DE102010029406A1 - Laser ignition plug for use in internal combustion engine of motor vehicle, has housing comprising cover for guiding laser radiation into combustion chamber, where distance between cover and laser radiation is less than specific mm - Google Patents

Abstract

The plug has a housing (38) comprising a cover (74) for guiding laser radiation into a combustion chamber of an internal combustion engine, where the cover is arranged at a side of a combustion chamber window (58). A focusing unit determines radiation form of the laser radiation passing through the cover, where distance between the cover and the laser radiation along projecting parts of an inner contour of the cover is less than 4mm. The housing connected with the chamber window comprises an inner casing (62) and an outer casing (64), where the cover comprises cooling channels.

Description

State of the art

The invention relates to a laser spark plug according to the preamble of claim 1.

For example, from the WO 2005/066488 A1 a device for igniting an internal combustion engine is known which comprises an ignition laser. The ignition laser has at its combustion chamber end a combustion chamber window which is transmissive to the laser pulses emitted by the ignition laser. At the same time, the combustion chamber window must withstand the high pressures and temperatures prevailing in the combustion chamber and seal the interior of the ignition laser against the combustion chamber. In particular, high surface temperatures and pressures as well as soiling, for example in the form of oil ash deposits, particles, etc., can occur on the surface of the combustion chamber window facing the combustion chamber.

In the known device, it is to be regarded as disadvantageous that certain components of exhaust gases, such as oil ash or soot damage the combustion chamber, for example, by such components deposit on the combustion chamber window and deteriorate its properties, in particular the transmission of laser radiation.

Disclosure of the invention

On the other hand, the present invention has the advantage of making the operation of the laser spark plug more reliable. In particular, measures are taken according to the invention to reduce deposits on the combustion chamber window. For this purpose, the invention provides that a laser spark plug for an internal combustion engine comprises at least one means for guiding, shaping and / or generating laser radiation and a combustion chamber window and a housing, wherein the housing on the opposite side of the center of the combustion chamber window, in particular on a On the combustion chamber side end of the housing, a diaphragm for the passage of the guided through the means, shaped and / or generated laser radiation has in a combustion chamber. The diaphragm affects the conditions to which the combustion chamber window is exposed, so that the formation of deposits on the combustion chamber window is reduced and the reliability of the laser spark plug is improved overall.

The means for guiding, shaping and / or for generating laser radiation may be, on the one hand, a solid-state laser, for example a passively Q-switched solid state laser, which is monolithic, for example. Devices for the optical excitation of the solid-state laser, in particular semiconductor lasers, may be included in the laser spark plug. Alternatively, it is possible to arrange devices for the optical excitation of the solid-state laser from the laser spark plug spaced. In this case, the means for guiding, shaping and / or generating laser radiation may be an optical window or an optical fiber, through which radiation serving for the optical excitation of the solid-state laser can enter the laser spark plug. The arrangement of one or more solid-state lasers, in particular of Q-switched or mode-locked solid-state lasers, which is spaced apart from the laser spark plug, is also possible. In this case, the emission of the laser spark plug can be supplied for example in an optical fiber, the laser spark plug itself does not laser active element, but only jet-guiding and / or jet-forming means, in particular lenses and / or mirrors includes.

The mountability of the laser spark plug to an internal combustion engine is ensured in particular by the housing. For this purpose, known fastening means may be provided, such as threads encompassed by the housing and / or sealing and / or abutment surfaces encompassed by the housing, which may interact with further clamping means, for example with clamping claws. The housing is also particularly the task of mechanically fixing at least one means for guiding, shaping and / or for generating laser radiation and the combustion chamber window.

The combustion chamber window is a transparent, consisting of at least one permanently heat and radiation resistant solid, such as a glass or crystal, for example sapphire, existing component. These are, in particular, the component of the aforementioned type encompassed in the radiation direction by the laser spark plug, so that the surface of the combustion chamber window facing the combustion chamber communicates with the combustion chamber.

In order to largely reduce contamination and / or damage to the combustion chamber exposed side of the combustion chamber window by prevailing conditions in the combustion chamber (high temperature, high pressure, high flow velocity) and media (particles, oil pockets, etc.), the invention provides that the housing has its the means for guiding, shaping and / or for generating laser radiation opposite side of the combustion chamber window, ie in particular on the combustion chamber side facing the combustion chamber window, a diaphragm. The Combustor window is thus arranged in particular between the means for guiding, shaping and / or for the generation of laser radiation and the diaphragm. Preferably, the diaphragm forms a combustion chamber-side end portion of the housing. In particular, it is possible to form the diaphragm in one piece with the housing of the laser spark plug and / or of the same material as the housing. Alternatively, the panel is designed as a separate component and attached to a further part of the housing, for example, welded or screwed. Optionally, further components of the laser spark plug, such as purged and / or unsprayed prechambers, are arranged on the combustion chamber side of the diaphragm.

The diaphragm is in particular a passage, in particular exactly one passage, exhibiting structure. The combustion chamber facing the side of the combustion chamber window communicates with the combustion chamber and / or with one of the diaphragm upstream antechamber of the laser spark plug, in particular exclusively, through the one passage of the diaphragm. The passage is bounded radially to the direction of radiation by the inner contour of the diaphragm. The passage is moreover provided for the passage of the laser radiation guided through the means, shaped and / or generated into a combustion chamber of an internal combustion engine, into an antechamber of the combustion chamber and / or into an antechamber of the laser spark plug arranged upstream of the diaphragm.

The invention is based on the idea that by the provision of a diaphragm, or by a suitable design of such a diaphragm, a protection of the combustion chamber window is possible, in particular protection of the combustion chamber window prevailing in a combustion chamber conditions, especially at high temperatures, high flow velocities and Media like oil ash etc.

The inventively provided aperture on the one hand reduces the amount of precipitating on the combustion chamber window pollution in the form of particles, oil pockets, etc. On the other hand, the impulse with which, for example, the particles impinge on the surface of the combustion chamber window is reduced. Both effects ensure that deposits on the combustion chamber window are significantly reduced and that the few deposits adhere less firmly to the combustion chamber window. As a result, the laser ignition device according to the invention is more reliable. Another effect of the shutter is that the temperature of the combustion chamber window is lowered. Due to the reduced temperature, a chemical reaction of the deposits or a chemical reaction of the combustion chamber window with the deposits, as it were a burn-in of the deposits and thus a permanent damage to the combustion chamber window, avoided. Remaining deposits thus adhere less firmly to the combustion chamber window and can be easily cleaned. A reduction in the pressure applied to the combustion chamber window, or the pressure change rates taking place there, can also be effected by means of an aperture according to the invention, from which reliability increases can also result.

In further advantageous embodiments of the invention, it is provided to selectively select the length of the diaphragm. In this case, the length of the aperture is to be understood as meaning, in particular, the length of the passage of the aperture in the jet direction. Alternatively, a longitudinal axis of the laser spark plug or a direction perpendicular to the surface of the combustion chamber window facing the combustion chamber can also be used. The length of the passage is further measured between the opening facing the combustion chamber (also: outlet opening) and the opening facing away from the combustion chamber (also: inlet opening) of the diaphragm. In the case of diaphragms or passages with irregularly shaped openings, it must be particularly important with respect to their position whether lateral shielding of the section which is to be considered as the passage is predominantly given. The avoidance of deposits on the combustion chamber window, in particular by means of flow deflection and by reducing the temperature of the combustion chamber window, takes place with orifices whose length is 4 mm or more. Increasingly good results are achieved with diaphragms whose minimum length is 6 mm, 8 mm, 10 mm or 12 mm. The upper limit for the length of the aperture is 25 mm, 20 mm or 15 mm. Even longer apertures could excessively increase the length and thus the space required for the installation of a laser spark plug.

In a further advantageous embodiment of the invention, additionally or alternatively, the targeted choice of the length of the diaphragm is provided in a laser spark plug for an internal combustion engine, comprising at least one means for guiding, shaping and / or generating laser radiation, further comprising a combustion chamber window and a housing, wherein the housing on the side opposite the center of the combustion chamber window, in particular at a combustion chamber end of the housing, a diaphragm for the passage of the guided, guided and / or generated laser radiation in a combustion chamber, the diaphragm, in particular a material of the diaphragm targeted to choose so that it has a high thermal conductivity.

Preferably, the material of the panel should also have a high wear resistance, in particular heat resistance, as can be achieved, for example, by high-alloy steels.

The material of the entire aperture can be uniform with that of the entire housing and have a high thermal conductivity. But it is also possible to form only the entire diaphragm of a material having a high thermal conductivity, while other components of the housing have a different, in particular lower, thermal conductivity. It is also possible, only parts of the diaphragm, for example, based on mass and / or volume predominant parts of the diaphragm and / or inside, as it were designed as "souls" formed parts of the diaphragm, from a material with a high thermal conductivity, while other parts of the diaphragm have a different, in particular lower, thermal conductivity. With such an arrangement is advantageously the setting of the desired heat conduction with high wear resistance achievable.

The avoidance of deposits on the combustion chamber window, in particular by reducing the temperature of the combustion chamber window, already occurs when the diaphragm has a material with a thermal conductivity of 60 W / (m · K) or more, in particular consists of such a material in whole or in sections , Increasingly particularly good results are achieved with diaphragms comprising a material with a thermal conductivity of 80 W / (m · K) or more or 120 W / (m · K) or more, in particular consisting of such a material. In particular, brass and nickel and copper and alloys of brass and nickel as well as copper alloys come into consideration, for internal, as it were designed as "souls", parts of the aperture especially copper.

Another measure for reducing the temperature of the combustion chamber window is, in a laser spark plug for an internal combustion engine, comprising at least one means for guiding, shaping and / or generating laser radiation, further comprising a combustion chamber window and a housing, wherein the housing on the means opposite side of the combustion chamber window, in particular at a combustion chamber end of the housing, a diaphragm for the passage of the guided, guided and / or generated laser radiation in a combustion chamber, to provide at least one cooling channel in the interior of the aperture. The cooling channel is provided in particular for the flow through with a cooling medium, for example a cooling liquid. The provision of a plurality of cooling channels and / or a cooling channel diameter of 1 mm ² or more and / or 5 mm ² or less is preferred. Such a cooling channel is in itself already suitable for reducing the temperature of the combustion chamber window. In conjunction with a diaphragm, which has a material with high thermal conductivity, the heat from the aperture can be particularly well supplied to the cooling channel and thus dissipate from the aperture.

