Internal combustion engine with spark plug and negative discharge position

Abstract

An internal combustion engine comprising: at least one cylinder, in which a combustion chamber is formed, the combustion chamber being defined by a side wall of the cylinder, a combustion chamber roof 20 formed by a cylinder head of the cylinder, and a piston movable within the cylinder; and a spark plug having a longitudinal axis, the spark plug having a housing including an end face facing the combustion chamber, an insulator arranged in the housing, a central electrode arranged on the insulator, and at least one ground electrode arranged on the housing and forming at least one ignition gap together with the central electrode, wherein the spark plug is assembled in a hole formed in the cylinder head and is configured to ignite a fuel-air mixture present in the combustion chamber, the ignition gap of the spark plug being arranged outside the combustion chamber.

Description

[Technical field]

[0001] The invention relates to an internal combustion engine according to claim 1. In particular, the internal combustion engine according to the invention is suitable for operation with a hydrogen-containing fuel. [Background technology]

[0002] Most vehicles, for example passenger cars or freight vehicles, have traditionally been powered by internal combustion or combustion engines that use gasoline or diesel as fuel. An increasing number of mobile and stationary internal combustion engines are now being powered by natural gas or hydrogen. In these cases, like in gasoline-powered combustion engines, the air-fuel mixture must be ignited by a spark in a hydrogen-powered internal combustion engine. For this purpose, typically a spark plug is used.

[0003] In hydrogen-powered internal combustion engines, a very lean air-fuel mixture (lambda > 1.8) is usually set up in order to meet emission regulations. This, together with the low heat value of the mixture of hydrogen, results in a high charge density and therefore a high pressure at the time of ignition. Another peculiarity when burning hydrogen in an internal combustion engine is the interaction between the autoignition temperature and the minimum required ignition energy. As a result, "cold spark plugs" are required for application in hydrogen-powered internal combustion engines, i.e. spark plugs with a very low heat value are required. The relative position of the spark plug or ignition gap to the combustion chamber also has a significant influence on the performance of the spark plug and the internal combustion engine.

[0004] Previously known spark plugs and internal combustion engines are usually optimized for operation in a gasoline-powered internal combustion engine. The position of the spark plug in the cylinder head or the ignition gap in the combustion chamber is selected accordingly. An example of a known arrangement of spark plugs in a cylinder of a gasoline-powered internal combustion engine is shown in FIG. 9. Previous spark plugs and internal combustion engines are therefore either not suitable for application in a hydrogen-powered internal combustion engine or suffer from reduced performance when applied to a hydrogen-powered internal combustion engine. Summary of the Invention [Problem to be solved by the invention]

[0005] SUMMARY OF THE DISCLOSURE It is therefore an object of the present invention to provide an internal combustion engine with a spark plug which meets the requirements imposed on a hydrogen-powered internal combustion engine. [Means for solving the problem]

[0006] The above object is achieved in the internal combustion engine according to the invention in that the ignition gap of the spark plug is arranged outside the combustion chamber.

[0007] The internal combustion engine according to the invention has at least one cylinder and a spark plug belonging to this cylinder. The at least one cylinder has a combustion chamber, which is defined by the cylinder side wall, a combustion chamber roof and a piston movable in the cylinder. In this case, the combustion chamber roof is the surface of the cylinder head which defines the combustion chamber. The cylinder head has a cylinder head bore, hereinafter referred to as bore, which leads to the combustion chamber. In this bore a spark plug is assembled, for example screwed in. The spark plug is designed to ignite the fuel-air mixture present in the combustion chamber.

[0008] The spark plug has a longitudinal axis extending from the end of the spark plug facing the combustion chamber to the end opposite the combustion chamber. The spark plug has a housing with an end face facing the combustion chamber. An insulator and a central electrode arranged on the insulator are arranged on the housing. At least one ground electrode is arranged on the housing. The at least one ground electrode forms an ignition gap together with the central electrode. In particular, the ignition gap can be formed radially or axially with respect to the longitudinal axis of the spark plug. The width of the ignition gap is then the distance between the mutually facing surfaces of the central electrode and the at least one ground electrode. The ignition gap is a volume between the ground electrode and the central electrode, which volume occurs between the overlapping projections of the mutually facing ignition surfaces of the electrodes. That is, the ignition surface of the central electrode is projected onto the ignition surface of the ground electrode and vice versa. The volume that extends across the two projections is the volume of the ignition gap. In that case, this volume is defined in one dimension by the ignition surface and in the other dimension by the overlap of the projected ignition surfaces. The ignition gap has a combustion chamber-side end. For example, in an axial ignition gap, this is the ignition surface of the ground electrode formed as a roof electrode (Dachelektrode). In a radial ignition gap, this is, for example, the combustion chamber-side end of the ignition gap volume between the opposing electrodes.

