DE2804562A1 - Internal combustion engine with reduced nitrogen oxide emission - having catalytic coating on wall of combustion chamber - Google Patents

Abstract

A multi-cylinder IC engine is claimed, in which the combustion chamber wall of each cylinder is coated with a catalytic material capable of reducing nitrogen oxides (NOx) formed during combustion. The coating is rpesent in at least those regions where the air/fuel mixt. is relatively rich ( =1) The system is esp. applicable to diesel engines (e.g. of the turbulent-chamber or direct-injection type) operating with a lean air/fuel mixt. NOx emission is effectively reduced without the use of external catalytic converters or exhaust gas recycle systems.

Description

VOLKSWAGENWERK ² ^ OA

AKTIENGESELLSCHAFT 5180 Wolfsburg

Our reference: K 2478
1702pt-we-jä

Multi-cylinder internal combustion engine

The invention relates to a multi-cylinder internal combustion engine with a combustion chamber assigned to each cylinder, in which a mixture of air and fuel is ignited and burned will.

When a fuel-air mixture is burned in the combustion chambers of internal combustion engines, the Pollutants harmful to the environment, such as carbon monoxide in particular, Hydrocarbons and nitrogen oxides. Various measures are taken in eliminating or reducing these pollutants known that either act on the combustion process itself in the sense of a reduced formation of these substances or the pollutants that have already arisen through subsequent treatment of the exhaust gases discharged from the combustion chambers Try to convert them into harmless substances.

The elimination or prevention of nitrogen oxides (N0 _v ) presents particular difficulties, and this is particularly the case with

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Chairman of the Board: Toni Sdimiidcer, Chairman - Horst Backsmann · Prot. techn. Ernst Fiale Dr. jur. Peter Frerk

of the Supervisory Board: Günter Hartwich Horst Münzner Dr. rer.pol. Werner P. Schmidt Gottlieb M. Strobl · Prof. Dr. rer. pole. Friedrich Thomee

Hans Birnbaum Seat of the company: Wolfsburg District Court Wolfsburg HRB

such internal combustion engines, such as the air-compressing, self-polluting diesel engines, with relatively low fuel consumption or air and oxygen-rich mixtures operated -.-, 'earth. A known subsequent elimination the stiococyte is namely only with the help of catalysts reducing atmosphere, i.e. if there is a lack of oxygen or air. Another known method of reducing the formation of nitrogen oxide by returning part of the exhaust gases to the combustion chambers can be used; however brings they have other disadvantages, particularly in the case of diesel engines, such as reduced performance and increased soot formation and the like.

The object on which the invention is based is therefore, in internal combustion engines of the type mentioned at the outset, in particular in internal combustion engines operated with relatively lean fuel-air mixtures, nitrogen oxide formation is effective and without acceptance to reduce major disadvantages.

The solution to this problem is, according to the invention, that the combustion chamber walls, at least in the areas in which the mixture of air and fuel is relatively rich (/ \ _ ü 1), a coating with a catalytic which reduces the nitrogen oxides produced during combustion Have material. The invention is based on the knowledge that, even in the case of internal combustion engines that are operated lean overall, certain areas in the combustion chamber have a reducing, that is to say low-air or fuel-rich, atmosphere and that, in the presence of catalytically active substances in terms of reducing nitrogen oxides, the The formation of nitrogen oxides is prevented at their point of origin, or the nitrogen oxides that have already formed can be eliminated. The catalytic material forming the coating can expediently consist of one or more noble metals, such as platinum or rodium, which are known as catalysts for the reduction of acid oxides in a low-air atmosphere. In the case of long-term thickening, self-igniting internal combustion engine:: it ϊ;: - 3, ΐζζ vOffeinspriisang should äji-ig ^ sns the im

3 CP? '' ~: "£ 1 kt

Zones of the combustion chamber walls lying in the area of the fuel injection steel be provided with this catalytic coating, because there certainly also in those internal combustion engines that are operated with a high excess of air, locally limited fuel-rich or areas with little air exist in which a reduction of nitrogen oxides by means of catalysts is possible is.

