Patent Application
20150160078
The invention relates to a method for diagnosing a gas storage system, preferably mounted on board a motor vehicle.
The invention applies in particular, but not exclusively, to diagnosing an ammonia storage system.
The invention applies also, but not exclusively, to diagnosing a hydrogen storage system.
In the remainder of this document, every effort will be made to describe the particular case of an ammonia storage system comprising plastic storage components. The ammonia is, for example, intended to be injected into the exhaust line on a vehicle in order to reduce the amount of nitrogen oxides (NOx) in the exhaust gases. Naturally, 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 diagnose the operating state 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.
The nitrogen oxides present in the exhaust gases of vehicles, in particular diesel vehicles, can be eliminated via the technique of selective catalytic reduction (generally referred to as SCR). 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, the ammonia is produced by the thermal decomposition of a precursor, generally an aqueous solution of urea. On-board systems for storing, dispensing and metering out a solution of standardized urea (such as that sold under the name Adblue®, a eutectic solution containing 32.5% urea in water) have thus been put on the market.
Another technique consists in storing the ammonia by sorption on a salt, usually an alkaline-earth metal chloride. Generally in this case, the storage system comprises a reservoir designed to contain the salt and a heating device configured in order to heat the salt. Thus, by heating the salt the ammonia is released. A pressure of ammonia is therefore generated. In such an ammonia storage system it is sought to obtain the pressure of ammonia released in order, for example, to verify that it corresponds to a required pressure of ammonia and, where appropriate, carry out corrective actions. It is also sought to detect the overheating of the salt heating device. This is even more important if the reservoir (formed by one or more storage components) is made of plastic, the mechanical properties of which are relatively temperature-sensitive. Generally, a pressure sensor or a pressure regulator is used to measure the pressure of ammonia released. These pressure sensors and regulators are expensive and bulky (compared to a temperature sensor). Generally, in order to detect the overheating of the salt heating device, the system uses a temperature sensor. Thus, the overheating is detected in a simple and effective manner. However, in certain cases it is desirable to be able to have other diagnostic information available, in particular to guarantee safe operation of the storage system and an effective reduction of the nitrogen oxides in the exhaust gases.
It is therefore desirable to provide a technique for diagnosing a gas storage system that makes it possible to obtain the pressure of the gas in the system without using a pressure sensor or pressure regulator.
It is also desirable to obtain a number of items 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, whatever gases and compounds are used.
In one particular embodiment of the invention, a method is proposed 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 suitable for controlling a heating device in order 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 comprising at least one temperature measurement of the system, then estimates the pressure of the gas in the system using a predetermined model of the gas desorption kinetics.
Thus, the present invention proposes to use one or more temperature measurements of the storage system in order to deduce therefrom the pressure of the gas in the system. The temperature measurement(s) is (are) obtained by means of one or more temperature sensors already present in the storage system. In one particular embodiment, the set of information that is used to estimate the pressure within the storage system comprises one or more temperature measurements carried out at a common instant (i.e. instantaneous measurements) and a history of temperature measurements, that is to say a set of temperature measurements carried out at instants preceding the common instant. In one embodiment variant, the set of information may comprise a functional of the history of these measurements. For example, such a functional (function of the function) may be an integral of the type:
Functional 1(t)=integral of (t−t1) at t of f(τ) T1(τ) dτ
with for example f(τ)=A*τ+B
where t denotes the time, T1 is the temperature measurement, t1, A and B are constants, and τ represents a time variable.
Usually, the desorption kinetics model for a given gas stored by sorption on a given compound is known. If this model is not known, it is possible to obtain it in a simple manner, for example, by measuring the desorption curve of the gas during the operation of the heating device. Using the desorption kinetics model it is possible to particularly accurately approach the pressure that actually exists within the storage system at the instant of the temperature measurement. The method according to invention thus makes it possible to very accurately calculate the pressure of the gas in the system, without using a pressure sensor or pressure regulator, which leads to a significant improvement in the assembly of the storage system and in the reduction of the cost of such a system.
