Control device for internal combustion engine and control method for internal combustion engine

Abstract

This control device for an internal combustion engine comprises: a nitrogen oxide amount acquisition unit that acquires the amount of nitrogen oxide in exhaust gas discharged from the internal combustion engine; an ammonia amount acquisition unit that acquires the amount of ammonia in the exhaust gas discharged from the internal combustion engine; and a flow rate control unit that gives a flow rate adjustment instruction for adjusting a flow rate of combustion gas guided to the internal combustion engine to a flow rate adjustment device that adjusts the flow rate of the combustion gas guided to the internal combustion engine such that the amount of the nitrogen oxide acquired by the nitrogen oxide amount acquisition unit and the amount of the ammonia acquired by the ammonia amount acquisition unit do not exceed threshold values, respectively, in a state in which the internal combustion engine is operated in a co-combustion operation mode in which both liquid fuel and ammonia gas are used as fuel.

Description

Control device for internal combustion engine and control method for internal combustion engine

[0001] This application claims priority to Japanese Patent Application No. 2023-209229, filed with the Japan Patent Office on December 12, 2023, the contents of which are incorporated herein by reference.

[0002] There are known internal combustion engines capable of dual-fuel combustion using both a liquid fuel such as diesel oil and ammonia gas as fuels. The internal combustion engines have an excess air ratio λ set so that nitrogen oxide emissions and ammonia emissions satisfy limit values ​​under standard environmental conditions and expected operating conditions (including transient operating conditions), and the amount of air introduced into the internal combustion engine is controlled by a device capable of manipulating the air amount so as to achieve the set excess air ratio λ (see, for example, Patent Document 1).

[0003] Patent No. 7160226

[0004] The relationship between the excess air ratio λ and the amount of nitrogen oxide or ammonia emissions can change depending on changes in the combustion state or exhaust gas catalyst performance due to changes in environmental conditions, etc. For this reason, it is difficult to set an excess air ratio λ that can be established under various conditions. Furthermore, when controlling the excess air ratio λ to approach a set value, there is a risk that the amount of nitrogen oxide or ammonia emissions will exceed the limit value due to changes in environmental conditions, etc.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a control device and a control method for an internal combustion engine that can control the emissions of nitrogen oxides and ammonia so that they meet limit values ​​even when changes in environmental conditions occur.

[0006] A control device for an internal combustion engine according to at least one embodiment of the present disclosure is a control device for an internal combustion engine for controlling operation of an internal combustion engine configured to be able to switch between a plurality of operating modes, the plurality of operating modes including a mono-fuel operation mode in which a liquid fuel is used as the fuel, and a multi-fuel operation mode in which both the liquid fuel and ammonia gas are used as the fuels, and the control device for the internal combustion engine includes: a nitrogen oxide amount acquisition unit configured to acquire the amount of nitrogen oxides in exhaust gas emitted from the internal combustion engine; an ammonia amount acquisition unit configured to acquire the amount of ammonia in the exhaust gas emitted from the internal combustion engine; and a flow rate control unit configured to, when the internal combustion engine is operating in the multi-fuel operation mode, give a flow rate adjustment instruction to a flow rate adjustment device configured to adjust the flow rate of the combustion gas introduced to the internal combustion engine so that each of the amount of nitrogen oxides acquired by the nitrogen oxide amount acquisition unit and the amount of ammonia acquired by the ammonia amount acquisition unit does not exceed a threshold value.

[0007] A control method for an internal combustion engine according to at least one embodiment of the present disclosure is a control method for an internal combustion engine for controlling operation of an internal combustion engine configured to be able to switch between a plurality of operating modes, the plurality of operating modes including a mono-fuel operation mode in which a liquid fuel is used as the fuel, and a multi-fuel operation mode in which both the liquid fuel and ammonia gas are used as the fuels, and the control method for the internal combustion engine includes: a nitrogen oxide amount acquisition step of acquiring an amount of nitrogen oxides in exhaust gas emitted from the internal combustion engine; an ammonia amount acquisition step of acquiring the amount of ammonia in the exhaust gas emitted from the internal combustion engine; and a flow rate control step of issuing a flow rate adjustment instruction to a flow rate adjustment device configured to adjust a flow rate of combustion gas introduced to the internal combustion engine so that each of the amount of nitrogen oxides acquired in the nitrogen oxide amount acquisition step and the amount of ammonia acquired in the ammonia amount acquisition step does not exceed a threshold value while the internal combustion engine is operating in the multi-fuel operation mode.

[0008] According to at least one embodiment of the present disclosure, a control device and a control method for an internal combustion engine are provided that can control the emissions of nitrogen oxides and ammonia so that they meet limit values ​​even when changes in environmental conditions occur.

[0009] Fig. 1 is a schematic diagram of an internal combustion engine system equipped with a control device for an internal combustion engine according to an embodiment of the present disclosure. Fig. 2 is an explanatory diagram for explaining the relationship between the amount of nitrogen oxides in exhaust gas, the amount of ammonia in exhaust gas, and an excess air ratio. Fig. 3 is an explanatory diagram for explaining the relationship between exhaust gas temperature, the amount of ammonia in exhaust gas, and an excess air ratio. Fig. 4 is a control flow diagram for an internal combustion engine according to an embodiment of the present disclosure. Fig. 5 is a control flow diagram for an internal combustion engine according to an embodiment of the present disclosure. Fig. 6 is an explanatory diagram for explaining a control map showing the relationship between the rotation speed and load of an internal combustion engine according to an embodiment of the present disclosure and operating conditions under which dual-fuel operation is possible. Fig. 7 is a control flow diagram for an internal combustion engine according to an embodiment of the present disclosure.

[0010] Hereinafter, several embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present disclosure.

[0011] (Internal Combustion Engine System) Fig. 1 is a schematic diagram of an internal combustion engine system 1 including a control device 3 for an internal combustion engine 2 according to an embodiment of the present disclosure. As shown in Fig. 1, the internal combustion engine system 1 includes an internal combustion engine (engine) 2 configured to generate power by burning fuel used therein, and a control device 3 configured to control operation and combustion of the internal combustion engine 2. In the following embodiments, a case will be described in which the internal combustion engine 2 is a four-stroke engine, but some embodiments of the present disclosure are also applicable to cases in which the internal combustion engine 2 is a two-stroke engine.

[0012] 1, the internal combustion engine 2 includes at least one (in the illustrated example, a plurality of) cylinders 21. Each of the plurality of cylinders 21 has a combustion chamber 22 for combusting fuel used. Although not shown, the combustion chamber 22 is formed between a cylinder body and a piston housed inside the cylinder body.

[0013] The internal combustion engine 2 is configured to be able to switch between a plurality of operating modes. The plurality of operating modes include a mono-fuel operation mode in which liquid fuel is used as the fuel, and a multi-fuel operation mode in which both the liquid fuel and ammonia gas are used as the fuels. When operating in the mono-fuel operation mode, the internal combustion engine 2 is configured to combust liquid fuel and combustion gas in each combustion chamber 22 of the plurality of cylinders 21. When operating in the multi-fuel operation mode, the internal combustion engine 2 is configured to combust liquid fuel, ammonia gas, and combustion gas in each combustion chamber 22 of the plurality of cylinders 21. Specific examples of liquid fuel include diesel, gasoline, and bioethanol.

[0014] As shown in FIG. 1 , the internal combustion engine 2 further includes a liquid fuel introduction line 4, a combustion gas introduction line 5, an ammonia gas introduction line 6, an exhaust gas discharge line 7, a plurality of liquid fuel side injectors 8, and a plurality of ammonia side injectors 9.

[0015] (Liquid Fuel Side Injector) The plurality of liquid fuel side injectors 8 are for injecting liquid fuel into the respective combustion chambers 22 of the plurality of cylinders 21. The liquid fuel side injector 8 is provided individually for each cylinder 21. Each of the plurality of liquid fuel side injectors 8 includes a fuel injection valve configured to inject liquid fuel into the corresponding combustion chamber 22.

