EP1957780A1

EP1957780A1 - Internal combustion engine and method for operating an internal combustion engine by means of a laser-ignition unit

Info

Publication number: EP1957780A1
Application number: EP06793830A
Authority: EP
Inventors: Manfred Vogel; Werner Herden; Heiko Ridderbusch
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2005-11-28
Filing date: 2006-09-26
Publication date: 2008-08-20
Also published as: CN101317003B; KR20080080100A; JP2009517590A; JP4740339B2; US20080257294A1; WO2007060046A1; US7765980B2; CN101317003A; DE102005056520A1

Abstract

The invention relates to a method for operating an internal combustion engine (20) comprising a fuel-injection unit (25) and a laser ignition-unit (26). According to the invention, during a compression cycle of the internal combustion engine, fuel is injected into the combustion chamber (29) by means of the fuel-injection unit (25) in such a way that an ignitable, round, flat mixed region (28) of fuel and air forms on a plunger (21) and a predetermined period elapses between the end of the fuel injection and the start of ignition in order to form the round flat mixed region (28). Ignition then takes place within the flat round mixed region (28) by means of the laser-ignition unit (26).

Description

description

title

Internal combustion engine and method for operating an internal combustion engine by means of laser ignition device

State of the art

The present invention relates to an internal combustion engine having a laser ignition device for gasoline direct injection and a method for operating such an internal combustion engine.

Internal combustion engines for gasoline direct injection are known from the prior art in various configurations. Such internal combustion engines have been increasingly used recently because they have lower fuel consumption at lower emissions. The known internal combustion engines have in common that they usually have an injection valve in a central position and a spark plug is arranged such that they are located on a spray rim of the injected fuel into the combustion chamber. The ignition of the substantially conically propagating from the fuel injector fuel takes place at the edge of the cone, since only here an ignitable air-fuel mixture is present. In practice, however, the positioning of the spark location of the spark plug results in problems in precisely positioning this spark location at the narrow edge zone in the area of the ignitable fuel-air mixture. On the one hand, this is due to component tolerances of the injection valve, spark plug and cylinder head and, on the other hand, to the scattering of the spray geometry from cycle to cycle, so that the ignitable edge zone can vary to a certain extent. In the case of the spark plug, cyclic scattering of the spark location within the electrode area may also occur, as well as the spray geometry due to age due to deposits or depending on the characteristic field of the spark plug

Internal combustion engine vary. These explained factors lead on the one hand to a reduced efficiency and on the other hand also to problems with the exhaust gases. Furthermore, it has recently been proposed to replace the conventional spark plug with a laser ignition device, wherein ignition also takes place at the edge of an injected fuel cloud.

Advantages of the invention

The inventive method for operating an internal combustion engine with the features of claim 1 has the advantage over that always a secure ignition can be guaranteed. Further, according to the invention, an efficiency can be increased, resulting in a fuel saving results and the exhaust emissions are improved. This is inventively achieved in that fuel is injected during a compression stroke of the internal combustion engine in a combustion chamber. In this case, the fuel is injected into the combustion chamber in such a way that an ignitable, patty-shaped mixture region of fuel and air is formed on the piston. The patty-shaped mixture region rests on the piston bottom surface of the piston. According to the invention, a predetermined period of time is waited between an end of the fuel injection and a start of ignition with a laser ignition device in order to allow the formation of the patty-shaped mixture region on the piston. The period of time is chosen such that a firing location of a laser beam directed into the combustion chamber of the laser ignition device lies in the interior of the ignitable, patty-shaped mixture region. As a result, an ignition takes place only in

