Spark plug with projection on a combustion chamber-side planar housing end face

Abstract

The invention relates to a spark plug (1) with a longitudinal axis X, having: - a housing (2) with a combustion chamber-side planar end face (21) which spans a plane E, and a thread (22) formed on its outer side (22), as a result of which a thread region is formed on the outer side of the housing (2), - an insulator (3), - a central electrode (4), - a ground electrode (5), - a spark gap (45) which is formed by the ground electrode (5) and the central electrode (4), wherein the combustion chamber-side planar end face (21) has a projection (25) which extends parallel to the longitudinal axis X of the spark plug (1) from the planar end face (21) in the direction of a combustion chamber, wherein a bore hole (20) with the diameter DB, in which the ground electrode (5) is arranged, is at least partially formed in the projection (25) and / or wherein a distance from the combustion chamber-side edge of the bore hole (20) to the combustion chamber-side end of the projection (25) is at least 0.5 mm.

Description

[0001] Description

[0002] title

[0003] Spark plug with projection on a flat surface on the combustion chamber side

[0004] Housing face

[0005] State of the art

[0006] The invention relates to a spark plug.

[0007] Spark plugs have been around for over 100 years, providing an ignition spark in internal combustion engines to ignite a fuel-air mixture at the right time. Over time, spark plugs have been used for various fuels such as gasoline, ethanol, methanol, CNG (compressed natural gas), hydrogen, or mixtures thereof.

[0008] Conventional spark plugs have a housing with a flat end face facing the combustion chamber. One or more ground electrodes are arranged or welded onto this flat end face and are then bent into the correct position to establish a defined axial or radial electrode spacing from a centrally positioned center electrode. This ground electrode is called a hook electrode. Depending on the application, the end face of the housing is approximately flush with the combustion chamber roof, so that the ground electrode always protrudes into the combustion chamber and absorbs a lot of heat from the combustion chamber. Conventional spark plugs have a positive spark position because the ignition gap, where the sparks are generated, is located outside the spark plug housing and typically within the combustion chamber. There are also spark plug designs in which the ignition gap is formed within the housing.In these concepts, the ground electrode is inserted into a through-hole formed in the housing wall, for example. When the end face of the housing is roughly flush with the combustion chamber roof, the ignition gap is located outside the combustion chamber. These spark plugs then have a negative spark position. Furthermore, these spark plugs have a relatively large breathing chamber volume, since in addition to the insulator and the center electrode, the ground electrode and the ignition gap are also located in the breathing chamber of the housing. Large breathing chambers have the challenge that they cannot be purged sufficiently, so that hot gases accumulate in the breathing chamber, leading to additional heat input both to the spark plug components and to the fresh, combustible fuel-air mixture.

[0009] If the ignition gap intersects the plane of the combustion chamber roof, which can be approximated as a plane near the spark plug position, then this is referred to as a neutral spark position. When spark plugs are mounted so that the combustion chamber-side end face of the housing lies in the plane of the combustion chamber roof, spark plugs in which the ignition gap intersects the plane spanned by the combustion chamber-side end face are considered to have a neutral spark position.

[0010] The axial or radial ignition gap is the volume between the center electrode and the ground electrode, whereby the volume of the ignition gap is limited by the ignition surfaces of the respective electrode and by the overlap of the projections of the ignition surfaces on each other.

[0011] Recently, spark plug development has focused on the development and optimization of spark plugs for hydrogen engines. Very low ignition energies are sufficient for hydrogen ignition. Even hot components can be sufficient to ignite the hydrogen-air mixture. Any ignition not triggered by the ignition spark is undesirable and should be avoided whenever possible.

[0012] It is therefore the object of this invention to provide a hydrogen spark plug that prevents unwanted ignition. Disclosure of the invention

[0013] Current findings in the development of hydrogen spark plugs (H2 spark plugs), which are specially developed for operation in a hydrogen engine, include the fact that the spark plugs must be as cold as possible and require a well-rinsed breathing space in the housing.

[0014] Cold spark plugs are characterized, among other things, by their very good heat dissipation from the electrodes via the cooler housing into the cylinder head as a heat sink. This goal can be achieved, for example, with a short insulator base, a short center electrode, a small seat offset (this refers to the axial distance from the contact surface of the center electrode in the insulator to the inner sealing ring), a small ground electrode protrusion, and a low spark position. The spark position is measured in relation to the combustion chamber roof. A low spark position means that the ignition gap, where the sparks are generated, is as close as possible to the combustion chamber roof. Applied to a spark plug whose combustion chamber-side end face of the housing lies in the plane of the combustion chamber roof, this means that with a spark plug with a low spark position, the ignition gap is as close as possible to the combustion chamber-side end face.

