Engine system

Abstract

To provide an engine system capable of suppressing deterioration of a catalyst of a reformer.SOLUTION: An engine system 1 includes: a reformer 25 for reforming ammonia gas; a reforming throttle valve 27 for controlling a flow rate of air to be supplied to the reformer 25; a reforming injector 30 for intermittently injecting ammonia gas toward the reformer 25; a downstream side reforming flow passage 33 in which reformed gas flows toward inside of a cylinder 10 of an ammonia engine 2; and a controller 42 for controlling the reforming throttle valve 27 and the reforming injector 30. In an intake period T from start of a stroke in which air is sucked into the cylinder 10 until start of a stroke in which air is sucked into the next cylinder 10, the controller 42 controls the reforming injector 30 so that the ammonia gas is injected in accordance with timing at which the flow rate of air to be supplied to the reformer 25 increases due to intake pulsation.SELECTED DRAWING: Figure 1

Description

[[TECHNICAL FIELD]]

[0001] The present invention relates to an engine system. [[BACKGROUND ART]]

[0002] As a conventional engine system, for example, as described in Patent Document 1, a technology is known in which fuel gas is reformed by a reformer to generate reformed gas mainly composed of hydrogen, and the reformed gas is combusted in an engine. The engine system described in Patent Document 1 includes a reformer, an ejector arranged on the upstream side of the reformer and having a main flow path and a secondary flow path, an air introduction path connecting an intake passage of the engine and the secondary flow path of the ejector, a reforming air control valve provided in the middle of the air introduction path for controlling the flow rate of reforming air, and an injector arranged facing the main flow path of the ejector and injecting reforming fuel gas into the ejector. The opening degree of the reforming air control valve is controlled so as to suppress fluctuation in the mixing ratio of the reforming air supplied from the ejector to the reformer and the reforming fuel gas with respect to changes in the intake pressure of the engine. [[PRIOR ART DOCUMENTS]] [[PATENT DOCUMENTS]]

[0003] [[Patent Document 1]] Japanese Patent Laid-Open No. 2015-10581 [[SUMMARY OF THE INVENTION]] [[Problem to be Solved by the Invention]]

[0004] Incidentally, in engine systems equipped with a reformer like the conventional technology described above, intake pulsations occur in the reforming passage, including the reformer, due to the up-and-down movement of the pistons in the engine, causing fluctuations in the airflow rate supplied to the reformer. In addition, the injector intermittently injects fuel according to the engine speed. As a result, the fuel and air supplied to the reformer are not uniform over time, and the air-fuel ratio (A / F) in the reformer becomes uneven over time. Due to these uneven air-fuel ratios, the catalytic reaction in the reformer is also not uniform over time, and if the air-fuel ratio is excessively high, temporary overheating of the reformer can occur, which can cause the catalyst in the reformer to deteriorate.

[0005] The object of the present invention is to provide an engine system that can suppress the deterioration of the catalyst in the reformer. [Means for solving the problem]

[0006] (1) An engine system according to one aspect of the present invention comprises an engine having a plurality of cylinders and pistons arranged in the cylinders, wherein fuel is burned together with hydrogen; an intake passage through which air supplied to the cylinder flows; a first flow control valve disposed in the intake passage for controlling the flow rate of air supplied to the cylinder; a first fuel injector that intermittently injects fuel into the cylinder; a reformer having a catalyst that decomposes fuel into hydrogen and reforms the fuel to produce a hydrogen-containing reformed gas; an upstream reforming passage through which air supplied to the reformer flows; a downstream reforming passage through which the reformed gas produced by the reformer flows into the cylinder; and a valve disposed in the upstream or downstream reforming passage for air supplied to the reformer. The engine comprises a second flow control valve for controlling the flow rate, a second fuel injector for intermittently injecting fuel toward the reformer, and a control unit for controlling the first flow control valve, the first fuel injector, the second flow control valve, and the second fuel injector. The engine sequentially performs multiple strokes, each including a stroke in which air is drawn into the cylinder, for each of the multiple cylinders. The control unit controls the second fuel injector so that fuel is injected from the second fuel injector in accordance with the timing when the flow rate of air supplied to the reformer increases due to intake pulsations generated from the stroke in which air is drawn into the cylinder from the start of the intake period until the start of the stroke in which air is drawn into the next cylinder.

[0007] In such an engine system, fuel and air are supplied to the reformer, generating a reformed gas containing hydrogen, which is then supplied to the engine cylinders. Additionally, when fuel and air are supplied to the engine cylinders, the fuel mixes with hydrogen and burns within the cylinders. In the engine, multiple strokes, including a stroke in which air is drawn into each cylinder, are performed sequentially. During the intake period, from the start of one cylinder's intake stroke to the start of the next, fuel is injected from the second fuel injector in accordance with the timing when the air flow rate supplied to the reformer increases due to intake pulsations generated from the intake strokes. Therefore, even if the air flow rate supplied to the reformer fluctuates due to intake pulsations, temporal fluctuations in the air-fuel ratio in the reformer are reduced. This suppresses overheating of the reformer, thereby inhibiting the deterioration of the reformer's catalyst.

[0008] (2) In the above (1), the engine system further comprises an intake pressure detection unit for detecting intake pressure into the cylinder, and the control unit may determine the timing based on the intake pressure detected by the intake pressure detection unit and control the second fuel injector so that fuel is injected from the second fuel injector according to that timing.

[0009] As the piston descends, negative pressure is generated inside the cylinder, drawing air into it. The higher the negative pressure inside the cylinder, the easier and faster air is drawn into the cylinder. Therefore, based on the intake pressure into the cylinder, the timing at which the airflow rate supplied to the reformer increases due to intake pulsations generated from the stroke in which air is drawn into the cylinder from the start of the intake period is determined, and fuel is injected from the second fuel injector at the appropriate timing according to the intake pressure into the cylinder during the intake period from the start of one stroke in which air is drawn into the cylinder to the start of the next stroke in which air is drawn into the cylinder. As a result, temporal fluctuations in the air-fuel ratio in the reformer are further reduced. Consequently, overheating of the reformer is further suppressed, and the deterioration of the reformer catalyst is further inhibited.

[0010] (3) In (1) above, the engine system further comprises an engine state detection unit for detecting the state of the engine, and the control unit may determine the timing based on the state of the engine detected by the engine state detection unit and control the second fuel injector so that fuel is injected from the second fuel injector according to that timing.

[0011] As mentioned above, the higher the negative pressure inside the cylinder, the easier it is for air to be drawn into the cylinder, and the faster the air is drawn in. However, the negative pressure inside the cylinder changes depending on the engine condition. Therefore, based on the engine condition, the timing at which the airflow rate supplied to the reformer increases due to intake pulsations generated from the stroke in which air is drawn into the cylinder from the start of the intake period is determined, and fuel is injected from the second fuel injector according to that timing. As a result, fuel is injected from the second fuel injector at the appropriate timing according to the engine condition. This further reduces the temporal unevenness of the air-fuel ratio in the reformer. Consequently, overheating of the reformer is further suppressed, and the deterioration of the catalyst in the reformer is further inhibited.

[0012] (4) In (2) above, the engine state detection unit may detect at least one of the engine speed and load as the engine state, and the control unit may determine the timing based on at least one of the engine speed and load.

