JP2024057745A - Engine System - Google Patents

Abstract

[Problem] To provide an engine system capable of suppressing leakage of nitrous oxide into the atmosphere. [Solution] The engine system 1 is connected to an ammonia engine 2 and includes an exhaust flow path 4 through which exhaust gas generated from a combustion chamber 14 flows, a three-way catalyst 8 disposed in the exhaust flow path 4 for adsorbing and oxidizing ammonia, a detoxification device 65 for detoxifying the ammonia flowing through the exhaust flow path 4, an abatement flow path 66 connecting a location in the exhaust flow path 4 between the ammonia engine 2 and the three-way catalyst 8 with the abatement device 65, and a first opening/closing valve 67 disposed in the abatement flow path 66 and opening to allow ammonia to be supplied to the abatement device 65. [Selected Figure] Figure 1

Description

The present invention relates to an engine system.

As a conventional engine system, for example, the technology described in Patent Document 1 is known. The engine system described in Patent Document 1 includes an engine block, an intake passage connected to an intake port of the engine block, an exhaust passage connected to an exhaust port of the engine block, a fuel supply means for supplying fuel into the engine block, a throttle valve provided in the intake passage, a fresh air introduction passage that connects the intake passage upstream of the throttle valve to a crank chamber in the engine block and introduces intake air (fresh air) in the intake passage into the crank chamber, a return passage that connects the intake passage downstream of the throttle valve to the crank chamber and returns blow-by gas remaining in the crank chamber to the intake passage, and a PCV valve provided in the return passage.

JP 2012-145057 A

In recent years, there are ammonia engines that use ammonia as fuel. Since ammonia blow-by gas remains in the crankcase, it is desired to suppress the ammonia blow-by gas from flowing into the atmosphere when removing the crankcase body, members spatially connected to the crankcase, or piping during maintenance, for example. It is also desired to suppress the ammonia remaining in the fuel piping from flowing into the atmosphere when removing the fuel piping through which the ammonia flows. Therefore, it is considered to purify the ammonia remaining in the crankcase or the fuel piping with an exhaust catalyst so that the ammonia does not flow into the atmosphere when removing the crankcase body, members spatially connected to the crankcase, or piping, or when removing the fuel piping. However, depending on the temperature of the exhaust catalyst, ammonia may react with the exhaust catalyst to generate nitrous oxide (N ₂ O), which has a high environmental load. In this case, N ₂ O may flow through the exhaust passage and leak into the atmosphere.

The object of the present invention is to provide an engine system that can suppress the leakage of nitrous oxide into the atmosphere.

(1) One aspect of the present invention is an engine system including an engine having a piston capable of reciprocating in a combustion chamber that burns ammonia, a crankshaft connected to the piston, and a crankcase that houses the crankshaft, the engine system including a first oxygen supply flow path connected to the engine and through which oxygen-containing gas to be supplied to the combustion chamber flows, a flow control valve disposed in the first oxygen supply flow path and controlling the flow rate of the oxygen-containing gas to be supplied to the combustion chamber, an exhaust flow path connected to the engine and through which exhaust gas generated from the combustion chamber flows, an exhaust catalyst disposed in the exhaust flow path and that adsorbs and oxidizes ammonia, a second oxygen supply flow path that connects the crankcase to a location upstream of the flow control valve in the first oxygen supply flow path and supplies oxygen-containing gas into the crankcase, and a flow control valve disposed in the crankcase to a location downstream of the flow control valve in the first oxygen supply flow path. The system includes a blow-by gas flow path that connects the engine and the exhaust catalyst to return the ammonia blow-by gas remaining in the crankcase to the first oxygen supply flow path, a blow-by gas return valve that is disposed in the blow-by gas flow path and adjusts the flow rate of the ammonia blow-by gas returned to the first oxygen supply flow path, a starter that rotates the crankshaft, a detoxification device that detoxifies the ammonia flowing in the exhaust flow path, a detoxification flow path that connects the detoxification device to a location in the exhaust flow path between the engine and the exhaust catalyst, an on-off valve that is disposed in the detoxification flow path and opens to allow ammonia to be supplied to the detoxification device, and a control unit that controls the opening of the flow control valve so that the blow-by gas is returned to the first oxygen supply flow path when the crankshaft is rotated by the starter, and controls the opening of the on-off valve so that the on-off valve is opened.

In such an engine system, the opening degree of the flow control valve is controlled so that the ammonia blow-by gas is returned to the first oxygen supply passage during any period between the time when the rotation of the crankshaft stops due to the end of the combustion of ammonia in the combustion chamber of the engine and the time when the combustion of ammonia occurs again in the combustion chamber, and the crankshaft is rotated by the starter. Then, the combustion chamber side portion of the first oxygen supply passage becomes negative pressure, so that the oxygen-containing gas flows through the second oxygen supply passage and is introduced into the crankcase, and the blow-by gas return valve is opened, so that the ammonia blow-by gas remaining in the crankcase flows through the blow-by gas passage together with the oxygen-containing gas and returns to the first oxygen supply passage. Then, the ammonia blow-by gas flows into the exhaust passage together with the oxygen-containing gas through the first oxygen supply passage and the combustion chamber of the engine. Here, the opening and closing valve is opened and the exhaust passage is blocked, so that the ammonia flows through the abatement passage and is supplied to the abatement device. Then, the ammonia is abatemented in the abatement device. At this time, since ammonia does not flow through the exhaust catalyst, the generation of nitrous oxide (N ₂ O), which has a high environmental impact, in the exhaust catalyst is suppressed, thereby suppressing the leakage of nitrous oxide into the atmosphere.

(2) In the above (1), the engine system further includes a reformer that generates a reformed gas containing hydrogen by reforming ammonia, a reforming oxygen supply passage that supplies an oxygen-containing gas to the reformer, a reforming flow control valve that is disposed in the reforming oxygen supply passage and controls the flow rate of the oxygen-containing gas supplied to the reformer, and a reformed gas passage that supplies the reformed gas generated by the reformer to the combustion chamber, and the control unit may control the opening of the reforming flow control valve so that blow-by gas is returned to the first oxygen supply passage when the crankshaft is rotated by the starter. In this configuration, the reformed gas containing hydrogen is supplied to the combustion chamber of the engine, making it easier for ammonia to be burned in the combustion chamber of the engine.

(3) An engine system according to another aspect of the present invention includes an engine to which ammonia is supplied from an ammonia amount adjustment unit, an ammonia tank for storing ammonia, an ammonia supply flow path connecting the ammonia tank and the ammonia amount adjustment unit, an exhaust flow path connected to the engine and into which exhaust gas from the engine flows, an exhaust catalyst disposed in the exhaust flow path and for adsorbing and oxidizing ammonia, a detoxification device for detoxifying the ammonia flowing in the exhaust flow path, an abatement flow path connecting a location in the exhaust flow path between the engine and the exhaust catalyst and the abatement device, a first opening/closing valve disposed in the ammonia supply flow path and opening to allow ammonia to be supplied to the abatement device, and a second opening/closing valve disposed in the ammonia supply flow path and closing The oxygen supply unit includes a second on-off valve that blocks the ammonia in the ammonia tank from being supplied to the ammonia amount adjustment unit by opening and closing the second on-off valve, an oxygen supply path that is connected to a location downstream of the second on-off valve in the ammonia supply flow path and supplies oxygen-containing gas to the ammonia supply flow path, a third on-off valve that is disposed in the oxygen supply path and is closed when the second on-off valve is open and opens after the second on-off valve is closed, an exhaust path that is connected to a location downstream of the location where the oxygen supply path is connected in the ammonia supply flow path and is provided so that the ammonia inside can be supplied to the exhaust catalyst, and a fourth on-off valve that is disposed in the exhaust path and opens after the second on-off valve is closed.

In such an engine system, the second on-off valve is opened during the operation of the engine, and ammonia in the ammonia tank is supplied to the ammonia amount adjustment unit through the ammonia supply flow path. When the engine stops, ammonia remains in the ammonia supply flow path. Therefore, by closing the second on-off valve after the engine stops, the ammonia in the ammonia tank is prevented from being supplied to the ammonia amount adjustment unit. By closing the second on-off valve and then opening the third on-off valve and the fourth on-off valve, an oxygen-containing gas is supplied to the ammonia supply flow path. As a result, the ammonia remaining inside the ammonia supply flow path flows into the exhaust flow path together with the oxygen-containing gas through the expulsion path. Here, by opening the first on-off valve and blocking the exhaust flow path, ammonia flows through the abatement flow path and is supplied to the abatement device. Then, the ammonia is abated in the abatement device. At this time, since ammonia does not flow to the exhaust catalyst, the generation of nitrous oxide (N ₂ O), which is a high environmental load, in the exhaust catalyst is suppressed. As a result, leakage of nitrous oxide into the atmosphere is suppressed.

(4) In the above (3), the exhaust catalyst is a three-way catalyst, and the engine system may further include a temperature adjustment section having a temperature adjustment path with one end connected to a location downstream of the three-way catalyst in the exhaust flow path and the other end connected to the ammonia supply flow path, a temperature adjustment valve disposed in the temperature adjustment path, and a pump provided in a closed circuit formed by a part of the ammonia supply flow path, the expulsion path, a part of the exhaust flow path, the three-way catalyst, and the temperature adjustment path. In this configuration, since the exhaust catalyst is a three-way catalyst, ammonia supplied to the three-way catalyst is oxidized by the three-way catalyst, and the temperature of the catalyst-passing gas flowing out from the three-way catalyst increases. By operating the pump, a part of the catalyst-passing gas flowing out from the three-way catalyst is supplied to a part of the ammonia supply flow path and the expulsion path through the temperature adjustment path. As a result, the part of the ammonia supply flow path and the expulsion path are heated, so that, for example, condensation caused by the latent heat of vaporization of ammonia remaining in the ammonia supply flow path can be suppressed.

