FR2914947A1 - Catalytic treatment device for internal combustion engine of motor vehicle, has reductor catalyst placed in upstream of silencer of exhaust line and associated to reduction units for reducing back pressure created in exhaust line - Google Patents

Abstract

The device has an oxidation catalyst (1) e.g. nitrogen oxide trap, and selective catalyst reductor (SCR) catalyst (4) that is placed in upstream of a silencer (6) of an exhaust line. The SCR catalyst is associated to reduction units for reducing back pressure created in the exhaust line. A bypass line (7) and a bypass control valve (8) are provided external to the SCR catalyst. The control valve controls access to the by-pass line. An independent claim is also included for a method for catalytic treatment of gas in an exhaust line.

Description

- 1 - DEVICE AND METHOD FOR CATALYTICALLY PROCESSING GASES

  The present invention relates to the treatment of exhaust gases at the outlet of an internal combustion engine, for example on a motor vehicle. More specifically, it relates to a device for catalytic treatment of gases in a vehicle exhaust line, comprising in series an oxidation catalyst, a particulate filter, and a selective reduction catalyst. The invention also relates to a catalytic process for treating gas in an exhaust line.

  To comply with the emission standards for nitrogen oxide (NOx) emissions of a combustion engine throughout the life of the engine, the vehicle is equipped with a specific after-treatment system, which can include, in accordance with the publication EP 1 617 051, a first treatment element, such as an oxidation catalyst, followed by a selective reduction catalyst or SCR catalyst (Selective Catalyst Reductor or SCR in English), with interposition of a particulate filter (FàP).

  The insertion of a SCR catalyst in an exhaust line, establishes a very strong back pressure therein, which results in a decrease in engine performance. The present invention aims to overcome this drawback, related to the implantation of a SCR catalyst. For this purpose, it proposes associating the SCR catalyst with means for reducing the back pressure it creates itself in the exhaust line.

  According to the invention, the SCR catalyst can be associated with, or integrated with, the muffler of the exhaust line. It may for example be arranged upstream thereof, with a bypass device.

  The invention also proposes that the SCR catalyst be bypassed over certain operating ranges of the engine. Other features and advantages of the present invention will become clear from reading the following description of non-limiting embodiments thereof, with reference to the accompanying drawings, in which: FIG. 1 illustrates the state of the technical, and - Figures 2 to 4, respectively illustrate three preferred embodiments of the invention. The exhaust line of FIG. 1 has, in this order, a first catalyst 1, such as an oxidation catalyst or a nitrogen oxide trap (NOx-trap), a particulate filter 2, an injector of reducing agent 3 (whose position may vary), such as urea, a catalyst RCS 4, and a silencer 6. In such an exhaust line, the treatment of hydrocarbons (HC) and oxides of carbon (CO ) is carried out within the oxidation catalyst 1, while the particles are trapped in the filter 2, which must be regenerated periodically. Finally, the selective reduction of nitrogen oxides NOx to nitrogen N is ensured in the second catalyst, such as a catalyst RCS 4, by the action of a reducing agent injected upstream thereof. Referring to Figure 2, it is found that the catalyst RCS 4 is integrated in the silencer 6. The catalyst RCS 4 and the silencer 6 are thus associated. This arrangement makes it possible, thanks to optimal sizing of the RCS and the silencer, and to a reduction in the volume of the system, to reduce the pressure losses at the cones of the exhaust line. Thus, the SCR catalyst 4 is associated with means for reducing the back pressure, which it itself creates in the exhaust line. In FIGS. 3 and 4, the RCS catalyst 4 is disposed upstream of the silencer 6. It has bypass means, constituted by a bypass line 7, the access of which is controlled by a bypass valve 8. In accordance with FIG. Invention, the RCS catalyst 4 can thus be doubled by an internal or external bypass line. This bypass is preferably operated under full load, in order to limit its loss of load only when it is highest. This guarantees efficient NOx treatment over a wide range of engine applications, without damaging the vehicle's usual overtaking capabilities. In FIG. 3, the bypass means 7, 8 are external to the RCS catalyst 4, whereas in FIG. 4 they are internal to the latter. - 4 - Different strategies for using the bypass line can be defined. A first strategy can be based on the activity of the driver's pedal, with recognition, like certain automatic transmissions, of a request for maximum performance by the user. It would thus be possible to limit the use of the bypass to the just necessary (on average 2% of the time of use of the engine), with a positive effect on the environment.

  According to the invention, the SCR catalyst is thus bypassed over certain operating ranges of the engine, preferably at full load. A second strategy can take into account the pressure level behind the SCR catalyst, through a spring valve (not shown), which opens depending on this pressure level. In both cases, a position sensor (on / off) can be used to diagnose faults in the system and ensure compliance with the On Board Diagnosis (OBD). In conclusion, it should be emphasized that the process implemented according to the invention makes it possible to treat NOx efficiently over a very wide range of use of the engine, without affecting the full load, and thus to extend the use of the -this.

Claims (10)

  A device for the catalytic treatment of gases in a vehicle exhaust line, comprising in series an oxidation catalyst (1) and a SCR catalyst (4), characterized in that the SCR catalyst (4) is associated with reduction means (6, 7, 8) of the back pressure it creates itself in the exhaust line.   2. Catalytic treatment device according to claim 1, characterized in that the RCS catalyst (4) is associated with the silencer (6) of the exhaust line.   3. catalytic treatment device according to claim 2, characterized in that the RCS catalyst is integrated in the silencer (6) of the exhaust line.   4. Catalytic treatment device according to claim 2, characterized in that the SCR catalyst (4) is disposed upstream of the silencer (6) of the exhaust line.   5. Catalytic treatment device according to claim 4, characterized in that it has bypass means (7, 8) of the SCR catalyst (4), comprising a bypass line (7) whose access is controlled by a bypass valve (8).   6. catalytic treatment device according to claim 5, characterized in that the bypass means (7, 8) are external to the catalyst RCS (4).   7. Catalytic treatment device according to claim 5, characterized in that the circumvention means (7,   8) are internal to the SCR catalyst (4). 8. Process for the catalytic treatment of gases in an exhaust line in which the gases pass through an oxidation catalyst (1) and a SCR catalyst (4), characterized in that the SCR catalyst (4) is bypassed on certain ranges engine operation.   9. Process for catalytic treatment according to claim 8, characterized in that the SCR catalyst (4) is bypassed at full load.   Process for the catalytic treatment of gases in an exhaust line in which the gases pass through an oxidation catalyst (1) and a SCR catalyst (4), characterized in that the SCR catalyst (4) is bypassed from a certain level of pressure behind it.