[0013] In this configuration, by detecting at least one of the engine speed and load as engine conditions, fuel is injected from the second fuel injector at an appropriate timing corresponding to at least one of the engine speed and load.

[0014] (5) In any of (1) to (4) above, the engine system further comprises a vaporizer for vaporizing liquid fuel, a fuel passage through which the fuel vaporized by the vaporizer flows toward a first fuel injector and a second fuel injector, a first pressure detection unit for detecting the pressure in the fuel passage as the upstream pressure of the second fuel injector, and a second pressure detection unit for detecting the pressure in the upstream reforming passage as the downstream pressure of the second fuel injector, and the control unit may control the second fuel injector such that when the pressure difference between the upstream pressure of the second fuel injector and the downstream pressure of the second fuel injector is greater than or equal to a predetermined value, the fuel injection time from the second fuel injector is shorter than when the pressure difference between the upstream pressure of the second fuel injector and the downstream pressure of the second fuel injector is lower than a predetermined value.

[0015] The amount of fuel injected from the second fuel injector changes depending on the upstream and downstream pressures of the second fuel injector. The larger the pressure difference between the upstream and downstream pressures of the second fuel injector, the greater the amount of fuel injected from the second fuel injector. Therefore, when the pressure difference between the upstream and downstream pressures of the second fuel injector is greater than a predetermined value, the fuel injection time from the second fuel injector is shortened compared to when the pressure difference is lower than a predetermined value. This causes the amount of fuel injected from the second fuel injector to become closer to a constant regardless of the upstream and downstream pressures of the second fuel injector. Consequently, fuel is injected appropriately from the second fuel injector depending on the engine state, such as immediately after engine startup.

[0016] (6) In any of (1) to (4) above, the engine system further comprises a vaporizer for vaporizing liquid fuel, a fuel passage through which the fuel vaporized by the vaporizer flows toward the first fuel injector and the second fuel injector, and a temperature detection unit for detecting the ambient temperature or the temperature of the coolant that cools the engine, and the control unit may control the second fuel injector such that when the ambient temperature or the coolant temperature is above a predetermined value, the fuel injection time from the second fuel injector is shorter than when the ambient temperature or the coolant temperature is below a predetermined value.

[0017] The amount of fuel injected from the second fuel injector changes depending on the pressure in the fuel passage. The higher the pressure in the fuel passage, the greater the amount of fuel injected from the fuel injector. The pressure in the fuel passage changes depending on the vaporization capacity of the carburetor. The vaporization capacity of the carburetor changes depending on the ambient temperature. Also, if the carburetor uses the coolant that cools the engine to vaporize liquid fuel, the vaporization capacity of the carburetor also changes depending on the temperature of the coolant. As the ambient temperature or coolant temperature increases, the vaporization capacity of the carburetor increases, and therefore the pressure in the fuel passage increases. So, when the ambient temperature or coolant temperature is above a predetermined value, the fuel injection time from the second fuel injector is shortened compared to when the ambient temperature or coolant temperature is below a predetermined value, so that the amount of fuel injected from the second fuel injector approaches a constant regardless of the ambient temperature or coolant temperature. Therefore, fuel is injected appropriately from the second fuel injector depending on the engine conditions, such as immediately after engine startup, in high-temperature environments, or in low-temperature environments. [Effects of the Invention]

[0018] According to the present invention, the deterioration of the catalyst in the reformer can be suppressed. [Brief explanation of the drawing]

[0019] [Figure 1] This is a schematic diagram showing an engine system according to the first embodiment of the present invention. [Figure 2] This is a cross-sectional view of an ammonia engine. [Figure 3]It is a conceptual diagram showing one cycle stroke of an ammonia engine. [Figure 4] It is a flowchart showing the procedure of reforming injector control processing executed by the valve control unit shown in FIG. 1. [Figure 5] It is a timing diagram showing the operation of the ammonia engine shown in FIG. 1. [Figure 6] It is a timing diagram showing the operation of an ammonia engine in a comparative example. [Figure 7] It is a schematic configuration diagram showing an engine system according to a second embodiment of the present invention. [Figure 8] It is a flowchart showing the procedure of reforming injector control processing executed by the valve control unit shown in FIG. 7. [Figure 9] It is a schematic configuration diagram showing an engine system according to a third embodiment of the present invention. [Figure 10] It is a flowchart showing the procedure of reforming injector control processing executed by the valve control unit shown in FIG. 9. [Figure 11] It is a schematic configuration diagram showing an engine system according to a fourth embodiment of the present invention. [Figure 12] It is a flowchart showing the procedure of injection time determination processing executed by the injection time determination unit shown in FIG. 11. [Figure 13] It is a schematic configuration diagram showing an engine system according to a fifth embodiment of the present invention. [Figure 14] It is a flowchart showing the procedure of injection time determination processing executed by the injection time determination unit shown in FIG. 13. [Figure 15] It is a schematic configuration diagram showing a modified example of an engine system according to the fifth embodiment of the present invention. Mode for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are denoted by the same reference numerals, and overlapping descriptions will be omitted.

[0021] Figure 1 is a schematic diagram showing an engine system according to a first embodiment of the present invention. In Figure 1, the engine system 1 of this embodiment is mounted on a vehicle (not shown). The engine system 1 comprises an ammonia engine 2, an intake passage 3, an exhaust passage 4, a main throttle valve 5, and a main injector 6.

[0022] Ammonia engine 2 is an engine that uses ammonia gas (NH3 gas) as fuel. In ammonia engine 2, hydrogen (H2) is mixed with the ammonia gas as a combustion aid to make the non-flammable ammonia gas easier to burn. Ammonia engine 2 is, for example, a four-stroke, four-cylinder engine.

[0023] As shown in Figures 2 and 3, the ammonia engine 2 has four cylinders 10 (referred to as cylinders 10A to 10D), four pistons 11 arranged to reciprocate within each cylinder 10, and four connecting rods 13 that connect each piston 11 to the crankshaft 12.

[0024] Each cylinder 10 is located in a cylinder block 14. A cylinder head 15 is mounted on the top of the cylinder block 14. The space defined by the cylinders 10, cylinder head 15, and piston 11 forms a combustion chamber 16 where ammonia gas burns with hydrogen to produce exhaust gas. In other words, the ammonia engine 2 has four combustion chambers 16.

[0025] The cylinder head 15 is provided with four intake ports 17 and four exhaust ports 18, each communicating with one of the combustion chambers 16. The intake ports 17 are opened and closed by intake valves 19. The exhaust ports 18 are opened and closed by exhaust valves 20. A spark plug 21 is also mounted on the cylinder head 15. The spark plug 21 ignites the mixture of ammonia gas and air, thereby igniting the ammonia gas.

[0026] Cylinders 10A to 10D are arranged in a line in one direction. Cylinder 10A is cylinder 1. Cylinder 10B is cylinder 2. Cylinder 10C is cylinder 3. Cylinder 10D is cylinder 4.

[0027] The intake passage 3 is connected to each combustion chamber 16 (inside each cylinder 10) of the ammonia engine 2. The intake passage 3 is the passage through which air supplied to each combustion chamber 16 flows. An air cleaner 7 is installed in the intake passage 3 to remove foreign matter such as dust and dirt contained in the air.

