EP0661447B1 - Diesel engine with direct fuel injection - Google Patents

Description

The invention relates to a diesel engine with direct fuel injection with the in the preamble of claim 1 mentioned generic features.

In diesel engines it is known to inject the fuel into the combustion chamber in such a way that it before and during the combustion as evenly as possible on the entire combustion air distributed. The dominant factor here is direct fuel injection using the jet atomization process, in which the fuel from a multi-hole nozzle obliquely down into the combustion air in the Combustion chamber is injected, this air when flowing in through the special shape of the Inlet channel was rotated about the cylinder axis. By rotating the Air is the desired distribution of the fuel across the entire combustion chamber, including Air created by atomizing the fuel when injecting through nozzle bores is taken immediately.

Due to this circulating air flow in the combustion chamber, in particular Burning process with a large swirl, the injection jets are very blown away. The individual overlap blown rays, local areas with excess fuel are formed below Burn lack of oxygen. The consequences of such an incomplete combustion are high Soot emissions. So that the injection jets are not blown overlapping in the manner described with this injection mold

Injectors with a limited number of injection bores used, the Bore spacing is chosen so that the individual injection jets even with strong Drift cannot overlap.

An injection nozzle of this type is known from EP 0 246 373 B1 and therein as an assembly described an entire fuel injector. In this known injection nozzle a total of three injection openings at equal distances from one another laterally on the circumference of the nozzle body. Depending on the position of a hollow cylinder Nozzle closure element, the three injection openings are opened or closed and so regulates the amount of fuel to be injected. With the injection ports fully open and The specified injection pressure is the maximum amount of fuel that can be injected through the entire fuel Cross-sectional area of the three injection openings of the same size are defined. The above described overlap of the predetermined by the injection openings and from Combustion air vortices are blown by the angular distance of each Avoided 120 °.

This known injection nozzle is due to its structural and functional so far explained Properties with the disadvantages that differ from the few, each Diameter-equal opening areas of the injection openings a relatively small Total opening area and thus result in relatively long injection times. Furthermore, the Air utilization during the combustion process of this swirl process with the usual three to five Injection openings small.

Improved air utilization and an increase in the rate of mixture formation will achieved with a multi-hole injection nozzle for a diesel engine, as in the German utility model G 85 21 912.6 is disclosed. Each of the three to five is there conventional nozzle holes replaced by at least two replacement holes, the Cross-sectional sum essentially the cross-section of the replaced conventional Corresponds to the nozzle bore. These replacement holes are each arranged in pairs so that their resulting beam direction with the beam direction of the conventionally designed Injection hole matches, but the core zones of their jet cones do not overlap. This will improve fuel atomization and therefore better Air utilization achieved at lower speeds and low swirl, with increasing swirl However, the core zones of the injection jets also overlap, resulting in soot formation Has.

Furthermore, from FR 22 38 059 A a two-stage multi-hole injection nozzle is known, as in swirl-free jet injection process is used. There are big and small Injection bores alternately formed symmetrically on a nozzle circumferential line, the large ones a first group and the small injection holes a second group form and the group of small injection holes to represent a pilot injection serves. For each group of injection bores, the flow rate and shape are the Injection bores matched to one another in such a way that the best possible jet atomization is achieved for shorter ignition delay times. Even a small swirl would cause the injection jets blow into each other and so lead to disadvantageous soot formation.

The invention is based on the problem with an injection nozzle of the type mentioned Shorter injection times and / or improved air utilization with a simultaneous reduction To allow soot emissions.

To achieve these objects, the invention is based on a generic Injection nozzle given by the features of claim 1.

Due to the arrangement evenly distributed in pairs over the entire circumference of the injection nozzle from small and large injection openings the small injection jet is in the slipstream of the large injection jet deflected without the club-shaped injection jets overlap. On the other hand, each pair of injection jets has a large combustion chamber sector up to that adjacent injection jet pair available, in which the fuel due to a strong Air swirls can be blown away.

