Engine system

Abstract

In the present invention, an engine system comprises: a first flow rate control valve for controlling the flow rate of air supplied to an engine; a first fuel injection valve for injecting fuel toward the engine; a reformer for reforming the fuel to generate reformed gas containing hydrogen; a second flow rate control valve for controlling the flow rate of air supplied to the reformer; a second fuel injection valve for injecting fuel toward the reformer; and a control unit for controlling the first flow rate control valve, the first fuel injection valve, the second flow rate control valve, and the second fuel injection valve on the basis of the value of a command directed at the engine. When the command value changes while the engine is running, the control unit sets a target opening degree of the first flow control valve that corresponds to the command value as a first target opening degree, sets a target opening degree of the second flow control valve that corresponds to the command value as a second target opening degree, and controls the first flow control valve and the second flow control valve such that the time the opening degree of the first flow control valve reaches the first target opening degree will be later than the time the opening degree of the second flow control valve reaches the second target opening degree.

Description

Engine System

[0001] The present disclosure relates to engine systems.

[0002] A known example of a conventional engine system is the technology described in Patent Document 1. The engine system described in Patent Document 1 includes a main reformer attached to the exhaust pipe of an internal combustion engine and reforming fuel using a reforming catalyst, a reformed gas supply pipe that supplies reformed gas produced by the main reformer, a gas injection valve that injects the reformed gas into the intake pipe, and multiple fuel injection valves with sub-reformers provided for each cylinder in a branch section of the intake pipe. If the supply of reformed gas from the main reformer and the gas injection valves is insufficient, the shortage is made up for by the fuel injection valves with sub-reformers. This makes it possible to supply a sufficient amount of reformed gas to the internal combustion engine even during transient states such as sudden acceleration.

[0003] Japanese Patent Application Laid-Open No. 2001-12321

[0004] However, in the above-mentioned conventional technology, in addition to the main reformer and gas injector, a sub-reformer-attached fuel injector is required for each cylinder of the engine (internal combustion engine). Furthermore, the addition of the sub-reformer-attached fuel injector also requires a temperature sensor to detect the temperature of the reforming catalyst in the sub-reformer and a pressure sensor to detect the pressure of the reformed gas in the sub-reformer. This results in a complex engine system configuration. Therefore, it is desirable to simplify the engine system configuration while ensuring an appropriate air-fuel ratio during engine transients.

[0005] An object of the present disclosure is to provide an engine system that can ensure an appropriate air-fuel ratio during engine transients while simplifying the system configuration.

[0006] (1) An engine system according to one aspect of the present disclosure includes an engine in which fuel is combusted with hydrogen, an intake passage through which air supplied to the engine flows, a first flow control valve disposed in the intake passage and configured to control the flow rate of the air supplied to the engine, a first fuel injection valve configured to inject fuel toward the engine, a reformer having a catalyst that decomposes the fuel into hydrogen and that reforms the fuel to generate a reformed gas containing hydrogen, an upstream reforming passage through which the air supplied to the reformer flows, a downstream reforming passage through which gas generated by the reformer flows toward the engine, a second flow control valve disposed in the upstream reforming passage or the downstream reforming passage and configured to control the flow rate of the air supplied to the reformer, and a second fuel injection valve configured to inject fuel toward the reformer. the control unit sets a target opening of the first flow control valve according to the command value as a first target opening, sets a target opening of the second flow control valve according to the command value as a second target opening, and controls the first flow control valve and the second flow control valve so that the timing at which the opening of the first flow control valve reaches the first target opening is later than the timing at which the opening of the second flow control valve reaches the second target opening.

[0007] In such an engine system, fuel and air are supplied to the reformer, and reformed gas containing hydrogen is generated by the reformer's catalyst, and the reformed gas is supplied to the engine. When fuel and air are supplied to the engine, the fuel is mixed with the hydrogen and burned in the engine. At this time, air flows through the intake passage and is supplied to the engine, and fuel is injected toward the engine from the first fuel injection valve. Meanwhile, air flows through the upstream reforming passage and is supplied to the reformer, and fuel is injected toward the reformer from the second fuel injection valve. Reformed gas is generated in the reformer, and the reformed gas flows through the downstream reforming passage and is supplied to the engine. Therefore, while the air flowing through the intake passage is quickly supplied to the engine, the reformed gas is supplied to the engine with a delay relative to the air. Therefore, when a command value for the engine changes while the engine is running, the flow rate of the reformed gas supplied to the engine changes with a delay compared to the flow rate of the air supplied to the engine. In this case, the appropriate air-fuel ratio is not maintained in the engine.

[0008] Therefore, when a command value for the engine changes during engine operation, a target opening of the first flow control valve corresponding to the command value is set as a first target opening, and a target opening of the second flow control valve corresponding to the command value is set as a second target opening. The first flow control valve and the second flow control valve are then controlled so that the timing at which the opening of the first flow control valve reaches the first target opening is later than the timing at which the opening of the second flow control valve reaches the second target opening. Therefore, the timing at which the opening of the first flow control valve reaches the first target opening is later than the timing at which the opening of the second flow control valve reaches the second target opening. This ensures that reformed gas and air are appropriately supplied to the engine even during transient periods when the engine operating conditions change, ensuring an appropriate air-fuel ratio. Furthermore, since a sub-reformer does not need to be provided for each cylinder of the engine, a valve for injecting fuel toward the sub-reformer is also not required. This simplifies the configuration of the engine system.

[0009] (2) In (1) above, when the command value output from the command value output unit changes in an increasing direction while the engine is running, the control unit may set the first target opening and the second target opening so that they increase in accordance with the command value.