[0009] According to the invention, it is provided that the ignition gap of the spark plug is arranged outside the combustion chamber. Outside the combustion chamber means that the ignition gap is in a bore or that its end facing the combustion chamber is flush with the combustion chamber roof, but does not protrude beyond the combustion chamber roof into the combustion chamber. The spark plug has a negative discharge position. This has the advantage that the electrode does not protrude into the combustion chamber, or protrudes as little as possible, and thus absorbs less heat from the combustion chamber. As a result, the spark plug absorbs less heat and is cooler, which avoids undesirable self-ignition.

[0010] Further advantageous embodiments of the invention are the subject matter of the dependent claims.

[0011] Advantageously, for example, the ignition gap has a distance of at least 0 mm, at most -15 mm, in particular more than -1 mm and / or less than -4 mm to the combustion chamber roof of the cylinder, the contour of the combustion chamber roof being continued by an imaginary line at the hole opening, which imaginary line is a reference plane with a value of 0 mm. The signs indicate the direction of the distance, but not the value of the distance. In particular, the distance from the reference plane in the direction of the end of the spark plug facing away from the combustion chamber takes on increasing values, in which case a negative sign indicates a direction away from the reference plane away from the combustion chamber. A positive sign value corresponds to the distance from the reference plane of the ignition gap in the direction of the combustion chamber, i.e. into the combustion chamber. The numerical value corresponds to the length of the distance, and when a range is mentioned in this connection, it means a distance. The distance is measured parallel to the longitudinal axis of the spark plug. The distance is measured from the end of the ignition gap facing the combustion chamber to the reference plane.

[0012] The feature of a distance between the ignition gap and the combustion chamber roof of greater than 0 mm means that the ignition gap is located completely in the bore, i.e. the spark plug has a negative discharge position. This has the advantage that the electrode is as far away as possible from the combustion chamber and therefore absorbs as little heat as possible from the combustion process taking place in the combustion chamber. It is therefore possible to obtain the coldest possible spark plug.

[0013] Limiting the distance to a maximum of -15 mm has the advantage that the distance that the flame occurring in the ignition gap has to travel to the combustion chamber is not too large. An ignition gap distance of -1 mm to -4 mm to the combustion chamber roof has been found to be a good compromise between a reduction in the heat absorbed by the spark plug from the combustion chamber and a good and sufficiently rapid propagation of the flame from the ignition gap to the combustion chamber. The greater the wall thickness of the spark plug housing, the smaller the distance between the ignition gap and the combustion chamber roof can be selected. The ratio V of the wall thickness B of the spark plug housing to the distance A (V=B / A) is 0.05-25, preferably the value V is 0.5-5. The wall thickness B of the spark plug housing is determined from the difference between the outer radius RA of the housing in the thread region, the tip of the thread belonging to the outer radius of the housing, and the inner radius RI of the housing in the intake and exhaust space (Atmungsraum), B=RA-RI, this radius being measured from the longitudinal axis of the spark plug in a direction perpendicular to this longitudinal axis.

[0014] In one advantageous embodiment of the internal combustion engine, the end face of the housing facing the combustion chamber is arranged outside the combustion chamber, which has the advantage that the ground electrode can also be formed on the end face of the housing, for example as a roof electrode or side electrode, while still maintaining the advantages of a cold spark plug.

[0015] In another advantageous embodiment of the internal combustion engine, the end face of the housing facing the combustion chamber is at least partially flush with the combustion chamber roof, in particular completely flush. This has the advantage that the housing fits the combustion chamber roof and the opening formed by the holes in the cylinder head is smaller. The influence of the housing on the flow in the combustion chamber is reduced. This advantage is further strengthened if the end face of the housing facing the combustion chamber has a shape that corresponds to the contour of the combustion chamber roof.

[0016] In one development of the internal combustion engine according to the invention, the spark plug is arranged in the region of the cylinder head, which region is a circular surface with the center point of the combustion chamber roof as the center point of the circle, and the inner cylinder radius R B15% of radius R M When determining whether the spark plug is located in the zone, the longitudinal axis of the spark plug is observed. If the longitudinal axis is within the zone, the spark plug is considered to be located in the zone. In particular, the spark plug is located at the center point of the combustion chamber roof, i.e. the longitudinal axis of the spark plug and the center point of the combustion chamber roof coincide. This central location of the spark plug in the cylinder head and in the combustion chamber roof ensures that the spark plug is centrally located, so that the flame front generated by the spark plug can propagate uniformly in the combustion chamber.