From the alternating arrangement of large and small injection openings, where each between two large injection openings, as was the case with conventional nozzles Are formed type, according to the invention additionally an injection opening with a smaller Opening cross section is provided, the technical advantage results that viewed across the entire injector, a much larger total cross-sectional area of all Injection openings at a nozzle is achieved than with conventional injection nozzles without the resulting injection jets only partially when injected into the vortex be blown into each other.

The overall cross-sectional area thus increased enables a significantly larger area Fuel flow than with conventional injectors, so that with conventional Injection pressure ratios the intended amount of fuel in a much shorter Duration than previously can be injected into the combustion chamber. This shorter injection period creates the advantage of a shorter burning time, which makes the effective specific Fuel consumption can be reduced.

Another significant advantage of the configuration of the injection openings according to the invention is that this achieved even distribution of the fuel into the air, resulting in a more homogeneous mixing and a much better result Air utilization in the cylinder leads. The combination of small and large has an effect here Injection orifices are particularly advantageous because you can use constant injection pressure with small Injection openings generally achieve a finer atomization than with large openings.

In a development of the invention it is provided that the axes of the large and small Injection openings each lie on different concentric conical shells, the Opening angles are different. As a special advantage of this embodiment, one achieves one Injection pattern, which is an overlapping blowing of the injection jets with an even larger one Excludes security and at the same time turbulent flow conditions for an improved Turbulence of fuel in the combustion air in the combustion chamber is supported.

The result of the homogeneous mixing and the resulting combustion process resulting significantly improved air utilization, results in a much lower Soot development with otherwise equal pollutant emissions.

Fig. 1

schematisch die Anordnung von Einspritzdüse und Kolben in einer Querschnittsdarstellung;

Fig. 2a

eine Horizontalschnittdarstellung durch die Düse entlang des Schnittverlaufs II-II in Fig. 1 gemäß eines ersten Ausführungsbeispiels der Erfindung;

Fig. 2b

einen Horizontalschnittverlauf durch die Düse entlang des Schnittverlaufs II-II in Fig. 1 gemäß eines zweiten Ausführungsbeispiels der Erfindung;

Fig. 3

das Einspritzmuster einer herkömmlichen Mehrlochdüse in Draufsicht;

Fig. 4

das Einspritzmuster eines Ausführungsbeispiels der erfindungsgemäßen Einspritzdüse in Draufsicht;

Fig. 5

die Darstellung der Einspritzrate über der Zeit im Vergleich zu herkömmlichen Einspritzraten.

An embodiment of the invention is shown in the drawings and will be described in more detail below. Show it:

Fig. 1

schematically the arrangement of the injector and piston in a cross-sectional view;

Fig. 2a

a horizontal sectional view through the nozzle along the section II-II in Figure 1 according to a first embodiment of the invention.

Fig. 2b

a horizontal section through the nozzle along the section II-II in Figure 1 according to a second embodiment of the invention.

Fig. 3

the injection pattern of a conventional multi-hole nozzle in plan view;

Fig. 4

the injection pattern of an embodiment of the injection nozzle according to the invention in plan view;

Fig. 5

the representation of the injection rate over time in comparison to conventional injection rates.

In Figure 1, injection ratios of an otherwise not shown are schematic Internal combustion engine shown. Opposite the piston, the injector 4 is coaxial with Piston center axis 5 arranged and not together with their nozzle holder in the drawing screwed into the cylinder head. Contrary to that shown here The coaxial arrangement of the injection nozzle is also any other placement of the nozzle in the cylinder possible without affecting the advantages achieved by the invention.

The piston 1 has a piston recess 2, which does not necessarily have to have the shape shown, but in any shape depending on the desired flow conditions can be. In Figure 1, the piston 1 is in its top dead center position (TDC), in which the Upper piston edge 14 is so far in the direction of the injector 4 that it at least partially protrudes into the piston recess 2.

The injection nozzle 4, which is designed here as a blind hole nozzle, is at a distance from Injection nozzle tip distributed over a circumferential line as injection bores 8, 9, 15, 16 trained injection openings.