In one preferred embodiment, the control device is on-board 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 of the vehicle, for example in a laboratory. Indeed, before being definitively mounted 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 (playing the role of control device) may adjust the desorption kinetics model of the gas to be used.
The desorption kinetics model of the gas is, for example, stored in a memory accessible to (i.e. readable by) the control device.
The gas may be of any type, preferably ammonia or hydrogen.
Advantageously, the control device is configured in order to determine operating conditions of the system from the set of information, and to select the model used from among a number of predetermined models of the gas desorption kinetics, as a function of the operating conditions determined.
In order to estimate the pressure of the gas in the system as accurately as possible, it is important to know under what conditions the system operates. This is because the operating conditions of the system have an influence on the desorption of the gas. This is why, according to one preferred embodiment of the invention, the control device chooses the gas desorption kinetics model that is most compatible with the operating conditions of the system. The various gas desorption kinetics models are, for example, stored in a memory accessible to (i.e. readable by) the control device. In one particular embodiment, the set of information comprises, in addition to the temperature measurement(s), an item of information (or a history) relating to the power dissipated by the heating device, an item of information (or a history) relating to the atmospheric pressure, or else an item of information (or a history) relating to the ambient temperature outside of the vehicle. This set of information is, for example, stored in a memory accessible to (i.e. readable by) the control device.
Advantageously, the model used is a Clausius-Clapeyron relation. The model used is a pressure/temperature relation governing the sorption of the gas on the compound. The Clausius-Clapeyron relation used in the method according to invention may be a theoretical relation (curve, table, formula, etc.), derived from the literature, preferably validated experimentally. Alternatively, this relation may be generated experimentally on models and/or prototypes.
Advantageously, the control device is configured in order to detect at least one item of information regarding the operating state of the system using the set of information and at least one of the following models:
Usually, the operating model of a given reservoir and the operating model of a given heating device are known. These models are, for example, theoretical curves, mappings or envelopes obtained experimentally for various operating states representative both of the operation of the reservoir and of the heating device. In one preferred embodiment, all or some of the information from the set of information is compared with predefined threshold ranges in order to diagnose the operating state of the storage system.
The information regarding 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 regarding the operating state of the system may for example be a detection of an abnormally high temperature, that is to say a temperature that may prove to be too critical for the long-term integrity of the reservoir. Information regarding the operating state of the system may for example be a gas fill level of the reservoir. Advantageously, a list of the various operating states possible is previously established and stored in a memory accessible to (i.e. readable by) the control device.
According to one advantageous feature, said reservoir comprises a storage cell equipped with at least one of the following sensors:
The sensor(s) may be mounted on the inside or outside (for example on the wall) of the cell. Some sensors may be mounted on the inside of the cell and other sensors outside of the cell. The sensors are spread over and/or in the cell as a function in particular of the geometry of the cell and of the diagnostic information that it is desired to obtain.
Advantageously, the storage cell comprises a wall wherein at least one housing is formed, each housing extending toward the inside of the cell and being configured in order to receive the sensor(s).
The mounting of the sensor(s) in the cell is therefore simple. Indeed, it is sufficient to insert it or them in the housing(s) provided for this purpose. Advantageously, one and the same housing may contain one or more sensors.
In one preferred embodiment, the cell is made of plastic.
Advantageously, the cell is covered with at least one of the following materials:
Advantageously, the cell is covered with an additional heating device.
Advantageously, the cell comprises a network of heat conductors.
Advantageously, the reservoir comprises at least one other storage cell. Thus, the reservoir may be constituted of a group of cells.
The method according to invention is particularly well suited to the case where the reservoir comprises a compound, preferably a solid, to which a gas (ammonia, hydrogen, etc.) is attached via sorption, preferably via chemisorption. It is generally an alkali, alkaline-earth or transition metal chloride. It may be in the pulverulent state or in the form of agglomerates. This compound is preferably an alkaline-earth metal chloride, and very particularly preferably an Mg, Ba or Sr chloride.
