EP2867168A1

EP2867168A1 - Method for diagnosing a system for storing a gas stored by sorption on a compound

Info

Publication number: EP2867168A1
Application number: EP13744658.9A
Authority: EP
Inventors: Jules-Joseph Van Schaftingen; François BOUGNIER; Dominique Madoux; Jean-Claude Habumuremyi
Original assignee: Inergy Automotive Systems Research SA
Current assignee: Plastic Omnium Advanced Innovation and Research SA
Priority date: 2012-06-29
Filing date: 2013-06-28
Publication date: 2015-05-06
Also published as: CN104540781A; WO2014001733A1; FR2992726A1; US20150160078A1; FR2992726B1

Abstract

The invention proposes a method for diagnosing a system for storing a gas, the gas being stored by sorption on a compound, the system being mounted onboard a vehicle and comprising a tank capable of containing the compound and a control device capable of controlling a heating device in order to increase the temperature of the compound in such a way as to release the gas. The control device is such that it obtains (E21) a set of information comprising at least one measurement of the temperature of the system, then carries out an estimation (E22) of the gas pressure in the system by using a predetermined kinetic model of desorption of the gas.

Description

Method for diagnosing a system for storing a gas stored by sorption on a compound

FIELD OF THE INVENTION

The invention relates to a method for diagnosing a system for storing a gas, preferably mounted on board a motor vehicle.

The invention applies in particular, but not exclusively, to the diagnosis of an ammonia storage system.

The invention also applies, but not exclusively, to the diagnosis of a hydrogen storage system.

In the remainder of this document, it is attempted to describe the particular case of an ammonia storage system comprising plastic storage elements. Ammonia is, for example, intended to be injected into the exhaust line of a vehicle to reduce the amount of nitrogen oxides (NOx) in the exhaust gas. Of course, the present invention applies to any other type of gas storage system mounted on board a vehicle and for which it is desired to obtain the pressure of the gas in the system and / or to obtain a diagnosis of the state operation of such a system. More generally, the invention applies to any type of gas (ammonia, hydrogen, etc.) that can be stored by sorption on a compound.

BACKGROUND TECHNOLOGY

Nitrogen oxides present in vehicle exhaust gases, especially diesel, can be removed by the selective catalytic reduction technique (commonly referred to as SCR or Selective Catalytic Reduction). According to this technique, doses of ammonia (NH3) are injected into the exhaust line upstream of a catalyst on which the reduction reactions take place. Currently, ammonia is produced by thermal decomposition of a precursor, usually an aqueous solution of urea. Embedded systems for storing, dispensing and dosing a standard urea solution (such as that sold under the name Adblue®, a eutectic solution containing 32.5% urea in water) have thus been placed on the market.

Another technique is to store ammonia by sorption on a salt, most often an alkaline earth metal chloride. Generally in this case, the storage system includes a reservoir designed to enclose the salt and a heater configured to heat the salt. Thus, by heating the salt ammonia is released. An ammonia pressure is generated. In such an ammonia storage system, it is sought to obtain the ammonia pressure released to, for example, verify that it corresponds to a requested ammonia pressure and, where appropriate, perform corrective actions. It is also intended to detect the overheating of the salt heating device. This is all the more important if the reservoir (formed by one or more storage elements) is plastic material whose mechanical properties are quite sensitive to temperature. Generally, a pressure sensor or a pressure regulator is used to measure the released ammonia pressure. But these sensor and pressure regulator are expensive and bulky (compared to a temperature sensor). Generally, to detect overheating of the salt heater, the system uses a temperature sensor. Thus, overheating is detected in a simple and effective manner. However, in certain cases it is desirable to have other diagnostic information available, in particular to ensure safe operation of the storage system and effective reduction of nitrogen oxides in the exhaust gas.

OBJECTIVES OF THE INVENTION

It is therefore desirable to provide a diagnostic technique of a gas storage system, to obtain the gas pressure in the system, without the use of a pressure sensor or pressure regulator.

It is also desirable to obtain a plurality of information relating to the operation of the gas storage system.