[0016] (Liquid Fuel Introduction Line) The liquid fuel introduction line 4 forms a flow path for supplying liquid fuel to each of the plurality of liquid fuel-side injectors 8, and is formed by, for example, piping, etc. In the illustrated embodiment, the liquid fuel introduction line 4 includes a common rail 41 capable of storing liquid fuel, a plurality of branch pipes 42 for introducing liquid fuel from the common rail 41 to each of the plurality of liquid fuel-side injectors 8, a liquid fuel pipe 44 for introducing liquid fuel from a liquid fuel supply source (e.g., a storage tank for storing liquid fuel) 43 to the common rail 41, and a pressure booster device (e.g., a pressure booster pump) 45 configured to boost the pressure of the liquid fuel introduced to the common rail 41.

[0017] One end of each of the plurality of branch pipes 42 is connected to the common rail 41, and the other end is connected to the liquid fuel-side injector 8 corresponding to the branch pipe 42. One end of a liquid fuel pipe 44 is connected to the common rail 41, and the other end is connected to a liquid fuel supply source 43. A pressure booster 45 is provided on the liquid fuel pipe 44. When the internal combustion engine 2 is operating in the exclusive combustion operation mode or the dual combustion operation mode, the liquid fuel pressurized by the pressure booster 45 is introduced into the liquid fuel-side injector 8 via the liquid fuel introduction line 4.

[0018] (Combustion Gas Introduction Line) The combustion gas introduction line 5 forms a flow path for guiding the combustion gas to each of the plurality of combustion chambers 22, and is formed by, for example, piping, etc. In the illustrated embodiment, the combustion gas introduction line 5 includes a compressor 51 configured to pressurize the combustion gas, a first combustion gas pipe 52 for guiding the combustion gas to the compressor 51, a second combustion gas pipe 53 for guiding the combustion gas from the compressor 51, and a plurality of air intake side branch pipes 54 for guiding the combustion gas from the second combustion gas pipe 53 to each of the plurality of combustion chambers 22.

[0019] Each of the multiple intake side branch pipes 54 has one end connected to a common second combustion gas pipe 53 and the other end connected to the combustion chamber 22 corresponding to the intake side branch pipe 54. One end of each of the first combustion gas pipe 52 and the second combustion gas pipe 53 is connected to a compressor 51. The other end (upstream end) of the first combustion gas pipe 52 may be open to the atmosphere or may be connected to a storage tank that stores combustion gas. When the internal combustion engine 2 is operated in the exclusive combustion operation mode or the dual combustion operation mode, the combustion gas pressurized by the compressor 51 is introduced into each of the multiple combustion chambers 22 via the combustion gas introduction line 5.

[0020] The internal combustion engine 2 may include a throttle valve (flow rate control device) 55 configured to be able to adjust the flow rate of the combustion gas flowing through the second combustion gas pipe 53. The throttle valve 55 has a valve arranged in the second combustion gas pipe 53. The throttle valve 55 can increase the flow rate of the combustion gas flowing through the second combustion gas pipe 53 by increasing the opening degree of the valve, and can decrease the flow rate of the combustion gas flowing through the second combustion gas pipe 53 by decreasing the opening degree of the valve.

[0021] The internal combustion engine 2 may include an intercooler 56 for cooling the combustion gas flowing through the second combustion gas pipe 53. The intercooler 56 performs heat exchange between the combustion gas flowing through the second combustion gas pipe 53 and a cooling heat medium, thereby cooling the combustion gas flowing through the second combustion gas pipe 53. In the illustrated embodiment, the intercooler 56 is arranged downstream of the throttle valve 55 in the flow direction of the combustion gas.

[0022] (Ammonia-side injector) The multiple ammonia-side injectors 9 are for injecting ammonia gas into the inside of the intake-side branch pipes 54 connected to the multiple combustion chambers 22, respectively. The ammonia-side injector 9 is provided individually for each intake-side branch pipe 54. Each of the multiple ammonia-side injectors 9 includes a fuel injection valve configured to inject ammonia gas into the corresponding intake-side branch pipe 54.

[0023] (Ammonia Gas Introduction Line) The ammonia gas introduction line 6 forms a flow path for supplying ammonia gas to each of the multiple ammonia-side injectors 9, and is formed by, for example, piping. In the illustrated embodiment, the ammonia gas introduction line 6 includes an ammonia gas supply source (for example, a gas tank for storing ammonia gas) 61, an ammonia gas pipe 62 for guiding ammonia gas from the ammonia gas supply source 61, and multiple ammonia gas side branch pipes 63 for introducing ammonia gas from the ammonia gas pipe 62 to each of the multiple ammonia-side injectors 9. The ammonia gas supply source 61 may store ammonia in a gaseous state or a liquid state.

[0024] Each of the multiple ammonia gas side branch pipes 63 has one end connected to a common ammonia gas pipe 62 and the other end connected to the ammonia side injector 9 corresponding to the ammonia gas side branch pipe 63. One end of the ammonia gas pipe 62 is connected to an ammonia gas supply source 61. When the internal combustion engine 2 is operated in a dual-fuel operation mode, ammonia gas is introduced into each of the multiple intake side branch pipes 54 via the ammonia gas introduction line 6 and the ammonia side injector 9. The ammonia gas is then introduced into the combustion chamber 22 in a mixed gas state by being mixed with combustion gas, and is combusted in the mixed gas state. In the illustrated embodiment, the ammonia gas stored in the ammonia gas supply source 61 is at a higher pressure than the combustion chamber 22 to which the gas is supplied, and is introduced into the combustion chamber 22 via the ammonia gas introduction line 6 due to the pressure difference.

[0025] (Exhaust Gas Discharge Line) The exhaust gas discharge line 7 forms a flow path through which exhaust gas discharged from the internal combustion engine 2 flows, and is formed by, for example, piping. In the illustrated embodiment, the exhaust gas discharge line 7 includes an exhaust gas pipe 71 for guiding exhaust gas, and a plurality of exhaust gas side branch pipes 72 for discharging exhaust gas from each of the plurality of combustion chambers 22 to the exhaust gas pipe 71. One end of each of the plurality of exhaust gas side branch pipes 72 is connected to the common exhaust gas pipe 71, and the other end is connected to the combustion chamber 22 corresponding to the exhaust gas side branch pipe 72. The exhaust gas discharged from each of the plurality of combustion chambers 22 flows through the exhaust gas discharge line 7. When the internal combustion engine 2 is operated in a dual-fuel operation mode, the exhaust gas flowing through the exhaust gas discharge line 7 may contain nitrogen oxides and ammonia.

[0026] The internal combustion engine 2 may include a turbine 73 provided in the exhaust gas discharge line 7 and configured to be driven by exhaust gas flowing through the exhaust gas discharge line 7. In the illustrated embodiment, the turbine 73 is connected to one end of the exhaust gas pipe 71 and configured to be driven by exhaust gas guided through the exhaust gas pipe 71. The internal combustion engine 2 is equipped with a turbocharger 11 including the above-mentioned compressor 51, the above-mentioned turbine 73, and a rotating shaft 74 that coaxially connects the compressor 51 and the turbine 73. The rotating shaft 74 has the turbine 73 attached to one end and the compressor 51 attached to the other end, and is configured to rotate together with the compressor 51 in conjunction with the rotation of the turbine 73. The internal combustion engine 2 may also include a generator 75 mechanically connected to the drive shaft of the turbine 73 and configured to convert the rotational force of the turbine 73 into electric power.

[0027] The internal combustion engine 2 may include a denitration catalyst 77 for removing nitrogen oxides from the exhaust gas flowing through the exhaust gas discharge line 7, and an ammonia decomposition catalyst 78 for removing ammonia from the exhaust gas flowing through the exhaust gas discharge line 7. In the illustrated embodiment, the denitration catalyst 77 and the ammonia decomposition catalyst 78 are arranged downstream of the turbine 73 in the flow direction of the exhaust gas in the exhaust gas discharge line 7. The exhaust gas discharge line 7 further includes an exhaust gas connection pipe 76 for guiding the exhaust gas from the turbine 73 to the denitration catalyst 77 and the ammonia decomposition catalyst 78, and an exhaust gas discharge pipe 79 for discharging the exhaust gas that has passed through the denitration catalyst 77 and the ammonia decomposition catalyst 78. The downstream end of the exhaust gas discharge pipe 79 may be open to the atmosphere or may be connected to equipment for discharging exhaust gas, such as a chimney.

