FR2964696A1 - System for treating exhaust gas of internal combustion engine of motor vehicle, has hydrocarbon injection system that is placed in upstream of nitrogen oxide trap and selective catalytic reduction system - Google Patents

Abstract

The system has a nitrogen oxide trap (13) to collect nitrogen oxides contained in exhaust gas and to reduce the nitrogen oxides. A selective catalytic reduction system (14) uses ammonia generated by the trap as a selective reducer to transform the nitrogen oxides into nitrogen. A hydrocarbon injection system (12) is placed in upstream of the trap and the selective catalytic reduction system. An electronic control unit (18) is connected to the hydrocarbon injection system. An independent claim is also included for a method for treating exhaust gas of an internal combustion engine of a motor vehicle.

Description

The present invention relates generally to the exhaust gas treatment systems of an internal combustion engine. BACKGROUND OF THE INVENTION The present invention relates generally to systems for treating the exhaust gases of an internal combustion engine. BACKGROUND OF THE INVENTION of a motor vehicle and in particular the systems for treating nitrogen oxides.

There are two types of systems for treating nitrogen oxides in an exhaust line of an internal combustion engine. It was first proposed to use a nitrogen oxide trap capable of capturing the nitrogen oxides contained in the exhaust gases and then reducing them during a regeneration phase called purge. Since the operation of the nitrogen oxide trap depends on both its temperature and the amount of catalyst used, the system must be located closer to the engine to increase its operating temperature.

Another type of treatment system uses a selective catalytic reduction. This treatment uses ammonia as a selective reductant to convert nitrogen oxides to nitrogen. The operation of the system also depends on its temperature.

The nitrogen oxide trap has the disadvantage of having to be placed near the engine, which limits the available volume and is likely to cause operating temperatures too high to treat the nitrogen oxides. This is particularly the case when the engine is operating at operating points where the heat output is highest. In addition to congestion problems, the selective catalytic reduction system has the disadvantage of requiring an ammonia injection system that is difficult to implement in motor vehicles.

FR2822498 discloses a gaseous effluent treatment system that proposes to combine the two approaches. This system comprises a nitrogen oxide trap located upstream of a selective catalytic reduction system and capable of generating the ammonia necessary for the continuous treatment of the nitrogen oxides by the selective catalytic reduction system. The purges of the nitrogen oxide trap which make it possible to obtain ammonia are obtained by wealth slots generated by the engine. In order to function, this combination needs high temperatures and richness slots greater than 1. This combination therefore has the disadvantage of causing a high dilution of the fuel in the oil. In addition, purges with a richness greater than 1 are only feasible over a reduced range of operating points of the engine. Flushes with a richness greater than 1 also generate high temperatures in the turbocharger of the engine. It has also been proposed to use a hydrocarbon injection system upstream of a selective catalytic reduction system and a particle filter. In this respect reference may be made to US2008 / 0022668. This hydrocarbon injection system makes it possible to regenerate a particulate filter located in an exhaust line. It has further been proposed to use an oxidation catalyst upstream of a particulate filter in an exhaust line, as described in FR2897643, to allow regeneration of the particulate filter at engine operating points. different. In view of the above, the present invention aims to overcome at least in part the disadvantages provided by the prior art and, in particular, to increase the production of ammonia necessary for the operation of the selective catalytic reduction system. Another object of the invention is to reduce the dilution of the fuel in the oil.

The object of the invention is also to make it possible to generate ammonia over an operating field of the enlarged engine. According to a first aspect, it is therefore proposed a system for treating the exhaust gases of an internal combustion engine of a motor vehicle comprising a nitrogen oxide trap capable of capturing the nitrogen oxides contained in the gases exhaust and reduce them and a selective catalytic reduction system that uses the ammonia generated by the nitrogen oxide trap as a selective reductant to convert nitrogen oxides to nitrogen.

