Internal-combustion engines – Precombustion and main combustion chambers in series – Having volumetric relation between precombustion and main...
Patent
1998-05-18
2000-05-02
Dolinar, Andrew M.
Internal-combustion engines
Precombustion and main combustion chambers in series
Having volumetric relation between precombustion and main...
123295, 123285, F02B 1910, F02B 1700
Patent
active
060559551
DESCRIPTION:
BRIEF SUMMARY
The invention is based on an internal combustion engine, particularly for motor vehicles, with direct fuel injection and externally supplied ignition.
In such internal combustion engines, the goal of direct fuel injection, that is, the injection of fuel directly into the combustion chamber and the aspiration of pure air via the inlet valve, has the goal of achieving a major reduction in fuel consumption by unthrottling in idling and at least lower partial load. To that end, it is necessary to achieve a charge stratification in the combustion chamber comprising on the one hand a homogeneous, readily ignitable and thoroughly combustible fuel-air mixture, and on the other as pure air as possible. Direct injection systems until now, however, cause major unsteady, location-dependent mixture formation in the combustion chamber.
In order to counteract the problem of nonhomogeneity within the mixture cloud, a changeover has been made in a known internal combustion engine to inject a fuel-air mixture into the combustion chamber (German Patent Disclosure DE 39 20 089 A1). An injection nozzle for a fuel-air mixture and an associated spark plug, which are disposed in the cylinder head, are oriented toward one another in such a way that the injection nozzle is aimed at the free space between the two ignition electrodes of the spark plug, protruding into the combustion chamber, where the ignition sparks occur, and the center of the combustion chamber is located downstream of the electrodes in terms of the injection direction of the injection nozzle.
ADVANTAGES OF THE INVENTION
The internal combustion engine of the invention has the advantage that while maintaining direct injection of pure fuel, extensive homogeneity of the mixture formation until ignition is attained, thus assuring more-reliable, thorough combustion. The result is an especially favorable behavior at the transition from idling to partial load and from partial load to full load. At the same time, there are advantages, especially the overcoming of problems in flame core formation, in homogenous lean operation, or in operation with exhaust gas recirculation.
In a preferred embodiment of the invention, the chamber is embodied as bell-shaped and its volume amounts to approximately 30 to 50% of the minimum combustion chamber volume present at top dead center of the reciprocating piston. As a result, it is attained that beginning at idling, as the load increases, a volumetric region of the chamber that grows steadily in the direction of the top of the bell is filled with a homogeneous, combustible mixture.
In an advantageous embodiment of the invention, a virtually symmetrical depression is formed in the middle of the end wall of the reciprocating piston that defines the combustion chamber, and this depression, together with the combustion chamber, adds to the bell shape of the chamber to make a pear shape. By means of this depression, between the end faces, facing one another, of the reciprocating piston and the cylinder wall, squish gaps form in the upward motion of the reciprocating piston from its bottom dead center to its top dead center, and through them air flows into the chamber in a defined way and reinforces the mixture preparation.
In a further embodiment of the invention, the fuel injection is controlled such that a fuel-air mixture formation takes place in the chamber at idling and lower partial load, and in the chamber and the combustion chamber at upper partial load and full load. Because of this definition of an injection time slot, the mixture homogeneity can be varied up until the instant of ignition, and the mixture formation can be controlled in such a way that it takes place either in the chamber or in the chamber and the combustion chamber, and there either a charge stratification or a homogeneous mixture formation is attained. This injection time slot, like the instant of ignition, can be controlled as a function of the engine load and rpm by means of a performance graph or can be regulated via "feedback" from the combustion chamber by
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Benedikt Walter
Herden Werner
Kuesell Matthias
Dolinar Andrew M.
Gimie Mahmoud M.
Greigg Edwin E.
Greigg Ronald E.
Robert & Bosch GmbH
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