Another goal of the invention is the combustion chamber walls to line with a ceramic material, which is in the combustion chamber wall parts having the catalytic coating serves as a carrier for this coating. Due to the ceramic lining of the combustion chamber walls proposed by the invention Not only is an advantageous carrier provided for the catalytic, nitrogen oxide-reducing coating, but it is it is also achieved that the heat dissipation from the entire combustion chamber is limited. This is particularly the case with diesel engines result in good and even ignition even at low speeds and loads. Further results from this measure Especially in the case of diesel engines, a reduction in the ignition delays and thus the combustion noise, as well as a shift of the injection point in the late direction, which results in a reduction in the combustion peak pressure, an improvement in the Fuel consumption and ultimately a reduction in nitrogen oxide formation becomes possible at all. Appropriately the ceramic lining should consist of a material containing zirconium or a zirconium compound. There For the effectiveness of a catalyst, the size of its surface exposed to the reacting substances is decisive is, for the purpose of increasing the catalytically coated surface, it is proposed that the ceramic lining, the yes to serve as a carrier for the catalytic coating, made of a material with a large microstructure Surface. An example of such a material is Y-alumina.

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In the drawing, exemplary embodiments of the invention are shown in a partly schematic manner of representation, the following are described in more detail. The drawing shows in

Figure 1 is a longitudinal section through a combustion chamber formed by a vortex chamber of an air-compressing, self-igniting internal combustion engine and

Figure 2 shows a section through a _{piston containing the combustion chamber f of} an air-compressing, self-igniting internal combustion engine.

In FIG. 1 of the drawing, 1 is a cylinder, 2 is a piston and 3 is a cylinder head of an air-compressing, self-igniting Internal combustion engine (diesel engine) referred to, the combustion chamber of which is essentially arranged in the cylinder head Vortex chamber 7 is formed, which via a firing channel 8 which opens essentially tangentially into the vortex chamber the cylinder combustion chamber which remains between the piston 2 and the cylinder head 3 and is essentially formed by a piston recess 9 10 is connected. The swirl chamber 7 is inserted into the cylinder head 3 by a two-part insert 4a> 4b formed, which consists of metal and as a carrier for a ceramic Lining 5a ·, 5b is used. This ceramic lining that the swirl chamber 7 largely protects against heat loss to the walls of the surrounding cylinder head 3, is in turn a carrier catalytically active coating 6, which in the example shown here on the entire surface of the vortex chamber 7 and the weft channel 8 is attached. This coating consists of a known per se, to reduce Nitrogen oxides in a low-oxygen atmosphere! I ^ i] suitable catalytic Material, in particular made of precious metals such as platinum or rhodium.

With 11 in Figure 1 is one in the wall of the vortex chamber insert arranged opening for a glow plug indicated, which is sufficient for self-ignition when the diesel engine is cold started Temperature level ready. 12 denotes a

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second opening through which an injection nozzle not further shown here protrudes into the swirl chamber 7. This injection nozzle supplies what is required for combustion in the internal combustion engine Fuel that is roughly at the top of the compression dead center is injected into the swirl chamber and ignited there.

The injection of the fuel into the swirl chamber 1 now has the effect that at least in the wall areas of the swirl chamber hit by the fuel jet, a zone with a relative fuel excess or a lack of air or oxygen is created. In this zone, however, the catalytic materials attached to the wall of the swirl chamber can be effective in terms of reducing the nitrogen oxides produced during combustion by either preventing the formation of nitrogen oxides or reducing nitrogen oxides that have already formed. Since a reduction in nitrogen oxides in the diesel internal combustion engine shown here will essentially only take place in the areas of the swirl chamber that are opposite the injection nozzle, it could be thought of preferring to carry out the catalytic coating or only in this area at all. In the embodiment shown in FIG. 1, this would be that wall area of the vortex chamber which lies in the direction of the air flow indicated by the arrow in the last section before the mouth of the firing channel 8. A thickening of the catalytic coating 6 is also provided here in the exemplary embodiment.