[0028] FIG. 2 is an explanatory diagram illustrating the relationship between the amount of nitrogen oxides in exhaust gas, the amount of ammonia in exhaust gas, and the excess air ratio. FIG. 2 shows a graph with the amount of nitrogen oxides in exhaust gas flowing through the exhaust gas discharge line 7 (nitrogen oxide emission amount) on the vertical axis and the amount of ammonia in exhaust gas flowing through the exhaust gas discharge line 7 (ammonia emission amount) on the horizontal axis. The graph shown in FIG. 2 shows a target region A1 in which both the nitrogen oxide emission amount and the ammonia emission amount are below their limit values, and a curve L1 showing the relationship between the nitrogen oxide emission amount and the ammonia emission amount versus the excess air ratio λ. As shown by the curve L1 in FIG. 2, increasing the excess air ratio λ and increasing the flow rate of the combustion gas introduced into the combustion chamber 22 can reduce the amount of nitrogen oxide emissions, but tends to increase the amount of ammonia emissions. Furthermore, decreasing the excess air ratio λ and decreasing the flow rate of the combustion gas introduced into the combustion chamber 22 can reduce the amount of ammonia emissions, but tends to increase the amount of nitrogen oxide emissions.

[0029] FIG. 3 is an explanatory diagram illustrating the relationship between the exhaust gas temperature, the amount of ammonia in the exhaust gas, and the excess air ratio. FIG. 3 shows a graph in which the temperature of the exhaust gas (exhaust gas temperature) flowing through the exhaust gas discharge line 7 is plotted on the vertical axis, and the amount of ammonia in the exhaust gas (ammonia emission amount) flowing through the exhaust gas discharge line 7 is plotted on the horizontal axis. The graph in FIG. 3 shows a target region A2 in which both the exhaust gas temperature and the ammonia emission amount are below their limit values, and a curve L2 showing the relationship between the exhaust gas temperature and the ammonia emission amount versus the excess air ratio λ. As shown by the curve L2 in FIG. 3 , increasing the excess air ratio λ and increasing the flow rate of the combustion gas introduced into the combustion chamber 22 reduces the exhaust gas temperature but tends to increase the ammonia emission amount. Furthermore, decreasing the excess air ratio λ and decreasing the flow rate of the combustion gas introduced into the combustion chamber 22 reduces the ammonia emission amount but tends to increase the exhaust gas temperature.

[0030] As indicated by the arrows in the figures, curve L1 shown in FIG. 2 and curve L2 shown in FIG. 3 (relationships of exhaust gas temperature, nitrogen oxide emissions, and ammonia emissions with respect to excess air ratio λ) can change depending on changes in combustion state and exhaust gas catalyst performance due to changes in environmental conditions, unexpected transient operation, equipment deterioration, and the like. For example, when exhaust gas catalysts (denitrification catalyst 77 and ammonia decomposition catalyst 78) are provided in the exhaust gas discharge line 7, these exhaust gas catalysts are highly temperature-dependent and exhibit complex behavior, such as a sudden increase in nitrogen oxide emissions when the exhaust gas temperature increases when the excess air ratio λ is reduced. Therefore, even if the excess air ratio λ is determined so that the nitrogen oxide emissions and ammonia emissions satisfy (are below) the limit values ​​under standard environmental conditions and the flow rate of the combustion gas introduced into the combustion chamber 22 is adjusted to achieve this determined excess air ratio λ, the nitrogen oxide emissions and ammonia emissions may exceed the limit values. Furthermore, it is difficult to determine in advance an excess air ratio λ that can accommodate changes in environmental conditions, unexpected transient operation, equipment deterioration, and the like.

[0031] The control device 3 of the internal combustion engine 2 is an electronic control unit that controls the operation of each device provided in the internal combustion engine 2, such as the liquid fuel side injector 8, the ammonia side injector 9, and the throttle valve 55 (flow rate control device 10). The control device 3 may be configured as a microcomputer including a central processing unit (CPU) including a processor, a random access memory (RAM), a read-only memory (ROM), an I / O interface, and the like. In the illustrated embodiment, the control device 3 is configured as an engine control unit. Note that in some other embodiments, the control device 3 may be implemented as one of the functions (programs or circuits) provided in the engine control unit. Furthermore, in some other embodiments, the control device 3 may be configured as an electronic control unit separate from the engine control unit.

[0032] As shown in Fig. 1 , a control device 3 for an internal combustion engine 2 according to some embodiments includes a nitrogen oxide amount acquisition unit 31, an ammonia amount acquisition unit 32, and a flow rate control unit 33. The nitrogen oxide amount acquisition unit 31 is configured to acquire the amount of nitrogen oxides in exhaust gas emitted from the internal combustion engine 2 (nitrogen oxide emission amount). The ammonia amount acquisition unit 32 is configured to acquire the amount of ammonia in exhaust gas emitted from the internal combustion engine 2 (ammonia emission amount). A control method for an internal combustion engine 2 according to some embodiments includes a nitrogen oxide amount acquisition step of acquiring the nitrogen oxide emission amount, and an ammonia amount acquisition step of acquiring the ammonia emission amount. In the following embodiments, the nitrogen oxide amount acquisition step is performed by the nitrogen oxide amount acquisition unit 31 of the control device 3, and the ammonia amount acquisition step is performed by the ammonia amount acquisition unit 32 of the control device 3.

[0033] In the illustrated embodiment, the internal combustion engine 2 includes a nitrogen oxide sensor 12 that measures the amount of nitrogen oxides in the exhaust gas flowing through the exhaust gas discharge line 7, and an ammonia sensor 13 that measures the amount of ammonia in the exhaust gas flowing through the exhaust gas discharge line 7. The amount of nitrogen oxides in the exhaust gas measured by the nitrogen oxide sensor 12 is sent from the nitrogen oxide sensor 12 to the nitrogen oxide amount acquisition unit 31. The amount of ammonia in the exhaust gas measured by the ammonia sensor 13 is sent from the ammonia sensor 13 to the ammonia amount acquisition unit 32. The nitrogen oxide sensor 12 and the ammonia sensor 13 are not limited to sensors that physically measure the amount of the detection target (nitrogen oxide, ammonia) in the exhaust gas, but may be sensors that calculate the amount of the detection target in the exhaust gas or estimate the amount from measurements of other sensors.

[0034] The flow rate control unit 33 is configured to issue a flow rate adjustment instruction to the flow rate control device 10, which is configured to adjust the flow rate of the combustion gas introduced to the internal combustion engine 2, so that the amount of nitrogen oxides acquired by the nitrogen oxide amount acquisition unit 31 and the amount of ammonia acquired by the ammonia amount acquisition unit 32 do not exceed their respective threshold values ​​when the internal combustion engine 2 is operating in the dual-fuel operation mode. In the illustrated embodiment, the flow rate adjustment device 10 is the above-mentioned throttle valve 55, but in other embodiments, the flow rate adjustment device 10 may be a device equipped with a flow rate adjustment mechanism other than the throttle valve 55. Specific examples of devices equipped with a flow rate adjustment mechanism include an electric compressor (not shown) provided in the combustion gas introduction line 5 and a variable nozzle (not shown) that changes the exhaust gas passage area of ​​a variable displacement turbocharger provided in the exhaust gas discharge line 7. A control method for the internal combustion engine 2 according to some embodiments includes a flow rate control step of issuing a flow rate adjustment instruction to the flow rate control device 10 to adjust the flow rate of the combustion gas introduced to the internal combustion engine 2. In the following embodiment, the flow rate control step is performed by the flow rate control unit 33 of the control device 3.

[0035] When environmental conditions or the like change, the combustion state or the like also changes, and therefore the relationship of the nitrogen oxide emissions and ammonia emissions to the excess air ratio λ is constantly changing. The control device 3 uses the amount of nitrogen oxides acquired by the nitrogen oxide amount acquisition unit 31 and the amount of ammonia acquired by the ammonia amount acquisition unit 32, rather than the excess air ratio λ, as control parameters for adjusting the flow rate of the combustion gas introduced into the internal combustion engine 2. Such a control device 3 is capable of adjusting the flow rate of the combustion gas so that the nitrogen oxide and ammonia emissions satisfy the limit values ​​even when environmental conditions or the like change.

