Ammonia engine system

Abstract

To early start an ammonia engine.SOLUTION: An ammonia engine system 10 includes: an ammonia engine 11; a first supply flow passage 12 for supplying air containing oxygen to the ammonia engine 11; a first regulating valve 15 provided in the first supply flow passage 12; a reformer 23; a second supply flow passage 24 for supplying ammonia to the reformer 23 together with the air containing oxygen; a second regulating valve 33 for regulating the amount of the air containing oxygen to be supplied to the second supply flow passage 24; a fuel injector 14 for supplying ammonia to the first supply flow passage 12; a third supply flow passage 31 for supplying hydrogen generated by the reformer 23 to the first supply flow passage 12; a first oxygen enrichment membrane 53 for supplying oxygen-enriched air having an increased oxygen concentration compared to air to the first supply flow passage 12; and a control section 37 that supplies ammonia from the fuel injector 14 to the first supply flow passage 12 and opens the first regulating valve 15 at start of the ammonia engine 11.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an ammonia engine system. [Background technology]

[0002] The ammonia engine system described in Patent Document 1 includes an ammonia engine that uses ammonia as fuel, a first supply flow path that supplies air to the ammonia engine, a first adjustment valve provided in the first supply flow path, and a reformer. The reformer has a reforming section that reforms ammonia to generate hydrogen, and a heating section that raises the temperature of the reforming section. The ammonia engine system further includes a second supply flow path that supplies ammonia together with air to the reformer, a second adjustment valve provided in the second supply flow path, and a supply section that supplies ammonia to the first supply flow path. The hydrogen generated in the reformer is supplied to the ammonia engine via the first supply flow path. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-173232 Summary of the Invention [Problem to be solved by the invention]

[0004] The reformer generates hydrogen after the temperature of the reformer is raised to an optimum temperature for decomposing ammonia into hydrogen by the temperature raising unit. As a result, when hydrogen generated in the reformer is supplied to the ammonia engine at the start of the ammonia engine, it takes time for the hydrogen generated in the reformer to be supplied to the ammonia engine, so there is a risk of delaying the start of the ammonia engine. [Means for solving the problem]

[0005] The ammonia engine system that solves the above-mentioned problems includes an ammonia engine that uses ammonia as fuel, a first supply flow path that supplies oxygen-containing air to the ammonia engine, a first adjustment valve that is provided in the first supply flow path and adjusts the amount of oxygen-containing air supplied to the ammonia engine from the first supply flow path, a reformer having a reforming unit that reforms ammonia to generate hydrogen and a heating unit that raises the temperature of the reforming unit, a second supply flow path that supplies ammonia together with the oxygen-containing air to the reformer, a second adjustment valve that adjusts the amount of oxygen-containing air supplied to the second supply flow path, a supply unit that supplies ammonia to the first supply flow path, a third supply flow path that supplies hydrogen generated by the reformer to the first supply flow path, an oxygen enrichment membrane that is provided upstream of the first adjustment valve in the first supply flow path and supplies oxygen-enriched air having a higher oxygen concentration than air to the first supply flow path, and a control unit that supplies ammonia from the supply unit to the first supply flow path and opens the first adjustment valve when the ammonia engine is started.

[0006] According to the above configuration, oxygen-enriched air having an oxygen concentration higher than that of air flows into the first supply passage by the oxygen enrichment membrane. As a result, even if the amount of hydrogen supplied from the reformer to the ammonia engine is reduced when the ammonia engine is started, oxygen-enriched air having an increased oxygen concentration can be supplied from the first supply passage to the ammonia engine, so that the ammonia engine can be started. Furthermore, since the generation of hydrogen by the reformer is performed after the temperature of the reformer is raised to an optimum temperature for decomposing ammonia into hydrogen by the temperature raising section before the ammonia engine is started, it takes time for the hydrogen generated by the reformer to be supplied to the ammonia engine. When the ammonia engine is started, the control section supplies ammonia from the supply section to the first supply passage and opens the first adjustment valve. As a result, when the ammonia engine is started, oxygen can be supplied from the first supply passage to the ammonia engine. Therefore, the ammonia engine can be started earlier than when oxygen is not supplied from the first supply passage to the ammonia engine and hydrogen is supplied from the reformer to the ammonia engine when the ammonia engine is started.

[0007] In the ammonia engine system, the control unit may control the first regulating valve and the second regulating valve so that an amount of oxygen supplied to the ammonia engine is equal to or less than a threshold value during high load operation of the ammonia engine.

[0008] According to the above configuration, the combustion temperature of the ammonia engine tends to increase as the amount of oxygen supplied to the ammonia engine increases. Also, the combustion temperature of the ammonia engine tends to increase as the amount of hydrogen supplied to the ammonia engine increases. However, the range of increase in the combustion temperature relative to the amount of hydrogen supplied to the ammonia engine is more gradual than the range of increase in the combustion temperature relative to the amount of oxygen supplied to the ammonia engine. When the ammonia engine is operating at high load, there is a concern that nitrogen oxides may be generated due to combustion in the ammonia engine. In such a case, the combustion temperature of the ammonia engine can be lowered by reducing the amount of oxygen supplied to the ammonia engine. Therefore, the generation of nitrogen oxides due to combustion in the ammonia engine can be suppressed.

[0009] In the ammonia engine system, the control unit may control the first regulating valve and the second regulating valve so that a ratio of an amount of oxygen supplied to the ammonia engine to a total amount of ammonia, oxygen, and hydrogen supplied to the ammonia engine is 23% or more and 60% or less during operation of the ammonia engine.

