Internal-combustion engines – Multiple cylinder – Cylinders in-line
Reexamination Certificate
1999-04-26
2001-01-30
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Multiple cylinder
Cylinders in-line
C123S568110, C123S568130
Reexamination Certificate
active
06178933
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to controlled self-ignition four-stroke internal-combustion engines.
2. Description of the Prior Art
Controlled self-ignition is a well-known phenomenon in two-stroke engines. This combustion type has advantages as regards emissions: low hydrocarbon and nitrogen oxides emissions are notably obtained. Furthermore, a remarkable cycle regularity is achieved during self-ignition combustion.
Self-ignition is a phenomenon that allows to initiatant of combustion by means of residual burned gases which remain in the combustion chamber after combustion.
Self-ignition is achieved by controlling the amount of residual gases and the mixing thereof with the fresh gases (not burned yet). The residual gases (hot burned gases) initiate the combustion of the fresh gases resultant from a combination of temperature and of presence of active species (radicals).
In two-stroke engines, the presence of residual gases is <<inherent>> in the combustion. In fact, when the load of the engine decreases, the amount of fresh gases decreases, which leads to an increase in the amount of residual gases (burned gases from the previous cycle or cycles which have not flowed out of the cylinder). The two-stroke engine thus works with an internal recirculation (or internal EGR) of the burned gases at partial load. However, the presence of this internal EGR is not sufficient to obtain the desired self-ignition running. Research work also shows that mixing between this internal EGR and the fresh gases has to be controlled and limited.
The controlled self-ignition technology applied to four-stroke engines is particularly interesting because it allows the engine to run with an extremely diluted mixture, with very low fue/air ratios and ultra-low NOx emissions.
However, this technology comes up against a significant technological difficulty insofar as, in order to obtain controlled self-ignition in a four-stroke engine, it is necessary to either significantly increase the compression ratio of the engine (with knocking problems at high load), or to considerably heat up the fresh gases admitted (several hundred degrees C), or to combine these two phenomena.
Solutions allowing the decreasing of pressure and temperature level requirements for four-stroke engines can be partly provided by suitable additives in the fuel. French patent application FR-2,738,594 illustrates a solution of this type.
It is well-known for four-stroke engines, for example from international patent application PCT WO-93/16,276, to combine a variable distribution adjustment with a non-return system at the intake in order to reduce pumping losses at partial load. This solution then allows operation with the intake throttle as wide open as possible.
French patent application EN.97/02,822 filed by the assignee describes another way of controlling self-ignition in a four-stroke engine. More precisely, this document recommends, at partial load, to minimize mixing of the fresh gases and of the burned gases confined in the combustion chamber by delaying closing of the exhaust as much as possible. This is an <<internal>> recycle that allows stratification of the gases in the combustion chamber.
French patent application EN.97/11,279 filed by the assignee also minimized, at partial load, mixing of the fresh gases and of the burned gases contained in the combustion chamber, in order to control and to favor self-ignition combustion. However, this prior art proposes transferring the recycled burned gases via a specific line opening into an air supply line just upstream from the combustion chamber. The fresh air-fuel feed is introduced separately and late via a second line. A successive introduction of the feeds is thus provided. However, this solution creates a substantial dilution of the burned gases by air prior to entering the combustion chamber.
SUMMARY OF THE INVENTION
The present invention proposes a simpler way to obtain, notably at partial load, self-ignition in a four-stroke engine.
Besides, the present invention allows a higher reliability resultant from a better burned gas supply security and a lesser dilution of the burned gases by fresh gases.
The present invention provides a self-ignition combustion process in a four-stroke internal-combustion engine comprising at least one cylinder having at least a first intake and at least a first exhaust.
According to the invention, the process at partial load, fills an external volume independent of the cylinder with burned gases, the volume being connected to the cylinder via a specific port and a specific line, and controls the flow and/or the pressure of the burned gases in the volume through a throttle device associated with a sealing device allowing selective sealing of the specific port such as a valve, in order to achieve stratification of the burned gases and of the fresh gases in the combustion chamber.
According to the invention, the lifting of the specific valve occurs around the end of the intake stroke.
Furthermore, the volume and the specific line(s) are thermally insulated.
According to an embodiment of the invention, the volume is supplied with burned gases coming only from the cylinder.
According to another embodiment of the invention, the volume is supplied with burned gases by means of a n auxiliary engine whose exhaust is connected to the volume.
In accordance with this embodiment of the invention, the lifting of the specific valve is such that it opens during the expansion stroke in order to allow filling of the volume with burned gases.
More particularly, the process can be used in a multicylinder engine having a common exhaust manifold.
The present invention also relates to a four-stroke internal-combustion engine working on the controlled self-ignition principle comprising at least one cylinder having at least a first intake and at least a first exhaust.
The cylinder(s) specifically comprise each a specific port and a specific line connected to a volume exterior to the cylinder and intended, at partial load, to be filled with burned gases. A throttle means is also provided to control the pressure and/or the flow of the gases in the volume, in order to achieve stratification of the burned gases and of the fresh gases in the combustion chamber.
The engine according to the invention can also comprise thermal insulation and/or heating of the specific line and of the volume filled with burned gases.
Without departing from the scope of the invention, the engine can further comprise an auxiliary engine whose exhaust is connected to the volume filled with burned gases. Several cylinders having a common exhaust manifold are then provided.
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patent: 5970944 (1999-10-01), Kawamura
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Antonelli Terry Stout & Kraus LLP
Institut Francais du Pe'trole
Wolfe Willis R.
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