Hydrogen internal combustion engine
The hydrogen internal combustion engine design with dual jets and charge motion ensures stable ignition and effective combustion by maintaining an ignitable mixture near the ignition source, addressing the challenge of varying operating conditions.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ROBERT BOSCH GMBH
- Filing Date
- 2025-09-23
- Publication Date
- 2026-06-11
AI Technical Summary
Achieving robust ignition of a hydrogen-oxygen mixture in internal combustion engines, especially under varying external conditions, is a challenge due to the difficulty in ensuring stable ignition across different operating situations.
A hydrogen internal combustion engine design featuring a cylinder with a central axis and a cylinder head defining a combustion chamber, incorporating a piston that moves between top and bottom dead centers, and a hydrogen injector that produces primary and secondary jets directed in opposite directions within the chamber, ensuring an ignitable mixture is present near the ignition source under all conditions, utilizing charge motion for mixture formation.
Enables stable ignition and effective combustion across varying operating conditions, independent of engine speed and air movement, with reduced pre-ignition risk and enhanced mixture formation, thereby ensuring robust engine performance.
Smart Images
Figure EP2025077123_11062026_PF_FP_ABST
Abstract
Description
[0001] R.417128
[0002] - 1 -
[0003] Description
[0004] title
[0005] Hydrogen combustion engine
[0006] State of the art
[0007] The present invention relates to a hydrogen internal combustion engine with an improved system layout for improving mixture formation between hydrogen and oxygen in a combustion chamber during direct injection of hydrogen into the combustion chamber, in particular to ensure robust ignition of the hydrogen in the combustion chamber in all operating situations.
[0008] There are currently increased efforts in the art to use hydrogen as a fuel for internal combustion engines. In particular, direct injection of hydrogen into the combustion chamber of the internal combustion engine is a promising concept. A problem here is achieving robust ignition of a hydrogen-oxygen mixture, especially under varying external conditions.
[0009] Disclosure of the invention
[0010] In contrast, the hydrogen combustion engine according to the invention, with the features of claim 1, has the advantage that stable ignition is possible in all operating situations of the hydrogen combustion engine when hydrogen is directly injected into a combustion chamber of the hydrogen combustion engine. Furthermore, the hydrogen combustion engine has a surprisingly simple and cost-effective design. R.417128
[0011] - 2 -
[0012] According to the invention, this is achieved by the hydrogen internal combustion engine comprising a cylinder with a central axis XX and a cylinder head, which define a combustion chamber of the hydrogen internal combustion engine. Furthermore, the hydrogen internal combustion engine comprises a piston which is movable back and forth in the combustion chamber between a bottom dead center and a top dead center. The movement of the piston over a complete piston stroke S1 defines a working area in the combustion chamber. A free area is also defined between the working area and the cylinder head. The free area is a region in the combustion chamber which remains open during operation without the piston passing over it; that is, the piston does not pass over the free area in the combustion chamber. The hydrogen internal combustion engine further comprises an ignition source, in particular a spark plug, and a hydrogen injector for injecting gaseous hydrogen.The ignition source and the hydrogen injector are located on the cylinder head. The hydrogen injector is designed to produce a primary jet (C) and a secondary jet (B) during injection. These two jets are directed in opposite directions within the combustion chamber. This ensures that an ignitable mixture is present in the vicinity of the ignition source during hydrogen injection into the combustion chamber under all operating conditions. This enables robust ignition of the hydrogen-oxygen mixture. Furthermore, the division into primary and secondary jets allows for multi-layered introduction of the gaseous hydrogen, resulting in sufficient mixing within the cylinder volume of the internal combustion engine.Furthermore, the jet's division enables stable jet guidance across the entire engine operating range, and in particular, independent of engine speed and / or the degree of air movement in the combustion chamber. Additionally, any charge motion present in the combustion chamber during jet injection can be used to improve mixture formation in the remaining combustion chamber, with minimal or no impact on the charge motion.
