Engine System

Abstract

To provide an engine system which can accurately detect whether or not the modification performance of a catalyst of a reformer is deteriorated more than necessary.SOLUTION: An engine system 1 comprises: a reformer 23 having a reforming catalyst 33 for resolving an ammonia gas into hydrogen, and generating a reformed gas containing the hydrogen by reforming the ammonia gas; a temperature sensor 38 for detecting a temperature of a reformed gas flowing in a reformed gas flow passage 27; a rotation variation detector 40 for detecting a rotation variation amount of an ammonia engine 2; and a deterioration detection part 51 for detecting whether or not the reformation performance of the reforming catalyst 33 of the reformer 23 is deteriorated on the basis of detection values of the temperature sensor 38 and the rotation variation detector 40. When the rotation variation amount of the ammonia engine 2 is equal to or larger than a threshold B in a state that the temperature of the reformed gas is equal to or higher than a threshold A in an idling period of the ammonia engine 2, the deterioration detection part 51 determines that the reformation performance of the reforming catalyst 33 is deteriorated.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, a technology as described in Patent Document 1 is known. The engine system described in Patent Document 1 includes an engine body, an intake branch pipe connected to the intake port of each cylinder of the engine body, an ammonia injector that injects ammonia toward each engine intake passage of the engine body, a hydrogen generating device that generates hydrogen from liquid ammonia, and a hydrogen injector that injects hydrogen toward each engine intake passage of the engine body. The hydrogen generating device includes a tank in which liquid ammonia is stored, an evaporator that heats and vaporizes the liquid ammonia, a supply pipe through which a portion of the gaseous ammonia generated by the evaporator flows toward the ammonia injector, a cracker that decomposes the gaseous ammonia generated by the evaporator, an inlet pipe through which air supplied to the cracker flows, a supply pipe through which hydrogen generated by the cracker flows toward the hydrogen injector, and an electric heater that heats a catalyst in the cracker.

[0003] Patent Document 2 also describes a hydrogen utilization system. The hydrogen utilization system includes a reformer that reforms ammonia gas to generate a reformed gas containing hydrogen, a reformed gas flow path through which the reformed gas generated by the reformer flows, a temperature sensor that detects the temperature of the reformed gas flowing through the reformed gas flow path, and a deterioration detection unit that detects deterioration of the reformer using the detection value of the temperature sensor. The reformer has a combustion catalyst that burns ammonia and a reforming catalyst that decomposes ammonia into hydrogen. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-211155 A [Patent Document 2] Patent Publication No. 2021-38121 Summary of the Invention [Problem to be solved by the invention]

[0005] The reforming catalyst used in the reformer deteriorates in reforming performance due to thermal deterioration, etc. For example, when the engine is always operated under the same conditions during idling, if the reforming performance of the reforming catalyst deteriorates, the amount of hydrogen generated by the reformer decreases, and the ratio of hydrogen supplied to the engine and the total gas amount (total amount of ammonia and hydrogen) decrease. This may cause misfires, which may cause the engine rotation to become unstable or the engine's exhaust characteristics to change. Therefore, depending on the deterioration of the reforming performance of the reforming catalyst, it may be necessary to replace the reforming catalyst. In the above-mentioned Patent Document 2, the deterioration of the reformer is detected using the temperature of the reformed gas. However, even if the temperature of the reformed gas is high, it is not possible to know whether the reforming performance of the reforming catalyst has deteriorated to the extent that replacement of the reforming catalyst is necessary.

[0006] An object of the present invention is to provide an engine system that can detect with high accuracy whether the reforming performance of a catalyst in a reformer has deteriorated more than necessary. [Means for solving the problem]

[0007] 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, an exhaust passage through which exhaust gas generated by the engine flows, a first flow control valve disposed in the intake passage and controlling the flow rate of the air supplied to the engine, a first fuel supply valve that supplies fuel to the engine, a reformer having a catalyst that decomposes fuel into hydrogen and that reforms the fuel to generate a reformed gas containing hydrogen, an air flow path through which air supplied to the reformer flows, a second flow control valve disposed in the air flow path and controlling the flow rate of the air supplied to the reformer, and the reformer includes a second fuel supply valve that supplies fuel, a reformed gas flow path through which the reformed gas generated by the reformer flows toward the engine, a temperature detection unit that detects the temperature of the reformed gas flowing through the reformed gas flow path, a rotational fluctuation detection unit that detects an amount of rotational fluctuation of the engine, and a deterioration detection unit that detects whether the reforming performance of the catalyst of the reformer has deteriorated based on the detection values ​​of the temperature detection unit and the rotational fluctuation detection unit, and the deterioration detection unit determines that the reforming performance of the catalyst has deteriorated when the temperature of the reformed gas is equal to or higher than a first threshold value and the amount of rotational fluctuation of the engine is equal to or higher than a second threshold value during an idle period of the engine.

[0008] In such an engine system, when fuel and air are supplied to the reformer, the catalyst in the reformer reforms the fuel, generating a reformed gas containing hydrogen, and the reformed gas flows through a reformed gas passage and is supplied to the engine. Then, when fuel and air are supplied to the engine, the fuel is mixed with hydrogen and burned in the engine. Here, if the reforming performance of the catalyst is deteriorated, the temperature of the reformed gas rises compared to normal. Also, if the reforming performance of the catalyst is deteriorated, the combustion of the fuel in the engine becomes unstable, and the rotation fluctuation amount of the engine increases compared to normal. Therefore, the temperature of the reformed gas and the rotation fluctuation amount of the engine are detected, and whether or not the reforming performance of the catalyst is deteriorated is detected based on the temperature of the reformed gas and the rotation fluctuation amount of the engine. Specifically, during an idle period of the engine, when the temperature of the reformed gas is equal to or higher than a first threshold value and the rotation fluctuation amount of the engine is equal to or higher than a second threshold value, it is determined that the reforming performance of the catalyst is deteriorated. In this way, by using not only the reformed gas temperature but also the engine rotation fluctuation amount to detect deterioration of the reforming performance of the catalyst, it is possible to detect with high accuracy whether the reforming performance of the catalyst has deteriorated more than necessary.

[0009] The deterioration detection unit may determine that the reforming performance of the catalyst has deteriorated when, during a first idle period at engine start-up, the temperature of the reformed gas is equal to or higher than a first threshold and the engine rotation fluctuation amount is equal to or higher than a second threshold.

[0010] During the first idle period at engine start-up, fuel and air are supplied to the reformer under the same stable conditions, so that it is possible to detect with even greater accuracy whether the reforming performance of the catalyst has deteriorated more than necessary.

[0011] The engine system may further include an oxygen detection unit that detects the concentration of residual oxygen contained in the reformed gas flowing through the reformed gas flow passage, and the deterioration detection unit may determine that the reforming performance of the catalyst has deteriorated when, during an idle period of the engine, the temperature of the reformed gas is equal to or higher than a first threshold value, the concentration of residual oxygen contained in the reformed gas is equal to or higher than a third threshold value, and the engine rotation fluctuation amount is equal to or higher than a second threshold value.

[0012] When the reforming performance of the reformer catalyst deteriorates, the amount of hydrogen generated by the reformer decreases, and the concentration of residual oxygen contained in the reformed gas becomes higher than normal. Therefore, by using the concentration of residual oxygen contained in the reformed gas in addition to the reformed gas temperature and engine rotation fluctuation amount to detect deterioration of the reforming performance of the catalyst, it is possible to detect with even greater accuracy whether the reforming performance of the catalyst has deteriorated more than necessary.

[0013] The engine system may further include a hydrogen detection unit that detects the concentration of hydrogen contained in the reformed gas flowing through the reformed gas flow path, and the deterioration detection unit may determine that the reforming performance of the catalyst has deteriorated when, during an idle period of the engine, the temperature of the reformed gas is equal to or higher than a first threshold value, the concentration of hydrogen contained in the reformed gas is equal to or lower than a third threshold value, and the engine rotation fluctuation amount is equal to or higher than a second threshold value.

[0014] When the reforming performance of the reformer catalyst deteriorates, the amount of hydrogen generated by the reformer decreases, and the concentration of hydrogen contained in the reformed gas becomes lower than normal. Therefore, by using the concentration of hydrogen contained in the reformed gas in addition to the reformed gas temperature and engine rotation fluctuation amount to detect deterioration of the reforming performance of the catalyst, it is possible to detect with even greater accuracy whether the reforming performance of the catalyst has deteriorated more than necessary.