[0028] The exhaust passage 4 is connected to each combustion chamber 16 of the ammonia engine 2. The exhaust passage 4 is the passage through which the exhaust gas generated in each combustion chamber 16 flows. Although not specifically shown in the diagram, the exhaust passage 4 is equipped with a three-way catalytic converter that purifies CO, HC, and NOx contained in the exhaust gas, and an SCR catalytic converter that removes NOx contained in the exhaust gas.

[0029] The main throttle valve 5 is located 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 combustion chamber 16 of the ammonia engine 2.

[0030] The number of main injectors 6 is four, the same as the number of cylinders in the ammonia engine 2. These main injectors 6 are electromagnetic first fuel injectors that intermittently inject ammonia gas into each combustion chamber 16 of the ammonia engine 2. Each main injector 6 may inject ammonia gas into each intake port 17 of the ammonia engine 2, or it may inject ammonia gas near the ammonia engine 2 in the intake passage 3. The amount of ammonia gas injected by the main injectors 6 can be adjusted by changing the time the needle valve is open.

[0031] Furthermore, the engine system 1 is equipped with an engine ECU 8. The engine ECU 8 consists of a CPU, RAM, ROM, and input / output interfaces, etc. The engine ECU 8 is an ECU (electronic control unit) that controls the ammonia engine 2.

[0032] Specifically, although not shown in the diagram, the engine ECU 8 controls the starter to start when the ignition switch is turned ON. Furthermore, as shown in Figure 3, after the starter is started, the engine ECU 8 controls the intake valve 19, exhaust valve 20, and spark plug 21 of the ammonia engine 2 to perform four strokes as one cycle: intake stroke, compression stroke, expansion stroke (combustion stroke), and exhaust stroke.

[0033] The intake stroke is the stroke in which the piston 11 moves down, drawing a mixture of ammonia gas and air into the cylinder 10. The compression stroke is the stroke in which the piston 11 moves up to top dead center, compressing the mixture. The expansion stroke is the stroke in which the ignited mixture burns, and the combustion gases expand, pushing the piston 11 down to bottom dead center. The exhaust stroke is the stroke in which the piston 11 moves up due to inertia, pushing the combustion gases out of the cylinder 10. In other words, in one cycle, the piston 11 makes two back-and-forth movements inside the cylinder 10, and the crankshaft 12 makes two rotations.

[0034] The engine ECU 8 controls the intake valve 19 to open during the intake stroke. The engine ECU 8 controls the spark plug 21 to ignite during the expansion stroke. The engine ECU 8 controls the exhaust valve 20 to open during the exhaust stroke.

[0035] At this time, the engine ECU 8 controls the intake valve 19, exhaust valve 20, and spark plug 21 to perform four strokes in the order of cylinder 10A (cylinder 1), cylinder 10C (cylinder 3), cylinder 10D (cylinder 4), and cylinder 10B (cylinder 2), as shown in Figure 3. In other words, the four strokes are performed sequentially for each of the four cylinders 10. Therefore, after the intake stroke of cylinder 10A is completed, the intake stroke of cylinder 10C is performed, after the intake stroke of cylinder 10C is completed, the intake stroke of cylinder 10D is performed, after the intake stroke of cylinder 10D is completed, the intake stroke of cylinder 10B is performed, and after the intake stroke of cylinder 10B is completed, the intake stroke of cylinder 10A is performed again (see Figure 5(a)). The same applies to the compression stroke, expansion stroke, and exhaust stroke.

[0036] The engine system 1 also includes a reformer 25, an upstream reforming passage 26, a reforming throttle valve 27, an ammonia cylinder 28, a vaporizer 29, a reforming injector 30, ammonia passages 31 and 32, a downstream reforming passage 33, and a cooler 34.

[0037] The reformer 25 produces a hydrogen-containing reformed gas by reforming ammonia gas using the heat generated by burning ammonia gas. The reformer 25 has a cylindrical housing 35 and a reforming catalyst 36 and an electric heater 37 housed inside the housing 35. The housing 35 is made of stainless steel or the like, which has corrosion resistance to ammonia gas.

[0038] The reforming catalyst 36 has, for example, a honeycomb structure. The reforming catalyst 36 is a catalyst that burns ammonia gas and decomposes ammonia gas into hydrogen. The reforming catalyst 36 is, for example, an ATR (Autothermal Reformer) type ammonia reforming catalyst. As the reforming catalyst 36, for example, a cobalt-based catalyst, a rhodium-based catalyst, a ruthenium-based catalyst, or a palladium-based catalyst can be used.

[0039] The electric heater 37 is located upstream of the reforming catalyst 36 within the housing 35. The electric heater 37 heats the ammonia gas and air supplied to the reforming catalyst 36, thereby heating (warming) the reforming catalyst 36 through the ammonia gas and air.

[0040] The upstream reforming passage 26 connects the intake passage 3 and the reformer 25. One end of the upstream reforming passage 26 is connected between the air cleaner 7 and the main throttle valve 5 in the intake passage 3. The other end of the upstream reforming passage 26 is connected to the inlet of the housing 35 of the reformer 25. The upstream reforming passage 26 is the passage through which the air supplied to the reformer 25 flows.

[0041] The reforming throttle valve 27 is located in the upstream reforming passage 26. The reforming throttle valve 27 is an electromagnetic second flow control valve that controls the flow rate of air supplied to the reformer 25.

[0042] Ammonia cylinder 28 is a container for storing ammonia in a liquid state. In other words, ammonia cylinder 28 stores liquid ammonia.

[0043] The vaporizer 29 is connected to the ammonia cylinder 28 via an ammonia flow path 38. The ammonia flow path 38 is a channel through which liquid ammonia stored in the ammonia cylinder 28 flows. The vaporizer 29 vaporizes the liquid ammonia to produce ammonia gas.

[0044] The reforming injector 30 is an electromagnetic second fuel injector that intermittently injects ammonia gas toward the reformer 25. The reforming injector 30 injects ammonia gas into the upstream reforming passage 26. Specifically, the reforming injector 30 injects ammonia gas between the reforming throttle valve 27 and the reformer 25 in the upstream reforming passage 26. As a result, ammonia gas also flows toward the reformer 25 in the upstream reforming passage 26. Similar to the main injector 6, the amount of ammonia gas injected by the reforming injector 30 can be adjusted by changing the time the needle valve is open.

[0045] The ammonia flow path 31 connects the vaporizer 29 to each main injector 6. The ammonia flow path 31 is a fuel flow path through which ammonia gas generated by the vaporizer 29 flows towards each main injector 6.

[0046] The ammonia flow path 32 connects the vaporizer 29 and the reforming injector 30. One end of the ammonia flow path 32 is branched off and connected to the ammonia flow path 31. The ammonia flow path 32 is a fuel flow path through which ammonia gas generated by the vaporizer 29 flows toward the reforming injector 30.

[0047] The downstream reforming passage 33 connects the reformer 25 and the intake passage 3. One end of the downstream reforming passage 33 is connected to the outlet of the housing 35 of the reformer 25. The other end of the downstream reforming passage 33 is connected between the main throttle valve 5 and the ammonia engine 2 in the intake passage 3. The downstream reforming passage 33 is the passage through which the reformed gas generated by the reformer 25 flows toward each combustion chamber 16 (inside each cylinder 10) of the ammonia engine 2.

[0048] The cooler 34 is located in the downstream reforming channel 33. The cooler 34 cools the reformed gas flowing through the downstream reforming channel 33.