Inside the patty-shaped mixture area. According to the invention, therefore, there is no longer an ignition at the edge of an injected fuel cloud, but rather inside a flat-shaped mixture region located on the piston. In this case, the injection is waited until the patty-shaped mixture region has formed on the piston, which moves in the opposite direction to the injection direction of the fuel during the compression phase. If the injected into the combustion chamber fuel is injected in the form of a jet, which increasingly evaporates with increasing depth of penetration into the combustion chamber, resulting in the jet, especially in the spray tip an ignitable shell of a gaseous fuel-air mixture, which acts like a kind of neck brace around a jet center lays. This gaseous shell has substantially the shape of a drop. Because the piston moves against the thus injected fuel, the piston deflects the fuel-air mixture horizontally to all sides, resulting in further turbulence-related mixing. As a result, the inventive flammable mixture-shaped area is formed on the piston head. Thus, during the period after injection and before ignition, the mixture region of the invention will be on the piston educated. The patty-shaped mixture region is surrounded by a non-flammable gas mixture, in particular air. In this case, the piston is moved further upwards in the direction of the cylinder head, with ignition only taking place when the focal point of the laser lies inside the mixture region. Since the ignition is thus generated inside the mixture area, a reliable ignition can be made possible. Furthermore, starting from the ignition point, the flame paths are significantly shorter up to the edge of the mixture region than in comparison with an ignition point at one edge, so that, moreover, a faster combustion is achieved. The use of a laser ignition device makes it possible to ignite at any point in the mixture area. When using conventional spark plugs only spark layers are possible, which extend approximately 8 mm into the combustion chamber, otherwise the candle electrodes and the candle ceramic are too hot. The use of the laser ignition device, however, can be arranged on the edge of a combustion chamber without a part of it projecting into the combustion chamber. Furthermore, a laser ignition device has no ignition energy losses due to quenching phenomena (heat dissipation) on metallic candle electrodes. This results in reduced cyclic fluctuations in the combustion process, since the laser ignition device enables a high reproducibility of the sensitive flame kernel formation. Furthermore, diluted mixtures can also be ignited by means of the laser ignition device. The ignition inside the mixture area also allows a faster burning of the mixture area, which is thermodynamically either in a faster burning process (it is a higher compression without knocking possible, resulting in fuel savings) and / or in a more possible mixture dilution (it is an emaciation or exhaust gas recirculation possible, which leads to a reduction in NOx and allows consumption advantages).

The dependent claims show preferred developments of the invention.

The injection of the fuel is preferably carried out by a plurality of individual jets, which is generated by means of a multi-hole valve with a number of holes preferably between 7 and 14, or by means of an outwardly opening annular gap valve (A-valve) with a Öffhungswinkel OC between 70 ° <OC <110 °.

Preferably, the time period between the end of the fuel injection and the start of the ignition is selected so that it corresponds to a Kurbelwinkelweg between 5 ° and 15 °, in particular between 5 ° and 10 ° and more preferably 7.5 °. - A -

In order to enable a faster and more secure formation of the patty-shaped mixture region, a trough is preferably provided in the piston head, in which the patty-shaped mixture region is formed. The trough is preferably circular and formed symmetrically.

It is particularly preferred to ignite near or at a central region of the patty-shaped mixture region in order to have the shortest possible flame paths through the entire mixture region.

More preferably, a projecting nose is formed on the piston head, over which the patty-shaped mixture region lays, in order to form a region projecting substantially in the axial direction of the piston in the patty-shaped mixture region. The ignition of the patty-shaped mixture region can preferably take place starting from the above range. It can thereby be achieved that the start of the ignition of the patty-shaped mixture region still takes place in an earlier movement section in the direction of the top dead center of the piston, so that exactly as complete combustion of the patty-shaped mixture region takes place in the efficiency-optimal crank angle region and then the expansion stroke takes place. In order to realize a positioning of the injection valve as centrally as possible in the cylinder head, the projecting nose is preferably arranged on an edge of the trough on the piston head. In order to achieve a faster formation of the patty-shaped mixture region, a fuel injection preferably takes place on the protruding from the piston crown nose.

The fuel injection preferably takes place in several successive intervals.

This ensures that a higher proportion of air in the patty-shaped mixture region is present, since there is a small air cushion between the individual intervals of the fuel injection.