[0013] The dependent claims describe preferred embodiments of the invention. R.417128
[0014] - 3 -
[0015] Preferably, the mass of the second main jet B is less than the mass of the first main jet C. This ensures robust ignition under all operating conditions of the internal combustion engine. The second main jet B is preferably designed such that its mass is less than half the mass of the first main jet.
[0016] Preferably, the first main jet C has a mass fraction in the range of 70% to 90% of the total injected hydrogen and / or the second main jet B preferably comprises an injected mass in the range of 10% to 30%. Particularly preferably, the first main jet has approximately 80% of the injected hydrogen and the second main jet has approximately 20% of the injected hydrogen.
[0017] Preferably, a first angle α between the first main jet C and the second main jet B lies in a range of 35° < α < 75°, particularly 40° < α < 70°, and more preferably 40° < α < 55°. Most preferably, the first angle α is approximately 50°. Since the first main jet C and the second main jet B form three-dimensional injection clouds for gaseous hydrogen, the first angle α is defined by the respective centers of mass of the first and second main jets B and C. Preferably, a second angle α between the first main jet C and a central axis of the hydrogen injector lies in a range of 0° < α < 34°, and most preferably in a range of 10° < α < 25°. More preferably, the first angle lies in a range of 15° < α < 20°.
[0018] Preferably, during the injection process, the first main jet C forms a first jet cloud and the second main jet B generates a second jet cloud, with an overlap zone forming between the first and second jet clouds. The overlap zone preferably comprises 0 to 30 mass percent, and in particular 10 to 20 mass percent, of the injected hydrogen.
[0019] The overlap of the first and second mixed clouds results in, in particular, a continuous supply of local, R.417128
[0020] - 4 - flammable mixture areas in the combustion chamber at the external ignition source, so that stable ignition and effective combustion can take place in the combustion chamber. Mixture formation is preferably supported by the charge movement in the combustion chamber.
[0021] The hydrogen injector preferably has a cap. The use of caps provides a degree of protection for the hydrogen injector from the hot combustion gases in the combustion chamber, and also allows for targeted hydrogen injection.
[0022] Preferably, the cap has exactly two cap holes. Preferably, one cap hole is parallel to a central axis of the hydrogen injector, and the other cap hole is formed at a predetermined oblique angle to the projection of the second cap hole. The first cap hole is preferably configured to form the first main jet C, and the second cap hole is configured to form the second main jet B.
[0023] Preferably, the combustion chamber of the hydrogen internal combustion engine is divided into a first region with increased charge motion and a second region with reduced charge motion, the second region completely encompassing the free zone, i.e., the region in which no piston movement takes place. The first region with increased charge motion is significantly larger than the second region with reduced charge motion.
[0024] Preferably, the second region with reduced charge motion is designed such that it encompasses part of the combustion chamber's working area. The second region is defined by a maximum distance S2 between a piston stroke position and the cylinder head and lies within a range of 0.05 x S1 < S2 < 0.2 x S1, and particularly within a range of 0.10 x S1 < S2 < 0.15 x S1, where S1 is the maximum piston stroke. R.417128
[0025] - 5 -
[0026] The cap is preferably a cap having exactly one first outlet opening for forming the first main jet C and a second outlet opening for forming the second main jet B. The cap thus has exactly two outlet openings. Preferably, the first outlet opening runs parallel to a central axis YY of the hydrogen injector, and the second outlet opening exits the cap at an angle c between 20° and 50°, preferably 25° to 35°.
[0027] Alternatively, the hydrogen injector cap is a semi-open cap, in which approximately half of the cap area is open. This allows hydrogen to be injected into a larger combustion chamber area compared to a single-hole cap. The semi-open cap is preferably designed to form, during the injection process, the first main jet C and the second main jet B, the mass of which is particularly smaller than that of the first main jet.
