Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
2000-11-08
2003-01-14
Kwon, John (Department: 3754)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S299000, C123S305000
Reexamination Certificate
active
06505601
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for operating a reciprocating-piston internal combustion engine in which an injection nozzle injects fuel directly into a working space which is formed in a cylinder between a cylinder head and a piston.
RELATED TECHNOLOGY
In modem high-speed reciprocating-piston internal combustion engines operating with diesel fuel and auto-ignition, the fuel is injected directly into a working space which usually includes a piston recess. The injected fuel forms a more or less homogeneous mixture of diesel fuel and air, the load of the reciprocating-piston internal combustion engine being regulated by the injected fuel quantity being varied. The fuel/air mixture ignites when there is an ignitable mixture in the working space and when the compression temperature in the working space reaches or exceeds the auto-ignition temperature of the fuel/air mixture.
For complete combustion, the aim is to ensure a good distribution of the fuel with the air charge. When the fuel is distributed homogeneously to the air charge in the working space, so as to give rise to a homogeneous fuel/air mixture, there is the risk, in the lower load range of the reciprocating-piston internal combustion engine, when a small fuel quantity meets a large air charge in the working space, that the ratio of fuel to air does not reach the precondition for ignitability at any location in the working space. On the other hand, in the full-load range of the reciprocating-piston internal combustion engine, when a large quantity of fuel is distributed uniformly to the air charge in the working space, there is the risk that the ignition conditions are reached at many locations in the working space and therefore the fuel bums with a rapid pronounced pressure rise and numerous pressure peaks, thus resulting in knocking combustion.
Efforts have been made to distributed fuel heterogeneously to the air charge in order to achieve a combustion which takes place harmoniously. This gives rise, in the working space, to zones with overenriched fuel/air mixtures which develop into ignitable mixtures due to the air movement in the working space, so that uniform combustion occurs.
SAE Paper 980505, 1998, Hashizume, T., Miyamato, T., Akagawa, H., Tsujimura, K.: Combustion and Emission Characteristics of Multiple Stage Diesel Combustion describes improving the combustion in a reciprocating-piston internal combustion engine by means of a two-phase injection of the fuel. In this case, two injection nozzles are arranged laterally in the combustion space diametrically to one another, and, for the formation of a homogeneous mixture, part of the fuel is injected through these in a first phase, approximately 150-70° before top dead center. In a second phase, the fulel is injected through a centrally arranged conventional six-hole or eight-hole nozzle or through a so-called “micronozzle” having relatively fine nozzle holes for the formation of a heterogeneous mixture around top dead center.
A fuel pump feeds the fulel for the lateral injection nozzles with a first maximum pressure into a first pressure accumulator, whilst a high-pressure generator feeds fuel into a second pressure accumulator with a second maximum pressure which is more than twice as high as the first maximum pressure. Correspondingly, the maximum injection pressure of the central injection nozzle is more than twice as high as the maximum injection pressure of the lateral injection nozzles. However, because of the complex arrangement of the injection nozzles, such a method necessitates a high outlay in structural and control terms.
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 depth of penetration of injection jets by two nozzle holes in a conventional injection nozzle being in each case arranged in such a way that the injection jets meet one another in a directed manner at a defined distance from the nozzle holes. As a result of the collision of the two injection jets, the momentum of the individual jets is reduced, the diameter of the fuel drops in the jet becomes smaller and a widening of the jet is achieved. As a result, an accretion of the fuel on the cylinder wall is avoided and, at the same time, a greater air volume is covered by the injection jet.
SUMMARY OF THE INVENTION
An object of the present invention is to improve mixture formation at a low outlay in structural terms over the operating range of a reciprocating-piston internal combustion engine with direct fuel injection and to avoid an undesirable accretion of the fuel during a phase for the formation of a homogeneous mixture.
The present invention provides a method for operating a reciprocating-piston internal combustion engine, in which an injection nozzle injects fuel directly into a working space which is formed in a cylinder between a cylinder head and a piston and which comprises a piston recess. In a lower part-load range (
21
), for the formation of a heterogeneous mixture the fuel is injected with a higher injection pressure (
29
) centrally into the working space (
8
) or into the piston recess (
6
) shortly before top dead center (
12
) or, optionally, an ignitable homogeneous mixture is formed locally, in the case of very early injection (180° to 20° crank angle (&phgr;) before top dead center), by defined charge stratification, via controlled coordination of air movement in the cylinder (
9
) and of injection pressure combined with timed injection, in a similar way to the direct-injection petrol engine, so that, even in this load range (
21
), homogeneous combustion can be produced. In a middle part-load range (
22
), for the formation of a homogeneous mixture, the fuel is injected with a lower injection pressure (
28
) in a phase (
25
) with a one hundred and eighty to twenty degree crank angle (&phgr;) before top dead center (
12
). In an upper part-load range (
23
) and/or full-load range (
24
), for the formation of a homogeneous mixture, part of the fuel is first injected into the working space (
8
) or the piston recess (
6
) with a lower injection pressure (
28
) in a phase (
25
) with a one hundred and eighty to twenty degree crank angle (&phgr;) before top dead center (
12
) and, for the formation of a heterogeneous mixture, the rest is injected into the working space (
8
) or the piston recess (
6
) with a higher injection pressure (
29
) in a phase (
31
,
27
) around top dead center (
12
).
In the method according to the present invention, first, for the formation of a heterogeneous mixture, in a lower part-load range the fuel is injected with a higher pressure centrally into the piston recess shortly before top dead center. This ensures that an ignitable mixture is formed, even when the fuel quantities are low in relation to the air charge. On account of the high compression in the phase at top dead center, despite the higher injection pressure there is no likelihood that fuel will accrete on the walls of the working space, particularly when, according to a refinement of the present invention, an injection nozzle with relatively small hole diameters is used.
Optionally, in the lower load range, an ignitable homogeneous mixture may be formed locally, even when the injection is very early (180° to 20° crank angle before top dead center), by defined charge stratification, via controlled coordination of air movement in the cylinder and injection pressure combined with timed injection, in a similar way to the direct-injection gasoline engine, so that, even in this load range, homogeneous combustion can be produced.
In a subsequent higher part-load range, for the formation of a homogeneous mixture, the fuel is injected with a lower injection pressure in a phase with 180° to 20° crank angle before top dead center. The fuel is thereby distributed uniformly to the air charge in the working space, so that a homogeneous mixture is formed. Due to early injection, sufficient time remains for homogenizing and vaporizin
Jorach Rainer Werner
König Gerhard
Raab Alois
Schloz Eckart
Stapf Petra
Daimler-Chrysler AG
Kenyon & Kenyon
Kwon John
LandOfFree
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