[0036] 1, the internal combustion engine 2 may include a selection device (switch) 15 for manually selecting an operation mode of the internal combustion engine 2. The control device 3 is configured to perform operation control and combustion control of the internal combustion engine 2 in accordance with information (signals) related to the operation mode sent from the selection device 15. When the internal combustion engine 2 is operated in the dual-fuel operation mode, the control device 3 monitors the ever-changing amounts of nitrogen oxides acquired by the nitrogen oxide amount acquisition unit 31 and the ammonia amount acquired by the ammonia amount acquisition unit 32.

[0037] 1 , the nitrogen oxide amount acquisition unit 31 is configured to acquire the amount of nitrogen oxides in exhaust gas flowing downstream of a denitration catalyst 77 for removing nitrogen oxides in the exhaust gas discharge line 7. In the illustrated embodiment, the nitrogen oxide sensor 12 is provided in an exhaust gas discharge pipe 79 through which exhaust gas flows that has passed through the denitration catalyst 77 and the ammonia decomposition catalyst 78, and is configured to measure the amount of nitrogen oxides in the exhaust gas flowing through the exhaust gas discharge pipe 79. The nitrogen oxide amount acquisition unit 31 acquires the measurement results of the nitrogen oxide sensor 12.

[0038] The amount of nitrogen oxides in the exhaust gas flowing downstream of the denitration catalyst 77 in the exhaust gas discharge line 7 is equivalent to the amount of nitrogen oxides actually discharged into the atmosphere. By using the amount of nitrogen oxides in the exhaust gas flowing downstream of the denitration catalyst 77 in the exhaust gas discharge line 7, acquired by the nitrogen oxide amount acquisition unit 31, for control in the control device 3, the control device 3 can more appropriately control the amount of nitrogen oxide emissions to satisfy the limit value.

[0039] 1 , the ammonia amount acquisition unit 32 is configured to acquire the amount of ammonia in the exhaust gas flowing downstream of an ammonia decomposition catalyst 78 for removing ammonia in the exhaust gas discharge line 7. In the illustrated embodiment, the ammonia sensor 13 is provided in an exhaust gas discharge pipe 79 through which exhaust gas flows that has passed through the denitration catalyst 77 and the ammonia decomposition catalyst 78, and is configured to measure the amount of ammonia in the exhaust gas flowing through the exhaust gas discharge pipe 79. The ammonia amount acquisition unit 32 acquires the measurement result of the ammonia sensor 13.

[0040] The amount of ammonia in the exhaust gas flowing downstream of the ammonia decomposition catalyst 78 in the exhaust gas discharge line 7 is equivalent to the amount of ammonia emitted actually discharged into the atmosphere. By using the amount of ammonia in the exhaust gas flowing downstream of the ammonia decomposition catalyst 78 in the exhaust gas discharge line 7, acquired by the ammonia amount acquisition unit 32, for control in the control device 3, the control device 3 can more appropriately control the amount of ammonia emissions to satisfy the limit value.

[0041] 4 is a control flow diagram of an internal combustion engine according to an embodiment of the present disclosure. The internal combustion engine 2 receives a dual-fuel operation start command from the control device 3 (step S1) and operates in a dual-fuel operation mode.

[0042] 4 , in some embodiments, when the internal combustion engine 2 is operating in the dual-fuel operation mode, if the amount ANO of nitrogen oxides acquired by the nitrogen oxide amount acquisition unit 31 satisfies a flow rate reduction condition that the amount ANO is equal to or less than the first nitrogen oxide threshold NOT1 ("Yes" in step S2), the flow rate control unit 33 is configured to issue a flow rate reduction instruction to the flow control device 10 to reduce the flow rate of the combustion gas introduced to the internal combustion engine 2 (step S3). The flow rate of the combustion gas introduced to the internal combustion engine 2 can be reduced within a range in which the amount ANO of nitrogen oxides acquired by the nitrogen oxide amount acquisition unit 31 does not exceed the first nitrogen oxide threshold NOT1. By reducing the flow rate of the combustion gas introduced to the internal combustion engine 2, it is possible to minimize ammonia emissions while satisfying the limit value of nitrogen oxide emissions.

[0043] In the embodiment shown in FIG. 4, when the amount ANO of nitrogen oxides acquired by the nitrogen oxide amount acquisition unit 31 exceeds the first nitrogen oxide threshold NOT1 ("No" in step S2), the control device 3 determines whether the amount AA of ammonia acquired by the ammonia amount acquisition unit 32 is equal to or less than the ammonia threshold AT (step S4).

[0044] (Transition to Exclusive-Fuel Operation Mode) In some embodiments, the control device 3 of the internal combustion engine 2 includes a first operation mode control unit 34. As shown in FIG. 4 , when the internal combustion engine 2 is operating in the exclusive-fuel operation mode, the first operation mode control unit 34 is configured to switch the operation mode of the internal combustion engine 2 to the exclusive-fuel operation mode when a combination-fuel operation stop condition is satisfied, the combination-fuel operation stop condition including both a determination condition that the amount of nitrogen oxides ANO acquired by the nitrogen oxide amount acquisition unit 31 exceeds the first nitrogen oxide threshold value NOT1 ("No" in step S2) and a determination condition that the amount of ammonia AA acquired by the ammonia amount acquisition unit 32 exceeds the ammonia threshold value AT ("No" in step S4). The internal combustion engine 2 stops the combination-fuel operation and transitions to the exclusive-fuel operation upon receiving an instruction from the control device 3 (step S8). A control method for the internal combustion engine 2 according to some embodiments includes a first operation mode control step of switching the operation mode of the internal combustion engine 2 to the exclusive-fuel operation mode when the combination-fuel operation stop condition is satisfied. In the following embodiment, the first operation mode control step is performed by the first operation mode control unit 34 of the control device 3.

[0045] When the above-mentioned conditions for stopping the multi-firing operation are met, it is difficult to continue the multi-firing operation so that both the nitrogen oxide and ammonia emissions meet their limit values ​​by adjusting the flow rate of the combustion gas. When the above-mentioned conditions for stopping the multi-firing operation are met, the control device 3 quickly stops the multi-firing operation and switches to mono-firing operation, thereby quickly improving (reducing) the nitrogen oxide and ammonia emissions.

[0046] 4 , in a state where the internal combustion engine 2 is operating in the dual-fuel operation mode, when flow rate increase conditions including both a determination condition that the amount of ammonia AA acquired by the ammonia amount acquisition unit 32 is equal to or less than the ammonia threshold value AT ("Yes" in step S4) and a determination condition that the amount of nitrogen oxide ANO acquired by the nitrogen oxide amount acquisition unit 31 exceeds the second nitrogen oxide threshold value NOT2 ("Yes" in step S5) are satisfied, the flow rate control unit 33 is configured to issue a flow rate increase instruction to the flow control device 10 to increase the flow rate of the combustion gas introduced to the internal combustion engine 2 (step S6). The second nitrogen oxide threshold value NOT2 is the same as or greater than the first nitrogen oxide threshold value NOT1.

[0047] The control device 3 reduces the flow rate of the combustion gas introduced to the internal combustion engine 2 as much as possible to reduce the amount of ammonia emissions as much as possible, but there may be a sudden increase in the amount of nitrogen oxide emissions due to changes in environmental conditions, etc. When the amount of nitrogen oxides ANO acquired by the nitrogen oxide amount acquisition unit 31 exceeds the second nitrogen oxide threshold NOT2, the control device 3 issues the flow rate increase command, thereby increasing the flow rate of the combustion gas introduced to the internal combustion engine 2 so that the amount of nitrogen oxide emissions satisfies the limit value.

