Engine system

Abstract

To provide an engine system capable of securing an appropriate air-fuel ratio at a transient time of an engine while promoting simplification of the configuration of the system.SOLUTION: An engine system 1 includes: a main throttle valve 5 that controls a flow rate of air to be supplied to an ammonia engine 2; a reformer 12 that reforms ammonia gas to generate reformed gas; a reforming throttle valve 14 that controls a flow rate of air to be supplied to the reformer 12; an accelerator sensor 30 that detects an opening of an accelerator; and a control unit 31 that when a detection value obtained by the accelerator sensor 30 changes during an operation of the ammonia engine 2, sets a target opening of each of the main throttle valve 5 and the reforming throttle valve 14 corresponding to the detection value, and controls the main throttle valve 5 and the reforming throttle valve 14 so that a time when the opening of the main throttle valve 5 reaches a first target opening is delayed from a time when the opening of the reforming throttle valve 14 reaches a second target opening.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] As a conventional engine system, for example, the technology described in Patent Document 1 is known. The engine system described in Patent Document 1 includes a main reformer that is attached to the exhaust pipe of the internal combustion engine and reforms fuel with a reforming catalyst, a reformed gas supply pipe that supplies the reformed gas generated by the main reformer, a gas injection valve that injects the reformed gas into the intake pipe, and a plurality of fuel injection valves with sub-reformers that are provided for each cylinder in the branch section of the intake pipe. When the supply of reformed gas from the main reformer and the gas injection valve is insufficient, the shortage is made up for by the fuel injection valve with sub-reformer. This makes it possible to supply a sufficient amount of reformed gas to the internal combustion engine even in a transient state such as during rapid acceleration. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-12321 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above conventional technology, in addition to the main reformer and gas injector, a fuel injector with a sub-reformer is required for each cylinder of the engine (internal combustion engine). Furthermore, with the addition of a fuel injector with a sub-reformer, a temperature sensor for detecting the temperature of the reforming catalyst in the sub-reformer and a pressure sensor for detecting the pressure of the reformed gas in the sub-reformer are also required. This makes the configuration of the engine system complicated. Therefore, it is desired to ensure an appropriate air-fuel ratio during engine transients while simplifying the configuration of the engine system.

[0005] An object of the present invention is to provide an engine system that can ensure an appropriate air-fuel ratio during engine transitions while simplifying the system configuration. [Means for solving the problem]

[0006] (1) An engine system according to one aspect of the present invention includes 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 toward the engine, a reformer having a catalyst for decomposing fuel into hydrogen and configured to reform 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 the 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 target openings of the first flow control valve and the second flow control valve according to the command value as a first target opening and a second target opening when the command value output from the command value output unit changes while the engine is running, and controls the first flow control valve and the second flow control valve so that the time taken for the opening of the first flow control valve to reach the first target opening is slower than the time taken for the opening of the second flow control valve to reach 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 catalyst of the reformer, and the reformed gas is supplied to the engine. In addition, fuel and air are supplied to the engine, and the fuel is mixed with 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, so that reformed gas is generated in the reformer, and the reformed gas flows through the downstream reforming passage and is supplied to the engine. For this reason, the air flowing through the intake passage is supplied to the engine quickly, but the reformed gas is supplied to the engine with a delay compared 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, an appropriate air-fuel ratio is not ensured in the engine.

[0008] Therefore, when a command value for the engine changes during operation of the engine, the target openings of the first flow control valve and the second flow control valve corresponding to the command value are set as the first target opening and the second target opening, respectively. Then, the first flow control valve and the second flow control valve are controlled so that the time when the opening of the first flow control valve reaches the first target opening is slower than the time when the opening of the second flow control valve reaches the second target opening. Therefore, the time when the opening of the first flow control valve reaches the first target opening is slower than the time when the opening of the second flow control valve reaches the second target opening. As a result, even during a transient period when the engine operating conditions change, the reformed gas and air are appropriately supplied to the engine, so that an appropriate air-fuel ratio is ensured. In addition, since there is no need to provide a sub-reformer for each cylinder of the engine, there is no need for a valve for injecting fuel toward the sub-reformer. Therefore, the configuration of the engine system is simplified.

[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 operating, the control unit may set the first target opening and the second target opening to increase in accordance with the command value.

[0010] In this configuration, when a 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 so as to increase in accordance with the command value. Therefore, the time it takes for the opening of the first flow control valve to increase to the first target opening is slower than the time it takes for the opening of the second flow control valve to increase 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 compared to the flow rate of air are suppressed.

