EXHAUST SYSTEM FOR A DIESEL ENGINE

Abstract

An exhaust gas system for a diesel engine comprises a filter 9 that includes channels extending in the direction of flow and having porous walls 13 which are clad with an SCR catalyst coating 25. Neighbouring channels are alternately shut off by end plugs 15, 17 at the inlet end and the outlet end, as a result of which the exhaust gas is forced to flow through the walls. The walls 13 are coated with an AMOX catalyst coating 29 from the end 21 over a distance 27. The end plugs 17 in the outlet ends have a length that at least equals said distance 27. As a result, one side of the wall sections coated with the AMOX catalyst coating is covered and the exhaust gas cannot but flow first through the wall sections coated with SCR catalyst coating 25 and only then can the exhaust gas flow past the wall sections coated with the AMOX catalyst coating 29.

Description

FIELD OF THE INVENTION

The invention relates to an exhaust gas system for a diesel engine comprising an inlet and an outlet and a filter located in between comprising a plurality of channels arranged next to one another and having porous walls, where neighbouring channels are alternately shut off by an end plug at the inlet end and the outlet end, as a result of which the exhaust gas is forced to flow through the walls which are at least partially coated with a first coating.

STATE OF THE ART

An exhaust system of this type is generally known in the form of a diesel particle filter (DPF) in which the walls of the channels are coated with a selective catalytic reduction catalyst (SCR catalyst). The end plugs are generally installed before the walls are coated.

Once the exhaust gas has flown through the DFP with the SCR catalyst on it, it is desirable to have the filtered exhaust gas flow past an ammonia oxidation catalyst (AMOX catalyst).

SUMMARY OF THE INVENTION

It is an object of the invention to provide an exhaust gas system of the type defined in the opening paragraph which is advantageously provided with an AMOX catalyst. For this purpose the exhaust gas system according to the invention is characterized in that from the outlet end to a distance from this outlet end, the walls are coated with a second coating, where the end plugs in the outlet ends have a length that is at least equal to said distance over which the walls are coated with the second coating. If the AMOX catalyst has not been coated in the place of the end plugs on the walls of the channels, the exhaust gas will partially flow through the AMOX catalyst coated wall sections and partially through the SCR catalyst coated wall sections. By covering one side of the sections of the walls which are coated with the AMOX catalyst, the exhaust gas cannot but flow first through the SCR catalyst coated sections of the walls. Not until then can the exhaust gas flow past the wall sections coated with the AMOX catalyst coating. By shutting off the wall sections coated with the AMOX catalyst coating by means of the end plugs, no extra closing means are required. Only the end plugs in the outlet end need to be made longer than normal.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The invention will be further described below in more detail with reference to an embodiment of the exhaust gas system according to the invention represented in the drawing figures, in which:

FIG. 1 shows an embodiment of the exhaust gas system according to the invention in longitudinal section; and

FIG. 2 gives a detailed representation of the interior of the exhaust gas system shown in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 shows an embodiment of the exhaust gas system for a diesel engine according to the invention. The exhaust gas system 1 comprises a housing 3 which has an inlet 5 and an outlet 7 and a filter 9 accommodated in the housing. The filter comprises channels 11A and 11B extending in the direction of flow and having porous walls 13. The channels are open at one end and closed at the other by means of an end plug 15, 17. The channels 11A open at the inlet end 19 and closed at the outlet end 21 are then surrounded by channels 19B open at the outlet end 21 and closed at the inlet end 19. As a result, the exhaust gas 19 is forced to flow through the walls 13.

FIG. 2 gives a detailed representation of the interior of the filter 9 in enlarged form. From the inlet end 19 onwards the walls 13 are coated with an SCR coating 25 over a first distance and coated with an AMOX catalyst coating 29 from the outlet end 21 onwards over a second distance 27. The end plugs 17 in the outlet ends have a length that at least equals said second distance 27 over which the walls are coated with the AMOX catalyst coating 29. As a result, one side of the wall sections coated with the AMOX catalyst coating is covered and the exhaust gas cannot but flow first through the wall sections 13 coated with SCR catalyst coating 25. Only then can the exhaust gas flow past the wall sections 13 coated with the AMOX catalyst coating 29.

Albeit the invention has been elucidated in the foregoing with reference to the drawing figures, it should be set out that the invention is not by any manner or means restricted to the embodiments shown in the drawing figures. The invention also extends to any embodiments deviating from the embodiments shown in the drawing figures within the spirit and scope defined by the claims.

Claims

1. An exhaust gas system for a diesel engine comprising an inlet and an outlet and a filter located in between comprising a plurality of channels arranged next to one another and having porous walls, where neighbouring channels are alternately shut off by an end plug at the inlet end and the outlet end, as a result of which the exhaust gas is forced to flow through the walls which are at least partially coated with a first coating, characterized in that from the outlet end to a distance from this outlet end, the walls are coated with a second coating, where the end plugs in the outlet ends have a length that is at least equal to said distance over which the walls are coated with the second coating.

2. An exhaust gas system as claimed in claim 1, characterized in that the filter is a diesel particle filter, in that the first coating is a selective catalytic reduction coating and in that the second coating is an ammonia oxidation catalyst coating.