FR2919338A1 - Exhaust gas line for internal combustion engine i.e. oil engine, of motor vehicle, has distributing circuit for distributing organometallic additive to injector to reduce temperature of combustion of particles accumulated in filter - Google Patents

Abstract

The line has a particle filter (7) associated with an oxidation catalyst (6) and an injector (4) introducing fluid i.e. fuel required to operate a pollution control device, into an exhaust conduit (2). An organometallic additive distributing circuit (19) distributes an organometallic additive to the injector to reduce temperature of combustion of particles accumulated in the filter. The injector is connected to an outlet of a fluid selector (10). An inlet of the selector is connected to a reducer fluid distribution circuit for selectively reducing nitrogen oxide in presence of the catalyst.

Description

The invention relates to a gas exhaust line equipped with

  depollution for an internal combustion engine of a motor vehicle and, more particularly for a motor operating in a lean mixture.

  The pollutants resulting from the combustion of a motor vehicle engine whether it is a diesel engine or gasoline, are mainly HC unburned hydrocarbons, nitrogen oxides (nitrogen monoxide NO and nitrogen dioxide NO2), carbon oxides (carbon monoxide CO) and in the case of diesel engines and gasoline direct injection engines operating in lean mixture, carbonaceous solid particles. In order to comply with international environmental standards, the control of HC, CO, NOx and particulate emissions is imperative and exhaust gas post-treatment technologies are essential. The clean-up of motor vehicles uses various after-treatment systems to remove the pollutants produced by the engine: catalysts, and the particulate filter in the case of diesel engines and gasoline operating in lean mixture. The treatment of HC hydrocarbons and carbon monoxide is carried out by oxidation catalysis. This reaction is facilitated in the case of diesel engines by the presence of a large excess of oxygen in the gas phase. The particulate filter filters out the solid particles present in the exhaust gas. Once trapped within the filter, the particles must be removed periodically by raising the temperature to 450-700 C in the filter to cause their combustion. This operation is commonly referred to as regeneration of the particulate filter. In order to achieve the combustion of the particles trapped in the filter, several methods are used by automobile manufacturers, for example, the additive fuel with an organometallic compound that significantly reduces the combustion temperature of the particles by regulating the oxygen level. , the oxidation by means of a specific catalytic formulation directly deposited on the walls of the particulate filter, or the oxidation of the particles continuously by reaction with the NO2, or by an electric heating technique. In addition, the combustion of the particles is initiated by a heat input upstream of the FAP which can come from several sources, such as the use of the engine post-injection and / or the modification of the injection means to increase the temperature of the fuel. exhaust gas up to a threshold of at least 500 C. In the case of the use of a post-injection it can burn completely or partially in the engine, generating a rise in the temperature of the gases. exhaust or, if it is sufficiently late, lead to an increase in the quantities of CO and HC in the exhaust which oxidize when arriving at the oxidation catalyst in order to generate heat. This method results in a high thermal stress on the catalyst closest to the engine which is subjected to each regeneration at a high temperature rise. In addition, the turbocharger and the exhaust manifold are also subjected to high temperatures. Finally, the heating methods resulting from the engine lead to the dilution of diesel oil in the lubricating oil thereof, which is detrimental to its service life. The use of diesel injection in the exhaust makes it possible to solve most of these problems. In this case the heating from the engine is greatly reduced and the heat is generated by combustion of the gas oil introduced to the exhaust on the catalyst upstream of the particulate filter. The oil dilution is then greatly reduced as are the thermal stresses on the exhaust manifold and the turbocharger.

  NOx treatment at the exhaust can be done using a NOx trap. The principle is based on a sequential engine operation with alternations in lean mode (excess oxygen at the exhaust, thus storage of NOx on the trap storage material which is preferably barium) and alternations mode rich (no excess oxygen in the exhaust, therefore destocking and reduction of NOx in N2). This system has the drawback of being sensitive to the sulfur contained in the fuels and of generating overconsumption and therefore an increase in the production of CO2. Another process known as SCR catalysis (Selective Catalytic Reduction) has the principle of selectively reducing NOx to nitrogen, in the presence of a specific catalyst, by the action of a reducing agent. This reducer is either already present in the exhaust gas or is injected upstream of the SCR catalyst. The reduction is carried out in a medium containing an excess of air. The reductant may be hydrocarbon (s), partially oxidized hydrocarbon species, or ammonia, or a compound, such as urea, generating ammonia by chemical decomposition. The use of the fuel additive method for lowering the particle combustion temperature in particle filter regeneration currently requires the provision of a specific reservoir containing the additive. This additive is then injected, in principle with each full of the fuel tank of the vehicle, in said tank. It should be noted, in the light of the preceding discussion, that the increasing complexity of the mandatory anti-pollution devices 30 multiplies the additions of fluids to the exhaust and, consequently, the necessary injection devices. The entire system therefore becomes particularly bulky and expensive.