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:
Exemplary embodiments are described below in relation to
As illustrated in
In this exemplary embodiment, the SCR system 3 comprises an ammonia storage system 5. The storage system 5 comprises a reservoir 54, stored in which is 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 heating device 53 (also referred to as heater) for heating the solid 52 so as to release the ammonia. The heating device 53 may be in the form of an electrical resistor. The reservoir 54 is connected to a dosing module 51 via a distribution duct (referenced 903 in
One particular embodiment of a diagnostic algorithm, as implemented within the control device 4, is now described in relation to
During a step E21, the control device 4 obtains a set of information.
In one particular embodiment, the temperature measuring device 6 may comprise a temperature sensor configured in order to measure the temperature at a given point of the reservoir. Thus, in step E21 the control device 4 may receive an instantaneous temperature measurement originating from the temperature sensor.
In one embodiment variant, the temperature measuring device 6 may comprise a plurality of temperature sensors positioned at several points of the reservoir. Thus, in this variant, in step E21 the control device 4 receives a set of temperature measurements.
In another embodiment variant, 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 may also obtain information on the ambient temperature and pressure. These may be instantaneous temperature and pressure measurements, histories of these measurements, functionals (function of function) or a combination of these measurement histories. Thus, for example, the control device 4 may obtain the average temperature measured on a sensor over the previous five minutes; or else an average temperature calculated by weighting the recent instants more than the instants further back in time. From such information, the control device 4 may determine the operating conditions under which the storage system will change.
In one particular embodiment, the control device 4 is capable of using a predetermined model of the gas desorption kinetics. This mathematical or experimental model may be, for example, stored in a memory.
In one embodiment variant, the control device 4 is capable of generating several models of the gas desorption kinetics. Indeed, the desorption kinetics of a given gas may vary as a function of environmental parameters such as, for example, the ambient pressure and temperature, the moisture content, or else the ageing of the reservoir. The desorption kinetics may also depend on the degree of gas loading of the system. For example, each model may be associated with an ambient pressure/temperature pairing. Thus, in an optional step (not represented) the control device 4 may select from among the various predetermined models for the gas desorption kinetics the one which is associated with the ambient temperature and pressure measurements obtained in the preceding step E21. In this way, having the best estimate of pressure of the gas in the system is always guaranteed.
In another optional step (not represented), the control device 4 may use the set of information obtained in the preceding step E21 (instantaneous measurements, histories, functionals, etc.) in combination with predetermined models of operation of the reservoir 54 and of the heating device 53 in order to verify the plausibility and criticality of the parameters measured, and also the operating state of the system. For example, the control device 4 may detect a possible component (reservoir, heater, etc.) malfunction or a possible risk, for example an abnormally high temperature that may degrade the integrity of the reservoir.
Next, during 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 the gas desorption kinetics. Then, this pressure estimate may be stored in a memory, so as to be able to constitute a history of the pressure estimates.
In one particular embodiment, the model is a curve linking the pressure of the gas to the temperature of the compound. For example, such a curve may be deduced from the Clausius-Clapeyron relation.
In one embodiment variant, the model comprises a table linking a functional value to a pressure value. For example, this functional value may be obtained by calculating an integral function from all of the instantaneous measurements obtained in step E21.
Finally, by way of example, during a step E23, the control device 4 makes it possible to determine the difference between the estimated pressure and a pressure setting provided, for example, by the engine control unit 2, and where appropriate to adjust the heating power of the heating device 53 in order to compensate for this difference. For example, if the pressure estimated by the control device 4 is greater than the pressure setting, then the control device 4 generates a signal 42 such that it decreases the supply power of the heating device 53.
In one preferred embodiment, the reservoir 54 comprises a plurality of storage cells that communicate with one another and with at least one orifice that communicates with the dosing module 51, via a distribution duct (referenced 903 in
The term “reservoir” is understood to denote a container or chamber that delimits at least one internal volume used to contain the compound. Preferably, the reservoir comprises at least one wall that delimits cells, i.e. cavities capable of containing said compound. These cavities may have any shape. Preferably, they all have the same shape. The shape and size of the cells are preferably suitable for being able to match at least one part of the outer surface of the agglomerates.