[0010] In this configuration, when the command value for the engine changes in an increasing direction while the engine is running, the first target opening and the second target opening are set to increase in accordance with the command value. Therefore, the timing at which the opening of the first flow control valve increases to the first target opening is delayed compared to the timing at which the opening of the second flow control valve increases to the second target opening. Therefore, an appropriate air-fuel ratio is ensured, and misfires caused by the flow rate of hydrogen contained in the reformed gas being low relative to the flow rate of air are suppressed.

[0011] (3) In the above (1) or (2), when the command value output from the command value output unit changes in a decreasing direction while the engine is running, the control unit may set the first target opening and the second target opening so that they decrease in accordance with the command value.

[0012] In this configuration, when a command value for the engine changes in a decreasing direction while the engine is running, the first target opening and the second target opening are set so as to decrease in accordance with the command value. Therefore, the timing at which the opening of the first flow control valve decreases to the first target opening is delayed compared to the timing at which the opening of the second flow control valve decreases to the second target opening. Therefore, an appropriate air-fuel ratio is ensured, thereby suppressing excessive combustion and unstable engine control caused by the flow rate of hydrogen contained in the reformed gas being higher than the flow rate of air.

[0013] (4) In any of the above (1) to (3), the control unit may control the first flow control valve and the second flow control valve so that the timing at which the opening of the first flow control valve starts to change is later than the timing at which the opening of the second flow control valve starts to change.

[0014] In this configuration, the timing at which the opening of the first flow control valve starts to change is later than the timing at which the opening of the second flow control valve starts to change. Therefore, the timing at which the opening of the first flow control valve reaches the first target opening is reliably later than the timing at which the opening of the second flow control valve reaches the second target opening. Furthermore, the rapid change in the opening of the first flow control valve makes it easier to control the flow rate of air supplied to the engine.

[0015] (5) In any of (1) to (3) above, the control unit may control the first flow control valve and the second flow control valve so that the opening and closing speed of the first flow control valve is slower than the opening and closing speed of the second flow control valve.

[0016] In this configuration, the opening and closing speed of the first flow control valve is slower than the opening and closing speed of the second flow control valve. Therefore, the timing at which the opening of the first flow control valve reaches the first target opening is surely slower than the timing at which the opening of the second flow control valve reaches the second target opening. Furthermore, since the opening of the first flow control valve changes gradually, the first flow control valve opens and closes smoothly.

[0017] (6) In any of the above (1) to (5), the second flow control valve may be disposed in the downstream reforming flow path and control the flow rate of the reformed gas supplied to the engine together with the flow rate of the air supplied to the reformer.

[0018] In this configuration, air flowing through the upstream reforming passage is supplied to the reformer to generate reformed gas, and the reformed gas flows through the downstream reforming passage and is supplied to the engine. The second flow control valve is disposed in the downstream reforming passage. Therefore, compared to when the second flow control valve is disposed in the upstream reforming passage, the amount of reformed gas supplied to the engine can be more quickly increased by increasing the aperture of the second flow control valve. The amount of reformed gas supplied to the engine can be more quickly decreased by decreasing the aperture of the second flow control valve.

[0019] According to the present disclosure, it is possible to ensure an appropriate air-fuel ratio during engine transients while simplifying the system configuration.

[0020] FIG. 1 is a schematic diagram showing an engine system according to an embodiment of the present disclosure. FIG. 2 is a flowchart showing the procedure of a control process executed by the control unit shown in FIG. 1. FIG. 3 is a flowchart showing details of the procedure of the control process when the accelerator opening is increased in step S104 shown in FIG. 2. FIG. 4 is a flowchart showing details of the procedure of the control process when the accelerator opening is decreased in step S105 shown in FIG. 2. FIG. 5(a) is a timing diagram showing the switching of an accelerator from OFF to ON. FIG. 5(b) is a timing diagram showing the operation of a main injector when the accelerator is switched from OFF to ON. FIG. 5(c) is a timing diagram showing the operation of a reforming injector when the accelerator is switched from OFF to ON. FIG. 5(d) is a timing diagram showing the operation of a main throttle valve when the accelerator is switched from OFF to ON. FIG. 5(e) is a timing diagram showing the operation of a reforming throttle valve when the accelerator is switched from OFF to ON. FIG. 6(a) is a timing diagram showing the switching of the accelerator from ON to OFF. FIG. 6(b) is a timing diagram showing the operation of the main injector when the accelerator is switched from ON to OFF. FIG. 6(c) is a timing diagram showing the operation of the reforming injector when the accelerator is switched from ON to OFF. FIG. 6(d) is a timing diagram showing the operation of the main throttle valve when the accelerator is switched from ON to OFF. FIG. 6(e) is a timing diagram showing the operation of the reforming throttle valve when the accelerator is switched from ON to OFF. FIG. 7(a) is a timing diagram showing the switching of the accelerator from OFF to ON. FIG. 7(b) is a timing diagram showing a modified operation of the main injector when the accelerator is switched from OFF to ON. FIG. 7(c) is a timing diagram showing a modified operation of the reforming injector when the accelerator is switched from OFF to ON. Figure 7(d) is a timing diagram showing a modified example of the operation of the main throttle valve when the accelerator is switched from OFF to ON, and Figure 7(e) is a timing diagram showing a modified example of the operation of the modified throttle valve when the accelerator is switched from OFF to ON.FIG. 8 is a schematic configuration diagram showing an engine system according to another embodiment of the present disclosure.

[0021] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are designated by the same reference numerals, and redundant description will be omitted.

[0022] Fig. 1 is a schematic configuration diagram showing an engine system according to an embodiment of the present disclosure. In Fig. 1, the engine system 1 of this embodiment is mounted on a vehicle (not shown). The engine system 1 includes an ammonia engine 2, an intake passage 3, an exhaust passage 4, a main throttle valve 5, and a main injector 6.

