WO2006058617A2

WO2006058617A2 - Diesel internal combustion engine

Info

Publication number: WO2006058617A2
Application number: PCT/EP2005/012328
Authority: WO
Inventors: Annette Jooss; Gerhard König; Alois Raab
Original assignee: Daimlerchrysler Ag
Priority date: 2004-12-04
Filing date: 2005-11-17
Publication date: 2006-06-08
Also published as: WO2006058617A3

Abstract

The invention relates to an internal combustion engine comprising at least one cylinder (1) in which a combustion chamber (5) is defined between a piston (3) and a cylinder head (2), a fuel injector (6) arranged in the cylinder head (2), and a piston cavity (4) arranged in the piston (3). Fuel is injected into the combustion chamber (5) during a working cycle, by means of an injection nozzle (6a), in the form of a plurality of partial quantities as a pre-injection, main injection and/or secondary injection. When the fuel meets the piston cavity (4), it is guided at least partially along a cavity bottom contour (11) between a compression projection (10) and a cavity edge (15), and the fuel parts guided along the cavity bottom contour (11) are at least partially separated from a cavity bottom surface or deviated by means of a change (16) in the incline of the cavity bottom (14) or by a convex region (R2) in the cavity bottom (14).

Description

Diesel engine

The invention relates to a method for operating an internal combustion engine according to the preamble of claim 1 and to a device, in particular a self-igniting direct-injection internal combustion engine, according to the preamble of claim 10.

In conventional internal combustion engines with auto-ignition combustion air is first compressed and then injected fuel, for example in the form of a plurality of jets, which is ignited by the heat of compression. The mixing of fuel and combustion air is essentially achieved by mixing the burning injection jets with the surrounding oxygen-rich gas during the injection process. In general, the injection jets with high momentum impinge on a recessed in a piston head trough, from which the fuel jets are deflected. This results in an intense turbulent charge movement, by which a complete mixing of the injected fuel with the combustion chamber air is to be achieved. The aim is to prevent the formation of fuel-rich zones in the combustion chamber and thus to reduce the formation of soot particles.

To optimize a diesel combustion different piston molds are used as well as load-dependent injection strategies performed, with which a specific combustion chamber configuration is set to influence the combustion in the combustion chamber. Accordingly, the mixture preparation can be intensified in the combustion chamber, the Emission formation in the exhaust gas improved and optimized the function of a downstream exhaust aftertreatment.

From DE 10213025 Al a combustion method is known in which a portion of the fuel is injected into the combustion chamber before the onset of auto-ignition to achieve a homogeneous premix. To set a high mean pressure of the internal combustion engine, after the first onset of homogeneous combustion, a further amount of fuel is introduced into the combustion chamber, which quickly ignites after a brief ignition delay. This combined homogeneous / heterogeneous combustion process, also known as HCCI or CHHC operation, minimizes thermal nitric oxide formation and particulate formation using CHHC as an abbreviation for Combined Homogeneous Heterogeneous Combustion. In the following after the homogeneous combustion phase heterogeneous combustion phase, the nitrogen oxide formation is to be significantly reduced by a late position of the fuel injection and due to a reduced oxygen concentration by the previous homogeneous fraction of combustion and an operation with exhaust gas recirculation (EGR). In addition, due to a reduction in the heterogeneous fuel injection quantity, the formation of fuel-rich or rich mixture zones in the combustion chamber, in particular at the end of the injection, should be reduced or avoided.

From DE 10213025 Al a diesel internal combustion engine with a piston recess shape is known, with which allows both a homogeneous and a heterogeneous diesel operation. The proposed in DE 10213025 Al piston recess is formed approximately plate-shaped, extending from the center of the piston recess, a projection in the direction of the injection nozzle. With the plate-like basic form is trying to avoid in the piston recess tight radii on the surface and to minimize cross-sectional jumps in the piston material, so that in the operation of the internal combustion engine on the trough quickly mix impinging fuel jets with air. Nevertheless, during a CHHC operation, especially during the heterogeneous combustion phase, fuel-rich zones can arise in the area of the trough bottom. These lead to increased formation of soot, especially at high speed and load ranges.

The invention is therefore based on the object to provide an internal combustion engine with auto-ignition, in which the mixture formation and combustion in the combustion chamber can be improved. This is inventively achieved in each case by a method having the features of claim 1 or by a device having the features of claim 10.

