JP7834005B2 - Engine system - Google Patents

Description

This invention relates to an engine system.

A conventional engine system is known, for example, the technology described in Patent Document 1. The engine system described in Patent Document 1 comprises an engine block, an intake passage connected to the intake port of the engine block, an exhaust passage connected to the 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 connecting the intake passage upstream of the throttle valve to the crankcase in the engine block and introducing intake air (fresh air) from the intake passage into the crankcase, a recirculation passage connecting the intake passage downstream of the throttle valve to the crankcase and returning blow-by gas remaining in the crankcase to the intake passage, and a PCV valve provided in the recirculation passage.

Japanese Patent Publication No. 2012-145057

In recent years, ammonia engines have emerged that use ammonia as fuel. However, ammonia blow-by gas remains in the crankcase, so it is desirable to suppress the leakage of ammonia blow-by gas into the atmosphere when removing the crankcase itself, components or piping spatially connected to the crankcase, for example, during maintenance. Similarly, when disconnecting fuel lines through which ammonia flows, it is desirable to suppress the leakage of ammonia remaining in the fuel lines into the atmosphere. Therefore, one approach is to purify the ammonia remaining in the crankcase or fuel lines with an exhaust catalyst to prevent ammonia from leaking into the atmosphere when removing the crankcase itself, components or piping spatially connected to the crankcase, or fuel lines. However, depending on the temperature of the exhaust catalyst, ammonia may react with the catalyst to produce nitrous oxide ( _N₂O ), which has a high environmental impact. In this case, _N₂O may flow through the exhaust passage and leak into the atmosphere.

The objective of this 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 comprising an engine having a piston capable of reciprocating in a combustion chamber for burning ammonia, a crankshaft connected to the piston, and a crankcase housing the crankshaft, the system comprising: a first oxygen supply passage connected to the engine and through which oxygen-containing gas supplied to the combustion chamber flows; a flow control valve disposed in the first oxygen supply passage and controlling the flow rate of 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 adsorbing and oxidizing ammonia; a second oxygen supply passage connecting the crankcase to a point upstream of the flow control valve in the first oxygen supply passage and supplying oxygen-containing gas into the crankcase; and the crankcase and the downstream of the flow control valve in the first oxygen supply passage. The system comprises a blow-by gas passage that connects to a point on the side and recirculates ammonia blow-by gas remaining in the crankcase to a first oxygen supply passage; a blow-by gas recirculation valve disposed in the blow-by gas passage and adjusting the flow rate of ammonia blow-by gas recirculating to the first oxygen supply passage; a starter that rotates the crankshaft; an ammonia removal device that removes ammonia flowing through the exhaust passage; an ammonia removal passage connecting the ammonia removal device to a point between the engine and the exhaust catalyst in the exhaust passage; an on-off valve disposed in the ammonia removal passage that, when opened, allows ammonia to be supplied to the ammonia removal device; and a control unit that controls the opening degree of a flow control valve so that blow-by gas is recirculated to the first oxygen supply passage when the crankshaft is rotating by the starter, and also controls the opening degree of an on-off valve so that the on-off valve is open.

In such an engine system, the opening of the flow control valve is controlled so that ammonia blow-by gas is recirculated into the first oxygen supply passage during any period between the time the crankshaft stops rotating due to the completion of ammonia combustion in the engine's combustion chamber and the time when ammonia combustion occurs again in the combustion chamber. At the same time, the crankshaft is rotated by the starter. As a result, the combustion chamber side of the first oxygen supply passage becomes negative pressure, causing oxygen-containing gas to flow through the second oxygen supply passage and be introduced into the crankcase. Simultaneously, the blow-by gas recirculation valve opens, allowing the ammonia blow-by gas remaining in the crankcase to flow through the blow-by gas passage together with the oxygen-containing gas and be recirculated into the first oxygen supply passage. The ammonia blow-by gas then flows through the first oxygen supply passage and the engine's combustion chamber together with the oxygen-containing gas into the exhaust passage. At this point, by opening the shut-off valve and closing the exhaust passage, the ammonia flows through the abatement passage and is supplied to the abatement device. The ammonia is then abated in the abatement device. In this case, since ammonia does not flow through the exhaust catalyst, the generation of nitrous oxide ( _N₂O ), which has a high environmental impact, in the exhaust catalyst is suppressed. As a result, the leakage of nitrous oxide into the atmosphere is suppressed.

(2) In the above (1), the engine system further comprises a reformer that generates a hydrogen-containing reformed gas by reforming ammonia, a reforming oxygen supply channel that supplies oxygen-containing gas to the reformer, a reforming flow control valve disposed in the reforming oxygen supply channel and controlling the flow rate of oxygen-containing gas supplied to the reformer, and a reformed gas channel that supplies the reformed gas generated by the reformer to the combustion chamber. The control unit may control the opening degree of the reforming flow control valve so that blow-by gas is recirculated into the first oxygen supply channel when the crankshaft is rotating by the starter. In such a configuration, since hydrogen-containing reformed gas is supplied to the engine's combustion chamber, ammonia is more easily burned in the engine's combustion chamber.

(3) An engine system according to another aspect of the present invention includes an engine supplied with ammonia from an ammonia quantity adjustment unit, an ammonia tank for storing ammonia, an ammonia supply passage connecting the ammonia tank and the ammonia quantity adjustment 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 for adsorbing and oxidizing ammonia, a decontamination device for decontaminating ammonia flowing through the exhaust passage, a decontamination passage connecting the point between the engine and the exhaust catalyst in the exhaust passage to the decontamination device, a first on-off valve disposed in the decontamination passage that, when opened, allows ammonia to be supplied to the decontamination device, and a valve disposed in the ammonia supply passage for closing. The system comprises: a second on-off valve that shuts off the supply of ammonia from the ammonia tank to the ammonia quantity adjustment unit; an oxygen supply path connected to a location downstream of the second on-off valve in the ammonia supply path and supplying oxygen-containing gas to the ammonia supply path; an oxygen supply unit disposed in the oxygen supply path and having a third on-off valve that closes when the second on-off valve is open and opens after the second on-off valve closes; an expulsion path connected to a location downstream of the oxygen supply path in the ammonia supply path and provided to supply the internal ammonia to the exhaust catalyst; and a fourth on-off valve disposed in the expulsion path and opening after the second on-off valve closes.

In this type of engine system, the second on-off valve is open while the engine is running, and ammonia from the ammonia tank is supplied to the ammonia quantity adjustment unit via the ammonia supply passage. When the engine stops, ammonia remains in the ammonia supply passage. Therefore, by closing the second on-off valve after the engine has stopped, the supply of ammonia from the ammonia tank to the ammonia quantity adjustment unit is cut off. By opening the third and fourth on-off valves after closing the second on-off valve, oxygen-containing gas is supplied to the ammonia supply passage. As a result, the ammonia remaining inside the ammonia supply passage flows into the exhaust passage through the expulsion passage along with the oxygen-containing gas. At this point, by opening the first on-off valve and blocking the exhaust passage, the ammonia flows through the abatement passage and is supplied to the abatement device. The ammonia is then abated in the abatement device. At this time, since ammonia does not flow to the exhaust catalyst, the generation of nitrous oxide ( _N₂O ), which has a high environmental impact, in the exhaust catalyst is suppressed. This suppresses the leakage of nitrous oxide into the atmosphere.

