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

[0002] Most vehicles, such as passenger cars or trucks, have traditionally been powered by internal combustion engines or combustion engines that use gasoline or diesel as fuel. Mobile and stationary internal combustion engines that use natural gas or hydrogen as fuel are becoming more common. In these cases, even in hydrogen-powered internal combustion engines, the air-fuel mixture must be ignited by a spark, just like in gasoline-powered combustion engines. A spark plug is typically used for this purpose.

[0003] In hydrogen-powered internal combustion engines, the air-fuel mixture is typically set to a very lean mixture (lambda > 1.8) to meet emission regulations. This, combined with the low calorific value of the hydrogen mixture, results in a high intake air density (Ladungsdichte) and therefore a high pressure at ignition. Another peculiarity of hydrogen combustion in internal combustion engines is the interaction between the autoignition temperature and the minimum required ignition energy. As a result, a "cold spark plug" (kalte Zuendkerze) is required for application in hydrogen-powered internal combustion engines, i.e., a spark plug with a very low calorific value. The relative position of the spark plug or ignition gap (Zuendspalt) to the combustion chamber also has a significant impact on the performance of the spark plug and the internal combustion engine.

[0004] Conventional spark plugs and internal combustion engines are typically optimized for operation in gasoline-driven internal combustion engines. 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-driven internal combustion engine is shown in Figure 9. Therefore, conventional spark plugs and internal combustion engines are either unsuitable for application to hydrogen-driven internal combustion engines, or their performance will be degraded if applied to hydrogen-driven internal combustion engines. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Therefore, the object of the present invention is to provide an internal combustion engine equipped with a spark plug that satisfies the requirements imposed on hydrogen-driven internal combustion engines. [Means for solving the problem]

[0006] The above problem is solved in the internal combustion engine according to the present invention by positioning the ignition gap of the spark plug outside the combustion chamber.

[0007] The internal combustion engine according to the present invention comprises at least one cylinder and a spark plug belonging to this cylinder. The at least one cylinder has a combustion chamber defined by the side wall of the cylinder, a combustion chamber roof (Brennraumdach), and a piston that is movable within the cylinder. In this case, the combustion chamber roof is the surface of the cylinder head that defines the combustion chamber. The cylinder head has a cylinder head hole, hereafter referred to as a hole, that extends into the combustion chamber. A spark plug is assembled into this hole, for example, by being screwed in. The spark plug is set to ignite the fuel-air mixture present in the combustion chamber.

[0008] A spark plug has a longitudinal axis extending from the end of the spark plug facing the combustion chamber to the end facing the opposite end. The spark plug has a housing that includes an end face facing the combustion chamber. The housing contains an insulator and a center electrode placed in the insulator. The housing contains at least one ground electrode. The at least one ground electrode together with the center electrode forms an ignition gap. In particular, the ignition gap can be formed radially or axially with respect to the longitudinal axis of the spark plug. In this case, the width of the ignition gap is the distance between the mutually facing faces of the center electrode and the at least one ground electrode. The ignition gap is a volume (Volumen) between the ground electrode and the center electrode, which arises between the overlapping projections of the mutually opposing ignition surfaces (Zuendflaeche) of the electrodes. That is, the ignition surface of the center electrode is projected onto the ignition surface of the ground electrode, and vice versa. The volume (ueberstreichen) extending across the two projections is the volume of the ignition gap. In this case, the volume is defined by one dimension by the ignition surface and the other dimension by the overlap of the projected ignition surfaces. The ignition gap has an end on the combustion chamber side. 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 opposing electrodes.

[0009] According to the present invention, the ignition gap of the spark plug is intended to be located outside the combustion chamber. Outside the combustion chamber means that the ignition gap is inside the hole, or the combustion chamber side end of the ignition gap 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 (negative funkenlage). This has the advantage that the electrode does not protrude into the combustion chamber, or protrudes as little as possible, thereby absorbing less heat from the combustion chamber. As a result, less heat is absorbed by the spark plug, the spark plug stays cool, and thus unwanted self-ignition is avoided.

[0010] Other advantageous embodiments of the present invention are the subject of the dependent claims.