[0049] The engine system 1 also includes a rotational speed sensor 40, a map memory 41, and a controller 42 (control unit).

[0050] The rotational speed sensor 40 is a sensor that detects the rotational speed (engine speed) of the ammonia engine 2. The engine speed is the number of rotations of the ammonia engine 2 per minute.

[0051] The map memory 41 is a memory unit that stores injection cycle map data representing the relationship between engine speed and the injection cycle of the modified injector 30. The injection cycle map data is acquired in advance through experiments or simulations.

[0052] The injection cycle map data is set so that the injection cycle of the reforming injector 30 is equal to the intake stroke cycle of the ammonia engine 2 (see Figures 5(a) and 5(b)). In this case, ammonia gas is injected once from the reforming injector 30 during the intake stroke of each cylinder 10 of the ammonia engine 2. In other words, ammonia gas is injected once from the reforming injector 30 during the intake period T from the start of the intake stroke of one cylinder 10 to the start of the intake stroke of the next cylinder 10.

[0053] The controller 42 consists of a CPU, RAM, ROM, and an input / output interface, etc. The controller 42 has an injection cycle determination unit 43 and a valve control unit 44. The controller 42 is executed when the ignition switch (not shown) is turned ON. The controller 42 receives control signals output from the engine ECU 8 to the ammonia engine 2.

[0054] The injection cycle determination unit 43 determines the injection cycle of ammonia gas from the reforming injector 30 based on the engine speed detected by the rotation speed sensor 40. Specifically, the injection cycle determination unit 43 determines the injection cycle corresponding to the engine speed detected by the rotation speed sensor 40 from the injection cycle map data stored in the map memory 41.

[0055] The valve control unit 44 controls the main injector 6 and the main throttle valve 5 so that a desired flow rate of ammonia gas and air is supplied to each combustion chamber 16 of the ammonia engine 2, and also controls the reforming injector 30 and the reforming throttle valve 27 so that a desired flow rate of ammonia gas and air is supplied to the reformer 25.

[0056] At this time, the valve control unit 44 controls the reforming injector 30 so that ammonia gas is injected from the reforming injector 30 at the injection cycle determined by the injection cycle determination unit 43. The valve control unit 44 controls the reforming injector 30 so that ammonia gas is injected once from the reforming injector 30 during the intake period T from when the intake stroke of cylinder 10 starts until the intake stroke of the next cylinder 10 starts, that is, during the intake period T from when the stroke in which air is drawn into cylinder 10 starts until the stroke in which air is drawn into the next cylinder 10 starts.

[0057] Furthermore, the valve control unit 44 controls the reforming injector 30 so that ammonia gas is injected from the reforming injector 30 in accordance with the timing when the airflow rate supplied to the reformer 25 increases due to intake pulsation (described later) generated from the intake pulsation (described later) caused by the airflow rate supplied to the reformer 25 from the start of the intake period T until the start of the next intake period T when air is drawn into the cylinder 10. Ideally, the injection of ammonia gas from the reforming injector 30 in accordance with the timing when the airflow rate supplied to the reformer 25 increases should be centered around the time of maximum airflow and have a width τ, but for example, it is sufficient if the injection occurs at least at the time of maximum airflow.

[0058] Figure 4 is a flowchart showing the procedure for the modified injector control process performed by the valve control unit 44.

[0059] In Figure 4, the valve control unit 44 first determines whether an open control signal has been output from the engine ECU 8 to the intake valve 19 of the ammonia engine 2 (procedure S101). The open control signal is a control signal for opening the intake valve 19.

[0060] When the valve control unit 44 determines that an open valve control signal has been output from the engine ECU 8 to the intake valve 19, it determines whether a specified time has elapsed since the open valve control signal was output (procedure S102).

[0061] The specified time is a time set in advance such that the ammonia gas injected from the reforming injector 30 is supplied to the reformer 25 at the timing when the flow rate of air supplied to the reformer 25 increases due to intake pulsation (described later). For example, the specified time is set such that the ammonia gas injected from the reforming injector 30 is supplied to the reformer 25 at the timing when the flow rate of air supplied to the reformer 25 reaches the maximum amount due to intake pulsation. The specified time is determined by experiment, simulation, or the like in consideration of the delay in the arrival time of ammonia gas caused by the distance from the reforming injector 30 to the reformer 25. Alternatively, the specified time may be a fixed ratio with respect to the intake period T, that is, n times the intake period T where 0 < n < 1.

[0062] When the valve control unit 44 determines that the specified time has elapsed after the valve opening control signal is output, the valve control unit 44 controls the reforming injector 30 such that ammonia gas is injected from the reforming injector 30 (step S103).

[0063] In the engine system 1 configured as described above, when an ignition switch (not shown) of the vehicle is turned ON, a starter (not shown) is turned ON, and thereby the ammonia engine 2 is cranked. Then, the reforming injector 30, the reforming throttle valve 27, the main injector 6, and the main throttle valve 5 are opened. As a result, ammonia gas and air are supplied to the reformer 25 and the ammonia engine 2.

[0064] When ammonia gas and air are supplied to the reformer 25, the ammonia gas and air are heated by the electric heater 37. Accordingly, the reforming catalyst 36 is heated by the heat of the ammonia gas and air, so that the temperature of the reforming catalyst 36 rises. When the temperature of the reforming catalyst 36 reaches an activation temperature (combustible temperature), the ammonia gas is combusted by the reforming catalyst 36. Specifically, as shown in the following formula, ammonia and oxygen in the air chemically react (exothermic reaction). NH3+3 / 4O2→1 / 2N2+3 / 2H2O+Q1 (exothermic) …(A)

[0065] Then, the heat of combustion of the ammonia gas (the self-heat of the reforming catalyst 36) further increases the temperature of the reforming catalyst 36. When the temperature of the reforming catalyst 36 reaches the reaction temperature (reformable temperature), the ammonia gas is reformed by the reforming catalyst 36. Specifically, as shown in the equation below, a decomposition reaction of ammonia occurs (endothermic reaction), and a reformed gas containing hydrogen is produced. NH3→3 / 2H2+1 / 2N2-Q2 (endothermic) …(B)

[0066] The reformed gas flows through the downstream reforming passage 33 and the intake passage 3 and is supplied to the ammonia engine 2. Then, in the ammonia engine 2, it transitions to a steady state in which the ammonia gas burns together with the hydrogen in the reformed gas.

[0067] Here, during the intake stroke of the ammonia engine 2, as shown in Figure 5(a), intake pulsation occurs due to the up-and-down movement of the piston 11 in the ammonia engine 2, causing fluctuations in the gas pressure and gas flow rate in the reformer 25. Specifically, as the piston 11 descends, negative pressure is generated in the combustion chamber 16 of the ammonia engine 2, and air is drawn into the combustion chamber 16. At this time, the negative pressure in the combustion chamber 16 is propagated to the reformer 25 through the intake passage 3 and the downstream reforming passage 33. Therefore, immediately after the start of the intake stroke, the flow rate of air supplied to the reformer 25 increases.