The system includes a hydrocarbon injection system upstream of the nitrogen oxide trap and the selective catalytic reduction system. Thus, the invention makes it possible to overcome the only variations in the engine's richness. By injecting hydrocarbons with the hydrocarbon injection system, the richness in the exhaust line is increased, which increases the production of ammonia necessary for the operation of the selective catalytic reduction system. It also makes it possible to achieve the wealth requirement necessary to purge the nitrogen oxide trap and to form ammonia while reducing the dilution of the fuel in the oil by limiting the contribution of the engine to reach the setpoint. of richness necessary for purging, and to generate ammonia on an expanded engine operating field. The system may further include an electronic control unit connected to the hydrocarbon injection system. According to a first embodiment, the system comprises a particulate filter between the nitrogen oxide trap and the selective catalytic reduction system or downstream of the selective catalytic reduction system. Attaching the nitrogen oxide trap and the selective catalytic reduction system allows the temperature of the selective catalytic reduction system to be raised more rapidly. Advantageously, the system may comprise an oxidation catalyst between the hydrocarbon injection system and the nitrogen oxide trap.

This oxidation catalyst makes it possible to reduce the supply of oxygen to the nitrogen oxide trap, which favors the production of ammonia during purges of the nitrogen oxide trap. The oxidation catalyst also makes it possible to generate dihydrogen and carbon monoxide, which favors the production of ammonia during the purges of the nitrogen oxide trap. The oxidation catalyst finally makes it possible to reduce the hydrocarbon emissions after a cold start while raising the temperature of the nitrogen oxide trap. According to another embodiment, the system comprises a hydrogen sulfide treatment catalyst downstream of the selective catalytic reduction system. In another embodiment, the selective catalytic reduction system comprises a hydrogen sulfide treatment catalyst.

According to yet another embodiment, the system comprises a particulate filter which comprises a hydrogen sulfide treatment catalyst. In another aspect, there is provided a method for treating the exhaust gases of an internal combustion engine of a motor vehicle comprising a nitrogen oxide trap capable of capturing the nitrogen oxides contained in the gases. exhaust and reduce them and a selective catalytic reduction system, which uses the ammonia generated by the nitrogen oxide trap as a selective reductant to transform nitrogen oxides into nitrogen.

According to a general characteristic of the process, hydrocarbons are injected upstream of the nitrogen oxide trap and the selective catalytic reduction system. As long as the temperature of the nitrogen oxide trap has not reached a threshold value, hydrocarbons are injected. This allows the temperature of the nitrogen oxide trap and the selective catalytic reduction system to be adjusted to optimize purge of the nitrogen oxide trap and storage of ammonia.

If the mass of nitrogen oxide stored in the nitrogen oxide trap is greater than a threshold value then the nitrogen oxide trap is purged. If the amount of ammonia contained in the catalytic reduction system is less than a threshold value then ammonia is transferred from the nitrogen oxide trap to the selective catalytic reduction system. A wealth deposit controls the purge of the nitrogen oxide trap, using the hydrocarbon injection system to increase the wealth. Thus, the injection of hydrocarbons makes it possible to overcome the only variations in the engine's richness. By injecting hydrocarbons with the hydrocarbon injection system, the richness in the exhaust line is increased, which increases the production of ammonia necessary for the operation of the selective catalytic reduction system. The injection of hydrocarbons also makes it possible to reach the setpoint of richness necessary for the purge of the nitrogen oxide trap and the formation of the ammonia while reducing the dilution of the fuel in the oil by limiting the contribution of the engine to achieve the setpoint of wealth required for purging, and generate ammonia on an expanded engine operating field. The contribution of the engine being limited, the ammonia generation is possible on an expanded motor operating field.