It is also desirable to provide such a technique that is simple to implement, regardless of the gases and compounds used.

SUMMARY OF THE INVENTION

In a particular embodiment of the invention, there is provided a method for diagnosing a system for storing a gas, the gas being stored by sorption on a compound, the system being mounted on board a vehicle and comprising a reservoir capable of containing the compound and a control device adapted to control a heating device to raise the temperature of the compound so as to release the gas. The control device is such that it obtains a set of information including at least one temperature measurement of the system, and then performs an estimation of the gas pressure in the system using a predetermined model of gas desorption kinetics. Thus, the present invention proposes to use one or more temperature measurement (s) of the storage system to deduce the gas pressure in the system. The temperature measurement (s) are obtained by means of one or more temperature sensors already present in the storage system. In a particular embodiment, the set of information that is used to estimate the pressure prevailing inside the storage system comprises one or more temperature measurement (s) performed at a current time (ie measurements instantaneous) and a history of temperature measurements, that is to say a set of temperature measurements made at times preceding the current time. In an alternative embodiment, this set of information may comprise a functional history of these measurements. For example, such functional (function function) can be an integral of the type:

Functional l (t) = integral of (t-tl) at t of f (x) Tl (x) dx

with for example f (x) = A * τ + B

where t denotes the time, Tl is the temperature measurement, tl, A and B are constants, and τ represents a time variable.

The desorption kinetics model for a given gas stored by sorption on a given compound is usually known. If this model is not known, it can be obtained in a simple manner, for example by measuring the desorption curve of the gas during operation of the heater. With the help of the desorption kinetics model, it is possible to approach in a particularly precise manner the pressure actually prevailing in the storage system at the instant of the measurement of the temperature. The method according to the invention thus makes it possible to calculate the pressure of the gas in the system in a very precise manner, without the use of a pressure sensor or a pressure regulator, which leads to a significant improvement in the assembly of the pressure system. storage and cost reduction of such a system.

In a preferred embodiment, the control device is embedded in the vehicle, for example, in the form of a microprocessor. In another embodiment, the control device is, for example, a computer (or server) located outside the vehicle, for example, in a laboratory. Indeed, before being mounted permanently on the destination vehicle, the storage system may, for example, during a test phase, be mounted on a test bench. For example, during this test phase, the computer (acting as a control device) can adjust the desorption kinetics model of the gas to be used. The gas desorption kinetics model is, for example, stored in an accessible memory (ie readable) by the control device.

The gas may be of any type, preferably ammonia or hydrogen.

Advantageously, the control device is configured to determine operating conditions of the system from the set of information, and to select the model used from among a plurality of predetermined models of gas desorption kinetics, as a function of operating conditions determined.

To estimate the gas pressure in the system as accurately as possible, it is important to know under which conditions the system is operating. Indeed, the operating conditions of the system affect the desorption of the gas. This is why, according to a preferred embodiment of the invention, the control device selects the gas desorption kinetics model most suited to the operating conditions of the system. The different models of gas desorption kinetics are, for example, stored in an accessible memory (i.e. readable) by the control device. In a particular embodiment, the set of information comprises, in addition to the temperature measurement (s), information (or history) relating to the power dissipated by the heating device, information (or a history) relating to atmospheric pressure, or information (or history) relating to the ambient temperature outside the vehicle. This set of information is, for example, stored in an accessible memory (i.e. readable) by the control device.

Advantageously, the model used is a Clausius-Clapeyron relationship.

The model used is a pressure / temperature relationship governing gas sorption on the compound. The Clausius-Clapeyron relationship used in the process according to the invention may be a theoretical (curve, table, formula, etc.) relationship, derived from the literature, preferably experimentally validated. Alternatively, this relation can be generated experimentally on models and / or prototypes.

Advantageously, the control device is configured to detect at least one information concerning the operating state of the system by using the set of information and at least one of the following models:

a predetermined model of reservoir operation; a predetermined model of operation of the heater.