Both the specific choice of the length of the aperture, as well as the specific choice of material and / or the provision of cooling channels are suitable alone, but especially in cooperation, to effect the reduction of the temperature of the combustion chamber window, in particular combinations of a specified, the length the feature concerned with a given, the heat conduction of the panel relevant feature in terms of the prevention of deposits on the combustion chamber window and thus in terms of the reliability of the laser spark plug are advantageous. The reduction in the temperature of sealing points arranged in the region of the combustion chamber window also improves the reliability of the laser spark plug.

In further advantageous embodiments of the invention, in addition to or alternatively to the specific choice of the length of the diaphragm and additionally or alternatively to the provision of high thermal conductivity of the diaphragm is provided that in a laser spark plug for an internal combustion engine, comprising at least one means for guiding, shaping and / or Generation of laser radiation, further comprising a combustion chamber window and a housing, wherein the housing on the opposite side of the center of the combustion chamber window, in particular at a combustion chamber end of the housing, a diaphragm for the passage of the guided, guided and / or generated laser radiation by the means in a Has combustion chamber, the combustion chamber window on the combustion chamber side upstream of a communicating with the interior of the aperture gap is provided, the height is deliberately selected low.

In this case, a gap is to be understood as meaning, in particular, a spatial region which is bounded axially on both sides, in particular on one side by the combustion chamber window and the diaphragm, and radially on the outside, in particular by the housing, and communicates with the interior of the diaphragm via its radial inner side. In a special embodiment, the gap is thus formed between the diaphragm and the combustion chamber window. Under the height of the gap, in particular, the distance between the gap axially limiting surfaces to understand. In the case of irregular geometries, it must be determined whether an axial limitation of the gap is predominantly given.

This refinement of the invention is based, on the one hand, on the knowledge that the temperature of a hot gas entering the gap formed according to the invention, in particular of a burning gas, is greatly reduced. As a result, there is a so-called quenching, with the extinction of the burning Gas and a soot formation within the gap go along. On the other hand, this embodiment of the invention is also based on the finding that the soot formed in this way also deposits on the side of the combustion chamber window facing the combustion chamber, but can be reliably ablated by laser radiation with intensities which usually occur in the region of the combustion chamber window. so that, in sum, the formation of soot occurring in the gap only results in a moderate impairment of the transparency of the combustion chamber window.

Surprisingly, it has been found that can be caused by the continuous deposition and ablation of soot on the combustion chamber side facing the combustion chamber window that the pollution of the combustion chamber facing side of the combustion chamber window by other substances, in particular by other combustion products such as oil ash avoided or can be significantly reduced. This fact is of particular importance, since such substances, in particular oil ash, by laser radiation with intensities, as they usually occur in the combustion chamber window, can not be ablated reliably or only partially or with increased effort.

The total resulting avoidance of deposits on the combustion chamber window occurs for gap heights which are not more than 1 mm, not more than 0.5 mm, not more than 0.3 mm or not more than 0.1 mm. The lower limit for the height of the gap is 0.05 mm and 0.08 mm. In too flat columns, not enough soot can be formed. It is also advantageous to directly advance the gap to the combustion chamber window and / or to choose the base area of the gap to be ring-shaped or sickle-shaped.

The surface area of the base area of the gap (hereinafter referred to as "gap cross-section") is preferably chosen to be sufficiently large so that the amount of the penetrating gas is sufficient for adequate soot formation. It is increasingly advantageous in this case if a region upstream of the gap on the combustion chamber side has an inlet cross section of the diaphragm and the gap cross section is at least 10% of the inlet cross section, at least 30% of the inlet cross section or at least 50% of the inlet cross section or at least twice as large as the inlet cross section or at least four times as large as the inlet cross section. As upper limits are gap cross sections into consideration, which are 25 times as large as the inlet cross section, in particular 10 times as large as the inlet cross section, since the laser spark plug would otherwise be excessively large.

Both the specific choice of the length of the diaphragm, the targeted choice of material and / or the provision of cooling channels as well as the provision of a gap of the type described above are in themselves already suitable to effect the reduction of the temperature in a combustion chamber window upstream volume. In particular, however, an efficient cooling in this volume and thus the bringing about of quenching effects and soot formation, by an interaction of the gap with a long and / or good heat-conducting aperture, wherein the trapped by the gap volume through the interaction with the combustion chamber window, which has a relatively low temperature, is cooled particularly effectively.

The above-described effect of soot formation, landfilling and ablation is particularly advantageous in the use of laser spark plugs in internal combustion engines whose lubrication of additized oils, in particular higher-oil oils, use, as in particular in the combustion of such oils oil pockets arise in other ways are difficult to remove. On the other hand, it is also to be remembered laser spark plugs for use in internal combustion engines whose lubrication of non-additized oils, d. H. Ashless oils, makes use of optimization, by completely or largely dispensed with a then unnecessary soot formation. In this sense, in a laser spark plug for an internal combustion engine, comprising at least one means for guiding, shaping and / or generating laser radiation, further comprising a combustion chamber window and a housing, wherein the housing on the opposite side of the center of the combustion chamber window, in particular on a combustion chamber-side end of the housing, a diaphragm for the passage of the guided through the means, shaped and / or generated laser radiation in a combustion chamber, the combustion chamber window on the combustion chamber side upstream a communicating with the interior of the diaphragm gap is provided to selectively select the height of the gap so that soot formation is completely or at least largely avoided. For this purpose, it is advantageous to choose the height of the gap not less than 0.3 mm, in particular not less than 1 mm. It is particularly safe to avoid soot formation if the gap is even higher, for example at least 2 mm or at least 3 mm high. The provision of a small gap cross-section compared to the inlet cross-section of the aperture is also favorable; in particular, it is advantageous that the gap cross-section is at most 100%, in particular at most 40%, preferably at most 20% of the inlet cross-section of the aperture.

In further advantageous embodiments of the invention is additionally or alternatively to the targeted Choice of the length of the diaphragm and additionally or alternatively to Provide a high thermal conductivity of the diaphragm and in addition or alternatively to the providence of the combustion chamber window combustion chamber side upstream, communicating with the interior of the diaphragm gap whose height is deliberately selected low, provided that in a laser spark plug for an internal combustion engine, comprising at least one means for guiding, shaping and / or generating laser radiation, further comprising a combustion chamber window and a housing, wherein the housing on the opposite side of the center of the combustion chamber window, in particular at a combustion chamber end of the housing, a diaphragm to Passage of guided by the means, shaped and / or generated laser radiation has in a combustion chamber, the aperture on its side facing away from the combustion chamber window side has a small opening cross-section (also: "outlet cross-section").

The outlet cross section of the diaphragm is in particular the open combustion chamber-side cross section of the passage of the diaphragm. In the case of passages having an irregularly shaped outlet opening, in particular, it should be made clear with regard to the outlet cross-section whether there is predominantly lateral shielding of the section which may be considered as the passage.

The smallness of the outlet cross-section of the diaphragm results in the advantageous effect that the combustion chamber window undergoes shielding from the conditions prevailing in the combustion chamber, in particular from high temperature, from rapid pressure fluctuations, from high flow velocity and / or from particles of oil pockets, soot and the like , Thus, deposits on the combustion chamber window can be avoided and the reliability of the laser spark plug can be increased. This effect occurs when the outlet cross section is 78 mm ² or less, in particular 19 mm ² or less. Increasingly particularly good results are achieved with outlet cross sections which are 7 mm ² or less, in particular 2 mm ² or less. The lower limit is 0.05 mm ² , 0.4 mm ² and 1 mm ² into consideration. With even smaller exit diameters, the passage of the laser radiation through the diaphragm may no longer be ensured with sufficient certainty.

The specific choice of the length of the aperture, the targeted choice of material and / or the provision of cooling channels are each already alone or in combinations with each other already suitable to reduce the temperature of the combustion chamber window, so that a "burning" of pollution on the combustion chamber window is reduced and thus the Reliability of the laser spark plug is increased. By the provision of a combustion chamber window upstream of the combustion chamber side gap, a similar effect can be achieved in the manner described above. If these measures combined with the provision of a small outlet cross-section of the aperture, the overall effect on the one hand that fewer particles reach the combustion chamber window, the combustion chamber window on the other hand is also more resistant to contamination by these remaining particles. The reliability of the laser spark plug can be significantly increased in this way.

Advantageous embodiments additionally or alternatively to the specific choice of the length of the diaphragm and additionally or alternatively to Provide a high thermal conductivity of the diaphragm and additionally or alternatively to Provse the combustion chamber window combustion chamber side upstream, communicating with the interior of the diaphragm gap whose height is deliberately selected low and additionally or alternatively providing a small exit area of the bezel, a laser spark plug for an internal combustion engine comprises at least one means for guiding, shaping and / or generating laser radiation and a combustion chamber window and housing, the housing being on the opposite side of the center Side of the combustion chamber window, in particular at a combustion chamber end of the housing, an aperture, in particular a cylindrical aperture, for the passage of the guided through the means, shaped and / or generated laser radiation in a combustion chamber in which the length of the stop is L and the exit area of the stop Q is _BA , where 1 <L / (4Q _BA / π) ^1/2 ≤ 10.

By this targeted adjustment of the length of the aperture on the opening cross-section and the opening diameter of the aperture, it is always ensured that an excessive load on the combustion chamber window by the action of harmful conditions, as prevail in combustion chambers of internal combustion engines, is avoided. It is essential here that the total effect of the length and aperture and of the aperture cross-section of the diaphragm is taken into account in the condition 1 <L / (4Q _BA (π) ^1/2 ≤ 10. This is based on the knowledge that even relatively short diaphragms On the other hand, diaphragms with a relatively large opening cross-section can still have a sufficient shielding effect, provided that the diaphragm has a large length, especially the technical effect indicated when 2 ≤ L / (4Q _BA (π) ^1/2 and / or L / (4Q _BA (π) ^1/2 ≤ 7, in particular L / (4Q _BA (π) ^1/2 ≤ 6) The special case of a round exit cross-section of the orifice is the size (4Q _BA (π) ^1/2 the exit diameter of the orifice.

In advantageous embodiments of the invention is additionally or alternatively to the specific choice of the length of the diaphragm and additionally or alternatively to Provide a high thermal conductivity of the diaphragm and additionally or alternatively to the provision of a combustion chamber window combustion chamber side upstream, communicating with the interior of the diaphragm gap whose height targeted is selected to be low, and additionally or alternatively to the provision of a small outlet cross-section of the diaphragm, that in a laser spark plug for an internal combustion engine, comprising at least one means for guiding, shaping and / or generating laser radiation, further comprising a combustion chamber window and a housing, wherein the housing on the side opposite the center of the combustion chamber window, in particular at a combustion chamber end of the housing, a diaphragm for the passage of the guided through the means, shaped and / or generated laser radiation in a combustion chamber au fweist, the inner contour of the aperture in a region which is spaced both from the combustion chamber facing the end of the aperture and from the combustion chamber remote from the end of the aperture, at least one edge, in particular a plurality of edges has.