According to a first aspect of the invention, the inventive method according to claim 1 characterized in that the fuel is injected by means of an injection nozzle in the combustion chamber during a cycle in the form of multiple subsets as pre-, main, and / or post-injection, wherein the Fuel is at least partially guided along a trough bottom contour between a compression projection and a trough edge when hitting the piston trough, and the fuel components guided along the trough bottom contour are at least partially offset by a change in pitch in the trough bottom or by a convexly configured region in the trough bottom Trough bottom surface to be detached or deflected.

The dissolution effects achieved by the change in pitch or by the convex section in the trough bottom enable targeted forward movement of the fuel droplets or the fuel jet or the largely vaporized fuel in the direction of a hot compression zone in a pinch region between the outer piston crown region and the cylinder head. Thus, even with smaller amounts of fuel, especially when the total fuel quantity in a pre-, main, and / or Subsequent injection is divided, achieved by the convex portion in the trough bottom optimized guidance of the injected fuel within the piston recess. As a result, intensive mixing of the fuel with the combustion air takes place before and / or during the combustion.

The proposed trough shape is due to the effects achieved especially for a CHHC operation in which the injected fuel quantities are treated within the piston recess according to the invention both for a homogeneous mixture formation phase and for a heterogeneous combustion phase favorably. Furthermore, the trough mold according to the invention is also suitable for a late post-injection, which serves to optimize the operation of a downstream exhaust aftertreatment system.

By virtue of the convex region provided according to the invention within the trough bottom, a surface of the trough interior comes about which prevents fuel enrichment, in particular in the trough edge region and on the trough bottom, due to the detachment effects in the trough bottom region. An effective reduction of the particle formation during the combustion is made possible, and a necessary post-oxidation of possibly already formed soot particles comes about in time.

In one embodiment of the invention, the pilot, main and / or post-injection are injected in a cone shape with a different spray hole cone angle in the combustion chamber. In this case, a steep spray-hole cone angle can be used for the homogeneous mixture-forming phase, so that the fuel jet essentially impinges on the piston recess. Consequently, a fuel application is avoided on the cylinder wall. Due to the open shape of the trough as well as through the intended convex area within the Further down the mixture zone, the mixture zone moves outward so that a fuel concentration in a limited partial volume of the combustion chamber is minimized, the mixture distribution is supported by the convex portion in the trough bottom in a late phase of the homogenization. Preferably, the fuel is injected in the subsequent heterogeneous combustion phase, both in the case of partial load and at full load with a flatter spray cone angle than in the homogeneous mixture formation phase. The well shape according to the invention results in the heterogeneous combustion phase, an appropriate combustion chamber detection and consequently an improved and almost complete heterogeneous combustion with low soot emissions.

In a further embodiment of the invention, the pilot injection is injected conically into the combustion chamber with a spray-hole cone angle of 50 ° to 100 °, preferably of 70 ° to 90 °. In accordance with the invention provided for the spray hole angle angle favorable conditions for an optimized impact of the fuel jets on the intended piston recess while reducing a fuel wall order, so that a targeted and advantageous fuel guide within the meaning of the invention within the piston recess is achieved. Preferably, the pre-injection is injected to form the homogeneous mixture in a crank angle range from 13O ⁰ KW to 30 ⁰ KW before top dead center.

In a further embodiment of the invention, the main injection is injected conically into the combustion chamber with a spray-hole angle of 90 ° to 140 ° or 100 ° to 120 °. By means of the piston recess, an adapted CHHC operation according to the fuel guide according to the invention along the piston recess contour is thus carried out and optimized with regard to the exhaust emissions. Preferably, the main injection is to form a heterogeneous mixture in a crank angle range from 2O ⁰ KW before the top dead center to 4O ⁰ KW injected after top dead center.

According to a further embodiment of the invention, the post-injection is injection-molded cone-shaped with a spray-hole angle of 80 ° to 140 °, preferably from 80 ° to 120 ° or 90 ° to 120 ° in the combustion chamber. In particular, when carrying out the post-injection with a spray cone angle of 80 ° to 120 ° in combination with the piston recess according to the invention, the injection jets of the post-injection are detected by the hot gas mixture of the main combustion or of the heterogeneous combustion. Because the hot gases are concentrated or transported due to the detachment effects in the trough bottom area in a region of the combustion chamber, in which penetrate the fuel jets of the post-injection. This accelerates the evaporation process of the post-injected fuel.