[0015] The engine system may further include a pressure detection unit that detects the pressure in the reformed gas passage or the intake passage, and the deterioration detection unit may determine that the reforming performance of the catalyst has deteriorated when, during an idle period of the engine, the temperature of the reformed gas is equal to or higher than a first threshold value, the pressure in the reformed gas passage or the intake passage is equal to or lower than a third threshold value, and the engine rotation fluctuation amount is equal to or higher than a second threshold value.

[0016] When the reforming performance of the reformer catalyst deteriorates, the amount of hydrogen generated by the reformer decreases, and the total flow rate of the reformed gas flowing through the reformed gas passage decreases. As a result, the pressure in the reformed gas passage and the intake passage becomes lower than normal. Therefore, by using the pressure in the reformed gas passage or the intake passage in addition to the temperature of the reformed gas and the amount of engine rotation fluctuation to detect deterioration of the reforming performance of the catalyst, it is possible to detect with even greater accuracy whether the reforming performance of the catalyst has deteriorated more than necessary.

[0017] The engine system may further include a nitrogen oxide detection unit that detects a concentration of nitrogen oxides contained in exhaust gas flowing through the exhaust passage, and the deterioration detection unit may determine that the reforming performance of the catalyst has deteriorated when, during an idling period of the engine, the temperature of the reformed gas is equal to or higher than a first threshold value, the concentration of nitrogen oxides is equal to or lower than a third threshold value, and the engine rotation fluctuation amount is equal to or higher than a second threshold value.

[0018] When the concentration of oxygen contained in exhaust gas is the same, the lower the proportion of hydrogen supplied to the engine, the lower the concentration of NOx contained in the exhaust gas. When the reforming performance of the reformer catalyst deteriorates, the amount of hydrogen generated by the reformer decreases, and the proportion of hydrogen supplied to the engine decreases. As a result, the concentration of nitrogen oxides contained in the exhaust gas becomes lower than normal. Therefore, by using the concentration of nitrogen oxides contained in the exhaust gas in addition to the temperature of the reformed gas and the amount of engine rotation fluctuation to detect deterioration of the reforming performance of the catalyst, it is possible to detect with even greater accuracy whether the reforming performance of the catalyst has deteriorated more than necessary.

[0019] The engine system may further include a control unit that, when the deterioration detection unit determines that the reforming performance of the catalyst has deteriorated, controls the second flow control valve so as to increase the flow rate of air supplied to the reformer.

[0020] When the reforming performance of the catalyst in the reformer deteriorates, the amount of hydrogen produced by the reformer decreases, and the total flow rate of the reformed gas supplied to the engine decreases. Therefore, when the reforming performance of the catalyst deteriorates, the total flow rate of the reformed gas supplied to the engine is ensured by increasing the flow rate of air supplied to the reformer.

[0021] The engine system may further include an exhaust oxygen detection unit that detects the concentration of oxygen contained in the exhaust gas flowing through the exhaust passage, and the control unit may determine whether the concentration of oxygen detected by the exhaust oxygen detection unit is below a target value, and when the oxygen concentration is higher than the target value, control the second fuel supply valve to increase the flow rate of fuel supplied to the reformer.

[0022] In this configuration, when the concentration of oxygen contained in the exhaust gas is higher than a target value, the flow rate of fuel supplied to the reformer increases, and the flow rate of unburned fuel contained in the reformed gas supplied to the engine increases. Therefore, by increasing the flow rate of air supplied to the reformer, the required air-fuel ratio in the engine is maintained even if the flow rate of air supplied to the engine increases. Effect of the Invention

[0023] According to the present invention, it is possible to detect with high accuracy whether the reforming performance of the catalyst in the reformer has deteriorated more than necessary. [Brief description of the drawings]

[0024] [Figure 1] 1 is a schematic configuration diagram showing an engine system according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing the configuration of the rotation fluctuation detector shown in FIG. 1 together with a cross-sectional view of an ammonia engine. [Diagram 3] 4 is a flowchart showing a procedure of a deterioration detection process executed by a deterioration detection unit shown in FIG. 1. [Figure 4] 4 is a flowchart showing a procedure of a startup control process executed by a startup control unit shown in FIG. [Diagram 5] FIG. 4 is a schematic configuration diagram showing an engine system according to a second embodiment of the present invention. [Figure 6] 6 is a flowchart showing a procedure of a deterioration detection process executed by a deterioration detection unit shown in FIG. 5. [Figure 7] FIG. 5 is a schematic configuration diagram showing an engine system according to a third embodiment of the present invention. [Figure 8] FIG. 11 is a schematic configuration diagram showing an engine system according to a fourth embodiment of the present invention. [Figure 9] FIG. 11 is a schematic configuration diagram showing an engine system according to a fifth embodiment of the present invention. [Figure 10] FIG. 11 is a schematic configuration diagram showing an engine system according to a sixth embodiment of the present invention. [Figure 11] 5 is a flowchart showing a modified example of the procedure of the starting control process shown in FIG. [Figure 12] 4 is a graph showing an example of reforming characteristics of a reforming catalyst. [Figure 13] 5 is a flowchart showing another modified example of the procedure of the starting control process shown in FIG. [Figure 14] 5 is a flowchart showing yet another modified example of the procedure of the starting control process shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] 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.

[0026] Fig. 1 is a schematic diagram showing an engine system according to a first embodiment of the present invention. In Fig. 1, an engine system 1 of this embodiment is mounted on a vehicle (not shown). The engine system 1 includes an ammonia engine 2, an intake passage 3, an exhaust passage 4, a main injector 5, and a main throttle valve 6.

[0027] The ammonia engine 2 is an engine that uses ammonia gas (NH3 gas) as fuel. In the ammonia engine 2, hydrogen (H2) is mixed into the ammonia gas as a combustion aid to facilitate combustion of the flame-retardant ammonia gas. Here, the ammonia engine 2 is a four-cylinder engine.

[0028] As shown in FIG. 2, the ammonia engine 2 has a cylinder 11, a piston 12 arranged so as to be able to reciprocate within this cylinder 11, and a connecting rod 14 that connects this piston 12 to a crankshaft 13.

[0029] The cylinder 11 is composed of a cylinder block 11a and a cylinder head 11b arranged on the upper part of the cylinder block 11a. The space defined by the cylinder block 11a, the cylinder head 11b, and the piston 12 is a combustion chamber 15 in which ammonia gas is burned together with hydrogen to generate exhaust gas.

[0030] The cylinder head 11b is provided with an intake port 16 and an exhaust port 17 which communicate with the combustion chamber 15. The intake port 16 is opened and closed by an intake valve 18. The exhaust port 17 is opened and closed by an exhaust valve 19. In addition, an ignition plug 20 is attached to the cylinder head 11b. The ignition plug 20 ignites the mixture of ammonia gas and air to ignite the ammonia gas.

[0031] The intake passage 3 is connected to an intake port 16 of the ammonia engine 2. The intake passage 3 is a passage through which air flows to be supplied to a combustion chamber 15 of the ammonia engine 2. An air cleaner 7 is disposed in the intake passage 3 to remove foreign matter such as dust and dirt contained in the air.

[0032] The exhaust passage 4 is connected to an exhaust port 17 of the ammonia engine 2. The exhaust passage 4 is a passage through which exhaust gas generated in a combustion chamber 15 of the ammonia engine 2 flows. A three-way catalyst 8 that purifies carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NOx), which are harmful components contained in the exhaust gas, and an SCR catalyst 9 that removes NOx contained in the exhaust gas are disposed in the exhaust passage 4.

[0033] The main injector 5 is an electromagnetic fuel injection valve that injects ammonia gas toward the combustion chamber 15 of the ammonia engine 2. The main injector 5 constitutes a first fuel supply valve that supplies ammonia gas to the ammonia engine 2.

[0034] The main throttle valve 6 is disposed in the intake passage 3. The main throttle valve 6 is an electromagnetic first flow control valve that controls the flow rate of air supplied to the ammonia engine 2.

[0035] The engine system 1 also includes an ammonia cylinder 21, a vaporizer 22, a reformer 23, an air passage 24, a reforming throttle valve 25, a reforming injector 26, a reformed gas passage 27, a cooler 28, and a flow rate control valve 29.

[0036] The ammonia cylinder 21 is a container that stores ammonia in a liquid state. That is, the ammonia cylinder 21 stores liquid ammonia.

