Internal combustion engine

Abstract

To securely ignite a small amount of hydrogen gas and burn ammonia without complicating a structure of an internal combustion engine.SOLUTION: An internal combustion engine includes: a combustion chamber 9; an ammonia supply section that supplies ammonia to the combustion chamber 9; a hydrogen gas supply section 12 that supplies hydrogen gas from a supply port opened in the combustion chamber 9 to an upper part of the combustion chamber 9; and ignition means 4 for burning the hydrogen gas through ignition in the upper part of the combustion chamber 9. After main combustion gas containing ammonia is supplied to the combustion chamber 9, while the main combustion gas in the combustion chamber 9 is compressed, the hydrogen gas is supplied to the upper part of the combustion chamber 9, and then, the hydrogen gas is burned through ignition in the upper part of the combustion chamber 9.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an internal combustion engine that uses ammonia as fuel and a method for operating the same. [Background technology]

[0002] Greenhouse gas CO 2 In order to reduce CO emissions, research is being conducted into using non-hydrocarbon gas fuels such as ammonia in internal combustion engines. However, ammonia is flame-retardant, so it is difficult to ignite it by itself, and even if it can be ignited, it is difficult to completely burn it. Therefore, unburned ammonia and CO 2 N, which has a much higher greenhouse effect than 2 There is concern that large amounts of intermediate products such as O will be generated.

[0003] Therefore, when using ammonia as fuel, it is possible to consider a method of co-firing it with heavy oil fuel. However, in order to burn ammonia, a considerable amount of heavy oil fuel must be supplied, and the amount of CO emitted by the heavy oil fuel is reduced. 2 occurs.

[0004] Another possible method is to mix ammonia with hydrogen to promote combustion of the ammonia. However, although hydrogen has good ignition properties, in order to increase the combustion efficiency of ammonia and suppress the generation of unburned ammonia and intermediate products, it is necessary to increase the amount of hydrogen supplied, which increases fuel costs.

[0005] For example, the following Patent Document 1 shows an engine in which a main combustion chamber and a pre-combustion chamber (auxiliary combustion chamber) are provided in a cylinder. Ammonia decomposition gas containing hydrogen is supplied to the pre-combustion chamber and burned, and the flame thus generated is ejected into the main combustion chamber to burn the premixed gas of ammonia and air supplied to the main combustion chamber. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-161921 Summary of the Invention [Problem to be solved by the invention]

[0007] 7 shows an example of an internal combustion engine having a main combustion chamber 104 and a pre-combustion chamber 105. The main combustion chamber 104 is formed by the inner circumferential surface of a cylinder liner 101, the lower surface of a cylinder cover 102, and the upper surface of a piston 103. The pre-combustion chamber 105 is formed inside a pre-combustion chamber housing 109 fixed to the cylinder cover 102. The pre-combustion chamber 105 communicates with the main combustion chamber 104 via an ejection hole 108 formed in the pre-combustion chamber housing 109. A hydrogen supply unit 106 and an ignition plug 107 are provided in the pre-combustion chamber housing 109. Hydrogen gas is supplied from hydrogen supply section 106 to pre-combustion chamber 105 (see arrow A), and then an ignition plug 107 is ignited to combust the hydrogen gas in pre-combustion chamber 105. The resulting flame is ejected from ejection hole 108 into main combustion chamber 104 (see arrow B), combusting the mixture of ammonia and air (main combustion gas) that fills main combustion chamber 104.

[0008] FIG. 8 shows another example of an internal combustion engine having a main combustion chamber 104 and a pre-combustion chamber 105. In this internal combustion engine, a pre-combustion chamber housing 109 is provided at the tip of an ignition plug 107. The ignition plug 107 is provided with a communication hole 107b for supplying hydrogen gas. Hydrogen gas supplied from a hydrogen supply unit 106 is supplied to the pre-combustion chamber 105 through the communication hole 107b of the ignition plug 107 (see dotted arrow A), and then the ignition plug 107 is ignited to combust the hydrogen gas in the pre-combustion chamber 105. The resulting flame is ejected from an ejection hole 108 into the main combustion chamber 104 (see arrow B), thereby combusting a mixture of ammonia and air (main combustion gas) filled in the main combustion chamber 104.