(4) In (3) above, the exhaust catalyst is a three-way catalyst, and the engine system may further include a temperature control unit having a temperature control path connected at one end 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 control on/off valve disposed in the temperature control path, and a pump provided in a closed circuit formed by a portion of the ammonia supply flow path, a discharge path, a portion of the exhaust flow path, the three-way catalyst, and the temperature control path. In such a configuration, since the exhaust catalyst is a three-way catalyst, the ammonia supplied to the three-way catalyst is oxidized by the three-way catalyst, and the temperature of the catalytic gas flowing out of the three-way catalyst rises. By operating the pump, a portion of the catalytic gas flowing out of the three-way catalyst is supplied to a portion of the ammonia supply flow path and a discharge path through the temperature control path. As a result, a portion of the ammonia supply flow path and a discharge path are heated, which can suppress condensation caused by the latent heat of vaporization of ammonia remaining in the ammonia supply flow path, for example.

According to this invention, the leakage of nitrous oxide into the atmosphere can be suppressed.

This is a schematic diagram showing an engine system according to the first embodiment of the present invention. Figure 1 is a cross-sectional view of the ammonia engine and intake system. Figure 1 is a flowchart showing an example of the procedure for the purge control process performed by the purge control processing unit. Figure 2 is a graph showing an example of the flow characteristics of a PCV valve. This flowchart shows an example of the procedure for the pollution control process performed by the pollution control processing unit shown in Figure 1. This is a schematic diagram showing an engine system according to a second embodiment of the present invention. Figure 6 is a flowchart showing an example of the procedure for the purge control process performed by the purge control processing unit shown. This is a schematic diagram showing an engine system according to a third embodiment of the present invention. Figure 8 is a flowchart showing the procedure for the purge control process performed by the purge control processing unit shown. Figure 8 is a schematic diagram showing a modified version of the engine system.

Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and redundant descriptions will be omitted.
[First Embodiment]

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

Ammonia engine 2 is an engine that uses ammonia gas ( _NH3 gas) as fuel. In ammonia engine 2, hydrogen ( _H2 ) is mixed with the ammonia gas as a combustion aid to make the non-flammable ammonia gas easier to burn. Ammonia engine 2 is, for example, a four-cylinder engine.

As shown in Figure 2, the ammonia engine 2 comprises a cylinder block 11, a cylinder head 12 assembled to the cylinder block 11, a plurality (four in this case) of pistons 13 reciprocally arranged 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 case) combustion chambers 14 where ammonia burns with hydrogen to produce exhaust gas. The combustion chambers 14 are defined by the space enclosed by the cylinder block 11, the cylinder head 12, and the piston 13.

The cylinder head 12 is provided with multiple intake ports 15 and exhaust ports 16 (four of each in this case) that communicate with 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 the crankshaft 20 via a connecting rod 19. The crankcase 21 is assembled to the end of the cylinder block 11 opposite to the end where the cylinder head 12 is located. An oil pan 22 for storing engine oil eo is detachably assembled to the end of the crankcase 21 opposite to the end where the cylinder block 11 is located. The interior of the crankcase 21 and oil pan 22 forms a crank chamber 23.

The first oxygen supply passage 3 comprises 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 passage 3 is the passage through which air supplied to each combustion chamber 14 of the ammonia engine 2 flows. Air is a gas containing oxygen (oxygen-containing gas). An air cleaner 7 is installed in the intake pipe 25 to remove foreign matter such as dust and dirt contained in the air.

The exhaust passage 4 comprises 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 passage 4 is the passage through which exhaust gas generated from each combustion chamber 14 of the ammonia engine 2 flows.

Returning to Figure 1, the exhaust passage 4 is equipped with a three-way catalyst 8 for purifying unburned ammonia and nitrogen oxides (NOx), which are harmful substances contained in the exhaust gas, and an SCR catalyst 9 for adsorbing unburned ammonia. The three-way catalyst 8 and the SCR catalyst 9 are installed in the exhaust pipe 27 described above.

The three-way catalyst 8 primarily oxidizes ammonia using the air flowing into it. Furthermore, the three-way catalyst 8 adsorbs ammonia, albeit in small amounts compared to the SCR catalyst 9. The SCR catalyst 9 adsorbs ammonia and also oxidizes it using NOx flowing into it. The NOx is then reduced. The three-way catalyst 8 and the SCR catalyst 9 constitute the exhaust catalyst installed in the exhaust flow path 4.

The main injector 5 is an electromagnetic fuel injection valve that injects ammonia gas into the combustion chamber 14 of the ammonia engine 2. There are, for example, as many main injectors 5 as there are cylinders in the ammonia engine 2 (in this case, four). 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 located 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 control commands from the controller 60, which will be described later.

Furthermore, the engine system 1 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 channel 30 connects the crankcase 21 to a point upstream of the main throttle valve 6 in the first oxygen supply channel 3. The second oxygen supply channel 30 supplies oxygen-containing air to the crankcase 21 (crank chamber 23).

As shown in Figure 2, the second oxygen supply passage 30 includes a pipe 33 connecting the area between the air cleaner 7 and the main throttle valve 6 in the intake pipe 25 to the cylinder head 12 of the ammonia engine 2, and a passage 34 provided in the cylinder head 12 and cylinder block 11 to connect this pipe 33 to the crankcase 23.

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

As shown in Figure 2, the blow-by gas passage 31 includes a pipe 35 connecting the cylinder head 12 of the ammonia engine 2 to the area between the main throttle valve 6 and the intake manifold 24 in the intake pipe 25, and a passage 36 provided in the cylinder head 12 and cylinder block 11 to connect this pipe 35 to the crankcase 23.

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

The PCV valve 32 comprises housings 37A and 37B assembled to be aligned axially, a valve body 38 movably housed within housing 37A, and a spring 39 that biases the valve body 38 toward housing 37B. The PCV valve 32 directs blow-by gas in only one direction, from the crankcase 23 to the first oxygen supply passage 3.

When the pressure inside the intake manifold 24 is positive, the biasing force of the spring 39 presses the valve body 38 against the valve seat 37a located at the end of the housing 37B on the housing 37A side, thereby 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 biasing force of the spring 39 towards the first oxygen supply passage 3, forming a passage and opening the PCV valve 32 (see A in Figure 2).

Returning to Figure 1, the engine system 1 comprises 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 reforming gas passage 46, a cooler 47, and a flow control valve 48.

The ammonia tank 40 is a container for storing 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 the ammonia supply channel 49. The vaporizer 41 vaporizes the liquid ammonia stored in the ammonia tank 40 to produce ammonia gas. The ammonia gas generated in the vaporizer 41 flows through the ammonia supply channel 50 and is supplied to the main injector 5, and also flows through the ammonia supply channel 51 and is supplied to the reforming injector 45.

The reformer 42 produces a hydrogen-containing reformed gas by reforming ammonia gas. The reformer 42 comprises a cylindrical housing 52 and a reforming catalyst 53 and a heater 54 housed within this housing 52.