[0017] In an alternative development of the internal combustion engine according to the invention, the spark plug is arranged outside the area of ​​the cylinder head, which area is a circular surface with the center point of the combustion chamber roof as the center point of the circle and the cylinder inner radius R B 15% of radius R M When determining whether a spark plug is arranged outside the region, the longitudinal axis of the spark plug is observed. If the longitudinal axis is outside the region or on the edge of the region, the spark plug is considered to be arranged outside the region. That is to say, every arrangement of the spark plug that is not in the region is considered to be outside the region. This decentralized arrangement of the spark plug in the cylinder head and in the combustion chamber roof has the advantage that the spark plug is arranged laterally on the combustion chamber roof and can be arranged towards a fuel injector or a gas exchange opening that may be in the cylinder. The arrangement of the spark plug towards other components that may be in the cylinder makes it possible to optimize the performance of the internal combustion engine depending on the corresponding arrangement.

[0018] In an advantageous embodiment of the internal combustion engine according to the invention, the end face of the housing facing the combustion chamber has a surface that corresponds to the contour of the combustion chamber roof. The combustion chamber roof can have various shapes, for example a flat surface or a conical surface with a center point on the longitudinal axis of the cylinder. The conical surface can have, for example, the shape of a hemisphere or one or more curved or straight surfaces that meet at the center point of the surface. Thus, when a cross section is observed along the longitudinal axis of the cylinder, the combustion chamber roof has different contours, such as straight, curved, etc.

[0019] Advantageously, the end face of the housing facing the combustion chamber has a surface that corresponds to the shape or contour of the combustion chamber roof. This advantage is particularly strengthened if the end face of the housing facing the combustion chamber is also flush with the combustion chamber roof, since the opening of the bore in the cylinder head on the combustion chamber side is thereby reduced. The opening in the combustion chamber roof formed by the bore in the cylinder head influences the flow of the fuel-air mixture and the propagation of the flame in the combustion chamber. The smaller the opening in the combustion chamber roof, the less the flow of the fuel-air mixture and the propagation of the flame in the combustion chamber are hindered. Furthermore, the flow of the mixture from the combustion chamber to the opening of the bore or the intake and exhaust space of the spark plug is reduced, so that less heat is conducted from the mixture to the electrode or the housing or the spark plug, and the electrode, the housing and therefore also the spark plug absorb less heat.

[0020] In an advantageous development, the surface of the end face of the housing facing the combustion chamber is a flat surface perpendicular to the longitudinal axis of the spark plug. This development has the advantage that no further process steps are necessary when manufacturing the housing of the spark plug, since the housing typically has a flat end face facing the combustion chamber oriented perpendicular to the longitudinal axis of the spark plug. This shape of the end face of the spark plug housing is particularly advantageous in combination with the arrangement of the spark plug in the region of the cylinder head around the center point of the combustion chamber roof, especially if the end face of the housing is flush with the combustion chamber roof. This shape of the end face of the spark plug housing facing the combustion chamber is also particularly advantageous if the end face of the housing facing the combustion chamber is arranged in a bore. Spark plugs with a flat end face of the housing facing the combustion chamber can be used for cylinders with various combustion chamber roof contours.

[0021] In an alternative advantageous development, the surface of the end face of the housing facing the combustion chamber is a flat surface which forms an angle α of less than 90°, in particular an angle of more than 30°, with the longitudinal axis of the spark plug, respectively smaller angles α being observed between the surface and the longitudinal axis. This, together with the flush arrangement of the end face of the housing facing the combustion chamber with the combustion chamber roof, has the advantage that in the case of a distal arrangement of the spark plug, the end face fits more closely to the contour of the combustion chamber roof than in a spark plug with a flat surface of the end face of the housing facing the combustion chamber which is oriented perpendicular to the longitudinal axis of the spark plug. In the distal arrangement of a spark plug with a flat end face of the housing facing the combustion chamber which is oriented perpendicular to the longitudinal axis, a flush arrangement of the end face of the housing facing the combustion chamber is only partially possible, since a part or parts of the housing protrude into the combustion chamber or end in a hole. This results in unfavorable edges on the combustion chamber roof for the flow of the fuel-air mixture in the combustion chamber, which are blocked by these edges, an effect which is avoided in the case of a flat end face of the housing which is angled with respect to the longitudinal axis and which faces towards the combustion chamber.

[0022] In another alternative advantageous development, the surface of the end face of the housing facing towards the combustion chamber has the shape of a curved surface which forms an angle α with the longitudinal axis of the spark plug smaller than 90°, in particular larger than 30°, respectively smaller angles formed between the surface and the longitudinal axis X are observed. For this purpose, if the curved surface is observed in cross section and projected together with the longitudinal axis of the spark plug onto a plane, a tangent to the curved surface is tangent to the point where the curved surface intersects with the longitudinal axis of the spark plug. This tangent forms an angle of 30° to 150° with the longitudinal axis of the spark plug, and a spark plug with a curved end face of the housing facing towards the combustion chamber is particularly advantageous, since the above-mentioned advantages are also achieved in this case in the case of an off-centre arrangement of the spark plug in the cylinder head and flush with the curved combustion chamber roof.