[0028] A distance A between the ignition source and the hydrogen injector is preferably in the range of 0.05 x D < A < 0.50 x D, where D is the diameter of the cylinder. Adhering to this specified distance between the ignition source and the hydrogen injector ensures that, when hydrogen is injected into the combustion chamber, an ignitable mixture is present in the vicinity of the ignition source in all operating situations, thus enabling robust ignition of the hydrogen-oxygen mixture.
[0029] The distance A between the ignition source and the hydrogen injector is determined from a central axis YY of the hydrogen injector to a central axis ZZ of the ignition source on an inner wall area of the cylinder head.
[0030] Preferably, the distance A is in a range of 0.05 x D < A < 0.50 x D, and in particular in a range of 0.10 x D < A < 0.35 x D, and further in particular 0.20 x D < A < 0.30 x D.
[0031] Particularly reliable and stable ignition is possible when the distance of the hydrogen injector to the cylinder's central axis XX is equal to the distance of the ignition source to the cylinder's central axis XX. R.417128
[0032] - 6 -
[0033] That is, the distance between the ignition source and the hydrogen injector and the central axis is the same.
[0034] Furthermore, a counterclockwise swirl is preferably formed in the working area of the combustion chamber.
[0035] Brief description of the drawings
[0036] Preferred embodiments of the invention are described in detail below with reference to the accompanying drawings. The drawing shows:
[0037] Figure 1 shows a schematic sectional view of a hydrogen internal combustion engine according to a first preferred embodiment of the invention, wherein a piston is located at bottom dead center.
[0038] Figure 2 is a schematic sectional view corresponding to Figure 1, with the piston at top dead center.
[0039] Figure 3 shows an enlarged partial sectional view of a hydrogen injector of the hydrogen combustion engine of Figure 1.
[0040] Figure 4 shows an enlarged partial sectional view of a hydrogen injector of a hydrogen internal combustion engine according to a second embodiment of the invention and
[0041] Figure 5 shows a schematic partial sectional view of a hydrogen injector of a hydrogen internal combustion engine according to a third embodiment of the invention.
[0042] Embodiments of the invention R.417128
[0043] - 7 -
[0044] Several embodiments of the invention are described in detail below, wherein identical or functionally identical parts are designated with the same reference numerals.
[0045] Figures 1 to 3 show in detail a hydrogen combustion engine 1 according to a first preferred embodiment of the invention.
[0046] Figure 1 shows the state of a piston 2 in a cylinder 3 of the hydrogen combustion engine at bottom dead center 11. Figure 2 shows the piston 2 at top dead center 12.
[0047] The hydrogen internal combustion engine 1 comprises the cylinder 3 with a central axis XX and a cylinder head 4 arranged on the cylinder 3. The cylinder 3 and the cylinder head 4 define a combustion chamber 5 of the hydrogen internal combustion engine.
[0048] Furthermore, the hydrogen combustion engine 1 includes the piston 2, which is movable back and forth in the combustion chamber 5 between bottom dead center 11 and top dead center 12 (double arrow H). Figures 1 and 2 schematically depict a complete piston stroke S1 of the piston 2 in the combustion chamber 5. The complete piston stroke S1 defines a working range 51 in the combustion chamber 5.
[0049] Furthermore, a free area 52 is defined in the combustion chamber 5, which extends between the working area 51 and the cylinder head 4. The free area is thus the area of the combustion chamber 5 that is not swept over by the piston 2 during the power stroke. In the first embodiment, the free area 52 is trapezoidal.
[0050] Figure 1 further includes an ignition source 6, in this embodiment a spark plug, and a hydrogen injector 7. The hydrogen injector 7 is configured to inject gaseous hydrogen into the combustion chamber 5. The ignition source 6 is configured to ignite a mixture of injected hydrogen and oxygen in the combustion chamber 5. R.417128
[0051] - 8 -
[0052] As can be seen from Figures 1 and 2, the ignition source 6 and the hydrogen injector 7 are arranged on the cylinder head 4. Thus, the hydrogen internal combustion engine is a so-called direct-injection internal combustion engine.