In Figure 2 is another embodiment of the invention shown on the basis of a so-called direct injection diesel engine. Here, the combustion chamber 21 is essentially in one Recess of the piston 20 is formed, the bottom of which has a metallic insert 22 with a contour of the combustion chamber forming ceramic lining 23 contains. This ceramic Liner 23 in turn serves as a support for a catalytic Coating 24, which is intended to prevent the formation of nitrogen oxides during combustion. With the dashed line 25

is the direction of the fuel entering the combustion chamber 21 injection jet indicated. In this embodiment, too, something already happened before that from the fuel injection jet hit wall parts of the combustion chamber 21 a zone with a relative lack of air, so that at least there a reduction in Nitrogen oxides formed during combustion are possible due to catalytic substances known per se.

As already mentioned above, the lining of the combustion chamber walls with ceramic materials serves to limit the dissipation of heat from the combustion chamber to the surrounding walls. Above all, materials that contain zirconium or its compounds be used, which have a particularly low thermal conductivity. As a result of the reduced heat losses The combustion chambers insulated in this way result in a reduction in ignition delays at low speeds, especially in diesel engines and loads, so that the resulting harsh combustion noise can be significantly reduced when idling (nailing). Another advantage of the combustion chamber insulation is that the injection time can be shifted in the late direction, without it to disrupt the combustion process, so that in this way the peak pressure during combustion is reduced, the combustion noise is reduced, and black smoke is formed in vortex chamber machines and finally the consumption can be improved. Together with the catalytic coating of the Combustion chamber walls, in particular in that of the fuel injection jet affected areas, a particularly favorable and also low-pollutant combustion process is achieved.

However, the application of the invention is not restricted to diesel engines limited. Rather, the invention can also be used to advantage in Otto engines, although this is often the case a subsequent removal of nitrogen oxides by catalytic converters exists if a sufficiently low-oxygen operation he follows. Again, there is the elimination or elimination of the

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Nitrogen oxides at their point of origin, namely in the combustion chamber, what can be achieved by catalytic coating of the combustion chamber walls is a desirable goal.

The same can generally be used as the catalytic coating Materials are used which are also used, for example, in the known so-called 3-way catalysts and those with air numbers of Λ- * ί1 not only nitrogen oxides through reduction but also carbon monoxides and hydrocarbons through oxidation remove.

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Claims (1)

AKTIENGESELLSCHAFT 3180 Wolfsburg Our reference: K 2478
1702pt-we-jä 01, fm 1978 AHSPSFCHE V \\ Multi-cylinder internal combustion engine with a combustion chamber assigned to each cylinder in which a mixture of air and fuel is ignited and burned, characterized in that the combustion chamber walls at least in the areas "in which the mixture of air and fuel is relatively rich (λ "= Ι)» 'have a coating (6, 24) with a catalytic material which reduces the nitrogen oxides produced during combustion. 2. Internal combustion engine according to claim 1, characterized in that the catalytic material consists of one or more noble metals, like platinum or rhodium. J. Internal combustion engine according to claim 1, in particular air-compressing, self-igniting internal combustion engine with fuel injection, characterized in that at least the im Area of the fuel injection jet lying parts of the combustion chamber wall are provided with the catalytic coating (6, · 24). 909832 / 0U2 Chairman of the Management Board: Toni Schmucker, Chairman ■ Horst Backsmann · Prol. Dr. techn. Ernst Fiala Dr. jur. Peter Frerk of the Supervisory Board : Günter Hartwich · Horst Münzner ■ Or. rer. p6 "l. Werner P. Schmidt Gottlieb M. Strobl · Prof. Dr. rer. pol. Friedrich Thomee Hans Birnbaum Seat of the company: Wollsburg District Court Wolfsburg HRB ORiGINAL INSPECTED 4 internal combustion engine in particular according to one of claims 1 up to 3> characterized in that the combustion chamber walls are lined with a ceramic material (5a »5b; 23), that in the combustion chamber wall sections containing the catalytic coating (6; 24) as a carrier for this coating serves. 5 · Internal combustion engine according to claim 4j, characterized in that that the ceramic lining (5a, 5b; 23) consists of a material containing zirconium. 6. Internal combustion engine according to claim 4, characterized in that the ceramic lining (5a, 5b; 23) is made of a material with a large surface in the microstructure. 7. Internal combustion engine according to claim 6, characterized in that that the ceramic lining (5a, 5 ^ j 23) made of a V -aluminium oxide consists. 9O9832 / 0U2