[0009] As described above, by supplying hydrogen gas to the pre-combustion chamber 105, which has a smaller volume than the main combustion chamber 104, the concentration of hydrogen gas in the pre-combustion chamber 105 becomes high, and by igniting the hydrogen gas in the pre-combustion chamber 105 in this state, even a small amount of hydrogen gas can be easily ignited. However, providing the pre-combustion chamber 105 complicates the structure of the internal combustion engine. In addition, since the pre-combustion chamber 105 becomes hot, if hydrogen, which has an extremely small ignition energy, is supplied to the pre-combustion chamber 105, there is a concern that unintended self-ignition (pre-ignition) of hydrogen may occur starting from a high-temperature member (the inner wall of the pre-combustion chamber 105).

[0010] Therefore, an object of the present invention is to reliably ignite a small amount of hydrogen gas to combust ammonia without complicating the structure of an internal combustion engine. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention provides an internal combustion engine including a combustion chamber, an ammonia supply unit that supplies ammonia to the combustion chamber, a hydrogen gas supply unit that supplies hydrogen gas to an upper part of the combustion chamber from a supply port that opens into the combustion chamber, and ignition means that ignites the upper part of the combustion chamber to burn the hydrogen gas.

[0012] In this way, the supply port of the hydrogen gas supply unit is opened to the combustion chamber, hydrogen gas is supplied from this supply port to the upper part of the combustion chamber, and then when the piston rises and the mixture in the combustion chamber is compressed, the hydrogen gas is forced upward, so that the concentration of hydrogen gas in the upper part of the combustion chamber becomes higher than the concentration of hydrogen gas in the lower part. The present invention utilizes the concentration difference of hydrogen gas generated in this way in the combustion chamber, and by igniting the upper part of the combustion chamber where the concentration of hydrogen gas is high, even a small amount of hydrogen gas can be reliably ignited and ammonia can be burned without providing a pre-combustion chamber.

[0013] The hydrogen gas is preferably generated from ammonia used as the main fuel (reformed hydrogen), which eliminates the need for a tank or the like for storing hydrogen gas.

[0014] In the above internal combustion engine, it is preferable that hydrogen gas is supplied from the hydrogen gas supply unit to the combustion chamber during the compression stroke in which the mixture in the combustion chamber is compressed. As the piston rises during the compression stroke, the hydrogen gas supplied to the combustion chamber is pushed into the upper part of the combustion chamber, so that the concentration of hydrogen gas in the upper part of the combustion chamber can be reliably increased.

[0015] By the way, if hydrogen gas is supplied to the combustion chamber at the end of the compression stroke, i.e. when the piston reaches near the top dead center, the hydrogen gas will not diffuse, so it may seem that it would be easier to create a region of high hydrogen gas concentration. However, in order to supply hydrogen to the compressed air-fuel mixture, the hydrogen gas needs to be compressed at high pressure, which is extremely difficult and, even if it could be done, a large-scale device would be required.

[0016] Therefore, it is preferable to supply hydrogen gas from the hydrogen gas supply unit to the combustion chamber in the first half of the compression stroke in which the mixture in the combustion chamber is compressed. In the first half of the compression stroke, the pressure of the mixture in the combustion chamber is relatively low, so it is easy to supply hydrogen gas to the combustion chamber. In particular, when the piston is at bottom dead center, the mixture in the combustion chamber is hardly compressed, so it is more preferable to supply hydrogen gas to the combustion chamber at this time.

[0017] The present invention can also be characterized as a method for operating an internal combustion engine, comprising: an intake process for supplying ammonia to a combustion chamber; a compression process for supplying hydrogen gas to an upper portion of the combustion chamber while compressing the mixture in the combustion chamber; and a combustion process for igniting the upper portion of the combustion chamber and burning the hydrogen gas. Effect of the Invention

[0018] As described above, according to the present invention, it is possible to reliably ignite a small amount of hydrogen gas and burn ammonia without complicating the structure of the internal combustion engine. [Brief description of the drawings]