In order to keep the flame propagation times from one ignition location through the patty-shaped mixture region as low as possible, a plurality of ignition locations is preferably provided in the interior of the mixture region. The plurality of ignition locations can be generated by means of a plurality of laser ignition devices or by means of a laser device which is actuated several times at different focal points. The plurality of ignition locations is preferably arranged symmetrically in the patty-shaped mixture region. The variety of ignition locations is preferably in a plane in order to achieve the most homogeneous flame propagation through the mixture region. It should, however, be noted that, depending on the geometrical conditions on the piston and / or combustion chamber, the multiplicity of ignition locations can also be arranged on different planes.

For example, to enable a load-dependent ignition in a simple manner, the focal length of the laser ignition device is preferably variable. As a result, the laser ignition device can be adapted to different environmental influences.

In order to achieve in particular a reduced noise during ignition of the patty-shaped mixture region at a plurality of ignition locations, the different ignition locations are preferably ignited at different times. This allows a further optimization of the combustion process.

The inventive method is preferably in a shift operation of

Internal combustion engine applied. Shift operation is understood to mean a mode in which only small loads are applied to the internal combustion engine. In stratified operation, combustion in the combustion chamber is essentially determined only by the injected fuel mass, wherein a throttle valve is usually wide open. However, the erfmdungsgemäße method can also be used in normal operation of the internal combustion engine.

Furthermore, according to the invention, an internal combustion engine is proposed for the direct injection of fuel into a combustion chamber, which comprises a laser ignition device, a piston and a fuel injection device. Furthermore, the internal combustion engine comprises a control device in order to determine an ignition point of the laser ignition device. The

Control device only activates the laser ignition device when the fuel injection process has been completed and an ignitable patty-shaped mixture region has formed on the piston. In other words, a predetermined period of time elapses between the end of the fuel injection process and the start of the ignition in order, on the one hand, to allow formation of the patty-shaped mixture region and, on the other hand, to initiate ignition only when a focal point (ignition location) of the laser is in the patty-shaped mixture region. This ensures that the mixture area is ignited in its interior, so that the flame paths are very short. The control device preferably determines the ignition timing as a function of a piston position. The position of the piston can preferably be determined based on a crank angle by means of a sensor.

In order to support the formation of the ignitable, pie-shaped mixture region, the piston preferably has a substantially circular depression on a piston bottom surface. The trough is preferably symmetrical to a piston central axis.

More preferably, the piston on the piston bottom surface on a protruding nose. The nose may preferably be provided in a circular trough or it is provided at the edge of the trough. By the protruding nose in the region of the trough it can be ensured that the patty-shaped mixture region also forms over the nose, so that a region of the mixture region protrudes in the direction of movement of the piston. In this case, the laser ignition device is then preferably arranged such that the focal point of the laser lies in the projecting region of the mixture region. As a result, for example, an ignition can be realized well before the top dead center of the piston, the ignition still takes place safely inside the mixture area.

According to a further preferred embodiment of the invention, the trough formed on the piston crown surface has an area inclined at an angle to the central axis of the piston. This makes it possible to arrange the laser ignition device in the center of the cylinder head and still allow a vertical fuel injection to the piston crown. The central arrangement of the laser ignition device also has space-related advantages.

Preferably, the laser ignition means comprises a focusable lens for changing a position of a focal point of the laser beam.

In order to enable a multiplicity of ignition locations in the flat-form mixture region, the internal combustion engine preferably comprises a multiplicity of laser ignition devices. The plurality of laser ignition devices are preferably arranged such that the ignition locations are arranged as symmetrically as possible in the flat-shaped mixture region. In this case, the control device preferably actuates the multiplicity of laser ignition devices at different points in time in order to enable an optimization of a desired firing profile, in particular with regard to a noise development and the flame propagation times through the mixture region. The fuel injection device is preferably a multi-hole valve with a number of holes between 7 and 14 or an outwardly opening annular gap valve (A-valve), preferably with an opening angle between 70 ° and 110 °.

drawing

Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. In the drawing is:

FIG. 1 shows a schematic sectional view of an internal combustion engine according to a first exemplary embodiment of the invention,