[0068] Therefore, as shown in Figure 5(b), during the intake period T from the start of the intake stroke of cylinder 10 to the start of the intake stroke of the next cylinder 10, ammonia gas is injected from the reforming injector 30 in accordance with the timing when the flow rate of air supplied to the reformer 25 increases due to intake pulsation. The controller 42 can determine the start of the intake period T by the operation of the intake valve 19 (i.e., the valve opening control signal) and can determine the length of the intake period T in accordance with the engine speed (i.e., by the injection cycle map data). The controller 42 can then determine the timing when the flow rate of air supplied to the reformer 25 increases due to intake pulsation from the start of the intake period T and the specified time mentioned above.

[0069] By the way, as shown in Figures 6(a) and (b), if ammonia gas is injected from the reforming injector 30 at a timing when the flow rate of air supplied to the reformer 25 is relatively low (in the middle of the intake period T in Figure 6) during the intake period T from the start of the intake stroke of cylinder 10 to the start of the intake stroke of the next cylinder 10, the following problems occur.

[0070] In other words, if ammonia gas is injected from the reforming injector 30 at a time when the airflow rate supplied to the reformer 25 is low, the air-fuel ratio (A / F) in the reformer 25 will not be uniform over time, as shown in Figure 6(c), resulting in an uneven air-fuel ratio D. The air-fuel ratio is the flow rate ratio of ammonia gas to air. Due to this uneven air-fuel ratio D, the reaction of the reforming catalyst 36 in the reformer 25 will also not be uniform over time. If the airflow rate is excessively high compared to the ammonia gas flow rate immediately after the start of the intake stroke, a temporary overheating of the reformer 25 will occur, causing the reforming catalyst 36 in the reformer 25 to deteriorate.

[0071] On the other hand, in this embodiment, as shown in Figures 5(a) and (b), during the intake period T from the start of the intake stroke of cylinder 10 to the start of the intake stroke of the next cylinder 10, ammonia gas is injected from the reforming injector 30 in accordance with the timing when the flow rate of air supplied to the reformer 25 increases due to intake pulsation. In this case, as shown in Figure 5(c), the temporal unevenness D of the air-fuel ratio in the reformer 25 is smaller compared to the comparative example shown in Figure 6.

[0072] As described above, according to this embodiment, when ammonia gas and air are supplied to the reformer 25, a reformed gas containing hydrogen is generated in the reformer 25, and the reformed gas is supplied into the cylinder 10 of the ammonia engine 2. Furthermore, when ammonia gas and air are supplied into the cylinder 10 of the ammonia engine 2, the ammonia gas mixes with hydrogen and burns in the cylinder 10. In the ammonia engine 2, for each of the multiple cylinders 10, multiple strokes are performed sequentially, including a stroke in which air is drawn into the cylinder 10. At this time, during the intake period T from the start of the stroke in which air is drawn into the cylinder 10 to the start of the stroke in which air is drawn into the next cylinder 10, ammonia gas is injected from the reforming injector 30 in accordance with the timing when the flow rate of air supplied to the reformer 25 increases due to intake pulsation caused by the stroke in which air is drawn into the cylinder 10 from the start of the intake period T. For this reason, even if the flow rate of air supplied to the reformer 25 fluctuates due to intake pulsation in the reformer 25, the temporal unevenness of the air-fuel ratio in the reformer 25 is reduced. This prevents the reformer 25 from overheating, thereby suppressing the deterioration of the reforming catalyst 36 in the reformer 25. As a result, the durability of the reforming catalyst 36 is improved.

[0073] Figure 7 is a schematic diagram showing an engine system according to a second embodiment of the present invention. In Figure 7, the engine system 1A of this embodiment includes an intake pressure sensor 61 and a map memory 62 in addition to the configuration of the first embodiment described above.

[0074] The intake pressure sensor 61 is an intake pressure detection unit that detects the intake pressure into the cylinder 10 of the ammonia engine 2. The intake pressure sensor 61 detects the pressure between the main throttle valve 5 and the ammonia engine 2 in the intake passage 3 as the intake pressure.

[0075] The map memory 62 is a storage unit that stores injection timing map data representing the relationship between the intake pressure into the cylinder 10 and the injection timing of ammonia gas from the reforming injector 30. The injection timing map data is set such that, when the intake pressure into the cylinder 10 is negative, the injection timing becomes progressively or continuously earlier as the intake pressure decreases (the negative pressure increases). The injection timing map data is acquired in advance through experiments or simulations.

[0076] Furthermore, the engine system 1A includes a controller 42A instead of the controller 42 in the first embodiment described above. The controller 42A includes the injection cycle determination unit 43 and the valve control unit 44A.

[0077] Similar to the first embodiment described above, the valve control unit 44A controls the reforming injector 30 so that ammonia gas is injected from the reforming injector 30 in accordance with the timing at which the flow rate of air supplied to the reformer 25 increases due to intake pulsations generated from the intake pulsations caused by the intake pulsations resulting from the intake pulsations from the start of the intake period T until the start of the next intake period T in which air is drawn into the cylinder 10.

[0078] At this time, the valve control unit 44A determines the timing at which the airflow rate supplied to the reformer 25 increases due to intake pulsation, based on the intake pressure detected by the intake pressure sensor 61 and the injection timing map data, and controls the reforming injector 30 so that ammonia gas is injected from the reforming injector 30 according to that timing.

[0079] Figure 8 is a flowchart showing the procedure for the reforming injector control process performed by the valve control unit 44A, and corresponds to Figure 4.

[0080] In Figure 8, the valve control unit 44A first executes the above procedure S101, and when it determines that an open control signal has been output from the engine ECU 8 to the intake valve 19, it acquires the detected value of the intake pressure sensor 61 (procedure S111).

[0081] Then, the valve control unit 44A uses the injection timing map data stored in the map memory 62 to determine the injection timing according to the intake pressure into the cylinder 10 (procedure S112). Subsequently, the valve control unit 44A controls the reforming injector 30 so that ammonia gas is injected from the reforming injector 30 at the determined injection timing (procedure S113).

[0082] As described above, during the intake stroke of the ammonia engine 2, the higher the negative pressure inside the cylinder 10, the easier it is for air to be drawn into the cylinder 10, and the more quickly air is drawn into the cylinder 10.

[0083] Therefore, in this embodiment, based on the intake pressure into the cylinder 10 of the ammonia engine 2, the timing at which the airflow rate supplied to the reformer 25 increases due to intake pulsation is determined, and ammonia gas is injected from the reforming injector 30 according to that timing. As a result, during the intake period T from the start of one stroke in which air is drawn into the cylinder 10 to the start of the next stroke in which air is drawn into the cylinder 10, ammonia gas is injected from the reforming injector 30 at an appropriate timing corresponding to the intake pressure into the cylinder 10. This further reduces the temporal unevenness of the air-fuel ratio in the reformer 25. Consequently, overheating of the reformer 25 is further suppressed, and the deterioration of the reforming catalyst 36 in the reformer 25 is further suppressed.

[0084] In this embodiment, the injection timing corresponding to the intake pressure inside the cylinder 10 is determined using injection timing map data stored in the map memory 62, but the system is not limited to this configuration. For example, the injection timing corresponding to the intake pressure may be calculated by calculating the time difference, etc., based on the intake pressure inside the cylinder 10 detected by the intake pressure sensor 61.

[0085] Figure 9 is a schematic diagram showing an engine system according to a third embodiment of the present invention. In Figure 9, the engine system 1B of this embodiment includes an accelerator sensor 65 and a map memory 66 in addition to the configuration of the first embodiment described above.

