WO2007110232A1

WO2007110232A1 - Combustion process of an internal combustion engine, and internal combustion engine

Info

Publication number: WO2007110232A1
Application number: PCT/EP2007/002711
Authority: WO
Inventors: Ulrich Spicher; Uwe Wagner; Amin Velji
Original assignee: MOT Forschungs- und Entwicklungsgesellschaft für Motorentechnik, Optik, Thermodynamik mbH
Priority date: 2006-03-27
Filing date: 2007-03-27
Publication date: 2007-10-04
Also published as: DE102006014071B3; EP1999350A1

Abstract

A combustion process for an internal combustion engine, in particular a compression-ignition internal combustion engine, is distinguished by the fact that preinjection is effected into regions of the combustion chamber different from the regions into which the main injection is effected.

Description

MOT Research and Development Company for Engine Technology, Optics, Thermodynamics mbH

M31187PCT

Combustion process of an internal combustion engine and internal combustion engine

The invention relates to a combustion method of an internal combustion engine according to the preamble of patent claim 1 and an internal combustion engine in which the combustion method is used.

In modern diesel engines, the direct fuel injection into the combustion chamber is usually subdivided into a plurality of partial injections such as a pilot injection, a main injection and possibly a post-injection. The individual partial injections are generally carried out with the same injection system components and therefore in identical areas of the combustion chamber. A small pre-injection amount upstream of the actual main injection achieves advantages in terms of noise and nitrogen oxide emissions compared to combustion without pre-injection. The pre-injected fuel burns before combustion of the main injection and increases the temperature in the combustion chamber. The ignition delay for the fuel of the main injection shortens and the proportion of premixed combustion becomes smaller in proportion to the diffusion-controlled combustion. This reduces the maximum pressure increase ("diesel shock") and the peak temperature during combustion, which both lowers the noise level of the engine and reduces the formation of nitrogen oxides during combustion.

The increase in the proportion of diffusion-controlled combustion, however, has a negative effect on the soot formation and thus the soot emission. This is particularly evident in the case of a pre-injection quantity which is only minimally above the ideal value and in which the soot emissions increase disproportionately. The higher soot emission is not only due to the larger proportion of diffusion-controlled combustion, but also to other influencing factors. On the one hand, the local air ratio for the main injection is reduced by the pre-injection fuel already reacted there, which both increases soot formation and reduces soot oxidation during combustion. On the other hand, there may be a direct contact of still liquid fuel of the main injection with the still possibly burning fuel of the pilot injection. EP 1 045 136 A1 discloses a combustion method having the features of the preamble of claim 1 and an internal combustion engine which operates according to this combustion method. There, the fuel is injected in a lower part load range at a shallow angle to the piston crown. In a higher part-load range, the fuel is injected at a steeper angle to the piston head in a central region of the combustion chamber.

The invention has for its object to provide a combustion method of an internal combustion engine with direct injection of the fuel into the combustion chamber by means of one or more injectors, are avoided in the soot formation and soot emission or at least greatly reduced.

This object is achieved by a combustion method according to claim 1 and an internal combustion engine according to claim 8.

In a combustion method according to the invention, load-independent always takes place a pilot injection into central regions of the combustion chamber and a main injection into the outer region of the combustion chamber. Due to the spatial separation of the pilot injection from the main injection, the formation of soot, which occurs during fuel injection into an already ignited combustion chamber volume, avoided or greatly reduced. As a result, soot emissions are largely avoided. By the stepped combustion, the temperature range of the nitrogen oxide formation can be left out, so that the formation of harmful nitrogen oxides is also kept low.

In common-rail injection diesel engines, post-injection is often provided both to improve exhaust emissions and to initiate particulate filter regeneration. Especially with a late post-injection, as is necessary for the exhaust gas temperature increase in a particle filter regeneration, penetrate the injection jets due to the already significantly reduced cylinder pressure far into the combustion chamber and even to the cylinder wall. This leads to wetting of the wall and an entry of fuel into the lubricating oil of the engine, whereby the lubricating properties of the oil deteriorate and the engine wear increases. A further development of the combustion process according to the invention therefore provides, according to dependent claim 5, a cylinder-axis post-injection into central combustion chamber regions, which avoids wetting of the cylinder wall and thus a possible lubricating oil dilution. With a combustion method and an internal combustion engine according to the invention, when used in a diesel engine, soot formation can be reduced to such an extent that the current limit values for soot emission, which are permitted by EU regulations, can be exceeded without the use of a particulate filter.