In particular, if the post-injection is injected in a crank angle range from 30 ⁰ KW to 150 ⁰ KW after top dead center, the nacheingespritzten fuel quantities are evaporated before reaching the cylinder wall. Consequently, a load-dependent optimized generation of a stoichiometric or enriched mixture in the exhaust gas of a diesel internal combustion engine is enabled, for NOx regeneration or desulphation of NOx storage catalysts, for onboard generation of NH3 for the regeneration of an SCR catalyst can be used in a selective catalytic reduction of nitrogen oxide emissions and / or for the thermal regeneration of a diesel particulate filter.

In a further embodiment of the invention, the proportion of injected fuel quantity to form the heterogeneous mixture in comparison to a total fuel amount between 60% and 100% at higher speed and Load ranges or at full load and between 30% and 70%, or by 50% at low and medium speed and load ranges. Due to the proposed fuel distribution, a CHHC operation adapted to the intended piston recess is carried out efficiently along the piston recess contour according to the fuel guide according to the invention and is optimized with regard to the exhaust emissions. Accordingly, an approximately complete conversion of the fuel in the trough area can be achieved while avoiding the formation of soot particles.

According to a second aspect of the invention, the device according to the invention according to claim 10 characterized in that the fuel is injected into the combustion chamber by means of an injection nozzle which is designed such that the fuel is injected during a cycle in the form of multiple subsets into the combustion chamber and the sub-quantities optionally emerge from the injection nozzle with different injection hole cone angles. Furthermore, it is provided that a piston recess is arranged in the piston, which has a trough bottom with a bowl depth, wherein the trough bottom extends from a compression projection to a trough edge. Furthermore, at least three rounded transition regions are formed between the compression projection and the depression edge, wherein the first transition region is concave or has a first radius with a center above the depression surface, the second transition region is convex or a second radius with a center below Trough surface and the third transition region is concave or has a third radius with a center above the trough surface. Furthermore, the three transition regions are arranged starting from the compression projection or from a piston center line in the radial direction to the outside or in the direction of the trough edge in a row. The inventive design of the piston rapid fuel mass propagation is caused within the piston recess and thus achieved a rapid mixing of the fuel with the air. A fuel particle guide in the direction of the pinch region of the piston is optimized by means of a separation of the fuel mass flow caused by the convex second transition region. For the purposes of the invention, the term "detachment" also means the deflection of the fuel into the free space of the piston.

In particular, when using a variable injection nozzle, which allows injection of the fuel in the form of subsets with different spray hole cone angles from the injection nozzle, an improved fuel separation or a fuel diversion from the trough bottom surface into the piston trough interior can be achieved depending on the load point. This results within the trough increased mixing of the fuel with the combustion air.

Therefore, the proposed combustion chamber configuration is suitable both for the use of an injection nozzle with a steep spray cone angle and for the use of an injection nozzle with a flat spray cone angle or for the use of an injection nozzle, which optionally allows different injection cone angle.

Consequently, by the combustion chamber configuration according to the invention, for example in a CHHC operation, an advantageous combustion can be achieved, in particular in combination with an injector with switchable variable geometry. Such injection nozzles, also known as Vario nozzles, are described, for example, in DE 199 16 485 C2 or in DE 199 22 964 C2. In such vario nozzles, a plurality of selectively selectable and freely switchable injection-hole boring provided for rows. These spray hole rows are designed differently, so that, depending on requirements, the fuel can be introduced into the combustion chamber at different times within a work cycle with activation of a specific, freely selectable spray hole bore row with different spray cone angles. With the use of a Variodüse can be achieved in combination with the intended Muldengeometrie an advantageous distribution of the combustion zones, so that an optimized control of the combustion process within the combustion chamber in the making a pre-main and / or post-injection is made possible. Such a distribution of the combustion zones can preferably be optimized in dependence on the load point in combination with a corresponding swirl also with regard to a regulation of a downstream exhaust gas aftertreatment device.

Further advantages will become apparent from the following description and the accompanying drawings. In the drawings, embodiments of the invention are shown. Show it:

1 is a schematic representation of an inventive combustion chamber configuration of an internal combustion engine with auto-ignition,

FIG. 2 shows a further schematic representation of the combustion chamber configuration according to FIG. 1, FIG.