[0086] The accelerator sensor 65 detects the opening degree of the accelerator (not shown) as the engine load. The rotation speed sensor 40 and the accelerator sensor 65 described above constitute an engine state detection unit that detects the state of the ammonia engine 2.

[0087] The map memory 66 is a storage unit that stores injection timing map data representing the relationship between engine speed, engine load, and the injection timing of the modified injector 30. The injection timing map data is set so that the injection timing of the modified injector 30 becomes progressively or continuously earlier as the intake airflow velocity increases with increasing engine speed. The injection timing map data is also set so that the injection timing of the modified injector 30 becomes progressively or continuously earlier as the intake airflow velocity increases with increasing engine load. The injection timing map data is acquired in advance through experiments or simulations.

[0088] Furthermore, the engine system 1B includes a controller 42B instead of the controller 42 in the first embodiment described above. The controller 42B includes the injection cycle determination unit 43 and the valve control unit 44B.

[0089] Similar to the first embodiment described above, the valve control unit 44B controls the reforming injector 30 so that ammonia gas is injected from the reforming injector 30 in accordance with the timing at which the flow rate of air supplied to the reformer 25 increases due to intake pulsations generated from the intake pulsations caused by the intake pulsations resulting from the intake pulsations from the start of the intake period T until the start of the next intake period T in which air is drawn into the cylinder 10.

[0090] At this time, the valve control unit 44B determines the timing at which the airflow rate supplied to the reformer 25 increases due to intake pulsation, based on the engine speed detected by the rotation speed sensor 40, the engine load detected by the accelerator sensor 65, and the injection timing map data, and controls the reforming injector 30 so that ammonia gas is injected from the reforming injector 30 according to that timing.

[0091] Figure 10 is a flowchart showing the procedure for the reforming injector control process performed by the valve control unit 44B, and corresponds to Figure 4.

[0092] In Figure 10, the valve control unit 44B first executes the above procedure S101, and when it determines that an open control signal has been output from the engine ECU 8 to the intake valve 19, it acquires the detected values ​​of the rotational speed sensor 40 and the accelerator sensor 65 (procedure S121).

[0093] Then, the valve control unit 44B uses the injection timing map data stored in the map memory 66 to determine the injection timing according to the engine speed and engine load (procedure S122). Subsequently, the valve control unit 44B controls the reforming injector 30 so that ammonia gas is injected from the reforming injector 30 at the determined injection timing (procedure S123).

[0094] As mentioned above, the higher the negative pressure inside cylinder 10, the easier it is for air to be drawn into cylinder 10, and the faster the air is drawn into cylinder 10. However, the negative pressure inside cylinder 10 changes depending on the state of the ammonia engine 2.

[0095] Therefore, in this embodiment, based on the state of the ammonia engine 2, the timing at which the airflow rate supplied to the reformer 25 increases due to intake pulsation is determined, and ammonia gas is injected from the reforming injector 30 according to that timing, so that ammonia gas is injected from the reforming injector 30 at an appropriate timing according to the state of the ammonia engine 2. As a result, temporal fluctuations in the air-fuel ratio in the reformer 25 are further reduced. Consequently, overheating of the reformer 25 is further suppressed, and the deterioration of the reforming catalyst 36 in the reformer 25 is further suppressed.

[0096] Furthermore, in this embodiment, the engine speed and engine load are detected as the state of the ammonia engine 2, and ammonia gas is injected from the reforming injector 30 at an appropriate timing corresponding to the engine speed and engine load.

[0097] In this embodiment, the injection timing according to the engine speed and engine load is determined using injection timing map data stored in the map memory 66, but the embodiment is not limited to this. For example, the injection timing according to the engine speed and engine load may be calculated based on the engine speed detected by the rotation speed sensor 40 and the engine load detected by the accelerator sensor 65.

[0098] Furthermore, in this embodiment, the timing at which the airflow rate supplied to the reformer 25 increases due to intake pulsation is determined based on both engine speed and engine load, but the embodiment is not limited to this configuration. The timing at which the airflow rate supplied to the reformer 25 increases due to intake pulsation may be determined based only on the engine speed detected by the speed sensor 40, or the timing at which the airflow rate supplied to the reformer 25 increases due to intake pulsation may be determined based only on the engine load detected by the accelerator sensor 65.

[0099] Figure 11 is a schematic diagram showing an engine system according to a fourth embodiment of the present invention. In Figure 11, the engine system 1C of this embodiment includes an upstream pressure sensor 51 and a downstream pressure sensor 52 in addition to the configuration of the first embodiment described above.

[0100] The upstream pressure sensor 51 is a first pressure detection unit that detects the pressure in the ammonia flow path 32 as the upstream pressure of the reforming injector 30. The downstream pressure sensor 52 is a second pressure detection unit that detects the pressure in the upstream reforming flow path 26 as the downstream pressure of the reforming injector 30. The downstream pressure sensor 52 detects the pressure between the reforming injector 30 and the reformer 25 in the upstream reforming flow path 26.

[0101] Furthermore, the engine system 1C includes a controller 42C instead of the controller 42 in the first embodiment described above. The controller 42C includes the injection cycle determination unit 43, the injection time determination unit 45, and the valve control unit 44C.

[0102] The injection time determination unit 45 determines the injection time τ (see Figure 5) of ammonia gas from the reforming injector 30 based on the upstream pressure of the reforming injector 30 detected by the upstream pressure sensor 51 and the downstream pressure of the reforming injector 30 detected by the downstream pressure sensor 52.

[0103] Figure 12 is a flowchart showing the procedure for the injection time determination process performed by the injection time determination unit 45. In Figure 12, the injection time determination unit 45 first acquires the detected values ​​of the upstream pressure sensor 51 and the downstream pressure sensor 52 (procedure S131).

[0104] Next, the injection time determination unit 45 calculates the pressure difference between the upstream pressure of the reforming injector 30 and the downstream pressure of the reforming injector 30 (procedure S132). Then, the injection time determination unit 45 determines whether the pressure difference between the upstream pressure of the reforming injector 30 and the downstream pressure of the reforming injector 30 is greater than or equal to a pressure threshold (procedure S133). The pressure threshold is a predetermined value.

[0105] The injection time determination unit 45 determines that the pressure difference between the upstream pressure and the downstream pressure of the reforming injector 30 is greater than or equal to a pressure threshold, and selects a short injection time as the injection time τ (procedure S134). The short injection time is a predetermined time.

[0106] The injection time determination unit 45 selects a long injection time as the injection time τ when it determines that the pressure difference between the upstream pressure and the downstream pressure of the reforming injector 30 is not equal to or greater than a pressure threshold (procedure S135). The long injection time is a predetermined time and is longer than the short injection time.

[0107] Returning to Figure 11, the valve control unit 44C, similar to the first embodiment described above, controls the reforming injector 30 so that ammonia gas is injected from the reforming injector 30 in accordance with the timing when the flow rate of air supplied to the reformer 25 increases due to intake pulsations generated as a result of the stroke in which air is drawn into the cylinder 10, during the intake period T from the start of the intake stroke of cylinder 10 to the start of the intake stroke of the next cylinder 10.