[0037] The vaporizer 22 vaporizes the liquid ammonia stored in the ammonia cylinder 21 to generate ammonia gas. The ammonia gas generated in the vaporizer 22 flows through an ammonia flow passage 30 and is supplied to the main injector 5, and also flows through an ammonia flow passage 31 and is supplied to the reforming injector 26.

[0038] The reformer 23 generates reformed gas containing hydrogen by reforming ammonia gas using heat generated by burning ammonia gas. The reformer 23 has a cylindrical housing 32, and a reforming catalyst 33 and an electric heater 34 housed in the housing 32. The housing 32 is made of a metal material such as stainless steel that is resistant to corrosion by ammonia gas.

[0039] The reforming catalyst 33 has, for example, a honeycomb structure. The reforming catalyst 33 is a catalyst that burns ammonia gas and decomposes the ammonia gas into hydrogen. The reforming catalyst 33 is, for example, an ATR (Autothermal Reformer) type ammonia reforming catalyst. As the reforming catalyst 33, for example, a cobalt-based catalyst, a rhodium-based catalyst, a ruthenium-based catalyst, a palladium-based catalyst, or the like is used.

[0040] The electric heater 34 is disposed upstream of the reforming catalyst 33 inside the housing 32. When energized by the power source 35, the electric heater 34 generates heat, and uses the heat to heat the reforming catalyst 33. Specifically, the heat generated by the electric heater 34 is transmitted to the reforming catalyst 33 through the housing 32 itself, and is also transmitted to the reforming catalyst 333 through the ammonia gas and air flowing inside the housing 32.

[0041] The air flow path 24 connects the intake passage 3 and the reformer 23. One end of the air flow path 24 is connected to a position in the intake passage 3 between the air cleaner 7 and the main throttle valve 6. The other end of the air flow path 24 is connected to an inlet portion of the housing 32 of the reformer 23. The air flow path 24 is a flow path through which air supplied to the reformer 23 flows.

[0042] The reforming throttle valve 25 is disposed in the air flow passage 24. The reforming throttle valve 25 is an electromagnetic second flow control valve that controls the flow rate of air supplied to the reformer 23.

[0043] The reforming injector 26 is an electromagnetic fuel injection valve that injects ammonia gas into the air passage 24. The reforming injector 26 injects ammonia gas between the reforming throttle valve 25 and the reformer 23 in the air passage 24. The reforming injector 26 constitutes a second fuel supply valve that supplies ammonia gas to the reformer 23.

[0044] The reformed gas passage 27 connects the reformer 23 and the intake passage 3. One end of the reformed gas passage 27 is connected to an outlet portion of the housing 32 of the reformer 23. The other end of the reformed gas passage 27 is connected to a portion of the intake passage 3 between the main throttle valve 6 and the ammonia engine 2. The reformed gas passage 27 is a passage through which the reformed gas generated by the reformer 23 flows toward the ammonia engine 2.

[0045] The cooler 28 is disposed in the reformed gas passage 27. The cooler 28 cools the reformed gas flowing through the reformed gas passage 27 by using engine cooling water that cools the ammonia engine 2, for example.

[0046] The flow rate regulating valve 29 is disposed downstream of the cooler 28 in the reformed gas flow passage 27. The flow rate regulating valve 29 is an electromagnetic valve that regulates the flow rate of the reformed gas supplied to the ammonia engine 2. Note that instead of the flow rate regulating valve 29, an electromagnetic opening / closing valve (ON / OFF valve) may be used.

[0047] The engine system 1 also includes temperature sensors 37 and 38, a λ sensor 39, and a rotation fluctuation detector 40.

[0048] The temperature sensor 37 is a sensor that detects the temperature of the reforming catalyst 33 of the reformer 23. The temperature sensor 38 is a sensor (temperature detection unit) that detects the temperature of the reformed gas flowing through the reformed gas flow passage 27. The λ sensor 39 is a sensor (exhaust oxygen detection unit) that detects the concentration of oxygen (O2) contained in the exhaust gas flowing through the exhaust passage 4.

[0049] The rotation fluctuation detector 40 is a rotation fluctuation detection unit that detects the amount of rotation fluctuation of the ammonia engine 2. As shown in Fig. 2, the rotation fluctuation detector 40 has a marker 41 provided on the crankshaft 13, a marker sensor 42, and a rotation fluctuation processing unit 43.

[0050] The marker 41 is attached, for example, to a portion of the periphery of the end face of the crankshaft 13. The marker sensor 42 detects the marker 41 by irradiating light onto a predetermined portion of the periphery of the end face of the crankshaft 13, for example.

[0051] The rotation fluctuation processing unit 43 is composed of a CPU, RAM, ROM, an input / output interface, etc. The rotation fluctuation processing unit 43 detects the amount of rotation fluctuation of the ammonia engine 2 based on the detection signal of the marker sensor 42. Specifically, the rotation fluctuation processing unit 43 measures the detection period of the marker 41 by the marker sensor 42 as the rotation period of the crankshaft 13. The rotation fluctuation processing unit 43 then detects the amount of fluctuation in the rotation period of the crankshaft 13 to detect the amount of rotation fluctuation of the ammonia engine 2.

[0052] However, the rotation fluctuation detector 40 is not limited to such a configuration. For example, the marker 41 may be provided on the periphery of a shaft portion that is one of the components of the crankshaft 13. Also, instead of providing the marker 41, a part of a toothed wheel of a gear that is one of the components of the crankshaft 13 may be removed, and the chipped part of the toothed wheel may be detected by a sensor.

[0053] The engine system 1 also includes a starter 45, an engine ECU 46, a controller 47, and an alarm 48.

[0054] The starter 45 starts the ammonia engine 2. Although not specifically shown, the starter 45 has a motor, a plurality of gears, and the like.

[0055] The engine ECU 46 is configured with a CPU, a RAM, a ROM, an input / output interface, etc. The engine ECU 46 is an ECU (electronic control unit) that controls the ammonia engine 2.

[0056] Specifically, the engine ECU 46 controls the intake valve 18, exhaust valve 19, and spark plug 20 (see FIG. 2) of the ammonia engine 2 so that one cycle consists of four strokes: an intake stroke, a compression stroke, an expansion stroke (combustion stroke), and an exhaust stroke. The engine ECU 46 controls the intake valve 18 to open during the intake stroke. The engine ECU 46 controls the spark plug 20 to ignite during the expansion stroke. The engine ECU 46 controls the exhaust valve 19 to open during the exhaust stroke.

[0057] When the ignition switch 49 is turned ON, the controller 47 executes predetermined processing based on the detection values ​​of the temperature sensors 37, 38, the λ sensor 39, the rotation fluctuation detector 40, etc., and controls the main injector 5, the main throttle valve 6, the reforming throttle valve 25, the reforming injector 26, the power supply 35 for the electric heater 34, the flow control valve 29, the starter 45, and the alarm 48, and also outputs a control start signal to the engine ECU 46.

[0058] The alarm 48 issues an alarm by displaying an alarm or sounding an alarm when, for example, the reforming performance of the reforming catalyst 33 of the reformer 23 deteriorates. The alarm 48 constitutes a notification unit that notifies a user that the reforming performance of the reforming catalyst 33 has deteriorated.

[0059] The controller 47 is configured with a CPU, a RAM, a ROM, an input / output interface, etc. The controller 47 has a deterioration detection unit 51 and a start control unit 52.

[0060] The deterioration detection unit 51 detects whether the reforming performance of the reforming catalyst 33 of the reformer 23 has deteriorated, based on the detection values ​​of the temperature sensor 38 and the rotation fluctuation detector 40. The deterioration detection unit 51 determines that the reforming performance of the reforming catalyst 33 has deteriorated when the temperature of the reformed gas is equal to or higher than threshold value A and the rotation fluctuation amount of the ammonia engine 2 is equal to or higher than threshold value B during the first idle period at the start of the ammonia engine 2.

[0061] The start control unit 52 controls the main injector 5, the main throttle valve 6, the reforming throttle valve 25, the reforming injector 26, the power supply 35 for the electric heater 34, the flow control valve 29, and the starter 45 so as to start the ammonia engine 2 according to the detection result by the deterioration detection unit 51.

[0062] The start-up control unit 52 constitutes a control unit that controls the reforming throttle valve 25 so as to increase the flow rate of air supplied to the reformer 23 when the deterioration detection unit 51 determines that the reforming performance of the reforming catalyst 33 has deteriorated.

[0063] 3 is a flowchart showing the procedure of the deterioration detection process executed by the deterioration detection unit 51. This process is executed when the ignition switch 49 is turned on. In other words, this process is executed during the fast idle period at the time of cold start of the ammonia engine 2.

