DE102005051740A1 - Combustion chamber of a self-igniting internal combustion engine - Google Patents

Abstract

The invention relates to a diesel internal combustion engine having at least one cylinder (1) in which a combustion chamber (5) is delimited between a piston (3) and a cylinder head (2), a fuel injector (6) arranged in the cylinder head (2) and one in the piston (3) arranged piston trough (4) having a trough bottom (14) with a maximum bowl depth (t), wherein the trough bottom (14) from a compression projection (10) extends to a trough edge (15), fuel by means of an injection nozzle (6a) is injected cone-shaped into the combustion chamber (5), the fuel when hitting the piston recess (4) at least partially along a trough bottom contour (11) between the compression projection (10) and the trough edge (15) is guided and wherein the along 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) at least partially from one Trough bottom surface are detached.

Description

The The invention relates to a method for operating an internal combustion engine according to the preamble of claim 1 and a device, in particular a self-igniting direct injection internal combustion engine, according to the preamble of the claim 8th.

at known conventional internal combustion engines with auto-ignition first Combustion air compressed and then fuel, for example injected in the form of several jets, which is ignited by the heat of compression. The mixing of fuel and combustion air is essentially achieved by that during of the injection process a mixture of the burning injection jets with the surrounding oxygen-rich gas. Usually meet the injection jets of high momentum on one in a piston bottom recessed trough from which the fuel jets deflected become. This results in an intense turbulent charge movement, through the one complete Mixing of the injected fuel with the combustion chamber air should be achieved. The goal here is the emergence of fuel-rich To prevent zones in the combustion chamber and thus the formation of soot particles to reduce.

It are known to be different for optimizing a diesel combustion Piston molds used with which a targeted combustion chamber configuration is determined to influence the combustion in the combustion chamber. Accordingly, you can the mixture preparation in the combustion chamber intensifies, the emission formation improved in the exhaust and the function of a downstream exhaust aftertreatment be optimized.

From the DE 10213025 A1 For example, a combustion method is known in which a portion of the fuel is injected into the combustion chamber prior to onset of auto-ignition to achieve a homogeneous premix. To set a high mean pressure of the internal combustion engine, a further amount of fuel is introduced into the combustion chamber after the first onset of homogeneous combustion, which quickly ignites after a brief Zündverzug. This combined homogeneous / heterogeneous combustion process, also known as HCCI or CHHC operation, minimizes thermal nitric oxide formation and particle formation, with CHHC originating from 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 the DE 10213025 A1 For example, a diesel internal combustion engine having a piston bowl shape is known which enables both homogeneous and heterogeneous diesel operation. The in the DE 10213025 A1 proposed piston recess is formed approximately plate-shaped, with extending from the center of the piston recess a projection in the direction of the injection nozzle. With the plate-like basic shape 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 the impinging during operation of the internal combustion engine on the trough fuel jets quickly mix with the 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 soot formation, especially at high speed and load ranges.

Of the Invention is therefore the object of an internal combustion engine to provide with auto-ignition, in which the mixture formation and combustion in the combustion chamber improved are. This is according to the invention respectively by a method having the features of claim 1 or by a device with the features of claim 8 solved.

According to one The first aspect of the invention is characterized by the method according to the invention according to claim 1, characterized in that fuel by means of the injector cone-shaped in the combustion chamber is injected, and the fuel on impact on the piston recess at least partially along a trough bottom contour between the compression projection and the trough edge, wherein the guided along the trough bottom contour fuel shares a slope change in the trough bottom or by a convex designed Area in the trough bottom are at least partially detached from a trough bottom surface.

The separation effects achieved by the change in pitch or by the convex portion in the trough bottom allow a targeted forward movement of the fuel droplets or of the fuel jet or the largely ver vaporized fuel toward a hot compression zone in a pinch region between the outer piston crown region and the cylinder head. Thus, surprisingly, an optimized guidance of the injected fuel within the piston recess with respect to the fuel distribution in the existing piston recess volume is brought about with a simple measure. Furthermore, intensive mixing of the fuel with the combustion air before and / or during combustion is achieved. By means of the convex region provided according to the invention within the trough bottom, an adapted surface of the trough interior comes about, with which a fuel enrichment, in particular in the trough edge region and on the trough bottom, is prevented by 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 An embodiment of the invention, the fuel with a Pointed hole cone angle of 70 ° to 130 ° or 85 ° to 120 °, in particular with a cone angle of approx. 90 ° in injected the combustion chamber. In the inventively provided region of the injection hole cone angle become cheap Requirements for optimized impact of the fuel jets on the intended Piston well created. Consequently, a targeted and advantageous Fuel management achieved within the piston recess within the meaning of the invention.

In Another embodiment of the invention is a first part of the fuel to form a homogeneous mixture in one Crank angle range of 130 ° KW up to 30 ° KW injected before a top dead center, with another part of the fuel to form a heterogeneous mixture in one Crank angle range of 20 ° KW before top dead center up to 40 ° CA injected after top dead center. This will be a combined Homogenous heterogeneous combustion process carried out with a Russfreie self-igniting Combustion with reduced NOx emissions is possible.