The housing 52 is made of a metal material such as stainless steel that has corrosion resistance to ammonia gas. The reforming catalyst 53 is coated on a carrier exhibiting a honeycomb structure, for example. The reforming catalyst 53 is a catalyst that burns ammonia gas and decomposes it into hydrogen. The reforming catalyst 53 is, for example, an ATR (Autothermal Reformer) type ammonia reforming catalyst.

The heater 54 is positioned upstream of the reforming catalyst 53 within the housing 52. The heater 54 heats the reforming catalyst 53. The heater 54 heats the ammonia gas flowing through the housing 52, utilizing the heat from the ammonia gas to heat the reforming catalyst 53. For example, an electrically heated catalyst (EHC) can be used as the heater 54. Alternatively, the heater 54 may directly heat the reforming catalyst 53.

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

The reforming throttle valve 44 is located 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 control commands from the controller 60, which will be described later.

The reforming injector 45 is an electromagnetic fuel injection valve that injects ammonia gas towards 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. There may be multiple reforming injectors 45 (two in this case) or just one. The reforming injector 45 operates in response to control commands from the controller 60, which will be described later.

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

The cooler 47 is installed in the reformed gas passage 46. The cooler 47 cools the reformed gas flowing through the reformed gas passage 46 using, for example, engine coolant used to cool the ammonia engine 2.

The flow control valve 48 is located downstream of the cooler 47 in the reformed gas flow path 46. The flow control valve 48 is a solenoid valve that adjusts the flow rate of reformed gas supplied to the ammonia engine 2. The flow control valve 48 operates in response to control commands from the controller 60 (described later). The flow control valve 48 may also be an on/off valve.

Furthermore, the engine system 1 includes a pollution control device 65, a pollution control flow path 66, a first on-off valve 67 (on-off valve), and a discharge on-off valve 68.

The ammonia removal device 65 is a device that removes ammonia flowing through the exhaust passage 4. The ammonia removal device 65 utilizes 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. The ammonia removal device 65 may also have a pump (not shown) that sucks up the ammonia flowing through the exhaust passage 4.

The abatement flow path 66 connects the abatement device 65 to the section of the exhaust flow path 4 between the ammonia engine 2 and the three-way catalytic converter 8. One end of the abatement flow path 66 is connected to the exhaust pipe 27 (see Figure 2) upstream of the three-way catalytic converter 8. The abatement flow path 66 is the flow path through which ammonia flows towards the abatement device 65.

The first on-off valve 67 is installed in the abatement flow path 66. The first on-off valve 67 controls whether or not ammonia is supplied to the abatement device 65. By opening the first on-off valve 67, it allows the supply of ammonia to the abatement device 65. By closing the first on-off valve 67, 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 control commands from the controller 60 described later.

The exhaust valve 68 is located downstream of the SCR catalyst 9 in the exhaust flow path 4. The exhaust valve 68 controls whether or not the gas that has passed through the three-way catalyst 8 and the SCR catalyst 9 (catalyst-transmitted gas) is discharged downstream of the valve 68. Opening the valve allows the catalyst-transmitted gas to be discharged downstream. Closing the valve blocks the discharge of the catalyst-transmitted gas downstream. The exhaust valve 68 is, for example, an electromagnetic ON/OFF valve and operates in response to control commands from the controller 60 described later.

Furthermore, the engine system 1 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 it may detect the temperature of the area surrounding the three-way catalyst 8 (for example, the case housing the three-way catalyst 8). The temperature sensor 58 transmits the detected temperature information 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, ROM, RAM, and an input/output interface. The controller 60 loads a program stored in the ROM into the RAM and executes that program using the CPU, thereby performing various control functions, including drive control of the ammonia engine 2.

When the vehicle starts, the controller 60 activates the power supply 55 to the starter 59 and heater 54, and controls the main injector 5, main throttle valve 6, reformer injector 45, and reformer throttle valve 44 to open. As a result, ammonia gas and air are supplied to the combustion chamber 14 and reformer 42 of the ammonia engine 2, and the reformed gas produced by the reformer 42 is supplied to the combustion chamber 14, causing the ammonia gas to burn 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 main throttle valve 6, the reforming injector 45, and the reforming throttle valve 44 so that an air-fuel ratio corresponding to the accelerator opening is obtained.

Furthermore, the controller 60 performs purging control to remove residual ammonia blow-by gas in the crankcase 21 (crank chamber 23) of the ammonia engine 2 during any period between the time the crankshaft 20 stops rotating due to the completion of ammonia gas combustion in the combustion chamber 14 of the ammonia engine 2, and the time when ammonia gas combustion occurs again in the combustion chamber 14. Blow-by gas is unburned gas that leaks into the crank chamber 23 through the gap between the cylinder block 11 and the piston 13.

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

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

The purge control processing unit 62 controls the opening degree of the first on-off valve 67 and the opening degree of the discharge on-off valve 68 based on the temperature of the three-way catalyst 8 detected by the temperature sensor 58 when the purge control processing is executed by the purge control processing unit 61.

Figure 3 is a flowchart showing an example of the purge control process performed by the purge control processing unit 61. In this embodiment, the process is initiated by the operator (in this case, the driver) after the rotation of the crankshaft 20 has stopped. The driver instructs the purging process to be performed, for example, before exiting the vehicle or before performing maintenance on the ammonia engine 2, using a manual switch such as an externally operable button.

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

In Figure 3, the purge control processing unit 61 first controls the opening degrees of the main throttle valve 6 and the modified throttle valve 44 (step S101). The purge control processing unit 61 controls the opening degrees of the main throttle valve 6 and the modified throttle valve 44 so that blow-by gas recirculates into the first oxygen supply passage 3. More specifically, when the crankshaft 20 is restarted by the starter 59, the purge control processing unit 61 controls the opening degrees of the main throttle valve 6 and the modified throttle valve 44 to maintain negative pressure inside the intake manifold 24.

Furthermore, the main throttle valve 6 and the modified throttle valve 44 at this time only need to be open enough to allow blow-by gas to be recirculated into the first oxygen supply passage 3 when the crankshaft 20 is restarted by the starter 59; they may be fully closed (zero opening).

Next, the purge control processing unit 61 activates the starter 59 (step S102). This causes the crankshaft 20 of the ammonia engine 2 to rotate, creating a negative pressure state inside the intake manifold 24. Note that step S102 may be performed before step S101, or steps S101 and S102 may be performed simultaneously.

At this time, because the intake manifold 24 is under negative pressure, the air in the first oxygen supply passage 3 flows through the second oxygen supply passage 30 and is supplied to the crankcase 23. This air, along with the ammonia blow-by gas remaining in the crankcase 23, flows through the PCV valve 32 and the blow-by gas passage 31, returning to the first oxygen supply passage 3. Furthermore, since 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.

Here, as shown in Figure 4, the PCV valve 32 has a flow characteristic where the blow-by gas flows more easily as the negative pressure in the intake manifold 24 increases until it reaches a specified pressure N. However, once the negative pressure in the intake manifold 24 exceeds the specified pressure N, the blow-by gas flow becomes more difficult. Therefore, it is preferable for the controller 60 to control the opening of the main throttle valve 6 and the modified throttle valve 44 so that the negative pressure in the intake manifold 24 reaches the specified pressure N. The specified pressure N is the negative pressure that maximizes the airflow rate per unit time through the PCV valve 32.