2a and 2b are schematic representations of the injection of fuel by means of a multi-hole valve,

FIG. 3 shows a schematic representation of a spray cloud of an outwardly opening annular gap valve (A valve),

FIGS. 4a and 4b show schematic views of an injection by means of a multi-hole valve according to a further exemplary embodiment of the invention,

FIGS. 5 and 6 show schematic sectional views of an internal combustion engine according to a second exemplary embodiment of the invention,

FIGS. 7 and 8 are schematic sectional views of an internal combustion engine according to a third embodiment of the present invention;

FIGS. 9 and 10 are schematic sectional views of an internal combustion engine according to a fourth embodiment of the present invention;

11 is a schematic sectional view of an internal combustion engine according to a fifth embodiment of the present invention; Figure 12 is a schematic sectional view of an internal combustion engine according to a sixth embodiment of the present invention, and

Figure 13 is a plan view of the patty-shaped mixture region of Figure 12 and

Figures 14a and 14b are plan views of patty-shaped mixture areas with different ignition locations.

Description of the embodiments

Hereinafter, an internal combustion engine 20 according to a first embodiment of the invention will be described with reference to Figures 1 and 2.

As shown in Figure 1, the internal combustion engine 20 comprises a piston 21 having a piston head 22 in which a circular trough 23 centrally and symmetrically to a

Center axis X-X of the piston is arranged. The piston 21 moves in a known manner in a cylinder, wherein in a cylinder head 24, an injection device 25 and a laser ignition device 26 are arranged. The injector 25 is centrally located in the cylinder head on the central axis X-X of the piston and is in this embodiment a multi-hole valve with ten holes. The arrangement of the holes can be seen in FIG. 2a. The laser ignition device 26 is controlled by a control device 34 and has an aspherical lens 26a. The laser ignition device further comprises a Q-switched optically pumped solid-state laser. The laser ignition device 26 generates a laser beam 27, which is directed into a combustion chamber 29. The laser ignition device 26 is formed flat to the inner wall of the cylinder head 24, so that the laser ignition device

26 does not protrude into the combustion chamber 29.

From FIGS. 2a and 2b, the injection of the fuel into the combustion chamber 29 becomes clear. The designated by the reference numerals 1 to 10 individual jets of the injector 25 are injected in the direction of the oncoming piston in the combustion chamber. Increasing penetration of each individual jet results in increasing evaporation, so that an envelope of a gaseous fuel-air mixture is generated around each injection jet 1 to 10, in particular in the area of the spray syringe of the injected fuel. This is indicated in Figure 2b with the large circles around each individual beam 1 to 10. The gaseous Krafstoff-Luftgemischhülle puts similar to a ruff around the beam and also the tip of the jet is formed by a gaseous fuel-air mixture. As can also be seen from FIG. 2 b, the fuel / air mixture envelopes of the individual jets are partly overlapped by turbulence and because the piston 21 moves counter to the jet direction and deflects the fuel / air mixture envelope horizontally. As a result, an ignitable, patty-shaped mixture region 28 forms on the piston head 22. The formation of the patty-shaped mixture region 28 is further enhanced by the intended depression 23 in the piston head 22. The patty-shaped mixture region 28 in this case has a circular shape with a thickness which decreases somewhat starting from a center in the direction of the outer edge. The mixture region 28 is a substantially homogeneous gaseous fuel-air mixture having an average lambda between 0.8 and 1.5.

According to the injection of fuel takes place at a crank angle of about 35 ° before top dead center TDC. The holes of the multi-hole valve are to be designed so that each individual jet has a possible bushy shape. For this purpose, a hole diameter of a single hole is preferably between about 130 microns and 200 microns. More preferably, tapered, in particular conical, outwardly opening holes or stepped holes favor a bushy spray form with the desired fuel-air mixture gas shells. As shown in Figure 2a, the beam axes of the holes of the multi-hole valve are chosen such that they have approximately the same space angle distance.