The present invention makes it possible to prevent nitrous oxide from leaking into the atmosphere.

1 is a schematic configuration diagram showing an engine system according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view of the ammonia engine and intake system shown in FIG. 1 . 2 is a flowchart showing an example of a procedure of a purge control process executed by a purge control processor shown in FIG. 1 . 3 is a graph showing an example of flow characteristics of the PCV valve shown in FIG. 2 . 2 is a flowchart showing an example of a procedure of an abatement control process executed by an abatement control processing unit shown in FIG. 1 . FIG. 5 is a schematic configuration diagram showing an engine system according to a second embodiment of the present invention. 7 is a flowchart showing an example of a procedure of a purge control process executed by a purge control processor shown in FIG. 6 . FIG. 11 is a schematic configuration diagram showing an engine system according to a third embodiment of the present invention. 9 is a flowchart showing a procedure of a purge control process executed by a purge control processor shown in FIG. 8 . FIG. 9 is a schematic configuration diagram showing a modified example of the engine system shown in FIG. 8 .

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the same or corresponding elements are designated by the same reference numerals, and duplicated description will be omitted.
[First embodiment]

Figure 1 is a schematic diagram showing an engine system according to a first embodiment of the present invention. In Figure 1, an engine system 1 according to this embodiment is mounted on a vehicle (not shown). The engine system 1 includes an ammonia engine 2, a first oxygen supply flow path 3, an exhaust flow path 4, a main injector (ammonia amount adjustment unit) 5, and a main throttle valve 6.

The ammonia engine 2 is an engine that uses ammonia gas ( _NH3 gas) as fuel. In the ammonia engine 2, hydrogen ( _H2 ) is mixed with the ammonia gas as a combustion improver to facilitate combustion of the flame-retardant ammonia gas. The ammonia engine 2 is, for example, a four-cylinder engine.

As shown in FIG. 2, the ammonia engine 2 has a cylinder block 11, a cylinder head 12 attached to the cylinder block 11, a number of pistons 13 (four in this example) arranged to be capable of reciprocating motion inside the cylinder block 11, a crankshaft 20 connected to the pistons 13, and a crankcase 21 housing the crankshaft 20.

The ammonia engine 2 has multiple (four in this example) combustion chambers 14 in which ammonia is burned together with hydrogen to generate exhaust gas. The combustion chambers 14 are defined by a space surrounded by a cylinder block 11, a cylinder head 12, and a piston 13.

The cylinder head 12 is provided with multiple intake ports 15 and exhaust ports 16 (four in this example) that are connected to each combustion chamber 14. The intake ports 15 are opened and closed by intake valves 17. The exhaust ports 16 are opened and closed by exhaust valves 18.

Each piston 13 is connected to a crankshaft 20 via a connecting rod 19. The crankcase 21 is attached to the end of the cylinder block 11 opposite the end where the cylinder head 12 is provided. An oil pan 22 that stores engine oil eo is removably attached to the end of the crankcase 21 opposite the end where the cylinder block 11 is provided. The interiors of the crankcase 21 and the oil pan 22 form a crank chamber 23.

The first oxygen supply flow passage 3 has an intake manifold 24 connected to each intake port 15 of the ammonia engine 2, and an intake pipe 25 connected to this intake manifold 24. The first oxygen supply flow passage 3 is a flow passage through which air flows to be supplied to each combustion chamber 14 of the ammonia engine 2. The air is a gas containing oxygen (oxygen-containing gas). An air cleaner 7 is provided in the intake pipe 25 to remove foreign matter such as dust and dirt contained in the air.

The exhaust flow path 4 includes an exhaust manifold 26 connected to each exhaust port 16 of the ammonia engine 2, and an exhaust pipe 27 connected to the exhaust manifold 26. The exhaust flow path 4 is a flow path through which exhaust gas generated from each combustion chamber 14 of the ammonia engine 2 flows.

Returning to FIG. 1, the exhaust flow path 4 is provided with a three-way catalyst 8 that purifies unburned ammonia and nitrogen oxides (NOx), which are harmful substances contained in the exhaust gas, and an SCR catalyst 9 that adsorbs unburned ammonia. The three-way catalyst 8 and the SCR catalyst 9 are provided in the exhaust pipe 27.

The three-way catalyst 8 oxidizes ammonia mainly using the air that flows into the three-way catalyst 8. The three-way catalyst 8 also adsorbs ammonia, although in smaller amounts than the SCR catalyst 9. The SCR catalyst 9 adsorbs ammonia and oxidizes the ammonia using NOx that flows into the SCR catalyst 9. The NOx is reduced. The three-way catalyst 8 and the SCR catalyst 9 constitute an exhaust catalyst disposed in the exhaust flow path 4.

The main injector 5 is an electromagnetic fuel injection valve that injects ammonia gas toward the combustion chamber 14 of the ammonia engine 2. For example, the number of main injectors 5 is equal to the number of cylinders of the ammonia engine 2 (four in this example). The main injectors 5 operate in response to control commands from the controller 60, which will be described later.

The main throttle valve 6 is disposed in the first oxygen supply passage 3. The main throttle valve 6 is an electromagnetic flow control valve that controls the flow rate of air supplied to the ammonia engine 2. The main throttle valve 6 operates in response to a control command from a controller 60, which will be described later.

The engine system 1 also includes a second oxygen supply passage 30, a blow-by gas passage 31, and a PCV valve 32 (Positive Crankcase Ventilation valve).

The second oxygen supply passage 30 connects a portion of the first oxygen supply passage 3 upstream of the main throttle valve 6 to the crankcase 21. The second oxygen supply passage 30 supplies air, which is an oxygen-containing gas, to the crankcase 21 (crank chamber 23).

As shown in FIG. 2, the second oxygen supply passage 30 has a pipe 33 that connects the intake pipe 25 between the air cleaner 7 and the main throttle valve 6 to the cylinder head 12 of the ammonia engine 2, and a passage 34 provided in the cylinder head 12 and the cylinder block 11 to connect the pipe 33 to the crank chamber 23.

The blow-by gas flow passage 31 connects the crankcase 21 to a point downstream of the main throttle valve 6 in the first oxygen supply flow passage 3. The blow-by gas flow passage 31 is a flow passage that returns ammonia blow-by gas remaining in the crankcase 21 (crank chamber 23) to the first oxygen supply flow passage 3.

As shown in FIG. 2, the blow-by gas flow passage 31 has a pipe 35 that connects the cylinder head 12 of the ammonia engine 2 to a location in the intake pipe 25 between the main throttle valve 6 and the intake manifold 24, and a passage 36 provided in the cylinder head 12 and the cylinder block 11 to connect the pipe 35 to the crank chamber 23.

The PCV valve 32 is disposed in the blow-by gas flow passage 31. The PCV valve 32 is a blow-by gas recirculation valve that adjusts the flow rate of ammonia blow-by gas recirculated to the first oxygen supply flow passage 3. As shown in FIG. 2, the PCV valve 32 is attached to, for example, the cylinder head 12 of the ammonia engine 2. The PCV valve 32 is disposed between the pipe 35 and the passage 36 in the blow-by gas flow passage 31.

The PCV valve 32 has housings 37A, 37B assembled so as to be arranged next to each other in the axial direction, a valve body 38 movably accommodated in the housing 37A, and a spring 39 that biases the valve body 38 toward the housing 37B. The PCV valve 32 allows blow-by gas to flow in only one direction, from the crank chamber 23 side to the first oxygen supply passage 3 side.

When the pressure inside the intake manifold 24 is positive, the force of the spring 39 presses the valve body 38 against the valve seat 37a provided at the end of the housing 37B on the housing 37A side, blocking the passage and closing the PCV valve 32. When the pressure inside the intake manifold 24 becomes negative, the valve body 38 moves against the force of the spring 39 toward the first oxygen supply flow path 3, forming a passage and opening the PCV valve 32 (see A in Figure 2).

Returning to FIG. 1, the engine system 1 includes an ammonia tank 40, a vaporizer 41, a reformer 42, a reforming oxygen supply passage 43, a reforming throttle valve 44, a reforming injector 45, a reformed gas passage 46, a cooler 47, and a flow control valve 48.

The ammonia tank 40 is a container that stores ammonia in a liquid state. In other words, the ammonia tank 40 stores liquid ammonia.

The vaporizer 41 is connected to the ammonia tank 40 via an ammonia supply passage 49. The vaporizer 41 vaporizes the liquid ammonia stored in the ammonia tank 40 to generate ammonia gas. The ammonia gas generated in the vaporizer 41 flows through the ammonia supply passage 50 and is supplied to the main injector 5, and also flows through the ammonia supply passage 51 and is supplied to the reforming injector 45.

The reformer 42 produces a reformed gas containing hydrogen by reforming ammonia gas. The reformer 42 has a cylindrical housing 52 and a reforming catalyst 53 and a heater 54 housed in the housing 52.

The housing 52 is made of a metal material such as stainless steel that is resistant to corrosion by ammonia gas. The reforming catalyst 53 is applied to a carrier having, for example, a honeycomb structure. The reforming catalyst 53 is a catalyst that burns ammonia gas and decomposes the ammonia gas into hydrogen. The reforming catalyst 53 is, for example, an ATR (Autothermal Reformer) type ammonia reforming catalyst.

