Combustion chamber surfaces of an internal combustion engine

Details Combustion chamber surfaces of an internal combustion engine Combustion chamber surfaces of an internal combustion engine

1989-10-23

1990-07-17

Cross, E. Rollins

Internal-combustion engines

Particular piston and enclosing cylinder construction

Cylinder detail

123669, 428215, F02B 7702

Patent

active

049414399

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to an arrangement of the combustion chamber surfaces of an internal combustion engine, in which these surfaces exhibit at least partially a thin surface layer which will influence the octane/cetane rating requirement of the engine so as to limit the knocking tendency of the engine. An arrangement of this kind is proposed in Swedish Patent Specification No. 85 05 302-3, this known arrangement being characterized in that when at least a part of the walls of combustion chamber are treated in the manner prescribed, the walls will absorb 90-95% of all thermal radiation in the energy-rich wave length range of interest for influencing engine combustion. Furthermore, since the radiation which is reflected into the combustion chamber is diffuse, radiation from the walls of the combustion chamber contributes towards the occurrence of knocking in the combustion process to only a very slight extent.
As the energy-rich radiation is absorbed into the combustion chamber walls it converts, however, to so-called joule's heat within the thin layer of material, which is therewith heated rapidly to such high temperatures as to eventually form a so-called "hot spot" during the combustion process, which initiates knocking. Some of this radiation is also reflected back into the combustion chamber as a result of the high surface temperatures that prevail, resulting in heat loss.
The object of the present invention is to provide an improved arrangement of the aforesaid kind in which the aforementioned drawbacks are fully or partially eliminated.


SUMMARY OF THE INVENTION

The invention is mainly characterized in that a heat buffer which has a special function is provided beneath said surface layer, and in that the nature of this surface layer is such that during combustion the layer is able to "capture" the energy-rich radiation and later, when the temperature of the combustion chamber has fallen to a level beneath the level of the layer temperature, to emit radiation effectively to the combustion chamber. The aforesaid special function of the heat buffer is to accumulate heat rapidly from the surface layer when the layer receives heat from the combustion chamber, while at the same time cooling said surface layer, i.e. the heat buffer must be capable of rapidly leading away heat and have a given thermal capacity. Subsequent hereto, it shall be possible to utilize as much of the stored heat as is possible, to heat the surface layer upon the termination of the combustion process. Cooling of the surface layer during the process of combustion counteracts knocking, while subsequent heating of said surface layer and the radiation of heat to the combustion chamber maintains the temperature level during expansion of the cumbustion gases, so as to obtain an improvement in efficiency. The simplest way of achieving such a transient heat buffer is to incorporate beneath the surface layer a layer of copper or silver having a thickness of about 1 mm.
These metals conduct heat very rapidly, which is the most important property expected of a good transient heat-buffer, i.e. there should be chosen a material which has a high value of thermal diffusivity according to the formula: ##EQU1## where .lambda.=thermal conductivity,
In order to utilize the material in the heat buffer to the best extent and to reduce the loss of heat therefrom to the engine cooling channels, the underlying layer is preferably arranged on a heat insulating layer, e.g. a thin layer of nickel.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the top of a piston according to one example of the invention, and
FIG. 2 is a diagram which illustrates temperature curves for two points in an internal combustion engine during a combustion cycle.


DETAILED DESCRIPTION

FIG. 1 illustrates the upper part of a piston 1 belonging to an internal combustion engine. The piston may be one which has been cast from a suitable aluminium alloy in accordance with conventional techniques. In accordance with the invention, the i

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patent: 3552370 (1969-02-01), Briggs
patent: 4254621 (1981-03-01), Nagumo
patent: 4471017 (1984-09-01), Poeschel et al.
patent: 4523554 (1985-06-01), Ryu
patent: 4538562 (1985-09-01), Matsui et al.
patent: 4776309 (1988-10-01), Wicen

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