In a further embodiment of the invention, the proportion of injected Amount of fuel to form the heterogeneous mixture in comparison to a total fuel quantity between 60% and 100% at higher engine speeds 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 planned fuel distribution is on the intended Piston recess adapted CHHC operation along the fuel guide according to the invention along the piston bowl contour performed efficiently and in terms of Optimized exhaust emissions. Accordingly, by means of the fuel distribution according to the invention nearly a complete one Burnout or almost 100 percent conversion of the fuel achieved in the trough area while avoiding soot particles become.

To In a second aspect of the invention, the device according to the invention is characterized Claim 8 characterized in that between the compression projection and the trough edge formed at least three rounded transition areas are, wherein the first transition region concave is formed or a first radius with a center above the trough surface has, the second transition area is formed convex or a second radius with a center below the trough surface and the third transition region is concave or a third radius with a center above the trough surface and wherein the three transition areas from the compression projection or from a piston centerline in radial direction to the outside or in the direction of the trough edge are arranged in a row.

By the embodiment of the invention Piston becomes a fast fuel mass spread within caused the piston recess and thus a rapid mixing of the fuel with the air. A fuel particle guide in the direction the squish area of the piston is by means of a convex trained second transition area caused detachment of the Fuel mass flow optimized. For the purposes of the invention, the term "detachment" is also the distraction to understand the fuel in the free space of the piston.

An above-average Fuel replacement or a fuel diversion away from the well bottom surface into the piston bowl interior is made possible so that a considerable mixing with the combustion air within the trough. It is thus a fuel-rich education Zones at critical points in the combustion chamber, for example within the piston recess, reduced to a minimum.

In An embodiment of the invention are the first transition region adjacent to the compression projection, the second transition region in a middle part of the trough bottom and / or the third transition region arranged adjacent to the trough edge. Due to the proposed arrangement of Rounded areas will be one on the CHHC operation as well as on one purely heterogeneous operation causes particularly well coordinated fuel guidance.

In a further embodiment of the invention, the trough bottom between the first transition area and the second transition area a trough bottom area and between the second transition area and the third transition area a trough bottom outside area, the trough bottom outside area shallower than the trough bottom interior is formed. Through a In the trough bottom built slope change is along the the trough bottom surface guided fuel shares a detachment process causes. It is thus a timely distraction of the guided fuel brought about. As a result, an effective onward transport of the detached fuel components towards the outer area of the Combustion chamber or the squish region of the piston can be accomplished.

In A further embodiment of the invention comprises the trough bottom inner region at least one funnel-shaped Section, with the piston center line at an angle of 65 ° to 80 °, in particular an angle of 70 ° to 73 °.

The intended embodiment of the piston recess causes a high acceleration the fuel components along the trough bottom surface and therefore more intense detachment as well as distraction effects. Leading especially for a timely and almost complete fuel combustion, so that a reduction of the soot particle entry into the lubricating oil is achieved becomes. Because the targeted fuel guide is a direct impact avoided by burning fuel jets on the cylinder wall. Thus, soot-laden combustion zones become near the cylinder wall minimized, thereby averting a soot particle entry into the lubricating oil. Furthermore, the thermal load of the piston material is through the achieved distraction of the burning fuel jets from the Piston bowl surface away into the trough interior significantly reduced.

In A further embodiment of the invention comprises the trough bottom outer region a section with a tangent that coincides with the center line an angle of 80 ° to 90 °, in particular an angle of 84 ° to 86 °, or around 85 °. hereby becomes the detachment process of the fuel from the trough bottom surface favors and further transport the deflected fuel components in the direction of the squish area of the piston optimized. Due to the planned trough geometry an advantageous distribution of the combustion zones is achieved which in particular causes a slight squish flow, so that the detachment behavior, preferably in combination with an adapted twist, further amplified.

In Another embodiment of the invention is between the trough edge and the piston bottom at least a fourth rounded transition region convex, wherein the transition region has a radius with a midpoint below the piston crown. The continuation the fuel content in the direction of the squish area becomes thereby further improved. Preferably, the trough edge region comprises at least a section with a tangent that coincides with the center line an angle of 15 ° to 50 °, in particular an angle of 25 ° 35 °, includes. As a result, will a further transport of the particular detached from the piston bowl bottom surface portions optimized in the direction of the pinch region of the piston such that a soot particle entry into the lubricating oil is prevented. Thus, will in the bowl edge area fuel enrichment or formation prevented by fuel-rich zones.

In a further embodiment of the invention, the trough edge is annular and has a maximum bowl diameter, where a ratio of maximum bowl diameter to piston diameter in one area between 0.75 and 0.95, in particular between 0.8 and 0.85. By the intended ratio is a vote of the bowl diameter on the piston diameter created in the one with regard to minimized particle formation adapted interaction between the trough contour course, a trough volume and the one from the injector leaking fuel mass within the piston recess caused becomes. This also results in an advantageous distribution of the combustion zones achieved, supported by a slight squish flow, so that the detachment effects, preferably in combination with an adapted twist, further be increased.