It should be noted that, depending on a distance to travel of a single jet to the piston crown, the hole diameters of the individual holes may be different. Internal beams, which in the central arrangement of the injector shown in FIG. 1 have the shortest path to the piston, can have a smaller hole diameter than the holes arranged on the circumference. Due to the smaller holes, the amount of fuel passed therethrough and thus the spray impulse becomes lower, so that even the internal jets are safely vaporized before they reach the piston crown 22. The choice of hole diameter and opening angle of the injection holes and the number of holes is to be chosen so that the injected fuel is just evaporated when it reaches the piston crown. This allows the oppositely moving piston a particularly good

Provide mixing and homogenization of the ignitable mixture region 28.

The formation of the mixture region 28 takes place in a range between 35 ° before top dead center and about 20 ° before top dead center. FIG. 1 shows the position approximately 20 ° before top dead center, in which the mixture region 28 is homogeneous at the piston bottom in FIG the trough 23 has formed. Ignition by means of the laser ignition device 26, however, takes place only as soon as a focal point of the laser 27 lies in the interior of the mixture region 28. This focal point defines the ignition location 27a in the interior of the mixture region. This is given at a piston position of about 20 ° before top dead center, as shown in Figure 1, with the ignition 27a located exactly on the center axis XX.

The control device 34 controls the ignition timing of the laser ignition device 26 as a function of the position of the piston 21. Preferably, the ignition point is at a crank angle of about 20 ° before top dead center. This can ensure that the mixture region 28 is completely combusted in the efficiency-optimal crank angle range and that a high degree of efficiency of the internal combustion engine is achieved. A period of time between an end of the fuel injection and the beginning of the ignition corresponds to a distance traveled by the piston over a crank angle between 5 ° to 10 °, preferably 7.5 °.

Due to the ignition in the interior of the mixture region 28, the flame paths are significantly reduced by the mixture region 28 in comparison with an ignition at the edge. As a result, on the one hand faster and more complete combustion can be achieved. Furthermore, a particularly stable combustion process is achieved, in particular in the stratified operation of the internal combustion engine. According to the invention, the patty-shaped mixture region 28 results from the interaction of the injecting fuel and the piston, with a certain period of time between the end of the injection and the start of the ignition to allow the mixture region to be formed and an ignition of the mixture region 28 in its interior perform. Furthermore, due to the internal ignition, the deviations occurring due to tolerances of the components can not lead to uneven combustion. Scattering of the spray geometry from cycle to cycle or map-dependent fluctuations of the spray geometry also have no influence on the process according to the invention. The laser ignition device also has the advantage that no ignition energy losses occur due to quenching phenomena (heat dissipation) on metallic candle electrodes as in the prior art. As a result, a high reproducibility of the sensitive flame kernel formation can be made possible for the first time in a gasoline engine.

FIG. 3 shows an alternative embodiment of an injection device 25 in the form of an outwardly opening annular gap valve (A valve). The illustrated annular gap valve injects the fuel tapered, so that results in the sectional view shown in Figure 3, an annular fuel area 30. On both sides of the fuel region 30 is formed in each case a shell 31 and 32 from a fuel-air mixture. An opening angle of the annular gap valve of Figure 3 is preferably between 70 ° and 110 °. By the injection by means of the annular gap valve is also a homogeneous, patty-like mixture region 28 as in

Figure 1 produced on the piston, wherein the piston deflects the impinging fuel-air-gas mixture horizontally both inwardly and outwardly.

Figures 4a and 4b show a further embodiment of an injector 25, which is also designed as a multi-hole valve. In this case, the multi-hole valve shown in Figures 4a and 4b twelve injection holes 1 to 12. The injection holes are distributed on two concentric circles and arranged on the circles offset from one another. This results in the spray distribution shown in Figure 4b to the individual beams. The large circles again represent the gaseous mixture envelopes. Otherwise, this embodiment corresponds to the first embodiment, so that reference can be made to the description given there.

