The invention relates to a fuel injection nozzle of the kind preferably employed for fuel injection and hence for use in an internal combustion engine.
In modern self-ignition internal combustion engines, the fuel is introduced under high pressure directly into the combustion chambers of the internal combustion engine. Here, the high pressure serves to finely atomize the fuel and thus to achieve an optimum mixing ratio between the fuel and the oxygen in the combustion chamber, this being indispensable for low-pollution and effective combustion. For this purpose, use is made of fuel injection valves of the kind known from the prior art, e.g. from DE 10 2004 050 048 A1. A fuel injection valve of this kind has a nozzle body in which a pressure chamber that can be filled with fuel under high pressure is formed and in which a nozzle needle is arranged in a longitudinally movable manner, said needle interacting with a body seat to open and close one or more injection openings. In this case, there is often, at the combustion-chamber end of the nozzle body, a “blind hole” which adjoins the body seat and from which the injection openings start. Here, the blind hole serves to distribute the fuel uniformly between the individual injection openings and hence to ensure correspondingly uniform distribution of the fuel in the combustion chamber. During injection, the fuel available in the pressure chamber, which is under high pressure, flows between the sealing surface of the nozzle needle and the body seat into the blind hole, from where the fuel flows into the injection openings and is finally atomized through the latter into the combustion chamber.
At the beginning of the opening stroke movement of the nozzle needle, i.e. when the latter rises from its contact with the body seat, the fuel flows through a very narrow gap between the sealing surface of the nozzle needle and the body seat into the blind hole, leading to swirling of the fuel in the blind hole. This improves atomization if the swirling is not so strong that the fuel is distributed nonuniformly between the injection holes. In the further course of the stroke motion, the gap between the nozzle needle and the body seat becomes larger, with the result that the fuel is subject to less swirling in the blind hole and the tendency of the fuel for atomization as it passes through the injection openings is lower.
In contrast, the fuel injection nozzle according to the invention has the advantage that the inflow of fuel to the injection holes is improved in the region of the blind hole since adequate turbulence is introduced into the spray hole even in the case of a partial stroke of the nozzle needle and therefore the breakup of the jet as the fuel emerges from the spray holes in the combustion chamber is intensified. For this purpose, the fuel injection nozzle has a nozzle body, in which is formed a pressure chamber fillable with fuel under high pressure and in which a longitudinally movable nozzle needle is arranged, wherein the nozzle needle has a sealing surface, by means of which it interacts with a conical body seat formed in the nozzle body and thereby opens and closes the connection from the pressure chamber to a blind hole. In this case, the blind hole directly adjoins the body seat and forms a cylindrical section there, with the result that an inlet edge is formed at the transition between the body seat and the blind hole. At least one injection opening, which opens into the blind hole, is furthermore formed in the nozzle body. At its end remote from the inlet edge, the cylindrical section of the blind hole makes a transition to a reduced diameter, with the result that a shoulder is formed at this point, wherein the at least one injection opening opens into the blind hole between the shoulder and the inlet edge, i.e. in the region of the cylindrical section.
Owing to the shoulder in the blind hole, the fuel flow is guided over this shoulder as it enters the blind hole and is thereby swirled, causing corresponding turbulence in the flow which leads to an intensification of the jet breakup as the fuel passes through the injection opening, that is to say that the fuel breaks up very rapidly as it emerges from the spray hole and forms a fine mist of fuel droplets, which burn effectively and cleanly with the available oxygen in the combustion chamber.
In a first advantageous embodiment, a substantially hemispherical blind hole base adjoins the shoulder. This promotes the flow of the fuel across the shoulder, with the result that the desired additional swirling is intensified by the should
In another advantageous embodiment, the shoulder is designed in the form of an annular disk, which can be produced in a simple manner. The relatively sharp edges which are formed by this means lead to significant swirling of the fuel in the blind hole. Provision can likewise also be made for the shoulder to be of conical design, which, while avoiding sharp edges at the transition, increases mechanical stability. The transitions from the cylindrical section of the blind hole to the edge and from the edge to the blind hole base can likewise be of rounded design, in particular in order to reduce notch stresses.
In another advantageous embodiment, the shoulder is formed with the same depth over the entire circumference of the blind hole, thus making the flow within the blind hole symmetrical and hence ensuring a supply to all the injection openings where there is a plurality thereof distributed over the circumference. Here, the depth of the shoulder is preferably 5 μm to 100 μm, ensuring, on the one hand, that the desired additional turbulence within the blind hole is achieved and, on the other hand, that the volume of the blind hole is not increased excessively.
In another advantageous embodiment, a plurality of injection openings is formed in the nozzle body, which open into the blind hole between the shoulder and the transitional edge and which are advantageously distributed uniformly over the circumference. The more injection openings are present, the more uniformly the fuel can be distributed in the combustion chamber and the better, in general, is combustion.
In another advantageous embodiment, there is at least one further injection opening, which opens into the conical body seat. This enables two different types of injection opening to be supplied simultaneously with fuel, namely those which start from the blind hole and those which start directly from the body seat and have a different jet characteristic, this potentially being advantageous, especially for supplying complex and large combustion chambers.
Various illustrative embodiments of the fuel injection nozzle according to the invention are shown in the drawing, in which:
If an injection is to take place, the nozzle needle 4 is moved in the longitudinal direction by a suitable mechanism, with the result that it rises from the body seat 7 and exposes a flow cross section between the sealing surface 5 and the body seat 7, as a result of which fuel flows under high pressure out of the pressure chamber 2 into the blind hole 10. From there, the fuel flows onward through one or more injection openings 14 and thus enters the combustion chamber. As it emerges from the injection openings 14, the fuel is atomized, i.e. the jet breaks up and forms a large number of small fuel droplets, which mix well with the oxygen in the combustion chamber and thus form a combustible mixture. To end injection, the nozzle needle 4 is pushed back into its closed position in contact with the body seat 7, thus ending the inflow of fuel into the blind hole 10.
The effect of the shoulder 16 is illustrated in
In
Number | Date | Country | Kind |
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10 2016 215 637.3 | Aug 2016 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2017/070285 | 8/10/2017 | WO | 00 |