Spark plug with a protrusion on the flat housing end surface facing the combustion chamber

Abstract

The spark plug (1) has a longitudinal axis X, and includes a housing (2) having a flat end face (21) facing the combustion chamber and defining a plane E, and threads (22) formed on the outer surface of the housing (2), thereby forming a threaded region on the outer surface of the housing (2); an insulator (3); a center electrode (4); a ground electrode (5); and a spark gap (45) formed by the ground electrode (5) and the center electrode (4). The flat end face (21) facing the combustion chamber has a protrusion (25), which extends from the flat end face (21) toward the combustion chamber parallel to the longitudinal axis X of the spark plug (1) and has a diameter D. B and wherein the hole (20) in which the ground electrode (5) is disposed is at least partially formed within the protrusion (25), and / or the distance from the edge of the hole (20) on the combustion chamber side to the end of the protrusion (25) on the combustion chamber side is at least 0.5 mm.

Description

[Technical Field]

[0001] The present invention relates to a spark plug. [Background technology]

[0002] Spark plugs have been known for over 100 years to provide the ignition spark in an internal combustion engine to ignite the fuel-air mixture at the correct time. Over time, spark plugs have been used for a variety of fuels, such as gasoline, ethanol, methanol, CNG (Compressed Natural Gas), hydrogen, or mixtures thereof.

[0003] Conventional spark plugs have a housing with a flat end surface facing the combustion chamber. One or more ground electrodes are disposed or welded to this flat end surface and then bent into position to achieve a specific axial or radial electrode spacing relative to a centrally located center electrode. These ground electrodes are called hook electrodes. Depending on the application, the end surface of the housing terminates approximately at the combustion chamber roof. As a result, the ground electrode always extends into the combustion chamber and receives a significant amount of heat from the combustion chamber. Conventional spark plugs have a positive spark position because the spark gap, where the spark occurs, is located outside the spark plug housing and typically within the combustion chamber.

[0004] Furthermore, there are several spark plug concepts in which the spark gap is formed in the housing. In these concepts, the ground electrode is inserted, for example, into a through-hole formed in the housing wall. If the end face of the housing also terminates approximately at the combustion chamber roof, the spark gap is located outside the combustion chamber. These spark plugs have a negative spark position in this case. Furthermore, these spark plugs have a relatively large ventilation chamber volume because, in addition to the insulator and center electrode, the ground electrode and the spark gap are also located within the ventilation chamber of the housing. A large ventilation chamber presents the problem that it cannot be purged sufficiently well, resulting in the accumulation of hot gases within the ventilation chamber, which leads to additional heat input to both the spark plug components and the fresh, combustible fuel-air mixture.

[0005] When the spark gap intersects with a plane of the combustion chamber roof that can be approximated as a plane in the vicinity of the spark plug position, this is called a neutral spark position. When the spark plug is installed so that the end face of the housing on the combustion chamber side is located within the plane of the combustion chamber roof, the spark plug whose spark gap intersects with the plane defined by the end face on the combustion chamber side is considered to have a neutral spark position.

[0006] The axial spark gap or radial spark gap, respectively, is the volume between the center electrode and the ground electrode, and the spark gap volume is defined by the firing surfaces of the respective electrodes and the overlap of the projections of these firing surfaces onto each other.

[0007] Recently, spark plug development has focused on developing and optimizing spark plugs for hydrogen engines. Extremely low ignition energy is sufficient for hydrogen ignition. Already hot parts can be sufficient to ignite a hydrogen-air mixture. Any ignition not triggered by an ignition spark is undesirable and should be avoided as much as possible. Summary of the Invention [Problem to be solved by the invention]

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a spark plug for hydrogen in which undesired ignition is avoided.

[0009] The latest developments in the development of hydrogen spark plugs (H2 spark plugs) that are specifically developed for operation in hydrogen engines are that the spark plugs must be as cool as possible and require a well-scavenged vent chamber within the housing.