[0015] Advantage of the invention

[0016] This problem is solved by the spark plug according to the invention.

[0017] The spark plug according to the invention has a longitudinal axis X and comprises a housing with a flat end face on the combustion chamber side, which spans a plane E, and a thread formed on its outer side, whereby a threaded region is formed on the outer side of the housing. Furthermore, the spark plug has an insulator, a center electrode, a ground electrode, and an ignition gap formed by the ground electrode and the center electrode. On the flat end face on the combustion chamber side, the spark plug has a projection which extends parallel to the longitudinal axis X of the spark plug from the flat end face in the direction of a combustion chamber, wherein a bore with the diameter DB, in which the ground electrode is arranged, is formed at least partially in the projection.

[0018] This offers the advantage that the spark plug can have a neutral or slightly positive spark position while simultaneously maintaining a small breathing chamber. The breathing chamber within the housing can be made very small because the ground electrode is located close to the combustion chamber end of the spark plug and not necessarily completely within the housing. This improves the scavenging behavior of the breathing chamber and prevents hot gas from accumulating in the breathing chamber and undesirably overheating the insulator, the inner housing wall, or the center electrode. Overall, the result is a spark plug with a laterally positioned ground electrode that has a good thermal connection to the housing and a small, easily scavenged breathing chamber.

[0019] As an alternative to at least partially arranging the bore in the projection, the distance from the combustion chamber-side edge of the bore to the combustion chamber-side end of the projection is at least 0.5 mm. This offers the advantage that the spark plug can also have a slightly negative spark position. In this case, for example, the bore would be formed in the housing wall. Furthermore, it has the advantage that the bore is sufficiently far from the combustion chamber-side end of the projection to ensure that there is sufficient material available for the ground electrode to be safely and reliably positioned and secured in the bore. If the ground electrode is welded in place, sufficient material from the projection is available for the weld seam. Furthermore, a certain amount of material must be present around the bore and the ground electrode so that the projection can transfer the heat absorbed by the ground electrode to the housing and cylinder head sufficiently quickly.

[0020] The combination of the features that the bore in which the ground electrode is arranged is at least partially formed in the projection and a distance of at least 0.5 mm from the edge of the bore on the combustion chamber side to the end of the projection on the combustion chamber side results in the above-mentioned advantages. For all three variants, the neutral or slightly positive or slightly negative spark position results from the arrangement of the ground electrode close to the combustion chamber end of the spark plug. Another advantage is that the ground electrode does not protrude as far into the combustion chamber as with a conventional spark plug which has a hook electrode as the ground electrode, and therefore absorbs less heat from the combustion chamber. If the ground electrode is short and rod-shaped, there is a further advantage that the heat paths from the ground electrode to the cooled housing are short, thus optimising heat transport from the ground electrode via the housing into the cylinder head.

[0021] Advantageous further training is the subject of the subclaims.

[0022] In a further development, the projection has a wall thickness h around the bore. For example, the wall thickness h can vary along the circumference of the bore. The wall thickness h is measured radially to the longitudinal extent of the bore. Advantageously, the wall thickness h is at least 0.5 mm. This ensures that the projection has sufficient wall volume so that the ground electrode can be placed and fastened safely and reliably in the bore. When the ground electrode is welded in place, sufficient material from the projection is available for the weld seam. Furthermore, a certain amount of material must be around the bore and around the ground electrode so that the projection can transfer the heat absorbed by the ground electrode to the housing and a cylinder head quickly enough.

[0023] In a further embodiment, the projection has a height L in relation to the flat end face on the combustion chamber side, where L > 0. The height L is a measure of how far the projection protrudes from the plane E spanned by the flat end face on the combustion chamber side. In particular, L < 5 mm. Further in particular, L < 2.5 mm. L must be greater than 0 so that the ignition gap lies on or in plane E and a slightly negative, neutral or slightly positive spark position results in relation to the end face on the combustion chamber side. At the same time, L must not be too large so that the projection and the ground electrode are not too far away from plane E and, in the case of a spark plug installed in a cylinder head, protrude too far into the combustion chamber and thus negatively influence the heat balance of the spark plug. For L > 5 mm, spark positions can result that can also be achieved with a conventional spark plug with a hook electrode.Furthermore, the larger L is, the more the projection projects beyond the plane E of the flat end face on the combustion chamber side and into a possible combustion chamber, whereby the advantages described above regarding reduced heat absorption are reduced.