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

[0012] The characteristic of having a distance greater than 0 mm between the ignition gap and the combustion chamber roof means that the ignition gap is completely located within the hole, meaning the spark plug has a negative discharge position. This has the advantage that the electrode is as far away from the combustion chamber as possible, and therefore absorbs as little heat as possible from the combustion process occurring in the combustion chamber. Thus, it is possible to obtain the coldest possible spark plug.

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

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

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

[0016] In one advanced form of the internal combustion engine according to the present invention, the spark plug is located within the region of the cylinder head, which is a circular surface having the center point of the combustion chamber roof as the center point of the circle, and the inner cylinder radius (innerer Zylinder-Radius) R B15% radius R M It has the following characteristics. When determining whether a spark plug is located within the region, the longitudinal axis of the spark plug is observed. If the longitudinal axis is within the region, the spark plug is considered to be located within the region. In particular, the spark plug is located at the center point of the combustion chamber roof. That is, the longitudinal axis of the spark plug and the center point of the combustion chamber roof coincide. This centralized placement of the spark plug in the cylinder head and combustion chamber roof means that the spark plug is centrally located and therefore 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 present invention, the spark plug is located outside the region of the cylinder head, which is a circular surface including the center point of the combustion chamber roof as the center point of the circle, with an internal cylinder radius R B 15% radius R M The spark plug has the following characteristics. When determining whether a spark plug is positioned outside the region, the longitudinal axis of the spark plug is observed. If the longitudinal axis is outside the region or at the edge of the region, the spark plug is considered to be positioned outside the region. In other words, each placement of a spark plug that is not within the region is considered to be outside the region. This placement, which is off-center (dezentral) of the spark plug in the cylinder head and combustion chamber roof, has the advantage that the spark plug is positioned laterally in the combustion chamber roof and can be directed towards a fuel injector or gas exchange opening (Ladungswechseloeffnung) that may be in the cylinder. The placement 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 placement.

[0018] In one advantageous embodiment of the internal combustion engine according to the present invention, the end face of the housing facing the combustion chamber has a surface corresponding to the contour of the combustion chamber roof. The combustion chamber roof can have various shapes, such as a flat surface or a conical surface whose center point is on the longitudinal axis of the cylinder. The conical surface can have, for example, a hemispherical shape or one or more curved or straight surfaces that intersect at the center point of the surface. Therefore, when a cross-section is observed along the longitudinal axis of the cylinder, the combustion chamber roof has different contours, such as straight lines and curves.

[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 reduces the opening of the hole in the cylinder head on the combustion chamber side, and this advantage is particularly enhanced when the end face of the housing facing the combustion chamber is also flush with the combustion chamber roof. The opening in the combustion chamber roof formed by the hole in the cylinder head affects 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 obstructed. Furthermore, there is less flow of the mixture from the combustion chamber to the opening of the hole or the intake / exhaust space of the spark plug, which reduces the conduction of heat from the mixture to the electrode, housing, or spark plug, and consequently, less heat is absorbed by the electrode, housing, and therefore the spark plug.

[0020] In an advantageous configuration, the end face of the housing facing the combustion chamber is a flat surface perpendicular to the longitudinal axis of the spark plug. This configuration has the advantage that when manufacturing the spark plug housing, the housing typically has a flat end face facing the combustion chamber that is perpendicular to the longitudinal axis of the spark plug, thus eliminating the need for other process steps. This shape of the end face of the spark plug housing is particularly advantageous when combined with positioning the spark plug within the region of the cylinder head around the center point of the combustion chamber roof, especially when 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 when the end face of the housing facing the combustion chamber is positioned within a hole. Spark plugs with a flat end face of the housing facing the combustion chamber can be used in cylinders with various combustion chamber roof contours.