Fig. 3 is a schematic representation of an early

Fuel injection with a Spritzlochkegel- angle of about 80 ° on a piston recess according to Fig. 1 and

Fig. 4 is a schematic representation of a

Main injection with a spray hole cone angle of about 120 ° on a piston recess according to FIG. 1.

In Fig. 1, an internal combustion engine is shown, the at least one cylinder 1 and a cylinder head. 2 having. Within the cylinder 1 a Brennrautn 5 between a piston 3 and the cylinder head 2 is limited. 2, a fuel injector 6 is arranged with an injection nozzle 6a in the cylinder head 2, which has a plurality of injection holes, not shown. The injection nozzle may comprise a plurality of superimposed injection well rows, at least one series including injection wells having a steep spray cone angle of between about 70 ° and 90 °, and another series including injection wells having a flat cone angle between about 100 ° and 120 °. The diameters of the steep injection-well bores are smaller than those of the flat injection-well bores, the number of steep injection-well bores preferably being smaller than the number of flat injection-well bores.

During operation, a plurality of fuel jets 8 emerge from the injection bores, wherein the injection nozzle 6a positioned almost centrally in the combustion chamber 5 preferably has two selectively selectable injection bore rows arranged one above the other. The fuel is thereby injected in a corresponding number of fuel jets 8 directly into the combustion chamber 5, so that a directly injecting internal combustion engine is realized. Preferably, a diesel fuel is injected into the combustion chamber 5, so that a self-igniting combustion is initiated.

A provided in the piston head 7 piston recess 4 is located on the cylinder head 2 facing side of the piston 3 and is bounded by an annular trough wall or such a trough edge 15 to the outside. The piston 3 has a piston diameter Db, the piston recess 4 being enclosed within a bowl rim diameter Dm. In the case of a flat piston head 7, which adjoins the depression edge 15 according to FIG. 4, a pinch region 12 is formed at the end of a compression stroke between the piston crown 7 and the cylinder head 2. As shown in Fig. 1, the piston recess 4 has a nearly centrally positioned, extending in the direction of the cylinder head 2 compression projection 10. The piston recess 4 is formed such that a central axis of the compression projection 10 preferably coincides with a cylinder axis 19 and a center axis of the fuel injector 6. The preferably executed in the form of a conical projection projection 10 has a projection cone angle αh and a rounded cone syringe. The formed elevation 10 is not limited to a conical structure. It can also be designed, for example, as a spherical projection. A high temperature load is thereby avoided in the apex. The distance Ak of the rounded conical tip from the cylinder head 2 is at a piston position around a top dead center about 4% to 6% of the piston diameter Db, preferably by 5%. The compression projection 10 in this case has a cone angle αh which corresponds approximately to that of the spray cone angle of the injection nozzle 6a used, ie approximately between 70 ° and 130 °, preferably around 100 °.

In Fig. 3, a piston position at about 5O ⁰ KW is shown after or before a top dead center OT. According to FIG. 3, starting from the compression projection 10, a trough contour 11 extends in the direction of a trough bottom 14 and then further in the direction of the trough edge 15. The trough edge 15 is to be understood as the end or outermost region of the piston trough 4. The piston crown surface 7 directly adjoins the bowl rim 15. At this limit, the maximum bowl diameter Dm according to FIG. 2 is measured.

According to FIG. 2, the injection nozzle 6a is arranged above the piston recess 4. Preferably, the piston recess 4 is arranged centrally in the combustion chamber 5 of the internal combustion engine. The depression contour 11 has, in a region adjacent to the compression projection 10, a rounded first transitional region. area Rl on. Within the first transition region Rl is preferably the lowest point of the piston recess 4 with a maximum distance t from the piston head 7. By the provided distance t remains for the guided along the trough contour 11 fuel portions enough space. Thus, the amount of fuel deflected or guided by the compression projection 10 can be optimally distributed. The transport of the fuel in the direction of the trough edge 15 is optimized by the configuration of the trough bottom 14 and the dimension of the bowl diameter Dm in comparison to the piston diameter Db.

The present invention proposes an embodiment of the well bottom 14 and / or a ratio Dm / Db of bowl diameter Dm to piston diameter Db, which has the consequence that the formation of fuel-rich zones for suppressing soot particle formation is minimized. Preferably, the bowl diameter Dm is about 75% to 90%, preferably 83% of the piston diameter Db taking into account the design criteria listed below.