The heater 54 is disposed upstream of the reforming catalyst 53 in the housing 52. The heater 54 heats the reforming catalyst 53. The heater 54 heats the ammonia gas flowing inside the housing 52, and uses the heat of the ammonia gas to heat the reforming catalyst 53. For example, an electrically heated catalyst (EHC) or the like is used as the heater 54. The heater 54 may also directly heat the reforming catalyst 53.

The reforming oxygen supply passage 43 connects the first oxygen supply passage 3 and the reformer 42. The reforming oxygen supply passage 43 is a passage through which air supplied to the reformer 42 flows. One end of the reforming oxygen supply passage 43 is connected to a location between the air cleaner 7 and the main throttle valve 6 in the first oxygen supply passage 3. The other end of the reforming oxygen supply passage 43 is connected to an inlet portion of the housing 52 of the reformer 42. The reforming oxygen supply passage 43 supplies oxygen-containing gas to the reformer 42.

The reforming throttle valve 44 is disposed in the reforming oxygen supply passage 43. The reforming throttle valve 44 is an electromagnetic reforming flow control valve that controls the flow rate of air supplied to the reformer 42. The reforming throttle valve 44 operates in response to a control command from the controller 60, which will be described later.

The reforming injector 45 is an electromagnetic fuel injection valve that injects ammonia gas toward the reformer 42. The reforming injector 45 injects ammonia gas between the reforming throttle valve 44 and the reformer 42 in the reforming oxygen supply passage 43. The number of reforming injectors 45 may be multiple (two in this example) or may be one. The reforming injector 45 operates in response to a control command from the controller 60, which will be described later.

The reformed gas flow passage 46 connects the reformer 42 and the first oxygen supply flow passage 3. One end of the reformed gas flow passage 46 is connected to the outlet of the housing 52 of the reformer 42. The other end of the reformed gas flow passage 46 is connected to a location in the first oxygen supply flow passage 3 between the main throttle valve 6 and the ammonia engine 2. The reformed gas flow passage 46 is a flow passage that supplies the reformed gas generated by the reformer 42 to the combustion chamber 14 of the ammonia engine 2.

The cooler 47 is disposed in the reformed gas flow passage 46. The cooler 47 cools the reformed gas flowing through the reformed gas flow passage 46, for example, by using engine cooling water that cools the ammonia engine 2.

The flow rate control valve 48 is disposed downstream of the cooler 47 in the reformed gas flow passage 46. The flow rate control valve 48 is an electromagnetic valve that adjusts the flow rate of the reformed gas supplied to the ammonia engine 2. The flow rate control valve 48 operates in response to a control command from a controller 60, which will be described later. The flow rate control valve 48 may be an on-off valve (ON/OFF valve).

The engine system 1 also includes a detoxification device 65, a detoxification flow path 66, a first on-off valve 67 (on-off valve), and an exhaust on-off valve 68.

The abatement device 65 is a device that abatements the ammonia flowing through the exhaust flow path 4. As the abatement device 65, a means capable of rendering ammonia harmless, such as an adsorbent that adsorbs ammonia, an oxidation catalyst that oxidizes and burns ammonia, or water that dissolves ammonia, is used. The abatement device 65 may have a pump (not shown) that sucks in the ammonia flowing through the exhaust flow path 4.

The abatement flow path 66 connects a portion of the exhaust flow path 4 between the ammonia engine 2 and the three-way catalyst 8 to the abatement device 65. One end of the abatement flow path 66 is connected to a portion of the exhaust pipe 27 (see FIG. 2) upstream of the three-way catalyst 8. The abatement flow path 66 is a flow path through which ammonia flows toward the abatement device 65.

The first on-off valve 67 is disposed in the abatement flow path 66. The first on-off valve 67 controls whether or not ammonia is supplied to the abatement device 65. When the first on-off valve 67 is open, it allows ammonia to be supplied to the abatement device 65. When the first on-off valve 67 is closed, it blocks the supply of ammonia to the abatement device 65. The first on-off valve 67 is, for example, an electromagnetic ON/OFF valve, and operates in response to a control command from the controller 60 described below.

The exhaust on-off valve 68 is disposed downstream of the SCR catalyst 9 in the exhaust flow path 4. The exhaust on-off valve 68 controls whether or not gas that has passed through the three-way catalyst 8 and the SCR catalyst 9 (catalyst passing gas) is discharged downstream of the exhaust on-off valve 68. When the exhaust on-off valve 68 is open, it allows the catalyst passing gas to be discharged downstream of the exhaust on-off valve 68. When the exhaust on-off valve 68 is closed, it blocks the catalyst passing gas from being discharged downstream of the exhaust on-off valve 68. The exhaust on-off valve 68 is, for example, an electromagnetic ON/OFF valve, and operates in response to a control command from the controller 60 described below.

The engine system 1 also includes a temperature sensor (temperature detection unit) 58, a starter 59, and a controller 60.

The temperature sensor 58 is a sensor that detects the temperature of the three-way catalyst 8. The temperature sensor 58 may directly detect the temperature of the three-way catalyst 8, or may detect the temperature around the three-way catalyst 8 (for example, the case that houses the three-way catalyst 8). The temperature sensor 58 transmits information about the detected temperature of the three-way catalyst 8 to the controller 60.

The starter 59 rotates the crankshaft 20 of the ammonia engine 2.

The controller 60 is an electronic control unit having, for example, a CPU, a ROM, a RAM, and an input/output interface. The controller 60 loads a program stored in the ROM into the RAM and executes the program with the CPU, thereby performing various control functions including drive control of the ammonia engine 2.

When the vehicle starts to operate, the controller 60 activates the power supply 55 for the starter 59 and the heater 54, and controls the main injector 5, the main throttle valve 6, the reforming injector 45, and the reforming throttle valve 44 to open. As a result, ammonia gas and air are supplied to the combustion chamber 14 and the reformer 42 of the ammonia engine 2, and the reformed gas generated by the reformer 42 is supplied to the combustion chamber 14, so that the ammonia gas is burned together with hydrogen in the combustion chamber 14.

During steady-state operation of the ammonia engine 2, the controller 60 controls the opening of the main injector 5, the opening of the main throttle valve 6, the opening of the reforming injector 45, and the opening of the reforming throttle valve 44 so as to obtain an air-fuel ratio that corresponds to the accelerator opening.

The controller 60 also performs purge control to remove ammonia blow-by gas remaining in the crankcase 21 (crank chamber 23) of the ammonia engine 2 during any period between the end of combustion of ammonia gas in the combustion chamber 14 of the ammonia engine 2, causing the crankshaft 20 to stop rotating, and the start of combustion of ammonia gas again in the combustion chamber 14. The blow-by gas is unburned gas that leaks into the crank chamber 23 from the gap between the cylinder block 11 and the piston 13.

Specifically, the controller 60 has a purge control processing unit (control unit) 61 and abatement control processing unit 62 (control unit).

The purge control processing unit 61 controls the opening of the main throttle valve 6 and the opening of the reforming throttle valve 44 so that blow-by gas is returned to the first oxygen supply passage 3 via the PCV valve 32 and the blow-by gas passage 31 when the rotation of the crankshaft 20 is resumed by the starter 59.

When the purge control processing unit 61 executes the purge control processing, the decontamination control processing unit 62 controls the opening degree of the first opening/closing valve 67 and the opening degree of the exhaust opening/closing valve 68 based on the temperature of the three-way catalyst 8 detected by the temperature sensor 58.

Figure 3 is a flowchart showing an example of the procedure of the purge control process executed by the purge control processing unit 61. In this embodiment, this process is started by instruction from an operator (here, the driver) after the rotation of the crankshaft 20 has stopped. The driver issues an instruction to perform purging using a manual switch such as a button that can be operated from the outside, for example, before getting off the vehicle or before performing maintenance on the ammonia engine 2.

When the combustion of ammonia gas ends in the combustion chamber 14 of the ammonia engine 2, the main injector 5, the main throttle valve 6, the reforming injector 45, and the reforming throttle valve 44 are basically in a closed state.

In FIG. 3, the purge control processing unit 61 first controls the opening of the main throttle valve 6 and the reforming throttle valve 44 (step S101). The purge control processing unit 61 controls the opening of the main throttle valve 6 and the opening of the reforming throttle valve 44 so that blow-by gas is returned to the first oxygen supply passage 3. More specifically, when the starter 59 resumes rotation of the crankshaft 20, the purge control processing unit 61 controls the opening of the main throttle valve 6 and the opening of the reforming throttle valve 44 so as to maintain a negative pressure inside the intake manifold 24.

At this time, the main throttle valve 6 and the reforming throttle valve 44 only need to be opened to such an extent that the blow-by gas can be returned to the first oxygen supply passage 3 when the rotation of the crankshaft 20 is resumed by the starter 59, and may be fully closed (zero opening).

Then, the purge control processing unit 61 starts the starter 59 (step S102). Then, the crankshaft 20 of the ammonia engine 2 rotates, and the inside of the intake manifold 24 becomes negative pressure. Note that step S102 may be performed before step S101, or steps S101 and S102 may be performed simultaneously.

At this time, because there is negative pressure inside the intake manifold 24, the air in the first oxygen supply passage 3 flows through the second oxygen supply passage 30 and is supplied to the crank chamber 23, and this air flows through the blow-by gas passage 31 via the PCV valve 32 together with the ammonia blow-by gas remaining in the crank chamber 23 and is returned to the first oxygen supply passage 3. In addition, because the main throttle valve 6 and the reforming throttle valve 44 are closed, the amount of air flowing through the second oxygen supply passage 30 increases accordingly.