Preferably, the cells are made of plastic. Thermoplastics give good results within the context the invention, in particular due to advantages of weight, of mechanical strength and chemical resistance and of easier processing (which precisely makes it possible to obtain complex shapes).
In particular, it is possible to use polyolefins, polyvinyl halides, thermoplastic polyesters, polyketones, polyamides, polyphthalamides and copolymers thereof. A blend of polymers or copolymers may also be used, as can a blend of polymeric materials with inorganic, organic and/or natural fillers such as, for example, but nonlimitingly: carbon, salts and other inorganic derivatives, natural fibers, glass fibers and polymeric fibers. It is also possible to use multilayer structures consisting of stacked layers that are firmly attached comprising at least one of the polymers or copolymers described above.
Excellent results have been obtained with polyphthalamide filled with glass fibers.
Preferably, the shape of the cells (all or some of them) and/or their method of production and/or assembly is such that at least one active component of the system (fulfilling a useful function such as heating, cooling or mechanical reinforcement) can be inserted in or between them. For example, a heating component or a phase change material (PCM, or material that stores or releases heat on changing phase depending on the temperature that surrounds it) is advantageously inserted in or between the cells.
The use of heating components or phase change materials makes it possible to stabilize the temperature of the reactant contained in the cell and to thus ensure a stable production of gas. Furthermore, the use of differentiated heating between cells and/or different relative amounts of phase change materials between cells makes it possible to deplete or enrich certain cells in terms of gas; for example, during a shutdown of the system (following for example stopping of the vehicle), the gas (for example ammonia) loading in the cells that cool more quickly (for example containing little or no phase change material) will increase at the expense of the cells that cool more slowly (for example containing a lot of phase change material). This may be particularly advantageous for ensuring a rapid provision of the gas after the vehicle has been stopped, for example by activating at this moment preferably the gas-rich cells.
In the variant of the invention according to which the reservoir comprises several cells, the use of one temperature sensor per cell or group of cells makes it possible to control each cell or group of cells independently in terms of temperature and therefore pressure. This temperature control of the various cells or group of cells makes it possible to ensure a transfer of gas from one cell or from one group of cells to another cell or another group of cells.
According to another advantageous aspect of the invention, the control device permanently monitors the reaching of a predetermined temperature threshold (i.e. predetermined model of operation of the reservoir, it being possible for this model to comprise several predetermined temperature thresholds or ranges). If the control device detects that the temperature measured is greater than this temperature threshold, then it turns off the heating. Any overheating of the SCR system is thus avoided. According to another advantageous aspect of the invention, by analyzing the change in temperature as a function of time, it is possible to estimate the gas content of the compound (for example a salt) separating the heater 53 from the temperature sensor 302. Specifically, the gas content affects the heat transfer within the compound, in particular since the desorption of the gas is endothermic, a high content of gas in the compound tends to slow down the temperature rise at the sensor 302. When the gas consumption is stable, the signal from the sensor 302 makes it possible to regulate the heating so as to stabilize the pressure; an increase in the gas consumption results in a temperature drop which may be compensated for by appropriate action of the control device on the heater 53; conversely, a reduction in consumption results in a temperature increase which may also be compensated for. In one embodiment variant, the temperature sensor 302 may be replaced by a heat flux sensor.
In one advantageous variant (not illustrated), it is proposed to use a heating device that itself has a PTC characteristic. In this way, it is possible to provide both the heating of the cell and the temperature measurement.
The configurations from
The configurations from
As illustrated in the example from
Other embodiment variants may be imagined without departing from the scope of the present invention, for example by combining the components of the various embodiments described above in connection with
In particular, the cells from
Furthermore, and as illustrated in
As is stated in
In one embodiment variant of
It is noted that the differential system presented above in connection with
In view of the description of
| Number | Date | Country | Kind |
|---|---|---|---|
| 1256289 | Jun 2012 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2013/051521 | 6/28/2013 | WO | 00 |