The operating model of a given reservoir and the operating model of a given heating device are usually known. These models are, for example, theoretical curves, mappings or envelopes obtained experimentally for different operating states representative of both the operation of the tank and the heating device. In a preferred embodiment, all or part of the information in the set of information is compared to predefined threshold ranges to diagnose the operating state of the storage system.

The information concerning the operating state of the system may for example be a detection of the absence of temperature rise with respect to a high heating power setpoint. The information concerning the operating state of the system may for example be a detection of an abnormally high temperature, that is to say a temperature which may be too critical for the long-term holding of the reservoir. The information concerning the state of operation of the system may for example be a level of gas charge of the tank. Advantageously, a list of the various possible operating states is pre-established and stored in an accessible memory (i.e. readable) by the control device.

According to an advantageous characteristic, said reservoir comprises a storage cell provided with at least one of the following sensors:

a temperature sensor;

- a heat flow sensor

The sensor (s) can (be) mounted inside or outside (for example on the wall) of the cell. Some sensors can be mounted inside the cell and other sensors on the outside of it. The sensors are distributed on and / or in the cell depending in particular on the geometry of the cell and the diagnostic information that is desired.

Advantageously, the storage cell comprises a wall in which is formed at least one housing, each housing extending towards the inside of the cell and being configured to receive the sensor (s).

Mounting the sensor (s) on the cell is therefore simple. Indeed, it is sufficient to insert them in the housing (s) provided for this purpose. Advantageously, the same housing can contain one or more sensor (s).

In a preferred embodiment, the cell is made of plastic. Advantageously, the cell is covered with at least one of the following materials:

- a thermal insulation material;

a phase change material.

Advantageously, the cell is covered with an additional heating device.

Advantageously, the cell comprises a thermal conductor network.

Advantageously, the reservoir comprises at least one other storage cell. Thus, the reservoir may consist of a group of cells.

The process according to the invention is particularly well suited to the case where the reservoir comprises a compound, preferably a solid, on which a gas (ammonia, hydrogen, etc.) is bound by sorption, preferably by chemisorption. It is usually an alkali metal, alkaline earth metal or transition metal chloride. It can be in the powdery state or in the form of agglomerates. This compound is preferably an alkaline earth metal chloride, and very particularly preferably a chloride of Mg, Ba or Sr.

LIST OF FIGURES

Other features and advantages of the invention will appear on reading the following description, given by way of indicative and nonlimiting example, and the appended drawings, in which:

FIG. 1 illustrates the structural architecture of an SCR system comprising a gas storage system, according to a particular embodiment of the invention;

FIG. 2 presents a particular embodiment of a diagnostic algorithm of the gas storage system of FIG. 1;

Figures 3 to 17 illustrate examples of cells included in the gas storage system of Figure 1.

DETAILED DESCRIPTION

In the following, embodiments of the invention, in which the gas sorbed on the compound is ammonia, are described with reference to FIGS. Of course, in an alternative embodiment the gas may be of any other type, including hydrogen.

As illustrated in Figure 1, the engine 1 of the vehicle is controlled by an electronic computer 2 (sometimes called ECU or Engine Control Unit). The engine 1 cooperates with a system SCR 3. At the output of the engine, the gases 11 are directed to an ammonia injection module 31, in which the ammonia 12 is mixed with the exhaust gas 11. The ammonia / exhaust gas mixture 13 then passes through a catalyst SCR 32 which allows the reduction of nitrogen oxides (NOx) by ammonia. The exhausted exhaust gas 14 is then directed to the exhaust outlet.