[0023] The ammonia engine 2 is a gas turbine engine. ３ The ammonia engine 2 uses hydrogen (H ) as a combustion aid to facilitate combustion of the flame-retardant ammonia gas. ２ ) is mixed with the ammonia gas. That is, in each cylinder of the ammonia engine 2, the ammonia gas is burned together with hydrogen to generate combustion gas. The ammonia engine 2 is, for example, a four-cylinder engine.

[0024] The intake flow path 3 is connected to each cylinder of the ammonia engine 2 via an intake manifold 7. The intake flow path 3 is a flow path through which air supplied to the ammonia engine 2 flows. An air cleaner 8 is disposed in the intake flow path 3 to remove foreign matter such as dust and dirt contained in the air.

[0025] The exhaust flow path 4 is connected to each cylinder of the ammonia engine 2 via an exhaust manifold 9. The exhaust flow path 4 is a flow path through which exhaust gas generated by the ammonia engine 2 flows. ３ and a three-way catalyst 10 that purifies NOx and NH that has passed through the three-way catalyst 10. ３ and an SCR catalyst 11 that adsorbs the

[0026] The main throttle valve 5 is disposed in the intake passage 3. The main throttle valve 5 is an electromagnetic first flow control valve that controls the flow rate of air supplied to each cylinder of the ammonia engine 2.

[0027] The main injector 6 is an electromagnetic first fuel injection valve that intermittently injects ammonia gas toward each cylinder of the ammonia engine 2. The main injector 6 injects ammonia gas into, for example, an intake manifold 7. The number of main injectors 6 is the same as the number of cylinders of the ammonia engine 2 (four in this example). By changing the opening of the main injector 6, it is possible to adjust the injection amount of ammonia gas.

[0028] The engine system 1 also includes a reformer 12, an upstream reforming flow path 13, a reforming throttle valve 14, an ammonia cylinder 15, vaporizers 16 and 17, ammonia flow paths 18 and 19, a reforming injector 20, a downstream reforming flow path 21, a cooler 22, and a stop valve 23.

[0029] The reformer 12 generates a reformed gas containing hydrogen by reforming ammonia gas using heat generated by burning the ammonia gas. The reformer 12 has a cylindrical housing 24 and a combustion catalyst 25, a reforming catalyst 26, and an electric heater 27 housed within the housing 24. The housing 24 is made of stainless steel or the like that is resistant to corrosion by ammonia gas.

[0030] The combustion catalyst 25 and the reforming catalyst 26 have, for example, a honeycomb structure. The combustion catalyst 25 is a catalyst that burns ammonia gas. The reforming catalyst 26 is arranged downstream of the combustion catalyst 25 within the housing 24. The reforming catalyst 26 is a catalyst that decomposes ammonia gas into hydrogen. The combustion catalyst 25 and the reforming catalyst 26 are, for example, ATR (Autothermal Reformer) type catalysts.

[0031] The electric heater 27 is disposed upstream of the combustion catalyst 25 within the housing 24. The electric heater 27 heats the ammonia gas and air introduced into the housing 24, thereby heating (warming up) the combustion catalyst 25 through the ammonia gas and air.

[0032] The upstream reforming flow path 13 is connected to an inlet of a housing 24 of the reformer 12. The upstream reforming flow path 13 is a flow path through which air supplied to the reformer 12 flows. An air cleaner 28 is disposed in the upstream reforming flow path 13 to remove foreign matter such as dust and dirt contained in the air. The upstream reforming flow path 13 is branched off and connected to, for example, the intake flow path 3.

[0033] The reforming throttle valve 14 is disposed in the upstream reforming flow path 13. The reforming throttle valve 14 is an electromagnetic second flow control valve that controls the flow rate of air supplied to the reformer 12.

[0034] The ammonia cylinder 15 is a container that stores ammonia in a liquid state. That is, the ammonia cylinder 15 stores liquid ammonia.

[0035] The vaporizers 16 and 17 are connected to the ammonia cylinder 15 via an ammonia flow path 29. The ammonia flow path 29 is a flow path through which the liquid ammonia stored in the ammonia cylinder 15 flows. The vaporizers 16 and 17 vaporize the liquid ammonia to generate ammonia gas.

[0036] The ammonia flow path 18 connects the vaporizer 16 and each main injector 6. The ammonia flow path 18 is a flow path through which the ammonia gas generated by the vaporizer 16 flows toward each main injector 6. The ammonia flow path 19 connects the vaporizer 17 and the reforming injector 20. The ammonia flow path 19 is a flow path through which the ammonia gas generated by the vaporizer 17 flows toward the reforming injector 20.

[0037] The reforming injector 20 is an electromagnetic second fuel injection valve that intermittently injects ammonia gas toward the reformer 12. The reforming injector 20 injects ammonia gas into a portion of the upstream reforming flow path 13 between the reforming throttle valve 14 and the reformer 12. By changing the opening of the reforming injector 20, it is possible to adjust the amount of ammonia gas injected.

[0038] The downstream reforming flow path 21 connects the reformer 12 and the intake flow path 3. One end of the downstream reforming flow path 21 is connected to an outlet portion of a housing 24 of the reformer 12. The other end of the downstream reforming flow path 21 is connected to a portion of the intake flow path 3 between the main throttle valve 5 and the ammonia engine 2. The downstream reforming flow path 21 is a flow path through which the reformed gas generated by the reformer 12 flows toward the ammonia engine 2.

[0039] The cooler 22 is disposed in the downstream reforming passage 21. The cooler 22 cools the reformed gas flowing through the downstream reforming passage 21.

