Internal-combustion engines – Combustion chamber – Having catalytic cambustion aid
Reexamination Certificate
1999-11-08
2001-06-05
Kwon, John (Department: 3747)
Internal-combustion engines
Combustion chamber
Having catalytic cambustion aid
Reexamination Certificate
active
06240912
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates generally to a method for reducing hydrocarbon emissions in direct injected spark ignition engines, and more particularly to such a method using a catalytic oxidative coating on a piston for post-combustion oxidation of hydrocarbons during an expansion stroke of the engine.
2. Background Art
There is world-wide interest directed to the development of internal combustion engines with fuel injection systems which introduce fuel directly into a combustion chamber. Direct injection is advantageous for several reasons, including improved efficiency and reduced fuel consumption. However, direct injected gasoline engines produce significantly higher levels of hydrocarbon (HC) emissions than comparable port-fuel injected engines. One of the main mechanisms responsible for high HC emissions in direct injected gasoline engines has been found to be attributable to the deposition of liquid fuel on the surfaces of the combustion chamber (i.e., the piston top, cylinder liner, etc.). This phenomenon is generally referred to as combustion chamber wall wetting, and is most predominant when fuel is injected late during the compression stroke. Most current directed injected, spark ignition (DISI) engines are designed so that some wetting of the piston top occurs during light-load operation. Recent research, as evidenced in “The Effect of In-Cylinder Wall Wetting Location on the HC Emissions from SI Engines”, Rudolf Stangimaier, et al. 1999 SAE Technical Paper Series, indicates that piston top wetting contributes significantly to the hydrocarbon emissions from DISI engines.
Catalytic coatings within combustion chambers have been used for ignition of the fuel/air mixture as a result of contact with the catalytic material present in the combustion chamber. This form of catalytic-ignition is described in U.S. Pat. Nos. 4,773,368; 4,811,707; 4,819,595; and 4,905,658, all issued to William C. Pfefferle. More recently, U.S. Pat. No. 5,806,483, issued Sep. 15, 1998, to Mitarai, et al describes a combustion method for preventing the occurrence of knock during engine operation by providing a two-stage combustion process which is substantially different from the normal spark-ignition combustion process. Cracking of carbon-to-carbon bonds in heavier fuel molecules immediately prior to combustion is described in U.S. Pat. No. 4,530,340, granted Jul. 23, 1985, to Millard C. Totman. Totman uses a catalytic coating within the combustion chamber to promote the pre-combustion cracking of the heavier fuel molecules. Earlier, U.S. Pat. No. 2,978,360 was issued to Samuel W. Bradstreet, et al on Apr. 4, 1961 for several specific catalyst formulations and methods for generating and applying catalytic coatings to combustion chamber surfaces. The coatings are provided for the purpose of maximizing the combustion process itself, and as a result of the more efficient combustion, reduced overall emissions.
The present invention is directed to overcoming the problem of piston top wetting and the resultant contribution to hydrocarbon emissions. It is desirable to have a direct injected spark ignition engine that promotes a catalytic reaction at the top of the piston whereby a higher fraction of the fuel which impinges on the piston top is oxidized during the expansion stroke. It is also desirable to have such an engine wherein the detrimental effects of wall wetting on hydrocarbon emissions are reduced.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a method for in-cylinder oxidation of hydrocarbons in a direct injected spark ignition engine includes coating the top surface of a piston with an oxidation catalyst comprising at least one metal selected from the group consisting of palladium, platinum and rhodium. The coated piston is then assembled in a direct injected spark ignition engine, and the engine is operated whereby the coated piston is moved between alternating compression and expansion strokes. A flow of air is directed into the combustion chamber, and a stream of a combustible material comprising a liquid fuel, is injected directly into the combustion chamber and onto the coated top surface of the piston during a compression stroke. The coated top surface of the piston is thereby wetted with a first portion of the liquid fuel. A second portion of the liquid fuel is mixed with the air directed into the chamber and thereby forms a combustible fuel-air mixture within the combustion chamber. An electrical spark is produced within the combustion chamber, thereby igniting and combusting the fuel-air mixture. Subsequently, at least a portion of the remaining first portion of the liquid fuel present on the top surface of the coated piston is oxidized during an expansion stroke of the engine by catalytic reaction between the remaining fuel and the catalytic coating on the top of the piston.
Other features of the method for in-cylinder oxidation of catalysts embodying the present invention includes the top surface of the piston being preferably coated with an oxidation catalyst comprising palladium.
REFERENCES:
patent: 2973360 (1961-04-01), Bradstreet et al.
patent: 4530340 (1985-07-01), Totman
patent: 4773368 (1988-09-01), Pfefferle
patent: 4811707 (1989-03-01), Pfefferle
patent: 4819595 (1989-04-01), Pfefferle
patent: 4905658 (1990-03-01), Pfefferle
patent: 5806483 (1998-09-01), Mitarai et al.
“The Effect of In-Cylinder Wall Wetting Location on the HC Emissions from SI Engines”, SAE Technical Paper Series 199-01-0502, Stanglmaier, R.H. and Li, Jianwen and Mathews, Ronald International Congress and Exposition, Detroit, Michigan, Mar. 1-4, 1999.
Roberts Charles E.
Stanglmaier Rudolf H.
Baker & Botts L.L.P.
Kwon John
Southwest Research Institute
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