[0048] As shown in FIG. 4 , when determining whether the flow rate increase condition is satisfied, if the amount of ammonia AA acquired by the ammonia amount acquisition unit 32 is equal to or less than the ammonia threshold value AT ("Yes" in step S4) and the amount of nitrogen oxide ANO acquired by the nitrogen oxide amount acquisition unit 31 is less than the second nitrogen oxide threshold value NOT2 ("No" in step S5), the control device 3 continues the dual-fuel combustion operation without issuing the flow rate increase command (step S7).

[0049] In some of the above-described embodiments, the control device 3 adjusts the flow rate of the combustion gas introduced into the combustion chamber 22 so that the nitrogen oxide emission amount and the ammonia emission amount satisfy the limit values. If the temperature of the exhaust gas flowing through the exhaust gas discharge line 7 becomes excessively high, there is a risk that the heat of the exhaust gas may damage the equipment, piping, etc. that constitutes the exhaust gas discharge line 7. Therefore, it is preferable that the control device 3 adjusts the flow rate of the combustion gas introduced into the combustion chamber 22 so that the exhaust gas temperature also satisfies the limit values.

[0050] In some embodiments, the control device 3 of the internal combustion engine 2 includes an exhaust gas temperature acquisition unit 35 configured to acquire the temperature of the exhaust gas flowing through the exhaust gas discharge line 7, as shown in FIG. 1 . In the illustrated embodiment, the internal combustion engine 2 includes a temperature sensor 14 that measures the temperature of the exhaust gas flowing through the exhaust gas discharge line 7. The exhaust gas temperature measured by the temperature sensor 14 is transmitted to the exhaust gas temperature acquisition unit 35 on a regular basis. The temperature sensor 14 is not limited to a sensor that physically measures the exhaust gas temperature; it may be a sensor that calculates the exhaust gas temperature or estimates the exhaust gas temperature from measurements of other sensors. When the internal combustion engine 2 is operating in a dual-fuel operation mode, the control device 3 monitors the exhaust gas temperature acquired by the exhaust gas temperature acquisition unit 35, which changes from moment to moment. A control method for the internal combustion engine 2 according to some embodiments includes an exhaust gas temperature acquisition step of acquiring the temperature of the exhaust gas flowing through the exhaust gas discharge line 7. In the following embodiments, the exhaust gas temperature acquisition step is performed by the exhaust gas temperature acquisition unit 35.

[0051] 5 is a control flow diagram of an internal combustion engine according to an embodiment of the present disclosure. In some embodiments, the flow rate reduction condition described above further includes a determination condition that the exhaust gas temperature GT acquired by the exhaust gas temperature acquisition unit 35 is equal to or less than the first temperature threshold value TT1. That is, as shown in FIG. 5 , when the internal combustion engine 2 is operating in the dual-fuel operation mode, the flow rate control unit 33 is configured to issue a flow rate reduction instruction to the flow control device 10 to reduce the flow rate of the combustion gas introduced into the internal combustion engine 2 (step S3) when the flow rate reduction conditions are satisfied, including both the determination condition that the amount of nitrogen oxides ANO acquired by the nitrogen oxide amount acquisition unit 31 is equal to or less than the first nitrogen oxide threshold value NOT1 and the determination condition that the exhaust gas temperature GT acquired by the exhaust gas temperature acquisition unit 35 is equal to or less than the first temperature threshold value TT1 ("Yes" in step S2).

[0052] In this case, the flow rate of the combustion gas introduced into the internal combustion engine 2 can be reduced within a range in which the amount of nitrogen oxides ANO acquired by the nitrogen oxide amount acquisition unit 31 does not exceed the first nitrogen oxide threshold NOT1 and the temperature of the exhaust gas GT acquired by the exhaust gas temperature acquisition unit 35 does not exceed the first temperature threshold TT1. By reducing the flow rate of the combustion gas introduced into the internal combustion engine 2, the amount of nitrogen oxide emissions and the temperature of the exhaust gas can be made to satisfy their limit values, while the amount of ammonia emissions can be reduced as much as possible. By performing control such that the temperature of the exhaust gas satisfies the limit value, the control device 3 can suppress damage caused by the heat of the exhaust gas to the equipment, piping, etc. that constitute the exhaust gas discharge line 7.

[0053] In the embodiment shown in FIG. 5 , when either the determination condition that the amount ANO of nitrogen oxides acquired by the nitrogen oxide amount acquisition unit 31 exceeds the first nitrogen oxide threshold NOT1 or the determination condition that the temperature GT of the exhaust gas acquired by the exhaust gas temperature acquisition unit 35 exceeds the first temperature threshold TT1 is satisfied ("No" in step S2), the control device 3 determines whether the amount AA of ammonia acquired by the ammonia amount acquisition unit 32 is equal to or less than the ammonia threshold AT (step S4).

[0054] 5 , the first operation mode control unit 34 is configured to switch the operation mode of the internal combustion engine 2 to the exclusive combustion operation mode when, while the internal combustion engine 2 is operating in the exclusive combustion operation mode, a combination combustion operation stop condition is satisfied, which includes both a determination condition that the exhaust gas temperature GT acquired by the exhaust gas temperature acquisition unit 35 exceeds the first temperature threshold TT1 ("No" in step S2) and a determination condition that the amount of ammonia AA acquired by the ammonia amount acquisition unit 32 exceeds the ammonia threshold AT ("No" in step S4). Upon receiving an instruction from the control device 3, the internal combustion engine 2 stops the combination combustion operation and transitions to the exclusive combustion operation (step S8).

[0055] 5 , when the internal combustion engine 2 is operating in the dual-fuel operation mode, the flow rate control unit 33 is configured to issue a flow rate increase instruction to the flow control device 10 to increase the flow rate of the combustion gas introduced into the internal combustion engine 2 (step S6) when a flow rate increase condition is satisfied, the flow rate increase condition including both a determination condition that the amount of ammonia AA acquired by the ammonia amount acquisition unit 32 is equal to or less than the ammonia threshold value AT ("Yes" in step S4) and a determination condition that the temperature of the exhaust gas GT acquired by the exhaust gas temperature acquisition unit 35 exceeds the second temperature threshold value TT2 ("Yes" in step S5). The second temperature threshold value TT2 is equal to or greater than the first temperature threshold value TT1.

[0056] 5 , the flow rate control unit 33 is configured to issue a flow rate increase instruction to the flow control device 10 to increase the flow rate of the combustion gas introduced into the internal combustion engine 2 (step S6) even when flow rate increase conditions including both a determination condition that the amount of ammonia AA acquired by the ammonia amount acquisition unit 32 is equal to or less than the ammonia threshold value AT ("Yes" in step S4) and a determination condition that the amount of nitrogen oxide ANO acquired by the nitrogen oxide amount acquisition unit 31 exceeds the second nitrogen oxide threshold value NOT2 ("Yes" in step S5) are satisfied when the internal combustion engine 2 is operating in the multi-fuel operation mode. In other words, the flow rate control unit 33 is configured to issue the flow rate increase instruction (step S6) when either the determination condition related to the exhaust gas temperature GT or the determination condition related to the amount of nitrogen oxide ANO is satisfied ("Yes" in step S5) and the determination condition related to the amount of ammonia AA is satisfied ("Yes" in step S4) when the internal combustion engine 2 is operating in the multi-fuel operation mode.

[0057] The control device 3 reduces the flow rate of the combustion gas introduced to the internal combustion engine 2 as much as possible to reduce ammonia emissions as much as possible, but the exhaust gas temperature may suddenly increase due to changes in environmental conditions, etc. When the exhaust gas temperature GT acquired by the exhaust gas temperature acquisition unit 35 exceeds the second temperature threshold value TT2, the control device 3 can increase the flow rate of the combustion gas introduced to the internal combustion engine 2 so that the exhaust gas temperature GT satisfies the limit value.

[0058] As shown in FIG. 5 , when determining whether the flow rate increase condition is satisfied, if the amount of ammonia AA acquired by the ammonia amount acquisition unit 32 is equal to or less than the ammonia threshold value AT ("Yes" in step S4), the amount of nitrogen oxide ANO acquired by the nitrogen oxide amount acquisition unit 31 is less than the second nitrogen oxide threshold value NOT2, and the temperature of the exhaust gas GT acquired by the exhaust gas temperature acquisition unit 35 is less than the second temperature threshold value TT2 ("No" in step S5), the control device 3 continues the dual-fuel combustion operation without issuing the flow rate increase command (step S7).