[0010] Cold-type spark plugs are characterized, inter alia, by their excellent heat conduction from the electrode through the relatively cool housing into the cylinder head as a heat sink. This can be achieved, for example, by a short insulator leg, a short center electrode, a small offset (the offset refers to the axial distance from the center electrode's seating surface in the insulator to the inner sealing ring), a small ground electrode overhang, and a low spark position. The spark position is measured with respect to the combustion chamber roof. A low spark position means that the spark gap, where the spark occurs, is located as close as possible to the combustion chamber roof. In the case of a spark plug whose housing's combustion chamber end lies in the plane of the combustion chamber roof, this means that the spark gap is located as close as possible to the combustion chamber end in the case of a spark plug with a low spark position. [Means for solving the problem]

[0011] The above problems are solved by the spark plug according to the present invention.

[0012] The spark plug according to the present invention comprises a housing having a longitudinal axis X, a flat end face facing the combustion chamber that defines a plane E, and threads formed on the outer surface of the housing, thereby forming a threaded region on the outer surface of the housing. The spark plug further comprises an insulator, a center electrode, a ground electrode, and a spark gap formed by the ground electrode and the center electrode. On the flat end face facing the combustion chamber, the spark plug comprises a protrusion that extends from the flat end face toward the combustion chamber parallel to the longitudinal axis X of the spark plug and has a diameter D. B A hole having a ground electrode disposed therein is formed at least partially within the protrusion. [Effects of the Invention]

[0013] This has the advantage that the spark plug can have a neutral or slightly positive spark position and at the same time have a small ventilation chamber. The ventilation chamber in the housing can be made very small because the ground electrode is located near the end of the spark plug facing the combustion chamber and is not necessarily located completely within the housing. This improves the purging behavior of the ventilation chamber and prevents hot gases from collecting in the ventilation chamber and undesirably overheating the insulator, the inner housing wall, or the center electrode. Overall, this results in a spark plug with a laterally located ground electrode, good thermal connection to the housing, and a small, well-scavenged ventilation chamber.

[0014] Instead of locating the hole at least partially within the protrusion, the distance from the combustion chamber-side edge of the hole to the combustion chamber-side end of the protrusion is at least 0.5 mm. This has the advantage that the spark plug can also have a slightly negative spark position. In this case, for example, the hole would be formed in the housing wall. Another advantage is that the hole is spaced far enough from the combustion chamber-side end of the protrusion that there is enough material to reliably and securely position and secure the ground electrode within the hole. When the ground electrode is secured by welding, the protrusion provides enough material for the weld seam. Furthermore, there must be a certain amount of material around the hole and around the ground electrode so that the protrusion can conduct the heat received by the ground electrode to the housing and cylinder head sufficiently quickly.

[0015] The combination of the features that the hole in which the ground electrode is located is formed at least partially within the protrusion and that the distance from the combustion chamber side edge of the hole to the combustion chamber side end of the protrusion is at least 0.5 mm results in the advantages listed above.

[0016] In all three variants, a neutral, slightly positive, or slightly negative spark position is achieved by positioning the ground electrode near the end of the spark plug facing the combustion chamber. A further advantage is that the ground electrode does not extend as far into the combustion chamber as in conventional spark plugs with a hook electrode, and accordingly receives less heat from the combustion chamber. A further advantage of a short, rod-shaped ground electrode is that the heat path from the ground electrode to the cooled housing is short, thereby optimizing heat transfer from the ground electrode through the housing into the cylinder head.

[0017] Advantageous developments are the subject of the dependent claims.