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. Therefore, blow-by gas can be discharged more efficiently compared to using a simple check valve.

Figure 5 is a flowchart showing an example of the procedure for the pollution control process performed by the pollution control processing unit 62. Similar to the purge control processing unit 61, this process is initiated by the driver at any time during the period between the end of ammonia gas combustion in the combustion chamber 14 of the ammonia engine 2 (when the crankshaft 20 stops rotating) and the start of ammonia gas combustion in the combustion chamber 14.

In Figure 5, the pollution control processing unit 62 first acquires the value detected by the temperature sensor 58 (step S111). Then, based on the value detected by the temperature sensor 58, the pollution control processing unit 62 determines whether the temperature of the three-way catalyst 8 is within the specified temperature range H (step S112). The specified temperature range H is the temperature range in which the three-way catalyst 8 reacts with ammonia to produce nitrous oxide ( _N₂O ) (for example, approximately 150°C to 350°C).

When the pollution control unit 62 determines that the temperature of the three-way catalyst 8 is within the specified temperature range H, it controls the first on-off valve 67 to open and the discharge on-off valve 68 to close (step S113), and then repeats step S111. At this time, the first on-off valve 67 may be opened before the discharge on-off valve 68 is closed, or the opening of the first on-off valve 67 and the closing of the discharge on-off valve 68 may be performed simultaneously.

When the decontamination control unit 62 determines that the temperature of the three-way catalyst 8 is not within the specified temperature range H, it controls the discharge valve 68 to open and the first valve 67 to close (step S114), and then repeats step S111. At this time, the discharge valve 68 may be opened before the first valve 67 is closed, or the discharge valve 68 may be opened and the first valve 67 may be closed simultaneously.

In the engine system 1 described above, when the driver instructs the removal of blow-by gas, the starter 59 is activated, which rotates the crankshaft 20 and adjusts the opening of the main throttle valve 6 and the modified throttle valve 44.

As a result, negative pressure is created inside the intake manifold 24, causing air in the first oxygen supply passage 3 to flow through the piping 33 and passage 34 of the second oxygen supply passage 30 and be supplied to the crankcase 23. This air, along with the ammonia blow-by gas remaining in the crankcase 23, flows through the passage 36 of the blow-by gas passage 31, the PCV valve 32, and the piping 35 of the blow-by gas passage 31, returning to the first oxygen supply passage 3. The ammonia blow-by gas then flows through the first oxygen supply passage 3 and the combustion chamber 14 of the ammonia engine 2 before entering the exhaust passage 4.

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

Specifically, if the temperature of the three-way catalyst 8 is higher than the upper limit of the specified temperature range H, ammonia is oxidized and burned by the three-way catalyst 8. If the temperature of the three-way catalyst 8 is lower than the lower limit of the specified temperature range H, ammonia is adsorbed by the SCR catalyst 9. This suppresses the discharge of ammonia blow-by gas through the exhaust passage 4.

On the other hand, when the temperature of the three-way catalyst 8 is within the specified temperature range H, the first on-off valve 67 is opened and the discharge on-off valve 68 is closed. Therefore, the ammonia blow-by gas flowing through the exhaust passage 4 is not supplied to the three-way catalyst 8 and the SCR catalyst 9, but instead flows through the abatement passage 66 and is supplied to the abatement device 65. The ammonia blow-by gas is then purified in the abatement device 65. Furthermore, because the discharge on-off valve 68 is closed, the discharge of catalyst-passing gas through the exhaust passage 4 is suppressed.

As described above, in this embodiment, the opening of the main throttle valve 6 and the reforming throttle valve 44 are controlled so that ammonia blow-by gas flows back into the first oxygen supply passage 3 during any period between the time the crankshaft 20 stops rotating due to the completion of ammonia gas combustion in the combustion chamber 14 of the ammonia engine 2 and the time when ammonia gas combustion occurs again in the combustion chamber 14, and the crankshaft 20 is rotated by the starter 59. As a result, a negative pressure is created inside the intake manifold 24, which is part of the first oxygen supply passage 3, so that air flows through the second oxygen supply passage 30 and is introduced into the crankcase 21, and the PCV valve 32 opens, causing the ammonia blow-by gas remaining in the crankcase 21 to flow back into the first oxygen supply passage 3 along with the air through the blow-by gas passage 31. The ammonia blow-by gas then flows into the exhaust passage 4 along with the air through the first oxygen supply passage 3 and the combustion chamber 14 of the ammonia engine 2. Here, by opening the first on-off valve 67 and closing the discharge on-off valve 68, the exhaust flow path 4 is blocked, allowing ammonia to flow through the abatement flow path 66 and be supplied to the abatement device 65. The ammonia is then abated in the abatement device 65. At this time, since ammonia does not flow to the three-way catalyst 8, the generation of nitrous oxide ( _N₂O ), which has a high environmental impact, in the three-way catalyst 8 is suppressed. As a result, leakage of nitrous oxide into the atmosphere is suppressed.

Furthermore, since 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 leakage of ammonia remaining in the crankcase 21 into the atmosphere is suppressed. Also, by regularly removing the ammonia blow-by gas remaining in the crankcase 21, for example, when the oil pan 22 is removed and the crankcase 21 is opened during maintenance, the leakage of large amounts of ammonia into the atmosphere is suppressed.

Furthermore, in this embodiment, since a hydrogen-containing reformed gas is supplied to the combustion chamber 14 of the ammonia engine 2, ammonia is more easily burned within the combustion chamber 14 of the ammonia engine 2.

Furthermore, in this embodiment, since the discharge valve 68 is used, the operator does not need to manually block the outlet of the exhaust passage 4. Therefore, the burden on the operator can be reduced.

Furthermore, in this embodiment, when the temperature of the three-way catalyst 8 is within the temperature range in which the three-way catalyst 8 generates nitrous oxide, the first on-off valve 67 is opened and the discharge on-off valve 68 is closed, so 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 outside the temperature range in which the three-way catalyst 8 generates nitrous oxide, the discharge on-off valve 68 is opened and the first on-off valve 67 is closed, so 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 lifespan 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 differs from the engine system 1 of the first embodiment in that it further includes a second on-off valve 75, an oxygen supply unit 70, and an exhaust path 80, and also 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 installed in the ammonia supply channel 49 connecting 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 ammonia from 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 supply of ammonia from the ammonia tank 40 to the main injector 5 and the reforming injector 45 through the vaporizer 41. The second on-off valve 75 operates, for example, in response to control commands from the controller 60A, described later.

The engine system 1A further includes an oxygen supply unit 70. The oxygen supply unit 70 comprises an air source 71, an oxygen supply path 72, a third on-off valve 76, and a check valve 73.

The air source 71 is a source of oxygen-containing gas for purging the ammonia supply passages 49-51. The air source 71 supplies, for example, atmospheric air as the oxygen-containing gas. The air source 71 includes a pump for dispensing atmospheric air. The air source 71 may also include an air tank for storing the compressed air dispensed by the pump.