Under the well volume is understood to mean a volume that is flat Includes piston bottom of a volume plane and the trough surface is. The volume plane is with the piston crown as a congruent horizontal surface displayed. Nevertheless, this level can vary depending on the course of the trough edge lie above the piston crown or below the piston crown.

In a further embodiment of the invention is a ratio of maximum bowl depth to piston diameter in a range between 0.1 and 0.2, in particular between 0.12 and 0.16. By the intended relationship comes about a combustion chamber configuration, with an advantageous Fuel management in view of the bowl depth and the fuel particles emerging from the injection nozzle is achieved within the piston recess.

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

1 a schematic representation of a combustion chamber configuration of an internal combustion engine according to the invention with auto-ignition,

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

3 a schematic representation of an early fuel injection with a spray hole angle of about 90 ° to a piston recess after 1 .

4 a schematic representation of a main injection with a spray hole angle of about 90 ° on a piston recess after 1 in the partial load range,

5 a schematic representation of a main injection with a spray hole angle of about 90 ° on a piston recess after 1 in the full load range,

6 a schematic representation of fuel jets of a 6-Locheinspritzdüse within the piston recess after 1 .

7 a schematic representation of an early fuel injection with a spray hole angle of about 120 ° on a piston recess after 1 .

8th a schematic representation of a late fuel injection with a spray hole angle of about 120 ° on a piston recess after 1 in the partial load range,

9 a schematic representation of an interaction between a squish flow and a swirl flow at moderate to high swirl within a piston recess after 1 .

10 a schematic representation of an interaction between a squish flow and a swirl flow at low swirl within a piston bowl after 1 .

11 a schematic representation of a course of deflected burning fuel jets with a spray hole angle of about 90 ° in pure heterogeneous operation within a piston recess after 1 .

12a a schematic representation of a course of a main injection in pure heterogeneous operation within a piston recess after 1 .

12b a schematic representation of a course of a post-injection made after the main injection in pure heterogeneous operation within a piston recess after 1 , and

12c a schematic representation of progressions of a burning main and post-injection in pure heterogeneous operation within a piston recess after 1 ,

In 1 is an internal combustion engine shown, the at least one cylinder 1 and a cylinder head 2 having. Inside the cylinder 1 is a combustion chamber 5 between a piston 3 and the cylinder head 2 limited. In the cylinder head 2 is a fuel injector 6 with an injection nozzle 6a according to 2 arranged, which has a plurality of injection holes, not shown. From the injection holes occur several fuel jets 8th out, with the injector 6a preferably has two selectively selectable Einspritzbohrungsreihen arranged one above the other. The fuel is thereby in a corresponding number of fuel jets 8th directly into the combustion chamber 5 injected, so that a direct-injection internal combustion engine is realized. Preferably, in the combustion chamber 5 injected a diesel fuel, so that a self-igniting combustion is initiated. An injection hole cone formed between the fuel jets 9 with a cone angle β is in a range between 50 ° and 160 ° or 70 ° and 130 °, in particular about 90 °.

One in the piston bottom 7 provided piston recess 4 is located at the cylinder head 2 facing side of the piston 3 and is of an annular trough wall or trough edge 15 limited to the outside. The piston 3 has a piston diameter Db, wherein the piston recess 4 is enclosed within a trough rim diameter Dm. For a flat piston crown 7 which according to 2 to the trough edge 15 is adjacent, at the end of a compression stroke between the piston crown 7 and the cylinder head 2 a pinch area 12 educated.

As in 1 is shown, the piston recess 4 an almost centrally positioned, in the direction of the cylinder head 2 extending compression projection 10 on. The piston recess 4 is formed such that a center axis of the compression projection 10 preferably with a cylinder axis 19 and a center axis of the fuel injector 6 coincides. The Vor preferably executed in the form of a conical bump Leap 10 has a projection cone angle αh and a rounded cone syringe. The trained survey 10 is not limited to a cone-shaped structure. It may also be different, for example, formed as a spherical projection. A high temperature load is thereby avoided in the apex. The distance Ak of the rounded cone 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 advantage 10 in this case has a cone angle αh, which is approximately equal to the used injection angle of the injection nozzle 6a corresponds, ie about 70 ° to 130 °, preferably by 100 °.

Preferably is the projection taper angle αh about 10 ° larger or smaller than the cone angle β, when the cone angle β steep is or is e.g. is about 90 ° to one preferably to avoid parallel injection course to the projection course.

In 3 is a piston position at about 50 ° CA after or before a top dead center OT shown. According to 3 extends from the compression projection 10 a trough contour 11 in the direction of a trough bottom 14 and then continue towards the trough edge 15 , Under the trough edge 15 is the end or the outermost region of the piston recess 4 to understand. The piston bottom surface 7 adjoins the edge of the trough 15 at. At this limit, the maximum bowl diameter Dm is measured.

