FR2884859A1 - Nitrogen oxide elimination system for e.g. private vehicle, has injector injecting reducing agent in exhaust gas, catalytic unit transforming nitrogen oxides into oxygen and water, and temperature sensor placed downstream of catalytic unit - Google Patents

Abstract

The system has an injector (7) that injects a reducing agent e.g. ammonia, in an exhaust gas of an internal combustion engine (3) of a motor vehicle. A reducing agent production unit (8) produces the reducing agent so as to eliminate nitrogen oxide. A catalytic unit (5) is situated on an exhaust line (2) of the engine and is provided for the selective transformation of nitrogen oxides into oxygen and water by catalytic reaction with the reducing agent. A temperature sensor (14) is placed downstream of the unit (5) for determining the temperature in the unit (5). An independent claim is also included for a method for the elimination of nitrogen oxide present in an exhaust gas of an internal combustion engine of a motor vehicle.

Description

System and method for removing nitrogen oxides from gases

  exhaust of an internal combustion engine of a motor vehicle

  The invention relates to the elimination of nitrogen oxides NO emitted by an internal combustion engine of a motor vehicle, including particular vehicles.

  Internal combustion engines produce exhaust gases that contain regulated pollutants, such as NOx, HC unburned hydrocarbons, carbon monoxide CO and particles that need to be treated.

  The permissible thresholds for pollutant gas emissions from 15 motor vehicles are regularly revised downwards as part of the evolution of pollution control regulations.

  Conventionally, the treatment of the nitrogen oxides emitted by the engine in the exhaust gas is treated with a nitrogen oxide trap installed in the exhaust line of the engine. Under normal exhaust conditions, ie when the fuel richness at the exhaust is low, the nitrogen oxide trap stores the nitrogen oxides in the form of nitrates at adsorption sites. , usually barium salt.

  Since the storage capacity of such a trap is limited, it is necessary to regenerate the trap regularly, by increasing the engine-controlled exhaust gas richness, to a value very slightly greater than 1. Under such conditions, the Nitrogen oxides are desorbed from storage sites and removed as nitrogen by a catalyst.

  These nitrogen oxide traps have an efficiency of the order of 80%, but has repercussions on the engine control. In certain driving conditions, the regeneration can even cause a driving inconvenience for the driver. It is then necessary to limit the regeneration in such situations. In addition, these nitrogen oxide traps are sensitive to sulfur and require thermal regeneration whose frequency increases with the aging of the trap.

  The invention aims in particular to increase the efficiency of the removal of nitrogen oxides released into the engine exhaust gas.

  The invention also aims to eliminate the nitrogen oxides released into the engine exhaust gas without affecting the operation of the engine.

  According to one aspect of the invention, there is provided a system for removing nitrogen oxides present in the exhaust gas of an internal combustion engine of a motor vehicle, embarked on board the vehicle. Said vehicle comprises an electronic control unit, and controlled means for injecting a reducing agent into the engine exhaust gas, upstream of a catalytic unit for selectively converting the nitrogen oxides into nitrogen and water through reaction with said reducing agent. Said catalytic unit is located on the exhaust line of the engine.

  The selective catalytic reduction does not require any intervention on the operation of the engine, and makes it possible to eliminate up to 90% of the nitrogen oxides present in the engine exhaust gases.

  In a preferred embodiment, the system comprises reducing agent producing means, controlled by production control means.

  Since the means of production of the reducing agent are on board the vehicle, problems of storage of large quantities of reducing agent and problems connected with setting up a distribution network of such a device are avoided. reducing agent.

  In an advantageous embodiment, the system further comprises a temperature sensor for determining the temperature in said catalytic unit.

  The arrangement of such a temperature sensor makes it possible to improve the destruction efficiency of the nitrogen oxides, since the catalyst of the catalytic unit makes it possible to eliminate the oxides of nitrogen in a particular temperature range, for example between 250 and 400 C.

  In addition, the system comprises reducing agent injection control means in the engine exhaust gas.