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

[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 time it takes for the opening of the first flow control valve to decrease to the first target opening is slower than the time it takes for the opening of the second flow control valve to decrease to the second target opening. Therefore, an appropriate air-fuel ratio is ensured, 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 (1) to (3) above, 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 time at which the opening of the first flow control valve reaches the first target opening is reliably later than the time 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 time it takes for the opening of the first flow control valve to reach the first target opening is surely slower than the time it takes for the opening of the second flow control valve to reach the second target opening. Furthermore, the gradual change in the opening of the first flow control valve allows the first flow control valve to open and close smoothly.

[0017] (6) In any of the above (1) to (5), the second flow control valve may be disposed in the downstream reforming passage 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 to be supplied to the engine, with the second flow control valve disposed in the downstream reforming passage. Therefore, compared to the case where the second flow control valve is disposed in the upstream reforming passage, the amount of reformed gas supplied to the engine can be increased more quickly by increasing the aperture of the second flow control valve, and the amount of reformed gas supplied to the engine can be decreased more quickly by decreasing the aperture of the second flow control valve. Effect of the Invention

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

[0020] [Figure 1] 1 is a schematic configuration diagram showing an engine system according to an embodiment of the present invention. [Diagram 2] 4 is a flowchart showing a procedure of a control process executed by a control unit shown in FIG. 1. [Diagram 3] 3 is a flowchart showing details of the control process performed in step S104 of FIG. 2 when the accelerator opening degree is increased. [Figure 4] 3 is a flowchart showing details of the control process performed at step S105 in FIG. 2 when the accelerator opening is decreased. [Diagram 5] FIG. 4 is a timing diagram showing the operations of the main injector, the reforming injector, the main throttle valve, and the reforming throttle valve when the accelerator is switched from OFF to ON. [Figure 6] FIG. 4 is a timing diagram showing the operations of the main injector, the reforming injector, the main throttle valve, and the reforming throttle valve when the accelerator is switched from ON to OFF. [Figure 7] FIG. 11 is a timing diagram showing a modified example of the operation of the main injector, the reforming injector, the main throttle valve, and the reforming throttle valve when the accelerator is switched from OFF to ON. [Figure 8] FIG. 4 is a schematic configuration diagram showing an engine system according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention 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 duplicated explanations will be omitted.

[0022] Fig. 1 is a schematic diagram showing an engine system according to an embodiment of the present invention. In Fig. 1, an engine system 1 according to the present 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 an engine that uses ammonia gas (NH3 gas) as fuel. In the ammonia engine 2, hydrogen (H2) is mixed with the ammonia gas as a combustion aid to facilitate combustion of the flame-retardant ammonia gas. That is, in each cylinder of the ammonia engine 2, the ammonia gas is burned together with the hydrogen to generate combustion gas. The ammonia engine 2 is, for example, a four-cylinder engine.

[0024] The intake passage 3 is connected to each cylinder of the ammonia engine 2 via an intake manifold 7. The intake passage 3 is a passage through which air supplied to the ammonia engine 2 flows. An air cleaner 8 is disposed in the intake passage 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. In the exhaust flow path 4, a three-way catalyst 10 that purifies NH3 and NOx contained in the exhaust gas, and an SCR catalyst 11 that adsorbs NH3 that has passed through the three-way catalyst 10 are disposed.

[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, for example, into 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 passage 13, a reforming throttle valve 14, an ammonia cylinder 15, vaporizers 16, 17, ammonia passages 18, 19, a reforming injector 20, a downstream reforming passage 21, a cooler 22, and a stop valve 23.

[0029] The reformer 12 generates 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 in 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 disposed downstream of the combustion catalyst 25 in 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 in the housing 24. The electric heater 27 heats the ammonia gas and air introduced into the housing 24, thereby heating (warming) the combustion catalyst 25 through the ammonia gas and air.

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

[0033] The reforming throttle valve 14 is disposed in the upstream reforming passage 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 passage 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 injection amount of ammonia gas.

