FR2812342A1 - DEVICE FOR REDUCING HARMFUL COMPONENTS IN THE EXHAUST GAS OF AN INTERNAL COMBUSTION ENGINE, ESPECIALLY A DIESEL ENGINE - Google Patents

Abstract

The invention relates to a device (1) which is intended for the reduction of harmful components in the exhaust gas of an internal combustion engine (3), in particular of a diesel engine, and which comprises a exhaust gas (2) in which are mounted one behind the other in the direction of the flow of the exhaust gas an oxidation catalytic converter (5), a catalytic converter (6) producing NO2 and a filter with particles (7). To avoid or at least reduce in the NO2 catalytic converter a back reaction of NO2 to NO, the oxidation catalytic converter (5) is a catalytic converter reducing hydrocarbons and/or carbon monoxide.

Description

The invention relates to a device which is intended for the reduction of

  noxious components of the exhaust gas of an internal combustion engine, especially a diesel engine, and which has an exhaust gas line in which are mounted one behind the other in the direction of gas flow exhaust an oxidation catalytic converter, a catalytic converter producing NO2 and a particulate filter. To remove particles in the exhaust gas of an internal combustion engine, in particular a diesel engine, a particle filter is preferably used which

  is installed in the exhaust gas line.

  However, the particle filter becomes clogged over time so that regeneration is necessary, which can be done for example by burning the particles on the filter. However, this requires a combustion temperature of around 550 C which cannot be reached

  under normal operating conditions.

  It is therefore desirable to have a continuous regeneration of the particulate filter by combustion. In a device of the type mentioned in the introduction, it has already been proposed for this purpose to connect upstream of the particle filter in the exhaust gas pipe an oxidation catalytic converter, cf. for example the document EP 0 341 832 B1, which can further oxidize the NO contained in the exhaust gas to NO2 with which the particles stored in the particle filter can be oxidized globally continuously. It is thus possible to decrease the transformation temperature for the particles to a temperature range above about 200 ° C. Such a system is known by the name of CRT system. A disadvantage of this system is that relatively large quantities of nitrogen oxide, which is itself a harmful product and which are subject to legal restrictions, are required for the regeneration of the particulate filter. Furthermore, the catalytic converter producing NO2 tends, in particular in the presence of hydrocarbons or CO in its operating zone, to allow a reaction to take place.

return from NO2 to NO.

  The object of the invention is to propose a device of the type mentioned in the introduction in which a reaction in

  NO2 to NO return is avoided or reduced.

  This problem is solved by a device of the type mentioned in the introduction and such that the catalytic oxidation converter reduces the hydrocarbons and / or the

  carbon monoxide contained in the exhaust gas.

  In the device according to the invention, an oxidation catalytic converter is connected upstream of the catalytic converter producing NO2 (catalytic converter to NO2) so that the exhaust gas arrives first at the catalytic oxidation converter and then at the NO2 catalytic converter, the oxidation catalytic converter being a catalytic converter which reduces hydrocarbons and / or carbon monoxide, i.e. which oxidizes the hydrocarbons and carbon monoxide present in the gas stream d carbon dioxide and water exhaust. As the NO2 to NO feedback reaction is promoted in the next NO2 catalytic converter by hydrocarbons and carbon monoxide which are avoided or reduced by the upstream connected oxidation catalytic converter, this feedback reaction is now at least reduced and the efficiency of the converter

  NO2 catalytic is significantly increased.

  In particular, zeolite and platinum are used.

as coating materials.

  According to a variant, the catalytic oxidation converter comprises a catalyst monolith with a platinum concentration of at least 50 g / ft3 (lft3 = 0.028 m3) and a dispersion of 30% (in the fresh state). Hydrocarbons and / or carbon monoxide are thus largely eliminated or at least reduced so that the effectiveness of the

  NO2 catalytic converter is significantly increased.

  The invention will be described in more detail below and other advantages which it makes it possible to achieve by means of advantageous designs of an exemplary embodiment and in

reference to the accompanying drawing.

  The drawing is a schematic representation of a device according to the invention. The device generally designated by 1 comprises an exhaust gas pipe 2 which extends from an internal combustion engine 3, in particular a diesel engine, and which is traversed, when the internal combustion engine 3 operates, by exhaust gas in the direction of flow indicated by arrow 4. In the exhaust gas line 2 are mounted one behind the other in the direction of flow 4 an oxidation catalytic converter 5, a catalytic converter producing NO2 6 (catalytic converter to NO2) and a particulate filter 7. The catalytic converter to NO2 can be

  a second conventional oxidation catalytic converter.

  The oxidation catalytic converter 5 adsorbs hydrocarbons and / or carbon monoxide. To this end, it has a coating. As the coating material, for example, zeolite or platinum should be used. The coating of the first catalytic oxidation converter 5 is designed such that the concentration of platinum in the catalyst monolith is at least g / ft3 for a dispersion of at least 30% (in the fresh state). In addition, for a spatial number of 15,000 h -1 with an exhaust gas which contains 50 ppm by mass (relative to propane) of hydrocarbons and 400 ppm by mass of carbon monoxide, the catalytic oxidation converter 5 has a temperature HC starting temperature of / 150/140 C maximum and a CO starting temperature of 150/140/130 C maximum (starting temperature =

% conversion).

  When the device 1 is operating, the exhaust gas flows from the internal combustion engine through the exhaust gas line 2. In so doing, the oxidation catalytic converter 5 converts hydrocarbons and carbon monoxide. A feedback reaction from NO2 to NO is thus prevented or at least reduced in the catalytic converter to NO2 6. The feedback reaction is in fact favored by hydrocarbons and carbon monoxide. These are largely removed by the oxidation catalytic converter 5 so that the efficiency of the NO2 catalytic converter 6 is increased. Although the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be readily understood by those skilled in the art that modifications in form and in detail can be made

  without departing from the spirit or the field of the invention.

LIST OF REFERENCES

  1 Device 2 Exhaust gas line 3 Internal combustion engine 4 Direction of flow Oxidation catalytic converter 6 Catalytic converter 7 Particulate filter

Claims (6)

  1. Device (1) which is intended for the reduction of harmful components in the exhaust gas of an internal combustion engine, in particular of a diesel engine, and which comprises an exhaust gas line (2) in which are mounted one behind the other in the direction of flow of the exhaust gas an oxidation catalytic converter (5), a catalytic converter (6) producing NO2 and a particle filter (7), characterized in that that the oxidation catalytic converter (5) reduces hydrocarbons and / or carbon monoxide   carbon contained in the exhaust gas.   2. Device according to claim 1, characterized in that the catalytic oxidation converter (5) comprises a coating adsorbing hydrocarbons and / or carbon monoxide.   3. Device according to claim 2, characterized in that the catalytic oxidation converter (5) has a zeolite coating.   4. Device according to claim 1 or 2, characterized in that the oxidation catalytic converter (5) has in the catalyst monolith a concentration of platinum of at least 50 g / ft3 (lft3 = 0.2028 m3) and   30% dispersion (fresh).   5. Device according to any one of   previous claims, characterized in that the   oxidation catalytic converter (5) with an exhaust gas which contains 50 ppm by mass (relative to propane) of HC and 400 ppm by mass of CO at a starting temperature HC of 160 C maximum and a starting temperature CO of About 150 C maximum, the spatial number of the catalytic oxidation converter (5) being from 15,000 h-1.   6. Device according to any one of   previous claims, characterized in that the   catalytic converter to NO2 (6) is a converter catalytic oxidation.