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

A third on-off valve 76 is provided in the oxygen supply path 72. The third on-off valve 76 is, for example, located 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 passages 49-51. When the third on-off valve 76 is open, it allows air from the air source 71 to be supplied to the ammonia supply passages 49-51. When the third on-off valve 76 is closed, it blocks the supply of air from the air source 71 to the ammonia supply passages 49-51. The third on-off valve 76 is, for example, an electromagnetic flow control valve and operates in response to control commands from the controller 60A described later.

The check valve 73 is located downstream of the third on-off valve 76 in the oxygen supply path 72. The check valve 73 prevents ammonia from flowing from the ammonia supply path 49 into the oxygen supply path 72. Even when the ammonia engine 2, which was in operation, stops, and the pressure in the ammonia supply path 49 is higher than the pressure in the oxygen supply path 72 due to residual ammonia, the check valve 73 blocks the inflow of ammonia from the ammonia supply path 49 to the oxygen supply path 72. When the residual ammonia is reduced and the pressure in the ammonia supply path 49 becomes lower than the pressure in the oxygen supply path 72, the check valve 73 allows ammonia to flow from the oxygen supply path 72 into the ammonia supply path 49.

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

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

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

The first discharge path 81 and the second discharge path 82 merge downstream of the fourth on-off valve 77 and the fifth on-off valve 78. The third discharge path 83 connects the point where the first discharge path 81 and the second discharge path 82 merge to the area upstream of the point where it connects to the abatement flow path 66 in the exhaust flow path 4. Alternatively, the first discharge path 81 and the second discharge path 82 may each be connected upstream of the point where they connect to the abatement flow path 66 in the exhaust flow path 4 without merging.

The engine system 1A includes a controller 60A. The controller 60A has a purge control processing unit 61A and the abatement control processing unit 62 described above. The purge control processing unit 61A controls the second on-off valves 75 to the fifth on-off valves 78 to perform purging of the ammonia supply passages 49 to 51.

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

In Figure 7, the purge control unit 61A opens the second on-off valve 75 during the operation of the ammonia engine 2, thereby supplying ammonia from the ammonia tank 40 to the main injector 5 via the ammonia supply passage 49, vaporizer 41, and ammonia supply passage 50. When the second on-off valve 75 is open, the purge control unit 61A closes the third on-off valve 76, the fourth on-off valve 77, and the fifth on-off valve 78 (step S121). During the operation of the ammonia engine 2, the three-way catalyst 8 and the SCR catalyst 9 are above their activation temperature (lights off).

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

The purge control processing unit 61A opens the third on-off valve 76 at the driver's instruction while the vehicle is stopped and before it resumes operation. That is, the purge control processing unit 61A closes the second on-off valve 75, which was open, before opening the third on-off valve 76. Furthermore, the purge control processing unit 61A opens the fourth on-off valve 77 and the fifth on-off valve 78 after the ammonia engine 2 has stopped operating. That is, the purge control processing unit 61A closes the second on-off valve 75, which was open, before opening the fourth on-off valve 77 and the fifth on-off valve 78. As an example, after the ammonia engine 2 has stopped operating, 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), before opening the third on-off valve 76 (step S124). By opening the fourth valve 77 and the fifth valve 78 before the third valve 76, the pressure in the ammonia supply passage 49 can be rapidly reduced even if the pressure in the ammonia supply passage 49 is higher than the pressure in the oxygen supply passage 72 due to residual ammonia. The purge control processing unit 61A may also open the third valve 76 before the fourth valve 77 and the fifth valve 78.

In the engine system 1A described above, ammonia remaining inside the ammonia supply passages 49-51 flows into the exhaust passage 4 via the discharge passage 80. At this time, if the temperature of the three-way catalyst 8 is not within the aforementioned specified temperature range H, the discharge valve 68 is opened and the first valve 67 is closed. Therefore, the ammonia flowing 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 on-off valve 67 is opened and the discharge on-off valve 68 is closed. Therefore, the ammonia flowing 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 open while the ammonia engine 2 is running, and ammonia in the ammonia tank 40 is supplied to the main injector 5 via the ammonia supply passages 49 and 50. When the ammonia engine 2 that was running stops, ammonia remains in the ammonia supply passages 49 and 50. Therefore, by closing the second on-off valve 75 after the ammonia engine 2 has stopped running, the supply of ammonia from the ammonia tank 40 to the main injector 5 is cut off. After closing the second on-off valve 75, the third on-off valve 76, the fourth on-off valve 77, and the fifth on-off valve 78 are opened, supplying air to the ammonia supply passages 49 and 50. As a result, the ammonia remaining inside the ammonia supply passages 49 and 50 flows into the exhaust passage 4 along with the air through the expulsion passage 80. At this point, by opening the first on-off valve 67 and closing the discharge on-off valve 68, the exhaust passage 4 is blocked, and the ammonia flows through the abatement passage 66 and is supplied to the abatement device 65. Then, ammonia is removed in the abatement device 65. At this time, since ammonia does not flow to the three-way catalyst 8, the generation of nitrous oxide ( _N₂O ), which has a high environmental impact, in the three-way catalyst 8 is suppressed. As a result, leakage of nitrous oxide into the atmosphere is suppressed.

Furthermore, since any ammonia remaining in the ammonia supply channels 49 and 50 is removed, it becomes possible to suppress the outflow of ammonia remaining in the ammonia supply channels 49 and 50 into the atmosphere when the ammonia supply channels 49 and 50 are removed after the ammonia engine 2 has been shut down.
[Third Embodiment]

Figure 8 is a schematic diagram showing an engine system according to the 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 exhaust path 80A instead of the exhaust path 80, a controller 60B instead of the controller 60, and further includes a temperature control unit 90.

The oxygen supply unit 70A, in addition to the configuration of the oxygen supply unit 70 described above, further includes an oxygen supply path 74 and a sixth on-off valve 79. The oxygen supply path 74 connects the air source 71A to a point downstream of the fourth on-off valve 77 in the discharge path 80A. In the example shown in Figure 8, the oxygen supply path 74 is connected to a point downstream of the fourth on-off valve 77 in the first discharge path 81. The sixth on-off valve 79 is installed 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. When the sixth on-off valve 79 is open, it allows air from the air source 71A to be supplied to the oxygen supply path 74. When the sixth on-off valve 79 is closed, it blocks the supply of air from the air source 71A to the oxygen supply path 74. The sixth on-off valve 79 is, for example, an electromagnetic flow control valve and operates in response to control commands from the controller 60B.

The temperature control unit 90 includes a temperature control path 91, a temperature control on/off valve 95, a check valve 92, and a temperature sensor (temperature detection unit) 93.

The temperature control path 91 connects a point downstream of the three-way catalyst 8 in the exhaust flow path 4 to a point downstream of the second on-off valve 75 in the ammonia supply flow path 49. In the example shown in Figure 8, one end of the temperature control 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 control path 91 is connected between the second on-off valve 75 and the vaporizer 41 in the ammonia supply flow path 49. The temperature control path 91 recirculates the catalytic converter gas that has passed through the three-way catalyst 8 back into the ammonia supply flow path 49. The catalytic converter gas is the exhaust gas of the ammonia engine 2, and is hotter than the outside air during operation and immediately after shutdown of the ammonia engine 2. During operation of the ammonia engine 2, the catalytic converter gas receives heat from the exothermic reaction associated with the purification (oxidation reaction) of the exhaust gas in the three-way catalyst 8. Immediately after shutdown of the ammonia engine 2, the catalytic converter gas receives residual heat from the three-way catalyst 8.