[0010] In the ammonia engine system, the ammonia engine includes a fourth supply flow path through which air flows, and an upstream regulating valve provided downstream of the oxygen enrichment membrane in the first supply flow path and upstream of the first regulating valve, wherein a portion of the first supply flow path upstream of the upstream regulating valve is defined as an upstream flow path, and a portion downstream of the upstream regulating valve is defined as a downstream flow path, and the control unit may adjust the upstream regulating valve in accordance with an operating state of the ammonia engine, thereby adjusting an amount of oxygen-enriched air flowing from the upstream flow path to the downstream flow path and an amount of air flowing from the fourth supply flow path to the downstream flow path.

[0011] According to the above configuration, in addition to oxygen-enriched air, air in a state in which the oxygen concentration is not increased can be supplied to the ammonia engine, so that a more appropriate amount of oxygen can be supplied to the ammonia engine depending on the operating state of the ammonia engine. Effect of the Invention

[0012] According to the present invention, the ammonia engine can be started quickly. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing an ammonia engine system in an embodiment. [Diagram 2] FIG. 2 is a graph showing the relationship between oxygen ratio and combustion speed in an ammonia engine. [Diagram 3] FIG. 3 is a schematic diagram showing an ammonia engine system in a modified example. [Figure 4] FIG. 4 is a schematic diagram showing an ammonia engine system in a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of an ammonia engine system will be described with reference to the drawings. <Basic configuration of an ammonia engine system> As shown in Fig. 1, the ammonia engine system 10 includes an ammonia engine 11 and a first supply flow passage 12. The ammonia engine system 10 in this embodiment is mounted on an engine vehicle. The ammonia engine 11 uses ammonia (NH3) gas as fuel. The ammonia engine 11 has a combustion chamber 11a. The ammonia engine 11 is, for example, a four-cylinder engine, and has, for example, four combustion chambers 11a.

[0015] The first supply flow passage 12 is a flow passage that supplies air containing oxygen to the ammonia engine 11. The first supply flow passage 12 is connected to the combustion chamber 11a. The air containing oxygen flowing through the first supply flow passage 12 is supplied to the combustion chamber 11a.

[0016] The ammonia engine system 10 includes an exhaust flow path 13. The exhaust flow path 13 is a flow path through which exhaust gas is discharged from the ammonia engine 11. The exhaust flow path 13 is connected to the combustion chamber 11a. The exhaust gas generated in the combustion chamber 11a flows through the exhaust flow path 13 after being discharged into the exhaust flow path 13.

[0017] The ammonia engine system 10 includes an exhaust catalyst unit 16. The exhaust catalyst unit 16 is provided in the exhaust flow passage 13. The exhaust catalyst unit 16 includes a three-way catalyst 17 and an SCR catalyst 18. Note that the exhaust catalyst unit 16 may include only one of the three-way catalyst 17 and the SCR catalyst 18.

[0018] The three-way catalyst 17 removes ammonia from the exhaust gas by oxidizing the ammonia remaining in the exhaust gas flowing through the exhaust flow passage 13. The three-way catalyst 17 is activated by the heat of the exhaust gas.

[0019] The SCR catalyst 18 is disposed downstream of the three-way catalyst 17 in the exhaust flow path 13. The SCR catalyst 18 is a selective catalytic reduction catalyst. The SCR catalyst 18 reduces nitrogen oxides (NOx) contained in the exhaust gas flowing through the exhaust flow path 13 to nitrogen (N2) using ammonia. Furthermore, the SCR catalyst 18 captures and removes ammonia that has passed through the three-way catalyst 17.

[0020] The ammonia engine system 10 includes an ammonia tank 21 and a vaporizer 22. The ammonia tank 21 stores liquid ammonia, which is ammonia in a liquid state. The vaporizer 22 vaporizes the liquid ammonia stored in the ammonia tank 21 to generate ammonia gas.

[0021] The ammonia engine system 10 includes a first regulating valve 15 and a fuel injector 14 serving as a supply unit. The fuel injector 14 is, for example, an electromagnetic injection valve. The fuel injector 14 is connected to a carburetor 22. Ammonia gas is supplied from the carburetor 22 to the fuel injector 14. The fuel injector 14 supplies ammonia to the first supply flow passage 12 by injecting ammonia gas into the first supply flow passage 12. The ammonia supplied from the fuel injector 14 to the first supply flow passage 12 flows into the combustion chamber 11a together with oxygen flowing through the first supply flow passage 12.

[0022] The first regulating valve 15 is provided in the first supply flow path 12. The first regulating valve 15 is, for example, an electromagnetic flow control valve. The first regulating valve 15 adjusts the amount of air supplied from the first supply flow path 12 to the ammonia engine 11 by adjusting the opening degree of the first supply flow path 12. In this way, the first regulating valve 15 adjusts the amount of air containing oxygen supplied from the first supply flow path 12 to the ammonia engine 11.

[0023] The ammonia engine system 10 includes a reformer 23. The reformer 23 has a reforming section 42 that reforms ammonia to generate hydrogen (H2). In detail, the reforming section 42 generates a reformed gas containing hydrogen. The reforming section 42 has, for example, a support (not shown) on which a reforming catalyst is applied. The support has, for example, a honeycomb structure. When the ammonia supplied to the reformer 23 passes through the reforming section 42, the ammonia is reformed in the reforming section 42 to generate a reformed gas. The reforming catalyst has a function of decomposing ammonia into hydrogen and a function of burning ammonia. The reforming catalyst is, for example, an ATR (Autothermal Reformer) type ammonia reforming catalyst.