  It is therefore advantageous to provide a single device installed in the exhaust line and for injecting several fluids simultaneously or alternately. However, this solution does not make it possible to suppress the injection of the fuel additive into the tank of the vehicle. The invention therefore proposes to directly inject the additive into the flow of the exhaust gas. For this purpose, the subject of the present invention is a gas exhaust line for a motor vehicle engine operating in a lean mixture equipped with pollution control devices comprising a particle filter associated with an oxidation catalyst and an injector intended to introduce in the exhaust duct the fluids necessary for the operation of the pollution control devices disposed upstream of the catalyst. This line is provided with a distribution circuit to the injector of a fluid additive to significantly reduce the combustion temperature of the particles accumulated in the particulate filter. According to other advantageous features of the invention: In a first embodiment of the invention: the injector is connected to the output of a two-position fluid selector of which one of the inputs communicates with a fuel distribution circuit and the other input is connected to the additive dispensing device. - In normal operation, the selector is placed in a first position in which the fuel distribution circuit is closed and the dispensing circuit of the additive open. 30 - In the regeneration phase of the particulate filter, the selector is placed in a second position in which the fuel distribution circuit is open and the additive distribution circuit closed. In a second embodiment: the injector is connected to the output of a two-position fluid selector of which one of the inputs is connected to an additive distribution circuit and the second input to a distribution circuit; distribution of a reducing agent for the selective reduction of NOx in nitrogen, in the presence of the catalyst. In normal operation, the selector is placed in a position in which the distribution circuit of the additive is closed and the distribution circuit of the gearbox open. In the regeneration phase of the particulate filter, the selector is placed in a position in which the additive distribution circuit and the reductant distribution circuit are both open. In a third embodiment: the injector is connected to the output of a three-way fluid selector and three positions, on the three inputs of which are connected, respectively, a distribution circuit 20 of the additive, a reducer distribution circuit and a fuel distribution circuit. In normal operation, the selector is placed in a position in which the fuel distribution circuit is closed and the distribution circuits of the additive and the reductant are open. - In the regeneration phase of the particulate filter, the selector is actuated in the position in which the additive and reductant distribution circuits are closed and the fuel distribution circuit is open. When the operating conditions of the depollution so require, the selector is actuated in the position in which the distribution circuit of the gearbox and the fuel distribution circuit are open and the distribution circuit of the additive is closed. In a fourth embodiment: the distribution circuit of the additive comprises a reservoir in which the additive necessary for the regeneration of the particulate filter is mixed with the reducing agent for the selective reduction of NOx into nitrogen, in the presence of the catalyst; . The injector is connected to the outlet of a two-way and three-position fluid selector on the two inlets from which the additive / reductant mixture distribution circuit and a fuel distribution circuit are respectively connected. In normal operation, the selector is in a position in which the additive / reductant mixture distribution circuit is open and the fuel distribution circuit is closed. - In regeneration phase of the particulate filter, the selector is placed in a position in which the additive / reductant mixture distribution circuit is closed and the fuel distribution circuit is open. When the operating conditions of the depollution require it, the selector is placed in a position in which the additive / reductant mixture distribution circuit and the fuel distribution circuit are open. • It will be noted again that: - A metering pump that is part of the additive distribution circuit is controlled by a computer to inject the additive when the estimated emissions of particles are greater than a predetermined threshold. - When the ignition of the vehicle is cut off, the reversible pump forming part of the reductant distribution circuit is actuated for a short time under vacuum, with the injector open, so as to purge the injector and the reductant line. As a variant, a mixer for injected fluids and exhaust gases is placed between the injector and the oxidation catalyst. - In another variant, an additional oxidation catalyst is disposed in the exhaust line downstream of the particulate filter. Other characteristics and advantages of the invention will become clear from reading the description below, given for information with reference to the accompanying drawings in which: FIG. 1 is a view of a first embodiment of the device according to the invention for alternately injecting additive or fuel into the exhaust pipe, FIG. 2 is a view of a second embodiment for injecting the additive simultaneously or alternatively and / Figure 3 is a view of a third embodiment for simultaneously or alternatively injecting the additive, a reducer and fuel into the exhaust duct, and Figure 4 is a view of a fourth embodiment in which the additive is mixed with the reducing fluid. FIG. 1 diagrammatically shows a motor vehicle engine 1 operating in a lean mixture, for example a diesel engine, as well as its exhaust line. This exhaust line has different depollution arrangements placed in the path of the exhaust gas to treat the various components thereof.

