DE3608292A1 - Arrangement for vehicles, especially motor vehicles - Google Patents

Abstract

The arrangement for vehicles, especially motor vehicles, has a mixture-compressing internal combustion engine (1), an uncontrolled mixture forming device (2) provided in its intake line (3) and a catalytic exhaust emission control device containing a multifunction catalyst (5) connected in the exhaust pipe (4). In order to improve the limited nitrogen oxide reduction possible with an arrangement of this type and at the same time to suppress the formation of ammonia produced when rich combustion exhaust gases are admitted to the multifunction catalyst, it is proposed that downstream of a first converter (5) containing the multifunction catalyst the exhaust emission control device has a second converter (6) with a catalyst reducing nitrogen oxides in an oxidising atmosphere using ammonia as the reducing agent. <IMAGE>

Description

Arrangement for vehicles, in particular

Motor vehicles The invention relates to an arrangement for Vehicles, in particular motor vehicles, according to the preamble of the patent claim 1.

In order to achieve optimal exhaust gas values in vehicles with mixture-compressing internal combustion engines (Otto engines) to achieve, systems are known in which a arranged in the exhaust system a converter containing a multifunctional catalyst with a regulated mixture formation system is combined, with the measured values of a the oxygen content of the exhaust gas can be used. A However, such a system means a considerable effort and can not can easily be used on vehicles that are already in operation.

As a retrofit solution for such vehicles that are already in operation, a design has become known in which only the converter with the multifunction catalytic converter in the exhaust system is switched on, dispensing with the lambda probe and the complex mixture control. These catalytic converters, which usually consist of a carrier body provided with a noble metal coating, only set the three exhaust gas pollutants, which are limited for reasons of air pollution, in a very narrow range around the stoichiometric fuel-air ratio of X = 1, namely carbon monoxide CO, hydrocarbons HC and nitrogen oxides NOx , simultaneously at. In the case of combustion exhaust gases from a rich mixture (t <1), on the other hand, they can essentially only reduce nitrogen oxides and in the case of exhaust gases from a lean mixture (Ar> 1) only carbon monoxides and hydrocarbons. There one with such a Multifunctional catalyst equipped n # rennkiaü ### aschine part of the retrofit solution mentioned is operated without a mixture control, the air ratio and thus also the conversion rate for the individual exhaust gas components is a function of the random operating mode of the vehicle. A conversion rate in the range between only 30 and 50% can therefore be expected.

In addition to this relatively low conversion rate, there is another one Disadvantage of this known system is that the multifunctional catalysts Mixture ratios t <1 a part of the nitrogen oxides not directly to nitrogen, but reduce to ammonia (NH3), whereby at least an odor nuisance can occur.

The object on which the invention is based is therefore to provide a To create an arrangement of the type mentioned in the preamble, in which an improvement pollutant emissions, especially nitrogen oxides, and at the same time a Avoidance of the release of ammonia is achieved.

The solution to this problem is achieved by the features mentioned in the characterizing part of claim 1. The catalyst contained in the second converter according to the invention corresponds in principle to the catalysts used and developed for the nitrogen oxide reduction in the exhaust gases from power stations and other industrial systems. Such catalysts, which for example consist of a support body with a coating of an oxide of a base metal, such as titanium, vanadium, cerium, copper, cobalt, tungsten, manganese, molybdenum, iron, chromium, niobium, activated coke or zeolites, have the property of reducing nitrogen oxides under net oxidizing conditions, for example in combustion exhaust gases from lean engine operation, using ammonia as a reducing agent. By using such a second converter according to the invention, the nitrogen oxide emission originating from the engine and the ammonia emission originating from the first converter are reduced at the same time. Depending on the catalyst used, the working temperatures are between about 150 and 5000C with an optimum between 250 and 3500C, thus in a range that can easily be reached in exhaust systems of internal combustion engines and, if necessary, can be maintained using a secondary air supply. It would be useful if the second converter has means for storing ammonia carried along with the exhaust gas. While zeolite Catalysts, but also activated coke catalysts, have a considerable storage capacity for ammonia due to their inherent structure, this property can be cultivated in other types of catalyst by a corresponding choice of material or doping of the catalyst carrier or intermediate carrier that has an effect on the structure.

In the drawing is based on a schematic circuit diagram of a Drive arrangement for a motor vehicle shows an embodiment of the invention, which is explained in more detail below. In the drawing, 1 is a mixture-compressing one Internal combustion engine (Otto engine) referred to in its intake line 3 a conventional Has unregulated mixture former 2. This mixture generator can be used as a carburetor, but also be designed as a mechanical or electrical injection device, whereby, as is usual in today's systems without a catalytic converter, a consumption-optimized one Adjustment with a slight excess of air in most of the map and with rich Shares only when idling, at full load, in acceleration and overrun phases as well provided when the engine is cold.