According to 2 is the injector 6a above the piston recess 4 arranged. Preferably, the piston recess 4 in the combustion chamber 5 the internal combustion engine arranged centrally. The trough contour 11 points in a compression projection 10 adjacent area on a rounded first transition area R1. Within the first transition region R1 is preferably the lowest point of the piston recess 4 with a maximum distance t from the piston crown 7 , By the provided distance t remains for along the trough contour 11 enough fuel leftover. Thus, the compression of the projection 10 Distribute deflected or guided fuel quantity optimally. The transport of the fuel in the direction of the trough edge 15 is due to the design of the trough bottom 14 and the dimension of the bowl diameter Dm determined in comparison to the piston diameter Db.

The present invention proposes an embodiment of the trough bottom 14 and / or a ratio Dm / Db of bowl diameter Dm to piston diameter Db, which has the result 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 to, by means of the combustion chamber configuration according to the invention in the combustion chamber 5 introduced fuel jets 8th at least partially along the trough bottom contour 11 between the compression projection 10 and the trough edge 15 to lead such that sufficient fuel shares by a separation projection 16 , in particular in the form of a change in pitch or a convexly designed area in the trough bottom 14 be detached from a trough bottom surface. The jump-off or detachment area provided for this purpose lies in a trough bottom section which is at a distance A from the cylinder axis 19 which is about 30% to 70%, in particular about 50% of the piston radius.

Thus, one according to 4 formed fuel cloud 13 or a fuel / air mixture along the trough bottom contour according to the invention 11 guided, timely detached 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 recess 4 or the combustion chamber 5 shifted, in which the larger volume fractions are located. This results in low-particle combustion. In 4 is a piston position at about 10 ° CA before or after the top dead center OT shown. With the help of the present combustion chamber configuration is a possible emergence of fuel-rich zones within the piston recess 4 avoided. As a result, autoignition combustion with intensive soot particulate oxidation is found 4 instead of. 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 Russpartikelfreie combustion according to when operating the internal combustion engine in the upper speed and load ranges 5 respectively. 11 is possible.

Starting from the compression projection 10 joins in the radial direction of the first transition region R1, so that a continuous transition into a flat outwardly rising trough contour 11 is trained. The vertex at the first rounded transition region R1 represents the lowest point of the piston bowl 4 In this case, the distance t is between 10% and 20%, preferably 14% of the combustion chamber diameter Db. The first transition region R1 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 area of the hollow 4 becomes an advantageous deflection of the fuel jets 8th along the trough contour 11 achieved. In addition, a reduction of the volume is achieved in a range that is already insufficiently detected by the combustion zones anyway.

The embodiment of the compression projection 10 thus leads to a prevention of early suction of the fuel jets 8th , known as a wallet effect. The adjoining the transition region R1 outwardly, preferably flat rising contour provides a Muldenbodeninnenbereich 17 in the form of a surface of a first cone K1 or a funnel-shaped portion, which has an angle αk1 of about 130 ° to 160 °, preferably about 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 of about 5% to 15%, preferably about 8% of the piston diameter Db in a compared to the trough bottom interior 17 shallow trough bottom outside area 18 passes. This zone likewise represents a short section of a surface of a second cone K2, which has an angle αk2 of approximately 140 ° to 180 °, preferably approximately 170 °.

The second transition region R2 acts as a small bump or as a takeoff edge. Outward 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 goes into the steeply rising trough edge 15 above. The trough edge region in turn represents 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 approximately parallel to the cylinder axis 19 educated.

The trough edge 15 merges into a fourth rounded transition region R4, which is on the flat piston crown 7 in the area of the pinch area 12 borders. The fourth transition region R4 has a radius of about 1% to 10%, preferably about 3% of the piston diameter Db. On 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 from the trough edge 15 deflected or guided fuel jets 8th thus stepping out of the trough 4 in the direction of the pinch area 12 or squish gap out.

A slightly steeper rise of the Muldenrands 15 in the outer area, ie at the transition to the piston crown 7 , leads to an increased deflection of the trough contour 11 sliding fuel jets 8th 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, especially when the piston 3 already further below the cylinder head 2 stands.

This will cause a direct impact of the burning fuel jets 8th according to 11 on the cylinder wall 1a prevented. The detachment effects guide or direct the fuel cloud 13 or the combustion gas cloud 13a towards the cylinder head 2 from. In 12a to 12c the effect of the diversion is clearly visible. There are no burning beam components in the unfavorable for the combustion squish area 12 or in a firebrigade 3a pushed. Accordingly, the present piston recess is suitable 4 also for a conventional or purely heterogeneous diesel combustion, in which preferably the total fuel quantity is divided into a first portion of a main injection HE and a second portion of the main injection HE as an accumulated post-injection NE, wherein the second portion or the post-injection NE immediately after completion of the first Share of the main injection HE in the combustion chamber 5 according to 12b is introduced. An interruption of the injection process between the main injection HE and post-injection NE takes place accordingly.