[0024] The reformer 23 has a temperature raising section 41 that raises the temperature of the reforming section 42. The temperature raising section 41 is, for example, an electric heater. The temperature raising section 41 raises the temperature of the reforming catalyst in the reforming section 42 to an optimum temperature for decomposing ammonia into hydrogen by raising the temperature of the reforming section 42. For example, the temperature raising section 41 raises the temperature of the reforming section 42 only when the temperature of the reforming section 42 is lower than a specified temperature, and does not raise the temperature of the reforming section 42 when the temperature of the reforming section 42 is equal to or higher than the specified temperature. When the temperature raising section 41 is an electric heater, the temperature raising section 41 raises the temperature of the reforming section 42 by being energized, and the temperature raising of the reforming section 42 is stopped by stopping the energization of the temperature raising section 41.

[0025] When the reforming section 42 reaches a specified temperature or higher, ammonia is burned in an upstream portion of the reforming section 42 in the direction of ammonia flow. A portion of the ammonia supplied to the reforming section 42 does not burn in the upstream portion, but reaches a downstream portion of the reforming section 42 in the direction of ammonia flow. In this downstream portion, the ammonia is reformed by the reforming catalyst. The temperature of the reforming section 42 is maintained at or above the specified temperature by the combustion heat generated by the combustion reaction in the reforming section 42. This allows the reforming of ammonia in the reforming section 42 to continue.

[0026] The ammonia engine system 10 includes a second supply passage 24. The ammonia engine system 10 further includes a reforming injector 27. The reforming injector 27 is, for example, an electromagnetic injection valve. The reforming injector 27 is connected to the vaporizer 22. Ammonia gas is supplied from the vaporizer 22 to the reforming injector 27. The reforming injector 27 injects the ammonia gas into the second supply passage 24, upstream of the reformer 23. The ammonia gas supplied from the reforming injector 27 to the second supply passage 24 flows into the reformer 23 together with the air flowing through the second supply passage 24. Therefore, the second supply passage 24 supplies ammonia to the reformer 23 together with air containing oxygen.

[0027] The temperature increasing section 41 heats the air and ammonia that flow into the reformer 23 from the second supply passage 24. The air and ammonia whose temperature has been increased by being heated by the temperature increasing section 41 are supplied to the reforming section 42. As a result, the temperature of the reforming section 42 increases.

[0028] The ammonia engine system 10 includes a third supply passage 31. The third supply passage 31 connects the reforming section 42 in the reformer 23 to the first supply passage 12. In detail, one end of the third supply passage 31 is connected to the reforming section 42, and the other end of the third supply passage 31 is connected to the first supply passage 12 downstream of the first adjustment valve 15. The third supply passage 31 is a passage that introduces the reformed gas containing hydrogen generated by the reforming section 42 into the first supply passage 12. In other words, the third supply passage 31 supplies the hydrogen generated by the reformer 23 to the first supply passage 12.

[0029] The ammonia engine system 10 includes a cooler 32. The cooler 32 is provided in the third supply passage 31. The cooler 32 cools the reformed gas flowing through the third supply passage 31. The cooler 32 cools the reformed gas flowing through the third supply passage 31, for example, by exchanging heat between cooling water flowing inside the cooler 32 and the reformed gas flowing through the third supply passage 31. The reformed gas cooled by the cooler 32 is introduced into the first supply passage 12 through the third supply passage 31. This makes it possible to suppress damage to intake system components such as the first adjustment valve 15 caused by the heat of the reformed gas. Since the volume expansion of the reformed gas is suppressed as the reformed gas is cooled, air easily flows into the combustion chamber 11a from the first supply passage 12.

[0030] The ammonia engine 11 includes a second regulating valve 33. The second regulating valve 33 is provided in the second supply flow path 24. The second regulating valve 33 is, for example, an electromagnetic flow control valve. The second regulating valve 33 adjusts the opening degree of the second supply flow path 24. In this way, the second regulating valve 33 adjusts the amount of air containing oxygen supplied to the second supply flow path 24. The second regulating valve 33 adjusts the amount of air supplied from the second supply flow path 24 to the reformer 23.

[0031] The ammonia engine system 10 includes a first air cleaner 51 and a second air cleaner 52. The first air cleaner 51 and the second air cleaner 52 remove foreign matter such as dust and dirt contained in the air. The first air cleaner 51 is connected to the upstream end of the first supply flow path 12. As a result, the first air cleaner 51 introduces the air from which the foreign matter has been removed into the first supply flow path 12. The second air cleaner 52 is connected to the upstream end of the second supply flow path 24. As a result, the second air cleaner 52 introduces the air from which the foreign matter has been removed into the second supply flow path 24.

[0032] <Oxygen enrichment membrane> The ammonia engine system 10 includes a first oxygen enrichment membrane 53 as an oxygen enrichment membrane. The first oxygen enrichment membrane 53 is provided upstream of the first adjustment valve 15 as an adjustment valve in the first supply flow passage 12. In detail, the first oxygen enrichment membrane 53 is provided between the first air cleaner 51 and the first adjustment valve 15 in the first supply flow passage 12. The air that flows from the first air cleaner 51 into the first supply flow passage 12 flows through the first oxygen enrichment membrane 53 to the downstream side of the first oxygen enrichment membrane 53 in the first supply flow passage 12. At this time, the oxygen concentration of the air flowing through the first supply flow passage 12 is increased by the first oxygen enrichment membrane 53. Therefore, the first oxygen enrichment membrane 53 supplies oxygen-enriched air having an oxygen concentration higher than that of air to the first supply flow passage 12. The oxygen-enriched air flows through the first supply flow passage 12 and is supplied to the ammonia engine 11.

[0033] The ammonia engine system 10 includes a second oxygen enrichment membrane 54. The second oxygen enrichment membrane 54 is provided in the second supply passage 24 between the second air cleaner 52 and the second adjustment valve 33. The air that flows from the second air cleaner 52 into the second supply passage 24 flows through the second oxygen enrichment membrane 54 to the downstream side of the second oxygen enrichment membrane 54 in the second supply passage 24. At this time, the oxygen concentration of the air flowing through the second supply passage 24 is increased by the second oxygen enrichment membrane 54. Therefore, the second oxygen enrichment membrane 54 supplies oxygen-enriched air, which has an oxygen concentration higher than that of air, to the second supply passage 24. The oxygen-enriched air flows through the second supply passage 24 and is supplied to the reformer 23.