[0019] [Figure 1]1 is a cross-sectional view of an internal combustion engine according to an embodiment of the present invention, showing a state in which a piston is near bottom dead center. [Diagram 2] FIG. 2 is a diagram showing the opening and closing timing of the intake valve and exhaust valve of the internal combustion engine, and the injection period of the main fuel gas (ammonia) and hydrogen gas. [Diagram 3] FIG. 2 is a cross-sectional view of the internal combustion engine, showing a state in which the piston has been raised from the state shown in FIG. 1. [Figure 4] 4 is a cross-sectional view of the internal combustion engine, showing a state in which the piston has been further raised from the state in FIG. 3 and is now near top dead center. [Diagram 5] FIG. 4 is a cross-sectional view of an internal combustion engine according to another embodiment of the present invention. [Figure 6] FIG. 11 is a cross-sectional view of an internal combustion engine according to still another embodiment of the present invention. [Figure 7] 1 is a cross-sectional view of an example of an internal combustion engine having a pre-chamber; [Figure 8] FIG. 2 is a cross-sectional view of another example of an internal combustion engine having a pre-chamber. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0021] Fig. 1 shows an engine as an internal combustion engine according to an embodiment of the present invention, and in particular, a marine engine mounted on a ship. This engine has a cylinder liner 1, a cylinder cover 2, a piston 3, an ignition plug 4 as an ignition means, an intake port 5 and an intake valve 6, and an exhaust port 7 and an exhaust valve 8. For convenience of explanation, the cylinder cover 2 side in the moving direction of the piston 3 (the vertical direction in Fig. 1) is referred to as the upper side, and the opposite side is referred to as the lower side, but this is not intended to limit the installation mode of the engine. Therefore, the engine may be installed so that the moving direction of the piston 3 is the vertical direction, or the moving direction of the piston 3 is the horizontal direction.

[0022] The space defined by the cylindrical inner circumferential surface of the cylinder liner 1, the lower surface of the cylinder cover 2, and the upper surface of the piston 3 becomes the combustion chamber 9. The ignition part 4a provided at the tip of the spark plug 4 protrudes downward from the lower surface of the cylinder cover 2 and is disposed in the upper part of the combustion chamber 9. The ignition part 4a of the spark plug 4 is provided at the center of the combustion chamber 9 (the axis of the cylinder liner 1) or in its vicinity. In the illustrated example, the spark plug 4 is attached to the cylinder cover 2 via a plug housing 10. The spark plug 4 is fixed to the plug housing 10 by screwing a male thread portion formed on the outer circumferential surface of the spark plug 4 into a female thread portion formed on the inner circumferential surface of the plug housing 10.

[0023] This engine is provided with an ammonia injector 11 as an ammonia supplying unit that supplies ammonia to the combustion chamber 9. In this embodiment, the ammonia injector 11 is provided in the intake port 5. Gaseous ammonia injected from the ammonia injector 11 into the intake port 5 is mixed with air in the intake port 5, and this mixture (main combustion gas) is supplied to the combustion chamber 9 when the intake valve 6 opens.

[0024] The engine is provided with a hydrogen gas supply passage 12 as a hydrogen gas supply unit that supplies hydrogen gas to the combustion chamber 9. The hydrogen gas supply passage 12 in this embodiment has a flow passage 12a provided in the cylinder cover 2 and a flow passage 12b provided in the plug housing 10. The hydrogen gas supply passage 12 opens to the upper part of the combustion chamber 9, and in the illustrated example, opens to the lower end surface of the plug housing 10. An opening 12c of the hydrogen gas supply passage 12 is provided near the ignition portion 4a of the spark plug 4. In the illustrated example, the ignition portion 4a of the spark plug 4 and the opening 12c of the hydrogen gas supply passage 12 are provided in a region of the upper part of the combustion chamber 9, which is closer to the center than the intake port 5 and the exhaust port 7.

[0025] In this embodiment, hydrogen gas (reformed hydrogen) generated by decomposing ammonia is supplied from a hydrogen gas supply passage 12. Specifically, the engine of this embodiment has an ammonia storage section that stores ammonia, which is the main fuel, a decomposition device that uses a catalyst to decompose the ammonia stored in the ammonia storage section to generate hydrogen gas and nitrogen gas, and a mixer that mixes the hydrogen gas and nitrogen gas generated by the decomposition device with air at a predetermined ratio to generate a combustion supporting gas. The combustion supporting gas generated by the mixer is supplied to the combustion chamber 9 via the hydrogen gas supply passage 12 (see dotted arrow C). In this way, by generating hydrogen gas by decomposing ammonia, which is the main fuel, there is no need to provide a separate storage section (tank) for storing hydrogen gas on the ship.

[0026] Fig. 2 shows the combustion cycle of the engine. The engine of this embodiment is a four-stroke engine in which one cycle is completed by two reciprocating movements of the piston 3. The angle in parentheses in the figure is the rotation angle of the crankshaft rotated by the up and down movement of the piston 3, and is defined as 0° when the piston 3 is at top dead center (TDC) during the explosion stroke.