According to the present invention, a shallow bowl edge angle αk3 results in that of the bowl rim 15 deflected fuel jets also flatter out of the trough 4 escape. The choice of the radius of the fourth transition region R4 and the trough edge angle αk3 depends on the set or selected spray hole cone angles β of the injection nozzle and / or the fuel injection times. Accordingly, when using a fuel injection system with high injection pressures, the configuration of the depression contour is preferably 11 to be selected so that the conical section K2 passes over the third transition region R3 in the conical section K3. Alternatively, the trough contour 11 formed such that the conical sections K1, K2, K3 by curved surfaces, each with large radii of curvature or free Contour to be replaced.

The piston bowl configuration according to the invention is suitable for both a combined homogeneous / heterogeneous mode of operation, known as CHHC operation, a diesel engine as well as for a purely heterogeneous or

conventional operation. A pure homogeneous mode of operation is also possible. The use of an injection nozzle 6a with in particular a steep spray hole angle β of about 80 ° to 90 ° has an advantageous effect on the proposed piston recess configuration, since the piston recess design relatively insensitive with respect to such an injection nozzle 6a is. Accordingly, the piston recess according to the invention is suitable 4 both for the use of an injection nozzle 6a with a steep spray hole angle β of 80 ° to 90 ° as well as for the use of injection nozzles 6a with a slightly shallow injection hole angle β, for example by 120 °. In particular, the use of an injection nozzle has an effect 6a with a steep spray hole angle β of about 90 ° in the different load cases during a homogeneous mixture formation in CHHC operation also advantageous.

In a further embodiment of the invention, the piston recess according to the invention has an effect 4 also in combination with the squish flow and / or one in the combustion chamber 5 formed swirl flow according to 9 relevant to combustion with auto-ignition. In particular, with a moderate to high twist D, a resulting flow results along the trough contour 11 into the hollow 4 according to 9 into flows. In such flow conditions, fuel-rich combustion zones detach from the trough edge 15 so that a rapid and effective oxidation of optionally formed soot particles is made possible. With little or no twist D, the squish flow is below the cylinder head 2 first to the center of the combustion chamber 5 directed. Accordingly, within the trough 4 a whirl W according to 10 educated. This also causes the formation of fuel-rich mixture zones within the trough 4 avoided. For the purposes of the invention, moderate swirl means a twist number according to Tippelmann which is greater than one, with a low swirl the twist number being between zero and one.

Furthermore, the piston recess according to the invention is suitable 4 in particular with the use of variable injection nozzles, in which at least two fuel injections bores arranged one above the other and selectively selectable are provided. Accordingly, a reduction in thermal NO x formation by optimized wall-guided autoignition combustion while avoiding local fuel rich zones, especially after the impact of the fuel jets 8th on the piston recess 4 allows.

The in 4 shown second transition region R2 in the form of an indicated hump 16 or a change of slope allows a detachment of the flame zones from the trough surface. In particular, during operation in the partial load range, where small heterogeneous injection quantities are injected with a relatively small fuel jet pulse, it is particularly when using an injection nozzle 6a with steep spray hole angle β to a slowing down of the entry speed of the fuel jet tips in the trough bottom area. Through the hump 16 is a detachment of the flame zones in accordance with the invention Muldenkonturgeometrie according to 5 supports and thereby achieves an advantageous mixing with the combustion air. As a result, additional contact zones to the combustion air or to the necessary oxygen of the combustion chamber air are created.

Thus, a burnout mechanism and soot oxidation are enhanced and accelerated. The directional deflection of the fuel jets caused by the change in pitch 8th is then inside the piston recess 4 accomplished in the region of the second transition region R2. Likewise, in the case of larger heterogeneous fuel quantities, detachment of the flame zones is subsequently promoted.

In an advantageous embodiment of the invention, the trough edge 15 steep to the cylinder axis 19 educated. Due to the relatively steep rise of the Muldenrands 15 become the fuel jets 8th , especially with larger heterogeneous injection quantities, reinforced upward in the direction of the cylinder head 2 diverted. As a result, a direct impact on a cylinder wall is avoided at later injection times, in particular when the piston is already further below the cylinder head 2 stands, as in 5 is shown. This leads to a reduction of a possible soot particle entry into the lubricating oil or in the wall film and reduces heat flow into the cylinder wall. In addition, a cooling of the combustion zones is reduced on the cylinder wall and thus counteracted a locally premature reduction of soot oxidation.

Nevertheless, the design of the rise of the Muldenrands should 15 not too steep and the radius at the transition should not be too small to avoid a pronounced formation of a recirculation zone. Because in such recirculation zones fuel-rich mixture zones form. Accordingly, according to 5 a slight deflection or vortex formation at the transition to Quetschfläche instead. These has a positive effect on the combustion and reduces the momentum of the fuel jets 8th or their orientation in the direction of the cylinder head 2 ,

This will make the main combustion zone below the cylinder head 2 concentrated. Heat input into this zone is reduced. In addition, a small pinch surface at the beginning of downward movement of the piston down to a kind of suction effect. This comes in the pinch area 12 above the pinch surface or the piston crown 7 a volume into which one from the piston recess 4 in the direction of the cylinder head 2 flowing mixture enters and spreads in it.