Other advantages and characteristics of the invention will become apparent upon studying the detailed description of embodiments and embodiments, taken by way of nonlimiting examples and illustrated by the appended drawings in which: FIG. 1 illustrates an embodiment of a system according to the invention; FIG. 2 illustrates the various stages of control of the engine and of the hydrocarbon injection system; - Figure 3 illustrates the control of the engine and the hydrocarbon injection system; FIG. 4 illustrates another embodiment of a system according to the invention comprising a particulate filter; FIG. 5 illustrates a third embodiment of a system according to the invention comprising a particulate filter; FIG. 6 illustrates a fourth embodiment of a system according to the invention comprising an oxidation catalyst; FIG. 7 illustrates a fifth embodiment of a system according to the invention comprising a hydrogen sulfide treatment catalyst; FIG. 8 illustrates a sixth embodiment of a system according to the invention in which the selective catalytic reduction system comprises a catalyst for treating hydrogen sulphides; and FIG. 9 illustrates another embodiment of a system according to the invention in which the particle filter comprises a catalyst for treating hydrogen sulphides. FIG. 1 illustrates the general architecture of an internal combustion engine 1 and its exhaust line 2. The internal combustion engine 1 here comprises four cylinders 3 provided with fuel injectors 4. Air is admitted into the cylinders by an intake manifold 5 while the exhaust gas is recovered at the outlet by an exhaust manifold 6. In the example illustrated, the engine comprises a partial recirculation circuit exhaust gas 7 to limit the amount of nitrogen oxide produced while avoiding the formation of smoke in the exhaust line. The recirculation circuit 7 also comprises a member 8 for cooling the exhaust gas. The recirculation circuit 7 further comprises a bypass duct or bypass duct 9, which has no cooling circuit and which therefore recycles uncooled exhaust gas. The intake and exhaust manifolds are provided with two flaps 10, 11 which selectively allow the exhaust gases to be re-circulated to the cylinders 3 via the bypass duct 9. The invention of course applies also to engines that do not have exhaust gas recirculation. The exhaust line 2 comprises a nitrogen oxide trap 13 situated downstream of the additional hydrocarbon injection system 12 and capable of capturing the nitrogen oxides contained in the exhaust gases and then reducing them by generating ammonia. The exhaust line 2 also comprises a selective catalytic reduction system 14 located downstream of the nitrogen oxide trap 13 and adapted to use the ammonia generated by the nitrogen oxide trap 13 as selective reducer. Furthermore, an additional hydrocarbon injection system 12 capable of injecting fuel directly into the exhaust line 2 is arranged upstream of the nitrogen oxide trap 13.