  In a first example, said reducing agent producing control means is adapted to manage variable rate continuous production of said reducing agent when the temperature of said catalytic unit is within a predetermined temperature range. The amount of reducing agent produced corresponds to the amount to be injected to remove said nitrogen oxides by said selective catalytic reaction.

  The amount of reducing agent required for the instantaneous need for removal of the nitrogen oxides emitted by the engine is continuously produced. If the temperature of the catalytic unit is outside of its operating temperature range, the production of reducing agent is stopped.

  In a second example, said reducing agent production control means are adapted to manage batch production at a constant rate of reducing agent, said produced reducing agent being stored in a tank. Said injection control means are adapted to manage, by controlling a flowmeter located upstream of the injection means, the injected quantity of reducing agent corresponding to the quantity necessary to remove said nitrogen oxides by said catalytic unit .

  The production of reducing agent is then intermittent or discontinuous, but of constant flow. This makes it possible to operate the production means of the reducing agent at an optimum operating point in terms of energy and in terms of concentrations obtained. This also avoids having to take into account high production peaks during peaks of emissions of nitrogen oxides by the engine, for example, during strong accelerations.

  In this example, a non-return valve located between the means for producing the reducing agent and said reservoir, and a flow meter controlled by said control means of the production of reducing agent.

  This keeps the reducing agent at high pressure in the tank.

  Advantageously, the system comprises means for determining the amount of nitrogen oxides present in the exhaust gases of the engine.

  For example, said determination means comprise a memorized map of the amount of nitrogen oxides present in the engine exhaust gas as a function of engine operating parameters.

  Depending on the parameters, the amount of reducing agent to be injected is known.

  In addition, said determination means comprise a sensor for measuring the amount of nitrogen oxides present in the exhaust gases of the engine.

  This allows to take into account a drift of emission of nitrogen oxides with the wear of the engine.

  For example, said engine operating parameters include the rotational speed of the engine, and / or the engine torque transmitted to the vehicle.

  In a preferred embodiment, said reducing agent is an ammonia agent, such as an ammonia gas, an ammonia solution, or urea.

  The ammonia agent being ammonia gas, said production means comprises a fuel reforming module. The fuel is already present in the vehicle.

  In addition, the production means comprise a compression module of said reformate.

  In a preferred embodiment, the production means 20 comprises an ammonia gas synthesis module from the compressed reformate.

  In an advantageous embodiment, said production means comprise a reformate purification module for reducing the presence of carbon monoxide in said reformate, or a module for purifying the output gases of said ammonia synthesis module to reduce the presence carbon monoxide in said output gas of said ammonia synthesis module.

  According to another aspect of the invention, there is also provided a method of removing nitrogen oxides present in the exhaust gas of an internal combustion engine of a motor vehicle. A reducing agent is injected into the engine exhaust, and selective catalytic conversion of the nitrogen oxides to nitrogen and water is effected by reaction with said reducing agent.

  Other aims, features and advantages of the invention will appear on reading the following description of some non-limiting examples and with reference to the appended drawings, in which: FIG. 1 is a block diagram of a mode of realization of a continuous production system with a variable flow rate of reducing agent, according to a first aspect of the invention; and FIG. 2 is a block diagram of one embodiment of a discontinuous flow rate reduction agent system according to another aspect of the invention.

  In Figure 1, there is shown a system 1 for removing nitrogen oxides present in the exhaust gas of a motor vehicle internal combustion engine according to one embodiment of the invention.

  The system 1 comprises an exhaust line 2 for treating the exhaust gas of an engine 3 before being released into the atmosphere.

  The system 1 also comprises an electronic control unit 4 capable of managing the operation of various elements of the vehicle.

  The system 1 comprises a catalytic unit 5 for selectively transforming the nitrogen oxides present in the vehicle exhaust gas by selective catalytic reaction between the nitrogen oxides and the reducing agent.

  The catalytic unit 5 is located on the exhaust line 2 of the engine 3.

  The exhaust line 2 generally comprises a catalytic oxidation module 6 for oxidizing carbon monoxide CO to carbon dioxide CO1.