[0038] The downstream reforming passage 21 connects the reformer 12 and the intake passage 3. One end of the downstream reforming passage 21 is connected to an outlet portion of a housing 24 of the reformer 12. The other end of the downstream reforming passage 21 is connected to a portion of the intake passage 3 between the main throttle valve 5 and the ammonia engine 2. The downstream reforming passage 21 is a passage 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 (depression amount) of an accelerator of a vehicle (not shown) and outputs the detected value 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. The change in the opening of the accelerator 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 openings of the main throttle valve 5 and the reforming throttle valve 14 according to the detection value of the accelerator sensor 30 as a first target opening and a second target opening, respectively, and controls the main throttle valve 5 and the reforming throttle valve 14 so that the time taken for the opening of the main throttle valve 5 to reach the first target opening is slower than the time taken for the opening of the reforming throttle valve 14 to reach 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 degree of the main throttle valve 5 starts to change is later than the timing at which the opening degree 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, based on the detection value of the accelerator sensor 30, whether the opening of the accelerator has changed.

[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 a first target opening and a second target opening which increase in accordance with the detection value of the accelerator sensor 30, and controls the main throttle valve 5 and the reforming throttle valve 14 so that the time taken for the opening of the main throttle valve 5 to reach the first target opening is slower than the time taken for the opening of the reforming throttle valve 14 to reach 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 a first target opening and a second target opening which decrease in accordance with the detection value of the accelerator sensor 30, and controls the main throttle valve 5 and the reforming throttle valve 14 so that the time taken for the opening of the main throttle valve 5 to reach the first target opening is slower than the time taken for the opening of the reforming throttle valve 14 to reach 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). At this time, 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 judges whether the accelerator opening has changed in an increasing direction (step S103). When the control unit 31 determines that the accelerator opening has changed in an increasing direction, it executes a control process when the accelerator opening has increased (step S104). When the control unit 31 determines that the accelerator opening has changed in a decreasing direction, it executes a control process when the accelerator opening has decreased (step S105).

[0054] After executing step S104 or step S105, the control unit 31 executes the above step S101 again. The control unit 31 also executes the above 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 opening degree of the accelerator and the flow rate of ammonia gas and air.

[0058] Next, the control unit 31 sets target openings of the main injector 6, the main throttle valve 5, the reforming injector 20, and the reforming throttle valve 14 based on the increased amounts of ammonia gas and air (step S112). The target openings of the main injector 6, the main throttle valve 5, the reforming injector 20, and the reforming throttle valve 14 are obtained from map data that indicates 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 also 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). Note that the order in which steps S113 and S114 are executed is not particularly limited to this, and step S114 may be executed before step S113, or steps S113 and S114 may be executed simultaneously.

[0060] Next, the control unit 31 determines whether or not 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 FIG. 5).

[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 also 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). Note that 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 in step S105 when the accelerator opening is decreased.

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

[0064] Next, the control unit 31 sets target openings of the main injector 6, the main throttle valve 5, the reforming injector 20, and the reforming throttle valve 14 based on the reduced amounts of ammonia gas and air (step S122). The target openings of the main injector 6, the main throttle valve 5, the reforming injector 20, and the reforming throttle valve 14 are obtained from map data that indicates 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 also 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). Note that the order in which steps S123 and S124 are executed is not particularly limited, and step S124 may be executed before step S123, or steps S123 and S124 may be executed simultaneously.

[0066] Next, the control unit 31 judges whether or not 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 FIG. 6). The specified time T is the same as the specified time T used in the above step S115.

[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 also 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). Note that 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, when the vehicle ignition switch (not shown) is turned ON, the ammonia engine 2 is started. 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. Then, when the temperature of the combustion catalyst 25 reaches an activation temperature (combustible temperature), the ammonia gas is combusted by the combustion catalyst 25. Specifically, ammonia chemically reacts with oxygen in the air (exothermic reaction) as shown in the following formula. NH3+3 / 4O2→1 / 2N2+3 / 2H2O+Q1(heat) …(A)

[0070] When ammonia gas is burned, the heat of combustion of the ammonia gas increases the temperature of the reforming catalyst 26. Then, 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 generated. NH3→3 / 2H2+1 / 2N2-Q2 (endothermic) …(B)

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

[0072] FIG. 5 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 is switched from OFF to ON, as an example of an increase in the accelerator opening.

[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, the main injector 6, the reforming throttle valve 14, and the reforming injector 20 are set so as to increase the flow rates of ammonia gas and air supplied to the ammonia engine 2 and the reformer 12. When the accelerator is OFF (idling), the main throttle valve 5, the main injector 6, the reforming throttle valve 14, and the reforming injector 20 are slightly open.