[0108] At this time, the valve control unit 44C controls the reforming injector 30 so that ammonia gas is injected from the reforming injector 30 for an injection time τ determined by the injection time determination unit 45, at an injection cycle determined by the injection cycle determination unit 43. In other words, when the pressure difference between the upstream pressure and the downstream pressure of the reforming injector 30 is greater than or equal to the pressure threshold, the valve control unit 44C controls the reforming injector 30 so that the injection time τ of ammonia gas is shorter compared to when the pressure difference between the upstream pressure and the downstream pressure of the reforming injector 30 is lower than the pressure threshold.

[0109] When the injection time τ is constant, the amount of ammonia gas injected from the reforming injector 30 varies depending on the upstream and downstream pressures of the reforming injector 30. Specifically, the larger the pressure difference between the upstream pressure and the downstream pressure of the reforming injector 30, the greater the amount of ammonia gas injected from the reforming injector 30.

[0110] Therefore, in this embodiment, when the pressure difference between the upstream pressure and the downstream pressure of the reforming injector 30 is greater than or equal to the pressure threshold, the injection time of ammonia gas from the reforming injector 30 is shortened compared to when the pressure difference between the upstream pressure and the downstream pressure of the reforming injector 30 is lower than the pressure threshold. This causes the amount of ammonia gas injected from the reforming injector 30 to become closer to a constant, regardless of the upstream and downstream pressures of the reforming injector 30. Consequently, ammonia gas is appropriately injected from the reforming injector 30 depending on the state of the ammonia engine 2, such as immediately after starting the ammonia engine 2.

[0111] In this embodiment, either a long injection time or a short injection time is selected as the ammonia gas injection time τ from the reforming injector 30, but the embodiment is not limited to this configuration. For example, as the pressure difference between the upstream pressure and the downstream pressure of the reforming injector 30 increases, the ammonia gas injection time τ may be shortened in stages or continuously. In this case as well, when the pressure difference between the upstream pressure and the downstream pressure of the reforming injector 30 is greater than or equal to a predetermined value, the ammonia gas injection time τ will be shorter than when the pressure difference between the upstream pressure and the downstream pressure of the reforming injector 30 is lower than the predetermined value.

[0112] Figure 13 is a schematic diagram showing an engine system according to a fifth embodiment of the present invention. In Figure 13, the engine system 1D of this embodiment includes a temperature sensor 55 in addition to the configuration of the first embodiment described above. The temperature sensor 55 is a temperature detection unit that detects the ambient temperature. The ambient temperature corresponds to the outside temperature.

[0113] Furthermore, the engine system 1D includes a controller 42D instead of the controller 42 in the first embodiment described above. The controller 42D includes the injection cycle determination unit 43, the injection time determination unit 46, and the valve control unit 44D.

[0114] The injection time determination unit 46 determines the injection time τ (see Figure 5) of ammonia gas from the reforming injector 30 based on the ambient temperature detected by the temperature sensor 55.

[0115] Figure 14 is a flowchart showing the procedure for the injection time determination process performed by the injection time determination unit 46. In Figure 14, the injection time determination unit 46 first acquires the detected value from the temperature sensor 55 (procedure S141). Next, the injection time determination unit 46 determines whether the ambient temperature is above a temperature threshold (procedure S142). The temperature threshold is a predetermined value.

[0116] The injection time determination unit 46 selects a short injection time as the injection time τ when it determines that the ambient temperature is above a temperature threshold (procedure S143). The short injection time is a predetermined time.

[0117] The injection time determination unit 46 selects a long injection time as the injection time τ when it determines that the ambient temperature is not above the temperature threshold (procedure S144). The long injection time is a predetermined time and is longer than the short injection time.

[0118] Returning to Figure 13, the valve control unit 44D, similar to the first embodiment described above, controls the reforming injector 30 so that ammonia gas is injected from the reforming injector 30 in accordance with the timing when the flow rate of air supplied to the reformer 25 increases due to intake pulsations generated as a result of the stroke in which air is drawn into the cylinder 10, during the intake period T from the start of the intake stroke of cylinder 10 to the start of the intake stroke of the next cylinder 10.

[0119] At this time, the valve control unit 44D controls the reforming injector 30 so that ammonia gas is injected from the reforming injector 30 for an injection time τ determined by the injection time determination unit 46, at an injection cycle determined by the injection cycle determination unit 43. In other words, when the ambient temperature is above the temperature threshold, the valve control unit 44C controls the reforming injector 30 so that the injection time τ of ammonia gas is shorter than when the ambient temperature is below the temperature threshold.

[0120] When the injection time τ is constant, the amount of ammonia gas injected from the reforming injector 30 changes depending on the pressure in the ammonia flow path 32. The higher the pressure in the ammonia flow path 32, the greater the amount of ammonia gas injected from the reforming injector 30. The pressure in the ammonia flow path 32 changes depending on the vaporization capacity of the vaporizer 29. Specifically, the vaporization capacity of the vaporizer 29 changes with the ambient temperature. The higher the ambient temperature, the higher the vaporization capacity of the vaporizer 29, and therefore the higher the pressure in the ammonia flow path 32.

[0121] Therefore, in this embodiment, when the ambient temperature is above the temperature threshold, the injection time of ammonia gas from the reforming injector 30 is shortened compared to when the ambient temperature is below the temperature threshold. This makes the amount of ammonia gas injected from the reforming injector 30 approach a constant regardless of the ambient temperature. Consequently, ammonia gas is appropriately injected from the reforming injector 30 depending on the state of the ammonia engine 2, such as immediately after starting the ammonia engine 2, or in a high-temperature or low-temperature environment.

[0122] Figure 15 is a schematic diagram showing a modified example of the engine system according to the fifth embodiment of the present invention. In Figure 15, the engine system 1D of this embodiment is equipped with a temperature sensor 56 instead of the temperature sensor 55 in the fifth embodiment described above. The temperature sensor 56 is a temperature detection unit that detects the temperature of the cooling water used to cool the ammonia engine 2.

[0123] A circulation passage 57 through which cooling water flows is connected to the ammonia engine 2 and the vaporizer 29. The circulation passage 57 may also be connected to the cooler 24. A pump 58 is installed in the circulation passage 57. The pump 58 circulates the cooling water in one direction in the circulation passage 57. The vaporizer 29 vaporizes liquid ammonia by performing heat exchange using the cooling water heated by the ammonia engine 2.

[0124] The vaporization capacity of the vaporizer 29 also changes with the temperature of the coolant. Specifically, immediately after starting the ammonia engine 2, the vaporization capacity of the vaporizer 29 is low because the temperature of the coolant is low. Consequently, the pressure in the ammonia passage 32 (upstream pressure of the reforming injector 30) is low. Subsequently, as the temperature of the coolant rises, the vaporization capacity of the vaporizer 29 increases, and the pressure in the ammonia passage 32 rises.

[0125] Therefore, in this modified example, when the temperature of the coolant used to cool the ammonia engine 2 is above the temperature threshold, the injection time of ammonia gas from the reforming injector 30 is shortened compared to when the temperature of the coolant is below the temperature threshold. This makes the amount of ammonia gas injected from the reforming injector 30 approach a constant regardless of the temperature of the coolant.