[0018] In one development, the protrusion has a wall thickness h around the hole. For example, the wall thickness h can vary along the circumference of the hole. The wall thickness h is measured radially to the longitudinal extension of the hole. Advantageously, the wall thickness h is at least 0.5 mm thick. This ensures that the protrusion has a sufficient wall volume so that the ground electrode can be securely and reliably positioned and fixed in the hole. When the ground electrode is fixed by welding, the protrusion provides sufficient material for the weld seam. Furthermore, there must be a certain amount of material around the hole and around the ground electrode so that the protrusion can conduct the heat received by the ground electrode to the housing and the cylinder head sufficiently quickly.

[0019] In another embodiment, the protrusion has a height L with respect to the flat end face facing the combustion chamber, where L>0. The height L is a measure of how far the protrusion extends from the plane E defined by the flat end face facing the combustion chamber. In particular, L≦5 mm. Even more particularly, L≦2.5 mm. L must be greater than 0 so that the spark gap is located along or within plane E and a slightly negative, neutral, or slightly positive spark position with respect to the end face facing the combustion chamber is achieved. At the same time, L must not be too large so that the protrusion and the ground electrode are not too far away from plane E and would extend too far into the combustion chamber when the spark plug is installed in the cylinder head, thereby negatively affecting the heat balance of the spark plug. With L>5 mm, a spark position that can be achieved with conventional spark plugs with hook electrodes can be achieved. Furthermore, the larger L, the more the protrusion protrudes from the plane E of the flat end surface facing the combustion chamber and into the combustion chamber that may be present there, and the above-described benefits of reduced heat acceptance are reduced.

[0020] The protrusions may, for example, be rounded, angular, cylindrical, elliptical, trapezoidal or oval in shape.

[0021] Additionally or alternatively, it is advantageous if the spark gap is partially formed within the housing, in which case the spark gap volume intersects with plane E of the flat end surface facing the combustion chamber. For example, approximately half of the spark 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.

[0022] Alternatively, the spark gap is formed in the housing and does not intersect with plane E, and the boundary of the spark gap facing plane E is spaced from plane E by 0 mm or more, in particular, less than 0.5 mm, thereby creating a slightly negative spark position at the spark plug.

[0023] Alternatively, the spark gap is formed outside the housing, and plane E does not intersect with the spark gap, so that the boundary of the spark gap facing plane E is axially spaced from plane E by more than 0 mm (LhD B ) where L≦5 mm and h≧0.5 mm, which results in a slightly positive spark position at the spark plug.

[0024] The spark plug typically includes a ventilation chamber formed within the housing and extending from the combustion chamber end of the insulator to a plane E on the combustion chamber end face of the housing.

[0025] In another embodiment, the spark plug of the present invention has a diameter of 200 mm. 3 The volume is preferably less than 120 mm, especially for spark plugs with threads smaller than M14. 3 This ensures that the vent chamber is not too large and is well scavenged. Good scavenging is important to ensure that hot combusted gases do not accumulate in the vent chamber and thereby carry heat to the insulator, center electrode, or inner housing walls, thereby preventing unwanted ignition of components.

[0026] Advantageously, in one embodiment, the hole into which the ground electrode is inserted is formed on the housing closer to the combustion chamber than the threaded area, so that the hole is not located within the threaded area, thereby enabling a neutral, slightly positive, or slightly negative spark position to be achieved in the spark plug.

[0027] The holes provided in the protrusions are typically through holes that extend radially from the inner surface to the outer surface of the protrusions relative to the longitudinal axis X of the spark plug.

[0028] The ground electrode is, for example, press-fit, screwed and / or welded into the hole, thereby ensuring that the ground electrode is fixed in the hole.

[0029] The ignition gap has a width of, for example, 0.3 mm or less, which is sufficient for igniting hydrogen, since the energy required for igniting hydrogen is less than that required for igniting a gasoline-air mixture, for example.

[0030] In one configuration of the spark plug, the spark plug has a second protrusion on the flat end face facing the combustion chamber, which, like the first protrusion, extends from the flat end face facing the combustion chamber parallel to the longitudinal axis X of the spark plug toward the combustion chamber, and a separate hole, in which the second ground electrode is located, is formed at least partially within the second protrusion, or the distance from the combustion chamber edge of the hole to the combustion chamber end of the protrusion is at least 0.5 mm. The first and second protrusions carrying the first and second ground electrodes are arranged symmetrically around the longitudinal axis of the spark plug on the flat end face facing the combustion chamber.