In this exemplary embodiment, the SCR system 3 comprises an ammonia storage system. The storage system 5 comprises a reservoir 54 in which is stored a compound 52, for example a solid (and preferably a salt). The ammonia is stored by sorption on the solid 52. The storage system 5 also comprises a control device 4 in charge of controlling a heater 53 (also called a driver) to heat the solid 52 so as to release the ammonia . The heater 53 may be in the form of an electrical resistor. The reservoir 54 is connected to a dosing module 51 ("dosing module") via a distribution conduit (referenced 903 in FIG. 9). The metering module 51 is controlled by the control device 4. In the exemplary embodiment illustrated in FIG. 1, the control device 4 is distinct from the electronic computer 2. In a variant embodiment, the control device 4 can be integrated in the electronic computer 2. In another alternative embodiment, the control device 4 can be integrated in the control unit of the fuel system (sometimes called FSCU or Fuel System Control Unit). The control device 4 according to the invention is able to estimate the ammonia pressure in the storage system 5. If a difference is found between the estimated pressure and a set pressure supplied by the electronic computer 2, the control device 4 can adjust the heating power of the heater 53 to compensate for this difference. As illustrated in FIG. 1, the tank 54 is equipped with a temperature measuring device 6.

A particular embodiment of a diagnostic algorithm, as implemented within the control device 4, will now be described with reference to FIGS. 1 and 2.

During a step E21, the control device 4 obtains a set of information.

In a particular embodiment, the temperature measuring device 6 may comprise a temperature sensor configured to measure the temperature at a particular point in the tank. Thus, in step E21, the control device 4 can receive an instantaneous temperature measurement from the temperature sensor. In an alternative embodiment, the temperature measuring device 6 may comprise a plurality of temperature sensors arranged at several points of the tank. Thus, in this variant, in step E21, the control device 4 receives a set of temperature measurements.

In another variant embodiment, in step E21, the control device 4 reads (and in this sense obtains) a history of temperature measurements stored, for example, in a memory.

Advantageously, in step E21 the control device 4 can also obtain temperature and ambient pressure information. These may include instantaneous temperature and pressure measurements, historical measurements of these measurements, functional (function function) or a combination of these measurement histories. For example, the control device 4 can obtain the average temperature measured on a sensor during the previous five minutes; or an average temperature calculated by weighting more recent times than times further back in time. From such information, the control device 4 can determine the operating conditions in which the storage system will evolve.

In a particular embodiment, the control device 4 is able to use a predetermined model of gas desorption kinetics. This mathematical or experimental model can be, for example, stored in a memory.

In an alternative embodiment, the control device 4 is able to manage several models of gas desorption kinetics. Indeed, the desorption kinetics of a given gas may vary depending on environmental parameters such as, for example, the pressure and the ambient temperature, the humidity level, or the aging of the reservoir. The desorption kinetics may also depend on the gas state of the system. For example, each model can be associated with a pressure / ambient temperature torque. Thus, in an optional step (not shown) the control device 4 can select among the different predetermined models of gas desorption kinetics that which is associated with the temperature and ambient pressure measurements obtained in the previous step E21. In this way, we always make sure we have the best gas pressure estimate in the system.

In another optional step (not shown), the control device 4 can use the set of information obtained in the previous step E21 (Instantaneous, historical, functional measurements, ...) in combination with predetermined models of operation of the reservoir 54 and the heater 53 to check the plausibility and criticality of the measured parameters, as well as the operating state of the system. For example, the control device 4 can detect a possible component malfunction (tank, driver, ...) or a possible risk, for example, an abnormally high temperature may degrade the integrity of the tank.

Then, during a step E22, the control device 4 estimates the pressure of the gas in the system on the basis of the set of information obtained and a predetermined (or preselected) model of gas desorption kinetics. Then, this pressure estimate can be stored in a memory, so as to be able to constitute a history of pressure estimates.

In a particular embodiment, the model is a curve connecting the pressure of the gas to the temperature of the compound. For example, such a curve can be deduced from the Clausius-Clapeyron relation.

In an alternative embodiment, the model comprises a table connecting a functional value to a pressure value. For example, this functional value can be obtained by calculating an integral function of the set of instantaneous measurements obtained in step E21.

Finally, by way of example, during a step E23, the control device 4 can determine the difference between the estimated pressure and a setpoint pressure supplied, for example, by the electronic computer 2, and if necessary, adjust the heating power of the heater 53 to compensate for this difference. For example, if the pressure estimated by the control device 4 is greater than the set pressure, then the control device 4 generates a signal 42 such that it reduces the power supply of the heater 53.