[0040] The stop valve 23 is disposed in the downstream reforming passage 21 downstream of the cooler 22. The stop valve 23 is an on-off valve that opens and closes the downstream reforming passage 21.

[0041] Here, the intake passage 3, the main throttle valve 5, and the main injector 6 constitute a main line 38. The upstream reforming passage 13, the reformer 12, the downstream reforming passage 21, the reforming throttle valve 14, the reforming injector 20, the cooler 22, and the stop valve 23 constitute a reforming line 39.

[0042] The engine system 1 also includes an accelerator sensor 30 and a control unit 31 .

[0043] The accelerator sensor 30 is a sensor that detects the opening degree (depression amount) of the accelerator of the vehicle and outputs the detected value of the accelerator opening degree as an electric signal. The electric signal output from the accelerator sensor 30 corresponds to a command value for the ammonia engine 2. Therefore, the accelerator sensor 30 constitutes a command value output unit that outputs a command value for the ammonia engine 2 after the ammonia engine 2 is started. A change in the accelerator opening degree while the ammonia engine 2 is operating corresponds to a transient state in which the operating conditions of the ammonia engine 2 change.

[0044] The control unit 31 is composed of a CPU, RAM, ROM, an input / output interface, etc. The control unit 31 constitutes a control section that controls the main throttle valve 5, the main injector 6, the reforming throttle valve 14, and the reforming injector 20 based on the detection value (command value) of the accelerator sensor 30.

[0045] When the detection value of the accelerator sensor 30 changes while the ammonia engine 2 is operating, the control unit 31 sets the target opening of the main throttle valve 5 corresponding to the detection value of the accelerator sensor 30 as a first target opening. When the detection value of the accelerator sensor 30 changes while the ammonia engine 2 is operating, the control unit 31 sets the target opening of the reforming throttle valve 14 corresponding to the detection value of the accelerator sensor 30 as a second target opening. The control unit 31 controls the main throttle valve 5 and the reforming throttle valve 14 so that the timing at which the opening of the main throttle valve 5 reaches the first target opening is later than the timing at which the opening of the reforming throttle valve 14 reaches the second target opening.

[0046] At this time, the control unit 31 controls the main throttle valve 5 and the reforming throttle valve 14 so that the timing at which the opening of the main throttle valve 5 starts to change is later than the timing at which the opening of the reforming throttle valve 14 starts to change.

[0047] The control unit 31 has an opening change determination section 32, an opening increase control section 33, and an opening decrease control section .

[0048] The opening change determination unit 32 determines whether the opening of the accelerator has changed based on the detection value of the accelerator sensor 30 .

[0049] When the opening change determination unit 32 determines that the accelerator opening has changed in an increasing direction, the opening increase control unit 33 sets the first target opening and the second target opening so as to increase in accordance with the detection value of the accelerator sensor 30. The opening increase control unit 33 controls the main throttle valve 5 and the reforming throttle valve 14 so that the timing at which the opening of the main throttle valve 5 reaches the first target opening is later than the timing at which the opening of the reforming throttle valve 14 reaches the second target opening.

[0050] When the opening change determination unit 32 determines that the accelerator opening has changed in a decreasing direction, the opening decrease control unit 34 sets the first target opening and the second target opening so as to decrease in accordance with the detection value of the accelerator sensor 30. The opening decrease control unit 34 controls the main throttle valve 5 and the reforming throttle valve 14 so that the timing at which the opening of the main throttle valve 5 reaches the first target opening is later than the timing at which the opening of the reforming throttle valve 14 reaches the second target opening.

[0051] 2 is a flowchart showing the procedure of the control process executed by the control unit 31. This process is executed when the ammonia engine 2 is started. When the ammonia engine 2 is started, the stop valve 23 opens.

[0052] 2, the control unit 31 first acquires the detection value of the accelerator sensor 30 (step S101). Then, the control unit 31 determines whether the accelerator opening has changed based on the detection value of the accelerator sensor 30 (step S102). The control unit 31 may determine that the accelerator opening has changed when the accelerator opening has changed by a predetermined amount or more.

[0053] When the control unit 31 determines that the accelerator opening has changed, it determines whether the accelerator opening has increased (step S103). When the control unit 31 determines that the accelerator opening has increased, it executes a control process for when the accelerator opening has increased (step S104). When the control unit 31 determines that the accelerator opening has decreased, it executes a control process for when the accelerator opening has decreased (step S105).

[0054] After executing step S104 or step S105, the control unit 31 executes step S101 again. The control unit 31 also executes step S101 again when it determines in step S102 that the accelerator opening has not changed.

[0055] Here, the opening change determination unit 32 executes the above steps S101 to S103. The opening increase control unit 33 executes the above step S104. The opening decrease control unit 34 executes the above step S105.

[0056] FIG. 3 is a flowchart showing the details of the control process performed in step S104 when the accelerator opening is increased.

[0057] 3, the control unit 31 first calculates the increase in the amount of ammonia gas and air (step S111) based on the detection value of the accelerator sensor 30. The increase in the amount of ammonia gas and air is calculated, for example, from map data that indicates the relationship between the accelerator opening and the flow rate of ammonia gas and air.

[0058] Next, the control unit 31 sets the target openings of each injector (main injector 6 and reforming injector 20) and each throttle valve (main throttle valve 5 and reforming throttle valve 14) based on the increased amounts of ammonia gas and air (step S112). The target openings of the main injector 6, main throttle valve 5, reforming injector 20, and reforming throttle valve 14 are obtained, for example, from map data that shows the relationship between the increased amounts of ammonia gas and air and each target opening.