The injection bores 8, 9, 15, 16, more precisely the mouth openings of these Injection bores 8, 9, 15, 16 lie on the common circumferential line, while the Center lines 10, 17 of the large injection bores 8, 15 lie on a conical surface 6 and the center lines 11, 18 of the small injection bores 9, 16 lie on a conical surface 7. Here, the opening angle α1 of this conical outer surface 6 is chosen larger than that Opening angle α2 of the surface of the cone 7. The emerging injection jets are in Direction directed to the piston recess 2 when the piston is in its top dead center position located as shown in Figure 1.

FIGS. 2a and 2b each show an embodiment of the injection nozzle 4 according to the invention shown as a section along the section line II-II in Figure 1, with the holes simplified in are shown lying on one level. These figures show the respective arrangement of the mouths of the injection bores 8, 9, 15, 16 on the common circumferential line of the injection nozzle 4. Here are a total of six injection bores 8 in the embodiment shown in Figure 2a large, conventional diameter and six further injection bores 9 with a smaller one Diameter at a uniform mutual distance over the circumference of the injection nozzle 4 distributed. As can be seen in FIG. 2a, there is a small injection hole in each case 9 arranged between two large injection bores 8, the circumferential angular distance 12, the center lines 10, 11 of a large injection bore 8 and a small injection bore 9 between them is half as large as the circumferential angle 13, which the center lines 10, 10th form two adjacent large injection bores 8 with each other.

The injection bores 8, 9, 15, 16 are each as fine bores in the injector tip manufactured. The shape of the injection bores 8, 9, 15, 16 is, however, not mandatory on the Training as a bore is restricted, but other shapes and forms can be used be provided, which are suitable for generating desired inlet flow conditions.

It is essential to the invention that the diameter of the large injection bores 8 and small injection bores 9 are dimensioned so that due to the intended Injection pressure through the individual injection bores 8, 9, 15, 16 forming fuel flow can each form an injection jet 22, 23, as shown in FIG. 4.

FIG. 3 shows an injection pattern as is the case with conventional injection nozzles each have the same size injection openings, here 6 pieces. The inflowing Combustion air was previously rotated using a corresponding inflow channel offset that an air vortex forms in the combustion chamber. This by means of the so-called swirl channel Special inflow channel with a large swirl of air is usually centralized by introduced into the combustion chamber at the top. The inflowing air pulls the fuel with it and thereby blows the injection jets 21 and 22, 23 away from those in FIGS. 3 and 4 injection lobes shown.

The diameters of these injection bores are chosen so that the individual blows Injection jets 21 do not overlap each other. However, as can be clearly seen from FIG. 3, Areas are formed in the areas between two adjacent injection jets 21, in which no fuel is mixed with air. The air present in these areas is therefore also not used in the combustion. This is where the invention begins and provides that seen in the swirl direction, the small injection bore 9 or 16 adjacent to the large one Injection bore 8 and 15, and that the circumferential angular distance 12 and 19 of the small Injection bore 9 or 16 of the large injection bore 8 or 15 is smaller than or equal to half the circumferential angular distance 13 or 20 of the large injection bores 8 or 15 among themselves. As a result, as shown with the injection pattern of FIG. 4, these gaps open between two adjacent injection jets 22, a smaller injection jet 23, which forms when the fuel emerges from a small injection bore 9, 16. Depending on the intensity of the air vortex, the diameters of the injection bores 8, 9, 15, 16 are so one on top of the other matched that the large and small injection jets 22, 23 in the blown state complete an area-wide supplementary injection pattern without them overlap each other.

The injection pattern shown in FIG. 4 is achieved, for example, with an injection nozzle, such as it is shown in Figure 2a. For embodiments in which a particularly strong air swirl is provided in the combustion chamber, brings the embodiment shown in Figure 2b Injection nozzle according to the invention further improvement. In this embodiment, the large injection bores and the small injection bores in pairs evenly over the entire circumference of the injector 4 is arranged distributed. Due to the small angular distance 19 the center lines 17 and 18 of this pair of openings, the smaller

Injection jet deflected in the slipstream of the large injection jet without the lobe-shaped injection jets overlap. On the other hand, this pair of injection jets has one compared to the larger combustion chamber sector shown in FIG. 4, in which the fuel can be blown away without interfering with the neighboring one Injection jet pair mixed.