[0021] In alternative, advantageous developmental forms, the end face of the housing facing the combustion chamber is a flat surface that forms an angle α less than 90°, particularly greater than 30°, with respect to the longitudinal axis of the spark plug, and a smaller angle α is observed between the surface and the longitudinal axis. This, combined with positioning the end face of the housing facing the combustion chamber flush with the combustion chamber roof, has the advantage that the end face fits more snugly to the contour of the combustion chamber roof than a spark plug with a flat surface on the end face of the housing facing the combustion chamber that is oriented perpendicular to the longitudinal axis of the spark plug, especially in the case of a spark plug positioned away from the center. In a spark plug positioned away from the center with a flat end face of the housing facing the combustion chamber that is oriented perpendicular to the longitudinal axis, a part or part of the housing protrudes into the combustion chamber or ends within the hole, so a flush position of the end face of the housing facing the combustion chamber is only partially possible. As a result, edges are formed on the combustion chamber roof that are unfavorable to the flow of the fuel-air mixture inside the combustion chamber, and these edges obstruct the flow. This effect is avoided when the housing has flat end faces that are angled with respect to the longitudinal axis and facing the combustion chamber.

[0022] In another alternative advantageous development form, the surface of the end face of the housing facing the combustion chamber has a curved surface shape that forms an angle α smaller than 90°, particularly an angle greater than 30°, with the longitudinal axis of the spark plug, and a smaller angle formed between the surface and the longitudinal axis X is observed. For this purpose, when the curved surface is observed in cross-section and projected onto a plane together with the longitudinal axis of the spark plug, the tangent of the curved surface touches at the point where the curved surface intersects the longitudinal axis of the spark plug. This tangent that touches forms an angle of 30° to 150° with the longitudinal axis of the spark plug. The spark plug whose end face of the housing facing the combustion chamber is curved is particularly advantageous because the above-mentioned advantages are also achieved in the case of a flush arrangement with the curved combustion chamber roof and at a distance from the center of the spark plug in the cylinder head.

[0023] In one development form, it is contemplated that the cylinder, particularly the cylinder head, and / or the spark plug each have markings, whereby the spark plug can be assembled in alignment with the cylinder. This has the advantage that when assembling the spark plug into the cylinder head, in the case of a spark plug whose end face of the housing facing the combustion chamber has an angle with respect to the longitudinal axis of the spark plug, the rotation angle and torque can be selected so that the assembly can be carried out with the end face on the combustion chamber side of the housing correctly positioned and assembled according to the contour of the combustion chamber roof. This is particularly advantageous when the spark plug is arranged away from the center in the cylinder head and the end face of the housing facing the combustion chamber should be flush with the combustion chamber roof. <0********* In another embodiment of the internal combustion engine according to the present invention, the spark plug has a thread on the outer surface of the housing, the thread having a thread for screwing the spark plug into a hole formed in the cylinder head and an outer sealing surface, and the housing has a region without a thread between the outer sealing surface and the end of the thread on the side opposite to the combustion chamber. In particular, the region without a thread is longer than the thickness of the outer seal disposed on the outer sealing surface in the longitudinal axis of the spark plug. This has the advantage that when the housing expands thermally in the threaded region, the spark plug still makes good contact with the cylinder head in the thread facing the combustion chamber, and thus the heat conduction is also good, whereby the spark plug or its electrodes are not overheated. In one development form, the region without a thread has a length that is at least 1.4 times the thickness of the outer seal when measured parallel to the longitudinal axis of the spark plug.

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

[0026] The ground electrode can be welded and / or press-fitted into the hole. The hole can be formed in the threaded region or under the threaded region. At least one ground electrode can be arranged relative to the central electrode such that these electrodes form an axial or radial ignition gap.

[0027] In one embodiment of the internal combustion engine according to the present invention, the width of the ignition gap is given by the electrode distance between the center electrode and at least one ground electrode, where the electrode distance between the center electrode and at least one ground electrode is 0.4 mm or less, particularly 0.2 mm or less, and 0.05 mm or more, particularly 0.1 mm or more. This has the advantage that a lower voltage is required for ignition and the increase in electrode distance is relatively small over the lifespan of the spark plug. Since the structural space within the housing is necessarily limited, the small electrode distance is further advantageous as it allows the electrodes, and therefore the ignition gap, to be positioned at least partially within the housing. This has the advantage that the electrodes do not protrude so far into the combustion chamber, thereby reducing the heat absorbed from the combustion chamber. Consequently, the heat absorbed by the spark plug as a whole is relatively small, resulting in a cold spark plug, which in turn avoids undesirable self-ignition.