[0027] After the piston 3 is pushed down from the top dead center (0°) in the explosion stroke, when the piston 3 rises beyond the bottom dead center (180°), the exhaust valve 8 is opened to discharge the exhaust gas in the combustion chamber 9 from the exhaust port 7 (exhaust stroke). Then, when the piston 3 falls beyond the top dead center (360°), the intake valve 6 is opened. At this time, ammonia is injected from the ammonia injector 11 into the intake port 5, a mixture of ammonia and air (main combustion gas) is generated in the intake port 5, and this main combustion gas is supplied to the combustion chamber 9 (intake stroke). The injection pressure of ammonia from the ammonia injector 11 is set to, for example, 1.0 MPa or less. In the illustrated example, the injection of ammonia from the ammonia injector 11 is performed across the exhaust stroke and the intake stroke. Specifically, the injection of ammonia is started before the intake valve 6 starts to open, and the injection of ammonia is completed when the intake valve 6 is in a fully open state (before the intake valve 6 starts to close).

[0028] Thereafter, when the piston 3 rises beyond the bottom dead center (540°), the main combustion gas in the combustion chamber 9 is compressed (compression stroke). In the first half of this compression stroke, i.e., between the bottom dead center (540°) and the time when the piston 3 reaches the center between the bottom dead center and the top dead center (630°), a combustion supporting gas containing hydrogen gas is supplied from the hydrogen gas supply passage 12 to the combustion chamber 9 (see dotted arrow C in FIG. 1). In the illustrated example, in the period spanning the intake stroke and the compression stroke, i.e., when the piston 3 is at the bottom dead center (540°), the combustion supporting gas is supplied from the hydrogen gas supply passage 12 to the combustion chamber 9 (see FIG. 2). When the piston 3 is near the bottom dead center, the main combustion gas in the combustion chamber 9 is hardly compressed, so that the combustion supporting gas containing hydrogen gas can be supplied to the combustion chamber 9 at a relatively low pressure.

[0029] As described above, the mixture (main combustion gas and supporting gas) in the combustion chamber 9 is compressed by supplying the supporting gas to the combustion chamber 9 to which the main combustion gas has been supplied while the piston 3 is rising (see FIG. 3). At this time, the mixture in the combustion chamber 9 is pushed up from below by the piston 3, so that the supporting gas D supplied to the upper part of the combustion chamber 9 is pushed into the upper part of the combustion chamber 9 without diffusing downward. In addition, a vertical vortex T called a tumble (vortex in a cross section in the axial direction of the cylinder) and a horizontal vortex S called a swirl (vortex in a cross section perpendicular to the axis of the cylinder) are generated in the combustion chamber 9. It is preferable to adjust the shape of the combustion chamber 9 and the opening and closing timing of the intake valve 6 and the exhaust valve 8 so that the supporting gas D is pushed into the center of the upper part of the combustion chamber 9 by the vortices T and S generated in the combustion chamber 9 in the compression stroke.

[0030] Then, just before the piston 3 reaches the top dead center (720°), as shown in FIG. 4, the supporting gas D is pushed into the center of the upper part of the combustion chamber 9 and gathers around the ignition part 4a of the spark plug 4. As a result, the hydrogen gas concentration in the upper part of the combustion chamber 9 (above the vertical center line L) is higher than the hydrogen gas concentration in the lower part of the combustion chamber 9 (below the vertical center line L), and the hydrogen gas concentration in the central part of the upper part of the combustion part 9 is higher than the hydrogen gas concentration in the outer periphery of the upper part of the combustion chamber 9. In this state, by igniting the ignition part 4a of the spark plug 4, the high concentration supporting gas D gathered around the ignition part 4a is ignited and combusted, and this combustion is propagated to the main combustion gas containing ammonia (explosion stroke). As a result, the piston 3 is pushed down from the top dead center (720°=0°).

[0031] As described above, by supplying the combustion supporting gas containing hydrogen gas to the upper part of the combustion chamber 9 and pushing this combustion supporting gas into the upper part of the combustion chamber 9 by the rise of the piston 3, the concentration of hydrogen gas in the upper part of the combustion chamber 9, i.e., around the ignition part 4a of the spark plug 4, is increased, making it easier to ignite even a small amount of hydrogen gas. This makes it possible to reduce the amount of hydrogen gas used and reduce fuel costs, and also to reliably ignite the hydrogen gas to burn the main combustion gas containing ammonia.