As shown in FIG. 4, the PCV valve 32 has a flow characteristic in which the higher the negative pressure in the intake manifold 24 is, the easier it is for blow-by gas to flow until it reaches the specified pressure N, but once the negative pressure in the intake manifold 24 exceeds the specified pressure N, the blow-by gas becomes less able to flow. For this reason, it is preferable for the controller 60 to control the opening of the main throttle valve 6 and the reforming throttle valve 44 so that the negative pressure in the intake manifold 24 becomes the specified pressure N. The specified pressure N is the negative pressure that maximizes the flow rate of air through the PCV valve 32 per unit time.

By controlling the opening of the main throttle valve 6 and the reforming throttle valve 44 in this way, the flow rate of air returning to the first oxygen supply passage 3 through the PCV valve 32 is directly controlled. This makes it possible to more efficiently exhaust blow-by gas than when a simple check valve is used.

Figure 5 is a flowchart showing an example of the procedure of the abatement control process executed by the abatement control processing unit 62. Like the purge control processing unit 61, this process is also started by the driver's command at any time between the time when the rotation of the crankshaft 20 stops due to the end of the combustion of ammonia gas in the combustion chamber 14 of the ammonia engine 2 and the time when the combustion of ammonia gas starts again in the combustion chamber 14.

5, the harm-elimination control processing unit 62 first obtains the detection value of the temperature sensor 58 (step S111). Then, based on the detection value of the temperature sensor 58, the harm-elimination control processing unit 62 determines whether the temperature of the three-way catalyst 8 is within a specified temperature range H (step S112). The specified temperature range H is a temperature range (e.g., about 150° C. to 350° C.) in which the three-way catalyst 8 reacts with ammonia to generate nitrous oxide (N ₂ O).

When the decontamination control processing unit 62 determines that the temperature of the three-way catalyst 8 is within the specified temperature range H, it controls the first opening/closing valve 67 to open and the exhaust opening/closing valve 68 to close (step S113), and executes the above step S111 again. At this time, the first opening/closing valve 67 may be opened and then the exhaust opening/closing valve 68 may be closed, or the first opening/closing valve 67 and the exhaust opening/closing valve 68 may be opened simultaneously.

When the abatement control processing unit 62 determines that the temperature of the three-way catalyst 8 is not within the specified temperature range H, it controls the exhaust opening/closing valve 68 to open and the first opening/closing valve 67 to close (step S114), and executes the above step S111 again. At this time, the exhaust opening/closing valve 68 may be opened and then the first opening/closing valve 67 may be closed, or the exhaust opening/closing valve 68 and the first opening/closing valve 67 may be opened simultaneously.

In the engine system 1 described above, when the driver issues a command to remove blow-by gas, the starter 59 is started to rotate the crankshaft 20 and adjust the opening of the main throttle valve 6 and the reforming throttle valve 44.

Then, since the inside of the intake manifold 24 becomes negative pressure, the air in the first oxygen supply flow passage 3 flows through the piping 33 and passage 34 of the second oxygen supply flow passage 30 and is supplied to the crank chamber 23, and the air flows together with the ammonia blow-by gas remaining in the crank chamber 23 through the passage 36 of the blow-by gas flow passage 31, the PCV valve 32, and the piping 35 of the blow-by gas flow passage 31, and is returned to the first oxygen supply flow passage 3. Then, the ammonia blow-by gas flows through the first oxygen supply flow passage 3 and the combustion chamber 14 of the ammonia engine 2 and flows into the exhaust flow passage 4.

At this time, if the temperature of the three-way catalyst 8 is not within the specified temperature range H, the exhaust opening/closing valve 68 is opened and the first opening/closing valve 67 is closed. Therefore, the ammonia blow-by gas flowing through the exhaust passage 4 is supplied to the three-way catalyst 8 and the SCR catalyst 9. Then, the ammonia blow-by gas is purified in the three-way catalyst 8 and the SCR catalyst 9.

Specifically, when the temperature of the three-way catalyst 8 is higher than the upper limit of the specified temperature range H, the ammonia is oxidized and burned by the three-way catalyst 8. When the temperature of the three-way catalyst 8 is lower than the lower limit of the specified temperature range H, the ammonia is adsorbed by the SCR catalyst 9. This prevents ammonia blow-by gas from flowing through the exhaust passage 4 and being discharged.

On the other hand, when the temperature of the three-way catalyst 8 is within the specified temperature range H, the first opening/closing valve 67 is opened and the exhaust opening/closing valve 68 is closed. Therefore, the ammonia blow-by gas flowing through the exhaust flow path 4 is not supplied to the three-way catalyst 8 and the SCR catalyst 9, but flows through the abatement flow path 66 and is supplied to the abatement device 65. The ammonia blow-by gas is then purified in the abatement device 65. In addition, because the exhaust opening/closing valve 68 is closed, the catalyst passing gas is prevented from flowing through the exhaust flow path 4 and being discharged.

As described above, in this embodiment, the opening degree of the main throttle valve 6 and the opening degree of the reforming throttle valve 44 are controlled and the crankshaft 20 is rotated by the starter 59 so that the ammonia blow-by gas is returned to the first oxygen supply passage 3 during an arbitrary period from when the rotation of the crankshaft 20 stops due to the end of the combustion of ammonia gas in the combustion chamber 14 of the ammonia engine 2 until the combustion of ammonia gas occurs again in the combustion chamber 14. Then, the inside of the intake manifold 24, which is a part of the first oxygen supply passage 3, becomes negative pressure, so that air flows through the second oxygen supply passage 30 and is introduced into the crankcase 21, and the PCV valve 32 opens, so that the ammonia blow-by gas remaining in the crankcase 21 flows together with the air through the blow-by gas passage 31 and is returned to the first oxygen supply passage 3. Then, the ammonia blow-by gas flows into the exhaust passage 4 through the first oxygen supply passage 3 and the combustion chamber 14 of the ammonia engine 2 together with the air. Here, the first on-off valve 67 is opened and the exhaust on-off valve 68 is closed to block the exhaust flow path 4, so that the ammonia flows through the abatement flow path 66 and is supplied to the abatement device 65. The ammonia is then abated in the abatement device 65. At this time, since the ammonia does not flow through the three-way catalyst 8, the generation of nitrous oxide (N ₂ O), which has a high environmental load, in the three-way catalyst 8 is suppressed. This suppresses leakage of nitrous oxide into the atmosphere.

In addition, because the ammonia blow-by gas remaining in the crankcase 21 is removed, for example, when the oil pan 22 is removed and the crankcase 21 is opened during maintenance, the ammonia remaining in the crankcase 21 is prevented from leaking into the atmosphere. In addition, if the ammonia blow-by gas remaining in the crankcase 21 is periodically removed, for example, when the oil pan 22 is removed and the crankcase 21 is opened during maintenance, the ammonia remaining in the crankcase 21 is prevented from leaking into the atmosphere in large amounts.

In addition, in this embodiment, reformed gas containing hydrogen is supplied to the combustion chamber 14 of the ammonia engine 2, making it easier for ammonia to be combusted in the combustion chamber 14 of the ammonia engine 2.

In addition, in this embodiment, because the exhaust opening/closing valve 68 is used, the worker does not need to manually block the outlet of the exhaust flow path 4. This reduces the burden on the worker.

Furthermore, in this embodiment, when the temperature of the three-way catalyst 8 is within the temperature range at which the three-way catalyst 8 generates nitrous oxide, the first on-off valve 67 is opened and the exhaust on-off valve 68 is closed, so that ammonia flows through the abatement flow path 66 and is supplied to the abatement device 65, where the ammonia is abated. When the temperature of the three-way catalyst 8 is not within the temperature range at which the three-way catalyst 8 generates nitrous oxide, the exhaust on-off valve 68 is opened and the first on-off valve 67 is closed, so that the ammonia is adsorbed and oxidized by the three-way catalyst 8. Therefore, the frequency of use of the abatement device 65 is reduced, and the life of the abatement device 65 can be extended.
[Second embodiment]

Figure 6 is a schematic diagram showing an engine system according to a second embodiment of the present invention. In Figure 6, the engine system 1A of this embodiment further includes a second opening/closing valve 75, an oxygen supply unit 70, and an exhaust path 80, and differs from the engine system 1 of the first embodiment in that it includes a controller 60A instead of the controller 60. Note that the starter 59 is omitted in Figure 6.

A second on-off valve 75 is disposed in the ammonia supply passage 49 that connects the ammonia tank 40 and the vaporizer 41. The second on-off valve 75 controls whether or not ammonia is supplied from the ammonia tank 40 to the main injector 5 and the reforming injector 45 through the vaporizer 41. When the second on-off valve 75 is open, it allows the ammonia in the ammonia tank 40 to be supplied to the main injector 5 and the reforming injector 45 through the vaporizer 41. When the second on-off valve 75 is closed, it blocks the ammonia in the ammonia tank 40 from being supplied to the main injector 5 and the reforming injector 45 through the vaporizer 41. The second on-off valve 75 operates in response to a control command from, for example, a controller 60A described below.

The engine system 1A further includes an oxygen supply unit 70. The oxygen supply unit 70 includes an air source 71, an oxygen supply path 72, a third opening/closing valve 76, and a check valve 73.

The air source 71 is a supply source of oxygen-containing gas for purging the ammonia supply flow paths 49 to 51. The air source 71 supplies, for example, atmospheric air as the oxygen-containing gas. The air source 71 includes a pump that delivers atmospheric air. The air source 71 may also include an air tank that stores the compressed air delivered by the pump.