In this case, an edge of the inner contour of the diaphragm is to be understood as meaning, in particular, a geometric object, in particular a line, against which different areas of the inner contour of the diaphragm meet at an angle different from zero. A region of the inner contour of the diaphragm which is spaced both from the end of the diaphragm facing the combustion chamber and from the end of the diaphragm facing away from the combustion chamber, is to be understood as meaning a central region of the inner contour of the diaphragm, in particular an area which, with respect to the longitudinal extent the aperture is centered. A region is in the center of the longitudinal extent of the diaphragm, in particular when it is arranged between a front fifth and a rear fifth of the diaphragm, in particular between a front quarter and a rear quarter of the diaphragm, or is arranged in a central third of the diaphragm , An inner contour which has an edge in a region is to be understood as meaning that at least parts of the edge are arranged in this region, wherein it is also possible for the edge to be arranged in but also outside this region. As an advantageous special case can always be provided that the edge is completely in the area.

The technical effect of an edge of the type described is that it represents a starting point for a disturbance of the flow of gases into the diaphragm or the flow in the diaphragm. In particular, starting from the edge, turbulence of the gas flowing into the orifice or of the gas flowing in the orifice can occur. Due to the disturbance, in particular as a result of turbulence, the interaction of the gas flowing into the orifice with the inner contour of the orifice is increased and due to this increased interaction also the tendency of particles contained in the gas to accumulate within the orifice and especially at the edges and not to penetrate to the combustion chamber window. In this way, the edge is almost the effect of a particle trap. There is thus a reduction of the deposits on the combustion chamber window and increased reliability of the laser spark plug.

Although the effect described already results from the provision of a single edge of the type described, particularly advantageous developments provide for the provision of a plurality of such edges. A plurality of edges are two or more edges, in particular more than two edges. Particularly effective is the arrangement of an edge or a plurality of edges, if it faces the combustion chamber solid at least along parts of the edge and / or the combustion chamber window unobstructed, ie without parts of the diaphragm between the parts of the edge and the parts of the combustion chamber windows are arranged , In this case, the edge is particularly suitable for introducing a disturbance or turbulence into the parts of the flow entering the orifice or of the flow in the orifice, which are directed predominantly toward the combustion chamber window.

A particularly advantageous arrangement of the edge or the plurality of edges is such that it comes to the formation of steps by the arrangement of the edge or by the arrangement of the plurality of edges and / or that the inner contour of the aperture at least partially in the direction of the combustion chamber facing end gradually tapered. In particular, at least two, in particular at least three, preferably at least four stages may be provided. In addition, at least one further stage, in particular a plurality of further stages, can be provided, at which the panel tapers in the direction of its end facing away from the combustion chamber. Here, a step of the inner contour is understood in particular to mean an arrangement of at least three partial surfaces of the inner contour, one of the partial surfaces being arranged in the longitudinal direction of the inner contour between the two other partial surfaces and the radial inclination of the one partial surface being related to the radial inclinations of all three partial surfaces extremal is. The partial surfaces may in particular have an annular shape, but other geometries are possible in principle.

In a production-technically favorable variant, the steps are almost rectangular (88 ° -92 °), in particular at right angles, formed, that is in particular, the two partial surfaces parallel to a longitudinal axis of the laser spark plug, while a partial surface is oriented perpendicular thereto. In particular, a plurality of such stages, for example, more than three or more than seven may be provided. Even steps that consist of surfaces that always or partially at obtuse angles or always or partially at acute angles, but preferably not in angles more than 25 °, collide, are conceivable and advantageous in each case in different ways. Combinations of stages of the mentioned types are in principle possible in a diaphragm.

Both the provision of a small outlet cross section of the diaphragm and the provision of at least one edge in a region which is spaced both from the end of the diaphragm facing the combustion chamber and from the end of the diaphragm facing away from the combustion chamber make it possible in each case to separate the diaphragm Reduce the number of particles striking the combustion chamber window. If both measures are combined, the synergetic effect results that the spatially concentrated by the small outlet cross-section of the aperture flow into the aperture by suitable edges particularly targeted disrupt, especially swirl. In this case, in particular outlet cross-sections of 78 mm ² or less, in particular 19 mm ² or less, preferably 7 mm ² or less, particularly preferably 2 mm ² or less, these outlet diameter can each advantageously be combined with a stepped inner contour of the diaphragm, in particular with a step-shaped inner contour of the diaphragm, which has a plurality of steps, in particular of rectangular steps, in particular steps, on which the cross-sectional area of the diaphragm respectively in the direction of the combustion chamber facing the end of the inner contour of the diaphragm to the combustion chamber facing away from the end of the inner contour the aperture increases by at least 10%, in particular by at least 35%.

The specific choice of the length of the aperture, the targeted choice of material and / or the provision of cooling channels are each alone or in combination with each other already suitable to reduce the temperature of the combustion chamber window, so that a "burning" of particles on the combustion chamber window reduces deposits and reduces thus the reliability of the laser spark plug is increased. The provision of a combustion chamber fixed to the combustion chamber side upstream gap can achieve a similar effect. If these measures combined with the provision of at least one edge in an area which is spaced both from the end of the diaphragm facing the combustion chamber and from the end of the diaphragm facing away from the combustion chamber, the overall effect is that on the one hand fewer particles on the other hand, the combustion chamber window is also more resistant to contamination by these few particles. The reliability of the laser spark plug can be significantly increased in this way.

In advantageous embodiments of the invention is additionally or alternatively to the specific choice of the length of the diaphragm and additionally or alternatively to Provide a high thermal conductivity of the diaphragm and additionally or alternatively to the provision of a combustion chamber window combustion chamber side upstream, communicating with the interior of the diaphragm gap whose height targeted is selected to be low, and additionally or alternatively to the provision of a small outlet cross section of the diaphragm and additionally or alternatively to the provision of an edge of the type described provided that in a laser spark plug for an internal combustion engine, comprising at least one means for guiding, shaping and / or for the production of Laser radiation, further comprising a combustion chamber window and a housing, wherein the housing on the opposite side of the center of the combustion chamber window, in particular at a combustion chamber end of the housing, a diaphragm for the passage through the Mit tel guided, shaped and / or generated laser radiation in a combustion chamber, wherein the aperture has an end facing away from the combustion chamber and an end facing away from the combustion chamber, the inner contour of the diaphragm in a region which both from the combustion chamber facing the end of the diaphragm and is spaced from the combustion chamber facing away from the end of the aperture, having an extreme cross-section.

An extreme cross-section of the inner contour of a diaphragm is to be understood in particular as a cross-section which, with respect to its surface area and with respect to the longitudinal direction of the laser spark plug, represents a local maximum, that is to say in particular, decreases in both longitudinal directions, or represents a local minimum, that is to say in particular enlarged in both longitudinal directions. The extreme cross-section of the diaphragm in a region which is spaced both from the end of the diaphragm facing the combustion chamber and from the end of the diaphragm facing away from the combustion chamber can be expressed in particular in that there is a cross section of the diaphragm which is larger than the diaphragm Inlet cross-section of the aperture and is greater than the outlet cross-section of the aperture, or that there is a cross-section of the aperture, which is smaller than the inlet cross-section of the aperture and smaller than the outlet cross-section of the aperture. The extremal cross section is in particular a cross-section which lies in a plane which is parallel to a plane in which the outlet cross-section of the diaphragm lies and / or which lies in a plane which is parallel to a plane in which the inlet cross-section of the diaphragm lies and / or is parallel to a plane in which the surface of the combustion chamber window facing the combustion chamber and / or is oriented perpendicular to a longitudinal axis of the laser spark plug.

The technical effect of the measure that the inner contour of the diaphragm in an area which is spaced from both the combustion chamber facing the end of the aperture and the combustion chamber facing away from the end of the aperture, has an extreme cross section, is that the area extremalen Cross-section represents a starting point for a disturbance of the influx of gases into the diaphragm or a disturbance of the flow in the diaphragm. In particular, starting from the area of extreme cross-section, turbulence of the exhaust gas flowing into the diaphragm or the flow in the diaphragm can occur. As a result of the disturbance, in particular as a result of turbulence, the interaction of the exhaust gas flowing into the orifice with the inner contour of the orifice is increased and due to this increased interaction also the tendency of particles contained in the exhaust gas to accumulate within the orifice and not penetrate to the combustion chamber window. In this way, the area of extremal cross-section is as it were the effect of a particle trap.

Although the effect described already by the provision of an area which is spaced both from the combustion chamber facing the end of the diaphragm and from the combustion chamber facing away from the end of the diaphragm and having an extreme cross-section, results in itself, developments that Aperture has an inlet cross section at its end facing the combustion chamber and at its end facing the combustion chamber has an outlet cross section and that the extremal cross section either at least 10%, in particular at least 20%, preferably at least 30%, smaller than the inlet cross section and at least 10%, in particular at least 20%, preferably at least 30%, is smaller than the outlet cross section or at least 10%, in particular at least 20%, preferably at least 30%, greater than inlet cross section and at least 10%, in particular at least 20%, preferably at least 30%, greater than the outlet cross-section is. An advantageous form of the inner contour of the diaphragm provides that the inner contour of the diaphragm has two sections, each having a frusto-conical shape, in particular in the form of a straight circular truncated cone, these two portions are preferably immediately adjacent, ie each with its larger or each adjacent to each other with their smaller face and thus form as it were a Doppelkegelstumpf. At the point where the truncated cones adjoin one another thus forms an edge which extends either along a constriction or along a bulge of the inner contour of the panel.