[0053] As can be seen from Figures 1 to 3, a distance A between the ignition source 6 and the hydrogen injector 7 is chosen such that the distance A lies within the range of 0.05 x D < A < 0.50 x D. Here, D is the diameter of the cylinder 3. In this embodiment, the distance A is 0.25 x D. The diameter D of the cylinder 3 ranges in absolute terms from 50 mm to 250 mm, with the smaller cylinder diameters being associated with PC (Passenger Car) applications, while the larger cylinder diameters D are intended for applications ranging from LCV (Light Commercial Vehicle) and CV (Commercial Vehicle) to off-road applications and LE (Large Engine).
[0054] The hydrogen injector 7 and the ignition source 6 are arranged such that half the distance A lies on the central axis XX of the cylinder 3. That is, the ignition source 6 and the hydrogen injector 7 are equidistant from the central axis.
[0055] XX encompassing plane removed, which is perpendicular to distance A.
[0056] In the first embodiment, a straight line, which denotes the distance A between ignition source 6 and hydrogen injector 7, intersects the central axis XX; however, it should be noted that it is also possible that the ignition source 6 and the hydrogen injector 7 are arranged such that a straight line defining the distance A is offset from the central axis XX of the cylinder 3 and does not intersect the central axis.
[0057] As further shown schematically in Figure 1, the combustion chamber 5 has a first region 53 with increased charge motion and a second region 54 with reduced charge motion. The second region 54 with reduced charge motion completely encompasses the free area 52 and also an upper section of the working area 51 (see Figure 1). The region with reduced charge motion 54 is designated S2 in Figure 2. S2 is defined by R.417128
[0058] - 9 - the length of the second region 54 in the direction of the central axis XX of the cylinder 3. S2 preferably lies in a range of 0.05 x S1 < S2 < 0.20 x S1 and in this embodiment is 0.12 x S1 , i.e., 12% of the piston stroke S1 .
[0059] Furthermore, the hydrogen injector 7 comprises a cap 70, which is designed as a semi-open cap. That is, the cap 70 has a semi-open area 74, through which the first main jet C (primary jet) and the second main jet B (secondary jet) are formed. As can be clearly seen from Figure 3, the semi-open area 74 of the cap 70 occupies more than 50% of the cap's surface area. This allows for a dual-jet injection of the gaseous hydrogen, with the mass flow rates of the primary and secondary jets being different.
[0060] The semi-open area 74 of the cap 70 thus ensures that a major portion of the injected hydrogen is directed towards the piston 2. A significantly smaller amount of hydrogen is directed towards the ignition source 6.
[0061] A first angle α is provided between the first main beam C and the second main beam B. The first angle α is defined by a line connecting the centers of mass of the two beams and preferably lies in a range of 35° < α < 75°.
[0062] A second angle b is formed between a central axis YY of the hydrogen injector 7 and the first main jet C. The second angle b preferably lies in a range of 0° < b < 25°.
[0063] The two angles a, b are defined by the respective lines of the centers of mass of the primary and secondary beams, since in reality three-dimensional injection clouds are generated during hydrogen injection.
[0064] It is also possible for the injection clouds of the primary and secondary jets to overlap. Additionally, according to the invention, as shown in Figure 1, the existing charge movement in the combustion chamber 5 is used for the continuous supply of R.417128.
[0065] - 10 - local flammable mixtures at the ignition source 6 are used to ensure stable ignition and effective combustion in the combustion chamber 5. Both high-load and part-load operating points can be ignited robustly, ensuring stable jet guidance for the primary and secondary jets at all operating points.
[0066] The semi-open cap 70 also has the advantage that increased rinsing is possible in the area of the semi-open cap, which can significantly reduce the tendency for pre-ignition.
[0067] Since a major portion of the injected hydrogen acts as a primary jet towards the piston 2, interacting with the charge motion 50 to form a mixture in the combustion chamber 5, a more stable secondary jet is also achieved towards the ignition source 6. This further reduces the risk of pre-ignition and results in more stable combustion.
