GB1589011A

GB1589011A - Internal combustion engines and pistons and cylinders therefor

Info

Publication number: GB1589011A
Application number: GB43172/77A
Authority: GB
Original assignee: Karl Schmidt GmbH
Current assignee: Karl Schmidt GmbH
Priority date: 1976-10-23
Filing date: 1977-10-17
Publication date: 1981-05-07
Also published as: DE2648034A1

Description

(54) INTERNAL COMBUSTION ENGINES AND PISTONS AND CYLINDERS THEREFOR (71) We, KARL SCHMIDT GmbH, a body corporate organised under the laws of the German Federal Republic, of Christian Schmidt-Strasse 8/12, 7107 Neckarsulm, German Federal Republic, do hereby declare the invention for which we pray that a patent, may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to an internal combustion engine and to a piston and a cylinder therefor.

The great increase in the density of traffic and the rapid expansion of industry have led to pollution of the atmosphere which causes injury to health as well as material damage. A substantial reduction of atmospheric pollution is therefore desirable. The exhaust gases of internal combustion engines operated with hydrocarbons, in particular, contain a number of components the emission of which into the atmosphere is undesirable because of their poisonous nature or for other reasons and examples of which are carbon monoxide, nitrogen oxides, and hydrocarbons. The emission of these harmful substances is increasingly limited by additional legislation.

According to the present state of knowledge a drastic reduction of the maximum values of permitted harmful substances and emission is possibly only by the aftercombustion of exhaust gases. Two procedures have been proposed for this after- combustion, namely: 1) After-combustion without catalysts.

2) After-combustion with the aid of catalysts.

In after-combustion without catalysts, the oxidisable components in the exhaust gas are burned with secondary air and with or without separate ignition at high temperatures. In order to eleminate nitrogen oxides, after-combustion in a reducing atmosphere is necessary while an excess of oxygen is required in order to eleminate carbon monoxide and hydrocarbons. This need to work both with a reducing atmosphere and with an oxidising atmosphere gave rise to the so-called double-bed process in which the proportion of air for combustion in the engine is kept lower than 1.

In the first bed of the after-combustion apparatus incorporated in the exhaust system, the reduction of nitrogen is first effected, whereupon air is mixed with the exhaust gas and the oxidation of hydrocarbon and carbon monoxides is effected in a second bed (Campeau, R.M.: New Emission Concept Vehicles, SAE Paper No.

710 294, 1971).

For after-combustion with the aid of catalysts, use is made of the property of catalysts of accelerating the adjustment of chemical equilibrium reactions in the direction of the required reaction products. It is a characteristic of after-combustion that, when catalysts are used, a heterogeneous oxidation catalysis occurs. Thus, with solid catalysts having an oxidising action, useful proportions of the gas mixture are converted into carbon dioxide and water, when secondary air is added, at a working temperature and space velocity dependent upon the type of catalyst Various types of catalyst have been proposed for this purpose, depending upon the type of engine, type of process used, fuel, space conditions, and so on, of which the following catalysts are the main groups: a) Catalysts in the form of loose material; b) Monolithic catalysts; and c) Solid metal catalysts.

The majority of carriers for catalysts in the form of loose material consist of aluminium oxides. Monolithic carriers, for example honeycomb structures, may consist of cordierite, mullite, aluminium oxide, silicon carbide, or metal alloys.

The active phases of the catalysts, e.g.

precious metals, oxidic compounds of nonprecious metals, or combinations of the two types, are generally applied in thin layers to the carriers for loose or monolithic material. In order to achieve better distribution of the active phases on the carrier structure, low-surface area skeleton structures are provided with a very thin inter mediate layer of a high-surface area carrier.

The oxides of copper, chromium, manganese, iron, cobalt, and nickel and combinations thereof, for example copper chromite, can be used as non-precious metal componds, while platinum, palladium, rhodium, and ruthenium are used as precious metal catalysts. As additional alternatives, non-precious metals may be doped with precious metals, or precious metals doped with non-precious metals, or with compounds thereof respectively. In many cases small amounts of other elements are added to the substances mentioned, for example elements from the series comprising the alkaline earth metals, the rare earths, or titanium or tin respectively, as so-called promoters, in order to improve certain properties of the catalyst system.

The catalysts are installed in the exhaust system of an internal combustion engine at a predetermined distance from the exhaust valve, the operating temperatures being the limiting conditions determining the position in which they are installed. The activity of the catalyst should commence as rapidly as possible at about 250 C, while the temperatures must not exceed 1000 C even for a short time, since otherwise the activity of the catalyst will be destroyed. Having regard to these conditions, a compromise is made in respect of the position in which the catalyst is installed. After its operating temperature of about 500 to 600"C has been reached, conversion proportions of from 70 to 99.5% are achieved for the harmful substances.

Since these conversion rates are achieved only at operating temperatures, attempts have been made to achieve similar conversion rates even before the operating temperature is reached, that is to say in the period directly after starting, when the engine has not yet reached its operating temperature.

According to one aspect of the present invention there is provided a piston for an internal combustion engine, wherein at least the head of the piston is coated with a layer of a catalyst material comprising a porous carrier material which is alumina, supporting a catalyst for catalytically reducing the emission df noxious substances generated by combustion when the piston is in use in the engine, said catalyst being a mixture of either platinum and palladium or platinum and rhodium.

According to another aspect of the present invention there is provided an internal combustion engine provided with at least one of the pistons just indicated. Preferably an internal region of the or each cylinder of the engine associated with said piston(s) is coated with a layer of said catalyst material, the region being one which, in use, is subjected to combustion and over which the piston is arranged not to travel.