  The gases circulate in the exhaust duct 2 in the direction of the arrow F and, from upstream to downstream of their flow, there is a first oxidation catalyst or pre-catalyst 3, placed close to the outlet of the gases of the engine that processes HC unburned hydrocarbons and CO carbon monoxide from the engine. An injector 4 allowing the introduction of fluids into the exhaust pipe 2 is disposed between the pre-catalyst 3 and a second catalyst 6 associated with a particulate filter 7. The catalyst 6 and the particulate filter 7 are arranged at a sufficient distance from the injector 4 in the exhaust duct to allow good homogenization of the gas / fluid mixture injected. To complete this mixing and improve the catalytic conversions, it is possible to have a mixer 8 between the injector and the catalyst 6. A last oxidation catalyst 9 is optionally placed downstream of the particulate filter to prevent any over-emission of HC in phase. system operation. The output of a two-position fluid selector 10 is connected to the injector 4. One of the inputs of this selector 20 communicates with a fuel distribution circuit 5. The circuit comprises a conduit 11 for supplying fuel from a reservoir 12. This reservoir is, advantageously, the fuel tank of the vehicle and the fuel is sent into the conduit 11 by the fuel distribution pump 13 at 25. motor 1. The second input of the selector 10 is connected to the output of a conduit 14 which is part of the distribution circuit 19 of the organometallic additive to reduce the combustion temperature of the particles by regulating the oxygen level. This distribution circuit comprises a reservoir 15 and a metering pump 16.

  The injection system including the injector 4 is specially coated with a material, polytetrafluoroethylene type (PTFE) compatible with the various fluids and avoiding possible deposits. All tasks are managed and controlled by a computer 17 5 connected to the engine computer, possibly integrated therewith. In normal operation, the selector 10 is placed in position 1 0. 1, the conduit 1 1 of the fuel supply is closed and the conduit 14 open ensures the shipment of the organometallic additive in the exhaust. The metering pump 16 is controlled by the computer to inject the additive when the estimated emissions of particles are greater than a predetermined threshold. The quantity of additive to be injected is calculated according to the parametric conditions of the vehicle, the engine and the environment, and thus as a function of the engine particulate emissions When a regeneration of the particulate filter 7 is required by the motor control, the selector 10 is actuated in position 10.2. The distribution of the additive is interrupted and the conduit 11 opened to allow fuel injection into the exhaust duct, by the injector 4. At the same time, the exhaust line is preheated, for example, by engine operation in post-injection. When a predetermined temperature (450, for example), upstream of the catalyst 6 is reached, the pump 13 is activated to inject the fuel into the exhaust duct. The oxidation of the hydrocarbons thus introduced into the catalyst 6 generates an exothermic reaction on this catalyst and causes a significant release of heat and, consequently, the regeneration of the particulate filter 7. At the end of regeneration, the selector 10 returns to its position. initial 10.1, the system is ready to distribute the additive again. FIG. 2 shows an exhaust line of a motor 1 identical to that of FIG. 1. However, the two-way fluid selector 18 is connected, on the one hand, to an additive distribution circuit 19 to the particulate filter 7 similar to that just described and, secondly, a circuit 20 for dispensing a reducing fluid for the selective reduction of NOx to nitrogen, in the presence of the catalyst 6. The The reducer distribution circuit 20 is composed of a conduit 21 supplying the fluid to the inlet of the selector 18, a reversible dosing pump 22 which sends said fluid into the conduit 21 from a reservoir 23. A regulator pressure 24 is also connected bypass on the pump 22. The tasks are managed and controlled by the computer 25. In normal operation, it actuates the selector 18 in position 18.2, 15 so as to pass the reducer contained in the reservoir 23 to the inject 4 to ensure the reduction of nitrogen oxides to nitrogen. The distribution circuit 19 of the additive is closed. The amount of gearbox to be injected is applied to the metering pump 22. When the estimated particle emissions are above a predetermined threshold, the computer 25 selects the switch 18 to position 18.1 in which both channels are open. In this way, the additive is sent to the particle filter by the injector 4, at the same time as the reducer. At the end of the regeneration, the selector 18 returns to the initial position 18.2. In the case of using a urea-type reducer, the gel point of the product being at -1 ° C., arrangements to avoid this gel must be taken to keep the system efficient at low temperature. One of these measures is, during the breaking of the vehicle contact, to activate the pump 22 for a brief moment under vacuum, injector 4 open, so as to purge the injector and the reducer line.