[0068] Figure 1 schematically illustrates the charge movements 50 in the combustion chamber 5 with circular arrows. In this embodiment, the charge movements 50 proceed counterclockwise and are thus formed as a so-called swirl motion. Alternatively, a tumble motion can also be provided.
[0069] The design of the internal combustion engine 1 in the first embodiment thus makes it possible to achieve robust ignition across the entire engine operating range, independent of engine speed and / or the degree of air movement of the mixture at the ignition source 6. The inventive jet guidance of the injected hydrogen allows the secondary jet to be directed onto a target area 9 below the ignition source 6. This ensures that a sufficient quantity of the hydrogen-oxygen mixture is supplied locally at the ignition source 6. Simultaneously, the existing charge motion 50 during the injection process is used to improve mixture formation in the remaining combustion chamber 5. The orientation of the outlet area of the R.417128
[0070] - 11 -
[0071] The hydrogen injector 7 is thus directed in the direction below the ignition source 6.
[0072] This allows for improved ignition and increased robustness against engine roughness. Simultaneously, the arrangement of the invention offers additional potential for performance enhancement. By injecting hydrogen into the second area 54 with reduced charge movement, the hydrogen is injected into an area with significantly lower gas movement. The charge movement 50 can further support mixture formation at the ignition source 6. The semi-open cap facilitates the targeted delivery of hydrogen to the target area 9 for mixture formation at the ignition source 6.
[0073] Furthermore, the first angle a ensures that no Coanda effect of the hydrogen occurs and thus prevents hydrogen from flowing along the inner wall 40 of the cylinder head 4, which approximates a convex shape.
[0074] Figure 4 schematically shows a partial sectional view of a hydrogen injector 7 of an internal combustion engine 1 for injecting hydrogen according to a second embodiment of the invention. As can be seen from Figure 4, the cap 70 of the hydrogen injector 7 of the second embodiment has a closed cap with exactly two outlet openings, namely a first outlet opening 71 and a second outlet opening 72. The first outlet opening 71 is arranged in a straight line and parallel to the central axis YY of the hydrogen injector 7. The second outlet opening 72 has, in section, an inverted C-shape with an angle c to the central axis YY of the hydrogen injector 7, resulting in an outlet angle of approximately 20° to 50°.This closed cap with exactly two outlet openings 71, 72 also allows for a two-jet injection into the combustion chamber 5 with a first main jet C and a second main jet B, whereby the two main jets B, C inject different quantities. R.417128.
[0075] - 12 -
[0076] Figure 5 schematically shows a third embodiment of the invention, wherein the hydrogen injector 7 is again designed with a semi-open cap 70. In contrast to the first embodiment, the cap 70 of the second embodiment has an impact zone 73, which forms a two-jet injection with a first main jet C and a second main jet B. Due to the deflection 76 of the gaseous hydrogen at the impact zone 73, different mass fractions of the first main jet C and the second main jet B result compared to the first embodiment. In particular, the deflection 76 leads to a reduced mass fraction of the second main jet B compared to the first embodiment.
[0077] In all described embodiments, the hydrogen injector 7 has outwardly opening injectors. However, it should be noted that the advantages of the invention are also achieved with inwardly opening injectors. Thus, by forming exactly two main jets B, C, directed in different directions within the combustion chamber 5, improved ignition and a reduction in pre-ignition can be achieved.
Claims
R.417128 - 13 - Claims 1. Hydrogen internal combustion engine comprising: a cylinder (3) with a central axis XX and a cylinder head (4) defining a combustion chamber (5), a piston (2) which is movable back and forth in the combustion chamber (5) between a bottom dead center (11) and a top dead center (12), wherein the movement of the piston (2) over a complete piston stroke S1 defines a working area (51) in the combustion chamber (5), a free area (52) between the working area (51) and the cylinder head (4), an ignition source (6), in particular a spark plug, and a hydrogen injector (7) for injecting hydrogen, wherein the ignition source (6) and the hydrogen injector (7) are arranged on the cylinder head (4), and wherein the hydrogen injector (7) is configured to form a first main jet C and a second main jet B during an injection process, which are directed in different directions in the combustion chamber (5).