The oxygen supply path 72 connects the air source 71 to a location downstream of the second on-off valve 75 in the ammonia supply flow path 49. The oxygen supply path 72 is connected, for example, between the second on-off valve 75 in the ammonia supply flow path 49 and the vaporizer 41. The oxygen supply path 72 supplies air to the ammonia supply flow paths 49 to 51. Note that the oxygen-containing gas may be oxygen instead of air.

A third on-off valve 76 is disposed in the oxygen supply path 72. The third on-off valve 76 is disposed, for example, between the air source 71 and the check valve 73 in the oxygen supply path 72. The third on-off valve 76 is a flow control valve that controls the flow rate of air supplied from the air source 71 to the ammonia supply paths 49-51. When the third on-off valve 76 is opened, it allows the air from the air source 71 to be supplied to the ammonia supply paths 49-51. When the third on-off valve 76 is closed, it blocks the air from the air source 71 from being supplied to the ammonia supply paths 49-51. The third on-off valve 76 is, for example, an electromagnetic flow control valve, and operates in response to a control command from a controller 60A described below.

The check valve 73 is disposed downstream of the third opening/closing valve 76 in the oxygen supply passage 72. The check valve 73 prevents ammonia from flowing from the ammonia supply passage 49 to the oxygen supply passage 72. When the ammonia engine 2 is stopped after operation, the check valve 73 blocks the flow of ammonia from the ammonia supply passage 49 to the oxygen supply passage 72 even if the pressure of the ammonia supply passage 49 is higher than the pressure of the oxygen supply passage 72 due to the remaining ammonia. When the remaining ammonia is reduced and the pressure of the ammonia supply passage 49 becomes lower than the pressure of the oxygen supply passage 72, the check valve 73 allows ammonia to flow from the oxygen supply passage 72 to the ammonia supply passage 49.

The engine system 1A includes a purge path 80 that is provided so that the ammonia remaining inside the ammonia supply passages 49-51 can be supplied to the three-way catalyst 8. The purge path 80 connects, for example, a point downstream of the point where the oxygen supply passage 72 is connected in the ammonia supply passage 49 to the upstream side of the three-way catalyst 8 in the exhaust passage 4. Specifically, the purge path 80 is connected upstream of a point where the exhaust passage 4 is connected to the abatement passage 66. The purge path 80 includes, for example, a first purge path 81, a second purge path 82, and a third purge path 83.

The first expulsion path 81 is connected to the ammonia supply flow path 51 near the reforming injector 45. A fourth on-off valve 77 is disposed in the first expulsion path 81. The fourth on-off valve 77 is a flow control valve that controls the flow rate of ammonia expelled from the ammonia supply flow path 51 to the exhaust flow path 4. When the fourth on-off valve 77 is opened, it allows ammonia in the ammonia supply flow path 51 to be supplied to the exhaust flow path 4. When the fourth on-off valve 77 is closed, it blocks ammonia in the ammonia supply flow path 51 from being supplied to the exhaust flow path 4. The fourth on-off valve 77 is, for example, an electromagnetic flow control valve, and operates in response to a control command from a controller 60A described later.

The second exhaust path 82 is connected to the ammonia supply flow path 50 near the main injector 5. A fifth on-off valve 78 is disposed in the second exhaust path 82. The fifth on-off valve 78 is a flow control valve that controls the flow rate of ammonia exhausted from the ammonia supply flow path 50 to the exhaust flow path 4. When the fifth on-off valve 78 is opened, it allows ammonia in the ammonia supply flow path 50 to be supplied to the exhaust flow path 4. When the fifth on-off valve 78 is closed, it blocks ammonia in the ammonia supply flow path 50 from being supplied to the exhaust flow path 4. The fifth on-off valve 78 is, for example, an electromagnetic flow control valve, and operates in response to a control command from a controller 60A described later.

The first and second exhaust paths 81 and 82 join downstream of the fourth on-off valve 77 and the fifth on-off valve 78. The third exhaust path 83 connects the joining point of the first and second exhaust paths 81 and 82 to the upstream side of the point where the exhaust path 4 is connected to the abatement path 66. Note that the first and second exhaust paths 81 and 82 may each be connected upstream of the point where the exhaust path 4 is connected to the abatement path 66 without joining.

The engine system 1A includes a controller 60A. The controller 60A includes a purge control processing unit 61A and the above-mentioned decontamination control processing unit 62. The purge control processing unit 61A controls the second on-off valve 75 to the fifth on-off valve 78 to purge the ammonia supply passages 49 to 51.

An example of the operation of the engine system 1A will be described with reference to FIG. 7. FIG. 7 is a flowchart showing an example of the procedure of the purge control process executed by the purge control processing unit 61A.

In FIG. 7, the purge control processing unit 61A opens the second on-off valve 75 while the ammonia engine 2 is operating, thereby supplying ammonia in the ammonia tank 40 to the main injector 5 via the ammonia supply passage 49, the vaporizer 41, and the ammonia supply passage 50. When the second on-off valve 75 is open, the purge control processing unit 61A closes the third on-off valve 76, the fourth on-off valve 77, and the fifth on-off valve 78 (step S121). Due to the operation of the ammonia engine 2, the three-way catalyst 8 and the SCR catalyst 9 are at or above their activation temperatures (light-off).

When the ammonia engine 2 that was in operation is stopped, the purge control processing unit 61A closes the second on-off valve 75 to block the supply of ammonia in the ammonia tank 40 to the main injector 5 via the ammonia supply flow path 49, the vaporizer 41, and the ammonia supply flow path 50 (step S122). At this time, ammonia remains in the ammonia supply flow paths 49 and 50.

The purge control processing unit 61A opens the third on-off valve 76 in response to an instruction from the driver after the vehicle stops and before the vehicle operation is resumed. That is, the purge control processing unit 61A closes the second on-off valve 75 that was open, and then opens the third on-off valve 76. The purge control processing unit 61A also opens the fourth on-off valve 77 and the fifth on-off valve 78 after the operation of the ammonia engine 2 is stopped. That is, the purge control processing unit 61A closes the second on-off valve 75 that was open, and then opens the fourth on-off valve 77 and the fifth on-off valve 78. As an example, after the operation of the ammonia engine 2 is stopped, the purge control processing unit 61A closes the second on-off valve 75 and opens the fourth on-off valve 77 and the fifth on-off valve 78 (step S123), and then opens the third on-off valve 76 (step S124). In this way, by opening the fourth on-off valve 77 and the fifth on-off valve 78 before the third on-off valve 76, the pressure in the ammonia supply flow path 49 can be quickly reduced even if the pressure in the ammonia supply flow path 49 is higher than the pressure in the oxygen supply path 72 due to remaining ammonia. Note that the purge control processing unit 61A may open the third on-off valve 76 before the fourth on-off valve 77 and the fifth on-off valve 78.

In the engine system 1A described above, ammonia remaining inside the ammonia supply passages 49-51 flows into the exhaust passage 4 through the expulsion passage 80. At this time, if the temperature of the three-way catalyst 8 is not within the above-mentioned specified temperature range H, the exhaust opening/closing valve 68 is opened and the first opening/closing valve 67 is closed. Therefore, the ammonia that flows into the exhaust passage 4 is purified by the three-way catalyst 8 and the SCR catalyst 9.

When the temperature of the three-way catalyst 8 is within the specified temperature range H, the first opening/closing valve 67 is opened and the exhaust opening/closing valve 68 is closed. Therefore, the ammonia that has flowed into the exhaust flow path 4 flows through the abatement flow path 66 and is supplied to the abatement device 65, where it is purified.

As described above, in this embodiment, the second on-off valve 75 is opened during operation of the ammonia engine 2, and ammonia in the ammonia tank 40 is supplied to the main injector 5 through the ammonia supply flow paths 49, 50. When the ammonia engine 2 that was operating is stopped, ammonia remains in the ammonia supply flow paths 49, 50. Therefore, by closing the second on-off valve 75 after the operation of the ammonia engine 2 is stopped, the supply of ammonia in the ammonia tank 40 to the main injector 5 is blocked. By closing the second on-off valve 75 and then opening the third on-off valve 76, the fourth on-off valve 77, and the fifth on-off valve 78, air is supplied to the ammonia supply flow paths 49, 50. As a result, the ammonia remaining inside the ammonia supply flow paths 49, 50 flows into the exhaust flow path 4 together with air through the expulsion path 80. Here, the first on-off valve 67 is opened and the exhaust on-off valve 68 is closed to block the exhaust flow path 4, and the ammonia flows through the abatement flow path 66 and is supplied to the abatement device 65. Then, the ammonia is removed in the removal device 65. At this time, since the ammonia does not flow through the three-way catalyst 8, the generation of nitrous oxide (N ₂ O), which has a high environmental load, is suppressed in the three-way catalyst 8. This suppresses the leakage of nitrous oxide into the atmosphere.

In addition, since the ammonia remaining in the ammonia supply passages 49, 50 is removed, it is possible to suppress the outflow of ammonia remaining in the ammonia supply passages 49, 50 into the atmosphere when the ammonia supply passages 49, 50 are disconnected after the operation of the ammonia engine 2 is stopped.
[Third embodiment]

Figure 8 is a schematic diagram showing an engine system according to a third embodiment of the present invention. In Figure 8, the engine system 1B of this embodiment differs from the engine system 1A of the second embodiment in that it includes an oxygen supply unit 70A instead of the oxygen supply unit 70, an expulsion path 80A instead of the expulsion path 80, a controller 60B instead of the controller 60, and further includes a temperature adjustment unit 90.