[0064] 3, the deterioration detection unit 51 first acquires the detection values ​​of the temperature sensor 38 and the rotation fluctuation detector 40 (step S101). Then, based on the detection value of the temperature sensor 38, the deterioration detection unit 51 determines whether the temperature of the reformed gas flowing through the reformed gas passage 27 is equal to or higher than a threshold value A (step S102). The threshold value A is, for example, a maximum value (first threshold value) of the temperature that guarantees the reforming performance of the reforming catalyst 33.

[0065] When the deterioration detection unit 51 determines that the temperature of the reformed gas is equal to or higher than the threshold A, it determines whether or not the rotation fluctuation amount of the ammonia engine 2 is equal to or higher than the threshold B based on the detection value of the rotation fluctuation detector 40 (step S103). The threshold B is, for example, the minimum value (second threshold) of the rotation fluctuation amount at which the combustion of ammonia gas in the ammonia engine 2 becomes unstable.

[0066] At this time, when the deterioration detection unit 51 determines that the temperature of the reformed gas is equal to or higher than threshold A for a predetermined consecutive time, it may determine whether or not the rotation fluctuation amount of the ammonia engine 2 is equal to or higher than threshold B. Furthermore, when the deterioration detection unit 51 determines that the temperature of the reformed gas is equal to or higher than threshold A for a predetermined consecutive time, it may determine whether or not the rotation fluctuation amount of the ammonia engine 2 is equal to or higher than threshold B for a predetermined consecutive time.

[0067] When the deterioration detection unit 51 determines that the rotation fluctuation amount of the ammonia engine 2 is equal to or greater than the threshold value B, it determines that the reforming performance of the reforming catalyst 33 has deteriorated (step S104). Then, the deterioration detection unit 51 outputs an alarm instruction signal to the alarm 48 (step S105). Then, the alarm 48 issues an alarm to the effect that the reforming performance of the reforming catalyst 33 has deteriorated.

[0068] When the deterioration detection unit 51 determines in step S102 that the temperature of the reformed gas is lower than threshold value A, or when the deterioration detection unit 51 determines in step S103 that the rotation fluctuation amount of the ammonia engine 2 is smaller than threshold value B, it determines that the reforming performance of the reforming catalyst 33 has not deteriorated (step S106).

[0069] After executing step S105 or step S106, the deterioration detection unit 51 outputs the deterioration determination result of the reforming performance of the reforming catalyst 33 to the start control unit 52 (step S107).

[0070] 4 is a flowchart showing the procedure of the start control process executed by the start control unit 52. Like the deterioration detection unit 51, this process is also executed when the ignition switch 49 is turned ON.

[0071] Before this process is executed, the main injector 5, main throttle valve 6, reforming throttle valve 25, reforming injector 26, and flow rate control valve 29 are all closed. In addition, the opening change flag is set to 0. The opening change flag is a flag that indicates that the opening of the reforming injector 26 has been changed in order to reduce the concentration of oxygen contained in the exhaust gas.

[0072] 4, the start control unit 52 first controls the power supply 35 of the electric heater 34 to be ON (step S111). The start control unit 52 also controls the starter 45 to be ON (step S112). The start control unit 52 also controls the flow rate adjustment valve 29 to be open (step S113).

[0073] Next, the starting control unit 52 controls the main throttle valve 6 to open (step S114). This causes air to be supplied to the ammonia engine 2. The starting control unit 52 also controls the reforming injector 26 and the reforming throttle valve 25 to open (step S115). This causes ammonia gas and air to be supplied to the reformer 23.

[0074] Next, the start-up control unit 52 acquires the detection value of the temperature sensor 37 (step S116). Then, the start-up control unit 52 determines whether the temperature of the reforming catalyst 33 is equal to or higher than the activation temperature based on the detection value of the temperature sensor 37 (step S117). The activation temperature is the temperature at which the reforming catalyst 33 becomes combustible.

[0075] When the start-up control unit 52 determines that the temperature of the reforming catalyst 33 is lower than the activation temperature, it executes the above-mentioned step S116 again. When the start-up control unit 52 determines that the temperature of the reforming catalyst 33 is equal to or higher than the activation temperature, it controls the power supply 35 of the electric heater 34 to be OFF (step S118).

[0076] Next, the start-up control unit 52 acquires the detection value of the temperature sensor 37 (step S119). Then, the start-up control unit 52 determines whether the temperature of the reforming catalyst 33 is equal to or higher than the reaction temperature based on the detection value of the temperature sensor 37 (step S120). The reaction temperature is the temperature at which the reforming catalyst 33 becomes capable of reforming. The reaction temperature is higher than the activation temperature. Specifically, the reaction temperature is the temperature at which a desired amount of hydrogen is produced by the reforming catalyst 33 (see FIG. 12).

[0077] When the start-up control unit 52 determines that the temperature of the reforming catalyst 33 is lower than the reaction temperature, it executes the above-mentioned step S119 again. When the start-up control unit 52 determines that the temperature of the reforming catalyst 33 is equal to or higher than the reaction temperature, it controls the opening degree of the reforming injector 26 (step S121). At this time, the start-up control unit 52 controls the opening degree of the reforming injector 26 so that the air-fuel ratio of the reformer 23 becomes an air-fuel ratio suitable for the reforming operation of ammonia gas.

[0078] Next, the start control unit 52 judges whether or not the reforming performance of the reforming catalyst 33 has deteriorated based on the detection result by the deterioration detection unit 51 (step S122). When the start control unit 52 judges that the reforming performance of the reforming catalyst 33 has deteriorated, it controls the reforming throttle valve 25 to increase the opening degree (step S123). As a result, the flow rate of air supplied to the reformer 23 increases.

[0079] Next, the start control unit 52 acquires the detection value of the λ sensor 39 (step S124). Then, based on the detection value of the λ sensor 39, the start control unit 52 determines whether the concentration of oxygen contained in the exhaust gas flowing through the exhaust passage 4 is equal to or lower than a predetermined target value (step S125).

[0080] When the start-up control unit 52 determines that the concentration of oxygen contained in the exhaust gas is higher than the target value, it controls the reforming injector 26 to increase its opening (step S126). This increases the flow rate of ammonia gas supplied to the reformer 23. Then, the start-up control unit 52 sets the opening change flag to 1 (step S127) and executes the above step S124 again.

[0081] When the start control unit 52 determines in step S125 that the concentration of oxygen contained in the exhaust gas is equal to or lower than the target value, it determines whether the opening change flag is 0 (step S128). When the start control unit 52 determines that the opening change flag is 0, it controls the main injector 5 to open (step S129). As a result, ammonia gas is supplied to the ammonia engine 2. At this time, the start control unit 52 controls the opening of the main injector 5 so that the air-fuel ratio of the ammonia engine 2 becomes an air-fuel ratio suitable for an idling state.

[0082] When the start control unit 52 determines that the opening change flag is 1, it controls the opening of the reforming injector 26 to return to the original opening (the opening set in the above step S121) (step S130).Then, the start control unit 52 controls the main injector 5 to open (step S129).

[0083] Furthermore, when the start control unit 52 determines in step S122 that the reforming performance of the reforming catalyst 33 has not deteriorated, it performs control to open the main injector 5 (step S129) without executing the above steps S123 to S128.

[0084] In the engine system 1 as described above, when the ignition switch 49 is turned ON, the electric heater 34 is energized and the flow rate control valve 29 is opened. In addition, the starter 45 is driven and the engine ECU 46 controls the intake valve 18, the exhaust valve 19, and the spark plug 20, thereby starting the ammonia engine 2.

[0085] Then, the main throttle valve 6 opens, and air is supplied to the combustion chamber 15 of the ammonia engine 2. Also, the reforming injector 26 and the reforming throttle valve 25 open, and ammonia gas and air are supplied to the reformer 23. At this time, the reforming catalyst 33 is heated by the electric heater 34. The ammonia gas and air supplied to the reformer 23 flow through the reformed gas flow path 27 and the intake passage 3, and are supplied to the combustion chamber 15 of the ammonia engine 2.

