JP7722271B2 - Engine System - Google Patents

Description

The present invention relates to an engine system that uses ammonia as fuel.

Conventionally, engines (hereinafter sometimes referred to as ammonia engines) that use ammonia supplied from an ammonia tank via a vaporizer and an ammonia gas flow path as fuel have been known (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2020-197211

In the technical field of ammonia engines, such as the above-mentioned conventional technology, ammonia remains in the ammonia gas flow path (ammonia supply path), which is the fuel pipe, after the operation of the ammonia engine is stopped, so it is desirable to prevent ammonia from leaking into the atmosphere when the ammonia supply path is disconnected.

The present invention aims to prevent ammonia remaining in the ammonia supply path from leaking into the atmosphere when the ammonia supply path is disconnected after an ammonia-fueled engine is shut down.

An engine system according to one aspect of the present invention includes an engine to which ammonia is supplied from an ammonia amount adjustment unit; an ammonia tank that stores ammonia; an ammonia supply path connecting the ammonia tank and the ammonia amount adjustment unit; an exhaust path connected to the engine and through which exhaust gas from the engine flows; an exhaust catalyst provided in the exhaust path that adsorbs and oxidizes ammonia; a first valve provided in the ammonia supply path that, when closed, blocks ammonia in the ammonia tank from being supplied to the ammonia amount adjustment unit; an oxygen supply path connected to a location downstream of the first valve in the ammonia supply path and supplies oxygen-containing gas to the ammonia supply path; an oxygen supply unit having a second valve provided in the oxygen supply path that closes when the first valve is open and opens after the first valve closes; a purge path connected to a location in the ammonia supply path downstream of the location where the oxygen supply path is connected and is capable of supplying ammonia contained therein to the exhaust catalyst; and a third valve provided in the purge path that opens after the first valve closes.

In an engine system according to one aspect of the present invention, the first valve is open while the engine is running, and ammonia in the ammonia tank is supplied to the ammonia amount adjustment unit via the ammonia supply path. When the engine is stopped, ammonia remains in the ammonia supply path. Therefore, by closing the first valve after the engine is stopped, the supply of ammonia in the ammonia tank to the ammonia amount adjustment unit is blocked. By closing the first valve and then opening the second and third valves, oxygen-containing gas is supplied to the ammonia supply path. This allows ammonia remaining in the ammonia supply path to be supplied to the exhaust catalyst through the expulsion path. As a result, the ammonia supplied to the exhaust catalyst can be adsorbed and oxidized by the exhaust catalyst. In this way, it is possible to prevent ammonia remaining in the ammonia supply path from leaking into the atmosphere when the ammonia supply path is disconnected after the operation of an ammonia-fueled engine is stopped.

In one embodiment, the exhaust catalyst is a three-way catalyst, and the engine system may include a temperature adjustment unit having a temperature adjustment path connected at one end to a location in the exhaust path downstream of the three-way catalyst and connected at the other end to the ammonia supply path, a fourth valve provided in the temperature adjustment path, and a pump provided in a closed circuit formed by a portion of the ammonia supply path, the purge path, a portion of the exhaust path, the three-way catalyst, and the temperature adjustment path. In this case, because the exhaust catalyst is a three-way catalyst, ammonia supplied to the three-way catalyst is oxidized in the three-way catalyst, raising the temperature of the catalyst-passed gas flowing out from the three-way catalyst. By operating the pump, a portion of the catalyst-passed gas flowing out from the three-way catalyst is supplied to a portion of the ammonia supply path and the purge path through the temperature adjustment path. This heats the portion of the ammonia supply path and the purge path, thereby suppressing condensation caused by the latent heat of vaporization of ammonia remaining in the ammonia supply path, for example.

In one embodiment, the pump may be provided in the purge path. In this case, the purge path is connected to a location downstream of the location where the oxygen supply path is connected to the ammonia supply path. Therefore, by operating the pump, ammonia remaining in the ammonia supply path can be supplied to the exhaust catalyst through the purge path without, for example, pumping oxygen-containing gas from the oxygen supply path to the ammonia supply path.

In one embodiment, the engine system includes a temperature detection unit provided in the temperature adjustment path that detects the gas temperature of the catalyst-passing gas flowing through the temperature adjustment path, and when the gas temperature is equal to or higher than a predetermined temperature threshold, the amount of gas supplied from the oxygen supply path to the ammonia supply path may be increased compared to when the gas temperature is below the temperature threshold. In this case, excessive heating of a portion of the ammonia supply path and the purge path can be prevented.