The design concept of the piston recess 4 aims at using the combustion chamber configuration according to the invention to guide the fuel jets 8 introduced into the combustion chamber 5 at least partially along the depression bottom contour 11 between the compression projection 10 and the depression rim 15 such that sufficient fuel components are removed by a detachment projection 16, in particular in shape a slope change or a convex designed area in the trough bottom 14 are detached from a trough bottom surface. The jump-off or separation region provided for this purpose lies in a trough bottom section which has a distance A from the cylinder axis 19 which is approximately 30% to 70%, in particular 50%, of the piston radius. Thus, an injected fuel jet 8 is guided along the trough bottom contour 11 according to the invention and detached in time from the trough bottom surface. At the same time thereby the separated fuel components are intensively mixed with the compressed combustion air and the position of the combustion zone in an outer free area of the piston bowl 4 and the combustion chamber 5 displaced, in which there are the larger volume fractions. This results in a soot particulate combustion. In FIG. 4, a piston position at about 1O ⁰ KW before or after the top dead center TDC is shown. With the help of the present combustion chamber configuration, a possible formation of fuel-rich zones within the piston recess 4 is avoided. As a result, autoignition combustion takes place with intensive soot particle oxidation. This is particularly important at operating points with large fuel masses, for example, in full load operation of great importance and advantageous, since thereby a particularly soot-free combustion is possible during operation of the internal combustion engine in the upper speed and load ranges.

Starting from the compression projection 10, the first transition region Rl adjoins it in the radial direction, so that a continuous transition into a trough contour 11 which rises in a flat manner towards the outside is formed. The vertex at the first rounded transition region Rl represents the lowest point of the piston recess 4. The distance t is between 10% and 20%, preferably 14% of the combustion chamber diameter Db. The first transition region Rl has a radius of about 8% to 15%, preferably about 11% of the combustion chamber diameter Db. By positioning the conical compression projection 10 in the central region of the trough 4, an advantageous deflection of the fuel jets 8 along the trough contour 11 is achieved. In addition, a reduction of the volume is achieved in an area that is insufficiently detected by the combustion zones. In order to avoid a possible parallel injection course to the projection course, the projection cone angle αh is preferably greater or smaller than the cone angle β by approximately 10 °, when the cone angle β is steep or is approximately 90 °, for example. The design of the compression projection 10 thus results in avoiding early suction of the fuel jets 8, known as the Walljet effect. The adjoining the transition region Rl outwardly, preferably flat rising contour represents a trough bottom inner region 17 in the form of a surface of a first cone Kl or a funnel-shaped portion having an angle αkl between about 130 ° and 160 °, preferably around 145 °.

At about half of the piston diameter Db, a second transition region R2 is arranged, which of the rising trough contour 11 with a radius between about 5% and 15%, preferably about 8% of the piston diameter Db in a lower compared to the trough bottom inner region 17 trough bottom outer region 18 passes. This zone likewise represents a short section of a surface of a second cone K2, which has an angle αk2 between approximately 140 ° and 180 °, preferably approximately 170 °.

The second transition region R2 acts as a small bump 16 or as a takeoff edge. Outwardly then follows a third in the direction of the cylinder head 2 rounded transition region R3 with a radius of about 4% to 10%, preferably 7% of the piston diameter Db. The flat conical zone between the second transition region R2 and the third transition region R3 can be shortened according to a further advantageous embodiment such that the transition regions R2 and R3 merge into one another or are connected to a common tangent.

The third transition region R3 in turn merges into the steeply rising trough edge 15. The Muldenrandbereich provides again a portion of a surface of a third cone K3, which has an angle αk3 of about 30 ° to 100 °, preferably about 60 °. Alternatively, the trough edge 15 is formed approximately parallel to the cylinder axis 19.

The trough edge 15 merges into a fourth rounded transition region R4, which adjoins the flat piston head 7 in the region of the pinch region 12. The fourth transition region R4 has a radius between about 1% and 10%, preferably about 3% of the piston diameter Db. With a steep course from the trough edge 15 and at small radii at the fourth transition region R4, a recirculation zone forms radially outside the transition. The deflected or guided by the trough edge 15 fuel jet 8 thus occur more intensified out of the trough 4 in the direction of the pinch region 12 and squish gap out. A somewhat steeper slope of the trough rim 15 in the outer area, i. at the transition to the piston head 7, leads to an increased deflection of the sliding at the trough contour 11 fuel jet 8 upwards in the direction of the cylinder head 2, especially for larger injection quantities, for example, in a heterogeneous operation. Thus, an impact of the fuel on the cylinder wall is avoided at later injection times, in particular when the piston 3 is already below the cylinder head 2.