[0024] The projection can, for example, have a round, square, cylindrical, elliptical, trapezoidal or oval shape.

[0025] Additionally or alternatively, it is advantageous if the ignition gap is partially formed within the housing. The volume of the ignition gap intersects the plane E of the flat end face on the combustion chamber side.

[0026] For example, approximately half of the ignition gap volume is located within the housing, i.e., on the side of plane E facing away from the combustion chamber. This ensures that the spark plug has a neutral spark position.

[0027] Alternatively, the ignition gap is formed within the housing and does not intersect plane E, wherein a distance from a boundary of the ignition gap facing plane E to plane E is 0 mm or greater, and in particular less than 0.5 mm. This results in a slightly negative spark position for the spark plug.

[0028] Alternatively, it is also advantageous if the ignition gap is formed outside the housing and plane E does not intersect the ignition gap, so that a boundary of the ignition gap facing plane E has an axial distance from plane E of 0 mm or greater and (L - h - DB) or less, where L < 5 mm and h > 0.5 mm. This results in a slightly positive spark position for the spark plug.

[0029] Spark plugs typically have a breathing chamber formed within the housing and extending from the combustion chamber end of the insulator to a plane E of the combustion chamber end face of the housing.

[0030] In a further embodiment, the spark plug according to the invention has a breathing chamber whose volume is less than 200 mm 3 In particular, the volume is less than 120 mm 3 This is especially true for spark plugs with a thread smaller than M14. This ensures that the breathing chamber is not too large and can be easily flushed out. Good flushing is important to prevent the hot combusted gases from accumulating in the breathing chamber and thereby transferring heat to the insulator, center electrode, or the inner wall of the housing, which could lead to unwanted ignition of the components.

[0031] Advantageously, in one embodiment, the hole into which the ground electrode is inserted is formed on the combustion chamber side of the threaded area in the housing. As a result, the hole is not located in the threaded area. This makes it possible to achieve a neutral, slightly positive, or slightly negative spark position for the spark plug.

[0032] The hole in the projection is typically a through hole that extends radially to the longitudinal axis X of the spark plug from the inside to the outside of the projection.

[0033] The ground electrode is pressed, screwed, and / or welded into the hole, for example. This ensures that the ground electrode is securely fastened in the hole.

[0034] The ignition gap, for example, has a width of less than or equal to 0.3 mm. This distance is sufficient for the ignition of hydrogen, since hydrogen ignition requires less energy than, for example, the ignition of a gasoline-air mixture.

[0035] In one embodiment of the spark plug, it has a second projection on the flat end face on the combustion chamber side. The second projection, like the projection parallel to the longitudinal axis X of the spark plug, extends from the flat end face on the combustion chamber side in the direction of a combustion chamber, wherein a further bore, in which a second ground electrode is arranged, is formed at least partially in the second projection, or wherein a distance from the edge of the bore on the combustion chamber side to the end of the projection on the combustion chamber side is at least 0.5 mm. The first and second projections with the first and second ground electrodes are arranged symmetrically about the longitudinal axis of the spark plug on the flat end face on the combustion chamber side. For example, the spark plug can also have a plurality of projections, in each of which a bore for a ground electrode is formed at least partially, and in which a ground electrode is arranged.

[0036] In a further development, it is provided that the combustion chamber-side flat end face has three or four projections which, like the first and second projections, extend parallel to the longitudinal axis X of the spark plug from the flat end face in the direction of a combustion chamber, wherein in the third or fourth projection, at least partially a bore is formed in each case, in which a further ground electrode is arranged, or wherein a distance from the combustion chamber-side edge of the bore to the combustion chamber-side end of the projection is at least 0.5 mm

[0037] In particular, the projections can have different heights, which allows a spark plug to be produced with different spark positions. For example, a spark plug can have a neutral, a slightly positive and a slightly negative spark position.

[0038] Furthermore, the invention also relates to a hydrogen engine powered by a hydrogen-containing fuel. The hydrogen engine has at least one cylinder and a combustion chamber associated with this cylinder, with a combustion chamber roof. The spark plug according to the invention is mounted in the cylinder in such a way that the spark plug has a neutral, slightly positive, or slightly negative spark position.