According to the present invention, when the ammonia supply path is disconnected after an ammonia-fueled engine is shut down, it is possible to prevent ammonia remaining in the ammonia supply path from leaking into the atmosphere.

1 is a schematic configuration diagram of an engine system according to a first embodiment. 2 is a flowchart showing an example of a control process of the controller of FIG. 1 . FIG. 10 is a schematic configuration diagram of an engine system according to a second embodiment. 4 is a flowchart showing an example of a control process of the controller of FIG. 3 . FIG. 4 is a schematic configuration diagram of a modified example of the engine system of FIG. 3 .

Embodiments of the present invention will now be described with reference to the drawings. In the following description, the same or equivalent elements will be designated by the same reference numerals, and duplicate descriptions will be omitted.

[First embodiment]
Fig. 1 is a schematic diagram of an engine system according to a first embodiment. In Fig. 1, an engine system 1 is mounted on a vehicle (not shown). The engine system 1 includes an ammonia engine 2, an intake path 3, an exhaust path 4, a main injector (ammonia amount adjuster) 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 ) as a combustion improver is mixed with the ammonia gas to make the flame-retardant ammonia gas more combustible. The ammonia engine 2 has a combustion chamber (not shown) in which the ammonia gas is burned together with the hydrogen to generate exhaust gas. The ammonia engine 2 is, for example, a four-cylinder engine.

The intake path 3 is connected to the combustion chamber of the ammonia engine 2. The intake path 3 is a passage through which air supplied to the ammonia engine 2 flows. An air cleaner 7 is disposed in the intake path 3 to remove foreign matter such as dust and dirt from the air.

The exhaust path 4 is connected to the combustion chamber of the ammonia engine 2. The exhaust path 4 is a passage into which exhaust gas from the ammonia engine 2 flows. The exhaust path 4 is equipped with a three-way catalyst 8 that purifies unburned ammonia and nitrogen oxides (NOx), which are harmful components contained in the exhaust gas, and an SCR catalyst 9 that adsorbs the ammonia contained in the exhaust gas. The three-way catalyst 8 oxidizes the adsorbed ammonia using an oxygen-containing gas (e.g., 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 adsorbed ammonia using nitrogen oxides that flow into the SCR catalyst 9 (nitrogen oxides are reduced).

Ammonia gas is supplied to the ammonia engine 2 from the main injector 5. The main injector 5 is an electromagnetic fuel injection valve that injects ammonia gas toward the combustion chamber of the ammonia engine 2. For example, the number of main injectors 5 provided is the same as the number of cylinders of the ammonia engine 2. The main injectors 5 operate in response to control commands from the controller 50, which will be described later.

The main throttle valve 6 is disposed in the intake path 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 control commands from the controller 50, which will be described later.

The engine system 1 also includes an ammonia tank 10, a vaporizer 11, a reformer 12, an air flow path 13, a reforming throttle valve 14, a reforming injector 15, a reformed gas flow path 16, a cooler 17, and a flow control valve 18.

The ammonia tank 10 is a container that stores ammonia in liquid form. The ammonia tank 10 and the main injector 5 are connected by an ammonia supply path 19.

A valve (first valve) V1 is provided in the ammonia supply path 19. The valve V1 is provided, for example, between the ammonia tank 10 and the vaporizer 11 in the ammonia supply path 19. The valve V1 controls whether ammonia is supplied from the ammonia tank 10 to the main injector 5 and the reforming injector 15. When the valve V1 is open, it allows ammonia in the ammonia tank 10 to be supplied to the main injector 5 and the reforming injector 15. When the valve V1 is closed, it blocks ammonia in the ammonia tank 10 from being supplied to the main injector 5 and the reforming injector 15. The valve V1 operates, for example, in response to a control command from the controller 50, which will be described later.

The vaporizer 11 vaporizes the liquid ammonia stored in the ammonia tank 10 to produce ammonia gas. The ammonia gas generated in the vaporizer 11 flows through the ammonia supply path 19 and is supplied to the main injector 5, and also flows through the ammonia flow path 20 and is supplied to the reforming injector 15.