[0034] Oxygen enrichment membranes include ceramic, polymer, and graphene membranes, with graphene membranes being preferred as they can be used at room temperature and supply a large amount of oxygen. <Ammonia engine system operation> When the first regulating valve 15 is opened, oxygen-enriched air is supplied to the first supply passage 12 via the first air cleaner 51 and the first oxygen enrichment membrane 53. When the second regulating valve 33 is opened, oxygen-enriched air is supplied to the second supply passage 24 via the second air cleaner 52 and the second oxygen enrichment membrane 54.

[0035] The fuel injector 14 injects ammonia gas toward the first supply passage 12. As a result, the ammonia is supplied from the first supply passage 12 to the ammonia engine 11 together with the oxygen-enriched air. The reforming injector 27 injects ammonia gas toward the second supply passage 24. As a result, the ammonia is supplied from the second supply passage 24 to the reformer 23 together with the oxygen-enriched air.

[0036] In the reformer 23, the temperature increasing section 41 starts increasing the temperature of the reforming section 42 before the start of the ammonia engine 11. As a result, the temperature increasing section 41 increases the temperature of the oxygen-enriched air and ammonia supplied to the reformer 23. When the temperature of the reforming catalyst in the reforming section 42 increases to an optimum temperature for decomposing ammonia into hydrogen, the reforming of ammonia by the reforming section 42 starts. As a result, a reformed gas containing hydrogen is generated by the reforming section 42. The generated reformed gas is supplied from the reformer 23 to the third supply flow path 31, and then supplied to the ammonia engine 11 via the third supply flow path 31 and the first supply flow path 12.

[0037] When air is supplied to the combustion chamber 11a, ammonia is burned together with oxygen in the air in the combustion chamber 11a. When reformed gas is supplied to the combustion chamber 11a, ammonia is burned together with hydrogen in the reformed gas in the combustion chamber 11a. Thus, ammonia is burned in the combustion chamber 11a.

[0038] <Control Unit> The ammonia engine system 10 includes a control unit 37. The control unit 37 includes a processor and a storage unit. The processor is, for example, a central processing unit (CPU), a graphics processing unit (GPU), or a digital signal processor (DSP). The storage unit includes a random access memory (RAM) and a read only memory (ROM). The storage unit stores program codes or instructions configured to cause the processor to execute processes. The storage unit, i.e., the computer-readable medium, includes any available medium accessible by a general-purpose or dedicated computer. The control unit 37 may be configured by a hardware circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). The control unit 37, which is a processing circuit, may include one or more processors that operate according to a computer program, one or more hardware circuits such as an ASIC or an FPGA, or a combination thereof.

[0039] The ammonia engine system 10 includes an ignition switch 35 and a temperature sensor 36. When the driver of the vehicle operates the ignition switch 35, the ignition switch 35 outputs an operation signal to the control unit 37. The temperature sensor 36 outputs a detection signal related to the temperature of the reforming unit 42 to the control unit 37.

[0040] <Control by the control unit> The control unit 37 performs various controls based on, for example, an operation signal of an ignition switch 35 and a detection signal of a temperature sensor 36. The control unit 37 controls the first regulating valve 15, the second regulating valve 33, the fuel injector 14, the reforming injector 27, the temperature raising unit 41, and the like.

[0041] The control unit 37 adjusts the aperture of the first adjusting valve 15 based on, for example, the size of the first adjusting valve 15 itself and the flow path cross-sectional area of ​​the first supply flow path 12. By adjusting the aperture of the first adjusting valve 15 in this manner, the control unit 37 adjusts the amount of oxygen-containing air supplied to the first supply flow path 12. In addition, the control unit 37 adjusts the aperture of the second adjusting valve 33 based on, for example, the size of the second adjusting valve 33 itself and the flow path cross-sectional area of ​​the second supply flow path 24. By adjusting the aperture of the second adjusting valve 33 in this manner, the control unit 37 adjusts the amount of oxygen-containing air supplied to the second supply flow path 24.

[0042] For example, the control unit 37 executes stop control to stop the ammonia engine 11. The control unit 37 executes the stop control on the condition that it has determined that the ignition switch 35 has been turned off based on an operation signal of the ignition switch 35.

[0043] In the stop control, the control unit 37 stops the injection of ammonia gas from the fuel injector 14 and the reforming injector 27, and closes the first regulating valve 15 and the second regulating valve 33. This stops the ammonia engine 11.

[0044] <Start-up control> The control unit 37 executes start-up control to start the ammonia engine 11. The control unit 37 performs the start-up control on the condition that it has determined that the ignition switch 35 has been turned on based on an operation signal from the ignition switch 35. In the start-up control, the control unit 37 does not inject ammonia gas from the reforming injector 27 and closes the second adjustment valve 33.

[0045] In the start control, the control unit 37 controls a starter motor (not shown) to crank the ammonia engine 11, thereby starting the ammonia engine 11.

[0046] In the startup control, the control unit 37 injects ammonia gas from the fuel injector 14 and opens the first adjustment valve 15. That is, when the ammonia engine 11 is started, the control unit 37 supplies ammonia from the fuel injector 14, which serves as a supply unit, to the first supply passage 12 and opens the first adjustment valve 15.

[0047] During execution of the startup control, ammonia is supplied together with oxygen-enriched air to the combustion chamber 11a from the first supply passage 12. In the combustion chamber 11a, the ammonia is burned together with oxygen. After the ammonia is burned in the combustion chamber 11a, the control unit 37 ends the startup control.