[0059] Next, the control unit 31 controls the reforming injector 20 so that the opening of the reforming injector 20 increases to the target opening (step S113). The control unit 31 controls the reforming throttle valve 14 so that the opening of the reforming throttle valve 14 increases to the target opening (second target opening) (step S114). The order in which steps S113 and S114 are performed is not particularly limited, and step S114 may be performed before step S113, or steps S113 and S114 may be performed simultaneously.

[0060] Next, the control unit 31 determines whether a specified time T has elapsed since the reforming throttle valve 14 was controlled in step S114 (step S115). The specified time T is a time that is determined in advance in consideration of a supply delay (described later) of the reformed gas relative to the air supplied to the ammonia engine 2 (see FIGS. 5(a) to 5(e)).

[0061] When the control unit 31 determines that the specified time T has elapsed, it controls the main injector 6 so that the opening of the main injector 6 increases to the target opening (step S116). The control unit 31 controls the main throttle valve 5 so that the opening of the main throttle valve 5 increases to the target opening (first target opening) (step S117). The order in which steps S116 and S117 are executed is not particularly limited, and step S117 may be executed before step S116, or steps S116 and S117 may be executed simultaneously.

[0062] FIG. 4 is a flowchart showing the details of the control process performed when the accelerator opening is decreased in step S105.

[0063] 4, the control unit 31 first calculates the amount of ammonia gas and air that has decreased (step S121) based on the detection value of the accelerator sensor 30. The amount of ammonia gas and air that has decreased is calculated, for example, from map data that indicates the relationship between the accelerator opening and the flow rate of ammonia gas and air, similar to step S111 described above.

[0064] Next, the control unit 31 sets the target openings of each injector (main injector 6 and reforming injector 20) and each throttle valve (main throttle valve 5 and reforming throttle valve 14) based on the reduced amounts of ammonia gas and air (step S122). The target openings of the main injector 6, main throttle valve 5, reforming injector 20 and reforming throttle valve 14 are obtained, for example, from map data that shows the relationship between the reduced amounts of ammonia gas and air and each target opening.

[0065] Next, the control unit 31 controls the reforming injector 20 so that the opening of the reforming injector 20 decreases to the target opening (step S123). The control unit 31 controls the reforming throttle valve 14 so that the opening of the reforming throttle valve 14 decreases to the target opening (second target opening) (step S124). The order in which steps S123 and S124 are performed is not particularly limited, and step S124 may be performed before step S123, or steps S123 and S124 may be performed simultaneously.

[0066] Next, the control unit 31 determines whether a specified time T has elapsed since the reforming throttle valve 14 was controlled in step S124 (step S125). The specified time T is a time that is determined in advance in consideration of a supply delay (described later) of the reformed gas relative to the air supplied to the ammonia engine 2 (see FIGS. 6(a) to 6(e)). The specified time T is the same as the specified time T used in step S115 above.

[0067] When the control unit 31 determines that the specified time T has elapsed, it controls the main injector 6 so that the opening of the main injector 6 decreases to the target opening (step S126). The control unit 31 controls the main throttle valve 5 so that the opening of the main throttle valve 5 decreases to the target opening (first target opening) (step S127). The order in which steps S126 and S127 are executed is not particularly limited, and step S127 may be executed before step S126, or steps S126 and S127 may be executed simultaneously.

[0068] In the engine system 1 as described above, the vehicle's ignition switch (not shown) is turned ON to start the ammonia engine 2. Then, the reforming injector 20, the reforming throttle valve 14, the main injector 6, and the main throttle valve 5 are opened. Then, ammonia gas and air are supplied to the reformer 12 and the ammonia engine 2.

[0069] When ammonia gas and air are supplied to the reformer 12, the ammonia gas and air are heated by the electric heater 27. Then, the combustion catalyst 25 is heated by the heat of the ammonia gas and air, and the temperature of the combustion catalyst 25 rises. When the temperature of the combustion catalyst 25 reaches an activation temperature (combustible temperature), the ammonia gas is burned by the combustion catalyst 25. Specifically, ammonia chemically reacts with oxygen in the air (exothermic reaction) as shown in the following formula: NH ３ +3 / 4O ２ →1 / 2N ２ +3 / 2H ２ O+Q1 (heat generation) ... (A)

[0070] When ammonia gas is burned, the heat of combustion of the ammonia gas increases the temperature of the reforming catalyst 26. When the temperature of the reforming catalyst 26 reaches a reaction temperature (reformable temperature), the ammonia gas is reformed by the reforming catalyst 26. Specifically, as shown in the following formula, a decomposition reaction of ammonia occurs (endothermic reaction), and a reformed gas containing hydrogen is produced. NH ３ →3 / 2H ２ +1 / 2N ２ -Q2 (endothermic)...(B)

[0071] The reformed gas flows through the downstream reforming flow path 21. At this time, the reformed gas is cooled by the cooler 22 and flows through the intake flow path 3 to be supplied to the ammonia engine 2. Then, in the ammonia engine 2, the state shifts to a steady state in which the ammonia gas is combusted together with the hydrogen in the reformed gas.

[0072] 5 is a timing diagram showing the operation of the main injector 6, the reforming injector 20, the main throttle valve 5, and the reforming throttle valve 14 when the accelerator is switched from OFF to ON, as an example of an increase in accelerator opening. "Accelerator OFF" means a state in which the accelerator is not being operated, such as when the engine is idling. "Accelerator ON" means a state in which the accelerator is being operated, such as when the engine is running steadily.

[0073] 5(a), when the accelerator is switched from OFF to ON in a steady state, the target openings of the main throttle valve 5, main injector 6, reforming throttle valve 14 and reforming injector 20 are set so as to increase the flow rates of ammonia gas and air supplied to the ammonia engine 2 and reformer 12. When the accelerator is OFF, the main throttle valve 5, main injector 6, reforming throttle valve 14 and reforming injector 20 are slightly open.