A temperature control valve 95 is installed in the temperature control path 91. The temperature control valve 95 is a flow control valve that controls the flow rate of catalyst-passing gas returning to the ammonia supply path 49 from downstream of the three-way catalyst 8 in the exhaust flow path 4. When the temperature control valve 95 is open, it allows the catalyst-passing gas to return to the ammonia supply path 49. When the temperature control valve 95 is closed, it blocks the return of catalyst-passing gas to the ammonia supply path 49. The temperature control valve 95 is, for example, an electromagnetic flow control valve and operates in response to control commands from the controller 60B described later.

The check valve 92 is located downstream of the temperature control valve 95 in the temperature control path 91. The check valve 92 prevents ammonia from flowing from the ammonia supply path 49 into the temperature control path 91. Even when the pressure in the ammonia supply path 49 is higher than the pressure in the temperature control path 91 due to the closing of the temperature control valve 95 when the ammonia engine 2 has stopped, the check valve 92 blocks the flow of ammonia from the ammonia supply path 49 into the temperature control path 91. When the amount of ammonia remaining in the ammonia supply path 49 is reduced and the pressure in the ammonia supply path 49 becomes lower than the pressure in the temperature control path 91, the check valve 92 allows the flow of catalyst-passing gas from the temperature control path 91 into the ammonia supply path 49.

A temperature sensor 93 is provided in the temperature control path 91. The temperature sensor 93 is, for example, positioned between the temperature control on/off valve 95 and the check valve 92 in the temperature control path 91. The temperature sensor 93 detects the gas temperature of the catalyst passing through the temperature control path 91. The temperature sensor 93 transmits the detected gas temperature information to the controller 60B.

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

The engine system 1B includes a controller 60B. The controller 60B comprises a purge control processing unit 61B and the abatement control processing unit 62 described above. The purge control processing unit 61B controls the second to sixth on-off valves 75 to 79, the temperature control on-off valve 95, and the pump 84 to perform purging of the ammonia supply passages 49 to 51.

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

In Figure 9, the purge control unit 61B opens the second on-off valve 75 while the ammonia engine 2 is running, thereby supplying ammonia from the ammonia tank 40 to the main injector 5 via the ammonia supply passage 49, vaporizer 41, and ammonia supply passage 50. When the second on-off valve 75 is open, the purge control 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 control on-off valve 95 (step S131).

When the ammonia engine 2 that was running is stopped, the purge control processing unit 61B closes the second on-off valve 75, thereby blocking the supply of ammonia from the ammonia tank 40 to the main injector 5 via the ammonia supply passage 49, vaporizer 41, and 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 at the driver's instruction (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 control on-off valve 95 (step S135), and operates the pump 84 in the discharge passage 80A (step S136).

More specifically, the purge control unit 61B circulates the gas in the closed circuit by operating the pump 84. In the example shown in Figure 8, when the pump 84 located in the third discharge path 83 is activated, the gas in the first discharge path 81 and the second discharge path 82 is sent upstream of the three-way catalyst 8 in the exhaust flow path 4. As the pump 84 draws in the gas from the first discharge path 81 and the second discharge path 82, the gas remaining in parts of the ammonia supply flow paths 49 and 50 further upstream is also drawn towards the pump 84. In the example shown in Figure 8, the parts of the ammonia supply flow paths 49 and 50 correspond to the section from the connection point with the second on-off valve 75 to the connection point with the first discharge path 81, and the section from the connection point with the second on-off valve 75 to the connection point with the second discharge path 82.

Furthermore, when the pump 84 is installed in the discharge path 80A, its operation pulls some of the gas remaining in the ammonia supply passages 49 and 50 towards the pump 84. In this case, the air source 71A does not necessarily have to pump air into the ammonia supply passage 49. The air source 71A may be configured without a pump and an air tank for storing compressed air. Incidentally, after the ammonia engine 2 stopped, the purge control processing unit 61B closed the second on-off valve 75, opened the fourth on-off valve 77 and the fifth on-off valve 78, and then opened the third on-off valve 76. However, it is also possible to supply air to the three-way catalyst 8 by opening the sixth on-off valve 79 while keeping the third on-off valve 76 closed. Even in this case, since the pump 84 is installed in the discharge path 80A, it is sufficient to circulate the gas within the closed circuit using the pump 84, and it is not necessarily required to push out the ammonia in the ammonia supply passages 49 and 50 with air from the oxygen supply path 72.

The purge control unit 61B opens the third on-off valve 76 to supply air from the air source 71A to the expulsion path 80A (the first expulsion path 81 in the example of Figure 8). The air supplied to the expulsion path 80A via the sixth on-off valve 79 is supplied to the three-way catalyst 8 via the exhaust passage 4. As a result, the amount of oxygen available for oxidizing ammonia in the three-way catalyst 8 increases. However, in the initial stage of ammonia expulsion after the ammonia engine 2 has stopped running, there is a period (a predetermined period) during which the air supplied from the oxygen supply passage 72 by opening the third on-off valve 76 expels the ammonia remaining inside the ammonia supply passages 49 and 50, but does not reach the three-way catalyst 8. During this predetermined period, the oxygen concentration in the three-way catalyst 8 is insufficient relative to the ammonia concentration. Therefore, by supplying air from the air source 71A to the expulsion path 80A via the sixth on-off valve 79, the deficiency of oxygen concentration relative to the ammonia concentration in the three-way catalyst 8 is mitigated. As a result, ammonia can be oxidized more appropriately in the three-way catalyst 8 during the initial stage of ammonia expulsion. Furthermore, the purge control unit 61B may open the sixth on-off valve 79 for the predetermined period after the ammonia engine 2 has stopped operating.

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

When the temperature control valve 95 is opened, the purge control processing unit 61B may increase the amount of air supplied from the oxygen supply path 72 to the ammonia supply paths 49 and 50 compared to when the gas temperature is below a predetermined temperature threshold (steps S137, S138). The temperature threshold is the temperature threshold of the gas passing through the catalyst used to determine whether the ammonia supply paths 49 and 50 are excessively heated by the gas passing through the catalyst. When the gas temperature is above the predetermined temperature threshold, the amount of air supplied from the oxygen supply path 72 to the ammonia supply paths 49 and 50 is increased, thus cooling the gas passing through the catalyst. This prevents the ammonia supply paths 49 and 50 from being excessively heated, even when the gas temperature is above the predetermined temperature threshold.

As described above, in this embodiment, since the exhaust catalyst is a three-way catalyst 8, the ammonia supplied to the three-way catalyst 8 is oxidized in the three-way catalyst 8, and the temperature of the catalytic gas flowing out of the three-way catalyst 8 rises. By operating the pump 84, a portion of the catalytic gas flowing out of the three-way catalyst 8 is supplied through the temperature control path 91 to a portion of the ammonia supply paths 49 and 50 and the discharge path 80A. As a result, a portion of the ammonia supply paths 49 and 50 and the discharge path 80A are heated, which can suppress condensation caused by the latent heat of vaporization of ammonia remaining in the ammonia supply paths 49 and 50, for example.