Preferably, the top land of the piston is also coated with a layer of the exhaust gas catalyst material.

In order to ensure reliable adhesion of the exhaust gas catalyst, the porous carrier material is disposed as an intermediate carrier layer between the piston or cylinder and a layer of the exhaust gas catalyst.

By these means it is ensured that the catalyst will come into action simultaneously with the commencement of combustion, that is to say the starting of the engine. Since the catalyst is disposed at those points in the combustion chamber where the proportions of noxious substances produced by combustion are relatively very high, good efficiency is achieved, so that the emission of noxious substances is considerably reduced at the commencement of the starting of the engine.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawing which is an elevation of an embodiment of a piston for an internal combustion engine in accordance with the present invention.

Referring now to the drawing, there is shown a piston 1 which, in the region of the piston head 2 and of the top land 3, is coated with a porous carrier layer 4 and, applied over the layer 4, a layer 5 of exhaust gas catalyst for catalytically reducing the emmission of noxious substances generated by combustion when the piston is in use.

The porous carrier layer 4 consists of alumina and the catalyst is either a mixture of platinum and palladium or a mixture of platinum and rhodium.

WHAT WE CLAIM IS:- 1. A piston for an internal combustion engine, wherein at least the head of the piston is coated with a layer of a catalyst material comprising a porous carrier material which is alumina, supporting a catalyst for catalytically reducing the emission of noxious substances generated by combustion when the piston is in use in the engine, said catalyst being a mixture of either platinum and palladium or platinum and rhodium.

2. A piston as claimed in claim I, wherein the top land of the piston is coated with said layer.

3. A piston for an internal combustion engine substantially as hereinbefore described with reference to the accompanying drawing.

4. An internal combustion engine provided with at least one piston as

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. mediate layer of a high-surface area carrier. The oxides of copper, chromium, manganese, iron, cobalt, and nickel and combinations thereof, for example copper chromite, can be used as non-precious metal componds, while platinum, palladium, rhodium, and ruthenium are used as precious metal catalysts. As additional alternatives, non-precious metals may be doped with precious metals, or precious metals doped with non-precious metals, or with compounds thereof respectively. In many cases small amounts of other elements are added to the substances mentioned, for example elements from the series comprising the alkaline earth metals, the rare earths, or titanium or tin respectively, as so-called promoters, in order to improve certain properties of the catalyst system. The catalysts are installed in the exhaust system of an internal combustion engine at a predetermined distance from the exhaust valve, the operating temperatures being the limiting conditions determining the position in which they are installed. The activity of the catalyst should commence as rapidly as possible at about 250 C, while the temperatures must not exceed 1000 C even for a short time, since otherwise the activity of the catalyst will be destroyed. Having regard to these conditions, a compromise is made in respect of the position in which the catalyst is installed. After its operating temperature of about 500 to 600"C has been reached, conversion proportions of from 70 to 99.5% are achieved for the harmful substances. Since these conversion rates are achieved only at operating temperatures, attempts have been made to achieve similar conversion rates even before the operating temperature is reached, that is to say in the period directly after starting, when the engine has not yet reached its operating temperature. According to one aspect of the present invention there is provided a piston for an internal combustion engine, wherein at least the head of the piston is coated with a layer of a catalyst material comprising a porous carrier material which is alumina, supporting a catalyst for catalytically reducing the emission df noxious substances generated by combustion when the piston is in use in the engine, said catalyst being a mixture of either platinum and palladium or platinum and rhodium. According to another aspect of the present invention there is provided an internal combustion engine provided with at least one of the pistons just indicated. Preferably an internal region of the or each cylinder of the engine associated with said piston(s) is coated with a layer of said catalyst material, the region being one which, in use, is subjected to combustion and over which the piston is arranged not to travel. Preferably, the top land of the piston is also coated with a layer of the exhaust gas catalyst material. In order to ensure reliable adhesion of the exhaust gas catalyst, the porous carrier material is disposed as an intermediate carrier layer between the piston or cylinder and a layer of the exhaust gas catalyst. By these means it is ensured that the catalyst will come into action simultaneously with the commencement of combustion, that is to say the starting of the engine. Since the catalyst is disposed at those points in the combustion chamber where the proportions of noxious substances produced by combustion are relatively very high, good efficiency is achieved, so that the emission of noxious substances is considerably reduced at the commencement of the starting of the engine. In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawing which is an elevation of an embodiment of a piston for an internal combustion engine in accordance with the present invention. Referring now to the drawing, there is shown a piston 1 which, in the region of the piston head 2 and of the top land 3, is coated with a porous carrier layer 4 and, applied over the layer 4, a layer 5 of exhaust gas catalyst for catalytically reducing the emmission of noxious substances generated by combustion when the piston is in use. The porous carrier layer 4 consists of alumina and the catalyst is either a mixture of platinum and palladium or a mixture of platinum and rhodium. WHAT WE CLAIM IS:-

1. A piston for an internal combustion engine, wherein at least the head of the piston is coated with a layer of a catalyst material comprising a porous carrier material which is alumina, supporting a catalyst for catalytically reducing the emission of noxious substances generated by combustion when the piston is in use in the engine, said catalyst being a mixture of either platinum and palladium or platinum and rhodium.

4. An internal combustion engine provided with at least one piston as

claimed in any preceding claim.

5. An internal combustion engine as claimed in claim 4, wherein an internal region of the or each cylinder of said engine associaied with said piston(s) is coated with a layer of said catalyst material, the region being one which, in use, is subjected to combustion and over which the piston is arranged not to travel.