  FIG. 3 represents a system in which it is possible to inject alternatively or simultaneously at least two of the three fluids required for the depollution treatments: fuel, additive and reducing agent into the exhaust duct 2.

  The exhaust duct 2, the additive distribution circuit 19 and the gear redistribution circuit 20 are identical to those just described, with reference to FIG. 2. The fluid selector 26 is a Three-way selector on the third channel of which is connected a fuel distribution circuit 27. This comprises a conduit 28, a pump 29 which sends the fuel into the conduit 28 from a reservoir, for example that of the vehicle 12. It further comprises a pressure regulator 30 connected bypass on the pump 29.

The computer 31 manages and controls the tasks. In normal operation, it controls the opening of the selector 26 in position 26.2. In this position, the fuel distribution circuit 27 is closed and the distribution circuits of the additive 19 and the gear 20 are open.

As in the previous embodiment, the additive is injected when the estimated particle emissions are above a predetermined threshold. And the amount of additive to be injected is calculated based on engine particulate emissions estimated from the operating conditions of the vehicle.

When a regeneration of the particle filter 7 is requested by the motor control, the selector 26 is actuated in position 26.1. The distribution of the additive and that of the reducer are interrupted and the duct 28 opened to allow the injection of fuel into the exhaust duct 2, by the injector 4.

At the same time, the exhaust line is preheated, for example, by post-injection engine operation. When a predetermined temperature (450, for example), upstream of the catalyst 6 is reached, the pump 29 is activated to inject the fuel into the exhaust duct. When the operating conditions of the depollution require it, the computer 31 controls the passage of the selector 26 in position 26.3 which opens, at the same time the conduit 21 of the gear redistribution circuit and the conduit 28 of the fuel distribution circuit. At the end of the regeneration of the particulate filter, the selector 26 returns to its initial position 26.2. As is well understood, the same injector is thus used to introduce into the exhaust duct the fluids required for the various depollution processes, which reduces both the size and the price of these systems. Of course, the invention is not limited to the embodiments that have just been described. In particular, the injection of the additive to the exhaust can be done in addition to the injection of the additive into the fuel tank, when the operating conditions require it. A variant also consists in mixing the additive and the reducing agent in the same tank. In this case, the injection system would, for example, conform to that shown in Figure 4. The exhaust pipe 2 and the fuel distribution circuit 27 are similar to those described above.

The fluid selector 32 is a two-way and three-position selector on the second channel of which is connected a distribution circuit 33 for the additive / reductant mixture. This comprises a duct 34, a pump 35 which sends the mixture into the duct 34 from a reservoir 36.

The computer 37 controls the system so that, in normal operation, the selector 32 is in its position 32.3 in which the feed pipe 34 of the mixture is open and the conduit 28 of the fuel closed. When a regeneration of the particle filter 7 is requested by the motor control, the selector 32 is actuated in position 32.1. The distribution of the additive / reductant mixture is interrupted and the duct 28 opened to allow the injection of fuel into the exhaust duct, by the injector 4. When the operating conditions of the depollution require it, the computer 37 controls the passage of selector lo 32 in position 32.2 which opens, at the same time the conduit 34 of the additive / reductant mixture distribution circuit and the conduit 28 of the fuel distribution circuit. At the end of regeneration of the particulate filter, the selector 32 is returned to the initial position 32.3. This configuration has the advantage of requiring only a single tank and a single distribution circuit for the additive and the reducer.