In addition to the configuration of the oxygen supply unit 70 described above, the oxygen supply unit 70A further includes an oxygen supply path 74 and a sixth on-off valve 79. The oxygen supply path 74 connects the air source 71A and a location downstream of the fourth on-off valve 77 in the expulsion path 80A. In the example of FIG. 8, the oxygen supply path 74 is connected to a location downstream of the fourth on-off valve 77 in the first expulsion path 81. A sixth on-off valve 79 is disposed in the oxygen supply path 74. The sixth on-off valve 79 is a flow control valve that controls the flow rate of air supplied from the air source 71A to the oxygen supply path 74. The sixth on-off valve 79 allows the air of the air source 71A to be supplied to the oxygen supply path 74 by opening the valve. The sixth on-off valve 79 blocks the air of the air source 71A from being supplied to the oxygen supply path 74 by closing the valve. The sixth on-off valve 79 is, for example, an electromagnetic flow control valve, and operates in response to a control command from the controller 60B.

The temperature adjustment unit 90 has a temperature adjustment path 91, a temperature adjustment opening/closing valve 95, a check valve 92, and a temperature sensor (temperature detection unit) 93.

The temperature adjustment path 91 connects a location downstream of the three-way catalyst 8 in the exhaust flow path 4 to a location downstream of the second opening/closing valve 75 in the ammonia supply flow path 49. In the example of FIG. 8, one end of the temperature adjustment path 91 is connected between the three-way catalyst 8 and the SCR catalyst 9 in the exhaust flow path 4. The other end of the temperature adjustment path 91 is connected between the second opening/closing valve 75 and the vaporizer 41 in the ammonia supply flow path 49. The temperature adjustment path 91 returns the catalyst passing gas that has passed through the three-way catalyst 8 to the ammonia supply flow path 49. The catalyst passing gas is exhaust gas from the ammonia engine 2, and is hotter than the outside air during operation of the ammonia engine 2 and immediately after the operation is stopped. During operation of the ammonia engine 2, the catalyst passing gas receives heat generated by the purification (oxidation reaction) of the exhaust gas in the three-way catalyst 8. Immediately after the operation of the ammonia engine 2 is stopped, the catalyst passing gas receives the residual heat of the three-way catalyst 8.

A temperature adjustment on-off valve 95 is disposed in the temperature adjustment path 91. The temperature adjustment on-off valve 95 is a flow control valve that controls the flow rate of the catalyst passing gas that is returned to the ammonia supply flow path 49 from downstream of the three-way catalyst 8 in the exhaust flow path 4. When the temperature adjustment on-off valve 95 is open, it allows the catalyst passing gas to be returned to the ammonia supply flow path 49. When the temperature adjustment on-off valve 95 is closed, it blocks the catalyst passing gas from being returned to the ammonia supply flow path 49. The temperature adjustment on-off valve 95 is, for example, an electromagnetic flow control valve, and operates in response to a control command from a controller 60B described below.

The check valve 92 is disposed downstream of the temperature adjustment on-off valve 95 in the temperature adjustment passage 91. The check valve 92 prevents ammonia from flowing from the ammonia supply passage 49 to the temperature adjustment passage 91. Even if the pressure in the ammonia supply passage 49 is higher than the pressure in the temperature adjustment passage 91 because the temperature adjustment on-off valve 95 is closed when the ammonia engine 2 that was in operation is stopped, the check valve 92 blocks the flow of ammonia from the ammonia supply passage 49 to the temperature adjustment passage 91. When the ammonia remaining in the ammonia supply passage 49 is reduced and the pressure in the ammonia supply passage 49 is lower than the pressure in the temperature adjustment passage 91, the check valve 92 allows the catalyst passing gas to flow from the temperature adjustment passage 91 to the ammonia supply passage 49.

The temperature adjustment path 91 is provided with a temperature sensor 93. The temperature sensor 93 is disposed, for example, between the temperature adjustment opening/closing valve 95 and the check valve 92 in the temperature adjustment path 91. The temperature sensor 93 detects the gas temperature of the catalyst passing gas flowing through the temperature adjustment path 91. The temperature sensor 93 transmits information on the detected gas temperature to the controller 60B.

In addition to the configuration of the purge path 80 described above, the purge path 80A further includes a pump 84. The pump 84 is provided in a closed circuit formed by a portion of the ammonia supply flow path 49, the vaporizer 41, a portion of the ammonia supply flow paths 50 and 51, the purge path 80A, a portion of the exhaust flow path 4, the three-way catalyst 8, and the temperature adjustment path 91. In the example of FIG. 8, the pump 84 is disposed in the third purge path 83. That is, the pump 84 is provided in the purge path 80A. The pump 84 is, for example, an electric pump, and operates in response to a control command from the controller 60B.

The engine system 1B includes a controller 60B. The controller 60B includes a purge control processing unit 61B and the above-mentioned decontamination control processing unit 62. The purge control processing unit 61B controls the second on-off valve 75 to the sixth on-off valve 79, the temperature adjustment on-off valve 95, and the pump 84 to purge the ammonia supply passages 49 to 51.

An example of the operation of the engine system 1B will be described with reference to FIG. 9. FIG. 9 is a flowchart showing an example of the procedure of the purge control process executed by the purge control processing unit 61B.

In FIG. 9, the purge control processing unit 61B opens the second on-off valve 75 while the ammonia engine 2 is operating, thereby supplying ammonia in the ammonia tank 40 to the main injector 5 via the ammonia supply passage 49, the vaporizer 41, and the ammonia supply passage 50. When the second on-off valve 75 is open, the purge control processing unit 61B closes the third on-off valve 76, the fourth on-off valve 77, the fifth on-off valve 78, the sixth on-off valve 79, and the temperature adjustment on-off valve 95 (step S131).

When the ammonia engine 2 is stopped, the purge control processing unit 61B closes the second on-off valve 75 to block the supply of ammonia in the ammonia tank 40 to the main injector 5 via the ammonia supply passage 49, the vaporizer 41, and the ammonia supply passage 50. At this time, ammonia remains in the ammonia supply passages 49 and 50. As an example, after the ammonia engine 2 is stopped, the purge control processing unit 61B closes the second on-off valve 75 in response to an instruction from the driver (step S132), opens the fourth on-off valve 77 and the fifth on-off valve 78 (step S133), and then opens the third on-off valve 76 (step S134). Furthermore, the purge control processing unit 61B opens the sixth on-off valve 79 and the temperature adjustment on-off valve 95 (step S135), and operates the pump 84 of the expulsion path 80A (step S136).

More specifically, the purge control processing unit 61B circulates the gas in the closed circuit by operating the pump 84. In the example of FIG. 8, when the pump 84 provided in the third purging path 83 is operated, the gas in the first purging path 81 and the second purging path 82 is sent upstream of the three-way catalyst 8 in the exhaust flow path 4. When the pump 84 draws in the gas in the first purging path 81 and the second purging path 82, the gas remaining in a part of the ammonia supply flow paths 49, 50 that is further upstream is also pulled toward the pump 84. In the example of FIG. 8, the part of the ammonia supply flow paths 49, 50 corresponds to the part from the connection point with the second opening/closing valve 75 to the connection point with the first purging path 81 and the part from the connection point with the second opening/closing valve 75 to the connection point with the second purging path 82.

When the pump 84 is provided in the expulsion path 80A, the gas remaining in a part of the ammonia supply flow paths 49 and 50 is pulled toward the pump 84 by the operation of the pump 84. In this case, the air source 71A does not necessarily have to pressurize air to the ammonia supply flow path 49. The air source 71A may be configured to omit the pump and the air tank for storing compressed air. Incidentally, after the operation of the ammonia engine 2 is stopped, the purge control processing unit 61B closes the second on-off valve 75, opens the fourth on-off valve 77 and the fifth on-off valve 78, and then opens the third on-off valve 76. However, the third on-off valve 76 may be kept closed and the sixth on-off valve 79 may be opened to supply air to the three-way catalyst 8. Even in this case, since the pump 84 is provided in the expulsion path 80A, it is sufficient to circulate the gas in the closed circuit using the pump 84, and it is not necessary to push out the ammonia in the ammonia supply flow paths 49 and 50 with air from the oxygen supply path 72.

The purge control processing unit 61B supplies air from the air source 71A to the expulsion path 80A (the first expulsion path 81 in the example of FIG. 8) by opening the third opening/closing valve 76. The air supplied to the expulsion path 80A via the sixth opening/closing valve 79 is supplied to the three-way catalyst 8 via the exhaust flow path 4. Thus, the amount of oxygen for oxidizing ammonia in the three-way catalyst 8 increases. Here, in the initial stage of ammonia expulsion after the operation of the ammonia engine 2 is stopped, there is a period (predetermined period) in which the air supplied from the oxygen supply path 72 by opening the third opening/closing valve 76 expels the ammonia remaining inside the ammonia supply flow paths 49, 50, but does not reach the three-way catalyst 8. In this predetermined period, the oxygen concentration is insufficient relative to the ammonia concentration in the three-way catalyst 8. Therefore, by supplying air from the air source 71A to the expulsion path 80A via the sixth opening/closing valve 79, the insufficiency of the oxygen concentration relative to the ammonia concentration in the three-way catalyst 8 is alleviated. Thus, ammonia can be more appropriately oxidized in the three-way catalyst 8 in the initial stage of ammonia expulsion. The purge control processing unit 61B may open the sixth opening/closing valve 79 for the predetermined period after the ammonia engine 2 stops operating.