The engine 1 and the exhaust line 2 comprise a number of sensors and probes. A first temperature sensor 15 indicates the temperature of the gases contained in the exhaust manifold 6 of the engine 1, a richness sensor 16 and a second temperature sensor 17, are furthermore located downstream of the oxide trap. 13. The assembly is connected to an electronic control unit 18 able to communicate by means of electrical connections 19 with the fuel injectors 4 of the engine, the additional hydrocarbon injection system 12, the first temperature 15 located in the exhaust manifold, the richness probe 16 located downstream of the nitrogen oxide trap 13 and the temperature probe 17 located downstream of the nitrogen oxide trap 13. Of course, the engine 1 and the exhaust line 2 may be further equipped with many additional members that have not been shown in the figure for simplification reasons. FIG. 2 illustrates the different control steps of the engine 1 and the hydrocarbon injection system 12. In a first step E100, if the temperature of the nitrogen oxide trap 13 is less than a threshold value noted Threshold 1, then a heating step E101 is implemented in which a set point C1 is sent to the additional hydrocarbon injection system 12 to cause the injection of hydrocarbons into the exhaust line 2 (step E102), and a heating setpoint C2 is sent to the engine 1 (step E103). The contribution of the engine 1 to heat the nitrogen oxide trap 13 and the selective catalytic reduction system 14 is reduced because of the hydrocarbon fuel input by the hydrocarbon injection system 12. In this respect, it will be noted that that the operating temperature of the nitrogen oxide trap 13 is about 200 ° C. Below this value, its operation is not optimal. On the other hand, if the temperature of the nitrogen oxide trap 13 has reached the threshold value Seuil_1, and the mass of nitrogen oxides stored in the nitrogen oxide trap 13 is greater than a threshold value noted Threshold_2 (step E104), then the system sends a setpoint C3 engine wealth (step E106) and a setpoint C4 purge nitrogen oxide trap 13 (step E105). If the quantity of ammonia contained in the selective catalytic reduction system 14 is less than a threshold value noted Threshold 3 (step E104), then ammonia is transferred from the nitrogen oxide trap 13 to the reduction system. This transfer corresponds to the transmission of the purge setpoint C4 of purging the nitrogen oxide trap 13 (step E105) and the setpoint C3 of the engine wealth (step E106). All the purges of the nitrogen oxide trap 13 thus contribute to refilling the selective catalytic reduction system 14 with ammonia. If the quantity of nitrogen oxides contained in the nitrogen oxide trap 13 is less than the value of threshold Threshold 2 and / or if the quantity of ammonia contained in the selective catalytic reduction system 14 is greater than a threshold value noted Threshold_3, a set point C5 of lean operating mode is sent to the engine (step E107). FIG. 3 illustrates the various models and measurements necessary for controlling the engine 1 and the hydrocarbon injection system 12. A first model M200 is used to evaluate the emissions at the output of the engine 1, to measure the quantities emitted hydrocarbons, carbon monoxide, oxides of nitrogen and oxygen. These measurements are necessary to evaluate the temperatures of the nitrogen oxide trap 13 and the amount of nitrogen oxide stored by the trap. The main inputs of the M200 emissions model are environmental conditions, engine operating points, engine temperature, and engine operating modes. The temperatures of the nitrogen oxide trap 13 and the selective catalytic reduction system 14 are also measured to be able to control and adjust them. A second model M202 is used to measure the storage efficiency of nitrogen oxides and the purge of the nitrogen oxide trap 13. The main input parameters of this model M202 are the quantities of nitrogen oxide upstream of the nitrogen oxide trap 13, the temperature of the nitrogen oxide trap 13. This model M202 is used to determine the ammonia emissions generated by the nitrogen oxide trap 13. This model M202 is is based on ammonia emission curves, and its main parameters are the temperature of the nitrogen oxide trap 13 and the amplitude and duration of the rich niche. The model M202 is also used to determine the amount of ammonia stored by the nitrogen oxide trap 13 and the amount of nitrous oxide treated. A third model M203 is then used to determine the ammonia requirements of the selective catalytic reduction system 14. These models are used to develop the controls of the engine 1 and the hydrocarbon injection system 12 as previously described. The invention is not limited to the embodiment described above with reference to FIG. 1. In fact, whereas in the embodiment according to FIG. 1, the exhaust line 2 is provided with an oxide trap. 13 and a selective catalytic reduction system 14, it is also possible, in other embodiments, to add other gaseous effluent treatment devices.