[0023] In one development, it is provided that the cylinder, in particular the cylinder head, and / or the spark plug respectively have markings, so that the spark plug can be assembled in the cylinder in an oriented manner. This has the advantage that when assembling the spark plug in the cylinder head, the rotation angle and torque can be selected in such a way that, in the case of a spark plug whose end face of the housing facing the combustion chamber is angled to the longitudinal axis of the spark plug, the end face of the housing facing the combustion chamber can be assembled in a correctly aligned manner according to the contour of the combustion chamber roof. This is particularly advantageous when the spark plug is arranged off-center in the cylinder head and the end face of the housing facing the combustion chamber is to be arranged flush with the combustion chamber roof.

[0024] In another embodiment of the internal combustion engine according to the invention, the spark plug has a thread on the outer surface of the housing for screwing the spark plug into a hole in the cylinder head and an outer sealing surface, the housing having an unthreaded area between the outer sealing surface and the end of the thread facing away from the combustion chamber, in particular the unthreaded area being longer in the longitudinal axis of the spark plug than the thickness of the outer seal arranged on the outer sealing surface. This has the advantage that if the housing expands due to heat in the threaded area, the spark plug still makes good contact with the cylinder head at the threads facing towards the combustion chamber and therefore there is also good heat conduction, so that the spark plug or its electrodes are not overheated. In one development, the unthreaded area has a length, measured parallel to the longitudinal axis of the spark plug, that is at least 1.4 times longer than the thickness of the outer seal.

[0025] The internal combustion engine according to the invention may also have a spark plug with at least one ground electrode disposed within the housing, in particular the ground electrode being inserted into a hole formed in the housing wall.

[0026] The ground electrodes may be welded and / or press fit into the holes. The holes may be formed in or under the threaded region. At least one ground electrode may be positioned relative to the center electrode such that the electrodes form an axial or radial spark gap.

[0027] In one embodiment of the internal combustion engine according to the invention, the width of the ignition gap is given by the electrode distance between the central electrode and the at least one ground electrode, which is equal to or less than 0.4 mm, in particular equal to or less than 0.2 mm, and equal to or more than 0.05 mm, in particular equal to or more than 0.1 mm. This has the advantage that less voltage is required for ignition and the increase in the electrode distance is relatively small over the life of the spark plug. Since the construction space in the housing is necessarily limited, a small electrode distance also advantageously makes it possible to arrange the electrodes, and thus also the ignition gap, at least partially in the housing. This has the advantage that the electrodes do not protrude too far into the combustion chamber and thus absorb less heat from the combustion chamber. Thus, the spark plug absorbs relatively less heat overall, resulting in a cold spark plug, whereby undesirable self-ignition is avoided.

[0028] For example, it is advantageous for the electrode distance to be less than 0.2 mm, in particular less than 0.15 mm. The smaller the electrode distance, the less voltage is required to generate the ignition spark. It is also advantageous for the electrode distance to be at least 0.05 mm, in particular more than 0.1 mm. This ensures that the electrode distance is not too small. Very small electrode distances impose special challenges of precision in spark plug production. With small electrode distances, deviations of the ignition surfaces of the electrodes from the most parallel orientation possible have greater effects than with larger electrode distances, for example uneven wear of the ignition surfaces. The lower limit of the electrode distance is therefore a good compromise between a small electrode distance in order to reduce the required ignition voltage and wear on the one hand, and the justifiable costs for a uniformly good positioning of the ignition surfaces in spark plug production on the other hand.

[0029] The spark plug can also have multiple ground electrodes, each forming an ignition gap together with the center electrode. The above-mentioned embodiments of the electrodes and ignition gaps also apply to multiple ground electrodes and ignition gaps. By having multiple ground electrodes in the spark plug, the wear of the ignition surface can be distributed to multiple ground electrodes, and the ignition surface of each ground electrode does not require as much volume of wear-resistant material as in the case of a single ground electrode. The useful life of the spark plug is improved. For example, two ground electrodes are symmetrically arranged on the inner surface of the housing. In that case, the longitudinal axis of the spark plug is the symmetrical axis for arranging the ground electrodes. The symmetrical arrangement of the ground electrodes has the technical effect that the flow of the fuel-air mixture in the intake and exhaust space is very uniform, which further favors good ignition of the fuel-air mixture in the spark plug and good ignition stability.