In a preferred embodiment, the reservoir 54 comprises a plurality of storage cells communicating with one another and with at least one orifice communicating with the dosing module 51 via a distribution conduit (referenced 903 in FIG. 9). Such a reservoir is, for example, described in the co-pending application EP 11183413.1 in the name of the applicant, the contents of which for this purpose is incorporated by reference in the present application.

By "reservoir" is meant a container or enclosure defining at least one internal volume serving as a container for the compound. Preferably, the reservoir comprises at least one wall delimiting cells, ie cells. cavities capable of containing said compound. These cavities can have a shape any. Preferably, they all have the same shape. The shape and size of the cells are preferably adapted to fit at least a portion of the outer surface of the agglomerates.

Preferably, the cells are made of plastic. Thermoplastic materials give good results in the context of the invention, in particular because of the advantages of weight, mechanical and chemical resistance and easier implementation (which makes it possible to obtain complex shapes).

In particular, it is possible to use polyolefins, polyvinyl halides, thermoplastic polyesters, polyketones, polyamides, polyphthalamides and their copolymers. A mixture of polymers or copolymers may also be used, as well as a mixture of polymeric materials with inorganic, organic and / or natural fillers such as, for example, but not limited to: carbon, salts and other inorganic derivatives, natural fibers, glass fibers and polymeric fibers. It is also possible to use multilayer structures consisting of stacked and solid layers comprising at least one of the polymers or copolymers described above.

Excellent results have been obtained with polyphthalamide loaded with glass fibers.

Preferably, the shape of the cells (all or part of them) and / or their embodiment and / or assembly is such that at least one active element of the system (fulfilling a useful function such as heating, cooling or mechanical reinforcement) can be inserted into or between them. For example, a heating element or a phase change material (MCP, or material storing or returning heat by changing phase according to the surrounding temperature) is advantageously inserted in or between the cells.

The use of heating elements or phase change materials makes it possible to stabilize the temperature of the reagent contained in the cell and thus ensure a stable production of gas. In addition, the use of differentiated heating between cells and / or different relative amounts of phase change material between cells allows to deplete or enrich some gas cells; for example, during a shutdown of the system (following for example a stopping of the vehicle), the gas load (ammonia for example) in the cells cooling faster (containing for example little or no phase change material) will increase at the expense of cooling more cells slowly (eg containing a lot of phase-change material). This can be particularly advantageous for ensuring a rapid release of the gas after stopping the vehicle, for example by activating at this time preferably the gas-rich cells.

In the variant of the invention according to which the reservoir comprises several cells, the use of a temperature sensor per cell or group of cells makes it possible to drive each cell or cell group in temperature and therefore in pressure independently . This temperature control of the different cells or group of cells makes it possible to ensure a transfer of gas from one cell or group of cells to another cell or another group of cells.

Figures 3 to 17 schematically illustrate examples of cells each provided with a temperature measuring device according to a particular embodiment of the invention.

FIG. 3 illustrates a configuration in which the heating device 53 is placed in a housing, hereinafter referred to as a heating chimney, situated in the center of the cell 301. In the example of FIG. 3, the measuring device of FIG. temperature according to the invention comprises a single temperature sensor 302. The temperature sensor 302 is mounted on the outer wall of the cell 301. The temperature sensor can be mounted by any conventional mechanical means. In particular, clipping or gluing on the wall are well suited for a plastic cell. In this case, when the driver 53 is activated in order to desorb the gas (for example, ammonia, hydrogen, etc.) (stored by sorption on a compound), an increase in temperature is observed after a certain time. According to an advantageous aspect of the invention, the fact of observing this increase in temperature makes it possible to ensure the plausibility of the signal of the sensor 302 and the good operation of the driver 53. The plausibility of the signal of the sensor 302 and the good functioning of the driver 53 are determined using a predetermined model of operation of the sensor and a predetermined model of operation of the driver 53.