In addition to rotationally symmetrical inner contours of the diaphragm, which provide in particular circumferential geometric features such as constrictions and / or bulges and / or provide an undercut, it is basically possible and advantageous in a laser spark plug for an internal combustion engine, comprising at least one means for guiding, shaping and / or for generating laser radiation, further comprising a combustion chamber window and a housing, the housing on the side opposite the center of the combustion chamber window, in particular at a combustion chamber end of the housing, a diaphragm for the passage of the guided, guided and / or generated laser radiation by the means in a Has combustion chamber to deviate from a rotationally symmetrical shape of the inner contour of the diaphragm. Such asymmetries have the effect that there is an increased interaction of the inflowing into the aperture exhaust gas with the inner contour of the diaphragm and as a result of this increased interaction and the tendency of particles contained in the exhaust gas to accumulate within the diaphragm and does not penetrate to the combustion chamber window is. The deposits on the combustion chamber window are thus reduced and the reliability of the laser spark plug is increased. Special inner contours with a non-rotationally symmetrical shape have at least one recess, in particular a multiplicity of recesses, which are spaced in particular both from the end of the diaphragm facing the combustion chamber and from the end of the diaphragm facing away from the combustion chamber. Also bulge, in particular a plurality of bulges, which are spaced in particular both from the combustion chamber facing the end of the diaphragm and from the combustion chamber remote from the end of the diaphragm are advantageous because the recess and / or the bulge a starting point for a disturbance Influence of exhaust gases in the aperture represent. In particular, starting from the recess and / or the bulge, turbulence of the gas flowing into the orifice may occur. Particularly advantageously, the bulge and / or the recess is located in a region of the diaphragm which is spaced both from the end of the diaphragm facing the combustion chamber and from the end of the diaphragm facing away from the combustion chamber and which has an extreme cross-section. The provision of other inner contours of the diaphragm, in particular those which are optimized in terms of flow, for example, not sharp-edged, but rounded and / or complete or are formed in sections as a Laval nozzle is conceivable in principle.

In a region of the inner contour of the diaphragm, which is spaced both from the end of the diaphragm facing the combustion chamber and from the end remote from the combustion chamber, both the provision of one or more edges and the provision of extreme cross sections and / or of Recesses or bulges, as described above, already for themselves in such a way that a disturbance of the influx of gases is shown in the aperture and that in particular there is a turbulence of the gas flowing into the aperture gas. This technical effect occurs to an increased extent in a diaphragm with several of the mentioned features.

The specific choice of the length of the aperture, the targeted choice of material and / or the provision of cooling channels are already suitable alone or in combination with each other to reduce the temperature of the combustion chamber window so that deposits are reduced to the combustion chamber window, thus increasing the reliability of the laser spark plug is. By provid- ing a gap of the type described above upstream of the combustion chamber window on the combustion chamber side, a similar effect can be achieved on its own and especially in combinations, as described above. If these measures are combined with the provision of an extreme cross-section in an area which is spaced both from the end of the diaphragm facing the combustion chamber and from the end of the diaphragm facing away from the combustion chamber, the overall effect is that fewer particles are applied to the combustion chamber window On the other hand, however, the combustion chamber window is also more resistant to contamination by these remaining particles. The life of the laser spark plug can be significantly increased in this way.

According to the invention, in addition to or alternatively to the specific choice of the length of the diaphragm and additionally or alternatively to the provision of a high thermal conductivity of the diaphragm and additionally or alternatively to the provision of the combustion chamber window combustion chamber side upstream, communicating with the interior of the diaphragm gap, the height deliberately low is selected, and additionally or alternatively to the provision of a small outlet cross section of the diaphragm and additionally or alternatively to the provision of an edge and / or an extreme cross section of the type described in a laser spark plug for an internal combustion engine comprising at least one means for guiding, shaping and / or Generation of laser radiation, further comprising a combustion chamber window and a housing, wherein the housing on the side opposite the center of the combustion chamber window, in particular at a combustion chamber end of the housing, a diaphragm for the passage d he has guided by the means, shaped and / or generated laser radiation in a combustion chamber, the laser spark plug at least one focusing means for determining a beam shape of the laser beam passing through the aperture and the distance between the aperture and laser radiation at least along predominant parts of the inner contour of the aperture a maximum distance does not exceed.

The at least one focusing means may be a focusing optics, for example one or more lenses and / or one or more mirrors, in particular one or more mirrors each having a curved surface. The design of the combustion chamber window and / or the formation of the means for guiding, shaping and / or for the generation of laser radiation as a focusing element is additionally or alternatively possible. The provision of the at least one focusing means basically defines a beam shape of the laser radiation passing through the diaphragm. In the case of laser spark plugs, where the beam shape of the laser radiation passing through the diaphragm depends on a further operating parameter of the laser spark plug, for example a current or a temperature, the beam shape determined by the focusing means is to be understood as the beam shape provided by the laser spark plug, when the operating parameter assumes a value intended for the operation of the laser spark plug. The beam shape of the laser radiation, in particular the beam position, beam dimensions and distances between the beam and the diaphragm are understood to mean and / or against the background of Standard DIN EN ISO 11145 ,

The provision that the distance between the diaphragm and laser radiation does not exceed a maximum distance, at least along predominant parts of the inner contour of the diaphragm, is based on the one hand knowledge that it to achieve a combustion chamber window shielding effect and to reduce deposits on the combustion chamber window along predominant parts of the inner contour the aperture, in particular along the entire inner contour of the aperture is conducive when the passage of the aperture is designed as narrow as possible. On the other hand, this requirement is contrary to the fact that the largest possible proportion of guided through the means for guiding, shaping and / or for generating laser radiation, shaped and / or generated laser radiation should pass through the aperture, so the aperture must not be too narrow, in particular , as also manufacturing tolerances are to be considered.

A good compromise between these two requirements is already given if a distance between the diaphragm and laser radiation is given along predominant parts of the inner contour of the diaphragm, but this does not exceed a maximum distance of 4 mm. Even better compromises provide that the maximum distance along predominant parts of the inner contour of the diaphragm 2 mm, in particular 1 mm, preferably 0.55 mm, and / or that a minimum distance along the major parts of the inner contour of the diaphragm is not exceeded, this Minimum distance is advantageously 0.1 mm, 0.25 mm or 0.45 mm. The predominant parts of the inner contour of the diaphragm may comprise 70% of the surface of the inner contour or more, 90% of the surface of the inner contour or more or even the entire inner contour.

The fact that a good compromise between the mentioned requirements has been found, can alternatively be expressed in the proportion of the laser radiation passing through the diaphragm instead of by geometrical dimensions related to the diaphragm and / or to the laser radiation. Thus, it is favorable if this proportion is between 50% and 100%, in particular between 70% and 95%, preferably between 85% and 93%, the remaining portion being absorbed and / or diffused in particular by the diaphragm. The remaining portion is no longer available for focusing the laser beam.

The measure according to the invention of providing a maximum distance and / or a portion of the laser radiation passing through the diaphragm and the related developments of the invention come into consideration for all embodiments and examples of the invention, even if not explicitly noted, in particular optionally.

Both by the provision of minimum and / or maximum distances in the manner described, as well as by other measures described above, in particular the provision of a small outlet cross section of the diaphragm, as well as by the provision of the described relationships between outlet cross section and length of the diaphragm and / or By adapting the inner contour of the diaphragm to the laser beam, a good shielding of the combustion chamber window from conditions prevailing in the combustion chamber can already be achieved on its own. By combining these measures, the shielding effect can be significantly increased again. Overall, deposits on the combustion chamber window can thus be reduced particularly effectively and the reliability of the laser spark plug can be increased considerably.

Also with the other measures described above or below, which cause a reduction of the combustion chamber window temperature and / or a reduction of the exposure of the combustion chamber window with particles, in particular targeted choice of the length of the aperture, targeted choice of material and / or provision of cooling channels and / or a gap in described manner, the provision of minimum and / or maximum distances in the manner described in mutual effect gain, so that overall results in a significant increase in the reliability of the laser spark plug.

In further advantageous embodiments of the invention it is provided that in addition to or alternatively to the specific choice of the length of the diaphragm and additionally or alternatively to Provide a high thermal conductivity of the diaphragm and additionally or alternatively to the provision of the combustion chamber window combustion chamber side upstream, communicating with the interior of the diaphragm gap whose height is intentionally low, and additionally or alternatively to the provision of a small outlet cross section of the diaphragm and additionally or alternatively to the provision of an edge and / or an extremal cross section of the type described in a laser spark plug for an internal combustion engine comprising at least one guide means, Forming and / or for generating laser radiation, further comprising a combustion chamber window and a housing, wherein the housing on the side opposite the center of the combustion chamber window, in particular at a combustion chamber end of the G ehäuses, a diaphragm for the passage of the guided through the means, shaped and / or generated laser radiation in a combustion chamber, wherein the inner contour of the diaphragm has the shape of the lateral surface of a truncated cone, wherein the truncated cone has an opening angle φ, focusing means for determining a beam divergence angle ψ the laser radiation passing through the diaphragm is provided, where 0 ≤ φ - ψ ≤ 30 °, in particular 0 <φ - ψ <30 °.

The beam shape of the laser radiation, in particular the beam divergence angle, beam position, beam dimensions and distances between the beam and the diaphragm are understood to be according to and / or against the background of Standard DIN EN ISO 11145 , With regard to the execution and the effect of the focusing means, the above applies.

The feature that 0 ≦ φ - ψ ≦ 30 °, in particular 0 <φ - ψ <30 ° results in the technical effect that an outlet cross-section of the aperture is relatively narrow, so that only a few particles can enter the interior of the aperture itself but the aperture in their combustion chamber window facing part widens relatively strong, whereby the areal extent of the inner contour of the aperture is relatively large. The penetrated by the laser radiation Area of the combustion chamber window, however, is relatively small due to the lower beam divergence angle ψ. Overall, these surface ratios result in the majority of the particles, which have penetrated into the diaphragm from the outset, accumulating on the diaphragm and not on the combustion chamber window. The deposits on the combustion chamber window are thus reduced and the reliability of the laser spark plug is increased.

This advantageous effect is particularly evident when the inner contour of the diaphragm has the shape of the lateral surface of a straight circular truncated cone, wherein the straight circular truncated cone has the opening angle φ, where 0 ≤ φ - ψ ≤ 30 °, in particular 0 <φ - Y <30 ° Further is preferred that the opening angle φ 90 ° or less, in particular 70 ° or less, preferably 60 ° or less, and / or that the opening angle φ is 3 ° or more, in particular 10 ° or more, and or 5 ° ≤ φ - ψ, in particular 13 ° ≤ φ - ψ and / or that φ - ψ ≤ 20 °, in particular φ - ψ ≤ 15 °.

Both by the choice of φ - ψ in the manner described, as well as by other measures described above, in particular the provision of a small outlet cross section of the diaphragm, as well as by the provision of the described relationships between outlet cross section and length of the diaphragm and / or by adaptation of Inner contour of the diaphragm to the laser beam can be achieved in each case already good shielding of the combustion chamber window of prevailing conditions in the combustion chamber. By combining these measures, the shielding effect can be significantly increased again, so that overall a significant reduction of deposits and a significant increase in the reliability of the laser spark plug results.

Also with other measures described above or below, which cause a reduction of the combustion chamber window temperature and / or a reduction of the exposure of the combustion chamber window with particles, in particular targeted choice of the length of the aperture, targeted choice of material and / or provision of cooling channels and / or a gap in In the manner described, the appropriate choice of φ - ψ in the manner described, results in mutual enhancement of action, so that overall a significant reduction of deposits and a significant increase in the reliability of the laser spark plug results.