[0028] For example, an electrode distance of 0.2 mm or less, and especially 0.15 mm or less, is advantageous. The smaller the electrode distance, the less voltage is required to generate the ignition spark. An electrode distance of at least 0.05 mm, and especially 0.1 mm or more, is also advantageous, as it prevents the electrode distance from becoming too small. Very small electrode distances impose a special challenge in precision in spark plug production. When the electrode distance is small, any deviation of the ignition surface of the electrode from being as parallel as possible has a greater impact than when the electrode distance is larger, for example, uneven wear of the ignition surface. Therefore, the lower limit of the electrode distance is a good compromise between a small electrode distance to reduce the required ignition voltage and wear, and a reasonable cost for uniform and high-quality positioning of the ignition surface in spark plug production.

[0029] A spark plug may also have multiple ground electrodes, each forming an ignition gap together with the center electrode. The above embodiments of the electrode and ignition gap also apply to multiple ground electrodes and ignition gaps. By having multiple ground electrodes in the spark plug, wear on the ignition surface can be distributed among the 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 effective life of the spark plug is improved. For example, two ground electrodes are arranged symmetrically on the inner surface of the housing. In this case, the longitudinal axis of the spark plug is the axis of symmetry when arranging the ground electrodes. By arranging the ground electrodes symmetrically, the flow of the fuel-air mixture in the intake and exhaust spaces becomes very uniform, which has the technical effect of further benefiting good ignition and good ignition stability of the fuel-air mixture in the spark plug.

[0030] For example, at least one ground electrode and / or center electrode each have one ignition surface made of a different material from the remaining electrodes, and these ignition surfaces together with the opposing electrodes form an ignition gap, and the ignition surface(s) are made of a noble metal or noble metal alloy, particularly 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-element proportion (Einzelanteil) in the alloy. These elements or alloys containing these elements are particularly wear-resistant. The electrodes themselves are made of, for example, nickel or a nickel alloy.

[0031] The housing is made of, for example, steel, low-carbon steel, or stainless steel.

[0032] The spark plug does not have a cap or similar feature on the end face of the housing facing the combustion chamber. The housing is open at its combustion chamber side, thereby allowing for the exchange of the mixture between the inside 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 operate using hydrogen or a hydrogen mixture as fuel. In particular, the internal combustion engine is operated at a lambda value of at least 1.8, at least within its partial operating range. [Brief explanation of the drawing]

[0034] [Figure 1] This figure shows a first embodiment of an internal combustion engine according to the present invention, equipped with a spark plug having a negative discharge position in the cylinder head. [Figure 2] This figure shows a second embodiment of the internal combustion engine according to the present invention, equipped with a spark plug having a negative discharge position in the cylinder head. [Figure 3] This figure shows a third embodiment of the internal combustion engine according to the present invention, which is equipped with a spark plug having a negative discharge position in the cylinder head. [Figure 4] This figure shows a fourth embodiment of the internal combustion engine according to the present invention, which is equipped with a spark plug having a negative discharge position in the cylinder head. [Figure 5] This figure shows an embodiment of a spark plug usable in an internal combustion engine according to the present invention, having a flat end face that faces the combustion chamber at a certain angle with respect to the longitudinal axis of the spark plug. [Figure 6] This figure shows an embodiment of a spark plug usable in an internal combustion engine according to the present invention, having a curved end face that faces the combustion chamber at a certain angle with respect to the longitudinal axis of the spark plug. [Figure 7] This figure shows an example of a spark plug usable in an internal combustion engine according to the present invention. [Figure 8] This figure shows another embodiment of a spark plug usable in an internal combustion engine according to the present invention. [Figure 9] This shows a conventional internal combustion engine in which the spark plug is positioned in the cylinder head in the positive discharge position. [Modes for carrying out the invention]