[0086] Then, when the temperature of the reforming catalyst 33 reaches the activation temperature, the ammonia gas is burned by the reforming catalyst 33. Specifically, as shown in the following formula, ammonia and oxygen in the air undergo a chemical reaction (exothermic reaction). NH3+3 / 4O2→1 / 2N2+3 / 2H2O+242kJ / mol

[0087] Furthermore, when the temperature of the reforming catalyst 33 reaches the activation temperature, the power supply to the electric heater 34 is stopped, but the temperature of the reforming catalyst 33 further rises due to the heat of combustion (self-heat) of the ammonia gas. Then, when the temperature of the reforming catalyst 33 reaches the reaction temperature, the ammonia gas is reformed by the reforming catalyst 33. 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 / 2N2-46kJ / mol

[0088] The reformed gas flows through the reformed gas flow passage 27 and the intake passage 3, and is supplied to the combustion chamber 15 of the ammonia engine 2. Then, in the combustion chamber 15, hydrogen in the reformed gas and unburned ammonia gas are combusted.

[0089] During such first idling immediately after the start of startup of the ammonia engine 2, in order to maintain the rotation stability and exhaust characteristics of the ammonia engine 2, it is necessary to operate the ammonia engine 2 in a state in which the ratio of hydrogen supplied to the ammonia engine 2, the total flow rate of the reformed gas, and the air-fuel ratio are within specified ranges.

[0090] However, the reforming catalyst 33 of the reformer 23 is more susceptible to deterioration in reforming performance than in oxidation performance due to thermal degradation and the like. When the reforming performance of the reforming catalyst 33 deteriorates, the amount of hydrogen generated by the reformer 23 decreases, and the ratio of hydrogen supplied to the ammonia engine 2 and the total flow rate of the reformed gas decrease. Therefore, misfire may cause the rotation of the ammonia engine 2 to become unstable, and the exhaust characteristics of the ammonia engine 2 may change. Furthermore, when the reforming performance of the reforming catalyst 33 deteriorates, the amount of heat absorbed by the reforming catalyst 33 decreases, and the temperature of the reformed gas increases.

[0091] Therefore, during the fast idle period of the ammonia engine 2, it is detected whether the reforming performance of the reforming catalyst 33 has deteriorated. Specifically, the temperature of the reformed gas flowing through the reformed gas passage 27 is detected by a temperature sensor 38, and the amount of rotational fluctuation of the ammonia engine 2 is detected by a rotational fluctuation detector 40.

[0092] When the temperature of the reformed gas is equal to or higher than threshold A and the rotational fluctuation amount of the ammonia engine 2 is equal to or higher than threshold B, it is determined that the reforming performance of the reforming catalyst 33 has deteriorated. Even if the temperature of the reformed gas is equal to or higher than threshold A, when the rotational fluctuation amount of the ammonia engine 2 is smaller than threshold B, it is determined that the reforming performance of the reforming catalyst 33 has not deteriorated. Also, even if the rotational fluctuation amount of the ammonia engine 2 is equal to or higher than threshold B, when the temperature of the reformed gas is lower than threshold A, it is determined that the reforming performance of the reforming catalyst 33 has not deteriorated.

[0093] When it is determined that the reforming performance of the reforming catalyst 33 has deteriorated, an alarm is issued by the alarm 48. Therefore, the user can immediately know from the alarm 48 that the reforming catalyst 33 needs to be replaced.

[0094] Furthermore, when it is determined that the reforming performance of the reforming catalyst 33 has deteriorated, the opening of the reforming throttle valve 25 increases, thereby increasing the flow rate of air supplied to the reformer 23. As a result, the total flow rate of the reformed gas generated by the reformer 23 increases.

[0095] After that, the main injector 5 opens, and ammonia gas is supplied to the combustion chamber 15 of the ammonia engine 2. Then, the ammonia gas is burned together with the hydrogen in the reformed gas. This completes the start-up operation of the ammonia engine 2, and transitions to a steady state.

[0096] As described above, in this embodiment, when ammonia gas and air are supplied to the reformer 23, the reforming catalyst 33 of the reformer 23 reforms the ammonia gas to generate a reformed gas containing hydrogen, and the reformed gas flows through the reformed gas flow passage 27 and is supplied to the ammonia engine 2. Then, when ammonia gas and air are supplied to the ammonia engine 2, the ammonia gas is mixed with hydrogen and burned in the ammonia engine 2. Here, if the reforming performance of the reforming catalyst 33 is deteriorated, the temperature of the reformed gas rises compared to normal. Also, if the reforming performance of the reforming catalyst 33 is deteriorated, the combustion of ammonia gas in the ammonia engine 2 becomes unstable, and the rotation fluctuation amount of the ammonia engine 2 increases compared to normal. Therefore, the temperature of the reformed gas and the rotation fluctuation amount of the ammonia engine 2 are detected, and whether the reforming performance of the reforming catalyst 33 has deteriorated is detected based on the temperature of the reformed gas and the rotation fluctuation amount of the ammonia engine 2. Specifically, during an idle period of the ammonia engine 2, when the temperature of the reformed gas is equal to or higher than threshold A and the rotation fluctuation amount of the ammonia engine 2 is equal to or higher than threshold B, it is determined that the reforming performance of the reforming catalyst 33 has deteriorated. In this way, by using not only the temperature of the reformed gas but also the rotation fluctuation amount of the ammonia engine 2 to detect the deterioration of the reforming performance of the reforming catalyst 33, it is possible to detect with high accuracy whether the reforming performance of the reforming catalyst 33 has deteriorated more than necessary. This makes it possible to know whether the reforming performance of the reforming catalyst 33 has deteriorated to the extent that replacement of the reforming catalyst 33 is necessary.

[0097] Furthermore, in this embodiment, during the first idle period at the start of the ammonia engine 2, when the temperature of the reformed gas is equal to or higher than threshold A and the rotation fluctuation amount of the ammonia engine 2 is equal to or higher than threshold B, it is determined that the reforming performance of the reforming catalyst 33 has deteriorated. During the first idle period at the start of the ammonia engine 2, ammonia gas and air are supplied to the reformer 23 under the same stable conditions. Therefore, it is possible to detect with even higher accuracy whether the reforming performance of the reforming catalyst 33 has deteriorated more than necessary.

[0098] Furthermore, in this embodiment, when it is determined that the reforming performance of the reforming catalyst 33 has deteriorated, the reforming throttle valve 25 is controlled to increase the flow rate of air supplied to the reformer 23. When the reforming performance of the reforming catalyst 33 deteriorates, the amount of hydrogen generated by the reformer 23 decreases, and the total flow rate of reformed gas supplied to the ammonia engine 2 decreases. Therefore, when the reforming performance of the reforming catalyst 33 has deteriorated, the flow rate of air supplied to the reformer 23 is increased, thereby ensuring the total flow rate of reformed gas supplied to the ammonia engine 2.

[0099] Furthermore, in this embodiment, when the concentration of oxygen contained in the exhaust gas flowing through the exhaust passage 4 is higher than a target value, the reforming injector 26 is controlled to increase the flow rate of ammonia gas supplied to the reformer 23. This increases the flow rate of unburned ammonia gas contained in the reformed gas supplied to the ammonia engine 2. Therefore, by increasing the flow rate of air supplied to the reformer 23, the air-fuel ratio required in the ammonia engine 2 is maintained even if the flow rate of air supplied to the ammonia engine 2 increases.

[0100] Fig. 5 is a schematic diagram showing an engine system according to a second embodiment of the present invention. In Fig. 5, the engine system 1A of this embodiment includes a λ sensor 61 in addition to the configuration in the first embodiment. The λ sensor 61 is a sensor (oxygen detection unit) that detects the concentration of residual oxygen contained in the reformed gas flowing through the reformed gas passage 27.

[0101] Moreover, the engine system 1A includes a controller 47A instead of the controller 47 in the first embodiment. The controller 47A includes a deterioration detection unit 51A and the start control unit 52 described above.

[0102] The deterioration detection unit 51A detects whether the reforming performance of the reforming catalyst 33 of the reformer 23 has deteriorated, based on the detection values ​​of the temperature sensor 38, the λ sensor 61, and the rotation fluctuation detector 40. The deterioration detection unit 51A determines that the reforming performance of the reforming catalyst 33 has deteriorated when, during the first idle period at the start of the ammonia engine 2, the temperature of the reformed gas is equal to or higher than threshold A, the concentration of residual oxygen contained in the reformed gas is equal to or higher than threshold C, and the rotation fluctuation amount of the ammonia engine 2 is equal to or higher than threshold B.

[0103] FIG. 6 is a flowchart showing the procedure of the deterioration detection process executed by the deterioration detection unit 51A, and corresponds to FIG.