The reformer 12 produces reformed gas containing hydrogen by reforming ammonia gas. The reformer 12 has a cylindrical housing 21 and a reforming catalyst 22 housed within this housing 21. The housing 21 is made of a metal material, such as stainless steel, that is resistant to corrosion by ammonia gas. The reforming catalyst 22 is applied to a carrier, for example, with a honeycomb structure. The reforming catalyst 22 is a catalyst that burns ammonia gas and decomposes the ammonia gas into hydrogen. The reforming catalyst 22 is, for example, an ATR (Autothermal Reformer) type ammonia reforming catalyst.

The air flow path 13 connects the intake path 3 and the reformer 12. The air flow path 13 is a path through which air supplied to the reformer 12 flows. One end of the air flow path 13 is connected to the intake path 3 between the air cleaner 7 and the main throttle valve 6. The other end of the air flow path 13 is connected to the inlet of the housing 21 of the reformer 12.

The reforming throttle valve 14 is disposed in the air flow path 13. The reforming throttle valve 14 is an electromagnetic flow control valve that controls the flow rate of air supplied to the reformer 12. The reforming throttle valve 14 operates in response to control commands from the controller 50, which will be described later.

The reforming injector 15 is an electromagnetic fuel injection valve that injects ammonia gas into the air flow path 13. The reforming injector 15 injects ammonia gas between the reforming throttle valve 14 and the reformer 12 in the air flow path 13. There may be multiple reforming injectors 15 (two in this example) or just one.

The reformed gas flow path 16 connects the reformer 12 and the intake path 3. One end of the reformed gas flow path 16 is connected to the outlet of the housing 21 of the reformer 12. The other end of the reformed gas flow path 16 is connected to the intake path 3 between the main throttle valve 6 and the ammonia engine 2. The reformed gas flow path 16 is a flow path through which the reformed gas generated by the reformer 12 flows toward the ammonia engine 2.

The cooler 17 is disposed in the reformed gas flow path 16. The cooler 17 cools the reformed gas flowing through the reformed gas flow path 16, for example, using engine cooling water that cools the ammonia engine 2.

The flow rate control valve 18 is disposed downstream of the cooler 17 in the reformed gas flow path 16. The flow rate control valve 18 is a solenoid valve that adjusts the flow rate of the reformed gas supplied to the ammonia engine 2. The flow rate control valve 18 operates in response to control commands from the controller 50, which will be described later. The flow rate control valve 18 may be an on/off valve (ON/OFF valve).

The engine system 1 includes an oxygen supply unit 30 having an air source 31, an oxygen supply path 32, a valve (second valve) V2, and a check valve 33.

The air source 31 is a source of oxygen-containing gas for purging the ammonia supply path 19. The air source 31 supplies, for example, atmospheric air as the oxygen-containing gas. The air source 31 includes a pump that outputs atmospheric air. The air source 31 may also include an air tank that stores compressed air output by the pump.

The oxygen supply path 32 connects the air source 31 to a location downstream of the valve V1 in the ammonia supply path 19. The oxygen supply path 32 is connected, for example, between the valve V1 in the ammonia supply path 19 and the vaporizer 11. The oxygen supply path 32 supplies air to the ammonia supply path 19. Note that the oxygen-containing gas may be oxygen instead of air.

A valve V2 is disposed in the oxygen supply path 32. The valve V2 is disposed, for example, between the air source 31 and the check valve 33 in the oxygen supply path 32. The valve V2 is a flow control valve that controls the flow rate of air supplied from the air source 31 to the ammonia supply path 19. When the valve V2 is open, it allows air from the air source 31 to be supplied to the ammonia supply path 19. When the valve V2 is closed, it blocks air from the air source 31 from being supplied to the ammonia supply path 19. The valve V2 is, for example, an electromagnetic flow control valve, and operates in response to control commands from a controller 50, which will be described later.

The check valve 33 is disposed downstream of the valve V2 in the oxygen supply path 32. The check valve 33 prevents ammonia from flowing from the ammonia supply path 19 into the oxygen supply path 32. When the ammonia engine 2 is stopped after operation, the check valve 33 blocks the flow of ammonia from the ammonia supply path 19 into the oxygen supply path 32, even if the pressure in the ammonia supply path 19 is higher than the pressure in the oxygen supply path 32 due to remaining ammonia. When the remaining ammonia is reduced and the pressure in the ammonia supply path 19 becomes lower than the pressure in the oxygen supply path 32, the check valve 33 allows ammonia to flow from the oxygen supply path 32 into the ammonia supply path 19.