[0048] <Control during low load operation> After the start control is completed, the control unit 37 performs control according to the load of the ammonia engine 11. During low load operation of the ammonia engine 11, the control unit 37 injects ammonia gas from the fuel injector 14 and opens the first adjustment valve 15. Furthermore, during low load operation of the ammonia engine 11, the control unit 37 injects ammonia gas from the reforming injector 27 and opens the second adjustment valve 33. Note that low load operation refers to the operation of the ammonia engine 11 when the amount of NOx emissions from the ammonia engine 11 is equal to or less than the reference value even without adjusting the amount of oxygen supplied to the ammonia engine 11, for example, when there is no rapid change in the accelerator pedal opening.

[0049] During low-load operation of the ammonia engine 11, the control unit 37 determines whether the temperature of the reforming unit 42 is equal to or higher than a specified temperature based on the detection value of the temperature sensor 36. The specified temperature is a temperature at which the reforming unit 42 can burn ammonia, and is, for example, about 200°C. When the control unit 37 determines that the temperature of the reforming unit 42 is equal to or higher than the specified temperature, it controls the temperature increasing unit 41 to stop increasing the temperature of the reforming unit 42 by the temperature increasing unit 41. As the temperature of the reforming unit 42 increases, the reforming unit 42 generates a reformed gas containing hydrogen. The reformed gas flows from the reformer 23 into the third supply passage 31.

[0050] During low load operation of the ammonia engine 11, ammonia is supplied from the fuel injector 14 together with oxygen-enriched air from the first supply passage 12 to the combustion chamber 11a, and reformed gas is supplied to the combustion chamber 11a from the third supply passage 31. In the combustion chamber 11a, the ammonia is combusted together with oxygen and hydrogen.

[0051] During low load operation of the ammonia engine 11, the apertures of the first regulating valve 15 and the second regulating valve 33 may be changed as appropriate. The total amount of ammonia, oxygen, and hydrogen supplied to the ammonia engine 11 is also referred to as total amount T. For example, during low load operation of the ammonia engine 11, the control unit 37 may adjust the ratio of oxygen and hydrogen to the total amount T by adjusting the apertures of the first regulating valve 15 and the second regulating valve 33. For example, during low load operation of the ammonia engine 11, the control unit 37 may make the ratio of oxygen to the total amount T greater than the ratio of hydrogen to the total amount T.

[0052] The control unit 37 may switch the opening of the first regulating valve 15 and the second regulating valve 33, for example, according to the rotation speed and torque of the ammonia engine 11. As a result, during low load operation of the ammonia engine 11, the first regulating valve 15 and the second regulating valve 33 may be switched between a case where one of the openings is larger than the other and a case where one of the openings is smaller than the other. Note that during low load operation of the ammonia engine 11, the openings of the first regulating valve 15 and the second regulating valve 33 may be adjusted in a state where one of the openings of the first regulating valve 15 and the second regulating valve 33 is larger than the other. In short, it is sufficient that the control unit 37 adjusts the openings of the first regulating valve 15 and the second regulating valve 33 so that the ratio of ammonia, oxygen, and hydrogen supplied to the ammonia engine 11 is a preferable ratio.

[0053] For example, the control unit 37 may estimate or detect the amount of oxygen supplied to the ammonia engine 11 from the first supply flow path 12 and the amount of hydrogen supplied to the ammonia engine 11 from the third supply flow path 31. Based on the results of the estimation or detection, the control unit 37 may adjust the opening degrees of the first adjustment valve 15 and the second adjustment valve 33.

[0054] <Control during high load operation> During high load operation of the ammonia engine 11, similarly to during low load operation, the control unit 37 injects ammonia gas from the fuel injector 14 and opens the first adjustment valve 15. The control unit 37 injects ammonia gas from the reforming injector 27 and opens the second adjustment valve 33. Note that during high load operation, for example, when the accelerator pedal opening degree continues to be at a constant amount and then increases, there is a risk that the amount of NOx emissions from the ammonia engine 11 will exceed the reference value unless the amount of oxygen supplied to the ammonia engine 11 is adjusted.

[0055] During high load operation of the ammonia engine 11, the ratio of hydrogen to the total amount T is greater than during start-up and low load operation of the ammonia engine 11. Therefore, during high load operation of the ammonia engine 11, the ratio R of the amount of oxygen supplied to the ammonia engine 11 to the total amount T is less than during start-up and low load operation of the ammonia engine 11. Therefore, during high load operation of the ammonia engine 11, the control unit 37 controls the first regulating valve 15 and the second regulating valve 33 so that the amount of oxygen supplied to the ammonia engine 11 is equal to or less than the threshold value. The threshold value is a value that is set in advance through experiments or the like. For example, the threshold value is set to a value that is less than the amount of oxygen supplied to the ammonia engine 11 when the amount of oxygen supplied to the ammonia engine 11 is equal to or less than the threshold value, and is set to a value that is less than the amount of oxygen supplied to the ammonia engine 11 when the ammonia engine 11 is started and is less than the amount of oxygen supplied to the ammonia engine 11 when the ammonia engine 11 is operated at low load.