[0030] For example, at least one ground electrode and / or center electrode has an ignition surface each made of a material different from the remaining electrodes, which ignition surface forms an ignition gap together with the opposing electrode, the ignition surface(s) being made of a noble metal or noble metal alloy, in particular Pt, Ir, Rh, Pd, Re, Au or alloys thereof. In this case, alloys with a high proportion of Ir are particularly advantageous, i.e. Ir is the element with the highest single proportion in the alloy. These elements or alloys containing these elements are particularly wear-resistant. The electrodes themselves are made, for example, of nickel or a nickel alloy.

[0031] The housing may be, for example, steel, low carbon steel, or stainless steel.

[0032] The spark plug does not have a cap or the like on the end face of the housing facing the combustion chamber, and the housing is open at its end facing the combustion chamber, allowing for an exchange of mixture between the interior of the housing, the intake and exhaust space of the spark plug, and the combustion chamber.

[0033] Advantageously, the internal combustion engine is configured to be operated on hydrogen or a hydrogen mixture as fuel, in particular the internal combustion engine is operated at a lambda value of at least 1.8 within at least a partial operating range. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 shows a first embodiment of an internal combustion engine according to the invention with a spark plug having a negative discharge position in the cylinder head. [Diagram 2] FIG. 2 shows a second embodiment of an internal combustion engine according to the invention with a spark plug having a negative discharge position in the cylinder head. [Diagram 3] FIG. 3 shows a third embodiment of an internal combustion engine according to the invention with a spark plug having a negative discharge position in the cylinder head. [Figure 4] FIG. 4 shows a fourth embodiment of an internal combustion engine according to the invention, with a spark plug having a negative discharge position in the cylinder head. [Diagram 5] FIG. 2 shows an embodiment of a spark plug usable in an internal combustion engine according to the present invention having a flat end face facing the combustion chamber that is oriented at an angle relative to the spark plug longitudinal axis. [Figure 6] FIG. 2 shows an embodiment of a spark plug usable in an internal combustion engine according to the present invention having a curved end face facing the combustion chamber that is oriented at an angle relative to the spark plug longitudinal axis. [Figure 7] 1 shows an embodiment of a spark plug that can be used in an internal combustion engine according to the present invention; [Figure 8] FIG. 1 shows another embodiment of a spark plug that can be used in an internal combustion engine according to the present invention. [Figure 9] 1 shows a prior art internal combustion engine in which a spark plug is positioned in a cylinder head in a positive discharge position. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] FIG. 1 shows a simplified cross-sectional view of an internal combustion engine 1 according to a first embodiment of the invention. The internal combustion engine 1 may comprise several cylinders 10, only one of which is shown in FIG. 1. The cylinder 10 has a combustion chamber 15, which is bounded by a piston movable therein, by a cylinder side wall 11 and at its upper end by a combustion chamber roof 13. The combustion chamber roof 13 is formed by a cylinder head 12 of the internal combustion engine 1. The combustion chamber roof 13 is preferably conically or tapered upwards, in particular with the roof apex forming the centre point of the combustion chamber roof 13. In that case, the centre point lies in the centre of the cylinder 10, in particular on the central axis 16 of the cylinder, which is in particular circular. The cylinder has an inner radius R 15 extending from the central axis 16 of the cylinder to the cylinder side wall 11. B has.

[0036] Although not shown here, the cylinders 10 may have gas exchange openings, such as at least one intake opening through which fresh air can enter the combustion chamber 15, and at least one exhaust opening through which exhaust gases after combustion can exit the combustion chamber 15. Furthermore, the internal combustion engine 1 may have, for each cylinder 10, a combustion chamber fuel injector arranged to inject fuel directly into the combustion chamber 15, or an intake manifold fuel injector arranged to inject fuel into an intake manifold connected to the combustion chamber 15 via the intake opening.

[0037] In addition, the internal combustion engine 1 has a spark plug 20 for each cylinder 10. The spark plug 20 has a housing 21, an insulator 22, a central electrode 23 and a ground electrode 24. The central electrode 23 is at least partially arranged in the insulator 22, which is also at least partially arranged in the housing 21. The ground electrode 24 is arranged in the housing 21. The spark plug 20 is a spark plug that is set to ignite the fuel-air mixture in the combustion chamber 15 by means of an electric spark. For this, the spark plug 20 has a central electrode 23 and a ground electrode 24 that together form an ignition gap 25. An ignition spark can be generated between the two electrodes 23, 24. The ignition gap 25 can be arranged radially or axially with respect to the longitudinal axis X of the spark plug 20. The ignition gap 25 has a volume that is defined on the one hand by the facing faces of the electrodes 23, 24 and by the overlapping projections of these faces.

