Patent Application
20150185101
The present invention relates to a device for measuring the pressure of a gas.
The invention applies in particular, but not exclusively, to measuring the pressure inside an energy storage system such as, for example, a hydrogen storage reservoir mounted on a motor vehicle.
The invention applies also, but not exclusively, to measuring the pressure of a gas circulating in a pollution control system intended to reduce the amount of nitrogen oxides (NOx) in the exhaust gases of a motor vehicle. In the remainder of this document, every effort will be made to describe, by way of illustrative example, this particular type of application.
Of course, the present invention applies to measuring the pressure of any type of gas that may be present in a pollution control or energy storage system.
The nitrogen oxides present in the exhaust gases of vehicles, in particular diesel vehicles, can be eliminated by a pollution control system using a 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 standardised 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 (for example, by acting on the heating power of the heating device). Generally, a pressure sensor or a pressure regulator is used to measure the pressure of ammonia released. However, these pressure sensors and regulators are expensive and bulky.
It is therefore desirable to provide a device that makes it possible to measure the pressure of a gas, without using a pressure sensor or pressure regulator.
It is also desirable to provide such a device which is simple to use in a pollution control or energy storage system for a motor vehicle.
It is also desirable to provide such a device which is compact.
It is moreover desirable to provide such a device which is particularly well suited to measuring the pressure of any type of gas that may be present in a pollution control or energy storage system, and in particular ammonia and hydrogen.
In one particular embodiment of the invention, a device is proposed for measuring the pressure of a gas in a pollution control or energy storage system comprising:
The measuring device according to invention is based on the use of a compound that has an exothermic reaction. The compound is capable of absorbing gas and consequently of generating heat. The gas may be of any type, preferably ammonia or hydrogen.
It is thus proposed to measure the temperature of the compound by means of a temperature sensor or a heat flux sensor, and to deduce therefrom the pressure of the gas on the basis of a pressure/temperature relationship that governs the sorption of the gas on the compound.
The measuring device according to the invention is particularly intended for energy storage or pollution control (for example SCR) systems for motor vehicles. Advantageously, it is possible to use a processor already present on-board the vehicle to act as (i.e. carry out the functions of) the processing unit according to the invention. For example, it is possible to use the processor of the vehicle's on-board computer (sometimes referred to as ECU or engine control unit) or the processor of the control unit of the pollution control system or energy storage system (sometimes referred to as FSCU or fuel system control unit). In this way, the cost of the measuring device according to invention is reduced. Furthermore, by using a processing unit external to the casing, a casing is obtained that is small and easy to assemble. With such a configuration, the measuring device according to invention is less expensive and less bulky than a conventional pressure sensor.
In certain cases, the processing unit may be housed in the casing.
The casing may be made from one or more parts assembled for example by welding. The shape and the dimensions of the casing are generally defined so that the connection of the casing to a component of the pollution control system or energy storage system (duct, reservoir, etc.) requires no or little modification at the component itself. However, an intermediate constituent (or connection end piece) may be placed between the casing inlet/outlet and the component of the pollution control system or energy storage system.
The measuring device according to invention is in particular well suited to the case where the compound (placed inside the casing) is solid. It may be 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.
Advantageously, the pressure/temperature relationship is a Clausius-Clapeyron relationship.
The Clausius-Clapeyron relationship used by the processing unit may be a theoretical relationship (curve, table, formula, etc.), derived from the literature, preferably validated experimentally. Alternatively, this relationship may be generated experimentally on models and/or prototypes. Such a Clausius-Clapeyron relationship has the advantage of being simple, which results, at the processing unit, in relatively short computing times.
The casing is preferably made of a thermoplastic. Thermoplastics give good results within the context of the invention. The term “thermoplastic” denotes any thermoplastic polymer, including thermoplastic elastomers, and also blends thereof. The term “polymer” denotes homopolymers and copolymers (binary or ternary copolymers in particular). Examples of such copolymers are, non-limitingly: random copolymers, sequential copolymers, block copolymers and graft copolymers. Use may be made of polyamides or polyphthalamides and copolymers thereof, which are preferred for their heat resistance. A blend of polymers or of 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 firmly attached stacked layers comprising at least one of the aforementioned polymers or copolymers.
Advantageously, the casing comprises an electrical connector via which the sensor is powered and/or via which the processing unit obtains the temperature measurement from the sensor.
Advantageously, the casing comprises means for guiding the gas toward the inlet.
The shape and the dimensions of these guide means are generally defined so that all or some of the gas is directed toward the inlet of the casing. The guide means are, for example, a plate, a tube or a cone. They may be made, for example, of metallic or plastic material.
Advantageously, the casing comprises thermal insulation means.
By using such thermal insulation means, the temperature measurement carried out by the sensor is more accurate.
In one advantageous embodiment, the casing comprises at least one phase-change material (PCM). This makes it possible to limit the potential disturbances of the temperature measurement signal, in particular in the vicinity of the phase-change temperature, and to have a signature, making it possible to ensure that the pressure is above a given value (use of a PCM material) or that the pressure is within a given range (use of 2 PCM materials).
In one particular embodiment, the measuring device according to the invention may be connected to a distribution duct that connects a gas storage reservoir to a dosing module. Preferably, the gas storage reservoir is configured in order to contain a salt on which the gas is stored via sorption, preferably via chemisorption. In this particular embodiment is described in detail below with reference to
In another embodiment, the invention relates to a pollution control system comprising one or more pressure measuring devices as described above.
In another embodiment, the invention relates to an energy storage system comprising one or more pressure measuring devices as described above.
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:
In the remainder of the description, and by way of example, the gas for which it is desired to measure the pressure is a gas intended to be injected into the exhaust line of a vehicle in order to reduce the amount of nitrogen oxides (NOx) in the exhaust gases. By way of example, the gas is considered to be ammonia. Of course, in an embodiment variant, the gas may be of any other type, and in particular hydrogen.
As illustrated in the example of
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 ammonia thus released circulates from the reservoir 54 to a dosing module 51, via a distribution duct 7. The dosing module 51 is controlled by the control device 4. In the exemplary embodiment illustrated in
In the embodiment illustrated in
In the embodiment illustrated in
In one embodiment variant, the pressure measuring device 6 according to invention may comprise several temperature and/or heat flux sensors.
Advantageously, the control device 4 may use the temperature measurement(s) (i.e. instantaneous measurements) and/or a history of temperature measurements in order to diagnose a possible leak in the storage system 5 or to detect a malfunction of a component of the system.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1256291 | Jun 2012 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2013/051520 | 6/28/2013 | WO | 00 |