[0056] For example, the control unit 37 adjusts the opening degree of the first regulating valve 15 and the opening degree of the second regulating valve 33 so that the amount of oxygen supplied to the ammonia engine 11 is equal to or less than the threshold value during high load operation of the ammonia engine 11. As a result, for example, during high load operation of the ammonia engine 11, the control unit 37 may adjust the ratio of oxygen and hydrogen to the total amount T by adjusting the opening degree of the first regulating valve 15 and the opening degree of the second regulating valve 33. For example, during high load operation of the ammonia engine 11, the control unit 37 may make the ratio of hydrogen to the total amount T greater than the ratio of oxygen to the total amount T. By adjusting the opening degrees of the first regulating valve 15 and the second regulating valve 33, the control unit 37 adjusts the amount of oxygen supplied to the ammonia engine 11 to be equal to or less than the threshold value. During high load operation of the ammonia engine 11, the opening degrees of the first regulating valve 15 and the second regulating valve 33 may be changed as appropriate. For example, the opening degrees of the first regulating valve 15 and the second regulating valve 33 may be switched depending on the rotation speed and torque of the ammonia engine 11.

[0057] During high load operation of the ammonia engine 11, similarly to during low load operation, ammonia is supplied together with oxygen-enriched air from the first supply passage 12 to the combustion chamber 11a, and reformed gas is supplied to the combustion chamber 11a from the third supply passage 31. In the combustion chamber 11a, ammonia is combusted together with oxygen and hydrogen.

[0058] <Amount of oxygen supplied to the ammonia engine> The control unit 37 controls the first regulating valve 15 and the second regulating valve 33 so that the ratio R of the amount of oxygen supplied to the ammonia engine 11 to the total amount T during operation of the ammonia engine 11 is 23% or more and 60% or less. In detail, the control unit 37 controls the first regulating valve 15 and the second regulating valve 33 so that, for example, the ratio R during low load operation of the ammonia engine 11 is higher than the ratio R during high load operation of the ammonia engine 11 within the above-mentioned range of 23% or more and 60% or less.

[0059] FIG. 2 was obtained by an engine test. FIG. 2 is a diagram showing the relationship between the ratio R of the amount of oxygen supplied to the ammonia engine 11 to the total amount T when the ammonia engine 11 is operating under conditions where the ammonia engine 11 can operate stably, and the combustion speed of the ammonia engine 11. In FIG. 2, the relationship between the ratio R and the combustion speed is shown by different line types for each ratio of the amount of hydrogen supplied to the ammonia engine 11 to the total amount T. When the ratio R is 21%, this corresponds to a case where it is assumed that air in a state where the oxygen concentration is not increased is supplied to the ammonia engine 11 from the first supply flow passage 12. In addition, under a situation where the ratio R is 21%, the ratio of the amount of hydrogen supplied to the ammonia engine 11 to the total amount T required when the ammonia engine 11 is operating is 20 to 50%.

[0060] As shown in Fig. 2, when the ratio of the amount of hydrogen supplied to the ammonia engine 11 to the total amount T is 50% and the ratio R is 21%, the combustion speed is a first combustion speed SP1. When the ratio of the amount of hydrogen supplied to the ammonia engine 11 to the total amount T is 0 (zero)%, in order to realize the first combustion speed SP1, the ratio R is 50%. When the ratio of the amount of hydrogen supplied to the ammonia engine 11 to the total amount T is 20% and the ratio R is 21%, the combustion speed is a second combustion speed SP2. When the ratio of the amount of hydrogen supplied to the ammonia engine 11 to the total amount T is 0 (zero)%, in order to realize the second combustion speed SP2, the ratio R is 27%.

[0061] Therefore, when the ratio of the amount of hydrogen supplied to the ammonia engine 11 to the total amount T is 0 (zero)%, the requirements for operation of the ammonia engine 11 can be met by adjusting the ratio R to 27% or more and 50% or less. In reality, when the ammonia engine 11 is operating, the ratio of the amount of hydrogen supplied to the ammonia engine 11 to the total amount T is not 0 (zero)%, so the ratio R is preferably set to 23% or more and 60% or less, which is wider than the above range. The control unit 37 satisfies the requirements for operation of the ammonia engine 11 by controlling the ratio R of the amount of oxygen supplied to the ammonia engine 11 to the total amount T to 23% or more and 60% or less when the ammonia engine 11 is operating.

[0062] [Actions and Effects of the Embodiments] According to the above embodiment, the following actions and effects can be obtained. (1-1) Oxygen-enriched air having an oxygen concentration higher than that of air flows into the first supply passage 12 by the first oxygen enrichment membrane 53 as an oxygen enrichment membrane. As a result, even if the amount of hydrogen supplied from the reformer 23 to the ammonia engine 11 is reduced when the ammonia engine 11 is started, oxygen-enriched air having an increased oxygen concentration can be supplied to the ammonia engine 11 from the first supply passage 12. Therefore, the ammonia engine 11 can be started. Furthermore, the generation of hydrogen by the reformer 23 is performed after the temperature of the reformer 42 is raised by the temperature raising unit 41 to an optimal temperature for decomposing ammonia into hydrogen before the ammonia engine 11 is started. Therefore, it takes time for the hydrogen generated by the reformer 23 to be supplied to the ammonia engine 11. When the ammonia engine 11 is started, the control unit 37 supplies ammonia from the fuel injector 14 as a supply unit to the first supply passage 12 and opens the first adjustment valve 15. As a result, when the ammonia engine 11 is started, oxygen can be supplied from the first supply passage 12 to the ammonia engine 11. Therefore, when starting the ammonia engine 11, the ammonia engine 11 can be started earlier than when oxygen is not supplied to the ammonia engine 11 from the first supply passage 12 and hydrogen is supplied to the ammonia engine 11 from the reformer 23.