FIGS. 5 and 6 show an internal combustion engine 20 according to a second exemplary embodiment of the invention, identical or functionally identical parts being designated by the same reference numerals. In contrast to the first embodiment, in the internal combustion engine 20 of the second embodiment, the laser ignition device 26 is disposed centrally on the center axis XX. The injection device 25 is arranged laterally of the laser ignition device 26 and at an angle OC to the central axis. The injection device 25 is again a multi-hole valve, wherein in Figure 5 schematically three injection jets are shown with a still liquid fuel jet 35 and a forming gaseous shell 36 of a fuel-air mixture. When the individual jets impinge on the piston head 22, they are completely evaporated, so that only a gaseous fuel-air mixture impinges on the piston crown. As can also be seen from FIG. 5, a protruding lug 37 is additionally formed in the trough 23 formed in the piston head 22. The projecting nose 37 is centrally located in the trough 23 on the central axis XX and has substantially the shape of a spherical section. The injection of fuel takes place exactly in the direction of the projecting nose 37. As shown in Figure 5, the piston position at the beginning of the injection is about 35 ° before top dead center. When the fuel injection is completed, the piston 21 continues to move toward the laser ignition device 26, then by the deflection at Piston bottom of the homogeneous, ignitable mixture region 28 forms (see Figure 6). In this case, the mixture region 28 is also formed over the projecting nose 37, so that, as shown in Figure 6, a spark location 27a in a protruding portion 28a of the mixture region 28 at a piston position of about 20 ° before top dead center. The position of the piston shown in Figure 6 shows the position in which the ignition of the mixture region 28 takes place. Since in this embodiment the laser ignition device 26 is arranged centrally on the center axis XX and the central axis XX is also an axis of symmetry for the mixture region 28, the flame paths from the ignition point 27a to the edges of the mixture region 28 in this embodiment are particularly short. This allows a particularly fast and complete combustion can be achieved.

Figures 7 and 8 show an internal combustion engine 20 according to a third embodiment of the invention, again with identical or functionally identical parts are denoted by the same reference numerals as in the previous embodiment. The internal combustion engine 20 of the third embodiment substantially corresponds to that of the second embodiment, but the protruding nose 37 is disposed in the third embodiment at an edge of the trough 23. Thereby, the injector 25 can be centrally located on the center axis X-X of the piston 21 and the laser ignition device 26 is arranged in the cylinder head 24 so as to be positioned over the protruding nose 37. As a result, the nose 37 and the laser ignition device 26 lie substantially on a common, parallel to the central axis X-X axis Y-Y. The injection of fuel is carried out directly into the well 23 formed in the piston head 22. In cooperation with the trough 23 and the direction opposite to the direction of movement of the piston 21, the mixture region 28 is formed in the trough 23 again after the end of the injection and before the ignition , where the mixture range

28 has a projecting portion 28a in the region of the protruding nose 27 (see Figure 8). In a position about 20 ° before top dead center, which is shown in Figure 8, the focal point of the laser 27 is in the protruding portion 28a of the mixture region 28, so that then ignition can take place in the interior of the mixture region 28. This also makes it possible that in comparison with the first embodiment, a previous ignition of the

Mixture region 28 is made possible because the laser ignition device ignites the protruding region 28a of the mixture region 28 and the flame paths pass from there through the entire mixture region 28. Otherwise, this embodiment corresponds to the previous embodiments, so that reference can be made to the description given there. FIGS. 9 and 10 show an internal combustion engine 20 according to a fourth exemplary embodiment of the invention, wherein in turn identical or functionally identical parts are designated by the same reference numerals as in the preceding exemplary embodiments. The fourth embodiment corresponds essentially to the second embodiment, wherein in the trough 23 in the piston head 22 also centrally a protruding nose 37 is formed. The laser ignition device 26 is again arranged centrally on the center axis XX of the piston 21 and the injector 25 at an angle α. In contrast to the second embodiment, however, the piston crown is arranged in the region of the trough 23 inclined to a plane E perpendicular to the central axis XX. The inclination is characterized in Figures 9 and 10 by the angle ß. The inclination of the trough 23 is preferably selected such that a central central injection jet is injected substantially perpendicular to the inclined trough surface. The central injection jet strikes in particular the projecting nose 37, which leads to a faster formation of the patty-shaped mixture region 28. As can be seen from FIGS. 9 and 10, FIG

Laser ignition 26 thereby again arranged over the protruding nose 37, so that an early ignition of the mixture area is possible. Otherwise, this embodiment corresponds to the previous embodiments, so that reference can be made to the description given there.