[0074] Then, as shown in Figure 5(c), the opening of the reforming injector 20 increases rapidly to the target opening, and as shown in Figure 5(e), the opening of the reforming throttle valve 14 increases rapidly to the target opening (second target opening).

[0075] After that, when a specified time T has elapsed, the opening of the main injector 6 suddenly increases to the target opening, as shown in Figure 5(b), and the opening of the main throttle valve 5 suddenly increases to the target opening (first target opening), as shown in Figure 5(d). In other words, the openings of the main injector 6 and main throttle valve 5 increase at a later timing than the openings of the reforming injector 20 and reforming throttle valve 14.

[0076] FIG. 6 is a timing diagram showing the operations of the main injector 6, the reforming injector 20, the main throttle valve 5 and the reforming throttle valve 14 when the accelerator pedal is switched from ON to OFF, as an example of when the accelerator pedal opening is decreased.

[0077] In a steady state, as shown in FIG. 6( a), when the accelerator is switched from ON to OFF, the target openings of the main throttle valve 5, the main injector 6, the reforming throttle valve 14 and the reforming injector 20 are set so that the flow rates of ammonia gas and air supplied to the ammonia engine 2 and the reformer 12 decrease.

[0078] Then, as shown in Figure 6(c), the opening of the reforming injector 20 is rapidly reduced to the target opening, and as shown in Figure 6(e), the opening of the reforming throttle valve 14 is rapidly reduced to the target opening (second target opening).

[0079] After that, when a specified time T has elapsed, the opening of the main injector 6 is rapidly reduced to the target opening as shown in Figure 6(b), and the opening of the main throttle valve 5 is rapidly reduced to the target opening (first target opening) as shown in Figure 6(d). In other words, the openings of the main injector 6 and main throttle valve 5 are reduced at a later timing than the openings of the reforming injector 20 and reforming throttle valve 14.

[0080] Incidentally, when the ammonia engine 2 is in transient operation, such as when the accelerator is switched from OFF to ON or from ON to OFF, if the openings of the main throttle valve 5 and the reforming throttle valve 14 are not appropriately adjusted in the main line 38 and the reforming line 39, gas may be unintentionally drawn into the ammonia engine 2. In this case, an appropriate A / F (air-fuel ratio) cannot be ensured in the ammonia engine 2, making it difficult to obtain a good combustion state.

[0081] Specifically, the main line 38 and the reforming line 39 have different pressure losses. The main line 38 responds quickly to changes in the opening of the main throttle valve 5. However, the reforming line 39 is equipped with the combustion catalyst 25, the reforming catalyst 26, and the cooler 22, which have large pressure losses. This causes a delay in the flow of the reformed gas. In addition, ammonia gas is supplied to the reforming line 39 upstream of the reformer 12, and the ammonia gas is reformed by the reformer 12 to produce the reformed gas. The reformed gas flows through the downstream reforming flow path 21 and merges with the intake flow path 3.

[0082] Therefore, when the accelerator is switched from OFF to ON, if the openings of the main throttle valve 5 and the reforming throttle valve 14 increase at the same time, the amount of air increases quickly in the main line 38, but the increase in the amount of reformed gas in the reforming line 39 is delayed compared to the main line 38. As a result, the ammonia engine 2 enters a state where the flow rate of air is high and the flow rate of hydrogen contained in the reformed gas is low. As a result, misfire may occur. In this case, unburned ammonia will flow out of the ammonia engine 2.

[0083] On the other hand, when the accelerator is switched from ON to OFF, if the openings of the main throttle valve 5 and the reforming throttle valve 14 decrease at the same timing, the amount of air in the main line 38 decreases quickly, but the amount of reformed gas in the reforming line 39 decreases slower than in the main line 38. For this reason, the supply of reformed gas to the ammonia engine 2 continues for a while. Therefore, the ammonia engine 2 enters a state where the flow rate of air is low and the flow rate of hydrogen contained in the reformed gas is high. As a result, the fuel suddenly burns and combustion becomes active, which can make the control of the ammonia engine 2 unstable.

[0084] Therefore, for example, when the accelerator is switched from OFF to ON, it is conceivable to equalize the A / F and prevent the lean fuel ratio from becoming larger by increasing the opening of the main injector 6 to increase the amount of ammonia gas injected from the main injector 6. However, even in this case, the amount of hydrogen, which is the auxiliary fuel for promoting the combustion of ammonia gas, is not increased, and the combustion of ammonia gas ends up being slowed down.

[0085] To address this issue, in this embodiment, when the detection value of the accelerator sensor 30 (a command value for the ammonia engine 2) changes while the ammonia engine 2 is operating, the target opening of the main throttle valve 5 corresponding to the detection value of the accelerator sensor 30 is set as a first target opening, and the target opening of the reforming throttle valve 14 corresponding to the detection value of the accelerator sensor 30 is set as a second target opening. The main throttle valve 5 and the reforming throttle valve 14 are then controlled so that the timing at which the opening of the main throttle valve 5 reaches the first target opening is later than the timing at which the opening of the reforming throttle valve 14 reaches the second target opening. Therefore, the timing at which the opening of the main throttle valve 5 reaches the first target opening is later than the timing at which the opening of the reforming throttle valve 14 reaches the second target opening. As a result, even during transient periods when the operating conditions of the ammonia engine 2 change, reformed gas and air are appropriately supplied to the ammonia engine 2, ensuring an appropriate A / F ratio. As a result, a good combustion state is obtained. Furthermore, since there is no need to provide a sub-reformer for each cylinder of the ammonia engine 2, there is no need for a valve or the like for injecting ammonia gas toward the sub-reformer, and therefore the configuration of the engine system 1 can be simplified.