Advantageous further embodiments of the invention, in particular developments of the embodiments explained above, relate to measures for guiding the flow in a region upstream of the diaphragm and / or in the region of the diaphragm and / or in a region of the outlet opening of the diaphragm and / or in the diaphragm. On the one hand, these measures may relate to an antechamber encompassed by the laser spark plug, in particular arranged at the combustion chamber end of the housing, in particular the targeted arrangement of at least one overflow channel which permits fluid communication between an interior of the prechamber and a combustion chamber surrounding the prechamber. On the other hand, measures for influencing the flow in the areas mentioned can also be provided in devices not covered by the laser spark plug, for example by designing the shape of the combustion chamber or the piston associated with the combustion chamber or other components of the internal combustion engine.

It is particularly advantageous, in addition or as an alternative to the above-described measures in a laser spark plug for an internal combustion engine comprising at least one means for guiding, shaping and / or generating laser radiation, further comprising a combustion chamber window and a housing, wherein the housing on the means opposite side of the combustion chamber window, a diaphragm for the passage of the guided, guided and / or generated laser radiation through the means arranged in the combustion chamber end of the housing antechamber, at least one fluid connection between an interior of the pre-chamber and the combustion chamber surrounding the combustion chamber enabling overflow provided is that the at least one overflow channel is arranged and designed so that when a fluid flows through the overflow into the interior of the prechamber a desired fluid flow results.

For this purpose it can be provided that the at least one overflow channel has a cross section which is not larger, in particular smaller than the outlet cross section of the panel and / or is not larger, in particular smaller than a minimum cross section of the panel. Additionally or alternatively it can be provided that the at least one overflow channel has a cross-section Q _Ü , which is not larger, in particular smaller, than a maximum cross-section, the maximum cross-section 10 mm ² , 6 mm ² , 4 mm ² , 2 mm ² or 1 mm ² can be. By means of these relatively small cross sections, the direction of the fluid flowing into the prechamber can be influenced in a particularly targeted manner. It is also additional or alternative to targeted influencing the inflowing into the prechamber fluid, if the length of the at least one overflow channel L _{Ü is} high compared to a cross section Q _Ü the at least one overflow channel, in particular L _Ü > (Q _Ü / π) ^1/2 , L _Ü > (16 · Q _Ü / π) ^1/2 or according to L _Ü > (36 · Q _Ü / π) ^1/2 . The targeted influencing of the fluid flowing into the prechamber, in particular in one of the types listed below, results in a reduction of the deposits on the combustion chamber window and thus an improvement in the reliability of the laser spark plug.

In this case, a region of the laser spark plug lying between the prechamber and the combustion chamber window can be understood, while under the prechamber, a region of the laser spark plug arranged on the combustion chamber side of the diaphragm can be understood, which in particular at least in sections opposite to the entire Aperture or the outlet opening of the diaphragm has enlarged cross-section.

Particularly advantageous is in a laser spark plug for an internal combustion engine, comprising at least one means for guiding, shaping and / or generating laser radiation, further comprising a combustion chamber window and a housing, wherein the housing on the opposite side of the center of the combustion chamber window, a diaphragm for the passage provided by the means guided, shaped and / or generated laser radiation in an arranged at the combustion chamber end of the housing antechamber, wherein at least one fluid connection between an interior of the pre-chamber and the combustion chamber surrounding the combustion chamber enabling Überströmkanal is provided that the at least one overflow arranged so and is formed so that when a fluid flows through the overflow into the interior of the pre-chamber, a fluid flow results in the interior at a finite minimum angle, in particular measured to the longitudinal axis of the laser spark plug the aperture occurs.

From the fact that the flow of a fluid through the overflow into the interior of the pre-chamber results in a fluid flow which occurs at a finite minimum angle ε, in particular measured to the longitudinal axis of the laser spark plug into the interior of the aperture, on the one hand results in the effect that the inflowing fluid is directed to the inner contour of the diaphragm and store particles contained in the fluid there. The number of particles reaching the combustion chamber window can thus be reduced, the deposits on the combustion chamber window are reduced and the reliability of the laser spark plug is increased.

The described effect already occurs when the minimum angle ε is 45 °, even more favorable minimum angles ε are 60 ° or 75 ° or 85 °, in each case in particular measured to the longitudinal axis of the laser spark plug. Alternatively, the measurement of the minimum angle is always possible also to a vertical on the entrance surface of the diaphragm and / or to a vertical on a, the combustion chamber facing surface of the combustion chamber window. In order to achieve this flow, it is preferably provided that the at least one overflow channel is arranged so that its longitudinal axis in the radial direction forms an angle with the longitudinal axis of the laser spark plug, which is less than about 25 °, preferably less than about 10 °. Alternatively or additionally, it can be provided that a plurality of overflow channels are provided. Additionally or alternatively it can be provided that additional means are provided, through which a purge gas is blown into the prechamber, and these means are arranged in particular and are operable so that together with the fluid flowing through the overflow a resulting total flow results below the minimum angle, as explained above, enters the interior of the diaphragm or at least substantially parallel to an outlet opening of the diaphragm. Always preferred, the flow is formed within the antechamber as a tumble flow.

The above-described effect of providing the minimum angle ε acts synergistically with a given minimum angle ε with a particularly long diaphragm and / or with a particularly slender diaphragm, in particular a diaphragm with a small outlet cross-section Q _BA , through which the fluid flow enters the interior of the diaphragm. together, since in such developments, the inner contour of the diaphragm is hit by the fluid flow particularly close to its combustion chamber end and particles are preferably deposited there on the inner contour of the diaphragm. It is preferred that the inner contour of the diaphragm is struck by the fluid flow in a half of the inner contour of the diaphragm facing the combustion chamber. Even more favorable is an impingement of the fluid flow in a combustion chamber facing end portion whose length in the longitudinal direction of the inner contour 1 / n of the total length of the inner contour of the diaphragm makes up, where n = 3, or n = 4 or n = 5 can be. A similar situation can also be expressed by the fact that the minimum angle ε, the length of the diaphragm L of the ratio n and the outlet cross-section of the diaphragm Q _BA fulfill one of the following conditions: n · tan ε = L / (QA / π) ^1/2 ; n = 2 ... 5.

Also with the other measures described above or below, which cause a reduction of the combustion chamber window temperature and / or a reduction of the exposure of the combustion chamber window with particles, in particular targeted choice of the length of the aperture, targeted choice of material and / or provision of cooling channels and / or a gap in the way described, the occurs Providing a minimum angle in the manner described in mutual effect amplification, so that overall results in a significant reduction of deposits and increase the reliability of the laser spark plug.

Particularly advantageous is in a laser spark plug for an internal combustion engine, comprising at least one means for guiding, shaping and / or generating laser radiation, further comprising a combustion chamber window and a housing, wherein the housing on the opposite side of the center of the combustion chamber window, in particular on a combustion chamber side End of the housing, a diaphragm for the passage of the guided through the means, shaped and / or generated laser radiation in an arranged at the combustion chamber end of the housing antechamber, at least one fluid communication between an interior of the prechamber and a combustion chamber surrounding the combustion chamber enabling Überströmkanal provided is that the at least one overflow channel is arranged and designed so that when a fluid flows through the overflow into the interior of the pre-chamber, a fluid flow, the at least one vortex in the region of the aperture has, which rotates about a vortex axis having a component in the direction of the longitudinal axis of the laser spark plug.

Here, in particular, an area of the diaphragm upstream of the diaphragm and / or a region of the outlet opening of the diaphragm is to be understood as being under the region of the diaphragm. Spaces are to be understood in particular as meaning spatial areas which have structure lengths which are slightly smaller, for example half as large or one quarter as a structure length of the inner contour of the diaphragm, the structural length being given in particular by the length, inlet diameter and / or outlet diameter of the diaphragm can be.

From such an arrangement and design of the overflow channel or the flow channels initially results in that the fluid flow in the region of the diaphragm has a component in the direction perpendicular to the longitudinal axis LA of the laser spark plug. Furthermore, owing to the vortex, a flow deflection results locally in a direction perpendicular to the local flow velocity. Since the particles transported by the flow have a finite inertia, they only follow this flow deflection to a limited extent and tend, especially in the case of sharp flow deflection, to strike the inner contour of the diaphragm or a side wall of the antechamber. Overall, the result is that the amount of the combustion chamber window reaching particles is reduced, so that deposits on the combustion chamber window is reduced and the reliability of the laser spark plug is increased.

Although the described technical effect already results if the swirl axis has only one component in the direction of the longitudinal axis of the laser spark plug, it is preferred that the swirl axis is at an angle with a longitudinal axis of the laser spark plug of at most 45 °, in particular at most 20 °, preferably at most 10 °, or parallel with the longitudinal axis LA of the laser spark plug. In the case that the swirl axis is parallel to the longitudinal axis LA of the laser spark plug, in addition to the coaxial arrangement, a spaced arrangement of the swirl axis and longitudinal axis LA of the laser spark plug is favorable, in particular if the distance between the swirl axis and longitudinal axis LA of the laser spark plug at least 2 mm, in particular at least 4 mm. The maximum distances are 6 and 10 mm. The result of the spacing is a shear flow perpendicular to the outlet opening of the diaphragm and the impact of the particles on the inner contour of the diaphragm.

The intended arrangement of the overflow channel can result, in particular, from the fact that its longitudinal axis in the tangential direction encloses an angle with the longitudinal axis of the laser spark plug which is more than approximately 10 °, preferably more than approximately 25 °.

Additionally or alternatively it can be provided that additional means are provided, through which a purge gas is blown into the pre-chamber, wherein the additional means are arranged and are operable so that together with the fluid flowing through the overflow a resulting total flow results forming a vortex as explained above. It is always preferred that the flow within the antechamber is formed as a swirl flow.

The above-described effect of providing a vortex acts synergistically for a given vortex with a particularly long diaphragm and / or with a diaphragm having a particularly slender geometry, in particular a diaphragm with a small outlet cross-section Q _BA , through which the fluid flow enters the interior of the diaphragm , together, since in such developments, the tangentially thrown particles hit the inner contour of the aperture particularly close to its combustion chamber end. It is preferred that the inner contour of the diaphragm is struck by the particles thrown tangentially in a half of the inner contour of the diaphragm facing the combustion chamber. Even more favorable is an impact of the tangentially thrown particles in a combustion chamber facing end portion whose length in the longitudinal direction of the inner contour 1 / n of the total length of the inner contour of the diaphragm makes up, where n = 3, or n = 4 or n = 5 can be.