Advantageous embodiments of the invention are specified in the subclaims.

The invention is explained in more detail below with further details based on embodiments. Show it:

1 shows a partial section through the upper part of a cylinder with piston, combustion chamber and injectors for pre-injection and main injection of an internal combustion piston engine according to the invention.

2 shows a partial section as in FIG. 1 of an embodiment of the invention with only one injector for the pilot and main injection;

3 shows the spatial orientation of pre-injection and time-dependent main injection in an internal combustion engine according to FIG. 2;

4 shows the spatial orientation of pre-injection and time-sequential main injection in an internal combustion engine according to FIG. 1; and

Fig. 5 is a partial section through the upper part of a cylinder with piston, combustion chamber and an injector for pilot and main injection in a further embodiment of the invention, wherein the part of the combustion chamber is stepped in the piston.

1 shows schematically cylinder 10 and piston 11 with combustion chamber 5 of a self-igniting internal combustion engine (diesel engine) with two independently controllable injectors, namely a vertically directed into the combustion chamber main injector 1 for the main injection 2 and a tilted into the combustion chamber 5 pre-injector. First, the pilot injection 3 takes place with the pre-injector 4 in central, ie near the cylinder axis, areas of the combustion chamber. Thereafter, the main injection 2 takes place with the main injector 1 in outer, ie with respect to the cylinder axis more radially located combustion chamber areas. This results in a complete spatial separation of the combustion chamber areas in which the pre-injected fuel burns, from the combustion chamber areas in which burns the main injected fuel. The piston 11 has a piston recess 6, which allows the greatest possible penetration depth of the pilot injection jets in the almost axial direction of the cylinder 10. However, the embodiment with the two injectors 1 and 4 also allows the use of a piston with a flat piston recess or a flat piston crown, because the pilot injection into central combustion chamber regions can also take place through the pre-injector in the nearly radial direction of the cylinder 10 parallel to the piston 11, such as this is described with reference to FIG. 5.

Fig. 2, in the same parts with like reference numerals as in Fig. 1 and are not described again, shows the structure for a basically same injection sequence as in Fig. 1, but with only one injector, the two groups of nozzle holes with groups has separate control of the nozzle holes and thus also allows the temporal and spatial separation of the injections and the fuel jets.

In Figs. 1 and 2, angles β for defining the pilot and main injection jets are indicated as follows: βi - angle of the outer envelope of the main injection jets ß _n - angle of the inner envelope of the main injection jets ß ₂ - tip cone angle of the main injection jets ß ₃ - tip cone angle of the pilot injection jets

The angles ßi, ß _n are in practice between 180 ° and 120 °. The angles β ₂ and β ₃ should be less than 120 °, preferably β ₂ <20 ° and β ₃ <30 °.

By the cylinder-axis pre-injection 3 in the direction of the piston 11, the impact of the pre-injected fuel can be used on the piston to improve the evaporation of the pre-injected fuel and thus the mixture formation and to accelerate the ignition by the increased component temperature of the piston.

FIGS. 3 and 4 show, by way of example, the spatial orientation of the conical injection jets of a pilot injection 3 into central combustion chamber regions in a piston depression 6 and of the conical injection jets of a main injection 2 into combustion chamber regions near the cylinder wall 9, which is common in modern diesel engines with direct injection. In this case, an embodiment with an injector 1 as shown in Fig. 2 is shown in Fig. 3.

The modified embodiment with two injectors 1, 4 results in a spatial orientation of the injection jets of pilot injection 3 and main injection 2 according to FIG. 4.

Fig. 5 shows in a further embodiment by way of example a piston 11 with a stepped piston recess 7.8, which may have different geometries such as rounding and angles. The piston bowl has a cup-shaped central region 8 penetrating deeply into the piston, which provides a large penetration depth for the injection jets of the pilot injection 3, and a plate-shaped, flat region 7 of larger diameter for the conventional main injection 2.