[0039] drawing

[0040] Figure 1 shows two examples of a spark plug according to the state of the art

[0041] Figure 2 shows a section of three examples of the spark plug according to the invention

[0042] Figure 3 shows the external view of an example of the spark plug according to the invention from two perspectives

[0043] Description of the exemplary embodiment Figure 1 shows, for two examples, each of the combustion chamber-side half of a spark plug 100 according to the prior art in a sectional view. The spark plug 100 has a longitudinal axis X that extends from the end of the spark plug 100 facing away from the combustion chamber. The spark plug 100 has a housing 200 that has a longitudinal bore parallel to the longitudinal axis X of the spark plug 100. The housing 200 has, at its combustion chamber-side end, a flat end face 210 on the combustion chamber side. On its outer side, the housing 200 typically has a thread 220 with which the spark plug 100 can be screwed into a cylinder head. The thread area typically extends from the start of the thread 222 on the combustion chamber side to the end of the thread facing away from the combustion chamber.

[0044] The insulator 300 is arranged and secured within the housing 200. The center electrode 400 typically protrudes from the insulator 300 at the combustion chamber end.

[0045] In the example shown in Figure 1 a), the ground electrode 400 projects into the breathing space 310 of the housing 200.

[0046] In this example, the ground electrodes 500 are inserted into holes formed in the housing wall and arranged in the threaded area. The holes are through holes that extend from the outside to the inside of the housing 200. The ground electrodes 500, together with the center electrode 400, each form a radial ignition gap 450. The radial ignition gap 450 is the volume between the mutually facing ignition surfaces of the electrodes 400, 500. In the axial direction, the ignition gap 450 is limited by the axial overlap of the projections of the ignition surfaces.

[0047] Since the spark plug 100 is typically mounted in a cylinder head such that the combustion chamber-side end face 210 of the housing 200 is flush with the combustion chamber roof, or alternatively, such that the thread start 222 is flush with the combustion chamber roof, this spark plug 100 clearly has a negative spark position according to Figure 1a). In the example shown in Figure 1b), the center electrode 400 protrudes from the breathing chamber 310.

[0048] In this example, the ground electrode 500 is arranged as a hook electrode on the combustion chamber-side end face of the housing 200. The ground electrodes 500, together with the center electrode 400, each form an axial ignition gap 450. The axial ignition gap 450 is the volume between the mutually facing ignition surfaces of the electrodes 400, 500. In the radial direction, the ignition gap 450 is limited by the radial overlap of the projections of the ignition surfaces.

[0049] Since the spark plug 100 is typically mounted in a cylinder head such that the combustion chamber-side end face 210 of the housing 200 lies in the same plane as the combustion chamber roof, or alternatively such that the thread start 222 lies in the plane of the combustion chamber roof, this spark plug 100 according to Figure 1 b) clearly has a positive spark position.

[0050] Figure 2 shows a schematic sectional view of the combustion chamber-side half of the spark plug 1 according to the invention for several exemplary embodiments.

[0051] In all of the exemplary embodiments shown, the spark plug 1 has a longitudinal axis X and a housing 2 with a flat end face 21 on the combustion chamber side. The flat end face 21 on the combustion chamber side defines a plane E which is perpendicular to the longitudinal axis X of the spark plug 1. On the combustion chamber side, a projection 25 extends from this plane E from the flat end face 21 on the combustion chamber side. A bore 20, into which a ground electrode 5 is inserted, is formed at least partially in this projection 25. The bore 20, into which the ground electrode 5 is inserted, is formed partly in the projection 25 and with its remaining part in the housing wall. The bore 20 extends in the projection 25 and in the housing 2 radially to the longitudinal axis X of the spark plug 1. In this example, the projection 25 has a height of L, where L is approximately the sum of the wall thickness h of the projection 25 and half the diameter DB of the bore 20.

[0052] Along the circumference of the bore 20 into which the ground electrode 5 is inserted, the projection 25 has a wall thickness h measured radially to the longitudinal axis of the bore 20. The longitudinal axis of the bore 20 extends perpendicular to the longitudinal axis X of the spark plug 1. The wall thickness h can vary along the circumference of the bore 20, as shown in Figure 3 c).