[0104] 6, the deterioration detection unit 51A first acquires the detection values ​​of the temperature sensor 38, the λ sensor 61, and the rotation fluctuation detector 40 (step S101A). Then, based on the detection value of the temperature sensor 38, the deterioration detection unit 51A determines whether the temperature of the reformed gas flowing through the reformed gas passage 27 is equal to or higher than the threshold value A (step S102).

[0105] When the deterioration detection unit 51A determines that the temperature of the reformed gas is equal to or higher than the threshold A, it determines whether or not the concentration of residual oxygen contained in the reformed gas is equal to or higher than a threshold C based on the detection value of the λ sensor 61 (step S108). The threshold C is a value (third threshold) according to the deterioration of the reforming performance of the reforming catalyst 33, and is determined in advance by experiments or the like.

[0106] When the deterioration detection unit 51A determines that the concentration of residual oxygen contained in the reformed gas is equal to or greater than the threshold C, it determines whether the rotation fluctuation amount of the ammonia engine 2 is equal to or greater than the threshold B based on the detection value of the rotation fluctuation detector 40 (step S103).

[0107] When the deterioration detection unit 51A determines that the rotation fluctuation amount of the ammonia engine 2 is equal to or greater than the threshold value B, it determines that the reforming performance of the reforming catalyst 33 has deteriorated (step S104). Then, the deterioration detection unit 51A sequentially executes the above steps S105 and S107.

[0108] When the deterioration detection unit 51A determines in step S102 that the temperature of the reformed gas flowing through the reformed gas passage 27 is lower than threshold A, when the deterioration detection unit 51A determines in step S108 that the concentration of residual oxygen contained in the reformed gas is lower than threshold C, or when the deterioration detection unit 51A determines in step S103 that the rotation fluctuation amount of the ammonia engine 2 is smaller than threshold B, it determines that the reforming performance of the reforming catalyst 33 has not deteriorated (step S106). Then, the deterioration detection unit 51A executes the above-mentioned step S107.

[0109] Incidentally, when the reforming performance of the reforming catalyst 33 of the reformer 23 deteriorates, the amount of hydrogen generated by the reformer 23 decreases, and the concentration of residual oxygen contained in the reformed gas becomes higher than in the normal state.

[0110] Therefore, in this embodiment, in addition to the temperature of the reformed gas and the rotational fluctuation amount of the ammonia engine 2, the concentration of residual oxygen contained in the reformed gas is also used to detect deterioration of the reforming performance of the reforming catalyst 33, thereby making it possible to detect with even greater accuracy whether the reforming performance of the reforming catalyst 33 has deteriorated more than necessary.

[0111] Fig. 7 is a schematic diagram showing an engine system according to a third embodiment of the present invention. In Fig. 7, an engine system 1B of this embodiment includes a hydrogen sensor 63 in addition to the configuration of the first embodiment. The hydrogen sensor 63 is a sensor (hydrogen detection unit) that detects the concentration of hydrogen contained in the reformed gas flowing through the reformed gas passage 27.

[0112] Moreover, the engine system 1B includes a controller 47B instead of the controller 47 in the first embodiment. The controller 47B includes a deterioration detection unit 51B and the start control unit 52 described above.

[0113] The deterioration detection unit 51B detects whether the reforming performance of the reforming catalyst 33 of the reformer 23 has deteriorated, based on the detection values ​​of the temperature sensor 38, the hydrogen sensor 63, and the rotation fluctuation detector 40. The deterioration detection unit 51B determines that the reforming performance of the reforming catalyst 33 has deteriorated when, during the first idle period at the start of the ammonia engine 2, the temperature of the reformed gas is equal to or higher than threshold A, the concentration of hydrogen contained in the reformed gas is equal to or lower than threshold D, and the rotation fluctuation amount of the ammonia engine 2 is equal to or higher than threshold B. The threshold D is a value (third threshold) according to the deterioration of the reforming performance of the reforming catalyst 33, and is determined in advance by experiments or the like.

[0114] Incidentally, when the reforming performance of the reforming catalyst 33 of the reformer 23 deteriorates, the amount of hydrogen generated by the reformer 23 decreases, and the concentration of hydrogen contained in the reformed gas becomes lower than in the normal state.

[0115] Therefore, in this embodiment, in addition to the temperature of the reformed gas and the rotational fluctuation amount of the ammonia engine 2, the concentration of hydrogen contained in the reformed gas is also used to detect deterioration of the reforming performance of the reforming catalyst 33, thereby making it possible to detect with even greater accuracy whether the reforming performance of the reforming catalyst 33 has deteriorated more than necessary.

[0116] Fig. 8 is a schematic diagram showing an engine system according to a fourth embodiment of the present invention. In Fig. 8, an engine system 1C of this embodiment includes a pressure sensor 65 in addition to the configuration of the first embodiment. The pressure sensor 65 is a sensor (pressure detection unit) that detects the pressure of the reformed gas passage 27.

[0117] Moreover, the engine system 1C includes a controller 47C instead of the controller 47 in the first embodiment. The controller 47C includes a deterioration detection unit 51C and the start control unit 52 described above.

[0118] The deterioration detection unit 51C detects whether the reforming performance of the reforming catalyst 33 of the reformer 23 has deteriorated, based on the detection values ​​of the temperature sensor 38, the pressure sensor 65, and the rotation fluctuation detector 40. The deterioration detection unit 51C determines that the reforming performance of the reforming catalyst 33 has deteriorated when, during a first idle period at the start of the ammonia engine 2, the temperature of the reformed gas is equal to or higher than threshold A, the pressure of the reformed gas passage 27 is equal to or lower than threshold E, and the rotation fluctuation amount of the ammonia engine 2 is equal to or higher than threshold B. The threshold E is a value (third threshold) according to the deterioration of the reforming performance of the reforming catalyst 33, and is determined in advance by experiments or the like.

[0119] Incidentally, when the reforming performance of the reforming catalyst 33 of the reformer 23 deteriorates, the amount of hydrogen generated by the reformer 23 decreases, and the total flow rate of the reformed gas flowing through the reformed gas passage 27 decreases. As a result, the pressure in the reformed gas passage 27 becomes lower than normal.

[0120] Therefore, in this embodiment, in addition to the temperature of the reformed gas and the rotational fluctuation amount of the ammonia engine 2, the pressure of the reformed gas passage 27 is also used to detect deterioration of the reforming performance of the reforming catalyst 33, so that it is possible to detect with even higher accuracy whether the reforming performance of the reforming catalyst 33 has deteriorated more than necessary.

[0121] Fig. 9 is a schematic diagram showing an engine system according to a fifth embodiment of the present invention. In Fig. 9, an engine system 1D of this embodiment includes an intake pressure sensor 67 in addition to the configuration in the first embodiment. The intake pressure sensor 67 is a sensor (pressure detection unit) that detects the pressure in the intake passage 3.

[0122] Moreover, the engine system 1D includes a controller 47D instead of the controller 47 in the first embodiment. The controller 47D includes a deterioration detection unit 51D and the start control unit 52 described above.

[0123] The deterioration detection unit 51D detects whether the reforming performance of the reforming catalyst 33 of the reformer 23 has deteriorated, based on the detection values ​​of the temperature sensor 38, the intake pressure sensor 67, and the rotation fluctuation detector 40. The deterioration detection unit 51D determines that the reforming performance of the reforming catalyst 33 has deteriorated when, during the first idle period at the start of the ammonia engine 2, the temperature of the reformed gas is equal to or higher than threshold value A, the pressure of the intake passage 3 is equal to or lower than threshold value F, and the rotation fluctuation amount of the ammonia engine 2 is equal to or higher than threshold value B. The threshold value F is a value (third threshold value) according to the deterioration of the reforming performance of the reforming catalyst 33, and is determined in advance by experiments or the like.

[0124] Incidentally, when the reforming performance of the reforming catalyst 33 of the reformer 23 deteriorates, the amount of hydrogen generated by the reformer 23 decreases, and the total flow rate of the reformed gas flowing through the reformed gas passage 27 decreases. As a result, the pressure in the intake passage 3 communicated with the reformed gas passage 27 becomes lower than normal.

[0125] Therefore, in this embodiment, in addition to the temperature of the reformed gas and the rotational fluctuation amount of the ammonia engine 2, the pressure of the intake passage 3 is also used to detect the deterioration of the reforming performance of the reforming catalyst 33, so that it is possible to detect with even higher accuracy whether the reforming performance of the reforming catalyst 33 has deteriorated more than necessary.

