Internal-combustion engines – Combustion chamber means having fuel injection only – Using multiple injectors or injections
Reexamination Certificate
2000-04-10
2003-02-04
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Using multiple injectors or injections
C123S305000, C123S307000, C123S269000, C123S276000, C123S279000
Reexamination Certificate
active
06513487
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for operating a reciprocating-piston internal combustion engine.
BACKGROUND OF THE INVENTION
In modern, fast-running reciprocating-piston internal combustion engines, which work with diesel fuel and self-ignition, the fuel is injected directly into a working chamber, which usually includes a piston recess. The injected fuel forms a more or less homogeneous mixture of diesel fuel and air, the throttle load of the reciprocating-piston internal combustion engine being regulated by varying the injected fuel quantity. The fuel-air mixture ignites when an ignitable mixture is present in the working chamber and when the compression temperature in the working chamber reaches or exceeds the self-ignition temperature of the fuel-air mixture.
To achieve a complete combustion, one strives to efficiently distribute the fuel with respect to the air charge. If the fuel is homogeneously distributed with respect to the air charge of the working chamber, forming a homogenous fuel-air mixture, one runs the risk in the light load range of the reciprocating-piston internal combustion engine, when a small fuel quantity meets with a large air charge in the working chamber, of the ratio of fuel to air not meeting the condition for ignitability at any location in the working chamber. On the other hand, in the full-load range of the reciprocating-piston internal combustion engine, when a large quantity of fuel is uniformly distributed over the air charge in the working chamber, one runs the risk of the conditions for ignition being met at many locations in the working chamber, so that the fuel burns with a rapid, substantial pressure rise and with numerous pressure peaks, resulting in combustion knocking.
It is known to distribute the fuel heterogeneously over the air charge to achieve a well-balanced combustion. In this context, zones of overly enriched fuel-air mixtures are formed in the working chamber, which develop into ignitable mixtures due to the movement of air in the working chamber, resulting in a uniform combustion.
In this type of heterogeneous combustion, the lack of air in the rich zones leads to particulate emission, and the combustion in stoichiometric zones leads to thermal NO
x
formation. Burning a homogeneous, lean fuel-air mixture greatly reduces NO
x
and particulate formation, as has already been established. Lean mixtures of this kind can only be burned by self-ignition, since an externally supplied spark ignition is not possible because of the overly lean mixture. Engine operation with a homogeneous, self-ignited mixture is only possible within a limited load range. The potential load range is upwardly limited by the very high conversion rates of self-ignited, homogeneous mixtures. The lower limit is determined by the self-ignition limit of the lean mixture.
SAE Paper 980505, 1998, by Hashizume, T., Miyamato, T., Akagawa, H., Tsujimura, K.: “Combustion and Emission Characteristics of Multiple Stage Diesel Combustion”, describes increasing the load of a reciprocating-piston internal combustion engine that works with homogeneous self-ignition by injecting the fuel in two phases. In this context, injector nozzles, through which fuel is injected in a first phase to form a homogeneous mixture, are arranged laterally in the combustion chamber. In a second phase, the fuel is injected through a centrally arranged, conventional six- or eight-orifice nozzle to form a heterogeneous mixture. A method of this kind requires substantial outlay for construction and control engineering.
Also, SAE Paper 950081, 1995, Potz, D., Kreh, A., Warga, J.: “Variable-Orifice Geometry Verified on the Two-Phase Nozzle (VRD)”, describes injecting fuel via a two-phase nozzle into the working chamber. This is an injector nozzle that opens to the outside and has two rows of orifices arranged one over the other in the opening direction. The nozzle is used for conventional, heterogeneous diesel combustion. The use of small orifices improves the mixture formation, since injection pressure is increased in the case of a small injection quantity. When working with a large injection quantity, too long of a spray duration is prevented by opening the second orifice row.
At a light load, the two-phase nozzle opens just wide enough to permit the fuel to be injected via an orifice row, while at a heavy load, the fuel arrives in the working chamber via the two orifice rows. The nozzle orifices of the first orifice row run essentially in parallel to the nozzle orifices of the second orifice row, so that they have the same angle of inclination with respect to the piston crown.
SAE 1999-01-0185, Iwabuchi, Y., Kawai, K., Shoji, T., Takeda, T.: “Trail of New Concept Diesel Combustion System—Premixed Compression-Ignition Combustion—”, describes reducing the penetration depth of injection jets in a conventional injector nozzle, by configuring the two nozzle orifices in such a way that the injection jets are targeted to hit one another at a specific distance from the nozzle orifices. The collision of the two injection jets has the effect of reducing the linear momentum of the individual jets, diminishing the diameter of the fuel droplets in the jet, and of expanding the jet. This prevents fuel from accumulating at the cylinder wall and, at the same time, the injection jet covers a greater volume of air.
In addition, German Patent No. 42 28 359 Al, describes an injector nozzle for internal combustion engines, which opens to the outside and, in the opening direction, has elongated orifice cross-sections. Here, the intention is to produce injection jets having a sharply concentrated flow profile and a constant flow angle. In addition, by configuring the openings with respect to the sealing surface of a closing head to be offset from the opening direction, it is ensured that sharply concentrated spray jets are not formed in response to a low fuel discharge pressure, i.e., a low speed, until the valve needle has run through an idle stroke. The valve needle is opened by the pressure of an injection pump, oppositely to the force of a closing spring. The time characteristic of the injection is able to be influenced in conjunction with the form design of the nozzle orifice cross-sections, with the closing spring characteristic, and with the pump rate.
Finally, German Patent No. 43 25 90
4
C2 describes a fuel injection system in which a high-pressure pump delivers the fuel into a supply line common to all injector nozzles. Actuators which are driven by an electronic control unit and which work in accordance with a piezoelectric or magnetostrictive principle, act directly or via a transmission element, on a valve needle of the injector valve that opens to the outside, the orifice cross-sections having an elongated and rectangular shape in the opening direction.
SUMMARY OF THE INVENTION
An object of the present invention is to improve the mixture formation over the operating range of a reciprocating-piston internal combustion engine having direct fuel injection, with little outlay for construction.
The present invention provides a method for operating a reciprocating-piston internal combustion engine, where an injector nozzle, which opens toward a working chamber, injects fuel directly into the working chamber, which is formed in a cylinder between a cylinder head and a piston and includes a piston recess. In a light part-load range (
37
), to produce a heterogeneous mixture, the fuel is injected centrally into the piston recess (
6
) shortly before the top dead center (
12
), at a flat angle (&agr;) to the piston crown (
7
). In a subsequent part-load range (
35
), to produce a homogeneous mixture, the fuel is injected within one range, at least partially at a steeper angle (&bgr;) to the piston crown (
7
), and that in a full-load range (
36
), a portion of the fuel is injected, initially to produce a homogeneous mixture, within a range of 180° to 20° crank angle (&phgr;) before the top dead center (
12
), at a steeper angle (&bgr;) to the piston crown (
7
). To produce a he
Jorach Rainer Werner
Raab Alois
Schloz Eckart
Schnabel Martin
Wirbeleit Friedrich
Argenbright Tony M.
Daimler-Chrysler AG
Huynh Hai H
Kenyon & Kenyon
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