[0031] For example, the spark plug may have more protrusions, each of which has a ground electrode hole at least partially formed therein and in which the ground electrode is disposed.

[0032] In one further development, the flat end face facing the combustion chamber has three or four protrusions, which, like the first and second protrusions, extend from the flat end face towards the combustion chamber parallel to the longitudinal axis X of the spark plug, and in the third or fourth protrusion, respectively, a hole is formed at least partially, in which a further ground electrode is arranged, or the distance from the edge of the hole facing the combustion chamber to the end of the protrusion facing the combustion chamber is at least 0.5 mm.

[0033] In particular, the protrusions may have different heights, thereby realizing a spark plug with different spark positions, for example, a spark plug may have a neutral spark position, a slightly positive spark position, and a slightly negative spark position.

[0034] The present invention also relates to a hydrogen engine that runs on a fuel containing hydrogen. The hydrogen engine has at least one cylinder and a combustion chamber associated with the cylinder, the combustion chamber having a combustion chamber roof. The spark plug according to the present invention is mounted in the cylinder, specifically, the spark plug is mounted so as to have a neutral, slightly positive, or slightly negative spark position. [Brief explanation of the drawings]

[0035] [Figure 1] 1A and 1B are diagrams showing two examples of prior art spark plugs; [Figure 2] 1A to 1C are cross-sectional views showing three examples of the spark plug according to the present invention. [Figure 3] 1A to 1C are external views of an example of an ignition plug according to the present invention, as viewed from two different viewpoints. DETAILED DESCRIPTION OF THE INVENTION

[0036] FIG. 1 shows cross-sectional views of the combustion chamber-side half of two examples of prior art spark plugs 100. The spark plug 100 has a longitudinal axis X that extends from the combustion chamber-side end of the spark plug 100 to the end away from the combustion chamber. The spark plug 100 includes a housing 200 having a longitudinal bore parallel to the longitudinal axis X of the spark plug 100. The housing 200 has a flat combustion chamber-side end face 210 at the combustion chamber-side end of the housing 200. The housing 200 typically has a thread 220 on its outer surface, which allows the spark plug 100 to be screwed into a cylinder head. The thread region typically extends from a thread start point 222 on the combustion chamber side to a thread end point away from the combustion chamber.

[0037] An insulator 300 is disposed and fixed within the housing 200. A center electrode 400 typically protrudes from the insulator 300 at the end of the insulator 300 on the combustion chamber side.

[0038] In the example shown in FIG. 1 a , the ground electrode 400 projects into the ventilation chamber 310 of the housing 200 .

[0039] In this example, the ground electrode 500 is inserted into a hole formed in the housing wall and located in the threaded region. These holes are through-holes that extend from the outer surface to the inner surface of the housing 200. The ground electrode 500, together with the center electrode 400, each form a radial spark gap 450. The radial spark gap 450 is the volume between the opposing spark surfaces of the electrodes 400, 500. In the axial direction, this spark gap 450 is defined by the axial overlap of the projections of the spark surfaces.

[0040] Typically, this spark plug 100 is mounted in the cylinder head so that the combustion chamber end 210 of the housing 200 is in the same plane as the combustion chamber roof, or alternatively so that the thread start 222 is in the plane of the combustion chamber roof, so that this spark plug 100 shown in Figure 1a) has a uniquely negative spark position.

[0041] In the example shown in FIG. 1 b , the central electrode 400 protrudes from the vent chamber 310 .