A similar situation can also be expressed by the fact that the maximum angle v, which forms the swirl axis with the longitudinal axis of the laser spark plug, the length of the diaphragm L, the ratio n and the outlet cross-section of the diaphragm Q _BA one of the following conditions: n · tan v = L / (QA / π) ^1/2 ; n = 2 ... 5.

Also with the other measures described above or below, which cause a reduction of the combustion chamber window temperature and / or a reduction of the exposure of the combustion chamber window with particles, in particular targeted choice of the length of the aperture, targeted choice of material and / or provision of cooling channels and / or a gap in In the manner described, the arrangement and formation of a transfer channel in the manner indicated in mutual effect gain, so that a total of a significant reduction of deposits and a significant increase in the reliability of the laser spark plug results.

Particularly advantageous is in a laser spark plug for an internal combustion engine, comprising at least one means for guiding, shaping and / or generating laser radiation, further comprising a combustion chamber window and a housing, wherein the housing on the opposite side of the center of the combustion chamber window, in particular on a combustion chamber side End of the housing, a diaphragm for the passage of the guided through the means, shaped and / or generated laser radiation in a combustion chamber, that the aperture on a side facing the combustion chamber has at least one outer edge whose contour deviates inwardly from a sharp-edged outer edge.

Concerning the term "sharpness" is on the Standard DIN ISO 13715: 2000 directed. In particular, an outer edge is considered sharp-edged if it only has erosions or transitions that are 50 μm or less.

The outer edge of the diaphragm can in particular limit the inner contour of the diaphragm. On the other hand, however, the outer edge of the diaphragm can in particular also be spaced from the inner contour of the diaphragm, in particular represent a radially outer boundary of the diaphragm and / or of the housing at its end on the combustion chamber side.

The providence of the deviation of the contour of the outer edge inward is based on the knowledge that laser spark plugs are exposed to the combustion chamber inside the combustion chamber ruling high temperatures during operation in an internal combustion engine. By thermal coupling of the laser spark plug on its side facing away from the combustion chamber on the other hand, an outflow of heat, so that the increase in the temperature of the laser spark plug is limited. It has been recognized that, especially from the combustion chamber side arranged sharp outer edges in the laser spark plug heat dissipation is deteriorated and consequently particularly high temperatures occur in these areas, which can lead to the occurrence of Glühzündungen in the combustion chamber and thus to a deteriorated operation of the internal combustion engine. Due to the deviation of the contour of the outer edge inwards areas of such high temperature increases are avoided and as a result, the occurrence of pre-ignition in the combustion chamber can be avoided.

Although the described technical effect already results if the diaphragm has on at least one outer edge on a side facing the combustion chamber whose contour deviates inwardly relative to a sharp-edged outer edge, it is preferred that the outer edge consist of a sharp-edged outer edge by an ablation of more than 0.075 mm , in particular of 0.1 mm or more, preferably 0.15 mm or more. 5 mm, 2 mm and 0.5 mm are considered as the upper limit for the ablation, as excessively large abradings could impair the mechanical stability of the diaphragm.

In preferred embodiments, it is provided that the outer edge of the diaphragm has a rounding and / or chamfering. In this case, it is further preferred that, in the case of a rounding, the radius of curvature, in the case of chamfering, the depth and / or the width of the chamfer, has 0.075 mm or more, in particular 0.15 mm or more. In this case, additionally or alternatively, it is preferred that, in the case of a rounding, the radius of curvature, in the case of chamfering, the depth and / or the width of the chamfer, be 5 mm or less, in particular 2 mm or less, preferably 0.5 mm or less. Chamfer angles in the range between 20 ° and 70 °, in particular in the range between 40 ° and 50 °, are preferred.

Of particular importance is the providence of the deviation of the contour of the outer edge to the inside, in particular the rounding and / or the chamfering at apertures, which have a large length, since these diaphragms are particularly exposed to the combustion chamber and thus particularly prone to excessive temperature increase are. Such an excessive increase in temperature can be avoided particularly effectively when the diaphragm, at least in the region of the outer edge, consists of a material with a high thermal conductivity, in particular brass, nickel and / or copper or an alloy of at least two of these substances.

An advantageous development of the laser ignition device according to the invention provides that the diaphragm is designed as a separate component and is attached to a further part of the housing of the laser spark plug, in particular on a shoulder. It is preferred to ensure a good dissipation of heat from the panel, which can be done by the joint between the panel and another part of the housing good thermal conductivity, in particular by means of a large-area soldering (at least 10 mm ² , in particular at least 20 mm ² ) and / or waiving welds, for example by a press fit executed. Alternatively or additionally, the diaphragm can also be screwed to the further part of the housing with a thread, it being preferred to provide a screw connection by means of a fine thread (thread pitch ≦ 0.5 mm, in particular ≦ 0.3 mm).

It is basically possible to generate a spark in the interior of the diaphragm by the laser spark plug. However, the generation of a spark in one of the aperture on the combustion chamber side upstream region, in particular in a combustion chamber or an antechamber, rather advantageous because it can avoid quenching losses in the ignition. In this case, a spark is preferably generated at least 1 mm, preferably at least 2 mm outside the diaphragm. As an upper limit for the distance between spark and exit surface of the diaphragm additionally or alternatively 30 mm, 10 mm and 5 mm into consideration, otherwise the exit cross section of the aperture would have to be chosen excessively large or a sufficient focusing of the laser radiation would be difficult. In particular, the position of a focus of the laser radiation generated or shaped by the laser spark plug can be regarded as the position of the spark.

In principle, in the context of the invention as a special case of a combustion chamber also fixed to the laser spark plug or fixed to the laser spark plug pre-chamber includes, in particular an antechamber whose volume is less than 10 cm ³ and which has at least one overflow channel whose cross-section less than 5 mm ² .

Brief description of the drawings

In the drawing shows:

1a a schematic representation of an internal combustion engine with a laser ignition device;

1b a schematic representation of the laser ignition from 1 and

2 to 21 Embodiments of inventive laser spark plugs.

Embodiments of the invention

An internal combustion engine carries in 1a Overall, the reference number 10 , It can serve to drive a motor vehicle, not shown. The internal combustion engine 10 includes several cylinders, one of which is in 1 only one with the reference numeral 12 is designated. A combustion chamber 14 of the cylinder 12 is from a piston 16 limited. Fuel or premixed fuel-air mixture enters the combustion chamber 14 through an injector 18 , the to a designated as rail fuel pressure accumulator 20 connected.

In the combustion chamber 14 injected fuel 22 or pre-mixed fuel-air mixture is by means of a laser radiation 24 ignited by a laser spark plug 100 comprehensive ignition device 27 in the combustion chamber 14 is emitted. For this purpose, the laser spark plug 100 via a light guide device 28 powered by a light, which may be in particular pump light, which is from a light source 30 provided. The immediate provision of light provided for the ignition can also be achieved by the light source 30 be provided. The light source 30 is from a control unit 32 controlled, that too the injector 18 controls.

How out 1b shows, the light source feeds 30 several optical fiber devices 28 for different laser spark plugs 100 , each one cylinder 12 the internal combustion engine 10 assigned. For this purpose, the light source 30 several individual laser light sources 340 on that with a pulse power supply 36 are connected. Due to the presence of several individual laser light sources 340 is a kind of "static" distribution of light, in particular pump light, to the different laser spark plugs 100 realized so that no optical distributor or the like between the light source 30 and the laser spark plugs 100 required are. Alternatively, the light source 30 even just a laser light source 340 have. In particular, each laser spark plug 100 exactly one light source 30 and / or exactly one laser light source 340 assigned.

The laser spark plug 100 has, for example, a laser-active solid 44 with a passive quality circuit 46 on that together with a coupling mirror 42 and a Auskoppelspiegel 48 forms an optical resonator. Optionally, further optical components, in particular lenses, for example for shaping the laser spark plug 100 supplied radiation or to the expansion of radiation, be provided.

Under pressure from the light source 30 generated light, in particular pump light, generates the laser spark plug 100 in a conventional manner laser radiation 24 through a focusing optics 52 on one in the combustion chamber 14 ( 1a ) located ignition point ZP is focused. The in the case 38 the laser spark plug 100 Existing components are through a combustion chamber window 58 from the combustion chamber 14 separated.

In the 2 to 21a is the detail X the 1b that the combustion chamber 14 facing the end 381 of the housing 38 the laser spark plug 100 , greatly enlarged in partial longitudinal section. From this greatly enlarged representation it becomes clear that the combustion chamber window 58 with the housing 38 is sealingly connected. The seal between housing 38 and combustion chamber windows 58 may be in the range of the reference 60 be formed in the form of a cohesive or non-positive connection.

The housing 38 can, as in these examples, be formed in two parts. It includes an inner sleeve 62 and an outer sleeve 64 , The outer sleeve 64 points to a combustion chamber 14 (please refer 1a ) end facing a paragraph 66 on. In particular, in the non-positive connection paragraph serves 66 to the combustion chamber window 58 against the inner sleeve 62 to press and thereby the tightness in the area of the connection 60 to increase. Also sealing means, for example sealing rings, in particular steel sealing rings, preferably copper-coated steel sealing rings, can be used and, in particular, be favorable with regard to thermal expansion compensation between the window material and the surrounding material.

In this example is on the outer sleeve 64 a female thread provided, which with a corresponding bolt thread of the inner sleeve 62 interacts. This thread, consisting of female thread and bolt thread, is in its entirety by the reference numeral 68 characterized. By bracing the outer sleeve 64 and inner sleeve 62 arises between the paragraph 66 and the combustion chamber window 58 another sealing surface 72 ,

In principle, in addition to the sealing forms shown in these examples, other sealing forms of the combustion chamber window 58 possible, for example, those in which, as in the DE 10 2009 000 540 A1 described, a cohesive seal between the combustion chamber window and a surrounding material is provided.

Inside the case 38 is located on the combustion chamber 14 opposite side of the combustion chamber window 58 a focusing optics 52 (please refer 1a and 1b ), which in the laser spark plug 100 generated or in the laser spark plug 100 fed laser radiation 24 to the ignition point ZP, which in this example the focus of the focusing optics 52 corresponds, focused. At the combustion chamber end 381 of the housing 38 is a blind 74 for the passage of the laser radiation 24 in the combustion chamber 14 intended.

In the 2 illustrated laser spark plug 100 has a housing 38 on whose combustion chamber side of the combustion chamber window 58 arranged section is sleeve-shaped and an aperture according to the invention 74 represents. The inner contour 71 the aperture 74 has, for example, the shape of a cylinder jacket whose height is the length L of the diaphragm 74 equivalent. The length L is thereby, for example, starting from the combustion chamber window 58 , Measured in the longitudinal direction of the laser spark plug and is in this example 13 mm.