According to an advantageous embodiment, an injection nozzle 6a provided with a spray hole cone angle β of about 90 °, wherein in particular during CHHC operation at higher speed and load ranges or in the full load range for the homogeneous mixture formation phase set a fuel injection at an interval of about 130 ° CA to 30 ° CA before top dead center becomes. In contrast, the fuel injection start for the heterogeneous main combustion phase in the partial load range at an interval of approx.

20 ° KW before the top dead center to about 40 ° CA after the top dead center, preferably selected about 5 ° CA before top dead center. there is in CHHC mode, the proportion of heterogeneously injected fuel quantity at higher Speed and load ranges or in the full load range approx. 70% to 100% and in the partial load range about 50%.

Accordingly, the fuel passes during the homogeneous mixture formation phase due to the cylinder head 2 slightly remote piston position into the flat area of the piston recess 4 according to 3 , In this case, the steep injection hole angle β of approximately 90 °, or 80 ° to 95 °, has a very advantageous effect, since the application of fuel to the cylinder wall 1a is largely minimized. In addition, the fuel increasingly mixed with the combustion air due to the relatively large free length of the fuel jets 8th , Due to the open shape of the piston recess 4 the mixture zone moves in both directions inwards and outwards, so that the concentration in a limited partial volume of the combustion chamber is avoided. The indicated hump or the detachment edge 16 supports in the late phase of homogenization, the mixture distribution.

In a part load range, the relatively low heterogeneous fuel injection quantity impacts the piston bowl with a lesser impulse 4 due to the short duration of injection and the small mass and therefore gets insufficiently into the outer combustion chamber area. According to 4 Nevertheless, a lift or a detachment of the flame zones is favored by the trough surface by the change of pitch in the second transition region R2. At an early start of injection at about 10 ° CA before top dead center, the mixture zone dissolves due to the onset of downward movement of the piston 3 partially from the wall surface and a more complete burnout is achieved.

Furthermore, meet in accordance with 5 in the heterogeneous combustion phase at about 10 ° CA after and before top dead center during fuel injection using the injector 6a with spray hole angle β of about 90 ° first on the compression projection 10 adjacent first transition region R1, in which the lowest point of the piston recess 4 located.

The fuel jets 8th After initially strong deflection along the flat outward or upwardly extending trough contour 11 guided. Partially spread the fuel jets 8th according to 6 to the side, meet in the form of mixture clouds on adjacent mixture clouds and mix with each other. As a rule, increases in the border zones 20 the fuel concentration. Nevertheless, by means of the detachment processes taking place by the change in gradient existing in the second transition region R2, the formation of fuel-rich zones within the boundary zones 20 minimized.

As a result, a heterogeneous diffusion combustion takes place substantially without thermal NOx formation. In order to avoid an increased NOx formation, preferably the combustion air is mixed with recirculated exhaust gas and / or retained in the combustion chamber. For this purpose, an EGR device is provided. In addition, due to the previous homogeneous combustion already reduced oxygen concentration in the combustion chamber 5 , which also counteracts the formation of NOx.

At high speed and load ranges, especially in the full load range, however, is during the heterogeneous combustion phase, a long fuel injection duration and therefore a high pulse of the fuel jets 8th in front. This will cause the fuel jets 8th by the separation effects in the second transition region R2 along the trough contour 11 transported to the outside. The slightly steeper rise of the Muldenrands 15 deflects the formed fuel clouds 13 according to 5 then upwards in the direction of the cylinder head 2 in the pinch area 12 into it. Consequently, there is no direct impact of the burning injection jets on the cylinder wall 1a according to 11 instead of. Due to the achieved deflection at the transition region R2 and the further deflection by the trough edge 15 will the Combustion gas cloud 13a or the combustion zone of the hot gases toward the combustion chamber side surface of the cylinder head 2 steered so that no stagnation point flow occurs in the pinch area. Thus, no beam components are in the flank 3a pressed in the pinch area. Because above the Feuerstegs 3a As a rule, no combustion takes place, or if a flame finds its way there, it extinguishes and thus leads to a heightened formation of soot particles. Accordingly, the penetration of soot particles with the blow-by gases into the crankcase is prevented and oil contamination is thereby reduced to a minimum.

Consequently, the piston recess according to the invention is suitable 4 also for a conventional diesel operation, in which preferably the total amount of fuel around top dead center as main injection HE and as post-injection NE according to 12b is introduced. Preferably, the total amount of fuel, ie, the main injection HE and the post-injection NE, in a range between 20 ° CA before TDC and 40 ° CA after TDC in the combustion chamber 5 according to 12a to 12c introduced, wherein the division of the amount of fuel into the main injection HE and the post-injection NE takes place such that the direct injection NE directly directly, ie between 0 ° CA and 20 ° CA after completion of the main injection HE is started. The Kolbenmuldenausbildung invention allows even at low Nacheinspritzmengen an advantageous mixing of nacheingespritzten Kraftstoffmneg with the center of the piston recess 4 located and still unused Verbrennunsgluft. Due to the lower amount of the main injection HE, as compared to a single block main injection, there is less overfatting in the outer zones on the trough wall.