[0035] Figure 1 shows a simplified cross-sectional view of an internal combustion engine 1 according to a first embodiment of the present invention. The internal combustion engine 1 may have a plurality of cylinders 10, but only one of the cylinders 10 is shown in Figure 1. The cylinder 10 has a combustion chamber 15, which is defined by a piston that is movable within the cylinder, the side walls 11 of the cylinder, and the upper end of the combustion chamber roof 13. The combustion chamber roof 13 is formed by the cylinder head 12 of the internal combustion engine 1. The combustion chamber roof 13 is preferably formed in a conical or tapering shape, in particular by the roof apex forming the center point of the combustion chamber roof 13. In this case, the center point is located at the center of the cylinder 10, especially on the central axis 16 of a circular cylinder. The cylinder has an inner radius R extending from the central axis 16 of the cylinder to the side walls 11 of the cylinder. B It has.

[0036] Although not shown herein, the cylinder 10 may have gas exchange openings, such as at least one intake opening through which fresh air can flow into the combustion chamber 15, and at least one exhaust opening through which exhaust gases after combustion can flow out of the combustion chamber 15. Furthermore, the internal combustion engine 1 may have, for each cylinder 10, a combustion chamber fuel injector configured to inject fuel directly into the combustion chamber 15, or an intake manifold fuel injector configured 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 center electrode 23, and a ground electrode 24. The center electrode 23 is at least partially located in the insulator 22, and the insulator is also at least partially located within the housing 21. The ground electrode 24 is located within the housing 21. The spark plug 20 is a spark plug set to ignite the fuel-air mixture in the combustion chamber 15 with an electric spark. For this purpose, the spark plug 20 has a center electrode 23 and a ground electrode 24 that together form an ignition gap 25. The ignition spark can be generated between the two electrodes 23, 24. The ignition gap 25 can be located radially or axially with respect to the longitudinal axis X of the spark plug 20. The ignition gap 25 has a volume defined on the one hand by the opposing surfaces of the electrodes 23, 24 and by the overlapping projections of these surfaces.

[0038] Furthermore, the spark plug 20 has a housing 21 on its outer surface, for example, with threads 211, which allow the spark plug 20 to be screwed into the hole 14. As shown in Figure 1, the spark plug 20 is positioned in the hole 14 in the cylinder head 12, and the hole 14 opens into the combustion chamber 15.

[0039] In the first embodiment shown in Figure 1, the spark plug 20 is located within region 40. Region 40 is formed as a circular surface of the combustion chamber roof 13, with the center point of the combustion chamber roof 13 being the center point of the circle. In this example, the center point of the combustion chamber roof 13 coincides with the central axis 16 of the cylinder 10. The circular surface of region 40 has a cylinder radius R B 15% radius R M The spark plug 20 is located within the region 40. 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 coincides with the center point of the combustion chamber roof 13.

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

[0041] As shown in Figure 1, the combustion chamber roof 13 may be a curved surface. Alternatively, the combustion chamber roof 13 can be composed of multiple flat surface segments that meet at the center point of the combustion chamber roof 13.

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

[0043] In the following diagrams, the same parts of the diagrams have the same names and reference numerals. For simplicity, the following diagrams will explain the differences from the previously mentioned diagrams.

[0044] Figure 2 shows a simplified cross-sectional view of an internal combustion engine 1 according to a second embodiment of the present invention. 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 hole 14. In this embodiment, the ground electrode 24 is positioned in the hole 214 of the housing 21 and, together with the center electrode 23 as a side electrode, forms a radial ignition gap 25. Alternatively, the ground electrode 24 may be a roof electrode and positioned in the housing 21 together with the center electrode 23 to form an axial ignition gap 25. In another alternative embodiment, the ground electrode 24 may be positioned on the end face 210 of the housing 21 facing the combustion chamber, thereby forming the ignition gap 25 on the outside of the housing 21 rather than on the inside, as shown in Figure 2. In that case, the ignition gap is set so that the spark plug 20 assembled to the cylinder 10 has a negative discharge position. 25 It is important that the electrodes 23 and 24 are positioned so that they are formed within the hole 14 of the cylinder head 12.