[0042] In this example, the ground electrode 500 is a hook electrode located at the combustion chamber end of the housing 200. The ground electrode 500 and the center electrode 400 each form an axial spark gap 450. The axial spark gap 450 is the volume between the opposing spark surfaces of the electrodes 400, 500. In the radial direction, the spark gap 450 is defined by the radial overlap of the projections of the spark surfaces.

[0043] Typically, this spark plug 100 is mounted in the cylinder head so that the combustion chamber end 210 of the housing 200 is in the same plane as the combustion chamber roof, or alternatively so that the thread start 222 is in the plane of the combustion chamber roof, so that this spark plug 100 shown in Figure 1b) has a uniquely positive spark position.

[0044] FIG. 2 shows, in a schematic cross-sectional view, the combustion chamber-side half of a spark plug 1 according to the invention for several exemplary embodiments.

[0045] In all the illustrated embodiments, the spark plug 1 comprises a housing 2 having a longitudinal axis X and a flat end surface 21 facing the combustion chamber. The flat end surface 21 defines a plane E, which is perpendicular to the longitudinal axis X of the spark plug 1. A protrusion 25 extends from the flat end surface 21 facing the combustion chamber toward the combustion chamber of the plane E. A hole 20 is at least partially formed in the protrusion 25, and a ground electrode 5 is inserted in the hole 20. The hole 20, into which the ground electrode 5 is inserted, is formed partially in the protrusion 25, with the remainder of the hole 20 formed in the housing wall. The hole 20 extends radially relative to the longitudinal axis X of the spark plug 1, within the protrusion 25 and within the housing 2. In this example, the protrusion 25 has a height L, where L is approximately the sum of the wall thickness h of the protrusion 25 and the diameter D of the hole 20. B The sum of this and half of

[0046] Along the circumference of the hole 20 in which the ground electrode 5 is inserted, the protrusion 25 has a wall thickness h measured radially to the longitudinal axis of the hole 20, which extends perpendicular to the longitudinal axis X of the spark plug 1. Along the circumference of the hole 20, the wall thickness h may vary, as shown in FIG. 3c).

[0047] The outer surface of the housing 2 is provided with a thread 22, by means of which the spark plug 1 can be screwed into the cylinder head. The thread start 22a of the thread 22 facing the combustion chamber is located in the plane E of the flat end face 21 facing the combustion chamber and on the side of the ground electrode 5 facing away from the combustion chamber. The hole 20 for the ground electrode 5 is located in the non-threaded section of the housing 2 and the protrusion 25.

[0048] The ventilation 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 surface 21. In this example, the radial spark gap 45 formed between the ground electrode 5 and the center electrode 4 is partially located within the ventilation chamber 31. The center electrode 4 protrudes from the plane E of the combustion chamber-side flat end surface 21 of the housing 2. Accordingly, the spark gap 45 also partially protrudes from the plane E. This spark plug 1 has a neutral spark position with respect to the combustion chamber-side flat end surface 21. Depending on how the spark plug 1 of this example is installed in the cylinder, this spark plug 1 has a neutral or slightly positive spark position with respect to the combustion chamber roof when the combustion chamber-side flat end surface 21 or the combustion chamber-side thread start 22a is located in the same plane as the combustion chamber roof.

[0049] The second embodiment shown in FIG. 2b) differs from the first embodiment shown in FIG. 2a) in that in this second embodiment, the spark plug 1 has two protrusions 25, each of which has an inserted ground electrode 5. The protrusions 25 and the ground electrode 5 are arranged symmetrically around the circumference of the flat end face 21 facing the combustion chamber. The ground electrodes 5 each form a spark gap 45 with the center electrode 4. In this embodiment, the spark gap 45 is located partly within the housing 2, and thus within the ventilation chamber 31 of the housing 2, and partly outside the housing 2. With respect to the plane E defined by the flat end face 21 facing the combustion chamber, the spark plug 1 has a neutral spark position.