The engine system 1 is equipped with a purge path 40 that is configured to supply ammonia remaining inside the ammonia supply path 19 to the exhaust catalyst. The purge path 40 connects, for example, a point in the ammonia supply path 19 downstream of the point where the oxygen supply path 32 is connected to the exhaust path 4 upstream of the three-way catalyst 8. The purge path 40 includes, for example, a first purge path 41, a second purge path 42, and a third purge path 43.

The first expulsion path 41 is connected to the ammonia flow path 20 near the reforming injector 15. A valve (third valve) V3 is disposed in the first expulsion path 41. The valve V3 is a flow control valve that controls the flow rate of ammonia expelled from the ammonia flow path 20 to the exhaust path 4. When opened, the valve V3 allows ammonia in the ammonia flow path 20 to be supplied to the exhaust catalyst. When closed, the valve V3 blocks ammonia in the ammonia flow path 20 from being supplied to the exhaust catalyst. The valve V3 is, for example, an electromagnetic flow control valve, and operates in response to control commands from a controller 50, described below.

The second purge path 42 is connected to the ammonia supply path 19 near the main injector 5. A valve (third valve) V4 is disposed in the second purge path 42. The valve V4 is a flow control valve that controls the flow rate of ammonia expelled from the ammonia supply path 19 to the exhaust path 4. When opened, the valve V4 allows ammonia from the ammonia supply path 19 to be supplied to the exhaust catalyst. When closed, the valve V4 blocks ammonia from the ammonia supply path 19 from being supplied to the exhaust catalyst. The valve V4 is, for example, an electromagnetic flow control valve, and operates in response to control commands from a controller 50, described below.

The first and second discharge paths 41 and 42 converge downstream of valves V3 and V4. The third discharge path 43 connects the point where the first and second discharge paths 41 and 42 converge with the upstream side of the three-way catalyst 8 in the exhaust path 4. Note that the first and second discharge paths 41 and 42 may each be connected to the upstream side of the three-way catalyst 8 in the exhaust path 4 without merging.

The engine system 1 includes a controller 50. The controller 50 is an electronic control unit that includes, for example, a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and an input/output interface. The controller 50 loads programs stored in the ROM into the RAM and executes the programs loaded into the RAM via the CPU, thereby realizing various functions, including operation of the ammonia engine 2.

An example of the operation of the engine system 1 will be described with reference to FIG. 2. FIG. 2 is a flowchart showing an example of the control process of the controller of FIG. 1. The controller 50 opens valve V1 while the ammonia engine 2 is operating, thereby supplying ammonia in the ammonia tank 10 to the main injector 5 via the ammonia supply path 19. When valve V1 is open, the controller 50 closes valves V2, V3, and V4 (step S01). Operation of the ammonia engine 2 causes the three-way catalyst 8 and SCR catalyst 9 to reach or exceed their activation temperatures (light-off).

When the ammonia engine 2 that has been operating is stopped, the controller 50 closes the valve V1 to block the supply of ammonia in the ammonia tank 10 to the main injector 5 via the ammonia supply path 19 (step S02). At this time, ammonia remains in the ammonia supply path 19.

The controller 50 opens valve V2 after the ammonia engine 2 is shut down. That is, the controller 50 closes valve V1, which was open, and then opens valve V2. The controller 50 also opens valves V3 and V4 after the ammonia engine 2 is shut down. That is, the controller 50 closes valve V1, which was open, and then opens valves V3 and V4. As an example, after the ammonia engine 2 is shut down, the controller 50 closes valve V1 and opens valves V3 and V4 (step S03), and then opens valve V2 (step S04). By opening valves V3 and V4 before valve V2 in this way, the pressure in the ammonia supply path 19 can be quickly reduced even if the pressure in the ammonia supply path 19 is higher than the pressure in the oxygen supply path 32 due to remaining ammonia. The controller 50 may also open valve V2 before valves V3 and V4.