Referring to FIGS. 4 to 9, in which elements identical to those described with reference to FIG. 1 bear the same reference numerals, additional processing means can thus be provided upstream, downstream or between the oxide trap and nitrogen 13 and the selective catalytic reduction system 14 or integrated therewith. For example, as can be seen in FIG. 4, the exhaust line comprises a particulate filter 20 located downstream of the nitrogen oxide trap 13 and upstream of the selective catalytic reduction system 14. In the embodiment of FIG. 5, a particulate filter 21 is placed downstream of the selective catalytic reduction system 14, which makes it possible to attach the nitrogen oxide trap 13 to the selective catalytic reduction system 14 and to raise the temperature of the catalytic reduction system 14. selective catalytic reduction 14 more rapidly. In the embodiment of FIG. 6, the exhaust line 2 comprises an oxidation catalyst 22 located downstream of the additional hydrocarbon injection system 12 and upstream of the nitrogen oxide trap 13. The combination oxidation catalyst 22 and nitrogen oxide trap 13 reduce the supply of oxygen to the nitrogen oxide trap 13, which promotes the production of ammonia during purges of the oxide trap. Nitrogen 13. The combination also generates dihydrogen and carbon monoxide, which promotes the production of ammonia. The combination also reduces hydrocarbon emissions while raising the temperature of the nitrogen oxide trap 13 after a cold start. According to yet another embodiment illustrated in FIG. 7, a hydrogen sulfide treatment catalyst 23 is disposed downstream of the selective catalytic reduction system 14. Referring to FIG. 8, the selective catalytic reduction system 14 may be internally provided with a hydrogen sulfide treatment catalyst 25, located downstream of the nitrogen oxide trap 13 and adapted to use the ammonia generated by the nitrogen oxide trap 13 as a selective reductant . According to yet another embodiment visible in FIG. 9, the exhaust line 2 is provided with a particulate filter 26 comprising a hydrogen sulphide treatment catalyst 27 and located downstream of the nitrogen oxide trap 13 and upstream of the selective catalytic reduction system 14. Note that these various embodiments can also be combined, an exhaust line 2 may comprise, in addition to the nitrogen oxide trap 13 and the catalytic reduction system 14 at least one of the elements or arrangement described with reference to Figures 4 to 9.

Claims (13)

REVENDICATIONS1. An exhaust gas treatment system of an internal combustion engine (1) of a motor vehicle comprising a nitrogen oxide trap (13) capable of capturing the nitrogen oxides contained in the exhaust gas and to reduce them and a selective catalytic reduction system (14) which uses the ammonia generated by the nitrogen oxide trap (13) as a selective reductant to convert the nitrogen oxides to nitrogen, characterized in that it comprises a hydrocarbon injection system (12) upstream of the nitrogen oxide trap (13) and the selective catalytic reduction system (14). 2. System according to claim 1, characterized in that it comprises an electronic control unit (18) connected to the hydrocarbon injection system (12). 3. System according to one of claims 1 and 2, characterized in that it comprises a particulate filter (20, 26) between the nitrogen oxide trap (13) and the selective catalytic reduction system (14, 24). 4. System according to one of claims 1 and 2, characterized in that it comprises a particulate filter (21) downstream of the selective catalytic reduction system (14). 5. System according to one of claims 3 and 4, characterized in that the particulate filter (26) comprises a hydrogen sulfide treatment catalyst (27). 6. System according to any one of claims 1 to 4, characterized in that it comprises an oxidation catalyst (22) between the hydrocarbon injection system (12) and the nitrogen oxide trap ( 13). 7. System according to one of claims 1 to 6, characterized in that it comprises a hydrogen sulfide treatment catalyst (23) downstream of the selective catalytic reduction system (14). 8. System according to one of claims 1 to 7, characterized in that the selective catalytic reduction system (24) comprises a hydrogen sulfide treatment catalyst (25). 9. A process for treating the exhaust gases of an internal combustion engine of a motor vehicle by means of a nitrogen oxide trap capable of capturing the nitrogen oxides contained in the exhaust gases and of reduce them and a selective catalytic reduction system that uses the ammonia generated by the nitrogen oxide trap as a selective reductant to transform nitrogen oxides into nitrogen, characterized in that one injects hydrocarbons upstream of the nitrogen oxide trap and the selective catalytic reduction system. 10. The method of claim 9, wherein the hydrocarbon is injected as the temperature of the nitrogen oxide trap has not reached a threshold value. 11. Method according to one of claims 9 and 10, wherein the nitrogen oxide trap is purged if the mass of nitrogen oxide stored is greater than a threshold value. The process according to any one of claims 9 to 11, wherein ammonia is transferred from the nitrogen oxide trap to the selective catalytic reduction system if the amount of ammonia contained in the reduction system. selective catalytic is less than a threshold value. 13. Method according to one of claims 9 to 12, wherein a rich setpoint controls the purge of the nitrogen oxide trap.