Therefore arise in the combustion chamber center according to 12b due to the accumulated post injection NE higher gas temperatures compared to an undivided main injection HE. This leads to more favorable conditions for Rußausbrand and thus to a lower soot emission. The dimensioning of the post-injection quantity is carried out in such a way that the post-injected fuel components do not leave the favorable region of the hollow interior again. Because the exterior of the combustion chamber 5 or the pinch area 12 have at the time of post-injection NE lower oxygen content than in the middle of the piston recess 4 ,

As a result, in the case of an accumulated post-injection NE, when using an injection nozzle with a spray cone angle of, for example, 90 °, the re-injected jets are produced in accordance with FIG 12a . 12b and 12c initially not in contact with the flame zones from the main combustion. As a result, they ignite relatively late. A subsequent ignition leads to a Ausmagerung in the beam and thus to a minimum soot formation. The combustion zones of the post-injection NE are increasingly located in the center of the combustion chamber with the aid of the intended injection strategy 5 , as in 12c shown, and extend from the piston 3 to the cylinder head 2 , Overall, a better clear detection of the trough volume is thereby achieved.

Due to the advantageous combustion, the fuel quantity of the post-injection NE, in contrast to a conventional conventional combustion chamber configuration, can be made larger. Due to the smaller amount of the first injection or main injection HE is a lower superfatting in the outer zones of the combustion chamber 5 achieved, so that the unused combustion air can be used with the second injection or post-injection NE. Thus, a small amount of thermal NO formation is caused since the injection of the total amount of fuel, main injection HE and post-injection NE, is allowed for a relatively late time in the compression stroke, eg, around top dead center. Preferably, the post-injection amount is between 5% and 35% or between 10% and 20% or 20% of the total amount of fuel.

According to a further advantageous embodiment, the injection nozzle 6a used with a spray hole cone angle β of about 120 °, which selected in particular during CHHC operation at higher speed and load ranges or in the full load range for the homogeneous mixture formation phase, a fuel injection start at an interval of about 130 ° CA to 30 ° CA before top dead center become.

On the other hand becomes the fuel injection start for the main heterogeneous combustion phase in the partial load range at an interval of approx. 20 ° CA before top dead center until about 40 ° KW after the top dead center, preferably selected about 5 ° CA before top dead center. there is in CHHC mode, the proportion of heterogeneously injected fuel quantity at higher Speed and load ranges or in the full load range approx. 70% to 100% and in the partial load range about 50%.

During the homogeneous mixture formation phase, the fuel hits the outside of the piston recess 4 and will according to 7 then turned to the outside and partially inward. At the transition to the pinch area 12 occurs a slight beam splitting effect. During the heterogeneous mixture formation phase, the fuel jets hit 8th according to 8th compared to the injector 6a with a Spray hole angle β of 90 ° a little further out on the piston crown 14 on. Due to the greater distance of the impingement point from the combustion chamber center, the deflected mixture clouds of adjacent fuel jets are formed when the deflected mixture clouds meet 8th less fuel-rich zones in the border zone area 20 ,

Otherwise, the result is a similar course as that of the injection nozzle with the spray hole angle β of 90 °. The mixture clouds 13 be along the trough contour 11 guided to the outside and through the trough edge 15 turned upwards. A direct impact on the cold cylinder wall is thereby avoided. Due to the pinch surface, the suction effect occurs. In particular, at full load, the vortex at the fourth transition region R4 is less pronounced with locally fuel rich zones and more evenly distributed over the circumference than at an injector 6a with a spray hole angle β of 90 °.

The combustion chamber configuration provided according to the invention is particularly suitable for self-ignition internal combustion engines which are operated both by CHHC operation and by means of a purely homogeneous or purely heterogeneous diesel combustion process. In addition, the piston recess according to the invention is suitable 4 in particular for the use of an injection nozzle 6a with a spray hole angle β of 80 °, 85 °, 90 ° or 120 °. The use of an injection nozzle 6a with a steep spray hole angle β of 80 ° counteracts a possible Schmierölverdünnung in formerly homogeneous mixture formation, as a possible fuel wall order due to a long range of the liquid fuel jet portions at early injection and steep injection cone angle at the piston bowl edge 15 and not on the cylinder wall. Furthermore, there is an extended free fuel jet route. Furthermore, an advantageous distribution of fuel takes place in the zones detected by the fuel, in particular in the squeeze zone or in the piston recess bottom region, so that a uniform mixture distribution in the combustion chamber 5 is achieved.