As described above, according to the engine system 1 of the first embodiment, valve V1 is open while the ammonia engine 2 is operating, and ammonia in the ammonia tank 10 is supplied to the main injector 5 via the ammonia supply path 19. When the ammonia engine 2 is stopped, ammonia remains in the ammonia supply path 19. Therefore, by closing valve V1 after the ammonia engine 2 is stopped, the supply of ammonia in the ammonia tank 10 to the main injector 5 is blocked. By closing valve V1 and then opening valves V2, V3, and V4, air (a gas containing oxygen) is supplied to the ammonia supply path 19. As a result, the ammonia remaining in the ammonia supply path 19 is supplied to the three-way catalyst 8 through the purge path 40. As a result, the ammonia supplied to the three-way catalyst 8 can be adsorbed and oxidized by the three-way catalyst 8. In this way, it is possible to prevent ammonia remaining in the ammonia supply path 19 from leaking into the atmosphere when the ammonia supply path 19 is disconnected after the ammonia engine 2 is stopped. In addition, ammonia can be detoxified without using special equipment for treating ammonia.

Second Embodiment
3 is a schematic diagram of an engine system according to a second embodiment. In FIG. 3, the engine system 1A differs from the engine system 1 according to the first embodiment in that the engine system 1A includes an oxygen supply unit 30A instead of the oxygen supply unit 30, an expulsion line 40A instead of the expulsion line 40, a controller 50A instead of the controller 50, and further includes a temperature adjustment unit 60.

In addition to the configuration of the oxygen supply unit 30 described above, the oxygen supply unit 30A further includes an oxygen supply path 34 and a valve V5. The oxygen supply path 34 connects the air source 31A to a location downstream of the third valve on the expulsion path 40. In the example shown in FIG. 3, the oxygen supply path 34 is connected to a location downstream of the valve V3 on the first expulsion path 41. The oxygen supply path 34 is provided with a valve V5. The valve V5 is a flow control valve that controls the flow rate of air supplied from the air source 31A to the oxygen supply path 34. When the valve V5 is open, it allows air from the air source 31A to be supplied to the oxygen supply path 34. When the valve V5 is closed, it blocks air from the air source 31A from being supplied to the oxygen supply path 34. The valve V5 is, for example, an electromagnetic flow control valve, and operates in response to a control command from the controller 50A.

The temperature adjustment unit 60 has a temperature adjustment path 61, a valve (fourth valve) V6, a check valve 62, and a temperature sensor (temperature detection unit) 63.

The temperature adjustment path 61 connects a location downstream of the three-way catalyst 8 in the exhaust path 4 with a location downstream of the valve V1 in the ammonia supply path 19. In the example shown in FIG. 3 , one end of the temperature adjustment path 61 is connected between the three-way catalyst 8 and the SCR catalyst 9 in the exhaust path 4. The other end of the temperature adjustment path 61 is connected between the valve V1 and the vaporizer 11 in the ammonia supply path 19. The temperature adjustment path 61 recirculates the catalyst-passed gas that has passed through the three-way catalyst 8 back to the ammonia supply path 19. The catalyst-passed gas is exhaust gas from the ammonia engine 2, and is hotter than the outside air while the ammonia engine 2 is operating and immediately after it is stopped. During operation of the ammonia engine 2, the catalyst-passed gas receives heat from the heat generated by the purification (oxidation reaction) of the exhaust gas in the three-way catalyst 8. Immediately after the ammonia engine 2 is stopped, the catalyst-passed gas receives residual heat from the three-way catalyst 8.

A valve V6 is provided in the temperature adjustment path 61. The valve V6 is a flow control valve that controls the flow rate of catalyst-passing gas that flows back to the ammonia supply path 19 from a point downstream of the three-way catalyst 8 in the exhaust path 4. When the valve V6 is open, it allows the catalyst-passing gas to flow back to the ammonia supply path 19. When the valve V6 is closed, it blocks the catalyst-passing gas from flowing back to the ammonia supply path 19. The valve V6 is, for example, an electromagnetic flow control valve, and operates in response to control commands from the controller 50, which will be described later.

Check valve 62 is disposed downstream of valve V6 in temperature adjustment path 61. Check valve 62 prevents ammonia from flowing from ammonia supply path 19 into temperature adjustment path 61. Even if valve V6 is closed when the ammonia engine 2 is stopped, causing the pressure in the ammonia supply path 19 to be higher than the pressure in the temperature adjustment path 61, check valve 62 blocks the flow of ammonia from ammonia supply path 19 into temperature adjustment path 61. When the ammonia remaining in the ammonia supply path 19 is reduced and the pressure in the ammonia supply path 19 becomes lower than the pressure in the temperature adjustment path 61, check valve 62 allows catalyst-passed gas to flow from temperature adjustment path 61 into ammonia supply path 19.