[0050] The third embodiment shown in FIG. 2c) differs from the second embodiment shown in FIG. 2b) in that the spark plug 1 in this third embodiment has two protrusions 25a, 25b, each with an inserted ground electrode 5a, 5b, with the two protrusions 25a, 25b having different heights L1, L2. The first protrusion 25a, having height L1, is higher than the second protrusion 25b, having height L2. This results in two spark gaps 45a, 45b, which are spaced apart from the plane E by different distances.

[0051] The first spark gap 45a is formed between the first ground electrode 5a and the center electrode 4. The first ground electrode 5a is disposed within the first protrusion 25a, and the first protrusion 25a has a height L1. The first spark gap 45a does not intersect with the plane E and is spaced from the plane E by a maximum distance (LhD). B ), so that the spark plug 1 has a first spark gap 45a with a slightly positive spark position.

[0052] The second spark gap 45b is formed between the second ground electrode 5b and the center electrode 4. The second ground electrode 5b is disposed within the second protrusion 25b, which has a height L2. The second spark gap 45a intersects with the plane E, thereby providing the spark plug 1 with the second spark gap 45b having a neutral spark position.

[0053] In one configuration not shown here, the spark plug may have a protrusion with L<0.5 mm, in which case the hole is formed in the housing wall rather than in the protrusion. The combustion chamber-side edge of the hole is spaced less than 0.5 mm from plane E. The protrusion is arranged so that the distance from the combustion chamber-side edge of the hole to the combustion chamber-side end of the spark plug is at least 0.5 mm. The protrusion and the combustion chamber-side end of the spark plug are in this case flush. Due to the protrusion, there is enough material on the combustion chamber side of the hole so that the ground electrode can be positioned and fixed firmly in the hole.

[0054] FIG. 3 shows an external view of the embodiment of the spark plug 1 according to the invention shown in FIG. 2. The same components as in FIG. 2 have the same reference numerals. FIG. 3a) corresponds in this case to a second embodiment. FIG. 3b) corresponds in this case to a view of FIG. 3a) rotated by 90° about the longitudinal axis. The view of FIG. 3b) can also be considered to represent the first embodiment shown in FIG. 2a). FIG. 3c) shows an enlarged view of FIG. 3b) in order to better see the combustion chamber-side end of the housing 2 with the projection 25.

[0055] 3c) it can be clearly seen that the hole 20 into which the ground electrode 5 is inserted is located partly in the protrusion 25 and partly in the housing 2. Furthermore, it can be seen that the thread 22 is formed on the hole 20 away from the combustion chamber and clearly spaced apart from the protrusion 25.

[0056] 3c) it is again possible to clearly see the wall thickness h of the protrusion 25 along the circumference of the hole 20. The wall thickness h varies such that h1, i.e., the wall thickness of the protrusion 25 parallel to the longitudinal axis X of the spark plug 1, is smaller than the wall thickness h2, which is the wall thickness at an angle of approximately 50° to the wall section of the protrusion 25 having the wall thickness h1. [Explanation of symbols]

[0057] 1 Spark plug (present invention) 2. Housing 3. Insulators 4 Center electrode 5 Ground electrode 5a First ground electrode 5b Second ground electrode 20 holes 21 Flat end surface on the combustion chamber side 22 threads 22a Thread start 25 Protrusion 25a First protrusion 25b Second protrusion 31 Ventilation chamber 45 Spark Gap 45a First spark gap 45b Second spark gap 100 Spark plug (conventional technology) 200 Housing 210 Flat end surface on the combustion chamber side 220 threads 222 thread start 300 Insulator 310 Ventilation Chamber 400 center electrode 450 ignition gap 500 ground electrode D B diameter E plane h, h1, h2 wall thickness L, L1, L2 height X Longitudinal Axis