Furthermore, in this embodiment, the discharge path 80A is connected downstream of the point where the oxygen supply path 72 is connected in the ammonia supply path 49, and a pump 84 is provided in the discharge path 80A. This allows, for example, the ammonia remaining in the ammonia supply paths 49 and 50 to be supplied to the three-way catalyst 8 via the discharge path 80A by operating the pump 84, even without pressurizing air from the oxygen supply path 72 to the ammonia supply paths 49 and 50.

Furthermore, in this embodiment, the engine system 1B is provided in the temperature control path 91 and includes a temperature sensor 93 that detects the gas temperature of the catalyst passing gas flowing through the temperature control path 91. When the gas temperature is above a predetermined temperature threshold, the engine system 1B increases the amount of air supplied from the oxygen supply path 72 to the ammonia supply paths 49 and 50 compared to when the gas temperature is below the temperature threshold. This prevents excessive heating of a portion of the ammonia supply paths 49 and 50 and the discharge path 80A.
[Variations]

Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above. The present invention can be implemented in various forms, starting with the embodiments described above, 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 described above can be modified into the engine system 1B shown in Figure 10. In Figure 10, the modified engine system 1C differs from engine system 1B mainly in that a pump 94 is provided in the temperature control path 91 instead of the pump 84 in the third discharge path 83. In engine system 1C, the discharge path 80A is returned to the discharge path 80, and the temperature control unit 90 becomes the temperature control unit 90C. Note that in the temperature control unit 90C, the temperature sensor in the temperature control path 91 is omitted.

In engine system 1C, since the pump 94 is located in the temperature control path 91, the gas in the first discharge path 81 and the second discharge path 82 is less likely to be pulled towards the pump 94 compared to the case where the pump 84 is located in the third discharge path 83 as in the example in Figure 8. Therefore, the oxygen supply unit 70B differs from the oxygen supply unit 70A of the third embodiment in that it returns to the air source 71 of the first embodiment, which is capable of pressurizing air. Furthermore, in engine system 1B of the third embodiment, the purge control processing unit 61B could have kept the third on-off valve 76 closed, circulated the gas in a closed circuit using the pump 84, and opened the sixth on-off valve 79 to supply air to the three-way catalyst 8. However, in engine system 1C, the pump 94 is solely used to pressurize the gas passing through the catalyst and return it to the ammonia supply paths 49 and 50. For example, the purge control unit 61B may open the third on-off valve 76 to push out the ammonia from the ammonia supply passages 49 and 50 with air from the oxygen supply passage 72.

Furthermore, in the first embodiment described above, 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 of the specified temperature range H, the operating time of the abatement device 65 can be shortened.

Furthermore, in the first embodiment described above, the temperature of the engine oil or engine coolant may be detected, and the opening degrees of the main throttle valve 6 and the modified throttle valve 44 may be controlled based on the temperature of the engine oil or engine coolant so that the main throttle valve 6 and the modified throttle valve 44 are closed. In this case, even if the negative pressure generated on the first oxygen supply passage 3 side of the ammonia engine 2 fluctuates due to the temperature of the ammonia engine 2, the closed state of the main throttle valve 6 and the modified throttle valve 44 can be adjusted to an appropriate opening degree according to the temperature of the ammonia engine 2.

Furthermore, while the three-way catalyst 8 is primarily used as the exhaust catalyst in the above embodiment, the exhaust catalyst is not limited to any particular form; it is sufficient to adsorb and oxidize ammonia using one or more types of catalysts. For example, the above-mentioned SCR catalyst 9 may be primarily used as the exhaust catalyst, or an oxidation catalyst may be used instead of the three-way catalyst 8 and the SCR catalyst 9.

Furthermore, in the above embodiment, purging and detoxification are performed by an operator, such as a driver, operating a button or other control unit after the ammonia engine 2 has stopped running or before maintenance of the ammonia engine 2. However, the configuration is not limited to this, and for example, purging and detoxification may be automatically started after a predetermined time has elapsed since the ammonia engine 2 stopped running.

Furthermore, in the above embodiment, the temperature of the three-way catalyst 8 is detected by the temperature sensor 58, but the system is not limited to this configuration. The temperature of the three-way catalyst 8 may be estimated from the operating history of the ammonia engine 2 (operating time, rotational speed, load), the temperature of the engine oil and engine coolant, or the NOx concentration downstream of the three-way catalyst 8 and SCR catalyst 9. For example, if the ammonia engine 2 has been operating at a predetermined rotational speed for a predetermined time and the engine coolant temperature is below 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 discharge valve 68 is closed to prevent ammonia from flowing to the three-way catalyst 8. Even if the ammonia engine 2 has been operating at a predetermined rotational speed for a predetermined time, if the engine coolant temperature is above 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 discharge valve 68 is opened to allow ammonia to flow to the three-way catalyst 8.

Furthermore, in the above embodiment, the first on-off valve 67 is opened and the discharge on-off valve 68 is closed when the temperature of the three-way catalyst 8 is within a specified temperature range H in which the three-way catalyst 8 reacts with ammonia to produce nitrous oxide ( _N₂O ), but the system is not limited to this configuration. When performing a purging process, the first on-off valve 67 may be opened and the discharge on-off valve 68 may be closed regardless of the temperature of the three-way catalyst 8. In this case, it is not necessary to use the temperature sensor 58 that detects the temperature of the three-way catalyst 8.

Furthermore, in the above embodiment, when the temperature of the three-way catalyst 8 is within the specified temperature range H, the first on-off valve 67 is opened and the discharge on-off valve 68 is closed. However, the embodiment is not limited to this configuration. For example, when the temperature of the three-way catalyst 8 is within the specified temperature range H, the discharge on-off valve 68 may be open, or the opening degree of the discharge on-off valve 68 may be controlled to be narrower than the opening degree of the first on-off valve 67.

Furthermore, in the above embodiment, when the temperature of the three-way catalyst 8 is not within the specified temperature range H, the discharge valve 68 is opened and the first valve 67 is closed. However, the system is not limited to this configuration. For example, when the temperature of the three-way catalyst 8 is not within the specified temperature range H, the first valve 67 may be open, or the opening degree of the first valve 67 may be controlled to be narrower than the opening degree of the discharge valve 68.

Furthermore, in the above embodiment, the first on-off valve 67 and the discharge on-off valve 68 are electromagnetic ON/OFF valves, but the first on-off valve 67 and the discharge on-off valve 68 are not particularly limited in form, and electromagnetic flow control valves may also be used.

Furthermore, in the above embodiment, the first on-off valve 67 and the discharge on-off valve 68 are solenoid valves and operate in response to control commands from controllers 60, 60A, and 60B, but the system is not limited to such configurations. For example, the first on-off valve 67 and the discharge on-off valve 68 may be manual ON/OFF valves, etc. In this case, the above effects are achieved by the operator manually performing a process similar to the flowchart in Figure 5 as a residual fuel treatment method. Similarly, the second on-off valves 75 to the fifth on-off valves 78 in the second embodiment and the second on-off valves 75 to the sixth on-off valves 79 and the temperature control on-off valve 95 in the third embodiment may also be manual flow control valves.