According to another advantageous aspect of the invention, the control device continuously monitors the attainment of a predetermined temperature threshold (ie predetermined model of operation of the reservoir, this model may comprise several predetermined thresholds or temperature ranges). If the control device detects that the measured temperature is above this threshold temperature, so it cuts the heat. This prevents overheating of the SCR system. According to another advantageous aspect of the invention, by analyzing the evolution of the temperature as a function of time it is possible to estimate the gas content of the compound (for example, a salt) separating the driver 53 from the temperature sensor 302 Indeed, the gas content affects the thermal transfer within the compound, in particular the desorption of the gas being endothermic, a high gas content in the compound tends to retard the temperature rise at the sensor 302. When the gas consumption is stable, the sensor signal 302 can regulate the heating so as to stabilize the pressure; an increase in gas consumption results in a drop in temperature which can be compensated by an appropriate action of the control device on the driver 53; conversely, a reduction in consumption results in an increase in temperature which can also be compensated. In an alternative embodiment, the temperature sensor 302 may be replaced by a heat flow sensor.

FIG. 4 illustrates a configuration in which a temperature sensor 402 is mounted on the outer wall of the cell 401 and in the vicinity of the heating stack. This arrangement is particularly advantageous for detecting any risk of overheating of the chimney to the right of the heating element. A particularly interesting case is constituted by a temperature sensor 402 at the same time playing the role of driver PTC (Positive Thermal Coefficient) whose resistance increases with temperature thus ensuring both the measurement and the heating function. These PTC type drivers also offer the advantage of limiting the heating power as the temperature rises, which reduces the risk of overheating.

In an advantageous variant (not shown), it is proposed to use a heating device having itself a PTC characteristic. In this way, it is possible to ensure both the heating of the cell and the temperature measurement.

FIG. 5 illustrates a configuration in which a temperature sensor 502 is mounted on the inner wall of the cell 501 and in the vicinity of the heating stack.

The configurations of FIGS. 4 and 5 have the advantage of allowing rapid detection of the risks of overheating. The security of the SCR system is therefore improved. FIG. 6 illustrates a configuration in which a temperature sensor 602 extends inside the cell 601. This configuration has the advantage of allowing a more precise measurement of the temperature of the compound, and thus of obtaining a released pressure estimate more accurate. The sensor may for example be directly placed in the compound during its placement in the cell.

FIG. 7 illustrates a configuration in which the temperature measuring device according to the invention comprises two temperature sensors 702 and 703. The temperature sensor 702 is mounted on the outer wall of the cell 701 and the temperature sensor 703 is extends inside the cell 701.

Figure 8 illustrates a configuration in which the cell 801 comprises two housings 804 and 805 (or transverse chimneys) formed in its wall. The housings 804 and 805 extend towards the heating stack so as to plunge into the compound. In this example, the temperature measuring device according to the invention comprises two temperature sensors 802 and 803. The housing 804 is configured to receive the temperature sensor 802, and the housing 805 is configured to receive the temperature sensor 803.

The configurations of FIGS. 7 and 8 each implement a combination of two temperature sensors. The combined use of two temperature sensors advantageously allows the control device to obtain temperature measurements from which it can estimate a heat flow. Such a heat flow if measured at specific points (for example at the periphery of the cell) makes it possible to evaluate the energy consumption. In an alternative embodiment, one of the two temperature sensors may be replaced by a heat flow sensor.

As illustrated in the example of FIG. 9, the temperature measuring device according to the invention may comprise a temperature sensor 902 mounted in the distribution duct 903 connecting the cell 901 to the dosing module (referenced 51 in the FIG. 1).

FIG. 10 illustrates an alternative embodiment of the configuration described above in relation with FIG. 3. In this variant, almost all of the outer wall of the cell 301 and the temperature sensor 302 (which is mounted on the outer wall of the cell) are covered with a layer 303 of thermally insulating material. For example, sheets made of Neoprene material give good results. The use of this layer 303 of insulating material advantageously makes it possible to avoid heat losses at the level of alveoli. This also makes it possible to reduce the disturbances on the temperature sensor 302, in particular the influence of the environment of the cells.