A temperature sensor 63 is provided in the temperature adjustment path 61. The temperature sensor 63 is disposed, for example, between the valve V6 and the check valve 62 in the temperature adjustment path 61. The temperature sensor 63 detects the gas temperature of the catalyst-passing gas flowing through the temperature adjustment path 61. The temperature sensor 63 transmits information about the detected gas temperature to the controller 50.

In addition to the configuration of the purge path 40 described above, the purge path 40A further includes a pump 44. The pump 44 is provided in a closed circuit formed by a portion of the ammonia supply path 19, the purge path 40, a portion of the exhaust path 4, the three-way catalyst 8, and the temperature adjustment path 61. In the example of FIG. 3, the pump 44 is disposed in the third purge path 43. That is, the pump 44 is provided in the purge path 40. The pump 44 is, for example, an electric pump, and operates in response to control commands from the controller 50A.

An example of the operation of engine system 1A will be described with reference to FIG. 4. FIG. 4 is a flowchart showing an example of the control process of the controller in FIG. 3. By opening valve V1 while the ammonia engine 2 is operating, controller 50A supplies ammonia in the ammonia tank 10 to the main injector 5 via the ammonia supply path 19. When valve V1 is open, controller 50 closes valves V2, V3, V4, V5, and V6 (step S11).

When the ammonia engine 2 that has been operating is stopped, the controller 50A closes valve V1, thereby blocking the supply of ammonia in the ammonia tank 10 to the main injector 5 via the ammonia supply path 19. At this time, ammonia remains in the ammonia supply path 19. As an example, after the ammonia engine 2 is stopped, the controller 50A closes valve V1 (step S12), opens valves V3 and V4 (step S13), and then opens valve V2 (step S14). Furthermore, the controller 50A opens valves V5 and V6 (step S15) and operates the pump 44 in the expulsion path 40 (step S16).

More specifically, the controller 50A circulates the gas in the closed circuit by operating the pump 44. In the example of FIG. 3, when the pump 44 provided in the third purge path 43 is activated, the gas in the first purge path 41 and the second purge path 42 is sent upstream of the three-way catalyst 8 in the exhaust path 4. As the pump 44 draws in the gas in the first purge path 41 and the second purge path 42, gas remaining in a portion of the ammonia supply path 19 located further upstream is also drawn toward the pump 44. In the example of FIG. 3, the portion of the ammonia supply path 19 corresponds to the section from the connection point with the valve V1 to the connection point with the first purge path 41 and the section from the connection point with the valve V1 to the connection point with the second purge path 42.

When the pump 44 is provided in the purge path 40, its operation draws gas remaining in part of the ammonia supply path 19 toward the pump 44. In this case, the air source 31A does not necessarily have to pressurize air into the ammonia supply path 19. The air source 31A may be configured without a pump and an air tank for storing compressed air. Incidentally, after the ammonia engine 2 stops operating, the controller 50A closes valve V1, opens valves V3 and V4, and then opens valve V2. However, air may be supplied to the three-way catalyst 8 by opening valve V5 while keeping valve V2 closed. Even in this case, since the pump 44 is provided in the purge path 40, it is sufficient to use the pump 44 to circulate gas within a closed circuit; it is not necessary to use air from the oxygen supply path 32 to push out ammonia from the ammonia supply path 19.

By opening valve V2, controller 50A supplies air from air source 31A to purge path 40A (first purge path 41 in the example shown in FIG. 3 ). Air supplied to purge path 40A via valve V5 is then supplied to three-way catalyst 8 via exhaust path 4. This increases the amount of oxygen available for oxidizing ammonia in three-way catalyst 8. During the initial stage of ammonia purge after ammonia engine 2 is shut down, there is a period (a predetermined period) during which air supplied from oxygen supply path 32 by opening valve V2 purges ammonia remaining in ammonia supply path 19 but does not reach three-way catalyst 8. During this period, the oxygen concentration in three-way catalyst 8 is insufficient relative to the ammonia concentration. Therefore, by supplying air from air source 31A to purge path 40A via valve V5, this insufficient oxygen concentration relative to the ammonia concentration in three-way catalyst 8 is alleviated. Therefore, ammonia can be more appropriately oxidized in three-way catalyst 8 during the initial stage of ammonia purge. The controller 50A may also open the valve V5 for the specified period after the operation of the ammonia engine 2 is stopped.