  The system 1 further comprises an injector 7 for injecting a reducing agent into the exhaust gas of the engine 2, upstream of the catalytic unit 5. Production means 8 make it possible to produce the necessary reducing agent the elimination of nitrogen oxides.

  In the remainder of the present description, the reducing agent is NH 3 ammonia gas.

  The electronic control unit 4 comprises a module 9 for controlling the production of ammonia gas, as well as a module 10 for controlling the injection of ammonia gas upstream of the catalytic unit 5. In addition, the control unit electronic control 4 comprises a module 11 for determining the amount of nitrogen oxides present in the exhaust gas of the engine 3.

  The determination means 11 comprise a memorized map 12 of the quantity of nitrogen oxides present in the exhaust gas of the engine 3 as a function of operating parameters of the engine 3. These operating parameters comprise, for example, the speed of rotation. of the engine, and / or the engine torque transmitted to the vehicle. The system further comprises an optional sensor 13 for measuring the amount of nitrogen oxides present in the exhaust gas of the engine 3, downstream of the catalytic unit 5.

  The system 1 further comprises a temperature sensor 14 for determining the temperature in said catalytic unit 5, placed for example downstream of said catalytic unit 5.

  The means for producing ammonia gas comprise a flow meter 15 for managing the quantity of fuel required for the production of ammonia gas. Fuel can be taken from the vehicle's fuel tank or taken directly from the engine's high-pressure fuel rail. This fuel is conveyed via a conduit 16 to a reforming module 17 supplied with air by an air pump 18.

  The reforming module 17 can perform steam reforming, partial oxidation reforming, auto-thermal reforming, or plasma reforming.

  The reformate is fed to a purification module 19 via a conduit 20. The purification module 19 converts the carbon monoxide to carbon dioxide by the reaction: CO + H2O has CO2 + H2. The reforming or purification may require the addition of water vapor, which can be obtained by condensation of the air conditioning, or by storage of water in a tank provided for this purpose, or by a combustion of diesel fuel followed by condensation of the water vapor obtained.

  A conduit 21 conveys the purified reformate to a compression module 22. The reformate, purified or not of its carbon monoxide CO, is at low pressure at the outlet of the reforming module 17.

  For the synthesis of NH3 ammonia gas, the reformate must be compressed at high pressure. Generally, the compression module 22 contains two compression stages in order to be able to compress the ammonia gas by a pressure of about 1 bar to a pressure of about 100 bar. This compression is necessary to obtain an effective synthesis efficiency of ammonia gas.

  A compromise can be made between the energy spent in compression and the ammonia production reaction efficiency.

  The compressed reformate is conveyed via a conduit 23 to an ammonia synthesis module 24. The ammonia gas is synthesized by contacting the high pressure compressed reformate with a specific catalyst, for example an alkaline oxide activated iron oxide catalyst. The catalyst is supported by a porous material and disposed in an enclosure whose volume is adjusted as a function of the resistance time required for the synthesis of ammonia gas.

  Typically, the synthesis conditions of the ammonia gas are a pressure of the order of 100 bars with a temperature of between 350 and 500 C. The high-pressure ammonia gas is supplied to an expansion valve 25 via a conduit 26. The expander 25 allows to lower the pressure of the ammonia gas at the pressure of the exhaust line 2 in order to be injected upstream of the catalytic unit 5. The expander is connected to the injector 7 via a conduit 27.

  The sensors 13 and 14 are connected to the electronic control unit 4 by respective connections 28 and 29. The flowmeter 15 and the pump 18 are respectively connected to the electronic control unit 4 via connections 30 and 31. reforming module 17, the purification module 19, the compression module 22, and the synthesis module 24, are respectively connected to the electronic control unit 4 by connections 32, 33, 34 and 35. The expander 25 is connected to the electronic control unit 4 by a connection 36.