FIG. 11 illustrates another alternative embodiment of the configuration described above in relation to FIG. 3. In this variant, the quasi-totality of the outer wall of the cell 301 and the temperature sensor 302 (which is mounted on the outer wall of the cell) are covered with a layer 304 of phase change material (PCM). In a preferred embodiment, the phase change temperature of the MCP material corresponds to the desorption temperature of the compound (i.e. salt) generating the pressure necessary for the exhaust of the vehicle (typically 2.8 bar absolute). The use of this layer 304 of MCP material advantageously makes it possible to stabilize the temperature of the compound, and the pressure of the gas, for example around the desired value for this pressure. In this variant, the temperature rise curve has a plateau at the phase change temperature of the MCP, which makes it possible to easily diagnose the attainment of the desired temperature. In addition, in case of high gas consumption, the temperature of the compound tends to fall and the MCP material then restores heat to the cell, thus stabilizing the temperature and pressure. In case of low consumption on the contrary, the MCP material stores heat.

Other alternative embodiments can be imagined without departing from the scope of the present invention, for example by combining the elements of the different embodiments described above in relation to FIGS. 3 to 11.

In particular, the cells of Figures 4 to 9 may each be covered with a layer of insulating material and / or a layer of MCP material.

Moreover, and as illustrated in FIG. 12, the temperature sensor 302 of FIG. 11 can be replaced by a heat flux sensor 305. In the example of FIG. 12, the heat flux sensor 305 makes it possible to measure the flux between the layer 304 of MCP material and the cell 301 and thus to determine to what extent the control device must compensate for energy losses.

As illustrated in FIG. 13, the layer 304 of MCP material of FIG. 11 may itself be covered with a layer 306 of thermally insulating material. This makes it possible to further improve the performance of the by the reduced effect of environmental conditions. It goes without saying that a variant with flux sensor can also be considered.

In an alternative embodiment of Figure 13, the temperature sensor 302 may be placed between the layer 304 of MCP material and the layer 306 of insulating material.

FIG. 14 illustrates another alternative embodiment of the configuration described above in relation to FIG. 3. In this variant, a first P1 portion of cell is left bare (ie non-insulated) and a second portion P2 of cell is covered with a layer 307 of thermally insulating material. Thus, such a configuration allows during the shutdown of the system to cool more quickly the PI portion, and thus to allow a transfer of gas from the still hot portion P2 to the already colder PI portion.

FIG. 15 illustrates an alternative embodiment of the configuration described above in relation with FIG. 14. In this variant, a differential heating device 400 is placed in the heating stack. Thus, to allow a quick start, the heating power can be concentrated in the zone containing the highest concentration of gas at startup, for example at the uninsulated PI portion. This differential heating can for example be obtained simply by arranging a heating wire in the heating stack, for example in the form of a helicoid and by varying the pitch of this helicoid (for example, not smaller in the PI portion to be heated quickly ).

FIG. 16 illustrates an alternative embodiment of the configuration described above in relation to FIG. 15. In this variant, the cell comprises inside it a network of thermal conductors 600. This network of thermal conductors 600 makes it possible to ensure a very fast heat transfer in the zone containing the highest concentration of gas at startup, for example at the level of the uninsulated PI portion. The thermal conductors 600 are, for example, perforated discs or grids made of a good thermal conductor. These thermal conductors 600 are placed on or in the compound, such that they allow rapid radial heat transfer between the heating channel (i.e., heating stack) and the periphery of the cell at the portion P1.

FIG. 17 illustrates an alternative embodiment of the configuration described above in relation to FIG. 16. In this variant, the portion P1 of the cell is covered with an additional heating device 700. In this way, it is reinforced the heating at the level Pl. In the example of the 17, the additional heating device 700 is mounted on the outer wall of the cell. Of course, in another embodiment, this additional heating device 700 can be mounted inside the cell. The additional heating device 700 may be controlled independently or not from the other heating devices of the cell.