The present combustion chamber configuration is particularly suitable for a CHHC operation, in which a portion of the fuel in the form of a pilot injection with a spray hole cone angle ß of about 70 ° to 90 ° is injected conically into the combustion chamber. This pre-injection takes place with activation or commissioning of a spray hole series with the steep spray cone angle in a crank angle range between 130 ⁰ KW and 30 ⁰ KW before a top dead center. Thereafter, a further amount of fuel is introduced as a main injection with a spray hole angle ß between 100 ° and 120 ° in the combustion chamber. The main injection takes place by commissioning another injection hole series with the flat spray cone angle in a crank angle range between 2O ⁰ KW before top dead center and 40 ⁰ KW after top dead center. In CHHC operation, the proportion of homogeneous and heterogeneously injected fuel quantity is adjusted depending on the load.

For the homogeneous mixture-forming phase, the fuel jet of FIG. 3 essentially reaches the trough. It is advantageous that a fuel order is avoided on the cylinder wall and a large free length of the injection jets 8 can be adjusted. Due to the open shape of the trough, the mixture zone can also move outward, so that the concentration in a limited partial volume of the combustion chamber is avoided. The indicated hump 16 according to FIG. 3 assists the mixture distribution in a late phase of the homogenization.

For the subsequent heterogeneous combustion phase, the fuel is preferably injected both in the case of partial load and at full load with a shallow spray cone angle ßbetween about 120 ° and 130 ° as shown in FIG. In the heterogeneous combustion phase, this results in a good combustion chamber detection and thus optimized and almost complete combustion of the main injection with low soot emissions.

In the case of a purely heterogeneous operation of the fuel as a main injection, for example, at full load with heterogeneous mixture formation also in an interval of about 20 ⁰ KW before top dead center to about 40 ° after top dead center. If the fuel is injected at a flat injection angle β of about 120 °, then there is also a useful combustion chamber detection and a almost complete heterogeneous combustion with low soot emissions.

If the number of injection hole bores having a steep spray cone angle β is chosen to be smaller than the number of injection hole bores having the steep spray cone angle β, different hydraulic flows result, that is, different HD values for the respective row. Preferably, the HD value of the series for the pilot injection is selected to be smaller than the HD value of the injection ports for the main injection or for the heterogeneous combustion.

The proposed combustion chamber configuration is also suitable for carrying out a post-injection, which is preferably injected conically into the combustion chamber with a spray-hole cone angle β between 80 ° and 140 ° or between 80 ° and 120 °. Is the after-injection, for example, injected in a crank angle range between ⁰ KW 3O and 15O ⁰ CA after top dead center, then, according to an embodiment of the invention, a regeneration of a downstream NOx storage catalytic converter are initiated. The post-injected fuel jets are vaporized by the proposed combustion chamber configuration in conjunction with the intended injection strategy before reaching the cylinder wall.

The post-injection is carried out to increase the fuel components in the exhaust gas, so that a substoichiometric or an enriched exhaust gas is generated. According to another embodiment of the invention, the post-injection may be for on-board generation of NH3 to regenerate an SCR catalyst. According to a further embodiment of the invention, the post-injection can also serve to regenerate a downstream particulate filter by raising the exhaust gas temperature, wherein the above-mentioned embodiments can be combined with each other. Preferably, in the post-injection, at least one spray hole bore row with a spray hole angle β between 80 ° and 140 ° is selected, so that in combination with the piston bowl 4 according to the invention and a low twist, preferably with a twist less than one, optimum evaporation of the re-injected fuel quantities takes place. For the purposes of the invention is meant a low twist spin number according to Tippelmann, which is smaller than one. Accordingly, due to the turbulent flow in the pinch region 12, the hot mixture cloud of the main combustion or heterogeneous combustion passes into the vicinity of the cylinder head 2 through the bump 16 arranged in the well bottom 14, so that the hot combustion gas is at the best possible position relative to the jet axis at the time of post-injection the nacheingespritzten fuel quantity lingers.