[0045] Figure 3 shows a simplified cross-sectional view of an internal combustion engine 1 according to a third embodiment of the present invention. 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 inside the combustion chamber 15. In this case, the ground electrode 24 is positioned inside the housing 21 so that the ignition gap 25 is also formed inside the housing 21 and outside the combustion chamber 15. The ground electrode 24 can be positioned as a side electrode that forms a radial ignition gap 25 together with the center electrode 23, as shown, or as a roof electrode that forms an axial ignition gap 25 together with the center electrode 23.

[0046] Figure 4 shows a simplified cross-sectional view of an internal combustion engine 1 according to a fourth embodiment of the present invention. The fourth embodiment differs from the first embodiment in that the hole 14 in the cylinder head 12, and therefore the spark plug 20, is located off-center, that is, outside the circular region 40 whose center point is the center point of the combustion chamber roof. The end face 210 of the spark plug 20 facing the combustion chamber roof 13It is positioned within the hole 14 so as to be at least partially flush with the surface. In particular, if the end face 210 of the housing 21 facing 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, the end face 210 of the housing facing the combustion chamber may only be partially flush with the combustion chamber roof 13.

[0047] Figures 5 and 6 show cross-sectional views of the combustion chamber-side end region of the spark plug 20, respectively. The housing 21, insulator 22, and center electrode 23 are partially visible. The inner radius RI of the housing is shown in the intake and exhaust space, and the outer radius RA of the housing is shown. 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 located in the hole 214 in the region of the thread 211 and together with the center electrode 23 forms a radial ignition gap 25. The ignition gap 25 is defined radially by the opposing faces of electrodes 23 and 24, and axially by the volume 251 of the projection of the opposing faces of electrodes 23 and 24. The extent of the projection is indicated by dashed lines (unterbrochene Linie). Ignition gap 25 and combustion chamber roof 13 The distance A30 is precisely measured from the combustion chamber side end of the ignition gap. The dashed line (gestrichelte Linie) clarifies the range of the ignition gap volume 251.

[0048] In Figures 5 and 6, the end face 210 of the housing 21 facing the combustion chamber differs from the end face 210 of the housing 21 facing the combustion chamber shown in the first four figures in that the end face 210 facing the combustion chamber is not a surface oriented perpendicular to the longitudinal axis X of the spark plug 20. In Figure 5, the end face 210 facing 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 the combustion chamber is a curved surface oriented at an angle to the longitudinal axis X of the spark plug 20. A tangent 210T is in contact with the curved surface, and this tangent forms an angle α with the longitudinal axis X. A spark plug 20 having an end face 210 of the housing 21 that faces the combustion chamber and is oriented at an angle to the longitudinal axis X of the spark plug is particularly advantageous when the spark plug 20 is positioned away from the center of the cylinder head 12, and the end face 210 of the spark plug housing 21 that faces the combustion chamber is flush with the combustion chamber roof 13.

[0049] Figures 7 and 8 show two alternative spark plugs 20 that can be used in an internal combustion engine 1 according to the present invention. Figure 7 shows a spark plug 20 having a plurality of ground electrodes 24. Each ground electrode 24 forms an ignition gap 25 with the center electrode 23. The ground electrodes 24 are here formed as side electrodes that, together with the center electrode 23, form a radial ignition gap 25.

[0050] In Figure 8, the ground electrode 24 is formed as a roof electrode that, together with the center electrode 23, forms an axial ignition gap 25. Naturally, the spark plug 20 may also have a roof electrode combined with one or more side electrodes as ground electrodes.

[0051] Figures 7 and 8 show the overall length of the spark plug 20. On the outer surface of the housing 21, an outer sealing surface 281 is also visible, formed above the end of the thread 211 opposite to the combustion chamber. A seal ring (Dichtring) 28 is positioned on the outer sealing surface 281 as an outer seal to seal the transition between the spark plug 20 and the cylinder head 12 when the spark plug 20 is assembled to the cylinder head 12. The housing 21 has a threadless region 212 between the outer sealing surface 281 and the end of the thread opposite to the combustion chamber. In particular, this region has a length measured parallel to the longitudinal axis X of the spark plug 20 that is longer than the thickness of the outer seal (Dichtung) 28 positioned on the outer sealing surface 281.