[0126] Fig. 10 is a schematic diagram showing an engine system according to a sixth embodiment of the present invention. In Fig. 10, an engine system 1E of this embodiment includes a NOx sensor 69 in addition to the configuration of the first embodiment. The NOx sensor 69 is a sensor (nitrogen oxide detection unit) that detects the concentration of nitrogen oxides (NOx) contained in the exhaust gas flowing through the exhaust passage 4.

[0127] Moreover, the engine system 1E includes a controller 47E instead of the controller 47 in the first embodiment. The controller 47E includes a deterioration detection unit 51E and the start control unit 52 described above.

[0128] The deterioration detection unit 51E detects whether the reforming performance of the reforming catalyst 33 of the reformer 23 has deteriorated, based on the detection values ​​of the temperature sensor 38, the NOx sensor 69, and the rotation fluctuation detector 40. The deterioration detection unit 51E determines that the reforming performance of the reforming catalyst 33 has deteriorated when, during a first idle period at the start of the ammonia engine 2, the temperature of the reformed gas is equal to or higher than threshold A, the concentration of NOx contained in the exhaust gas is equal to or lower than threshold G, and the rotation fluctuation amount of the ammonia engine 2 is equal to or higher than threshold B. The threshold G is a value (third threshold) according to the deterioration of the reforming performance of the reforming catalyst 33, and is determined in advance by experiments or the like.

[0129] Incidentally, when the concentration of oxygen contained in the exhaust gas is the same, the concentration of NOx contained in the exhaust gas decreases as the ratio of hydrogen supplied to the ammonia engine 2 decreases. When the reforming performance of the reforming catalyst 33 of the reformer 23 deteriorates, the amount of hydrogen generated by the reformer 23 decreases, and the ratio of hydrogen supplied to the ammonia engine 2 decreases. As a result, the concentration of NOx contained in the exhaust gas becomes lower than in the normal state.

[0130] Therefore, in this embodiment, in addition to the temperature of the reformed gas and the rotational fluctuation amount of the ammonia engine 2, the concentration of NOx contained in the exhaust gas is also used to detect the deterioration of the reforming performance of the reforming catalyst 33, so that it is possible to detect with even higher accuracy whether the reforming performance of the reforming catalyst 33 has deteriorated more than necessary.

[0131] In addition, as described above, when the reforming performance of the reforming catalyst 33 deteriorates, the ratio of hydrogen supplied to the ammonia engine 2 decreases, and the concentration of NOx contained in the exhaust gas becomes lower than normal. Therefore, the concentration of ammonia contained in the exhaust gas becomes higher than normal. Therefore, instead of the NOx sensor 69, an ammonia sensor that detects the concentration of ammonia contained in the exhaust gas may be used.

[0132] Although several embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments. For example, the second to sixth embodiments may be combined and practiced.

[0133] Furthermore, in the above embodiment, when it is determined that the reforming performance of the reforming catalyst 33 of the reformer 23 has deteriorated, the start-up control unit 52 controls the reforming throttle valve 25 so as to increase the flow rate of air supplied to the reformer 23, but the control method by the start-up control unit 52 is not particularly limited to this form and can be modified in various ways.

[0134] FIG. 11 is a flowchart showing a modified example of the procedure of the starting control process executed by the starting control unit 52, and corresponds to FIG.

[0135] In FIG. 11, after sequentially executing the above steps S111 to S115, the start control unit 52 determines whether the reforming performance of the reforming catalyst 33 of the reformer 23 has deteriorated based on the detection result by the deterioration detection unit 51 (step S132).

[0136] When the start-up control unit 52 determines that the reforming performance of the reforming catalyst 33 has deteriorated, it changes the setting of the reaction temperature (described above) used as a comparison value in step S120 so that it is higher than the normal reaction temperature t0 when the reforming performance of the reforming catalyst 33 has not deteriorated (step S133). That is, as shown in Fig. 12, the start-up control unit 52 changes the reaction temperature to temperature t1 that is higher than the normal reaction temperature t0. Temperature t1 is the reaction temperature at which a desired amount of hydrogen is produced when the reforming performance of the reforming catalyst 33 has deteriorated. Then, the start-up control unit 52 sequentially executes the above steps S116 to S121 and S129.

[0137] When the start control unit 52 determines in step S132 that the reforming performance of the reforming catalyst 33 has not deteriorated, it does not execute step S133, but executes the above steps S116 to S121 and S129 in sequence.

[0138] In this modified example, by setting the reaction temperature higher than normal, even if the reforming performance of the reforming catalyst 33 of the reformer 23 deteriorates, the reforming catalyst 33 continues to be heated by the electric heater 34 until the desired amount of hydrogen is produced by the reformer 23.

[0139] FIG. 13 is a flowchart showing another modified example of the procedure of the starting control process executed by the starting control unit 52, and corresponds to FIG.

[0140] In FIG. 13, after sequentially executing the above steps S111 to S115, the start control unit 52 determines whether the reforming performance of the reforming catalyst 33 of the reformer 23 has deteriorated based on the detection result by the deterioration detection unit 51 (step S132).

[0141] When the start control unit 52 determines that the reforming performance of the reforming catalyst 33 has deteriorated, it outputs an ignition timing change instruction signal to the engine ECU 46 to make the ignition timing of the ammonia engine 2 earlier than normal (step S135). Then, the start control unit 52 sequentially executes the above steps S116 to S121, S129.

[0142] When the engine ECU 46 receives the ignition timing change instruction signal from the start control unit 52, it controls the ignition plug 20 so that the ignition timing of the ammonia engine 2 becomes earlier than normal.

[0143] When the start control unit 52 determines in step S132 that the reforming performance of the reforming catalyst 33 has not deteriorated, it does not execute step S135, but executes the above steps S116 to S121 and S129 in sequence.

[0144] Incidentally, when the ratio of hydrogen supplied to the ammonia engine 2 decreases with the deterioration of the reforming performance of the reforming catalyst 33, the combustion speed in the ammonia engine 2 decreases, and there is a possibility that the combustion will not be completed before the exhaust port 17 is opened by the exhaust valve 19.

[0145] In this modified example, when the reforming performance of the reforming catalyst 33 deteriorates, the ignition timing of the ammonia engine 2 is advanced so that combustion can be completed before the exhaust valve 19 opens the exhaust port 17.

[0146] FIG. 14 is a flowchart showing yet another modified example of the procedure of the starting control process executed by the starting control unit 52, and corresponds to FIG.

[0147] In FIG. 14, after sequentially executing the above steps S111 to S115, the start control unit 52 determines whether the reforming performance of the reforming catalyst 33 of the reformer 23 has deteriorated based on the detection result by the deterioration detection unit 51 (step S132).

[0148] When the start control unit 52 determines that the reforming performance of the reforming catalyst 33 has deteriorated, it controls the main injector 5 to open (step S137). This causes ammonia gas to be supplied to the combustion chamber 15 of the ammonia engine 2. Then, the start control unit 52 sequentially executes the above steps S116 to S121. When the start control unit 52 determines that the reforming performance of the reforming catalyst 33 has not deteriorated, it does not execute step S137, but sequentially executes the above steps S116 to S121.

[0149] After executing step S121, the start control unit 52 controls the opening degree of the main injector 5 (step S138). At this time, the start control unit 52 controls the opening degree of the main injector 5 so that the air-fuel ratio of the ammonia engine 2 becomes an air-fuel ratio suitable for an idle state, for example.

[0150] In this modified example, when the reforming performance of the reforming catalyst 33 deteriorates, ammonia gas is supplied to the ammonia engine 2 by the main injector 5, so that the decrease in the total flow rate of the reformed gas supplied to the ammonia engine 2 can be compensated for.

[0151] These modifications may be implemented in combination with the above-described embodiment, or each modification may be implemented in combination with another modification.

[0152] In addition, in the above first to sixth embodiments, when the temperature of the reformed gas is equal to or higher than threshold value A and the rotation fluctuation amount of the ammonia engine 2 is equal to or higher than threshold value B, it is determined that the reforming performance of the reforming catalyst 33 has deteriorated. However, the threshold values ​​A and B may be changed taking into account the outside air pressure condition, the outside air temperature, the engine oil temperature, the engine coolant temperature, or the temperature of the reforming catalyst 33, etc.

[0153] For example, when the engine oil temperature and the engine coolant temperature are low in cold regions and the oxygen concentration is low at high altitudes, the amount of hydrogen required to maintain fast idle increases, so the air-fuel ratio in the reformer 23 is increased. For this reason, the threshold value A may be increased.