The timing of pre-injection, main injection and post-injection is the same as in conventional processes, with pre-injection always beginning before main injection and always before post-injection. The individual injection phases can, as usual, take place completely separated from one another over time. According to the invention, however, a temporal overlap of the individual injection phases is possible.

Spatially, in all embodiments of the invention, the pilot injection 3 is carried out in combustion chamber regions which are separated from the regions of the following main injection 2.

The invention is not limited to application to diesel engines. It can also be applied to today's gasoline engines with direct injection.

The features disclosed in the foregoing description, the claims and the drawings may be of importance both individually and in any combination for the realization of the invention in its various forms. MOT Research and Development Company for Engine Technology, Optics, Thermodynamics mbH

M31187PCT

LIST OF REFERENCE NUMBERS

1 injection device

2 main injection

3 pilot injection

4 injection device

5 combustion chamber

6 central area

7 plate-shaped area

8 cup-shaped area

9 cylinder wall

10 cylinders

11 piston ßl, ßn cone angle of the envelope for the main injection h peak cone angle of the main injection ß ₃ peak cone angle of the pilot injection

Claims

claims

1. combustion method of an internal combustion engine, in which fuel is injected by means of one or more injection devices directly into the combustion chamber (5), wherein the injection process is divided into at least two partial injections (2,3) in different areas (5,6,7, 8) of the combustion chamber, characterized in that a pilot injection (3) into central regions (6,8) and a main injection (2) in outer regions (7) of the combustion chamber (5) is directed with a free spatial arrangement of the injection jets.

2. combustion method according to claim 1, characterized in that the pilot injection (3) has at least one injection jet.

3. combustion method according to claim 1 or 2, characterized in that the main injection (2) has at least one injection jet and that the number of pre- and main injection jets is the same or different.

4. combustion method according to one of claims 1 to 3, characterized in that the pre-injected fuel quantity is smaller than the main injection fuel quantity.

5. Combustion process according to one of claims 1 to 4, characterized in that after the main injection, a post-injection takes place in areas near the cylinder axis (6, 8) of the combustion chamber.

6. combustion method according to one of claims 1 to 5, characterized in that the injection jets are formed conically with the same or different cone angles.

7. Application of a combustion method according to one of claims 1 to 6 in a self-igniting internal combustion engine.

8. internal combustion engine with combustion chamber (5) and an injection device (1.4) for injecting fuel into the combustion chamber (5), wherein the injection device is designed so that they take place at least two, during different periods of injections (2,3) in each different areas (6,7,8) of the combustion chamber allows, namely a pilot injection into a central, in particular in a piston recess (6, 7, 8), located area of the combustion chamber, and a main injection in a region located outside the central region, in particular near a cylinder wall (9).

9. Internal combustion engine according to claim 8, characterized in that the injection device has at least two injectors (1,4), of which one (1) for the pilot injection (3) in the central region (6,8) and another (4) for the main injection (2) are formed in the outlying region of the combustion chamber (5).

10. Internal combustion engine according to claim 9, characterized in that each injector (1,4) has a plurality of nozzle holes, the groups are each directed at different times for dispensing fuel and in said different areas of the combustion chamber (5).

11. Internal combustion engine according to claim 8, characterized in that the injection device comprises a single injector (1), which has two groups of nozzle holes, which are directed in each case in the said different areas of the combustion chamber (5) and in groups separately timed controlled.

12. Internal combustion engine according to claim 11, characterized in that the one group of nozzle holes are aligned substantially radially and the other group of nozzle holes substantially axially with respect to a cylinder (10) of the internal combustion engine.

13. Internal combustion engine according to one of claims 8 to 12, characterized in that the combustion chamber (5) in a cylinder (10) and / or a piston (11) slidable therein is provided, and that the part of the combustion chamber in the piston (11) Stepped is formed with a flat plate-shaped area (7) for the main injection (2) and with a cup-shaped deep area (8) for the pilot injection (Figure 6).