[0038] Furthermore, the spark plug 20 has a housing 21 including, for example, a thread 211 on its outer surface, by means of which the spark plug 20 can be screwed into the bore 14. As shown in Figure 1, the spark plug 20 is disposed in the bore 14 in the cylinder head 12, the bore 14 opening into the combustion chamber 15.

[0039] In the first embodiment shown in FIG. 1, the spark plug 20 is disposed within an area 40. The area 40 is formed as a circular surface of the combustion chamber roof 13, and the circular surface has a center point at the center point of the combustion chamber roof 13. In this example, the center point of the combustion chamber roof 13 and the central axis 16 of the cylinder 10 coincide with each other. The circular surface of the area 40 is formed by a circular surface that is circumferentially spaced apart from the cylinder inner radius R B 15% of radius R M When determining whether the spark plug 20 is located within the region 40, the longitudinal axis X of the spark plug 20 is observed. If the longitudinal axis X is within the region 40, the spark plug 20 is considered to be located within the region 40. In particular, the spark plug 20 is located at the center point of the combustion chamber roof 13. That is, the longitudinal axis X of the spark plug 20 and the center point of the combustion chamber roof 13 coincide.

[0040] The spark plug 20 is arranged in the bore 14 such that the end face 210 of the housing 21 facing towards the combustion chamber is flush with the combustion chamber roof 13. Furthermore, the end face 210 of the housing 21 facing towards the combustion chamber is flat and oriented perpendicular to the longitudinal axis X of the spark plug 20.

[0041] 1, the combustion chamber roof 13 may be a curved surface. Alternatively, the combustion chamber roof 13 may be comprised of multiple flat surface segments that meet at a center point of the combustion chamber roof 13.

[0042] The cylinder head 12 has a hole 14 through the combustion chamber roof 13. In this hole 14 a spark plug 20 is assembled, for example screwed in. To determine whether the ignition gap 25 of the spark plug 20 is arranged outside the combustion chamber, the contour of the combustion chamber roof is continued by an imaginary line 15a in the region of the hole. This imaginary line 15a is used as a reference plane with a value of 0 mm. A distance A30 of the ignition gap 25 to the reference plane is greater than 0 mm, the sign indicating the direction of the distance A30. The "+" sign means that the distance extends from the reference plane into the combustion chamber. The "-" sign means that the distance extends from the reference plane in the direction towards the outside and away from the combustion chamber. The ignition gap 25 advantageously has a distance 30 from the reference plane of at least 0 mm to -15 mm. For example the distance is -1 mm to -4 mm.

[0043] In the following figures, like parts of the figures have like names and like reference numbers, and for the sake of simplicity, the following figures will only describe the differences from the previous figures.

[0044] FIG. 2 shows an internal combustion engine 1 according to a second embodiment of the invention in a simplified cross-sectional view. The second embodiment differs from the first embodiment in that the end face 210 of the housing 21 facing the combustion chamber of the spark plug 20 ends in the bore 14. In this example, the ground electrode 24 is arranged in the bore 214 of the housing 21 and forms a radial ignition gap 25 together with the central electrode 23 as a side electrode. Alternatively, the ground electrode 24 may be a roof electrode and arranged in the housing 21 so as to form an axial ignition gap 25 together with the central electrode 23. In another alternative, the ground electrode 24 can also be arranged on the end face 210 of the housing 21 facing the combustion chamber, so that the ignition gap 25 is formed on the outside of the housing 21 and not on the inside as in FIG. 2. In that case, it is important that the electrodes 23, 24 are arranged in such a way that the ignition gap 24 is formed in the bore 14 of the cylinder head 12, in order that the spark plug 20 assembled in the cylinder 10 has a negative discharge position.

[0045] 3 shows an internal combustion engine 1 according to a third embodiment of the invention in a simplified cross-sectional view. The third embodiment differs from the first and second embodiments in that the end face 210 of the housing 21 of the spark plug 20 facing the combustion chamber ends in the combustion chamber 15. In that case, the ground electrode 24 is arranged in the housing 21 so that an ignition gap 25 is also formed inside the housing 21 and outside the combustion chamber 15. The ground electrode 24 can be arranged as a side electrode forming a radial ignition gap 25 together with the central electrode 23 as shown, or as a roof electrode forming an axial ignition gap 25 together with the central electrode 23.

[0046] 4 shows an internal combustion engine 1 according to a fourth embodiment of the invention in a simplified cross-section. The fourth embodiment differs from the first embodiment in that the hole 14 of the cylinder head 12, and therefore also the spark plug 20, is off-center, i.e. outside the circular area 40 whose center point is the center point of the combustion chamber roof. The spark plug 20 is arranged in the hole 14 such that its end face 210 facing towards the combustion chamber is at least partially flush with the combustion chamber roof 15. The end face 210 of the housing facing towards the combustion chamber can only be partially flush with the combustion chamber roof 13, especially if the end face 210 of the housing 21 facing towards the combustion chamber is a flat surface and the combustion chamber roof 13 does not have a straight contour in the area around the hole 14.