[0086] In this embodiment, when the detection value of the accelerator sensor 30 changes in an increasing direction while the ammonia engine 2 is operating, the first target opening and the second target opening are set so as to increase in accordance with the detection value of the accelerator sensor 30. The timing at which the opening of the main throttle valve 5 increases to the first target opening is later than the timing at which the opening of the reforming throttle valve 14 increases to the second target opening. Therefore, an appropriate A / F is ensured, and misfires caused by the flow rate of hydrogen contained in the reformed gas being low compared to the flow rate of air are suppressed.

[0087] In this embodiment, when the detection value of the accelerator sensor 30 changes in a decreasing direction while the ammonia engine 2 is operating, the first target opening and the second target opening are set so as to decrease in accordance with the detection value of the accelerator sensor 30. The timing at which the opening of the main throttle valve 5 decreases to the first target opening is later than the timing at which the opening of the reforming throttle valve 14 decreases to the second target opening. Therefore, an appropriate A / F is ensured, and excessive combustion and unstable engine control caused by the flow rate of hydrogen contained in the reformed gas being higher than the flow rate of air are suppressed.

[0088] In this embodiment, the timing at which the opening of the main throttle valve 5 starts to change is later than the timing at which the opening of the reforming throttle valve 14 starts to change. Therefore, the timing at which the opening of the main throttle valve 5 reaches the first target opening is reliably later than the timing at which the opening of the reforming throttle valve 14 reaches the second target opening. Furthermore, the rapid change in the opening of the main throttle valve 5 makes it easier to control the flow rate of air supplied to the ammonia engine 2.

[0089] In this embodiment, the timing at which the opening of the main throttle valve 5 starts to change is later than the timing at which the opening of the reforming throttle valve 14 starts to change, but this is not a particular limitation and can be modified as shown in Figure 7.

[0090] 7, the control unit 31 controls the main throttle valve 5 and the reforming throttle valve 14 so that the opening / closing speed of the main throttle valve 5 is slower than the opening / closing speed of the reforming throttle valve 14. Therefore, the control unit 31 controls the main throttle valve 5 and the reforming throttle valve 14 so that the timing at which the opening of the main throttle valve 5 reaches the first target opening is slower than the timing at which the opening of the reforming throttle valve 14 reaches the second target opening.

[0091] When the accelerator is switched from OFF to ON (see FIG. 7(a)), the openings of the reforming injector 20 and the reforming throttle valve 14 increase rapidly to their target openings (see FIGS. 7(c) and 7(e)), and the openings of the main injector 6 and the main throttle valve 5 also begin to increase (see FIGS. 7(b) and 7(d)). Then, after a specified time T0 has elapsed, the openings of the main injector 6 and the main throttle valve 5 reach their target openings.

[0092] When the accelerator is switched from ON to OFF, the openings of the reforming injector 20 and the reforming throttle valve 14 rapidly decrease to their target openings, and the openings of the main injector 6 and the main throttle valve 5 also begin to decrease. Then, after a specified time T0 has elapsed, the openings of the main injector 6 and the main throttle valve 5 reach their target openings.

[0093] In this case, the opening increase control section 33 of the control unit 31 does not execute step S115 of FIG. 3, but instead makes the valve opening speed of the main injector 6 slower than the valve opening speed of the reforming injector 20 in step S116 of FIG. 3, and also makes the valve opening speed of the main throttle valve 5 slower than the valve opening speed of the reforming throttle valve 14 in step S117 of FIG.

[0094] The opening reduction control section 34 of the control unit 31 does not execute step S125 of FIG. 4, but instead makes the valve closing speed of the main injector 6 slower than the valve closing speed of the reforming injector 20 in step S126 of FIG. 4, and also makes the valve closing speed of the main throttle valve 5 slower than the valve closing speed of the reforming throttle valve 14 in step S127 of FIG.

[0095] As described above, in this modified example, the opening and closing speed of the main throttle valve 5 is slower than the opening and closing speed of the reforming throttle valve 14. Therefore, the timing at which the opening of the main throttle valve 5 reaches the first target opening is surely later than the timing at which the opening of the reforming throttle valve 14 reaches the second target opening. By gradually changing the opening of the main throttle valve 5, the main throttle valve 5 opens and closes smoothly.

[0096] Fig. 8 is a schematic diagram showing an engine system according to another embodiment of the present disclosure. In Fig. 8, an engine system 1A of this embodiment differs from the engine system 1 of the above embodiment in that the locations of the reforming throttle valve 14 and the stop valve 23 are swapped. That is, the reforming throttle valve 14 is disposed in the downstream reforming flow passage 21. The stop valve 23 is disposed in the upstream reforming flow passage 13.

[0097] The reforming throttle valve 14 controls the flow rate of the air supplied to the reformer 12 as well as the flow rate of the reformed gas supplied to the ammonia engine 2. Specifically, before the reformed gas is produced by the reformer 12, the reforming throttle valve 14 controls the flow rate of the air supplied to the reformer 12. After the reformed gas is produced by the reformer 12, the reforming throttle valve 14 controls the flow rate of the air and the flow rate of the reformed gas supplied to the reformer 12.

[0098] In this embodiment, air flowing through the upstream reforming passage 13 is supplied to the reformer 12 to generate reformed gas. The reformed gas flows through the downstream reforming passage 21 and is supplied to the ammonia engine 2. A reforming throttle valve 14 is arranged in the downstream reforming passage 21. Therefore, compared to when the reforming throttle valve 14 is arranged in the upstream reforming passage 13, by increasing the opening of the reforming throttle valve 14, the amount of reformed gas supplied to the ammonia engine 2 can be increased more quickly. By decreasing the opening of the reforming throttle valve 14, the amount of reformed gas supplied to the ammonia engine 2 can be decreased more quickly.