Furthermore, in the above embodiment, the discharge valve 68 is located downstream of the SCR catalyst 9 in the exhaust flow path 4. However, the configuration is not limited to this, and the discharge valve 68 may be located between the point where the exhaust flow path 4 connects to the abatement flow path 66 and the three-way catalyst 8.

Furthermore, in the above embodiment, the main injector 5 was exemplified as an example of the ammonia quantity adjustment unit, but the ammonia quantity adjustment unit may also be a carburetor.

Furthermore, in the above embodiment, the second oxygen supply passage 30 has a pipe 33 connecting the first oxygen supply passage 3 and the cylinder head 12 of the ammonia engine 2, and a passage 34 provided in the cylinder head 12 and cylinder block 11 to connect this pipe 33 to the crankcase 23. However, it is not limited to this configuration. The second oxygen supply passage 30 may also be a pipe directly connecting the first oxygen supply passage 3 and the crankcase 23.

Furthermore, in the above embodiment, the blow-by gas passage 31 has a pipe 35 connecting the first oxygen supply passage 3 and the cylinder head 12, and a passage 36 provided in the cylinder head 12 and cylinder block 11 to connect this pipe 35 to the crankcase 23. However, it is not limited to this configuration. The blow-by gas passage 31 may be a pipe directly connecting the crankcase 23 and the first oxygen supply passage 3. In this case, the PCV valve 32 would be installed in this pipe.

Furthermore, in the above embodiment, the discharge valve 68 is located downstream of the point where the abatement passage 66 is connected in the exhaust passage 4, but the discharge valve 68 is not required. If it is desired to suppress the discharge of catalyst-passing gas downstream of the discharge valve 68, a cover that blocks the outlet of the exhaust pipe 27 in the exhaust passage 4 may be used, for example.

Furthermore, in the second and third embodiments described above, the discharge paths 80 and 80A are pre-installed in the ammonia engine 2, but the system is not limited to this configuration. The discharge paths 80 and 80A may be attached to the ammonia engine 2 as add-on components when removing the ammonia supply passages 49-51 of the ammonia engine 2. In this case, couplers or the like can be used to connect the discharge paths 80 and 80A.

Furthermore, in the above embodiment, the reforming oxygen supply channel 43 is connected to the first oxygen supply channel 3. However, the reforming oxygen supply channel 43 is not particularly limited in form and may be a channel through which air supplied from a different route than the first oxygen supply channel 3 flows.

Furthermore, in the above embodiment, the reformer 42 has a reforming catalyst 53 that combines the functions of burning ammonia gas and decomposing ammonia gas into hydrogen, but it is not limited to such a configuration. The reformer 42 may have a combustion catalyst for burning ammonia gas and a reforming catalyst for decomposing ammonia gas into hydrogen separately.

Furthermore, 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.

Furthermore, in the above embodiment, a reformed gas containing hydrogen is generated by the reformer 42 and supplied to the ammonia engine 2 together with ammonia. However, 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 catalytic converter (exhaust catalytic converter), 9...SCR catalytic converter (exhaust catalytic converter), 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 return valve), 40...Ammonia tank, 42...Reformer, 43...Oxygen supply passage for reforming, 44...Reforming Throttle valve (reformation 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 control unit, 91…Temperature control path, 94…Pump, 95…Temperature control on-off valve.

Claims (4)

An engine system comprising an engine having a piston capable of reciprocating within a combustion chamber for burning ammonia, a crankshaft connected to the piston, and a crankcase housing the crankshaft,
A first oxygen supply channel is connected to the engine and through which oxygen-containing gas supplied to the combustion chamber flows,
A flow control valve is provided in the first oxygen supply channel and controls the flow rate of the oxygen-containing gas supplied to the combustion chamber,
An exhaust passage is connected to the aforementioned engine and through which exhaust gas generated from the combustion chamber flows,
An exhaust catalyst is installed in the aforementioned exhaust passage and adsorbs and oxidizes ammonia,
A second oxygen supply channel connects the first oxygen supply channel upstream of the flow control valve to the crankcase and supplies the oxygen-containing gas into the crankcase,
A blow-by gas passage connects the crankcase to a point downstream of the flow control valve in the first oxygen supply passage, and recirculates the ammonia blow-by gas remaining in the crankcase to the first oxygen supply passage.
A blow-by gas recirculation valve is provided in the blow-by gas passage and adjusts the flow rate of the ammonia blow-by gas that recirculates to the first oxygen supply passage.
A starter that rotates the aforementioned crankshaft,
A detoxification device for detoxifying ammonia flowing through the aforementioned exhaust passage,
A decontamination passage connecting the portion of the exhaust passage between the engine and the exhaust catalyst and the decontamination device,
A shut-off valve is provided in the aforementioned abatement flow path and, when opened, allows ammonia to be supplied to the abatement device.
An engine system comprising: a control unit that controls the opening degree of the flow control valve so that the blow-by gas flows back into the first oxygen supply passage when the crankshaft is rotating by the starter, and controls the opening degree of the on-off valve so that the on-off valve is open. A reformer that produces a hydrogen-containing reformed gas by reforming ammonia,
A reforming oxygen supply channel for supplying the oxygen-containing gas to the reformer,
A reforming flow control valve is provided in the reforming oxygen supply channel and controls the flow rate of the oxygen-containing gas supplied to the reformer.
The system further comprises a reformed gas flow path for supplying the reformed gas generated by the reformer to the combustion chamber,
The engine system according to claim 1, wherein the control unit controls the opening of the reforming flow control valve so that the blow-by gas is recirculated into the first oxygen supply passage when the crankshaft is rotating by the starter. An engine supplied with ammonia from an ammonia quantity adjustment unit,
Ammonia tanks for storing ammonia,
An ammonia supply channel connecting the ammonia tank and the ammonia quantity adjustment unit,
An exhaust passage is connected to the engine and into which exhaust gas from the engine flows,
An exhaust catalyst is installed in the aforementioned exhaust passage and adsorbs and oxidizes ammonia,
A detoxification device for detoxifying ammonia flowing through the aforementioned exhaust passage,
A decontamination passage connecting the portion of the exhaust passage between the engine and the exhaust catalyst and the decontamination device,
A first on/off valve is provided in the aforementioned abatement flow path and, when opened, allows ammonia to be supplied to the abatement device.
A second on-off valve is provided in the ammonia supply channel and, when closed, blocks the supply of ammonia from the ammonia tank to the ammonia quantity adjustment unit.
An oxygen supply unit having an oxygen supply path connected to a location downstream of the second on-off valve in the ammonia supply path and supplying oxygen-containing gas to the ammonia supply 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,
An expulsion path is connected to a location downstream of the location where the oxygen supply path is connected in the ammonia supply channel, and is provided to supply the ammonia inside to the exhaust catalyst,
An engine system comprising a fourth on-off valve disposed in the aforementioned discharge path, which opens after the second on-off valve has closed. The exhaust catalyst is a three-way catalyst,
A temperature control unit having a temperature control 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 control on/off valve disposed in the temperature control path,
The engine system according to claim 3, further comprising a pump provided in a closed circuit formed by a portion of the ammonia supply path, the discharge path, a portion of the exhaust path, the three-way catalyst, and the temperature control path.