[0047] 5 and 6 each show the end region of the spark plug 20 facing the combustion chamber in a cross-section. The housing 21, the insulator 22 and the central electrode 23 are partially visible. The inner radius RI of the housing is shown in the intake and exhaust space, as well as the outer radius RA of the housing. The outer radius RA extends from the longitudinal axis X of the spark plug 20 to the thread tip of the thread 211 formed on the outer surface of the housing 21. The inner radius RI extends from the longitudinal axis X of the spark plug 20 to the inner surface of the housing 21 in the intake and exhaust space. In this example, the ground electrode 24 is arranged in a hole 214 in the region of the thread 211 and forms a radial ignition gap 25 together with the central electrode 23. The ignition gap 25 is defined in the radial direction by the facing surfaces of the electrodes 23, 24 and in the axial direction by the volume 251 of the projection of the facing surfaces of the electrodes 23, 24. The extent of the projection is indicated by dashed lines. The distance A30 between the ignition gap 25 and the combustion chamber roof 15 is measured precisely from the end of the ignition gap facing the combustion chamber.

[0048] In Figures 5 and 6, the end face 210 of the housing 21 facing towards the combustion chamber differs from the end face 210 of the housing 21 facing towards the combustion chamber shown in the first four figures in that the end face 210 facing towards the combustion chamber is not oriented perpendicularly to the longitudinal axis X of the spark plug 20. In Figure 5, the end face 210 facing towards the combustion chamber is a flat surface oriented at an angle to the longitudinal axis X of the spark plug 20. The surface of the end face 210 and the longitudinal axis X form an angle α. In Figure 6, the end face 210 facing towards the combustion chamber is a curved surface oriented at an angle to the longitudinal axis X of the spark plug 20. A tangent 210T touches the curved surface, which tangent forms an angle α with the longitudinal axis X. A spark plug 20 having an end face 210 of the housing 21 facing the combustion chamber oriented at an angle relative to the longitudinal axis X of the spark plug is particularly advantageous in the case of an off-center arrangement of the spark plug 20 in the cylinder head 12, where the end face 210 of the spark plug housing 21 facing the combustion chamber is flush with the combustion chamber roof 13.

[0049] In Figures 7 and 8, two alternative spark plugs 20 that can be used in the internal combustion engine 1 according to the invention are shown. In Figure 7, a spark plug 20 is shown having a number of ground electrodes 24. The ground electrodes 24 each form an ignition gap 25 with the central electrode 23. The ground electrodes 24 are here configured as side electrodes which correspondingly form a radial ignition gap 25 together with the central electrode 23.

[0050] 8, the ground electrode 24 is formed as a roof electrode that together with the center electrode 23 forms an axial ignition gap 25. Of course, the spark plug 20 can also have a roof electrode in combination with one or more side electrodes as a ground electrode.

[0051] 7 and 8 show the entire length of the spark plug 20. Also visible is an outer sealing surface 281 formed above the end of the thread 211 facing away from the combustion chamber on the outer surface of the housing 21. A sealing ring 28 is arranged on the outer sealing surface 281 as an outer seal which seals the transition between the spark plug 20 and the cylinder head 12 when the spark plug 20 is assembled in the cylinder head 12. The housing 21 has a threadless area 212 between the outer sealing surface 281 and the end of the thread facing away from the combustion chamber. In particular, this area has a length, measured parallel to the longitudinal axis X of the spark plug 20, which is greater than the thickness of the outer seal 28 arranged on the outer sealing surface 281.

[0052] In Fig. 9 an internal combustion engine is shown having a known arrangement of spark plugs in a cylinder head. The spark plug is arranged in the cylinder head so that the electrodes 23, 24 and the spark gap 25 are located in the combustion chamber. This spark plug has a positive discharge position. [Explanation of symbols]

[0053] 1. Internal combustion engine 10 Cylinders 11 Side wall 12. Cylinder head 13 Combustion chamber roof 14 holes 15 Combustion chamber 15a Virtual Line 16 Cylinder central axis 20 Spark plug 21 Housing 210 End face 211 Thread 212 Non-threaded area 251 Volume 22 Insulators 23 Center electrode 24 Ground electrode 25 Ignition gap 28 Seals, seal rings 281 Sealing surface 40 areas A30 distance R B Inner Radius R M radius X Longitudinal Axis

