), such that an interval between subsequent igniter activations is determined based on the gas detector (7a) signal.

5. The battery module according to claim 3 or 4, characterized by further comprising a humidity sensor (7b) provided within a casing (3a) of the battery module (3), wherein the humidity sensor (7b) is configured to produce a signal indicative of relative humidity prevailing within the casing (3a), wherein the humidity sensor is operationally coupled to the ignition control unit (6), and wherein the ignition control unit (6) is further configured to:- monitor relative humidity prevailing within the casing (3a) for detecting a peak increase in said relative humidity, and- upon detection of a peak increase in said relative humidity, determine an occurrence of a combustion within the casing (3a), and to generate a combustion alarm signal indicative of a combustion event within the casing (3a).

6. The battery module (3) according to any of the preceding claims 3-5, characterized in that the ignition control unit (6) is coupled to one or more battery cells (4), so as to be powered therefrom.

7. The battery module (3) according to any of the preceding claims 1-6, characterized in that the one or more igniters (5) are coupled to one or more battery cells (4), so as to be powered therefrom.

8. A battery energy storage system (1), characterized by comprising multiple battery modules (3) according to any of the preceding claims 1-7b, and an enclosure (2) housing said battery modules (3).

9. The battery energy storage system (1) according to claim 8, characterized in that the battery modules (3) being arranged as either or both of multiple battery modules (3) superimposed one above another, and multiple battery modules (3) positioned adjacent one next to another.

10. The battery energy storage system (1) according to claim 8 or 9 and comprising multiple battery modules according to any of the preceding claims 1 or 2, characterized in that the system further comprises an ignition control unit (6) operationally coupled to the igniters (5) of the multiple battery modules (3), wherein the ignition control unit (6) is configured to activate at least one igniter (5) periodically; activate at least one igniter (5) in response to manual input, and activate at least one igniter (5) in response to a gas detector (7a) signal indicative of gas venting from one or more of the battery cells (4).

11. The battery energy storage system (1) according to claim 10, characterized in that the ignition control unit (6) is configured to activate at least one igniter (5) periodically in response to the gas detector (7a) signal indicative of gas venting from one or moreof the battery cells (4), such that an interval between subsequent igniter activations is determined based on the sensor signal.

12. The battery energy storage system (1) according to claim 10 or 1 1 , characterized in that the system further comprises a humidity sensor (7b) provided within a casing (3a) of one or more battery modules (3), wherein the humidity sensor (7b) being configured to produce a signal indicative of relative humidity prevailing within said casing (3a), wherein the humidity sensor being operationally coupled to the ignition control unit (6), and wherein the ignition control unit (6) is further configured to: monitor relative humidity prevailing within the casing (3a) for detecting a peak increase in said relative humidity, and upon detection of a peak increase in said relative humidity, determine an occurrence of a combustion within the casing (3a), and generate a combustion alarm signal indicative of a combustion event within said casing.

13. The battery energy storage system (1) according to any of the preceding claims I Q-12, characterized in that either or both of the ignition control unit (6) and the one or more igniters (5) are coupled to at least one battery module (3), so as to be powered therefrom.

14. The battery energy storage system (1) according to any of the preceding claims I Q-13, characterized by comprising a primary power interface (8) for coupling the energy storage system (1) to an electrical network (10) such that the battery cells (4) can be charged from and discharged to said electrical network (10), wherein either or both of the ignition control unit (6) and the one or more igniters (5) are coupled to the primary power interface (8) so as to be powered therefrom.

15. The battery energy storage system (1) according to any of the preceding claims I Q-14, characterized by comprising a secondary power interface (9) for coupling an UPS system, wherein the ignition control unit (6) and I or the one or more igniters (5) are coupled to the secondary power interface (9) so as to be powered therefrom.

16. A method of preventing build-up of a combustible gaseous mixture resulting from gas venting from one or more battery cells (4) in a battery energy storage system (1), comprising the steps of: providing multiple battery modules (3), each module (3) having a casing (3a) holding a plurality of battery cells (4), and providing an enclosure (2) housing said battery modules (3), and characterized in by further comprising the steps of providing one or more igniters (5) within a casing (3a) of at least one battery module (3), the igniter (5) being configured to produce a spark when activated so as to ignite a combustible mixture of fumes within the casing (3a), said fumes resulting from gas venting from one or more of the battery cells (4), and wherein the method comprises one or more of the following steps:- activating the igniter (5) periodically; activating the igniter (5) in response to manual input, and activating the igniter (5) in response to a gas detector (7a) signal indicative of gas venting from one or more of the battery cells (4).

17. The method according to claim 16, characterized in that igniter (5) is activated periodically in response to the gas detector (7a) signal indicative of gas venting from one or more of the battery cells (4), such that an interval between subsequent igniter activations is determined based on the gas detector (7a) signal.

18. The method according claim 16 or 17, characterized by further comprising the steps of providing a humidity sensor (7b) configured to produce a signal indicative of relative humidity prevailing within a casing (3a) of at least one battery module (3); monitoring relative humidity prevailing within the casing (3a), and upon detection of a peak increase in said relative humidity, determining an occurrence of a combustion within the casing (3a), and upon determination of a combustion within the casing (3a), producing a combustion alarm signal indicative of a combustion event within the casing (3a).

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