The purge control processing unit 61B opens the temperature adjustment on-off valve 95 to return the catalyst passing gas downstream of the three-way catalyst 8 in the exhaust flow path 4 to the ammonia supply flow paths 49, 50 via the temperature adjustment path 91. When the catalyst passing gas is returned to the ammonia supply flow paths 49, 50, the catalyst passing gas heats the ammonia supply flow paths 49, 50. In the ammonia supply flow paths 49, 50, when the ammonia remaining in the ammonia supply flow paths 49, 50 is expelled to the expulsion path 80A, condensation due to the latent heat of vaporization of ammonia may occur. By heating the ammonia supply flow paths 49, 50 with the catalyst passing gas, condensation due to the latent heat of vaporization of ammonia can be suppressed. For example, if the ammonia remaining inside the ammonia supply flow paths 49, 50 has been sufficiently expelled but condensation remains in the ammonia supply flow paths 49, 50, the purge control processing unit 61B may close the third and sixth opening and closing valves 76 and 79 while leaving the temperature adjustment opening and closing valve 95 open, thereby stopping the supply of air from the air source 31A.

When the temperature control opening/closing valve 95 is opened and the gas temperature is equal to or higher than a predetermined temperature threshold, the purge control processing unit 61B may increase the amount of air supplied from the oxygen supply path 72 to the ammonia supply flow paths 49, 50 compared to when the gas temperature is less than the temperature threshold (steps S137, S138). The temperature threshold is a threshold value for the temperature of the catalyst-passing gas for determining whether the ammonia supply flow paths 49, 50 are excessively heated by the catalyst-passing gas. When the gas temperature is equal to or higher than the predetermined temperature threshold, the amount of air supplied from the oxygen supply path 72 to the ammonia supply flow paths 49, 50 is increased, so that the catalyst-passing gas is cooled by the air. This makes it possible to prevent the ammonia supply flow paths 49, 50 from being excessively heated even when the gas temperature is equal to or higher than the predetermined temperature threshold.

As described above, according to this embodiment, since the exhaust catalyst is the three-way catalyst 8, the ammonia supplied to the three-way catalyst 8 is oxidized by the three-way catalyst 8, and the temperature of the catalyst-passing gas flowing out from the three-way catalyst 8 increases. By operating the pump 84, a portion of the catalyst-passing gas flowing out from the three-way catalyst 8 is supplied to a portion of the ammonia supply passages 49, 50 and the expulsion passage 80A through the temperature adjustment passage 91. As a result, the portion of the ammonia supply passages 49, 50 and the expulsion passage 80A are heated, so that, for example, condensation due to the latent heat of vaporization of ammonia remaining in the ammonia supply passages 49, 50 can be suppressed.

In addition, in this embodiment, the expulsion path 80A is connected to a location downstream of the location where the oxygen supply path 72 is connected in the ammonia supply flow path 49, and a pump 84 is provided in the expulsion path 80A. As a result, for example, even if air is not pumped from the oxygen supply path 72 to the ammonia supply flow paths 49, 50, the ammonia remaining in the ammonia supply flow paths 49, 50 can be supplied to the three-way catalyst 8 through the expulsion path 80A by operating the pump 84.

Moreover, in this embodiment, the engine system 1B includes a temperature sensor 93 that is provided in the temperature adjustment path 91 and detects the gas temperature of the catalyst passing gas flowing through the temperature adjustment path 91. When the gas temperature is equal to or higher than a predetermined temperature threshold, the engine system 1B increases the amount of air supplied from the oxygen supply path 72 to the ammonia supply flow paths 49, 50, compared to when the gas temperature is below the temperature threshold. This makes it possible to suppress excessive heating of a portion of the ammonia supply flow paths 49, 50 and the expulsion path 80A.
[Modification]

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments. The present invention can be implemented in various forms, including the above-mentioned embodiments, with various modifications and improvements based on the knowledge of those skilled in the art.

For example, the engine system 1B of the third embodiment can be modified to an engine system 1B as shown in FIG. 10. In FIG. 10, the engine system 1C according to the modified example differs from the engine system 1B mainly in that a pump 94 is provided in the temperature adjustment path 91 instead of the pump 84 in the third exhaust path 83. In the engine system 1C, the exhaust path 80A is returned to the exhaust path 80, and the temperature adjustment unit 90 becomes a temperature adjustment unit 90C. In the temperature adjustment unit 90C, the temperature sensor is omitted in the temperature adjustment path 91.

In the engine system 1C, the pump 94 is provided in the temperature adjustment path 91, so that the gas in the first and second expulsion paths 81 and 82 is less likely to be drawn to the pump 94 side, compared to the case in which the pump 84 is provided in the third expulsion path 83 as in the example of FIG. 8. Therefore, the oxygen supply unit 70B differs from the oxygen supply unit 70A of the third embodiment in that the air is returned to the air source 71 of the first embodiment, which is capable of pumping air. In addition, in the engine system 1B of the third embodiment, the purge control processing unit 61B could circulate the gas in the closed circuit using the pump 84 while keeping the third opening/closing valve 76 closed, and supply air to the three-way catalyst 8 by opening the sixth opening/closing valve 79, but in the engine system 1C, the pump 94 exclusively pumps the catalyst passing gas back to the ammonia supply flow paths 49, 50. For example, the purge control processing unit 61B may open the third opening/closing valve 76 to push out the ammonia in the ammonia supply flow paths 49 and 50 with air from the oxygen supply path 72.

In addition, in the first embodiment, the three-way catalyst 8 may be heated by a heater. In this case, for example, by heating the three-way catalyst 8 to a temperature higher than the upper limit value of the specified temperature range H, the operating time of the detoxification device 65 can be shortened.

In addition, in the first embodiment, the temperature of the engine oil or engine coolant may be detected, and the openings of the main throttle valve 6 and the reforming throttle valve 44 may be controlled so that the main throttle valve 6 and the reforming throttle valve 44 are closed based on the temperature of the engine oil or engine coolant. In this case, even if the negative pressure generated on the first oxygen supply flow path 3 side of the ammonia engine 2 varies depending on the temperature of the ammonia engine 2, the main throttle valve 6 and the reforming throttle valve 44 in the closed state can be adjusted to an appropriate opening according to the temperature of the ammonia engine 2.

In addition, in the above embodiment, the three-way catalyst 8 is mainly used as the exhaust catalyst, but the exhaust catalyst is not limited to that form in particular, and it is sufficient that one or more types of catalyst adsorb and oxidize ammonia. For example, the above-mentioned SCR catalyst 9 may be mainly used as the exhaust catalyst, or an oxidation catalyst may be used instead of the three-way catalyst 8 and the SCR catalyst 9.

In addition, in the above embodiment, after the operation of the ammonia engine 2 is stopped or before maintenance of the ammonia engine 2, an operator such as a driver operates an operation unit such as a button to perform the purging process and the detoxification process, but this is not particularly limited to this form, and for example, the purging process and the detoxification process may be started automatically after a predetermined time has elapsed since the operation of the ammonia engine 2 is stopped.

In the above embodiment, the temperature of the three-way catalyst 8 is detected by the temperature sensor 58, but the present invention is not limited to such a configuration. The temperature of the three-way catalyst 8 may be estimated from the operating history (operating time, rotation speed, load) of the ammonia engine 2, the temperature of the engine oil or engine coolant, or the NOx concentration downstream of the three-way catalyst 8 or the SCR catalyst 9. For example, when the ammonia engine 2 is operated for a predetermined time at a rotation speed of a predetermined number or more and the temperature of the engine coolant is less than a predetermined value, the temperature of the three-way catalyst 8 is estimated to be within the specified temperature range H. In this case, the exhaust opening/closing valve 68 is closed to prevent ammonia from flowing to the three-way catalyst 8. When the ammonia engine 2 is operated for a predetermined time at a rotation speed of a predetermined number or more and the temperature of the engine coolant is equal to or higher than a predetermined value, the temperature of the three-way catalyst 8 is estimated to be higher than the specified temperature range H. In this case, the exhaust opening/closing valve 68 is opened to allow ammonia to flow to the three-way catalyst 8.

In the above embodiment, when the temperature of the three-way catalyst 8 is within the specified temperature range H where the three-way catalyst 8 reacts with ammonia to produce nitrous oxide ( _N2O ), the first on-off valve 67 is opened and the exhaust on-off valve 68 is closed, but this is not particularly limited to such an embodiment. When performing the purging process, the first on-off valve 67 may be opened and the exhaust on-off valve 68 may be closed regardless of the temperature of the three-way catalyst 8. In this case, the temperature sensor 58 for detecting the temperature of the three-way catalyst 8 may not be used.

In addition, in the above embodiment, when the temperature of the three-way catalyst 8 is within the specified temperature range H, the first opening/closing valve 67 is opened and the exhaust opening/closing valve 68 is closed, but this is not limited to a particular form. For example, when the temperature of the three-way catalyst 8 is within the specified temperature range H, the exhaust opening/closing valve 68 may be open, or the opening of the exhaust opening/closing valve 68 may be controlled so that it is narrower than the opening of the first opening/closing valve 67.

In addition, in the above embodiment, when the temperature of the three-way catalyst 8 is not within the specified temperature range H, the exhaust opening/closing valve 68 is opened and the first opening/closing valve 67 is closed, but this is not limited to a particular form. For example, when the temperature of the three-way catalyst 8 is not within the specified temperature range H, the first opening/closing valve 67 may be open, or the opening of the first opening/closing valve 67 may be controlled so that it is narrower than the opening of the exhaust opening/closing valve 68.