[0063] (1-2) The control unit 37 controls the first adjusting valve 15 and the second adjusting valve 33 so that the amount of oxygen supplied to the ammonia engine 11 is equal to or less than a threshold value during high-load operation of the ammonia engine 11. The greater the amount of oxygen supplied to the ammonia engine 11, the higher the combustion temperature of the ammonia engine 11 tends to be. Also, the greater the amount of hydrogen supplied to the ammonia engine 11, the higher the combustion temperature of the ammonia engine 11 tends to be. However, the increase in the combustion temperature relative to the amount of hydrogen supplied to the ammonia engine 11 is more gradual than the increase in the combustion temperature relative to the amount of oxygen supplied to the ammonia engine 11. During high-load operation of the ammonia engine 11, there is concern about the generation of nitrogen oxides due to combustion in the ammonia engine 11. In such a case, the amount of oxygen supplied to the ammonia engine 11 is reduced, thereby lowering the combustion temperature in the ammonia engine 11. Therefore, the generation of nitrogen oxides due to combustion in the ammonia engine 11 can be suppressed.

[0064] (1-3) The size of the reformer 23 can be made smaller than when oxygen is not supplied to the ammonia engine 11 from the first supply passage 12 and hydrogen is supplied to the ammonia engine 11 from the reformer 23. Therefore, the size of the ammonia engine system 10 can be made smaller.

[0065] [Example of change] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0066] As shown in FIG. 3, the ammonia engine 11 may include a fourth supply passage 62 through which air flows, and an upstream adjustment valve 63. In detail, a third air cleaner 61 is provided at the upstream end of the fourth supply passage 62. The fourth supply passage 62 is not provided with an oxygen enrichment membrane. Therefore, the air that flows into the fourth supply passage 62 through the third air cleaner 61 flows through the fourth supply passage 62 to the downstream end of the fourth supply passage 62. The downstream end of the fourth supply passage 62 is connected between the first oxygen enrichment membrane 53 and the first adjustment valve 15 in the first supply passage 12. The upstream adjustment valve 63 is provided at the connection destination of the fourth supply passage 62 in the first supply passage 12. Thus, the upstream adjustment valve 63 is provided downstream of the first oxygen enrichment membrane 53 as the oxygen enrichment membrane in the first supply passage 12 and upstream of the first adjustment valve 15. In the first supply flow path 12, a portion upstream of the upstream regulating valve 63 is defined as the upstream flow path 12a, and a portion downstream of the upstream regulating valve 63 is defined as the downstream flow path 12b. The control unit 37 adjusts the upstream regulating valve 63 in accordance with the operating state of the ammonia engine 11 to adjust the amount of oxygen-enriched air flowing from the upstream flow path 12a to the downstream flow path 12b and the amount of air flowing from the fourth supply flow path 62 to the downstream flow path 12b. Note that the control unit 37 may switch the flow path that communicates with the downstream flow path 12b between the upstream flow path 12a and the fourth supply flow path 62 in accordance with the operating state of the ammonia engine 11. According to this modification example, the following effects can be obtained.

[0067] (2-1) The control unit 37 adjusts the amount of oxygen-enriched air flowing from the upstream flow path 12a to the downstream flow path 12b and the amount of air flowing from the fourth supply flow path 62 to the downstream flow path 12b by adjusting the upstream regulating valve 63 in accordance with the operating state of the ammonia engine 11. This makes it possible to supply air in a state in which the oxygen concentration is not increased to the ammonia engine 11 in addition to the oxygen-enriched air, so that a more appropriate amount of oxygen can be supplied to the ammonia engine 11 in accordance with the operating state of the ammonia engine 11.

[0068] As shown in FIG. 4, the second supply passage 24, the reformer 23, and the third supply passage 31 may be omitted from the ammonia engine system 10 in the embodiment. More specifically, the second air cleaner 52, the second oxygen enrichment membrane 54, the second adjustment valve 33, and the cooler 32 are further omitted from the ammonia engine system 10 in the embodiment. As a result, the hydrogen generated by the reformer 23 is not supplied to the ammonia engine 11, and oxygen-enriched air is supplied from the first supply passage 12. According to this modification, the supply system of hydrogen from the ammonia engine system 10 to the ammonia engine 11 can be omitted, so that the size of the ammonia engine system 10 can be reduced accordingly. In addition, all of the ammonia stored in the ammonia tank 21 can be used to supply to the ammonia engine 11. Therefore, compared to the case where a portion of the ammonia stored in the ammonia tank 21 is supplied to the reformer 23, the ammonia tank 21 can be reduced by the amount of ammonia used for the combustion reaction in the reformer 42. Therefore, the installation space of the ammonia tank 21 can be reduced.

[0069] The control unit 37 may control the first regulating valve 15 and the second regulating valve 33 so that, when the ammonia engine 11 is operating, the ratio R of the amount of oxygen supplied to the ammonia engine 11 to the total amount T supplied to the ammonia engine 11 is less than 23%. The control unit 37 may control the first regulating valve 15 and the second regulating valve 33 so that, when the ammonia engine 11 is operating, the ratio R of the amount of oxygen supplied to the ammonia engine 11 to the total amount T supplied to the ammonia engine 11 is higher than 60%.

[0070] ○ Hydrogen has a property of having a small unit calorific value, so when hydrogen is supplied to the ammonia engine 11, the torque of the ammonia engine 11 is unlikely to increase due to hydrogen. On the other hand, when hydrogen is supplied to the ammonia engine 11 and the amount of oxygen supplied to the ammonia engine 11 is increased, the torque of the ammonia engine 11 is likely to increase. Therefore, the control unit 37 may adjust the aperture of the first adjustment valve 15 and the second adjustment valve 33 so that the amount of oxygen supplied to the ammonia engine 11 according to the torque required during high load operation of the ammonia engine 11 is greater than that during low load operation. The control unit 37 may adjust the amount of oxygen supplied to the ammonia engine 11 according to the operating state of the ammonia engine 11 by adjusting the aperture of the first adjustment valve 15 and the second adjustment valve 33.