[0052] In Figure 9, an internal combustion engine having a known arrangement of spark plugs in the cylinder head is shown. The spark plug is positioned in the cylinder head and is formed such that electrodes 23, 24 and an ignition gap 25 are located within 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 Plugs 21 Housing 210 End face 211 threads 212 Area without threads 251 Volume 22 Insulator 23 Center electrode 24 Ground electrode 25 ignition gap 28 seals, sealing rings 281 Seal surface 40 Region A30 Distance R B Inner radius R M Radius X Longitudinal axis

Claims

1. An internal combustion engine (1), - A cylinder comprising at least one cylinder (10), wherein a combustion chamber (15) is formed in the cylinder, and the combustion chamber (15) is defined by the side wall (11) of the cylinder (10), a combustion chamber roof (13) formed by the cylinder head (12) of the cylinder (10), and a piston that is movable within the cylinder (10), - An internal combustion engine comprising a spark plug (20) including a longitudinal axis, having a housing (21) including an end face (210) facing the combustion chamber, an insulator (22) disposed in the housing (21), a central electrode (23) disposed in the insulator (22), and at least one ground electrode (24) disposed in the housing (21) and together with the central electrode (23) forming at least one ignition gap (25), wherein the spark plug (20) is assembled into a hole (14) formed in the cylinder head (12) and is configured to ignite the fuel-air mixture present in the combustion chamber (15), The ignition gap (25) of the spark plug (20) is positioned outside the combustion chamber (5), An internal combustion engine characterized in that the ignition gap (25) is at least -1 mm and / or up to -4 mm away (30) from the combustion chamber roof (13) of the cylinder (10), the contour of the combustion chamber roof (13) is continued by a virtual line in the hole (14), and the virtual line (15a) is a reference plane with a value of 0 mm.

2. The internal combustion engine (1) according to claim 1, characterized in that the ignition gap (25) has a distance (30) of -1 mm with respect to the combustion chamber roof (13) of the cylinder (10).

3. The internal combustion engine (1) according to claim 1 or 2, characterized in that the end face (210) of the housing (21) facing the combustion chamber is positioned within the hole (14) for the spark plug (20).

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

5. The spark plug (20) is positioned within the region (40), and the region (40) is defined as the center point of the combustion chamber roof (13) as the center point of a circle, and the cylinder radius R Ｂ The radius R is 15% of Ｍ An internal combustion engine (1) according to claim 1 or 2, characterized in that it is formed by a circular surface including the following.

6. The spark plug (20) is not positioned outside the region (40), and the region (40) is defined as the center point of the combustion chamber roof (13) as the center point of a circle, and the cylinder radius R Ｂ The radius R is 15% of Ｍ An internal combustion engine (1) according to claim 1 or 2, characterized in that it is formed by a circular surface including the following.

7. The internal combustion engine (1) according to claim 1 or 2, characterized in that the end face (210) of the housing (21) facing the combustion chamber has a surface, and the shape of the surface corresponds to the contour of the combustion chamber roof (13).

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

9. The internal combustion engine (1) according to claim 7, characterized in that the surface forms an angle less than 90° with the longitudinal axis X of the spark plug (20), and a smaller angle is observed between the surface and the longitudinal axis X.

10. The internal combustion engine (1) according to claim 8, characterized in that the surface is a curved surface that forms an angle of 90° or less with the longitudinal axis X of the spark plug (20), and a smaller angle is observed between the surface and the longitudinal axis X.

11. The internal combustion engine (1) according to claim 10, characterized in that all or part of the cylinder (10) and / or the spark plug (20) each have markings so that the spark plug (20) can be assembled to face the cylinder (10).

12. 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), and the housing (21) has a threadless region (212) between the outer sealing surface (281) and the end of the thread opposite to the combustion chamber, according to claim 1 or 2, the internal combustion engine (1).

13. The internal combustion engine (1) according to claim 1 or 2, characterized in that the width of the ignition gap (25) is given by the 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 0.4 mm or less.

14. The internal combustion engine (1) according to claim 1 or 2, characterized in that it is capable of operating with hydrogen or a hydrogen mixture as fuel.

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