Further, the nacheingespritzte fuel amount can preferably be made by means of a block injection in the expansion stroke in a crank angle range between 30 ⁰ KW and 15O ⁰ KW after top dead center, where alternatively the post-injection in the form of a two- to seven-fold clocked injection in a crank angle range between 30 ° KW and 150 ° CA after top dead center can be made. In this case, the cycle duration during the post-injection can be varied so that the fuel sub-quantities of the post-injection are dimensioned differently. Preferably, the cycle time of the individually nacheingespritzten subsets of the post-injection decreases with increasing number of cycles, if the injection pressure decreases after the main injection. Alternatively, at a constant duty cycle, the injection pressure may be lowered to a lower level than the main injection. In order to avoid an increase in any soot particle emission possibly formed during the post-injection, the first post-injection cycle can optionally be selected according to the invention are reduced with respect to the subsequent Nacheinspritzitzakt with respect to the injection quantity, in which case the further Nacheinspritzakte be performed with continuously decreasing amount of fuel.

Claims

DaimlerChrysler AGPatent claims

1. A method for operating an internal combustion engine with at least one cylinder (1), in which a combustion chamber (5) between a piston (3) and a cylinder head (2) is limited, in the cylinder head (2) arranged fuel injector (6) and a in the piston (3) arranged piston recess (4), wherein

- Fuel is injected by means of an injection nozzle (6a) into the combustion chamber (5) during a cycle in the form of multiple subsets as a pre-, main, and / or post-injection, characterized in that

- The fuel when hitting the piston recess (4) at least partially along a trough bottom contour (11) between a compression projection

(10) and a trough edge (15) is guided, and

- The fuel along the trough bottom contour (11) guided fuel components by a pitch change (16) in the trough bottom (14) or by a convex configured region (R2) in the trough bottom (14) are at least partially detached or deflected by a trough bottom surface.

2. The method according to claim 1, characterized in that the pre-main and / or post-injection optionally with a different spray hole angle (ß) in the combustion chamber (5) are injected cone-shaped.

3. The method according to claim 1 or 2, characterized in that the pre-injection with a spray hole angle (ß) of 50 ° to 100 ° or 70 ° to 90 ° in the combustion chamber (5) is injected conically.

4. The method according to any one of claims 1 to 3, characterized in that the main injection with a spray hole angle {ß) from 90 ° to 140 ° or 100 ° to 120 ° in the combustion chamber (5) is injected conically.

5. The method according to any one of claims 1 to 4, characterized in that the post-injection with a spray hole angle (/?) From 80 ° to 140 ° or 90 ° to 120 ° in the combustion chamber (5) is injected cone-shaped.

6. The method according to any one of claims 1 to 5, characterized in that the pilot injection is injected to form a homogeneous mixture in a crank angle range from 130 ⁰ KW to 30 ⁰ KW before top dead center.

7. The method according to any one of claims 1 to 6, characterized in that the main injection is injected to form a heterogeneous mixture in a crank angle range of 20 ⁰ KW before top dead center to 40 ⁰ KW after top dead center.

8. The method according to any one of claims 1 to 7, characterized in that the post-injection is injected in a crank angle range from 30 ⁰ KW to 15O ⁰ KW after top dead center.

9. The method according to any one of claims 1 to 8, characterized in that the proportion of the injected fuel quantity to form a heterogeneous mixture compared to a total amount of fuel between 60% and 100% at higher speed and load ranges and VoIHast and between 30% and 70% at low and medium speed and load ranges.

10. internal combustion engine, in particular for carrying out a method according to one of claims 1 to 9, with

- At least one cylinder (1), in which a combustion chamber

(5) is delimited between a piston (3) and a cylinder head (2),

- An injection nozzle, which is designed such that the fuel is injected during a cycle in the form of multiple subsets into the combustion chamber and the subsets selectively exit with different injection hole angle from the injection nozzle, and

- A arranged in the piston piston recess (4) having a trough bottom (14) having a bowl depth (t), wherein the trough bottom (14) from a compression projection (10) extends to a trough edge (15), characterized in that

- Between the compression projection (10) and the trough edge (15) at least three rounded transition areas are formed, wherein

- The first transition region (Rl) is concave or has a first radius with a center above the trough surface,

- The second transition region (R2) is convex or has a second radius with a center below the trough surface and the third transition region (R3) is concave or has a third radius with a midpoint above the trough surface, and wherein the three transitional regions extend radially outward from the compression projection (10) or from a piston centerline (19) Muldenrandes (15) are arranged in a row.