[0099] The present disclosure is not limited to the above embodiment. For example, in the above embodiment, the timing at which the opening of the main injector 6 starts to change is equal to the timing at which the opening of the main throttle valve 5 starts to change, but the present disclosure is not particularly limited to such an embodiment. The timing at which the opening of the main injector 6 starts to change may be different from the timing at which the opening of the main throttle valve 5 starts to change, as long as the timing at which the opening of the main injector 6 starts to change is later than the timing at which the opening of the reforming injector 20 starts to change.

[0100] In the above embodiment, as long as the opening / closing speed of the main injector 6 is slower than the opening / closing speed of the reforming injector 20, the opening / closing speed of the main injector 6 may be equal to the opening / closing speed of the main throttle valve 5, or may be different from the opening / closing speed of the main throttle valve 5.

[0101] In the above embodiment, the reformer 12 has a combustion catalyst 25 that burns ammonia gas and a reforming catalyst 26 that decomposes the ammonia gas into hydrogen, but the present invention is not limited to this. The reformer 12 may have a catalyst that has both the function of burning ammonia gas and the function of decomposing the ammonia gas into hydrogen.

[0102] In the above embodiment, the main line 38 and the reforming line 39 are respectively provided with air cleaners 8, 28, but this is not a particular limitation. For example, the upstream reforming passage 13 may be branched off and connected to a portion of the intake passage 3 between the air cleaner 8 and the main throttle valve 5, eliminating the air cleaner 28. In this case, the system configuration can be simplified.

[0103] In the above embodiment, the ammonia gas generated by the vaporizer 16 flows through the ammonia flow path 18 and is supplied to the main injector 6, and the ammonia gas generated by the vaporizer 17 flows through the ammonia flow path 19 and is supplied to the reforming injector 20, but the present invention is not limited to such an embodiment. For example, the number of vaporizers may be one, and the ammonia flow paths 18 and 19 may be connected to that vaporizer. In this case as well, the system configuration can be simplified.

[0104] In the above embodiment, the main injector 6 that injects ammonia gas toward the ammonia engine 2 is provided for each cylinder of the ammonia engine 2, but the number of main injectors 6 is not particularly limited to a plurality and may be one. In this case, the main injector 6 is arranged so as to inject ammonia gas near the ammonia engine 2 in the intake flow path 3.

[0105] The engine system 1 in the above embodiment is mounted on a vehicle, but is not particularly limited to this form, and may be mounted on, for example, a ground-based power generation device, etc. In this case, for example, an operating device operated by an operator constitutes a command value output unit that outputs a command value for the ammonia engine 2 after the ammonia engine 2 is started.

[0106] In the above embodiment, ammonia gas is used as the fuel, but the present disclosure is also applicable to engine systems that use hydrocarbons or the like as fuel.

[0107] 1, 1A...engine system, 2...ammonia engine (engine), 3...intake flow path, 5...main throttle valve (first flow control valve), 6...main injector (first fuel injection valve), 12...reformer, 13...upstream reforming flow path, 14...reforming throttle valve (second flow control valve), 20...reforming injector (second fuel injection valve), 21...downstream reforming flow path, 25...combustion catalyst (catalyst), 26...reforming catalyst (catalyst), 30...acceleration sensor (command value output section), 31...control unit (control section).

Claims

1. An engine in which fuel is burned together with hydrogen; an intake passage through which air supplied to the engine flows; a first flow control valve disposed in the intake passage and configured to control the flow rate of the air supplied to the engine; a first fuel injection valve configured to inject fuel towards the engine; a reformer having a catalyst for decomposing the fuel into hydrogen and configured to reform the fuel to produce a reformed gas containing the hydrogen; an upstream reforming passage through which the air supplied to the reformer flows; a downstream reforming passage through which the reformed gas produced by the reformer flows towards the engine; a second flow control valve disposed in the upstream reforming passage or the downstream reforming passage and configured to control the flow rate of the air supplied to the reformer; a second fuel injection valve configured to inject fuel towards the reformer; a command value output unit configured to output a command value for the engine after the engine is started; and a control unit configured to control the first flow control valve, the first fuel injection valve, the second flow control valve and the second fuel injection valve based on the command value output from the command value output unit, When the command value output from the command value output unit changes during operation of the engine, the control unit sets a target opening of the first flow control valve corresponding to the command value as a first target opening, sets a target opening of the second flow control valve corresponding to the command value as a second target opening, and controls the first flow control valve and the second flow control valve so that the timing at which the opening of the first flow control valve reaches the first target opening is slower than the timing at which the opening of the second flow control valve reaches the second target opening.

2. An engine system as described in claim 1, wherein the control unit sets the first target opening and the second target opening so as to increase in response to the command value output from the command value output unit when the command value changes in an increasing direction while the engine is operating.

3. An engine system as described in claim 1, wherein the control unit sets the first target opening and the second target opening so as to decrease in accordance with the command value output from the command value output unit when the command value changes in a decreasing direction during operation of the engine.

4. An engine system as described in claim 1, wherein the control unit controls the first flow control valve and the second flow control valve so that the timing at which the opening of the first flow control valve starts to change is later than the timing at which the opening of the second flow control valve starts to change.

5. An engine system according to claim 1, wherein the control unit controls the first flow control valve and the second flow control valve so that the opening and closing speed of the first flow control valve is slower than the opening and closing speed of the second flow control valve.

6. An engine system according to claim 1, wherein said second flow control valve is disposed in said downstream reforming passage and controls the flow rate of the reformed gas supplied to said engine together with the flow rate of the air supplied to said reformer.

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