To eliminate the contained in the exhaust gases of the internal combustion engine 1 Pollutants is provided in the exhaust pipe 4, a first converter 5, the one Has so-called multifunctional catalyst and usually from a with a There is noble metal coating on a carrier body provided with an intermediate layer. The catalyst of this first converter 5 starts at the stoichiometric fuel-air ratio (# = 1) all three limited exhaust gas pollutants at the same time while getting out of the exhaust gases a rich combustion mixture with; <1 essentially only the nitrogen oxides and from the exhaust gases of a lean combustion mixture with> 1 only the carbon monoxides and converts the hydrocarbons.

This first converter 5 is a second converter in the exhaust pipe 4 6 downstream, the catalyst of which should have the property of converting nitrogen oxides into using ammonia as a reducing agent. Such catalysts are in principle from nitrogen oxide reduction systems in power plants and other industrial plants and can be made from zeolites, for example Activated coke or from a carrier body provided with a non-metal oxide coating exist, where the base metal consists of titanium, vanadium, cerium, Copper, cobalt, tungsten, manganese, molybdenum, iron, chromium or niobium. In particular the catalysts consisting of zeolites or activated coke have due to their internal structure has the beneficial property that used as a reducing agent and store ammonia discharged from the first converter.

If a catalyst made from a base metal oxide is used, must Such an ammonia storage capacity, for example by cultivating a corresponding structure of the carrier body or the intermediate carrier layer attached to it be brought about. Ammonia storage is therefore of particular importance because in this way that during the implementation of the resulting from the rich combustion Combustion gases generated in the first converter 5 and stored in the second converter 6 Ammonia in subsequent operating states with combustion of lean mixtures for the then necessary and also possible nitrogen oxide reduction in the second converter 6 can be used.

In order to reduce the oxygen content in the exhaust gas in the second Keeping converter 6 in optimal ranges of e.g. 4 to 5% can be between first converter 5 and the second converter 6 one indicated by 7 in the drawing Secondary air supply, for example in the form of an automatic air intake, be provided. This secondary air supply can also be used to cool the exhaust gas are used to achieve an optimal operating temperature in the second converter to be able to maintain in the range between 250 and 3500 C.

In the system shown in the drawing, the internal combustion engine sucks 1 a fuel-air mixture via the intake line 3 with the unregulated mixture generator 2 and indicates the exhaust gas produced during combustion in the internal combustion engine Via the exhaust pipe 4 and the two converters 5 and 6 to the environment again away. The motor-driven mode changes according to the unsteady mode of operation of the vehicle Air-fuel-air ratio between the basic lean setting and rich Proportions, especially during acceleration, deceleration and full load phases. In In the rich operating phases, the first converter 5 sets the nitrogen oxides to a # m determined Part of it, mostly to nitrogen, a smaller part to ammonia. This ammonia is used in the second converter 6 to reduce further nitrogen oxides. This nitrogen oxide reduction in the second converter 6, which preferably takes place in an oxidizing atmosphere, i.e. when there is excess air can therefore be carried out in lean operating phases of the internal combustion engine, however only as long as ammonia is stored in the bulk of the catalyst. Carbon monoxide and unburned hydrocarbons are burned in the first converter 5, and essentially only during the lean operating phases with> 1. The if necessary, secondary air supply 7 integrated into the system, which for example at a venturi-like narrowing of the exhaust line 4 between the two converters 5 and 6 can be provided, allows an admixture of air to the exhaust gas, which an oxygen concentration required for the second catalyst to function optimally in the exhaust gas and, if necessary, one to maintain an optimal operating temperature required exhaust gas temperature control guaranteed.

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Claims (8)

CLAIMS @ arrangement for vehicles, especially motor vehicles, with a mixture-compressing internal combustion engine, one provided in the intake line, unregulated mixture former and with one switched on in the exhaust pipe, one Multifunctional catalytic converter containing catalytic exhaust gas cleaning device, characterized in that the exhaust gas cleaning device in the flow direction behind a first converter (5) containing the multifunctional catalyst second converter (6) with a nitrogen oxide in an oxidizing atmosphere and below Having use of ammonia as a reducing agent reducing catalyst. 2. Arrangement according to claim 1, characterized in that the second Converter (6) has means for storing ammonia carried along with the exhaust gas. 3. Arrangement according to claim 2, characterized in that the second Converter (6) has an ammonia-storing catalytic coating. 4. Arrangement according to claim 2, characterized in that the second Converter (6) an ammonia-storing carrier material or intermediate carrier material having. 5. Arrangement according to claim 1, characterized in that the catalytic Coating of the second converter (6) from oxides of single or multiple base metals like titanium, vanadium, cerium, copper, cobalt, tungsten, manganese, molybdenum, iron, chromium, Niobium is made. 6. Arrangement according to claim 1, characterized in that the catalyst of the second converter (6) consists of activated coke. 7. Arrangement according to claim 1, characterized in that the catalyst of the second converter consists of zeolites. 8. Arrangement according to one of claims 1 to 7, characterized in that that between the first converter (5) and the second converter (6) a secondary air supply (7) is provided.