[0059] 1 , the exhaust gas temperature acquisition unit 35 is configured to acquire the temperature of the exhaust gas flowing upstream of the turbine 73 in the exhaust gas discharge line 7. In the illustrated embodiment, the temperature sensor 14 is provided in the exhaust gas pipe 71 and measures the temperature of the exhaust gas flowing through the exhaust gas pipe 71. The exhaust gas temperature acquisition unit 35 acquires the measurement result of the temperature sensor 14.

[0060] The temperature of the exhaust gas discharge line 7 upstream of the turbine 73 is higher than the temperature of the exhaust gas downstream of the turbine 73. By using the temperature of the exhaust gas flowing upstream of the turbine 73 in the exhaust gas discharge line 7, which is relatively high temperature, for control in the control device 3, the control device 3 can more appropriately control the exhaust gas temperature to satisfy the limit value. This makes it possible to more effectively suppress damage caused by the heat of the exhaust gas to the equipment, piping, etc. that constitute the exhaust gas discharge line 7.

[0061] 1 , the control device 3 for the internal combustion engine 2 includes a parameter acquisition unit 36, an association information acquisition unit 37, and an operating condition determination unit 38. According to some embodiments, a control method for the internal combustion engine 2 includes a parameter acquisition step of acquiring a plurality of parameters related to the operating state of the internal combustion engine 2, an association information acquisition step of acquiring association information that associates the plurality of parameters with operating conditions under which a multi-fuel operation mode is possible, and an operating condition determination step of determining, based on the association information, whether the plurality of parameters acquired in the parameter acquisition step satisfy the operating conditions under which the multi-fuel operation mode is possible. In the following embodiments, the parameter acquisition step is performed by the parameter acquisition unit 36. The association information acquisition step is performed by the association information acquisition unit 37. The operating condition determination step is performed by the operating condition determination unit 38.

[0062] The parameter acquisition unit 36 ​​is configured to acquire a plurality of parameters related to the operating state of the internal combustion engine 2. The parameter acquisition unit 36 ​​acquires the plurality of parameters from the internal combustion engine 2, devices, sensors, etc. mounted on the internal combustion engine 2. The sensors for acquiring the parameters are not limited to those that physically measure the parameters, but may be those that calculate the parameters or estimate the parameters from measurements of other sensors. The plurality of parameters related to the operating state of the internal combustion engine 2 include a parameter related to the rotation speed of the internal combustion engine 2 and a parameter related to the load of the internal combustion engine 2. Specific examples of the parameters include the rotation speed of the internal combustion engine 2, the load of the internal combustion engine 2, the fuel injection amount of the liquid fuel side injector 8, the intake pressure (e.g., the pressure downstream of the throttle valve 55 in the flow direction of the combustion gas in the second combustion gas pipe 53), the output of the generator 75, etc.

[0063] The association information acquisition unit 37 is configured to acquire association information that associates multiple parameters with operating conditions under which the multi-fuel operation mode is possible. The association information indicates the correspondence between the multiple parameters and the operating conditions under which the multi-fuel operation mode is possible. When two or more types of multiple parameters are input, it is sufficient that the association information can acquire, as output information, information regarding whether the operating conditions corresponding to the multiple parameters that are the input information are operating conditions under which the multi-fuel operation mode is possible. The association information includes lists, tables, maps, functions, machine learning models, etc. that indicate the correspondence between the input information and the output information. The association information may be created based on steady-state test data, or may be created based on past performance values, experimental values, numerical analysis results, etc. other than steady-state test data.

[0064] 7 is a control flow diagram of an internal combustion engine according to an embodiment of the present disclosure. The operating condition determination unit 38 is configured to determine whether or not the plurality of parameters acquired by the parameter acquisition unit 36 ​​satisfy the operating conditions based on the association information acquired by the association information acquisition unit 37 when the internal combustion engine 2 is operating in the dedicated combustion operation mode (the area surrounded by the dotted line in FIG. 7) (step S9).

[0065] When the internal combustion engine 2 is operated in the mono-fuel operation mode, the operating condition determination unit 38 monitors the above-mentioned multiple parameters acquired by the parameter acquisition unit 36, which change from moment to moment, and determines whether or not the operating conditions for the dual-fuel operation mode are met.

[0066] 6 is an explanatory diagram for explaining a control map showing the relationship between the rotation speed and load of the internal combustion engine 2 and the operating conditions under which dual-fuel operation is possible according to one embodiment of the present disclosure. In some embodiments, the association information includes a control map showing the relationship between multiple parameters and the operating conditions under which dual-fuel operation is possible, as shown in FIG. 6, in which an area A3 under which the dual-fuel operation mode is possible is set on the map configured by the multiple parameters. The operating condition determination unit 38 is configured to determine whether the multiple parameters acquired by the parameter acquisition unit 36 ​​satisfy the operating conditions by referring to the control map.

[0067] Fig. 6 shows a two-dimensional map with the rotation speed of the internal combustion engine 2, which is one of the above parameters, on the horizontal axis and the load of the internal combustion engine 2, which is also one of the above parameters, on the vertical axis. A region A3 in which the dual-fuel operation mode is possible under standard environmental conditions and a line L3 indicating a specified maximum torque are preset in the two-dimensional map shown in Fig. 6. By referring to the two-dimensional map shown in Fig. 6, the operating condition determination unit 38 can determine whether the operating state of the internal combustion engine 2 is possible for the dual-fuel operation mode (whether the operating state belongs to region A3) from the rotation speed and load of the internal combustion engine 2 acquired by the parameter acquisition unit 36.

[0068] When determining whether the multiple parameters acquired by the parameter acquisition unit 36 ​​satisfy the operating conditions, the operating condition determination unit 38 may refer to a two-dimensional map having at least one parameter different from the two-dimensional map shown in Figure 6, a three-dimensional map showing the relationship between the three types of parameters and the operating conditions under which the dual-fuel operation mode is possible, or association information other than the control map. The operating condition determination unit 38 may refer to association information stored in the memory unit 30 of the control device 3, or may refer to association information stored in a device external to the control device 3.

[0069] The operating condition determination unit 38 can determine whether the multiple parameters acquired by the parameter acquisition unit 36 ​​satisfy the operating conditions under which the multi-fuel operation mode is possible. When the determination result by the operating condition determination unit 38 is favorable, the control device 3 permits switching to the multi-fuel operation mode, thereby attempting multi-fuel operation when the operating state is unlikely to be established in the multi-fuel operation mode, thereby suppressing unnecessary ammonia emissions. Furthermore, by using a control map in which a region where the multi-fuel operation mode is possible under standard environmental conditions for the determination by the operating condition determination unit 38, it is possible to appropriately and quickly determine whether the operating state of the internal combustion engine 2 is appropriate for the multi-fuel operation mode.

[0070] In some embodiments, as shown in FIG. 1 , the control device 3 for the internal combustion engine 2 includes a second operation mode control unit 39. As shown in FIG. 7 , the second operation mode control unit 39 is configured to switch the operation mode of the internal combustion engine 2 to the multi-combustion operation mode when, while the internal combustion engine 2 is operating in the mono-combustion operation mode, a multi-combustion operation enabling condition is satisfied, including a determination condition that the above-mentioned plurality of parameters satisfy an operating condition enabling the multi-combustion operation mode. The second operation mode control unit 39 of the control device 3 may automatically switch the operation mode of the internal combustion engine 2 to the multi-combustion operation mode when the multi-combustion operation enabling condition is satisfied. The internal combustion engine 2 stops the mono-combustion operation and switches to multi-combustion operation upon receiving an instruction from the control device 3 (step S10). According to some embodiments, a control method for the internal combustion engine 2 includes a second operation mode control step of switching the operation mode of the internal combustion engine 2 to the multi-combustion operation mode when it is determined in the operating condition determination step that the above-mentioned multi-combustion operation enabling condition is satisfied. In the following embodiments, the second operation mode control step is performed by the second operation mode control unit 39 of the control device 3.