[0053] On the outside of the housing 2, a thread 22 is formed, with which the spark plug 1 can be screwed into a cylinder head. The combustion chamber-side thread start 22a of the thread 22 is located away from the plane E of the flat end face 21 facing the combustion chamber and the ground electrode 5. The bore 20 for the ground electrode 5 is arranged in a thread-free section of the housing 2 and the projection 25.

[0054] The breathing chamber 31 of the housing 2 extends from the combustion chamber-side end of the insulator 3 to the plane E of the combustion chamber-side flat end face 21. In this example, the radial ignition gap 45, which is formed between the ground electrode 5 and the center electrode 4, is partially arranged in the breathing chamber 31. The center electrode 4 protrudes beyond the plane E of the combustion chamber-side flat end face 21 of the housing 2. Accordingly, the ignition gap 45 also partially protrudes beyond the plane E. The spark plug 1 has a neutral spark position relative to the combustion chamber-side flat end face 21. Depending on how the spark plug 1 is mounted in a cylinder according to this example, the spark plug 1 has a neutral or a slightly positive spark position with respect to the combustion chamber roof if the flat end face 21 on the combustion chamber side or the thread start 22a on the combustion chamber side is in a plane with the combustion chamber roof.

[0055] The second exemplary embodiment according to Figure 2 b) differs from the first exemplary embodiment according to Figure 2 a) in that in the second exemplary embodiment the spark plug 1 has two projections 25, each with an inserted ground electrode 5. The projections 25 and ground electrodes 5 are arranged symmetrically along the circumference of the flat end face 21 on the combustion chamber side. The ground electrodes 5 each form an ignition gap 45 with the center electrode 4. In this exemplary embodiment, the ignition gap 45 lies partly within the housing 2 and thus in the breathing chamber 31 of the housing 2 and partly outside the housing 2. Relative to the plane E spanned by the flat end face 21 on the combustion chamber side, the spark plug 1 has a neutral spark position.The third embodiment according to Figure 2 c) differs from the second embodiment according to Figure 2 b) in that in the third embodiment, the spark plug 1 has two projections 25a, 25b, each with an inserted ground electrode 5a, 5b, wherein the two projections 25a, 25b have different heights L1, L2. The first projection 25a with height L1 is higher than the second projection 25b with height L2. This results in two ignition gaps 45a, 45b with different distances from plane E.

[0056] The first ignition gap 45a is formed between the first ground electrode 5a and the center electrode 4. The first ground electrode 5a is arranged in the first projection 25a, which has a height L1. The first ignition gap 45a does not intersect the plane E and has a distance from the plane E of a maximum of (L- h - DB), as a result of which the spark plug 1 has a first ignition gap 45a with a slightly positive spark position.

[0057] The second ignition gap 45b is formed between the second ground electrode 5b and the center electrode 4. The second ground electrode 5b is arranged in the second projection 25b, which has a height L2. The second ignition gap 45a intersects the plane E, thus the spark plug 1 has a second ignition gap 45b with a neutral spark position.

[0058] In a design not shown here, the spark plug can have a projection with L < 0.5 mm, whereby the bore is not formed in the projection but in the housing wall. The edge of the bore on the combustion chamber side has a distance to plane E of less than 0.5 mm. The projection is arranged such that the distance from the edge of the bore on the combustion chamber side to the end of the spark plug on the combustion chamber side is at least 0.5 mm. The end of the projection and the spark plug on the combustion chamber side are identical in this case. Due to the projection, there is enough material on the combustion chamber side of the bore for a ground electrode to be placed and fastened firmly in the bore.

[0059] Figure 3 shows an external view of the embodiments according to Figure 2 of the spark plug 1 according to the invention. Identical components have the same reference numerals as in Figure 2. Figure 3 a) corresponds to the second embodiment. Figure 3 b) corresponds to a view of the view according to Figure 3 a) rotated by 90° around the longitudinal axis. The view shown in Figure 3 b) can also represent the first embodiment according to Figure 2 a). Figure 3 c) shows an enlargement of the view according to Figure 3 b) so that the combustion chamber-side end of the housing 2 with the projection 25 can be better seen.

[0060] In Figure 3 c) it can be clearly seen that the bore 20, in which the ground electrode 5 is inserted, is arranged partly in the projection 25 and partly in the housing 2. Furthermore, it can be seen that the thread 22 is facing away from the combustion chamber to the bore 20 and significantly spaced from the

[0061] projection 25 is formed.