2. Hydrogen combustion engine according to claim 1, wherein a mass of the second main jet B is smaller than a mass of the first main jet C.
3. Hydrogen combustion engine according to claim 2, wherein a mass fraction of the first main jet C is in a range of 70 mass-% to 90 mass-% and / or a mass fraction of the second main jet B is in a range of 10 mass-% to 30 mass-%.
4. Hydrogen combustion engine according to one of the preceding claims, wherein between the first main jet C and the R.417128 - 14 - second principal ray B a first angle a is formed, wherein the first angle a lies in a range of 35° < a < 75°, in particular in a range of 30° < a < 70° and further in particular in a range of 40° < a < 55°.
5. Hydrogen combustion engine according to one of the preceding claims, wherein a second angle b between the first main jet C and a central axis YY of the hydrogen injector (7) lies in a range of 0° < b < 34° and in particular in a range of 10° < b < 25°.
6. Hydrogen combustion engine according to one of the preceding claims, wherein the first main jet C generates a first jet cloud and the second main jet B generates a second jet cloud, wherein an overlap area results between the first and the second jet cloud.
7. Hydrogen combustion engine according to claim 6, wherein the overlap area between the first and second jet cloud comprises a maximum of 30 mass-% of the injected hydrogen, in particular a maximum of 20 mass-% of the injected hydrogen.
8. Hydrogen internal combustion engine according to one of the preceding claims, wherein the combustion chamber (5) is divided into a first area (53) with increased charge motion and a second area (54) with reduced charge motion, wherein the second area (54) completely encompasses the free area (52).
9. Hydrogen internal combustion engine according to claim 8, wherein the second region (54) comprises a part of the working region (51) of the combustion chamber (5) such that the second region (54) is defined by a maximum distance S2 in a piston position between a piston crown of the piston (2) and the cylinder head (4) in a range of 0.05 x S1 < S2 < 0.2 x S1, in particular in a range of 0.10 x S1 < S2 < 0.15 x S1, wherein S1 is a maximum piston stroke of the piston (2). R.417128 - 15 - 10. Hydrogen internal combustion engine according to one of the preceding claims, wherein the hydrogen injector (7) has a cap (70).
11. Hydrogen combustion engine according to claim 10, wherein the cap (70) has exactly one first outlet opening (71) for forming the first main jet C and one second outlet opening (72) for forming the second main jet B.
12. Hydrogen combustion engine according to claim 11, wherein the first outlet opening (71) runs parallel to a central axis YY of the hydrogen injector (7) and wherein the second outlet opening (72) exits the cap (70) at an angle c between 20° and 50°, preferably 25° to 35°.
13. Hydrogen internal combustion engine according to claim 10, wherein the cap (70) is a semi-open cap with a semi-open area (74), wherein the semi-open area occupies approximately 50% of the total cap.
1. Hydrogen combustion engine according to claim 13, wherein the semi-open cap (74) is configured to form the first main jet C and the second main jet B during an injection process, wherein in particular a mass of the second main jet B is smaller than a mass of the first main jet C.
15. Hydrogen internal combustion engine according to one of the preceding claims, wherein a distance A between the ignition source (6) and the hydrogen injector (7) is in a range of 0.05 x D < A < 0.50 x D, where D is the diameter of the cylinder (3).
16. Hydrogen combustion engine according to claim 15, wherein the distance A is in the range of 0.10 x D < A < 0.35 x D, in particular in a range of 0.20 x D < A < 0.30 x D. R.417128 - 16 - 17. Hydrogen combustion engine according to one of claims 15 or 16, wherein the distance of the hydrogen injector (7) to the central axis X-X of the cylinder (3) is equal to the distance of the ignition source (6) to the central axis XX.