Figure 11 shows a fifth embodiment of an internal combustion engine according to the invention, again identical or functionally identical parts are denoted by the same reference numerals as in the preceding embodiments. The fifth embodiment corresponds essentially to the second embodiment, wherein, in contrast to the second embodiment, both the injector 25 and the

Laser ignition device 26 are arranged at an angle γ and δ to a central axis X-X. The inclination angle γ, δ of the injector 25 and the laser ignition device 26 are the same and differ only by the sign. A projecting nose 37 in the trough 23 in the piston head 22 is again arranged below the laser ignition device 26, so that there is an asymmetrical design of the trough. The flat-shaped

Mixture region 28 again forms with a protruding region 28a via protruding nose 37, so that an ignition location 27a of mixture region 28 lies in this protruding region 28a. Otherwise, this embodiment corresponds to the previous embodiment, so that reference can be made to the description given there. Hereinafter, an internal combustion engine according to a sixth embodiment of the invention will be described with reference to Figures 12 and 13, again like or functionally identical parts are denoted by the same reference numerals as in the preceding embodiments. The internal combustion engine of the sixth embodiment has, as shown in FIG. 12, two laser ignition devices 26. An injection device 25 is arranged centrally on a center axis XX of the piston 21. The two laser ignition devices 26 are arranged laterally at an angle γ and δ to the central axis XX, wherein the angle γ and. δ is the same size. The arrangement of two laser ignition devices 26 makes it possible for two ignition locations 27a to be in the form of a patty

Mixture region 28 can be generated. As a result, in particular the flame paths within the mixture region 28 can be kept short. In FIGS. 12 and 13, the flame paths are shown schematically by the short arrows around the ignition locations 27a. An ignition of the patty-shaped mixture region 28 is preferably carried out simultaneously, since the patty-shaped mixture region 28 is formed symmetrically to the central axis X-X. The two ignition locations 27a lie on a plane F perpendicular to the central axis X-X. Otherwise, this embodiment corresponds to the previous embodiments, so that reference can be made to the description given there.

FIGS. 14a and 14b show two different examples for igniting the patty-shaped mixture region 28 by means of a plurality of ignition locations. In FIG. 14a three ignition locations 27a are arranged, which are arranged in a mixture region 28 with a circular circumference starting from a central axis X-X at an angle of approximately 120 ° to each other. The distances from each ignition location 27a to the edge of the mixture region 28 are chosen to be the same. FIG. 14b shows an embodiment with four ignition locations 27a, which are arranged symmetrically with respect to a central axis X-X. As can be seen from FIG. 14b, this arrangement with four ignition locations 27a is particularly advantageous, since the flame paths are essentially the same length from each ignition location 27a through the entire mixture region 28 until the entire mixture region 28 has been ignited.

It should be noted that, of course, a multiple injection can also be performed in all illustrated embodiments. This has the particular advantage that the mixture region 28 is constructed in a layered manner, wherein in each case a thin air layer is present between two fuel-air mixture layers. As a result, the proportion of air in the mixture region 28 can be increased. A further advantage of the method according to the invention in all described exemplary embodiments is that, to produce the mixture region 28, it is possible to use injection devices which produce symmetrical spray geometries (without a spray gap for the spark plug). This also eliminates an assignment of the injector to a protruding into the combustion chamber spark plug. In addition, there is no wetting of the laser ignition device with liquid fuel, which reduces the ignitability of a spark plug in the prior art.

An internal combustion engine according to the invention can be used both in vehicles and stationary.