[0071] The multi-fuel operation enabling condition may further include a determination condition that the multi-fuel operation mode is selected by the selection device 15. In this case, when the multi-fuel operation mode is manually selected by the selection device 15 in a state in which the above-mentioned plurality of parameters satisfy the operating conditions that enable the multi-fuel operation mode, the second operation mode control unit 39 of the control device 3 switches the operation mode of the internal combustion engine 2 to the multi-fuel operation mode (step S10).

[0072] The control device 3 permits the switching operation to the multi-combustion operation mode when the determination result of the operating condition determination unit 38 is favorable, thereby enabling the switching to the multi-combustion operation mode when the operating state of the internal combustion engine 2 is appropriate for the multi-combustion operation mode. Note that even after the multi-combustion operation mode is not established and the operation mode is switched to the exclusive combustion operation mode, the control device 3 can return to the multi-combustion operation mode when the determination result of the operating condition determination unit 38 is favorable. Furthermore, even when the control device 3 attempts to switch to the multi-combustion operation mode for the first time after the internal combustion engine 2 is started, the permission of the switching operation to the multi-combustion operation mode may be limited to cases when the determination result of the operating condition determination unit 38 is favorable.

[0073] The above-mentioned thresholds (first nitrogen oxide threshold NOT1, second nitrogen oxide threshold NOT2, ammonia threshold AT, first temperature threshold TT1, second temperature threshold TT2) may be stored in the above-mentioned storage unit 30. Each unit of the above-mentioned control device 3 (flow rate control unit 33, first operation mode control unit 34, second operation mode control unit 39) may refer to the above-mentioned thresholds stored in the storage unit 30.

[0074] In this specification, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions expressing that things are in an equal state, such as "identical," "equal," and "homogeneous," not only express a state in which there is a strict equivalence, but also express a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions expressing shapes such as a rectangular shape or a cylindrical shape not only express shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components.

[0075] The present disclosure is not limited to the above-described embodiments, but also includes modifications to the above-described embodiments and appropriate combinations of these modifications.

[0076] The contents of the above-described embodiments can be understood, for example, as follows.

[0077] 1) A control device (3) for an internal combustion engine (2) according to at least one embodiment of the present disclosure is a control device (3) for an internal combustion engine (2) for controlling operation of the internal combustion engine (2) configured to be able to switch between a plurality of operation modes, the plurality of operation modes including a mono-fuel operation mode in which a liquid fuel is used as the fuel, and a multi-fuel operation mode in which both the liquid fuel and ammonia gas are used as the fuels, the control device (3) for the internal combustion engine (2) comprising: a nitrogen oxide amount acquisition unit (31) configured to acquire the amount of nitrogen oxides in exhaust gas emitted from the internal combustion engine (2); and an ammonia amount acquisition unit (32) configured to acquire the amount of ammonia in the exhaust gas emitted from the internal combustion engine (2); and a flow control unit (33) configured to give a flow rate adjustment instruction to adjust the flow rate of the combustion gas introduced to the internal combustion engine (2) to a flow rate adjustment device (10) configured to adjust the flow rate of the combustion gas introduced to the internal combustion engine (2) so that, when the internal combustion engine (2) is operated in the multi-fuel operation mode, the amount of nitrogen oxides acquired by the nitrogen oxide amount acquisition unit (31) and the amount of ammonia acquired by the ammonia amount acquisition unit (32) do not exceed threshold values.

[0078] According to the configuration of 1) above, when environmental conditions or the like change, the combustion state or the like also changes, and therefore the relationship of the nitrogen oxide emissions and the ammonia emissions to the excess air ratio is constantly changing. The control device (3) uses the amount of nitrogen oxides acquired by the nitrogen oxide amount acquisition unit (31) and the amount of ammonia acquired by the ammonia amount acquisition unit (33) as control parameters for adjusting the flow rate of the combustion gas introduced into the internal combustion engine (2), rather than the excess air ratio. Such a control device (3) is capable of adjusting the flow rate of the combustion gas so that the nitrogen oxide and ammonia emissions satisfy the limit values ​​even when environmental conditions or the like change.

[0079] 2) In some embodiments, in the control device (3) for an internal combustion engine (2) described in 1) above, the flow rate control unit (33) is configured to issue a flow rate reduction instruction to the flow rate adjustment device (10) to reduce the flow rate of the combustion gas introduced to the internal combustion engine (2) when, in a state where the internal combustion engine (2) is operated in the multi-fuel operation mode, the amount of nitrogen oxides (ANO) acquired by the nitrogen oxide amount acquisition unit (31) satisfies a flow rate reduction condition including at least a determination condition that the amount of nitrogen oxides (ANO) is equal to or less than a first nitrogen oxide threshold value (NOT1).

[0080] According to the configuration 2), the flow rate of the combustion gas introduced into the internal combustion engine 2 can be reduced within a range in which the amount of nitrogen oxides (ANO) acquired by the nitrogen oxide amount acquisition unit 31 does not exceed the first nitrogen oxide threshold value (NOT1). By reducing the flow rate of the combustion gas introduced into the internal combustion engine 2, the amount of ammonia emissions can be reduced as much as possible while the amount of nitrogen oxide emissions satisfies the limit value.

[0081] 3) In some embodiments, in the control device (3) for an internal combustion engine (2) described in 1) above, the flow rate control unit (33) is configured to issue a flow rate increase instruction to the flow rate adjustment device (10) to increase the flow rate of the combustion gas introduced to the internal combustion engine (2) when a flow rate increase condition is satisfied, the flow rate increase condition including both a determination condition that the amount of ammonia (AA) acquired by the ammonia amount acquisition unit (32) is equal to or less than an ammonia threshold value (AT) and a determination condition that the amount of nitrogen oxides (ANO) acquired by the nitrogen oxide amount acquisition unit (31) exceeds a second nitrogen oxide threshold value (NOT2) that is equal to or greater than the first nitrogen oxide threshold value (NOT1) while the internal combustion engine is operating in the multi-fuel operation mode.

[0082] According to the configuration 3), when the amount of nitrogen oxides (ANO) acquired by the nitrogen oxide amount acquisition unit (31) exceeds the second nitrogen oxide threshold value (NOT2), the flow rate of the combustion gas introduced into the internal combustion engine (2) can be increased so that the amount of nitrogen oxide emissions satisfies the limit value.

[0083] 4) In some embodiments, the control device (3) for an internal combustion engine (2) according to any one of 1) to 3) above further comprises a first operation mode control unit (34) configured to switch the operation mode of the internal combustion engine (2) to the mono-fuel operation mode when a multi-fuel operation stop condition is satisfied, the multi-fuel operation stop condition including both a determination condition that the amount of nitrogen oxides (ANO) acquired by the nitrogen oxide amount acquisition unit (31) exceeds a first nitrogen oxide threshold value (NOT1) and a determination condition that the amount of ammonia (AA) acquired by the ammonia amount acquisition unit (32) exceeds an ammonia threshold value (AT) while the internal combustion engine (2) is operating in the multi-fuel operation mode.

[0084] According to the configuration of 4) above, when the condition for stopping the multi-fuel operation is satisfied, it is difficult to continue the multi-fuel operation so that both the nitrogen oxide and ammonia emissions meet their limit values ​​by adjusting the flow rate of the combustion gas. When the condition for stopping the multi-fuel operation is satisfied, the control device (3) quickly stops the multi-fuel operation and switches to the mono-fuel operation, thereby quickly improving (reducing) the nitrogen oxide and ammonia emissions.

[0085] 5) In some embodiments, the control device (3) for the internal combustion engine (2) described in 2) or 3) above further comprises an exhaust gas temperature acquisition unit (35) configured to acquire the temperature of the exhaust gas, and the flow rate reduction condition further includes a determination condition that the temperature (GT) of the exhaust gas acquired by the exhaust gas temperature acquisition unit (35) is equal to or lower than a first temperature threshold (TT1).