It is further provided in this example that the aperture 74 consists of a material with a thermal conductivity of 60 W / (m · K) or more or even with a thermal conductivity of 80 W / (m · K) or more, for example brass, nickel or copper or at least one of these substances alloy , For this purpose, in this example, the entire housing 38 made of this material. Alternatively, it would also be possible only in the region of the combustion chamber end 381 of the housing 38 to provide this material. Also, the provision of the material only inside the panel, enclosed by other material whose thermal conductivity may be lower, for example, from a high-alloy steel, is possible. Such a variant is in the 3 shown and points inside the panel 74 a deposit 80 on, which consists for example of copper and by the rapid dissipation of heat from the area of the aperture 74 in one farther from the combustion chamber 14 remote area of the housing 38 is possible. In another alternative are in place of the deposit 80 cooling channels 81 inside the aperture 74 provided as in 4 shown. Through these cooling channels 81 can heat out the area of the aperture 74 in one farther from the combustion chamber 14 remote area of the housing 38 , For example, by circulation of water or other cooling medium discharged.

In 5 an example of a laser spark plug is shown, which differs from the previously shown in that the combustion chamber window 58 upstream of the combustion chamber, there is a gap 82 is arranged. The gap 82 is in this example axially on the combustion chamber 14 facing side through the aperture 74 , on the combustion chamber 14 opposite side through the combustion chamber window 58 and after outside through the aperture 74 limited. Inside, the gap communicates 82 over the interior of the panel 74 with one in front of the aperture 74 lying area, for example a combustion chamber 14 , The gap 82 has in this example, the base of a ring having an outer diameter D _SA of 15 mm and an inner diameter D _SI of 6 mm, so that the gap cross-section Q _S 148 mm ² . The gap cross section Q _S is thus a multiple of the inlet cross section Q _BE , which is 28 mm ² , with an inlet diameter D _{BE of} the diaphragm 74 of 6 mm. The height H _{S of} the gap 82 in this example is 0.15 mm.

In another example, which is particularly relevant for laser spark plugs, which are intended for use in internal combustion engines whose lubrication makes use of low-additive oils, or whose lubrication makes use of non-additized oils, the height of the gap is 2 mm and the Gap cross section Q _S is only 20% of the inlet cross section Q _{BE of} the diaphragm 74 , namely 0.56 mm ² .

6 shows another example of a laser spark plug 100 , which differs from the one shown above in that the aperture 74 has a particularly small outlet cross-section Q _BA , which is 3 mm ² in this example, with an outlet diameter D _{BA of} the aperture of 2 mm. The length L, the aperture 74 is 12 mm in this example, so that the quotient L / (4Q _BA / π) ^1/2 results in the value 6.

In the 7 to 10 in each case a further example of a laser spark plug is shown, which differs from the one shown above in that the inner contour of the diaphragm 74 in a region which is both from the combustion chamber facing the end of the aperture 74 as well as from the combustion chamber facing away from the end of the aperture 74 is spaced, at least one edge 83 , in particular a plurality of edges 83 , having. The in the 7 illustrated laser spark plug 100 has an aperture 74 on, in a central area two edges 83 , an inner edge and an outer edge, which together form a right-angled step 84 form. In 8th is a laser spark plug 100 shown a variety of edges 83 and formed from them rectangular steps 84 wherein the actual number of stages 84 Representatively, for example, for 3, 7 or 8 stages is to be construed, in particular in a central region of the aperture 74 are arranged. Also not right-angled steps 84 are possible. Next to the steps shown above 84 on which the aperture 74 in the direction of her the combustion chamber 14 tapered end, are also steps 84 possible, at which the aperture 74 in the direction of her the combustion chamber 14 tapered away from the end. In 9 an example is shown in which such stages 84 on which the aperture 74 in the direction of her the combustion chamber 14 facing end tapered, upstream combustion chamber side.

10 shows another example of a laser spark plug 100 with a panel 74 , the inner contour 71 a circumferential edge 83 having.

In the 11 to 15 each is another example of a laser spark plug 100 shown a diaphragm 74 has, with the peculiarity that the inner contour 71 the aperture 74 in one area, both from the combustion chamber 14 facing the end of the aperture 74 as well as from the combustion chamber 14 opposite end of the panel 74 is spaced apart, has an extreme cross section Q _X.

The in the 11 illustrated laser spark plug 100 has an aperture 74 on, in a central area a sharp-edged constriction 85 having. In the area of constriction 85 is the diameter D _X and thus the cross section of the aperture Q _X minimal, namely about half or quarter as large as each of the inlet and outlet cross-section Q _BE , Q _{BA of} the diaphragm. Above and below the sharp-edged constriction 85 has the inner contour 71 the aperture 74 in this example in each case the shape of straight Kreistrlt stump coats on. Alternatively, it is also possible a constriction 85 rounded off, see 12 ,

The in the 13 illustrated laser spark plug 100 has an aperture 74 on, in a central area a sharp-edged bulge 86 having. In the area of the bulge 86 is the diameter D _X and thus the cross section of the aperture Q _X maximum, namely about twice to four times as large as each of the inlet and outlet cross-section Q _BE , Q _{BA of} the diaphragm. Above and below the sharp-edged bulge 86 has the inner contour 71 the aperture 74 in this example in each case the shape of straight Kreistrlt stump coats on. Alternatively, it is also possible a bulge 86 rounded off, see 14 , 15 shows another variant in which the aperture 74 an underdog 87 having. The undercut is executed in this example as Innenfreistich and rectangular and has a maximum cross-section of the aperture Q _X , which is about twice to four times as large as each of the inlet and outlet cross-section Q _BE , Q _{BA of} the aperture.

In the 16 and 17 each is another example of a laser spark plug 100 shown a diaphragm 74 has, with the peculiarity that the aperture 74 on the combustion chamber 14 facing side at least one outer edge 88 whose contour is opposite to a sharp-edged Outer edge deviates inwards. In the 16 illustrated laser spark plug 100 has an aperture 74 with a sleeve-shaped basic shape, wherein the inner combustion chamber side edge 89 the sleeve a rounding 91 having. The fillet radius is 0.5 mm in this example. Also the rounding 91 the outer edge of the combustion chamber side 90 the sleeve is additionally or alternatively, for example, with a radius of curvature of 0.5 mm, possible. Even small and / or larger radii of curvature are possible in principle. In the 17 illustrated laser spark plug 100 has an aperture 74 with a sleeve-shaped basic shape, wherein the inner combustion chamber side edge 89 the sleeve a chamfer 92 having. The chamfering 92 (Length and width) is in this example 10.5 mm, the chamfer angle is 45 °. Also the chamfering 92 the outer edge of the combustion chamber side 90 the sleeve is additionally or alternatively, for example, with a length and width of 0.5 mm, possible. Also small and / or larger chamfers 92 are possible in principle. Of course, in addition to the in 16 and 17 outer edges shown 88 , further outer edges 88 executable whose contour deviates inwardly from a sharp-edged outer edge, for example, outer edges with an exact or nearly elliptical, parabolic or hyperbolic shape or with an irregular shape. Also combinations of chamfers 92 and fillets 91 are conceivable.

In the 18 and 19 each is another example of a laser spark plug 100 shown a diaphragm 74 and the focusing means 53 , in particular a focusing optics 52 , establishing a beam shape through the aperture 74 passing laser radiation 24 has (see 1B ). The laser spark plugs proposed in these examples 100 have the peculiarity that the shape of the aperture 74 in terms of the shape of the laser radiation passing therethrough 24 is chosen advantageous. The shape of the laser radiation 24 is in these figures by the conical envelope lines 99 indicated that intersect approximately in the ignition point ZP. The shape of the laser radiation 24 In the context of this invention, statements concerning themselves are to be understood in accordance with or in the context of Standard DIN EN ISO 11145 ,

The in the 18 illustrated laser spark plug 100 has an aperture 74 on that along their entire inner contour 71 a distance A to the laser radiation passing therethrough 24 of about 0.5 mm. The illustrated laser spark plug 100 moreover, has the property that 88% of that through the combustion chamber window 58 transmitted laser radiation 24 through the aperture 58 as focusable laser radiation 24 passes while the remaining laser radiation 24 along the inner contour 71 the aperture 74 undergoes a distraction or absorption and is not available for focussing. The in the 18 illustrated providence of a distance A in the manner described and / or the provision of a transmission through the diaphragm 58 in the manner described, where not explicitly excluded, are also contemplated in the other embodiments and examples of the invention.

The in the 19 illustrated laser spark plug 100 has an aperture 74 on, whose inner contour 71 has the shape of a straight circular truncated cone whose opening angle φ is 45 °. The laser radiation passing through the diaphragm 24 is focused in this example so that the beam divergence angle ψ (far-field divergence) is 30 °.

In the 20 and 21 each is an example of a laser spark plug 100 shown a diaphragm 74 for the passage of laser radiation 24 in a combustion chamber end of the housing 38 arranged antechamber 110 having. For the fluid connection between the interior 111 the antechamber 110 and the combustion chamber is a transfer port 120 intended.

At the in 20 the example shown is the longitudinal axis KLA of the overflow 120 with respect to the longitudinal axis LA of the laser spark plug 100 off-center, staggered. The longitudinal axis KLA of the overflow bore 120 and the longitudinal axis LA of the laser spark plug 100 In this example, they are parallel to one another; alternatively, they can also be arranged at an angle to one another in the radial and / or tangential direction. With an inflow of a fluid F forms within the prechamber 110 a vortex so that the fluid flow along the outlet opening of the diaphragm 74 largely parallel to the outlet opening of the diaphragm 74 runs. Nevertheless, in the interior of the aperture 74 As a result, entering fluid enters the diaphragm at an angle ε 74 a measured at the longitudinal axis LA of the laser spark plug is almost 90 °, in particular always at least 75 °. The inside of the aperture 74 forming fluid flow is in particular a tumble flow. In this example, the length L of the diaphragm is 5 mm and the exit diameter D _{AE of} the diaphragm is 6 mm. It is thus by the interaction of the angle ε, under which the fluid F in the interior of the diaphragm 74 Entered, given the length L and the exit diameter D _{AE of} the diaphragm in this example that the fluid flow F the combustion chamber window 58 not immediately, but only after deflections on the inner contour 71 the aperture 74 meets.