Claims

claims

1. A method for operating an internal combustion engine (20) with a Kraftstoffeinspritzein- direction (25) and a laser ignition device (26), wherein the laser ignition device (26) generates a laser beam (27) in a combustion chamber (29), wherein during a compression tract of the internal combustion engine Fuel is injected by means of the fuel injection device (27) into the combustion chamber (29), and wherein the fuel is injected into the combustion chamber (29) such that on a piston (21) an ignitable, patty-shaped mixture region (28) of fuel and air is formed, and is waited between an end of the fuel injection and a start of ignition for a predetermined period of time to form the patty-shaped mixture region (28) and then ignition inside the patty-shaped mixture region (28) by means of the laser ignition device (26).

2. The method according to claim 1, characterized in that the injection of the fuel by means of a multi-hole valve with a plurality of injection holes (1-12) or by means of an outwardly opening annular gap valve.

3. The method according to any one of the preceding claims, characterized in that the time period between the end of the fuel injection and the start of the ignition corresponds to a time in which the piston (21) over a crank angle of 5 ° to 15 °, in particular of the fifth ° to 10 °, in particular 7.5 °, moves.

4. The method according to any one of the preceding claims, characterized in that in the piston head (22) of the piston (21) has a trough (23) is formed and the patty-shaped mixture region (28) forms in the trough (23).

5. The method according to any one of the preceding claims, characterized in that the mixture region (28) is ignited as close to or in its center.

6. The method according to any one of the preceding claims, characterized in that on the piston (21) has a protruding lug (37) is formed to form an axially projecting portion (28a) in the patty-shaped mixture region (28).

7. The method according to claim 6, characterized in that an ignition of the mixture region (28) in the above region (28a) takes place.

8. The method according to any one of the preceding claims, characterized in that the fuel injection takes place at several intervals and / or with a plurality of injection devices.

9. The method according to any one of the preceding claims, characterized in that the patty-shaped mixture region (28) at a plurality of ignition locations (27a) in the interior of the

Mixture area (28) is ignited.

10. The method according to claim 9, characterized in that the plurality of ignition locations (27a) in the patty-shaped mixture region (28) is arranged symmetrically.

11. The method according to any one of the preceding claims, characterized in that a focal length of the laser ignition device (26) is variable.

12. The method according to any one of claims 9 to 11, characterized in that an ignition of a first and a second ignition location (27a) takes place at different times.

13. The method according to any one of the preceding claims, characterized in that the method is carried out in the stratified operation of the internal combustion engine.

14. Internal combustion engine for direct injection of gasoline, comprising a

Laser ignition device (26), a piston (21), a fuel injection device (25) which injects fuel into a combustion chamber (29) at a compression stroke such that an ignitable, pancake-shaped mixture region (28) on the piston (21) is formed, and a Control means (34) for determining an ignition timing of the laser ignition device (26), wherein the control means (34) determines the ignition timing such that the

Laser ignition device (26) is only then transmitted an ignition signal when a focal point of a laser beam (27) of the laser spark plug (26) is located in the interior of the mixture region (28).

15. Internal combustion engine according to claim 14, characterized in that the control device (34) determines the ignition timing in dependence on a piston position.

16. Internal combustion engine according to claim 15, characterized in that the piston position can be determined by determining a crank angle.

17. Internal combustion engine according to any one of claims 14 to 16, characterized in that the piston (21) on the piston bottom surface (22) has a substantially circular recess.

18. Internal combustion engine according to any one of claims 14 to 17, characterized in that the piston on the piston bottom surface (22) has a protruding nose (37).

19. Internal combustion engine according to any one of claims 17 or 18, characterized in that the trough (23) has a center axis (X-X) of the piston (21) at an angle (ß) inclined base.

The internal combustion engine according to any one of claims 14 to 19, characterized in that the laser ignition means (26) comprises a focusable lens (26a) for changing a position of a focal point of the laser beam (27).

21. Internal combustion engine according to any one of claims 14 to 20, characterized by a plurality of laser ignition devices (26).

22. Internal combustion engine according to claim 21, characterized in that the control device (34) activates the plurality of laser ignition devices (26) at different times.