By opening valve V6, controller 50A returns catalyst-passing gas downstream of three-way catalyst 8 in exhaust path 4 to ammonia supply path 19 via temperature adjustment path 61. When catalyst-passing gas is returned to ammonia supply path 19, it heats the ammonia supply path 19. When ammonia remaining in ammonia supply path 19 is expelled to expulsion path 40A, condensation may occur in the ammonia supply path 19 due to the latent heat of vaporization of ammonia. By heating the ammonia supply path 19 with catalyst-passing gas, condensation due to the latent heat of vaporization of ammonia can be suppressed. Note that, for example, if condensation remains in the ammonia supply path 19 even after sufficient ammonia has been expelled, controller 50A may close valves V2 and V5 while leaving valve V6 open to stop the supply of air from air source 31A.

When valve V6 is opened and the gas temperature is equal to or higher than a predetermined temperature threshold, controller 50A may increase the amount of air supplied from oxygen supply path 32 to ammonia supply path 19 compared to when the gas temperature is below the temperature threshold (steps S17 and S18). The temperature threshold is a threshold value for the temperature of the catalyst-passing gas used to determine whether the ammonia supply path 19 will be 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 oxygen supply path 32 to ammonia supply path 19 is increased, thereby cooling the catalyst-passing gas with the air. This prevents the ammonia supply path 19 from being excessively heated even when the gas temperature is equal to or higher than the predetermined temperature threshold.

As described above, in the engine system 1A of the second embodiment, the exhaust catalyst is a three-way catalyst 8, and therefore ammonia supplied to the three-way catalyst 8 is oxidized by the three-way catalyst 8, raising the temperature of the catalyst-passing gas flowing out from the three-way catalyst 8. By operating the pump 44, a portion of the catalyst-passing gas flowing out from the three-way catalyst 8 is supplied to a portion of the ammonia supply path 19 and the purge path 40A through the temperature adjustment path 61. This heats the portion of the ammonia supply path 19 and the purge path 40A, making it possible to suppress condensation caused by the latent heat of vaporization of ammonia remaining in the ammonia supply path 19, for example.

In engine system 1A, a purge path 40A is connected to the ammonia supply path 19 at a location downstream of where the oxygen supply path 32 is connected, and a pump 44 is provided in the purge path 40A. As a result, by operating the pump 44, ammonia remaining in the ammonia supply path 19 can be supplied to the three-way catalyst 8 through the purge path 40A, for example, without pressurizing air from the oxygen supply path 32 to the ammonia supply path 19.

The engine system 1A is provided with a temperature sensor 63 in the temperature adjustment path 61 that detects the gas temperature of the catalyst-passing gas flowing through the temperature adjustment path 61. When the gas temperature is equal to or higher than a predetermined temperature threshold, the engine system 1A increases the amount of air supplied from the oxygen supply path 32 to the ammonia supply path 19 compared to when the gas temperature is below the temperature threshold. This prevents a portion of the ammonia supply path 19 and the expulsion path 40A from being excessively heated.

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

For example, the engine system 1A of the second embodiment described above can be modified into an engine system 1B as shown in Figure 5. In Figure 5, the modified engine system 1B differs from engine system 1A mainly in that a pump 64 is provided in the temperature adjustment path 61 instead of the pump 44 in the third discharge path 43. In engine system 1B, the discharge path 40A is returned to the discharge path 40, and the temperature adjustment unit 60 becomes temperature adjustment unit 60B. Note that in temperature adjustment unit 60B, the temperature sensor in the temperature adjustment path 61 is omitted.

In engine system 1B, because pump 64 is provided in temperature adjustment path 61, gas in first purge path 41 and second purge path 42 is less likely to be drawn toward pump 64 than when pump 44 is provided in third purge path 43 as in the example of FIG. 3 . Therefore, oxygen supply unit 30B differs from oxygen supply unit 30A of the second embodiment in that air is returned to air source 31 of the first embodiment, which is capable of pumping air. Furthermore, in engine system 1A of the second embodiment, controller 50A could circulate gas within a closed circuit using pump 44 while keeping valve V2 closed, and supply air to three-way catalyst 8 by opening valve V5. However, in engine system 1B, pump 64 exclusively pumps catalyst-passed gas back to ammonia supply path 19. For example, controller 50B may open valve V2 to use air from oxygen supply path 32 to push ammonia out of ammonia supply path 19.