Further versions of laser spark plugs 100 with atria 110 an overflow channel 120 is arranged and formed so that when flowing in a fluid through the overflow 120 in the interior 111 the antechamber 110 a fluid flow F results, which at a minimum angle ε, in particular measured to the longitudinal axis of the laser spark plug, from 45 °, 60 ° or 75 ° in the interior of the diaphragm 74 is possible, and in particular provide that several overflow 120 are provided. Additionally or alternatively, it is also possible that additional means (not shown) are provided, through which a purge gas is blown into the prechamber. It is provided in particular that these means for injecting purge gas together with the overflow channel 120 cooperate in such a way that a total of fluid flow is formed, so that when flowing in a fluid through the overflow 120 in the interior 111 the antechamber 110 a fluid flow F results, which at a minimum angle ε, in particular measured to the longitudinal axis of the laser spark plug, from 45 °, 60 ° or 75 ° in the interior of the diaphragm 74 entry.

21 shows another example of a laser spark plug 100 , in part a as a partial longitudinal section along the longitudinal axis LA of the laser spark plug 100 , in part b in the direction of B in part a and in part c in a section along the line CC in part b of 21 , This laser spark plug 100 indicates the fluid connection between the interior 111 the antechamber 110 and the combustion chamber five transfer channels 120 on, each offset by 72 ° to each other, are arranged symmetrically. The longitudinal axes KLA of the overflow holes 120 are inclined both in the radial and in the tangential direction, such that the longitudinal axes KLA of the overflow holes 120 in view of the laser spark plug ( 21b ) form a regular pentagon. Due to the arrangement and the orientation of the overflow holes 120 forms during the inflow of a fluid F in the antechamber 110 a vortex, whose vortex axis WB inside the antechamber 110 and in the area of the aperture 74 with the longitudinal axis LA of the laser spark plug 100 coincides. From the flow conditions in the area of the aperture 74 results in that especially heavy particles, which leave the flow tangentially in the region of a vortex, the inner contour 71 the aperture 74 meet and not to the combustion chamber window 58 penetrate.

The inside of the aperture 74 forming fluid flow represents in particular a swirl flow. In this example, the length L of the diaphragm is 5 mm and the outlet diameter D _{BE of} the diaphragm is 6 mm. It is thus by the interaction of the angle v, under which the swirl axis WB is tilted against the longitudinal axis LA of the laser spark plug (here: 0 °), the length L and the exit diameter DAS of the diaphragm 74 given in this example that said particles are the combustion chamber window 58 do not hit if they leave the flow in a tangential direction. Also for tan v ≦ L / D _BE , this effect is at least partly given, in particular for n · tan v ≦ L / D _BE ; n = 2, 3, 4.

It is also possible that additional means (not shown) are provided, through which a purge gas in the prechamber 110 is inflatable. It is provided in particular that these means for injecting purge gas together with an overflow channel 120 or more overflow channels 120 cooperate in such a way that a total of fluid flow is formed, so that when flowing in a fluid through the overflow 120 or the transfer channels into the interior 111 the antechamber 110 results in a fluid flow having a vortex which rotates about a vortex axis WB, which is a component in the direction of the longitudinal axis LA of the laser spark plug 100 has, in particular parallel or coaxial with the longitudinal axis LA of the laser spark plug 100 is.

Although for those in the 2 to 21 shown aperture 74 on the one hand, as drawn, an axisymmetric shape is preferred, deviations from an axis symmetry can be advantageously provided.

The invention is not limited to the above and / or to the explicitly explained and / or explicitly illustrated in the figures embodiments and examples, but further embodiments and examples are by combinations of the explanations to the individual embodiments and examples in a reproducible for the skilled person Given way. Of these combinations, especially those are of importance whose advantageous effect has already been explicitly emphasized above.

In particular, embodiments are also advantageous and can be reproduced by those skilled in the art, which are based on an interaction of one or, if they do not exclude each other, several of the above-disclosed features of two or more than two of the following feature groups: Previously marked as advantageous lengths L of cover 74 previously referred to as advantageously marked selections of the material of the panel 74 Previously marked as advantageous embodiments of the combustion chamber window 58 on the combustion chamber side upstream gap 82 , previously referred to as advantageous cross-sections of the aperture 74 , previously characterized as advantageous relationships between lengths L and cross-sectional areas Q of the diaphragm 74 , previously characterized as advantageous features of the inner contour 71 the aperture 74 , especially edges 83 and extreme cross sections of the aperture 74 Previously characterized as advantageous features, the advantageous design of the shape of the panel 74 in terms of the shape of them passing laser radiation 24 relate to previously characterized as advantageous features that the design of an outer edge 88 the aperture 74 relate to previously characterized as advantageous features that the design of an antechamber 110 , in particular an overflow channel 120 , affect.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2005/066488 A1 [0002]
• DE 102009000540 A1 [0102]

Cited non-patent literature

• Standard DIN EN ISO 11145 [0049]
• Standard DIN EN ISO 11145 [0057]
• Standard DIN ISO 13715: 2000 [0081]
• Standard DIN EN ISO 11145 [0115]

Claims (14)

Laser spark plug for an internal combustion engine ( 10 ) comprising at least one agent ( 26 ) for guiding, shaping and / or for generating laser radiation ( 24 ), further comprising a combustion chamber window ( 58 ) and a housing ( 38 ), characterized in that the housing ( 38 ) on the means ( 26 ) opposite side of the combustion chamber window ( 58 ), in particular at a combustion chamber end ( 381 ) of the housing, an aperture ( 74 ) for the passage of the 26 ) guided, shaped and / or generated laser radiation in a combustion chamber ( 14 ), wherein the laser spark plug ( 100 ) Focusing means for defining a beam shape through the aperture ( 74 ) passing laser radiation ( 24 ), wherein the distance (A) between aperture ( 74 ) and laser radiation ( 24 ) at least along predominant parts of the inner contour ( 71 ) the aperture ( 74 ) Does not exceed 4 mm. Laser spark plug according to claim 1, characterized in that the distance between the diaphragm ( 74 ) and laser radiation ( 24 ) at least along predominant parts of the inner contour ( 71 ) the aperture ( 74 ) Does not exceed 2 mm, in particular 1 mm, preferably 0.55 mm. Laser spark plug according to one of claims 1 or 2, characterized in that the distance between the diaphragm ( 74 ) and laser radiation ( 24 ) at least along predominant parts of the inner contour ( 71 ) the aperture ( 74 ) 0.1 mm, in particular 0.25 mm, preferably 0.45 mm does not fall below. Laser spark plug according to one of claims 1 to 3, characterized in that the at least predominant parts of the inner contour ( 71 ) 50% of the surface of the inner contour ( 71 ) or more. Laser spark plug according to one of claims 1 to 4, characterized in that the at least predominant parts of the inner contour ( 71 ) 70% of the surface of the inner contour ( 71 ) or more, in particular 90% of the surface of the inner contour ( 71 ) or more, preferably the entire inner contour ( 71 ) the aperture ( 74 ). Laser spark plug according to the preamble of claim 1, in particular according to one of claims 1 to 5, characterized in that the housing ( 38 ) on the means ( 26 ) opposite side of the combustion chamber window ( 58 ), in particular at a combustion chamber end ( 381 ) of the housing, an aperture ( 74 ) for the passage of the 26 ) guided, shaped and / or generated laser radiation in a combustion chamber ( 14 ), wherein the laser spark plug ( 100 ) Focusing means for defining a beam shape through the aperture ( 74 ) passing laser radiation ( 24 ) and that through the aperture ( 74 ) a portion of the through the combustion chamber window ( 58 ) emerging laser radiation ( 24 ), which is between 50% and 100%, in particular between 70% and 95%, preferably between 85 and 90%. Laser spark plug according to one of the preceding claims, characterized in that the length (L) of the diaphragm ( 74 ) Is 4 mm or more, in particular 12 mm or more. Laser spark plug according to one of the preceding claims, characterized in that the length (L) of the diaphragm ( 74 ) Is 20 mm or less, especially 15 mm or less. Laser spark plug according to one of the preceding claims, characterized in that the diaphragm ( 74 ) has a material with a thermal conductivity of 60 W / (m · K) or more, in particular consists of such a material in whole or in sections. Laser spark plug according to one of the preceding claims, characterized in that the diaphragm ( 74 ) at least one cooling channel ( 81 ), in particular a plurality of cooling channels ( 81 ), having. Laser spark plug according to one of the preceding claims, characterized in that the inner contour ( 71 ) the aperture ( 74 ) in an area that is both from the combustion chamber ( 14 ) facing the end of the aperture ( 74 ) as well as from the combustion chamber ( 14 ) facing away from the end of the aperture ( 74 ), at least one edge ( 83 ) having. Laser spark plug according to one of the preceding claims, characterized in that the inner contour ( 71 ) the aperture ( 74 ) has the shape of the lateral surface of a truncated cone, wherein the truncated cone has an opening angle φ and wherein the beam divergence angle of the through the diaphragm ( 74 ) passing laser radiation ( 24 ) ψ, where 0 <φ - ψ <30 °. Laser spark plug according to one of the preceding claims, characterized in that the housing ( 38 ) on the means ( 26 ) opposite side of the combustion chamber window ( 58 ) an aperture ( 74 ) for the passage of the 26 ) guided, shaped and / or generated laser radiation ( 24 ) into a combustion chamber end ( 381 ) of the housing ( 38 ) arranged antechamber ( 110 ), wherein at least one fluid connection between an interior ( 111 ) the antechamber ( 110 ) and one the antechamber ( 110 ) surrounding combustion chamber enabling overflow channel ( 120 ) is provided, wherein the at least one overflow channel ( 120 ) is arranged and formed so that when flowing in a fluid through the Overflow channel ( 120 ) in the interior ( 111 ) the antechamber ( 110 ) results in a fluid flow (F), which at a minimum angle ε, in particular measured to the longitudinal axis of the laser spark plug, of 45 ° in the interior of the diaphragm ( 74 ) entry. Laser spark plug according to one of the preceding claims, characterized in that the housing ( 38 ) on the means ( 26 ) opposite side of the combustion chamber window ( 58 ) an aperture ( 74 ) for the passage of the 26 ) guided, shaped and / or generated laser radiation ( 24 ) into a combustion chamber end ( 381 ) of the housing ( 38 ) arranged antechamber ( 110 ), wherein at least one fluid connection between an interior ( 111 ) the antechamber ( 110 ) and one the antechamber ( 110 ) surrounding combustion chamber enabling overflow channel ( 120 ) is provided, wherein the at least one overflow channel ( 120 ) is arranged and formed so that when flowing in a fluid through the overflow channel ( 120 ) in the interior ( 111 ) the antechamber ( 110 ) gives a fluid flow (F), which in the region of the diaphragm ( 74 ) has at least one vortex which rotates about a vortex axis (WB) which is a component in the direction of the longitudinal axis (LA) of the laser spark plug (US Pat. 100 ) having.

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