  In this embodiment, the ammonia gas is injected continuously into the exhaust line 2, with a variable flow rate. The nitrogen oxides are completely eliminated if, in the exhaust 2, the ratio of the mole fraction to ammonia gas and the mole fraction to nitrogen oxides is close to 1, for example between 0.8 and 1 , 2, because the reaction of elimination of nitrogen oxides with the ammonia gas is equimolar.

  The emission of nitrogen oxides at the outlet of the engine 3 defines the quantity of ammonia gas to be injected into the exhaust line. For example, for a given engine rotation speed and engine torque, the memorized map 12 provides the quantity of ammonia gas to be injected, therefore in this embodiment, to produce, to verify such a ratio substantially equal to 1.

  The optional presence of the sensor 13 making it possible to directly measure the quantity of nitrogen oxides present in the exhaust 2 makes it possible to take account of a drift in the emission of the nitrogen oxides as a function of the wear of the engine 3 and / or the emission dispersion of nitrogen oxides from one engine to another.

  With such a configuration, in a first step, for a given engine rotation speed and engine torque, the stored map 12 makes it possible to estimate the quantity of ammonia gas to be injected, and therefore to produce. The production control module 9 then controls the production of the estimated quantity, and the injection control module controls the injection of the ammonia gas produced by the injector. In this embodiment, the entire quantity of ammonia gas produced is injected, and the quantity produced is adapted to the quantity of nitrogen oxides to be removed.

  Once this quantity has been injected, either the sensor 13 no longer detects nitrogen oxides at the outlet of the catalytic unit 5, or the sensor 13 detects nitrogen oxides at the outlet of the catalytic unit 5.

  If the sensor 13 no longer detects nitrogen oxides, the ammonia production control module 9 and the ammonia gas injection control module 10 control the reduction in the quantity of ammonia gas produced and injected into the ammonia gas. the exhaust line 2.

  On the contrary, if the sensor 13 detects nitrogen oxides in the exhaust, the module 9 controls an increase in the amount of ammonia gas produced and injected into the exhaust line 2. This decrease or increase in the amount of ammonia gas is for example a predetermined fraction of the production and injection of ammonia gas, for example 5%. By iteration, the production and the injection of ammonia gas is then stabilized at the minimum level allowing a total treatment of the nitrogen oxides.

  In addition, the temperature sensor 14, for example placed downstream of the catalytic unit 5, makes it possible to determine a temperature range for which the catalytic unit 5 has an optimal operation for the selective catalytic reduction. When the temperature of the exhaust gas delivered by the sensor 14 is not in this range, the production and injection of ammonia is stopped. Typically, the temperature range for this selective catalytic reaction is 250-400 C. The term selective means that any troublesome reactions of ammonia with oxygen are avoided.

  Alternatively, when the system 1 is devoid of a module 19 for purifying the reformate produced by the reforming module 17, a purification module implanted on the exhaust line 2 between the injector 7 and the unit can be used. catalytic 5, to remove hydrogen and carbon monoxide injected with ammonia gas.

  In Figure 2, according to another embodiment, the system 1 produces ammonia gas at a constant rate discontinuously. With respect to the system of Figure 1, the system of Figure 2 is devoid of expander 25, but includes a reservoir 37 for storing ammonia gas under pressure. The pipe 26 is, for example, provided with a check valve 38.

  The system 1 also comprises a flowmeter 39, located on the conduit 27, between the reservoir 37 and the injector 7. The flowmeter 39 is connected to the electronic control unit 4 by a connection 40. In such a system 1, the Ammonia gas is produced intermittently at a fixed rate.

  It is then possible to operate the reforming module 17 at an optimum operating point in terms of reforming production consumption.

  It is thus also possible to avoid having to take into account high production of ammonia gas during emission peaks of the engine 3 in nitrogen oxides, for example during acceleration phases of the vehicle. The volume of the reformer can therefore be limited.

  These advantages are also valid for the compression module 22. Such a system 1 allows optimization of the energy used and the size of the system. The injection control module 10 further controls the flowmeter 39 to manage the quantity of ammonia gas to be injected by the injector 7.