Note that the differential system presented above in connection with Figures 15 to 17 may be implemented at a group of cells, or between cell group. This differential system can be optimized according to the temperature and heat transfer conditions prevailing in the vehicle environment. For example, uninsulated areas will be placed in rapidly cooling locations, while isolated areas will be placed in hot spots for a longer time when the vehicle is shut down.

In view of the description of FIGS. 1 to 17 above, the control device according to the invention is able to implement different heating strategies, and in particular the following:

a heating strategy applied to cells as described above consisting in maintaining the heating in certain areas of the cells or in certain cells or in certain groups of cells so as to transfer the gas to the zones cooling more rapidly;

a heating strategy generating, during driving or during certain particular taxiing phases during which the consumption of gas is low, a transfer of gas to particular areas of the entire storage system, for example heated in certain groups of cells and stopping the heating in others;

a heating strategy to avoid overheating of the heating stack (plastic) and consisting, for example, chopping or modulating the heating power so as to allow the evacuation of thermal energy in the compound by conduction . A PWM type signal whose periodicity is adapted to the characteristic thermal transfer time corresponding to the geometry and properties of the materials is particularly advantageous;

a heating strategy based on the gas charge state of the cells or portions of plastic cells. This state of charge in gas is derived from the relationship between the signals of the temperature sensor (s) and the time profile of the control or the heating commands of these cells: the desorption of the gas being endothermic, the heating pulsations are will have little effect on the outer wall and a temperature sensor placed close to it if the compound (ie salt) is heavily loaded;

a heating strategy based on a measurement of the heat flow in the vicinity of the outer wall of the cells or group of cells or of the storage system or in the vicinity of this wall;

a heating strategy based on a measurement of the heat flow and the temperature at the outer wall of the cells or group of cells or storage system;

a heating strategy based on a measurement of the temperature located in a pocket (or housing) dug at any point in the wall of the cells or group of cells or of the plastic storage system and giving access to the temperature of the compound at somewhere.

Claims

A method of diagnosing a storage system (5) of a gas, the gas being sorbed on a compound, the system being mounted on board a vehicle and comprising a reservoir (54) capable of containing the compound and a control device (4) adapted to control a heating device (53) for raising the temperature of the compound so as to release the gas, characterized in that the control device obtains (E21) a set of information comprising at least one temperature measurement of the system and then making an estimate (E22) of the gas pressure in the system using a predetermined model of gas desorption kinetics; the reservoir comprising a storage cell provided with at least one of the following sensors:

a temperature sensor;

a heat flow sensor.

Method according to claim 1, characterized in that the control device is configured to determine operating conditions of the system from the set of information, and to select the model used from among a plurality of predetermined models of kinetics desorption of the gas, depending on the operating conditions determined.

3. Method according to any one of claims 1 and 2, characterized in that the model used is a Clausius-Clapeyron relationship.

4. Method according to any one of claims 1 to 3, characterized in that the control device is configured to detect at least one information about the operating state of the system using the set of information and at least l one of the following models:

a predetermined model of reservoir operation;

a predetermined model of operation of the heater.

5. Method according to any one of claims 1 to 4, characterized in that the storage cell comprises a wall in which is formed at least one housing, each housing extending towards the interior of the cell and being configured to receive the sensor (s).

6. Method according to any one of claims 1 to 5, characterized in that the cell is plastic.

7. Method according to any one of claims 1 to 6, characterized in that the cell is covered with at least one of the following materials:

- a thermal insulation material;

a phase change material.

8. Method according to any one of claims 1 to 7, characterized in that the cell is covered with an additional heating device.

9. Method according to any one of claims 1 to 8, characterized in that the cell comprises a thermal conductor network.

10. Method according to any one of claims 1 to 9, characterized in that said reservoir comprises at least one other storage cell.

11. Method according to any one of claims 1 to 10, characterized in that the compound is a solid.

12. Method according to any one of claims 1 to 11, characterized in that the gas is ammonia.

13. Method according to any one of claims 1 to 11, characterized in that the gas is hydrogen.