[0032] The present invention is not limited to the above embodiment. Other embodiments of the present invention will be described below, but redundant description of points similar to the above embodiment will be omitted.

[0033] The configuration of the hydrogen gas supply passage 12 is not limited to the above. In the embodiment shown in Fig. 5, the ignition plug 4 is provided with a flow passage 12d that functions as part of the hydrogen gas supply passage 12. An opening 12c at the lower end of the flow passage 12d is provided on the lower end surface of the ignition plug 4 and opens to the upper part of the combustion chamber 9. The supporting gas is supplied to the upper part of the combustion chamber 9 through the flow passages 12a, 12b, and 12d. Note that the intake port 5 and the intake valve 6, and the exhaust port 7 and the exhaust valve 8 are not shown in Fig. 5.

[0034] In the embodiment shown in Fig. 6, a gap 12e between the outer peripheral surface of the ignition plug 4 and the inner peripheral surface of the plug housing 10 functions as a part of the hydrogen gas supply passage 12. Specifically, a threaded connection portion 12f is provided at an upper portion of the fitting portion between the outer peripheral surface of the ignition plug 4 and the inner peripheral surface of the plug housing 10, where thread grooves formed on these surfaces are screwed together. Meanwhile, at a lower portion of the fitting portion between the outer peripheral surface of the ignition plug 4 and the inner peripheral surface of the plug housing 10, these surfaces are both cylindrical surfaces and face each other via a gap 12e. The supporting gas is supplied to the upper portion of the combustion chamber 9 through the passages 12a, 12b and the gap 12e.

[0035] The timing of supplying hydrogen gas to the combustion chamber 9 is not limited to the above. For example, the supply of hydrogen gas to the combustion chamber 9 may be started immediately after the start of the compression stroke, that is, immediately after the piston 3 passes the bottom dead center (540°) (see dotted arrow E in FIG. 2). In addition, the supply of hydrogen gas to the combustion chamber 9 may be stopped after the intake valve 6 is closed and before ignition (see dotted arrow F in FIG. 2).

[0036] The ignition means is not limited to an ignition plug, and may be, for example, a heavy oil injection unit that injects heavy oil into the combustion chamber 9.

[0037] In the above embodiment, the case where only ammonia is supplied from the ammonia supply unit has been described, but the present invention is not limited to this. For example, a mixed gas of ammonia and hydrogen may be supplied from the ammonia supply unit. [Explanation of symbols]

[0038] 1 Cylinder liner 2 Cylinder cover 3 Piston 4 Spark plug (means of ignition) 4a Ignition part 5 Intake port 6 Intake valve 7 Exhaust port 8 Exhaust valve 9. Combustion chamber 10 Plug housing 11 Ammonia injection section (ammonia supply section) 12 Hydrogen gas supply path (hydrogen gas supply section) D. Combustion support gas

Claims

1. A combustion chamber; An ammonia supply unit that supplies ammonia to the combustion chamber; a hydrogen gas supply unit that supplies hydrogen gas to an upper portion of the combustion chamber from a supply port that opens into the combustion chamber; and an ignition means for igniting the hydrogen gas at an upper portion of the combustion chamber to combust the hydrogen gas.

2. 2. The internal combustion engine according to claim 1, wherein the hydrogen gas is produced from the ammonia.

3. 2. The internal combustion engine according to claim 1, wherein hydrogen gas is supplied from the hydrogen gas supply unit to the combustion chamber during a compression process of compressing the air-fuel mixture in the combustion chamber.

4. 2. The internal combustion engine according to claim 1, wherein hydrogen gas is supplied from the hydrogen gas supply unit to the combustion chamber during a first half of a compression stroke of compressing the air-fuel mixture in the combustion chamber.

5. 2. The internal combustion engine according to claim 1, wherein the hydrogen gas is supplied from the hydrogen gas supply section to the combustion chamber when the piston is at bottom dead center.

6. 2. The internal combustion engine according to claim 1, wherein immediately before ignition by the ignition means, the concentration of the hydrogen gas in the upper part of the combustion chamber is higher than the concentration of the hydrogen gas in the lower part of the combustion chamber.

7. an intake step of supplying a main combustion gas containing ammonia to a combustion chamber; a compression step of supplying hydrogen gas to an upper portion of the combustion chamber while compressing a main combustion gas in the combustion chamber; and a combustion step of igniting the upper portion of the combustion chamber to combust the hydrogen gas.

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