In addition, in the above embodiment, the first opening/closing valve 67 and the exhaust opening/closing valve 68 are electromagnetic ON/OFF valves, but the first opening/closing valve 67 and the exhaust opening/closing valve 68 are not limited to this form, and electromagnetic flow control valves may also be used.

In the above embodiment, the first on-off valve 67 and the exhaust on-off valve 68 are solenoid valves and operate in response to control commands from the controllers 60, 60A, and 60B, but are not limited to such a form. For example, the first on-off valve 67 and the exhaust on-off valve 68 may be manual ON/OFF valves. In this case, the above-mentioned effects are achieved by an operator manually performing a process similar to the process in the flowchart of FIG. 5 as a remaining fuel processing method. The second on-off valve 75 to the fifth on-off valve 78 in the second embodiment and the second on-off valve 75 to the sixth on-off valve 79 and the temperature adjustment on-off valve 95 in the third embodiment may also be manual flow control valves.

In addition, in the above embodiment, the exhaust opening/closing valve 68 is disposed downstream of the SCR catalyst 9 in the exhaust flow path 4, but this is not a particular configuration, and the exhaust opening/closing valve 68 may be disposed between the point in the exhaust flow path 4 where it is connected to the abatement flow path 66 and the three-way catalyst 8.

In addition, in the above embodiment, the main injector 5 is given as an example of the ammonia amount adjustment unit, but the ammonia amount adjustment unit may be a carburetor.

In the above embodiment, the second oxygen supply flow path 30 has a pipe 33 that connects the first oxygen supply flow path 3 and the cylinder head 12 of the ammonia engine 2, and a passage 34 provided in the cylinder head 12 and the cylinder block 11 to communicate the pipe 33 with the crank chamber 23, but is not limited to such a form. The second oxygen supply flow path 30 may be a pipe that directly connects the first oxygen supply flow path 3 and the crank chamber 23.

In the above embodiment, the blow-by gas flow passage 31 has a pipe 35 that connects the first oxygen supply flow passage 3 and the cylinder head 12, and a passage 36 provided in the cylinder head 12 and the cylinder block 11 to communicate the pipe 35 with the crank chamber 23, but is not limited to this form. The blow-by gas flow passage 31 may be a pipe that directly connects the crank chamber 23 with the first oxygen supply flow passage 3. In this case, the PCV valve 32 is disposed in the pipe.

In addition, in the above embodiment, the exhaust valve 68 is disposed downstream of the point where the abatement flow path 66 is connected in the exhaust flow path 4, but the exhaust valve 68 does not have to be provided. If it is desired to prevent the catalyst passing gas from being discharged downstream of the exhaust valve 68, for example, a lid that blocks the outlet of the exhaust pipe 27 of the exhaust flow path 4 may be used.

In the second and third embodiments, the exhaust passages 80, 80A are incorporated in the ammonia engine 2 in advance, but the present invention is not limited to such a configuration. The exhaust passages 80, 80A may be attached to the ammonia engine 2 as retrofit members when removing the ammonia supply passages 49-51 from the ammonia engine 2. In this case, a coupler or the like can be used to connect the exhaust passages 80, 80A.

In addition, in the above embodiment, the reforming oxygen supply flow passage 43 is connected to the first oxygen supply flow passage 3, but the reforming oxygen supply flow passage 43 is not limited to this form and may be a flow passage through which air supplied from a route other than the first oxygen supply flow passage 3 flows.

In the above embodiment, the reformer 42 has a reforming catalyst 53 that has both the function of burning ammonia gas and the function of decomposing ammonia gas into hydrogen, but is not limited to such a form. The reformer 42 may have a combustion catalyst that burns ammonia gas and a reforming catalyst that decomposes ammonia gas into hydrogen separately.

In addition, in the above embodiment, air is supplied to the ammonia engine 2 and the reformer 42, but instead of air, only oxygen may be supplied to the ammonia engine 2 and the reformer 42.

In addition, in the above embodiment, the reformer 42 generates a reformed gas containing hydrogen, and the reformed gas is supplied to the ammonia engine 2 together with ammonia, but the present invention is also applicable to engine systems in which hydrogen is not supplied to the ammonia engine 2.

1, 1A, 1B, 1C...engine system, 2...ammonia engine (engine), 3...first oxygen supply passage, 4...exhaust passage, 5...main injector (ammonia amount adjustment section), 6...main throttle valve (flow control valve), 8...three-way catalyst (exhaust catalyst), 9...SCR catalyst (exhaust catalyst), 13...piston, 14...combustion chamber, 20...crankshaft, 21...crankcase, 30...second oxygen supply passage, 31...blow-by gas passage, 32...PCV valve (blow-by gas reflux valve), 40...ammonia tank, 42...reformer, 43...reforming oxygen supply passage, 44...reforming Throttle valve (reforming flow control valve), 46... reformed gas flow path, 49, 50, 51... ammonia supply flow path, 59... starter, 61, 61A, 61B... purge control processing unit (control unit), 62... abatement control processing unit (control unit), 65... abatement device, 66... abatement flow path, 67... first on-off valve (on-off valve), 70, 70A, 70B... oxygen supply unit, 72... oxygen supply path, 75... second on-off valve, 76... third on-off valve, 77... fourth on-off valve, 78... fifth on-off valve, 80, 80A... purge path, 84... pump, 90, 90C... temperature adjustment unit, 91... temperature adjustment path, 94... pump, 95... temperature adjustment on-off valve.

Claims (4)

An engine system including an engine having a piston capable of reciprocating in a combustion chamber for burning ammonia, a crankshaft connected to the piston, and a crankcase accommodating the crankshaft,
a first oxygen supply passage connected to the engine and through which an oxygen-containing gas to be supplied to the combustion chamber flows;
a flow control valve disposed in the first oxygen supply passage and configured to control a flow rate of the oxygen-containing gas supplied to the combustion chamber;
an exhaust passage connected to the engine and through which exhaust gas generated from the combustion chamber flows;
an exhaust catalyst disposed in the exhaust passage and configured to adsorb and oxidize ammonia;
a second oxygen supply passage connecting a portion of the first oxygen supply passage upstream of the flow control valve to the crankcase and supplying the oxygen-containing gas into the crankcase;
a blow-by gas flow passage that connects the crankcase and a portion of the first oxygen supply flow passage downstream of the flow control valve and returns ammonia blow-by gas remaining in the crankcase to the first oxygen supply flow passage;
a blow-by gas reflux valve disposed in the blow-by gas flow passage and configured to adjust the flow rate of the ammonia blow-by gas refluxed to the first oxygen supply passage;
A starter that rotates the crankshaft;
a detoxification device that detoxifies ammonia flowing through the exhaust passage;
an abatement flow passage connecting a portion of the exhaust flow passage between the engine and the exhaust catalyst and the abatement device;
an on-off valve disposed in the abatement flow path and opening to allow ammonia to be supplied to the abatement device;
a control unit that controls an opening degree of the flow control valve so that the blow-by gas is returned to the first oxygen supply passage when the crankshaft is rotated by the starter, and controls an opening degree of the on-off valve so that the on-off valve is opened. a reformer that generates a reformed gas containing hydrogen by reforming ammonia;
a reforming oxygen supply passage for supplying the oxygen-containing gas to the reformer;
a reforming flow rate control valve disposed in the reforming oxygen supply passage for controlling a flow rate of the oxygen-containing gas supplied to the reformer;
a reformed gas flow path that supplies the reformed gas generated by the reformer to the combustion chamber,
2. The engine system according to claim 1, wherein the control unit controls an opening degree of the reforming flow control valve so that the blow-by gas is returned to the first oxygen supply passage when the crankshaft is rotated by the starter. an engine to which ammonia is supplied from an ammonia amount adjusting unit;
an ammonia tank for storing ammonia;
an ammonia supply flow path connecting the ammonia tank and the ammonia amount adjusting unit;
an exhaust passage connected to the engine and into which exhaust gas from the engine flows;
an exhaust catalyst disposed in the exhaust passage and configured to adsorb and oxidize ammonia;
a detoxification device that detoxifies ammonia flowing through the exhaust passage;
an abatement flow passage connecting a portion of the exhaust flow passage between the engine and the exhaust catalyst and the abatement device;
a first on-off valve that is disposed in the abatement flow path and opens to allow ammonia to be supplied to the abatement device;
a second on-off valve that is disposed in the ammonia supply flow path and that, when closed, blocks the ammonia in the ammonia tank from being supplied to the ammonia amount adjustment unit;
an oxygen supply section including an oxygen supply path connected to a location downstream of the second on-off valve in the ammonia supply flow path and supplying an oxygen-containing gas to the ammonia supply flow path, and a third on-off valve disposed in the oxygen supply path and closed when the second on-off valve is open and opened after the second on-off valve is closed;
a discharge passage that is connected to a portion of the ammonia supply flow passage downstream of a portion to which the oxygen supply passage is connected and that is provided so as to be capable of supplying the ammonia therein to the exhaust catalyst;
a fourth on-off valve disposed in the exhaust path and opened after the second on-off valve is closed. The exhaust catalyst is a three-way catalyst,
a temperature adjustment section including a temperature adjustment path having one end connected to a location downstream of the three-way catalyst in the exhaust flow path and the other end connected to the ammonia supply flow path, and a temperature adjustment on-off valve disposed in the temperature adjustment path;
4. The engine system according to claim 3, further comprising: a pump provided in a closed circuit formed by a portion of the ammonia supply passage, the expulsion passage, a portion of the exhaust passage, the three-way catalyst, and the temperature adjustment passage.

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