Claims (16)

Method for operating an internal combustion engine having at least one cylinder ( 1 ), in which a combustion chamber ( 5 ) between a piston ( 3 ) and a cylinder head ( 2 ) is limited, one in the cylinder head ( 2 ) arranged fuel injector ( 6 ) and one in the piston ( 3 ) arranged piston recess ( 4 ), which form a trough bottom ( 14 ) having a maximum bowl depth (t), wherein - the well bottom ( 4 ) from a compression projection ( 10 ) to a trough edge ( 15 ), - fuel by means of an injection nozzle ( 6a ) conical in the combustion chamber ( 5 ) is injected, and - the fuel when hitting the piston recess ( 4 ) at least partially along a trough bottom contour ( 11 ) between the compression projection ( 10 ) and the trough edge ( 15 ), characterized in that - along the trough bottom contour ( 11 ) guided fuel shares by a change of slope ( 16 ) in the trough bottom ( 14 ) or by a convexly shaped area (R2) in the trough bottom ( 14 ) are at least partially detached from a trough bottom surface. A method according to claim 1, characterized in that the fuel with a spray hole cone angle (β) of 70 ° to 130 °, in particular 85 °, 90 ° or 120 ° in the combustion chamber ( 5 ) is injected. Method according to claim 1 or 2, characterized that a first part of the fuel to form a homogeneous Mixture in a crank angle range from 130 ° CA to 30 ° CA before top dead center is injected, with another part of the fuel for Formation of a heterogeneous mixture in a crank angle range of 20 ° KW ago the top dead center to 40 ° KW injected after top dead center. Method according to one of claims 1 to 3, characterized that the proportion of injected fuel quantity to form the heterogeneous mixture compared to a total amount of fuel between 60% and 100% at higher speeds and load ranges as well as at full load and between 30% and 70% low and medium speed and load ranges. Method according to claim 1 or 2, characterized that the total fuel quantity between 20 ° KW before the top dead center to 40 ° KW after the top dead center is injected. Method according to claim 5, characterized in that that the total amount of fuel injected into a main injection (HE) and an attached post-injection (NE) is divided. Method according to Claim 6, characterized that the distance between the beginning of post-injection (NE) and the end of the main injection (HE) is between 0 ° CA to 20 ° CA. Internal combustion engine, in particular for carrying out a method according to one of claims 1 to 7 with at least one cylinder ( 1 ), in which a combustion chamber ( 5 ) between a piston ( 3 ) and a cylinder head ( 2 ) is limited, one in the cylinder head ( 2 ) arranged fuel injector ( 6 ) and a piston recess arranged in the piston ( 4 ), the one Trough bottom ( 14 ) having a maximum bowl depth (t), wherein the well bottom ( 14 ) from a compression projection ( 10 ) to a trough edge ( 15 ), characterized in that - between the compression projection ( 10 ) and the trough edge ( 15 ) are formed at least three rounded transition regions, wherein - the first transition region (R1) is concave or has a first radius with a center above the trough surface, - the second transition region (R2) is convex or a second radius with a center has the third transition region (R3) is concave or has a third radius with a center above the trough surface, and wherein - the three transition regions starting from the compression projection ( 10 ) or from a piston centerline ( 19 ) in the radial direction to the outside or in the direction of the trough edge ( 15 ) are arranged in a row. Internal combustion engine according to claim 8, characterized in that the first transition region (R1) adjacent to the compression projection ( 10 ), the second transition region (R2) in a middle part of the trough bottom ( 14 ) and / or the third transition region (R3) adjacent to the trough edge ( 15 ) are arranged. Internal combustion engine according to claim 8 or 9, characterized in that the well bottom ( 14 ) between the first transition region (R1) and the second transition region (R2) a trough bottom inner region ( 17 ) and between the second transition region (R2) and the third transition region (R3) a trough bottom outer region ( 18 ), wherein the trough bottom outer region ( 18 ) shallower than the trough bottom interior area ( 17 ) is trained. Internal combustion engine according to one of claims 8 to 10, characterized in that the trough bottom inner region ( 17 ) comprises at least one funnel-shaped section which coincides with the piston center line ( 19 ) includes an angle of 65 ° to 80 °, in particular an angle of 70 ° to 73 °. Internal combustion engine according to one of claims 8 to 11, characterized in that the trough bottom outer region ( 18 ) includes a portion having a tangent which is aligned with the piston centerline ( 19 ) includes an angle of 70 ° to 90 °, in particular an angle of 84 ° to 86 °. Internal combustion engine according to one of claims 8 to 12, characterized in that between the trough edge ( 15 ) and the piston crown ( 14 ) at least a fourth rounded transition region (R4) is convex, wherein the transition region (R4) has a radius with a center below the piston crown ( 14 ) having. Internal combustion engine according to one of claims 8 to 13, characterized in that the trough edge region ( 15 ) comprises at least one section with a tangent which encloses an angle of 15 ° to 50 °, in particular an angle of 25 ° to 35 ° with the Kobenmittellinie. Internal combustion engine according to one of claims 8 to 14, characterized in that the trough edge ( 15 ) is annular and has a maximum bowl diameter (DM), the piston ( 2 ) has a piston diameter (Db), and wherein a ratio (DM / Db) of maximum bowl diameter (DM) to piston diameter (Db) is in a range between 0.75 and 0.95, in particular between 0.8 and 0.85 Internal combustion engine according to one of claims 8 to 15, characterized in that a ratio (t / Db) of maximum Dump depth (t) to piston diameter (Db) in a range between 0.1 and 0.2, in particular between 0.12 and 0.16.