[0062] Figure 3 c) clearly shows the wall thickness h of the projection 25 along the circumference of the bore 20. The wall thickness h varies. Thus, h1, the wall thickness of the projection 25 parallel to the longitudinal axis X of the spark plug 1, is smaller than a wall thickness h2, which is the wall thickness at an angle of approximately 50° to the wall section of the projection 25 with the wall thickness h1.

Claims

Claims 1 . Spark plug (1) with a longitudinal axis X, comprising: - A housing (2) with a combustion chamber-side flat end face (21) which spans a plane E, and a thread (22) formed on its outer side, whereby a threaded area is formed on the outer side of the housing (2), - An insulator (3), - A central electrode (4), - A ground electrode (5), - An ignition gap (45) formed by the ground electrode (5) and the center electrode (4), characterized in that the combustion chamber-side planar end face (21) has a projection (25) extending parallel to the longitudinal axis X of the spark plug (1) from the planar end face (21) in the direction of a combustion chamber, wherein a bore (20) with the diameter DB, in which the ground electrode (5) is arranged, is formed at least partially in the projection (25) and / or wherein a distance from the combustion chamber-side edge of the bore (20) to the combustion chamber-side end of the projection (25) is at least 0.5 mm 2. Spark plug (1) according to claim 1, characterized in that - the projection (25) has a wall thickness h around the bore (20), in particular that the wall thickness h varies along the circumference of the bore (20).

3. Spark plug (1) according to claim 2, characterized in that the wall thickness h is at least 0.5 mm.

4. Spark plug (1) according to one of the preceding claims, characterized in that the projection (25) has a height L in relation to the combustion chamber-side flat end face (21), where L > 0 and in particular L < 5 mm.

5. Spark plug (1) according to one of the preceding claims, characterized in that the ignition gap (45) is partially formed within the housing (2) and intersects the plane E of the combustion chamber-side flat end face (21).

6. Spark plug (1) according to one of the preceding claims 1-5, characterized in that the ignition gap (45) is formed within the housing (2) and does not intersect the plane E, wherein a distance from a boundary of the ignition gap (45) facing the plane E to the plane E is 0 mm or greater, and in particular less than 0.5 mm 7. Spark plug (1) according to one of the preceding claims 2-5, characterized in that the ignition gap (45) is formed outside the housing (2) and does not intersect the plane E, wherein a boundary of the ignition gap (45) facing the plane E has a distance from the plane E of 0 mm or greater and (L - h - DB) or less in the axial direction.

8. Spark plug (1) according to one of the preceding claims, characterized in that a breathing chamber (31) which is formed within the housing (2) and extends from the combustion chamber-side end (30) of the insulator (3) to plane E of the combustion chamber-side flat end face (21) of the housing (2) has a volume of less than 200 mm 3 , especially smaller than 120 mm 3 has.

9. Spark plug (1) according to one of the preceding claims, characterized in that the bore (20) into which the ground electrode (5) is inserted is formed on the combustion chamber side of the threaded area in the housing (2).

10. Spark plug (1) according to one of the preceding claims, characterized in that the combustion chamber-side flat end face (21) has a second projection (25a) which, like the first projection (25), extends parallel to the longitudinal axis X of the spark plug (1) from the flat end face (21) in the direction of a combustion chamber, wherein a further bore (20b), in which a second ground electrode (5b) is arranged, is formed at least partially in the second projection (25b) and / or wherein a distance from the combustion chamber-side edge the respective bore (20) to the combustion chamber end of the respective projection (25) is at least 0.5 mm 11. Spark plug (1) according to claim 11, characterized in that the combustion chamber-side flat end face (21) has three or four projections (25) which, like the first and the second projection (25a, 25b), extend parallel to the longitudinal axis X of the spark plug (1) from the flat end face (21) in the direction of a combustion chamber, wherein in the third and in the fourth projection (25) in each case at least partially a bore (20) is formed, in which a further ground electrode (5) is arranged and / or wherein a distance from the combustion chamber-side edge of the respective bore (20) to the combustion chamber-side end of the respective projection (25) is at least 0.5 mm.

12. Spark plug (1) according to claim 11 or 12, characterized in that the projections (25a, 25b) have different heights L.

13. Hydrogen engine with a cylinder and a combustion chamber belonging to the cylinder with a combustion chamber roof, characterized in that the spark plug (1) according to one of the preceding claims is mounted in the cylinder and is mounted so that the spark plug (1) has a neutral or a slightly positive or a slightly negative spark position.

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