JPS5941624A - Combustion chamber for internal-combustion engine - Google Patents

Abstract

PURPOSE:To prevent the generation of soot, by coating the surface of a combustion chamber with ceramic and sticking an oxidizing catalyst on the surface of the ceramic to utilize the heat-insulating property of the ceramic to keep the temperature of the surface of the catalyst so high that the reaction of the catalyst is activated. CONSTITUTION:A ceramic and catalyst area A is provided on the surfaces of main and auxiliary chambers 2, 3 of a cylinder head 1, the bottom of an exhaust valve 4, the top of a piston 5, etc. To manufacture the area A, the surface of a metal on which previous treatment is effected is heated so that powder of ceramic which contains zirconia as the main constituent and has a relatively large coefficient of expansion is melt-sprayed on the surface of the metal and the surface is thereafter coated with ceramic containing alumina as the main constituent. After that, the metal surface is further coated with a catalyst. The alumina layer on the metal surface is porous and has a large surface area so that the layer holds the catalyst well and sufficiently intercepts heat from the metal. For that reason, the purpose is attained.

Description

[Detailed description of the invention] The present invention relates to a combustion chamber of an internal combustion engine.

The mechanism by which soot is generated in the combustion chamber of an internal combustion engine is (1
) When there is a lack of sufficient oxygen necessary for combustion, and (2)
This is a phenomenon that occurs when part of the flame generated during the combustion process is lowered below the ignition temperature for some reason, and in particular, the ionized carbon atoms (C2 ions) that are instantaneously generated within the flame are cooled. It has been theoretically proven that they lose their activity and combine to form soot. Therefore, item (2) is especially important for preventing soot generation. In response to this, we previously proposed a method of coating the combustion chamber of an internal combustion engine with a catalyst film, but in this method, the catalyst film promotes the oxidation reaction even at the point of oxygen deficiency as described in item (1), resulting in -1: ( Regarding item 2), the aim was to lower the ignition temperature.

However, when implementing this method, there are fewer problems if the structural material inside the combustion chamber is ceramic, but in the case of metal materials that are commonly used today, this method is not necessarily perfect. hard. That is, when a flame comes into contact with a metal surface coated with a catalyst film, even if the thin catalyst film does catalyze the oxidation reaction.

For example, the inside of the cylinder hem P or piston crown is cooled to prevent its surface from becoming hot and sharp. Therefore, the problem remains that the amount of heat generated on the surface of the catalyst film coated on the metal surface is immediately taken away by the metal with good thermal conductivity and the temperature of the catalyst surface decreases, so that the catalyst cannot function satisfactorily.

The purpose of the present invention is to compensate for the above-mentioned drawbacks by applying pre-treatment to coat the metal surface with a ceramic material having poor thermal conductivity (2) before coating the catalyst film. This is because the walls that make up the combustion chamber are coated with a ceramic material, and an oxidation catalyst is attached to the surface of the ceramic material.

Examples according to the present invention will be described below.

The thermal conductivity of ceramic materials is at least 1/15 that of metals.
The material must be ~1/10 or less, and alumina, silica, magnesia, zirconia, titania, etc. are mainly used.

An important technical issue is that these heat-resistant materials have different coefficients of thermal expansion than metals, so there is a risk that the ceramic film will peel off from the metal surface due to the thermal stress caused by the difference in expansion between the two. It is a certain thing. The coating thickness is therefore limited to less than 100 microns.

FIG. 1 is an explanatory diagram showing a combustion chamber of an embodiment according to the present invention.

In the figure, the wall surface of the main chamber 2 of the cylinder head 1, the wall surface of the auxiliary chamber 3, the bottom surface of the umbrella portion of the exhaust valve 4, the top surface of the piston 5, etc.
That is, the wall surface constituting the combustion chamber is subjected to the following treatment to form the ceramic catalyst section indicated by A.

A method is used in which a pre-treated metal surface is heated, a zirconia-based ceramic with a relatively high expansion coefficient, and kus powder is thermally sprayed onto the surface in the first step, and alumina-based ceramic coating is applied in the second step. It will be done.

That is, zircon, which has a large thermal expansion, has good adhesive strength with metals, and if it is used as a base, other ceramics, such as powders of alumina, silica, and magnesia, can be easily bonded thereon.

These ceramic spraying processes may be performed in two to four stages, but in either case, the final surface material is a powder mainly composed of alumina. The reason for this is that the alumina layer on the final surface is porous and has a large surface area, which has excellent catalyst retention properties, and also has good insulation properties with the metal, meaning that the heat of reaction generated during contact with the flame is not transmitted to the metal. This is because the temperature of the ceramic itself increases, so it has the effect of suppressing the generation of soot as much as possible.

The method of catalyst coating is as follows.

That is, 20 parts by weight of an aqueous solution of chromic acid anhydride and the same amount of an aqueous cobalt acetate solution are mixed in advance, and this volume and the same amount of a 50% propylene glycol aqueous solution are mixed to allow the esterification reaction to proceed sufficiently.

A catalyst solution obtained by mixing aqueous chloroplatinic acid and palladium chloride solution is applied to a ceramic-treated metal surface, dried at 150°C for 1 hour, and then heated at 400°C for 1 hour.
A heat treatment is performed at 600° C. for 0.5 hour, and the process is completed.

Combustion chamber (pre-combustion chamber, cylinder head,
Using a diesel engine (3500 rpm, Loops) equipped with a piston crown and intake and exhaust valves
When operating in mode, soot (Part 1culate
) The occurrence rate of soot was 0.09 g/mile, and the soot removal performance was about 74 mm compared to the untreated case of 0.34 g/mile.

(5)

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a combustion chamber of one embodiment according to the present invention. 1...Cylinder spatula P, 2...Main chamber, 3...Sub-chamber, 4...Exhaust valve, 5...Piston. 71 yen) Patent attorney Masahiro Isoda

Claims (1)

[Claims] ] A combustion chamber for an internal combustion engine characterized in that the wall surface constituting the combustion chamber is coated with a ceramic material, and an oxidation catalyst is attached to the surface of the ceramic material.