  The tank 37 is equipped with a pressure sensor 41 connected to the electronic control unit 4 by a connection 42. When the energy and reagents, as well as to limit the methane clean to almost all pressure technologies to the interior of the tank 37 is less than a first predetermined pressure value, the control module 9 for producing ammonia gas controls the production of ammonia gas. When the pressure inside the reservoir 37 is greater than or equal to a second predetermined pressure value, the control module 9 for producing ammonia gas controls a stop of the production of ammonia gas.

Claims (17)

  A system for removing oxides of nitrogen present in the exhaust gases of an internal combustion engine (3) of a motor vehicle, on board the vehicle, said vehicle comprising an electronic control unit (4), characterized in that it comprises controlled injection means (7) of a reducing agent in the engine exhaust gas, upstream of a catalytic unit (5) for the selective transformation of nitrogen oxides into nitrogen and water by reaction with said reducing agent, said catalytic unit (5) being located on the exhaust line (2) of the engine.   2. System according to claim 1, characterized in that it comprises means for producing (8) reducing agent, controlled by production control means (9).   3. System according to claim 2, characterized in that it further comprises a temperature sensor (14) for determining the temperature in said catalytic unit (5).   4. System according to claim 2 or 3, characterized in that it comprises means for controlling the injection (10) of reducing agent into the exhaust gas of the engine.   5. System according to any one of claims 2 to 4, characterized in that said reducing agent production control means (9) are adapted to manage a variable-rate continuous production of said reducing agent when the temperature of said unit. catalytic converter (5) is within a predetermined temperature range, the amount of reducing agent corresponding to the amount required to remove said nitrogen oxides by said catalytic unit (5).   6. System according to any one of claims 2 to 4, characterized in that said production control means (9) of reducing agent are adapted to manage batch production at a constant rate of reducing agent, said reducing agent produces being stored in a reservoir (37), and in that said injection control means (10) are adapted to manage, by controlling a flowmeter (39) located upstream of the injection means (7), the injected amount of reducing agent corresponding to the amount necessary to remove said nitrogen oxides by said catalytic unit (5).   7. System according to claim 6, characterized in that it comprises a nonreturn valve (38) located between the production means (8) of the reducing agent and said reservoir (37), and a flow meter (39). controlled by said production control means (9) for reducing agent.   8. System according to any one of claims 4 to 7, characterized in that it comprises means for determining (11) the amount of nitrogen oxides present in the exhaust gas of the engine.   9. System according to claim 8, characterized in that said determining means (11) comprise a memorized map (12) of the amount of nitrogen oxides present in the engine exhaust gas as a function of operating parameters. of the engine (3).   10. System according to any one of the preceding claims, characterized in that it further comprises a sensor (13) for measuring the amount of nitrogen oxides present in the exhaust gas of the engine.   11. System according to claim 9 or 10, characterized in that said operating parameters of the engine comprise the rotational speed of the engine, and / or the engine torque transmitted to the vehicle.   12. System according to any one of claims 2 to 11, characterized in that said reducing agent is an ammonia agent, such as an ammonia gas, an ammonia solution, or urea.   13. System according to claim 12, characterized in that, the ammonia agent being ammonia gas, said production means (8) comprise a reforming module (17) of fuel.   14. System according to claim 13, characterized in that the production means (8) further comprise a compression module (22) of said reformate.   15. System according to claim 14, characterized in that the production means (8) further comprises an ammonia gas synthesis module (24) from the compressed reformate.   16. System according to claim 15, characterized in that said production means (8) further comprises a reformate purification module for reducing the presence of carbon monoxide in said reformate, or a module for purifying the gas from output of said ammonia gas synthesis module to reduce the presence of carbon monoxide in said output gas of said ammonia gas synthesis module.   17. A method for removing nitrogen oxides present in the exhaust gas of an internal combustion engine (3) of a motor vehicle characterized in that a reducing agent is injected into the exhaust gas of the engine. and selective catalytic conversion of the nitrogen oxides to nitrogen and water is effected by reaction with said reducing agent.