[0154] Furthermore, when the transition conditions to the fast idle operating conditions are steeper than the operating conditions immediately before the fast idle operating conditions, threshold value B may be increased.

[0155] In the second embodiment described above, the threshold value C may be changed depending on the conditions of the ammonia gas and air supplied to the reformer 23 or the temperature of the reforming catalyst 33 immediately before the fast idle period.

[0156] For example, when the temperature of the reforming catalyst 33 immediately before the first idle period is high, the reforming activity condition of the reformer 23 is high, so if gas of the same amount and composition as during the first idle period during a normal cold start is supplied to the reformer 23, the amount of reformed gas generated will be greater than during the first idle period during a normal cold start. Therefore, the total amount of gas output from the reformer 23 increases, and the concentration of remaining oxygen decreases. For this reason, the threshold value C may be made smaller.

[0157] In the above third embodiment, the threshold value D may be changed depending on the conditions of the ammonia gas and air supplied to the reformer 23 or the temperature of the reforming catalyst 33 immediately before the fast idle period.

[0158] For example, when the temperature of the reforming catalyst 33 immediately before the first idle period is high, the reforming activity condition of the reformer 23 is high, so if gas of the same amount and composition as that during the first idle period during a normal cold start is supplied to the reformer 23, the amount of hydrogen generated will be greater than that during the first idle period during a normal cold start. Therefore, the concentration of hydrogen contained in the reformed gas will be higher. For this reason, the threshold value D may be made large.

[0159] In the fourth and fifth embodiments described above, the threshold values ​​E and F may be changed depending on the conditions of the ammonia gas and air supplied to the reformer 23 or the temperature of the reforming catalyst 33 immediately before the fast idle period.

[0160] For example, when the temperature of the reforming catalyst 33 immediately before the first idle period is high, the reforming activity condition of the reformer 23 is high, so if gas of the same amount and composition as during the first idle period during a normal cold start is supplied to the reformer 23, the amount of reformed gas generated will be greater than during the first idle period during a normal cold start. Therefore, the total amount of gas output from the reformer 23 increases, and the pressure in the reformed gas flow passage 27 and the intake passage 3 will increase. For this reason, the threshold values ​​E and F may be made large.

[0161] In addition, in the above embodiment, whether or not the reforming performance of the reforming catalyst 33 of the reformer 23 has deteriorated is detected during the first idle period at the cold start of the ammonia engine 2. However, the timing for detecting the deterioration of the reforming performance of the reforming catalyst 33 is not particularly limited to the first idle period, and may be, for example, an idle period between travelling as long as no load is applied to the ammonia engine 2.

[0162] Further, in the above embodiment, the reforming catalyst 33 of the reformer 23 is heated by the electric heater 34, but this is not particularly limited to the form, and the reforming catalyst 33 may be heated by a combustor such as a tubular flame burner.

[0163] In the above embodiment, the rotation fluctuation detector 40 has the rotation fluctuation processing unit 43 that calculates the amount of rotation fluctuation of the ammonia engine 2, but is not limited to this form. The function of the rotation fluctuation processing unit 43 may be included in the controller 47, for example.

[0164] In the above embodiment, the reformer 23 has the reforming catalyst 33 that has both the function of burning ammonia gas and the function of decomposing the ammonia gas into hydrogen, but is not particularly limited to such a form. The reformer 23 may have a combustion catalyst that burns ammonia gas and a reforming catalyst that decomposes the ammonia gas into hydrogen separately.

[0165] 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]

[0166] Reference Signs List 1, 1A, 1B, 1C, 1D, 1E...engine system, 2...ammonia engine (engine), 3...intake passage, 4...exhaust passage, 5...main injector (first fuel supply valve), 6...main throttle valve (first flow control valve), 23...reformer, 24...air flow path, 25...reforming throttle valve (second flow control valve), 26...reforming injector (second fuel supply valve), 27...reformed gas flow path, 33...reforming catalyst (catalyst), 38...temperature sensor (temperature detection unit), 39... λ sensor (exhaust oxygen detection section), 40...rotational fluctuation detector (rotational fluctuation detection section), 51, 51A, 51B, 51C, 51D, 51E...deterioration detection section, 52...start control section (control section), 61...λ sensor (oxygen detection section), 63...hydrogen sensor (hydrogen detection section), 65...pressure sensor (pressure detection section), 67...intake pressure sensor (pressure detection section), 69...NOx sensor (nitrogen oxide detection section), A...threshold (first threshold), B...threshold (second threshold), C, D, E, F, G...threshold (third threshold).

Claims

1. an engine in which fuel is combusted with hydrogen; an intake passage through which air supplied to the engine flows; an exhaust passage through which exhaust gas generated by 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 supply valve that supplies the fuel to 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 air flow path through which air supplied to the reformer flows; a second flow control valve disposed in the air flow passage and configured to control a flow rate of air supplied to the reformer; a second fuel supply valve that supplies the fuel to the reformer; a reformed gas flow path through which the reformed gas generated by the reformer flows toward the engine; a temperature detection unit that detects a temperature of the reformed gas flowing through the reformed gas flow passage; A rotation fluctuation detection unit that detects a rotation fluctuation amount of the engine; a deterioration detection unit that detects whether or not the reforming performance of the catalyst of the reformer is deteriorated based on the detection values ​​of the temperature detection unit and the rotational fluctuation detection unit, The deterioration detection unit determines that the reforming performance of the catalyst has deteriorated when, during an idle period of the engine, the temperature of the reformed gas is equal to or higher than a first threshold and the engine rotation fluctuation amount is equal to or higher than a second threshold.

2. 2. The engine system according to claim 1, wherein the deterioration detection unit determines that the reforming performance of the catalyst has deteriorated when, during a first idle period at the start of the engine, the temperature of the reformed gas is equal to or higher than the first threshold value and the engine rotation fluctuation amount is equal to or higher than the second threshold value during an idle period of the engine.

3. an oxygen detector that detects a concentration of residual oxygen contained in the reformed gas flowing through the reformed gas flow passage; 2. The engine system according to claim 1, wherein the deterioration detection unit determines that the reforming performance of the catalyst has deteriorated when, during an idle period of the engine, the temperature of the reformed gas is equal to or higher than the first threshold value, the concentration of the residual oxygen contained in the reformed gas is equal to or higher than a third threshold value, and an amount of fluctuation in engine rotation is equal to or higher than the second threshold value.

4. a hydrogen detector that detects a concentration of the hydrogen contained in the reformed gas flowing through the reformed gas flow passage, 2. The engine system according to claim 1, wherein the deterioration detection unit determines that the reforming performance of the catalyst has deteriorated when, during an idle period of the engine, the temperature of the reformed gas is equal to or higher than the first threshold value, the concentration of the hydrogen contained in the reformed gas is equal to or lower than a third threshold value, and the engine rotation fluctuation amount is equal to or higher than the second threshold value.

5. A pressure detection unit is further provided to detect a pressure in the reformed gas passage or the intake passage, The engine system according to claim 1, wherein the deterioration detection unit determines that the reforming performance of the catalyst has deteriorated when, during an idle period of the engine, the temperature of the reformed gas is equal to or higher than the first threshold value, the pressure of the reformed gas flow path or the intake passage is equal to or lower than a third threshold value, and the engine rotation fluctuation amount is equal to or higher than the second threshold value.

6. a nitrogen oxide detection unit that detects a concentration of nitrogen oxides contained in the exhaust gas flowing through the exhaust passage, 2. The engine system according to claim 1, wherein the deterioration detection unit determines that the reforming performance of the catalyst has deteriorated when, during an idle period of the engine, the temperature of the reformed gas is equal to or higher than the first threshold value, the concentration of nitrogen oxides is equal to or lower than a third threshold value, and the engine rotation fluctuation amount is equal to or higher than the second threshold value.

7. The engine system according to any one of claims 1 to 6, further comprising a control unit that controls the second flow control valve so as to increase the flow rate of air supplied to the reformer when the deterioration detection unit determines that the reforming performance of the catalyst has deteriorated.

8. an exhaust gas oxygen detector that detects a concentration of oxygen contained in the exhaust gas flowing through the exhaust passage; 8. The engine system according to claim 7, wherein the control unit determines whether the concentration of oxygen detected by the exhaust oxygen detection unit is equal to or lower than a target value, and when the concentration of oxygen is higher than the target value, controls the second fuel supply valve so as to increase the flow rate of the fuel supplied to the reformer.

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