[0126] In this embodiment and its modified examples, either a long injection time or a short injection time is selected as the ammonia gas injection time τ from the reforming injector 30, but the embodiment is not limited to such configurations. For example, the ammonia gas injection time τ may be shortened in stages or continuously as the ambient temperature or cooling water temperature increases. In this case as well, when the ambient temperature or cooling water temperature is above a predetermined value, the ammonia gas injection time τ will be shorter than when the ambient temperature or cooling water temperature is below a predetermined value.

[0127] Although several embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, in the above embodiments, it is determined whether the timing is such that the flow rate of air supplied to the reformer 25 increases due to intake pulsations generated due to the intake stroke of the ammonia engine 2, based on the valve opening control signal output from the engine ECU 8 to the intake valve 19 of the ammonia engine 2, but the invention is not limited to such an embodiment. For example, an airflow meter for detecting the flow rate of air flowing through the intake passage 3 may be installed downstream of the air cleaner 7 in the intake passage 3, and it may be determined whether the timing is such that the flow rate of air supplied to the reformer 25 increases due to intake pulsations generated due to the intake stroke of the ammonia engine 2, based on the detected value of the airflow meter.

[0128] Alternatively, instead of using the valve opening control signal from the engine ECU 8 and the detected value from the airflow meter, it may be determined, for example, based on the detected value from the intake pressure sensor 61 as in the second embodiment described above, whether the timing is such that the flow rate of air supplied to the reformer 25 increases due to intake pulsations generated during the intake stroke of the ammonia engine 2.

[0129] Furthermore, in the above embodiment, the reformer 25 has a reforming catalyst 36 that has both the function of burning ammonia gas and the function of decomposing ammonia gas into hydrogen, but it is not limited to such a configuration. The reformer 25 may have a combustion catalyst for burning ammonia gas and a reforming catalyst for decomposing ammonia gas into hydrogen separately.

[0130] Furthermore, in the above embodiment, the reformer 25 is supplied with air through the intake passage 3, where the air cleaner 7 is located, and the upstream reforming passage 26, but it is not limited to this configuration. The reformer 25 may also be supplied with ambient air directly through an air cleaner different from the air cleaner 7.

[0131] Furthermore, although the ammonia engine 2 in the above embodiment is a four-cylinder engine, the ammonia engine 2 is not particularly limited to that, and any multi-cylinder engine having multiple sets of cylinders 10 and pistons 11 is acceptable.

[0132] Furthermore, in the above embodiment, the ammonia engine 2 is a four-stroke engine, but the ammonia engine 2 is not limited to that and may be a two-stroke engine or the like. In a two-stroke ammonia engine 2, one cycle consists of two strokes: an intake / compression stroke and a combustion / exhaust stroke. In this case, air is drawn into the cylinder 10 during the intake / compression stroke.

[0133] Furthermore, in the above embodiment, the reforming throttle valve 27 is located in the upstream reforming passage 26, but it is not limited to this, and the reforming throttle valve 27 may also be located in the downstream reforming passage 33.

[0134] Furthermore, although ammonia gas is used as fuel in the above embodiment, the present invention is also applicable to engine systems that use hydrocarbons or the like as fuel. [Explanation of Symbols]

[0135] 1, 1A, 1B, 1C, 1D…Engine system, 2…Ammonia engine (engine), 3…Intake passage, 5…Main throttle valve (first flow control valve), 6…Main injector (first fuel injection valve), 10…Cylinder, 10A, 10B, 10C, 10D…Cylinder, 11…Piston, 25…Reformer, 26…Upstream reforming passage, 27…Reforming throttle valve (second flow control valve), 29…Carburetor, 30…Reforming injector (second fuel injection valve), 31, 32…Ammonia flow Fuel passage, 33... Downstream reforming passage, 36... Reforming catalyst (catalyst), 40... Rotation speed sensor (engine state detection unit), 42, 42A, 42B, 42C, 42D... Controller (control unit), 51... Upstream pressure sensor (first pressure detection unit), 52... Downstream pressure sensor (second pressure detection unit), 55... Temperature sensor (temperature detection unit), 56... Temperature sensor (temperature detection unit), 61... Intake pressure sensor (intake pressure detection unit), 65... Accelerator sensor (engine state detection unit), T... Intake period, τ... Injection time.

Claims

1. An engine having multiple cylinders and multiple pistons arranged within the cylinders, in which fuel is burned together with hydrogen, An intake passage through which air supplied into the cylinder flows, A first flow control valve is disposed in the intake passage and controls the flow rate of air supplied into the cylinder, A first fuel injection valve intermittently injects fuel into the cylinder, A reformer having a catalyst for decomposing the fuel into hydrogen, and reforming the fuel to produce a reformed gas containing hydrogen, The upstream reforming channel through which the air supplied to the reformer flows, A downstream reforming channel through which the reformed gas generated by the reformer flows toward the cylinder, A second flow control valve is provided in the upstream reforming channel or the downstream reforming channel to control the flow rate of air supplied to the reformer, A second fuel injection valve intermittently injects fuel toward the reformer, The system comprises 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, The engine sequentially performs a plurality of strokes, each of the plurality of cylinders, which includes a stroke in which air is drawn into the cylinder. The control unit controls the second fuel injector during the intake period from the start of a stroke in which air is drawn into the cylinder to the start of the next stroke in which air is drawn into the cylinder, so that fuel is injected from the second fuel injector in accordance with the timing at which the flow rate of air supplied to the reformer increases due to intake pulsations generated from the stroke in which air is drawn into the cylinder from the start of the intake period.

2. The system further includes an intake pressure detection unit for detecting the intake pressure into the cylinder, The engine system according to claim 1, wherein the control unit determines the timing based on the intake pressure detected by the intake pressure detection unit and controls the second fuel injector so that fuel is injected from the second fuel injector according to that timing.

3. The engine further comprises an engine state detection unit for detecting the state of the engine, The engine system according to claim 1, wherein the control unit determines the timing based on the engine state detected by the engine state detection unit, and controls the second fuel injector so that fuel is injected from the second fuel injector according to that timing.

4. The engine state detection unit detects at least one of the engine speed and load as the engine state, The engine system according to claim 3, wherein the control unit determines the timing based on at least one of the engine speed and load.

5. A vaporizer that vaporizes liquid fuel, A fuel passage through which the fuel vaporized by the carburetor flows toward the first fuel injector and the second fuel injector, A first pressure detection unit detects the pressure in the fuel passage as the upstream pressure of the second fuel injection valve, The system further includes a second pressure detection unit that detects the pressure in the upstream reforming channel as the downstream pressure of the second fuel injection valve, The engine system according to claim 1, wherein the control unit controls the second fuel injector such that when the pressure difference between the upstream pressure of the second fuel injector and the downstream pressure of the second fuel injector is greater than or equal to a predetermined value, the fuel injection time from the second fuel injector is shorter than when the pressure difference between the upstream pressure of the second fuel injector and the downstream pressure of the second fuel injector is lower than the predetermined value.

6. A vaporizer that vaporizes liquid fuel, A fuel passage through which the fuel vaporized by the carburetor flows toward the first fuel injector and the second fuel injector, The system further includes a temperature detection unit that detects the ambient temperature or the temperature of the coolant used to cool the engine, The engine system according to claim 1, wherein the control unit controls the second fuel injector so that when the ambient temperature or the coolant temperature is above a predetermined value, the fuel injection time from the second fuel injector is shorter than when the ambient temperature or the coolant temperature is below the predetermined value.

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