Claims

1. A spark plug (1) having a longitudinal axis X, a housing (2) having a flat end surface (21) facing the combustion chamber and defining a plane E, and a thread (22) formed on an outer surface of the housing (2), thereby forming a threaded region on the outer surface of the housing (2); an insulator (3); A central electrode (4), A ground electrode (5); a spark gap (45) formed by the ground electrode (5) and the center electrode (4); In a spark plug (1) comprising: the flat end surface (21) facing the combustion chamber has a protrusion (25) that extends from the flat end surface (21) toward the combustion chamber parallel to the longitudinal axis X of the spark plug (1); Diameter D Ｂ and / or a hole (20) in which the ground electrode (5) is located is formed at least partially in the protrusion (25); and The distance from the edge of the hole (20) on the combustion chamber side to the end of the protrusion (25) on the combustion chamber side is at least 0.5 mm. A spark plug (1) characterized in that:

2. 2. The spark plug (1) according to claim 1, characterized in that the protrusion (25) has a wall thickness h around the hole (20), in particular the wall thickness h varies along the circumference of the hole (20).

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

4. 4. The spark plug (1) according to claim 1, wherein the protrusion (25) has a height L relative to the flat end face (21) facing the combustion chamber, L>0, in particular L≦5 mm.

5. 5. The spark plug (1) according to claim 1, wherein the spark gap (45) is formed partly within the housing (2) and intersects with the plane E of the flat end face (21) facing the combustion chamber.

6. 6. The spark plug (1) according to claim 1, wherein the spark gap (45) is formed in the housing (2) and does not intersect with the plane E, and the distance of the boundary of the spark gap (45) facing the plane E to the plane E is 0 mm or more, in particular less than 0.5 mm.

7. The spark gap (45) is formed outside the housing (2), does not intersect with the plane E, and the boundary of the spark gap (45) facing the plane E is axially spaced from the plane E by 0 mm or more (L-h-D Ｂ 6. A spark plug (1) according to any one of claims 2 to 5, characterized in that it has a spacing of less than 0.5 mm.

8. The ventilation chamber (31) formed in the housing (2) and extending from the combustion chamber side end (30) of the insulator (3) to the plane E of the flat end surface (21) of the housing (2) on the combustion chamber side is 200 mm ３ Less than, especially 120 mm ３ Spark plug (1) according to any one of claims 1 to 7, characterized in that it has a volume of less than 1000 .mu.m.

9. 9. The spark plug (1) according to claim 1, wherein the hole (20) into which the ground electrode (5) is inserted is formed on the combustion chamber side of the housing (2) relative to the threaded region.

10. the flat end surface (21) on the combustion chamber side has a second protrusion (25a), and the second protrusion (25a) extends from the flat end surface (21) toward the combustion chamber in parallel to the longitudinal axis X of the spark plug (1), similar to the first protrusion (25); another hole (20b) in which a second ground electrode (5b) is arranged, is formed at least partially in said second protrusion (25b); and / or the distance from the edge of each of the holes (20) on the combustion chamber side to the end of each of the protrusions (25) on the combustion chamber side is at least 0.5 mm; Spark plug (1) according to any one of claims 1 to 9, characterized in that it

11. the flat end surface (21) facing the combustion chamber has three or four protrusions (25), which, like the first and second protrusions (25a, 25b), extend from the flat end surface (21) toward the combustion chamber in a direction parallel to the longitudinal axis X of the spark plug (1); a hole (20) formed at least partially in each of the third and fourth protrusions (25), in which a further ground electrode (5) is disposed; and / or the distance from the edge of each of the holes (20) on the combustion chamber side to the end of each of the protrusions (25) on the combustion chamber side is at least 0.5 mm; Spark plug (1) according to claim 11, characterized in that

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

13. A hydrogen engine, A cylinder; a combustion chamber belonging to said cylinder; wherein the combustion chamber has a combustion chamber roof. In hydrogen engines, An ignition plug (1) according to any one of claims 1 to 12 is mounted in the cylinder, the ignition plug (1) being mounted to have a neutral, slightly positive, or slightly negative spark position. A hydrogen engine characterized by:

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