As can be seen from a comparison of the injection pattern according to FIG. 3 and the pattern according to FIG. 4, the injection nozzle according to the invention thus enables the combustion air in the combustion chamber to be used much more extensively. Apart from the area-wide injection form, the injection nozzle according to the invention has a considerably enlarged total cross-sectional area of the injection openings, which means that the amount of fuel required in each case can be injected into the combustion chamber in a significantly shorter time t _E. This larger mass flow, or also flow rate v ˙, is depicted in FIG. 5 as a function of time over an overall injection process. In this diagram, curve 26 represents the inflow rate of a conventional injection nozzle, and curve 27 represents the injection rate, as is possible with the injection nozzle according to the invention. The area enclosed under the respective curve 26, 27 and the time axis corresponds to the amount of fuel injected. If the injection nozzle is completely open after the PREMIX area, then the injection nozzle according to the invention enables the flow rate 27 to rise to a significantly higher maximum value than that of conventional nozzles. Furthermore, the injection process with the injection nozzle 4 according to the invention is completed significantly earlier t _E than in the case of conventional injection nozzles t _H due to its larger overall hole cross section. As a result of this comparison, the area center of gravity F _{E of} the inflow rate of the nozzle according to the invention is clearly shifted forward by the distance s compared to the center of gravity F _{H of} conventional nozzles.

Consequently, with the injection nozzle 4 according to the invention, a larger amount of fuel can be used can be injected into the combustion chamber in a shorter time without it being too local Fuel accumulations and therefore too much soot and because of insufficient air utilization Pollutant developments are coming.

Claims (5)

1. Diesel engine with direct fuel injection into a swirled combustion air in the combustion space (2) which is assigned an injection nozzle (4) which is designed as a perforated nozzle and which has, distributed along a circumferential line of the nozzle, a plurality of mouths of injection orifices (8, 9; 15, 16), the injection orifices (8, 9; 15, 16) in each case being arranged so as to be distributed in pairs uniformly over the circumferential line of the nozzle, characterized in that an alternating arrangement of large and small injection orifices (8, 9; 15, 16) is provided, the diameters of the injection orifices (8, 9; 15, 16) being coordinated with one another in such a way that the injection jets from the large (8, 15) and small (9, 16) injection orifices complete one another, in the scattered state, to form an injection pattern covering an entire area, without overlapping one another.
2. Diesel engine according to Claim 1, characterized in that the injection orifices are designed as injection bores (8, 9, 15, 16), and the centre lines (10, 11; 17, 18) of the large injection bores (8; 15) and of the small injection bores (9; 16) lie on a common conical surface area (6).
3. Diesel engine according to Claim 1, characterized in that the injection orifices are designed as injection bores (8, 9; 15, 16), and the centre lines (10; 17) of the large injection bores (8; 15) lie on a first conical surface area (6) and the centre lines (11; 18) of the small injection bores (16) lie on a second conical surface area (7), the aperture angle (α1) of the first conical surface area (6) being greater than the aperture angle (α2) of the second conical surface area (7).
4. Diesel engine according to one of Claims 2 or 3, characterized in that the centre lines of the small injection bores (9) are arranged in each case at a circumferential angular distance (12) from the centre lines of the adjacent large injection bores (8) which is half the circumferential angular distance (13) between the said centre lines.
5. Diesel engine according to one of Claims 2 or 3, characterized in that the circumferential angular distance (19) between the centre line of the small injection bores (16) and the centre line of the large injection bores (15) is smaller than half the circumferential angular distance (20) between the centre lines of the adjacent large injection bores (15), and in that in a top view, as seen in the swirl direction, in each case the small injection bore (16) is adjacent to and upstream of the large injection bore (15), so that in each case the injection jet (23) from the small injection bore (16) is deflected in the lee of the injection jet (22) from the large injection-bore (16), without the injection jets (22, 23) overlapping one another.

Images