Claims

1. An internal combustion engine (1), at least one cylinder (10) in which a combustion chamber (15) is formed, said combustion chamber (15) being defined by a side wall (11) of said cylinder (10), a combustion chamber roof (13) formed by a cylinder head (12) of said cylinder (10) and a piston movable within said cylinder (10); an internal combustion engine comprising a spark plug (20) having a housing (21) with a longitudinal axis, the housing (21) having an end face (210) facing towards a combustion chamber, an insulator (22) arranged in the housing (21), a central electrode (23) arranged in the insulator (22), and at least one ground electrode (24) arranged in the housing (21) and forming at least one ignition gap (25) together with the central electrode (23), the spark plug (20) being assembled in a hole (14) formed in the cylinder head (12) and configured to ignite a fuel-air mixture present in the combustion chamber (15), An internal combustion engine, characterized in that the ignition gap (25) of the spark plug (20) is arranged outside the combustion chamber (5).

2. 2. An internal combustion engine (1) according to claim 1, characterized in that the ignition gap (25) has a distance (30) of at least 0 mm and at most -15 mm, in particular at least -1 mm and / or at most -4 mm, relative to the combustion chamber roof (13) of the cylinder (10), the contour of the combustion chamber roof (13) being continued by an imaginary line at the hole (14), the imaginary line (15a) being a reference plane with a value of 0 mm.

3. 3. An internal combustion engine (1) according to claim 1 or 2, characterized in that an end face (210) of the housing (21) facing towards the combustion chamber is arranged outside the combustion chamber (15), in particular within the hole (14) for the spark plug (20).

4. 3. An internal combustion engine (1) according to claim 1 or 2, characterized in that an end face (210) of the housing (20) facing towards the combustion chamber is at least partially, in particular completely, flush with the combustion chamber roof (13).

5. The spark plug (20) is arranged within a region (40), the region (40) being defined by a center point of the combustion chamber roof (13) as a center point of a circle and an inner cylinder radius R Ｂ A radius R that is 15% of Ｍ 5. An internal combustion engine (1) according to claim 1, characterized in that the inner periphery of the inner periphery of the inner periphery of the cylinder is formed by a circular surface including:

6. The spark plug (30) is not disposed outside of a region (40), and the region (40) is defined by a center point of the combustion chamber roof (13) as a center point of a circle and a radius R Ｂ A radius R that is 15% of Ｍ 5. An internal combustion engine (1) according to claim 1, characterized in that the inner periphery of the inner periphery of the inner periphery of the cylinder is formed by a circular surface including:

7. 7. An internal combustion engine (1) according to claim 1, characterized in that the end face (210) of the housing (21) facing towards the combustion chamber has a surface, the shape of which corresponds to the contour of the combustion chamber roof (13).

8. 8. An internal combustion engine (1) according to claim 7, characterized in that said surface is a flat surface perpendicular to the longitudinal axis of the spark plug (20).

9. 8. An internal combustion engine (1) according to claim 7, characterized in that the face forms an angle with the longitudinal axis X of the spark plug (20) that is smaller than 90°, in particular larger than 30°, each smaller angle formed between the face and the longitudinal axis X being observed.

10. 9. An internal combustion engine (1) according to claim 8, characterized in that the surface is a curved surface which forms an angle with the longitudinal axis X of the spark plug (20) of less than 90°, in particular more than 30°, the smaller the angle formed between the surface and the longitudinal axis X being observed.

11. 12. An internal combustion engine (1) according to claim 10 or 11, characterized in that the cylinder (10), in particular the cylinder head (12) and / or the spark plug (20), respectively, have markings, by means of which the spark plug (20) can be assembled in the cylinder (10) in an oriented manner.

12. 12. The internal combustion engine (1) according to claim 1, wherein the spark plug (20) has a thread (211) on the outer surface of the housing (21) for screwing the spark plug (20) into the hole (14) formed in the cylinder head (21) and an outer sealing surface (281), the housing (21) having an unthreaded area (212) between the outer sealing surface (281) and an end of the thread opposite the combustion chamber, in particular the unthreaded area being longer in the longitudinal axis of the spark plug (20) than a thickness of an outer seal (28) arranged on the outer sealing surface (281).

13. 13. The internal combustion engine (1) according to claim 1, characterized in that the width of the ignition gap (25) is given by an electrode distance between the central electrode (23) and the at least one ground electrode (24), and the electrode distance between the central electrode (23) and the at least one ground electrode (24) is equal to or less than 0.4 mm, in particular equal to or less than 0.2 mm, and equal to or more than 0.05 mm, in particular equal to or more than 0.1 mm.

14. The internal combustion engine (1) according to any one of claims 1 to 13, characterized in that the internal combustion engine (1) can be operated using hydrogen or a hydrogen mixture as fuel, in particular at a lambda value of at least 1.8 within at least a partial operating range.

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