Claims (10)

  Motor vehicle exhaust line (1) operating in a lean mixture equipped with pollution control devices comprising a particulate filter (7) associated with an oxidation catalyst (6) and an injector (4) for introducing into the exhaust duct (2) the fluids necessary for the operation of the depollution devices arranged upstream of the catalyst (6), characterized in that it is provided with a circuit (19), (33) lo dispensing to the injector (4) a fluid additive that significantly reduces the combustion temperature of the particles accumulated in the particulate filter (7).   Gas exhaust line according to Claim 1, characterized in that the injector (4) is connected to the outlet of a two-position fluid selector (10), one of whose inputs communicates with a fuel distribution circuit (5) and whose other input is connected to the additive dispensing device (19).   3. Gas exhaust line according to claim 2, characterized in that, in normal operation, the selector (10) is placed in a first position (10.1) in which the cicuit (5) of fuel distribution is closed and the circuit (19) for dispensing the open additive.   4. Gas exhaust line according to claim 3, characterized in that, in the regeneration phase of the particulate filter (7), the selector (10) is placed in a second position (10.2) in which the cicuit ( 5) the fuel distribution is open and the circuit (19) for dispensing the additive closed.   5. gas exhaust line according to claim 1 characterized in that the injector (4) is connected to the output of a fluid selector (18) at two positions, one of which is connected to a circuit additive distribution device (19) and the second input to a reductant distribution circuit (20) for selectively reducing NOx to nitrogen in the presence of the catalyst (6).   6. gas exhaust line according to claim 5, characterized in that, in normal operation, the selector (18) lo is placed in a position (18.2) in which the circuit (19) for dispensing the additive is closed the distribution circuit (18) of the open gear.   7. gas exhaust line according to claim 6, characterized in that, in the regeneration phase of the particle filter (7), the selector 18 is placed in a position (18.1) in which the circuit (19) of distribution of the additive and the distribution circuit (18) of the gearbox are both open.   8. Gas exhaust line according to claim 1, characterized in that the injector (4) is connected to the outlet of a three-way and three-position fluid selector (26), on the three inputs of which an additive distribution circuit (19), a reducer distribution circuit (18) and a fuel distribution circuit (27) are respectively connected.   9. gas exhaust line according to claim 8, characterized in that, in normal operation, the selector (26) is placed in a position (26.2) in which the fuel distribution circuit (27) is closed and the distribution circuits of the additive (19) and the reducer (20) are open.   10. Gas exhaust line according to claim 9, characterized in that, in the regeneration phase of the particulate filter (7), the selector (26) is actuated in position (26.1) in which the distribution channels of the additive (19) and the gearbox (20) are closed and the fuel distribution circuit (27) is open. Gas exhaust line according to claim 10, characterized in that, when the operating conditions of the depollution require it, the selector (26) is actuated in position (26.3) in which the gear reducer distribution circuit (20) and the fuel distribution circuit (27) is open and the additive dispensing circuit (19) is closed. 12. gas exhaust line according to one of the preceding claims, characterized in that a metering pump (16) which is part of the circuit (19) for dispensing the additive is controlled by a computer to inject l additive when the estimated particle emissions are above a predetermined threshold. 13. Gas exhaust line according to claim 1, characterized in that the circuit (33) for dispensing the additive 1s comprises a reservoir (36) in which the additive necessary for the regeneration of the particulate filter (7). ) is mixed with the reducing agent for selectively reducing NOx to nitrogen in the presence of the catalyst (6). 14. gas exhaust line according to claim 13, characterized in that the injector (4) is connected to the output of a fluid selector (32) with two channels and three positions, the two inputs of which the additive / reductant mixture distribution circuit (33) and a fuel distribution circuit (27) are respectively connected. 15. Gas exhaust line according to claim 14, characterized in that in normal operation, the selector (32) is in a position (32.3) in which the additive / reductant mixture distribution circuit (33) is open. and the fuel distribution circuit (27) is closed. Gas exhaust line according to claim 15, characterized in that, in the regeneration phase of the particulate filter (7), the selector (32) is placed in a position (32.1) in which the distribution circuit (33) additive / reductant mixture is closed and the fuel distribution circuit (27) is open. 17. A gas exhaust line according to claim 16, characterized in that, when the operating conditions of the depollution require it, the selector (32) is placed in a position (32.2) in which the distribution circuit (33) ) of the additive / reductant mixture and the fuel distribution circuit (27) are open. 18. Gas exhaust line according to one of claims 5 to 17, characterized in that, during the breaking of the vehicle contact, the reversible pump (22), (35) forming part of the circuit (20) , (33) of distribution of the reducer is actuated briefly for a vacuum, injector (4) open, so as to purge the injector and the reducer line. 19. Gas exhaust line according to one of the preceding claims, characterized in that a mixer (8) injected fluids and exhaust gas is disposed between the injector (4) and the catalyst of oxidation (6). 20. Gas exhaust line according to one of the preceding claims, characterized in that it comprises an oxidation catalyst (9) downstream of the particulate filter.