In the above embodiment, an example was described in which the three-way catalyst 8 was primarily used as the exhaust catalyst, but the exhaust catalyst may be one or more types of catalyst capable of adsorbing and oxidizing ammonia. The SCR catalyst 9 may be primarily used as the exhaust catalyst, or an oxidation catalyst may be used instead.

In the above embodiment, the main injector 5 was used as an example of an ammonia amount adjustment unit, but the ammonia amount adjustment unit may also be a carburetor.

In the above embodiment, valves V1 to V6 operate in response to control commands from controllers 50, 50A, and 50B in conjunction with the shutdown of the ammonia engine 2, as shown in the flowcharts of Figures 2 and 4. However, this is not limited to this. For example, an operating unit such as a button that can be operated by an operator from the outside may be provided, and the operator may operate the operating unit after the ammonia engine 2 has been shut down to activate the valves (for example, an automated operation mode such as service purge mode).

In the above embodiment, valves V1 to V6 are electromagnetic flow control valves that operate in response to control commands from controllers 50, 50A, and 50B, but this is not limited to this. For example, valves V1 to V6 may also be manual flow control valves. In this case, the above-described effects can be achieved by an operator manually performing steps similar to those in the flowcharts of Figures 2 and 4 as a residual fuel processing method.

In the above embodiment, the discharge path 40 was pre-installed in the ammonia engine 2, but this is not limited to this. The discharge path 40 may be attached to the ammonia engine 2 as a retrofit member when removing the ammonia supply path 19 from the ammonia engine 2. In this case, a coupler or the like can be used to connect the discharge path 40.

1, 1A, 1B...engine system, 2...ammonia engine (engine), 4...exhaust path, 5...main injector (ammonia amount adjustment unit), 8...three-way catalyst (exhaust catalyst), 10...ammonia tank, 19...ammonia supply path, 30, 30A, 30B...oxygen supply unit, 32, 34...oxygen supply path, 40, 40A...exhaust path, 44, 64...pump, 60, 60B...temperature adjustment unit, 61...temperature adjustment path, 63...temperature sensor (temperature detection unit), V1...valve (first valve), V2...valve (second valve), V3, V4...valve (third valve), V6...valve (fourth valve).

Claims (4)

an engine to which ammonia is supplied from an ammonia amount adjusting unit;
an ammonia tank for storing ammonia;
an ammonia supply path connecting the ammonia tank and the ammonia amount adjuster;
an exhaust path connected to the engine and into which exhaust gas from the engine flows;
an exhaust catalyst provided in the exhaust path for adsorbing and oxidizing ammonia;
a first valve that is provided in the ammonia supply path and that, when closed, blocks the ammonia in the ammonia tank from being supplied to the ammonia amount adjuster;
an oxygen supply unit including: an oxygen supply path connected to a location downstream of the first valve in the ammonia supply path and supplying a gas containing oxygen to the ammonia supply path; and a second valve provided in the oxygen supply path, closed when the first valve is open and opened after the first valve is closed;
a purge path connected to a location in the ammonia supply path downstream of a location to which the oxygen supply path is connected, and provided so as to be able to supply the ammonia therein to the exhaust catalyst;
a third valve provided in the exhaust path and opened after the first valve is closed. the exhaust catalyst is a three-way catalyst,
a temperature adjustment unit including a temperature adjustment path having one end connected to a location in the exhaust path downstream of the three-way catalyst and the other end connected to the ammonia supply path, and a fourth valve provided in the temperature adjustment path;
2. The engine system according to claim 1, further comprising: a pump provided in a closed circuit formed by a portion of the ammonia supply path, the purge path, a portion of the exhaust path, the three-way catalyst, and the temperature adjustment path. The engine system of claim 2, wherein the pump is provided in the expulsion path. a temperature detection unit that is provided in the temperature adjustment path and detects the temperature of the catalyst-passing gas that flows through the temperature adjustment path;
4. The engine system according to claim 2, wherein when the gas temperature is equal to or higher than a predetermined temperature threshold, the amount of the gas supplied from the oxygen supply path to the ammonia supply path is increased compared to when the gas temperature is lower than the temperature threshold.