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

[0075] After that, when a specified time T has elapsed, the opening of the main injector 6 rapidly increases to the target opening as shown in Fig. 5(b), and the opening of the main throttle valve 5 rapidly increases to the target opening (first target opening) as shown in Fig. 5(d). In other words, the openings of the main injector 6 and the main throttle valve 5 increase at a later timing than the openings of the reforming injector 20 and the 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 is switched from ON to OFF, as an example of a decrease in the accelerator opening.

[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 FIG. 6(c), the opening degree of the reforming injector 20 is abruptly decreased to the target opening degree, and, as shown in FIG. 6(e), the opening degree of the reforming throttle valve 14 is abruptly decreased to the target opening degree (second target opening degree).

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

[0080] Incidentally, during transient operation of the ammonia engine 2, such as when the accelerator is switched ON / 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 will be unintentionally drawn into the ammonia engine 2, and an appropriate A / F (air-fuel ratio) will not 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 in their paths. The main line 38 responds quickly to changes in the opening of the main throttle valve 5. However, the reforming line 39 has the combustion catalyst 25, reforming catalyst 26, and cooler 22, which have large pressure losses, arranged therein, causing a delay in the flow of the reformed gas. Also, in the reforming line 39, ammonia gas is supplied upstream of the reformer 12, and the ammonia gas is reformed by the reformer 12 to generate 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 and the openings of the main throttle valve 5 and the reforming throttle valve 14 increase at the same time, the air increases quickly in the main line 38, but the increase in the amount of reformed gas in the reforming line 39 is delayed. As a result, the ammonia engine 2 enters a state where the air flow rate is high and the hydrogen flow rate contained in the reformed gas is low, which may cause a misfire. In this case, unburned ammonia flows out of the ammonia engine 2.

[0083] On the other hand, when the accelerator is switched from ON to OFF and the openings of the main throttle valve 5 and the reforming throttle valve 14 are reduced at the same timing, the amount of air is promptly reduced in the main line 38, but the reduction in the amount of reformed gas is delayed in the reforming line 39. For this reason, the supply of reformed gas to the ammonia engine 2 continues for a while. Therefore, in the ammonia engine 2, the air flow rate is low and the hydrogen flow rate contained in the reformed gas is high, and the fuel suddenly burns and combustion becomes vigorous, which may cause the control of the ammonia engine 2 to become unstable.

[0084] Therefore, for example, when the accelerator is switched from OFF to ON, it is conceivable to increase the opening of the main injector 6 to increase the amount of ammonia gas injected from the main injector 6, thereby making the A / F uniform and preventing the leanness from occurring. However, even in this case, this does not contribute to increasing the amount of hydrogen, which is the auxiliary fuel for promoting the combustion of ammonia gas, and therefore the combustion of ammonia gas becomes slower.

[0085] To address such a problem, in this embodiment, when the detection value of the accelerator sensor 30 (command value for the ammonia engine 2) changes while the ammonia engine 2 is operating, the target openings of the main throttle valve 5 and the reforming throttle valve 14 according to the detection value of the accelerator sensor 30 are set as the first target opening and the second target opening, respectively. Then, the main throttle valve 5 and the reforming throttle valve 14 are controlled so that the time when the opening of the main throttle valve 5 reaches the first target opening is slower than the time when the opening of the reforming throttle valve 14 reaches the second target opening. Therefore, the time when the opening of the main throttle valve 5 reaches the first target opening is slower than the time when the opening of the reforming throttle valve 14 reaches the second target opening. As a result, even during a transient period when the operating conditions of the ammonia engine 2 change, the reformed gas and air are appropriately supplied to the ammonia engine 2, and an appropriate A / F is ensured. 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] Furthermore, 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 following the detection value of the accelerator sensor 30. Therefore, the time taken for the opening of the main throttle valve 5 to increase to the first target opening is slower than the time taken for the opening of the reforming throttle valve 14 to increase 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] Furthermore, 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. Therefore, the time taken for the opening of the main throttle valve 5 to decrease to the first target opening is slower than the time taken for the opening of the reforming throttle valve 14 to decrease 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] Furthermore, 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 time at which the opening of the main throttle valve 5 reaches the first target opening is reliably later than the time 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 degree of the main throttle valve 5 starts to change is slower than the timing at which the opening degree of the reforming throttle valve 14 starts to change, but this is not particularly limited to this form 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 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. For this reason, the control unit 31 controls the main throttle valve 5 and the reforming throttle valve 14 so that the time it takes for the opening degree of the main throttle valve 5 to reach the first target opening degree is slower than the time it takes for the opening degree of the reforming throttle valve 14 to reach the second target opening degree.