[0071] The control unit 37 may control the first regulating valve 15 and the second regulating valve 33 so that the amount of oxygen supplied to the ammonia engine 11 during high-load operation of the ammonia engine 11 is greater than a threshold value.

[0072] The control unit 37 may supply ammonia from the reforming injector 27 to the second supply passage 24 and open the second adjustment valve 33 when the ammonia engine 11 is started. In other words, when the ammonia engine 11 is started, the control unit 37 may supply ammonia from the fuel injector 14, which serves as a supply unit, to the first supply passage 12 and open the first adjustment valve 15.

[0073] The control unit 37 may determine whether the temperature of the reforming unit 42 is equal to or higher than a specified temperature based on the operating conditions of the ammonia engine 11, the amount of air supplied to the reformer 23, the injection amount from the reforming injector 27, the time for which electricity is applied to the temperature raising unit 41, etc. In this case, the temperature sensor 36 may be omitted from the ammonia engine 11.

[0074] The second adjustment valve 33 may be provided in the third supply passage 31. The second adjustment valve 33 in this modified example adjusts the amount of air supplied from the second supply passage 24 to the reformer 23 via the third supply passage 31 by adjusting the opening degree of the third supply passage 31. In this way, the second adjustment valve 33 in this modified example adjusts the amount of oxygen-containing air supplied to the second supply passage 24.

[0075] The ammonia engine system 10 may include a supply unit other than the fuel injector 14. In this case, the supply unit is, for example, a mixer. Furthermore, the ammonia engine system 10 may include a mixer that injects ammonia gas into the second supply passage 24, instead of the reforming injector 27.

[0076] The vaporizer 22 may be omitted from the ammonia engine system 10. In this case, the ammonia tank 21 is connected to each of the fuel injector 14 and the reforming injector 27. As a result, liquid ammonia stored in the ammonia tank 21 is supplied to the fuel injector 14 and the reforming injector 27. The fuel injector 14 and the reforming injector 27 inject liquid ammonia. In this case, the ammonia engine system 10 may have a pump for fuel injection. Liquid ammonia may be supplied from the ammonia tank 21 to the fuel injector 14 and the reforming injector 27 by the fuel injection pump.

[0077] The second oxygen enrichment membrane 54 may be omitted from the ammonia engine system 10. Instead of the first air cleaner 51 and the second air cleaner 52, one air cleaner may be provided in the ammonia engine system 10. For example, the air cleaner in this case is provided in the first supply flow passage 12. The upstream end of the second supply flow passage 24 is connected between the air cleaner and the first oxygen enrichment membrane 53 in the first supply flow passage 12. As a result, oxygen-enriched air whose oxygen concentration has been increased by the first oxygen enrichment membrane 53 flows downstream of the first oxygen enrichment membrane 53 in the first supply flow passage 12. Air whose oxygen concentration has not been increased by the first oxygen enrichment membrane 53 flows in the second supply flow passage 24. The upstream end of the second supply flow passage 24 may be connected between the first oxygen enrichment membrane 53 and the first adjustment valve 15 in the first supply flow passage 12. [Explanation of symbols]

[0078] R...proportion, T...total amount, 10...ammonia engine system, 11...ammonia engine, 12...first supply flow path, 12a...upstream flow path, 12b...downstream flow path, 14...fuel injector as supply unit, 15...first adjustment valve, 23...reformer, 24...second supply flow path, 31...third supply flow path, 33...second adjustment valve, 37...control unit, 41...heating unit, 42...reforming unit, 53...first oxygen enrichment membrane as oxygen enrichment membrane, 62...fourth supply flow path, 63...upstream adjustment valve.

Claims

1. an ammonia engine that uses ammonia as fuel; A first supply passage for supplying air containing oxygen to the ammonia engine; a first adjusting valve provided in the first supply passage and configured to adjust an amount of oxygen-containing air supplied from the first supply passage to the ammonia engine; A reformer having a reforming unit that reforms ammonia to generate hydrogen and a temperature raising unit that raises the temperature of the reforming unit; a second supply passage for supplying ammonia together with oxygen-containing air to the reformer; a second adjusting valve that adjusts the amount of oxygen-containing air supplied to the second supply line; a supply unit that supplies ammonia to the first supply flow path; a third supply passage that supplies hydrogen generated by the reformer to the first supply passage; an oxygen enrichment membrane provided upstream of the first adjustment valve in the first supply flow path and configured to supply oxygen-enriched air having a higher oxygen concentration than air to the first supply flow path; a control unit that supplies ammonia from the supply unit to the first supply line and opens the first adjustment valve when the ammonia engine is started.

2. 2. The ammonia engine system according to claim 1, wherein the control unit controls the first regulating valve and the second regulating valve so that an amount of oxygen supplied to the ammonia engine is equal to or less than a threshold value during high load operation of the ammonia engine.

3. 3. The ammonia engine system according to claim 1 or 2, wherein the control unit controls the first regulating valve and the second regulating valve so that a ratio of an amount of oxygen supplied to the ammonia engine to a total amount of ammonia, oxygen, and hydrogen supplied to the ammonia engine during operation of the ammonia engine is 23% or more and 60% or less.

4. The ammonia engine comprises: a fourth supply flow path through which air flows; an upstream regulating valve provided in the first supply flow path downstream of the oxygen enrichment membrane and upstream of the first regulating valve; In the first supply flow path, a portion upstream of the upstream regulating valve is defined as an upstream flow path, and a portion downstream of the upstream regulating valve is defined as a downstream flow path.

3. The ammonia engine system according to claim 1 or 2, wherein the control unit adjusts the upstream regulating valve in accordance with an operating state of the ammonia engine, thereby adjusting an amount of oxygen-enriched air flowing from the upstream flow path to the downstream flow path and an amount of air flowing from the fourth supply flow path to the downstream flow path.

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