[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 (e)), and the openings of the main injector 6 and the main throttle valve 5 also begin to increase (see FIGS. 7(b) and (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] Furthermore, although not shown, when the accelerator is switched from ON to OFF, the openings of the reforming injector 20 and the reforming throttle valve 14 are rapidly decreased 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 makes the opening speed of the main injector 6 slower than the opening speed of the reforming injector 20 in step S116 of FIG. 3, and makes the opening speed of the main throttle valve 5 slower than the opening speed of the reforming throttle valve 14 in step S117 of FIG. 3.

[0094] Furthermore, the opening degree decreasing control section 34 of the control unit 31 does not execute step S125 of FIG. 4, but makes the closing speed of the main injector 6 slower than the closing speed of the reforming injector 20 in step S126 of FIG. 4, and also makes the closing speed of the main throttle valve 5 slower than the 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 time taken for the opening of the main throttle valve 5 to reach the first target opening is reliably slower than the time taken for the opening of the reforming throttle valve 14 to reach the second target opening. Furthermore, 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 invention. In Fig. 8, an engine system 1A of this embodiment differs from the engine system 1 in the above-described embodiment in that the locations of the reforming throttle valve 14 and the stop valve 23 are interchanged. That is, the reforming throttle valve 14 is disposed in the downstream reforming passage 21. The stop valve 23 is disposed in the upstream reforming passage 13.

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

[0098] In this embodiment, air flowing through the upstream reforming passage 13 is supplied to the reformer 12 to generate reformed gas, and the reformed gas flows through the downstream reforming passage 21 to be supplied to the ammonia engine 2, with the downstream reforming passage 21 being provided with the reforming throttle valve 14. Therefore, compared to the case where the reforming throttle valve 14 is provided 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, and 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 invention 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 invention 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 slower than the timing at which the opening of the reforming injector 20 starts to change.

[0100] In addition, 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 the opening / closing speed of the main injector 6 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 embodiment. The reformer 12 may have a catalyst that has both a function of burning ammonia gas and a function of decomposing the ammonia gas into hydrogen.

[0102] In addition, in the above embodiment, the air cleaners 8, 28 are provided in the main line 38 and the reforming line 39, respectively, but the present invention is not limited to this configuration. For example, the upstream reforming passage 13 may be branched and connected to a portion of the intake passage 3 between the air cleaner 8 and the main throttle valve 5, thereby 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 the vaporizer. In this case as well, the system configuration can be simplified.

[0104] In addition, 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 disposed so as to inject ammonia gas near the ammonia engine 2 in the intake passage 3.

[0105] Furthermore, although the engine system 1 of the above embodiment is mounted on a vehicle, the present invention is not particularly limited to this form, and may be mounted on, for example, a ground 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] Furthermore, in the above embodiment, ammonia gas is used as the fuel, but the present invention is also applicable to engine systems that use hydrocarbons or the like as fuel. [Explanation of symbols]

[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...accelerator sensor (command value output section), 31...control unit (control section).

Claims

1. 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 a flow rate of air supplied to the engine; a first fuel injection valve that injects fuel toward the engine; a reformer having a catalyst for decomposing the fuel into the hydrogen and for reforming the fuel to generate a reformed gas containing the hydrogen; an upstream reforming flow passage through which air supplied to the reformer flows; a downstream reforming passage through which the reformed 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 a flow rate of air supplied to the reformer; a second fuel injection valve that injects fuel toward the reformer; a command value output unit that outputs a command value for the engine after the engine is started; a control unit that controls 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 while the engine is operating, the control unit sets target openings of the first flow control valve and the second flow control valve according to the command value as a first target opening and a second target opening, respectively, and controls the first flow control valve and the second flow control valve so that the time taken for the opening of the first flow control valve to reach the first target opening is slower than the time taken for the opening of the second flow control valve to reach the second target opening.

2. 2. The engine system according to claim 1, wherein the control unit sets the first target opening degree and the second target opening degree so as to increase in accordance with the command value output from the command value output unit when the command value output from the command value output unit changes in an increasing direction during operation of the engine.

3. 2. The engine system according to claim 1, wherein the control unit sets the first target opening amount and the second target opening amount 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. 2. The engine system according to claim 1, wherein the control unit controls the first flow control valve and the second flow control valve so that a change in the opening degree of the first flow control valve starts later than a change in the opening degree of the second flow control valve.

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

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

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