[0086] According to the configuration of 5) above, the flow rate of the combustion gas introduced into the internal combustion engine (2) can be reduced within a range in which the amount of nitrogen oxides (ANO) acquired by the nitrogen oxide amount acquisition unit (31) does not exceed the first nitrogen oxide threshold value (NOT1) and the temperature of the exhaust gas (GT) acquired by the exhaust gas temperature acquisition unit (35) does not exceed the first temperature threshold value (TT1). By reducing the flow rate of the combustion gas introduced into the internal combustion engine (2), the amount of nitrogen oxide emissions and the temperature of the exhaust gas can be made to satisfy their limit values, while the amount of ammonia emissions can be reduced as much as possible. By performing control such that the temperature of the exhaust gas satisfies the limit value, the control device (3) can suppress damage caused by the heat of the exhaust gas to equipment, piping, etc. that constitute the exhaust gas discharge line (7) through which the exhaust gas discharged from the internal combustion engine (2) flows.

[0087] 6) In some embodiments, in the control device (3) for an internal combustion engine (2) described in 5) above, the flow rate control unit (33) is configured to issue a flow rate increase instruction to the flow rate adjustment device (10) to increase the flow rate of the combustion gas introduced to the internal combustion engine (2) when a flow rate increase condition including both a determination condition that the amount of ammonia (AA) acquired by the ammonia amount acquisition unit (32) is equal to or less than an ammonia threshold value (AT) and a determination condition that the temperature of the exhaust gas (GT) acquired by the exhaust gas temperature acquisition unit (35) exceeds a second temperature threshold value (TT2) that is the same as the first temperature threshold value (TT1) or a value greater than the first temperature threshold value (TT1) is satisfied while the internal combustion engine (2) is operating in the multi-fuel operation mode.

[0088] According to the configuration of 6) above, when the temperature (GT) of the exhaust gas acquired by the exhaust gas temperature acquisition unit (35) exceeds the second temperature threshold value (TT2), the flow rate of the combustion gas introduced into the internal combustion engine (2) can be increased so that the temperature (GT) of the exhaust gas satisfies the limit value.

[0089] 7) In some embodiments, the control device (3) for an internal combustion engine (2) described in any of 1) to 6) above further includes: a parameter acquisition unit (36) that acquires a plurality of parameters related to the operating state of the internal combustion engine (2); an association information acquisition unit (37) that acquires association information that associates the plurality of parameters with operating conditions under which the dual-fuel operation mode is possible; and an operating condition determination unit (38) that determines whether or not the plurality of parameters acquired by the parameter acquisition unit (36) satisfy the operating conditions based on the association information acquired by the association information acquisition unit (37) when the internal combustion engine (2) is operating in the mono-fuel operation mode.

[0090] According to the configuration of 7) above, the operating condition determination unit (38) can determine whether the plurality of parameters acquired by the parameter acquisition unit (36) satisfy the operating conditions under which the multi-combustion operation mode is possible. When the determination result of the operating condition determination unit (38) is favorable, the control device (3) permits the switching operation to the multi-combustion operation mode, thereby attempting the multi-combustion operation in an operating state where the multi-combustion operation mode is unlikely to be established, and thereby suppressing the wasteful emission of ammonia.

[0091] 8) In some embodiments, the control device (3) for the internal combustion engine (2) described in 7) above further includes a second operation mode control unit (39) configured to switch the operation mode of the internal combustion engine (2) to the multi-fuel operation mode when, in a state in which the internal combustion engine (2) is operated in the mono-fuel operation mode, a multi-fuel operation enabling condition is satisfied, including a determination condition that the plurality of parameters satisfy the operating condition.

[0092] According to the configuration of 8) above, the control device (3) permits the switching operation to the multi-fuel operation mode when the determination result of the operating condition determination unit (38) is favorable, thereby making it possible to switch to the multi-fuel operation mode when the operating state of the internal combustion engine (2) is appropriate for the multi-fuel operation mode. Note that even after the multi-fuel operation mode is not established and the control device (3) has switched to the exclusive-fuel operation mode, the control device (3) can return to the multi-fuel operation mode when the determination result of the operating condition determination unit (38) is favorable.

[0093] 9) In some embodiments, in the control device (3) for the internal combustion engine (2) described in 7) or 8) above, the association information includes a control map that indicates a relationship between the plurality of parameters and the operating conditions, and in which an area in which the dual-fuel operation mode is possible is set on a map configured by the plurality of parameters.

[0094] According to the configuration 9) above, by using a control map in which a region in which the dual-fuel operation mode is possible under standard environmental conditions for the determination in the operating condition determination unit (38), it is possible to appropriately and quickly determine whether the operating state of the internal combustion engine (2) is appropriate for the dual-fuel operation mode.

[0095] 10) In some embodiments, in the control device (3) for an internal combustion engine (2) described in any one of 1) to 9) above, the nitrogen oxide amount acquisition unit (31) is configured to acquire the amount of nitrogen oxides in the exhaust gas flowing downstream of a denitrification catalyst (77) for removing the nitrogen oxides in an exhaust gas discharge line (7) through which the exhaust gas discharged from the internal combustion engine (2) flows.

[0096] According to the configuration of 10) above, the amount of nitrogen oxides in the exhaust gas flowing downstream of the denitration catalyst (77) in the exhaust gas discharge line (7) is equivalent to the amount of nitrogen oxides actually discharged into the atmosphere. By using the amount of nitrogen oxides in the exhaust gas flowing downstream of the denitration catalyst (77) in the exhaust gas discharge line (7), acquired by the nitrogen oxide amount acquisition unit (31), for control in the control device (3), the control device (3) can more appropriately control the amount of nitrogen oxide emissions to satisfy the limit value.

[0097] 11) In some embodiments, in the control device (3) for an internal combustion engine (2) described in any one of 1) to 10) above, the ammonia amount acquisition unit (32) is configured to acquire the amount of ammonia in exhaust gas flowing downstream of an ammonia decomposition catalyst (78) for removing the ammonia in an exhaust gas discharge line (7) through which the exhaust gas discharged from the internal combustion engine (2) flows.

[0098] According to the configuration of 11), the amount of ammonia in the exhaust gas flowing downstream of the ammonia decomposition catalyst (78) in the exhaust gas discharge line (7) is equal to the amount of ammonia discharged into the atmosphere. By using the amount of ammonia in the exhaust gas flowing downstream of the ammonia decomposition catalyst (78) in the exhaust gas discharge line (7), which is acquired by the ammonia amount acquisition unit (32), for control in the control device (3), the control device (3) can more appropriately control the amount of ammonia discharged to satisfy the limit value.

[0099] 12) In some embodiments, in the control device (3) for the internal combustion engine (2) described in 5) or 6) above, the exhaust gas temperature acquisition unit (35) is configured to acquire the temperature of the exhaust gas flowing upstream of a turbine (73) in an exhaust gas discharge line (7) through which the exhaust gas discharged from the internal combustion engine (2) flows.

[0100] According to the configuration of 12), the temperature of the exhaust gas discharge line (7) upstream of the turbine (73) is higher than that of the downstream of the turbine (73). By using the temperature of the exhaust gas flowing upstream of the turbine (73) in the exhaust gas discharge line (7), which is relatively high temperature, for control in the control device (3), the control device (3) can more appropriately control the exhaust gas temperature to satisfy the limit value.

[0101] 13) A control method for an internal combustion engine (2) according to at least one embodiment of the present disclosure is a control method for an internal combustion engine (2) for controlling operation of the internal combustion engine (2) configured to be able to switch between a plurality of operation modes, the plurality of operation modes including a mono-fuel operation mode in which a liquid fuel is used as the fuel, and a multi-fuel operation mode in which both the liquid fuel and ammonia gas are used as the fuels, the control method for the internal combustion engine (2) comprising: a nitrogen oxide amount acquisition step of acquiring an amount of nitrogen oxides in exhaust gas emitted from the internal combustion engine (2); and an ammonia amount acquisition step of acquiring an amount of ammonia in the exhaust gas emitted from the internal combustion engine (2). and a flow rate control step of issuing a flow rate adjustment instruction to a flow rate adjustment device configured to adjust the flow rate of the combustion gas introduced to the internal combustion engine (2) so that, while the internal combustion engine (2) is operated in the multi-fuel operation mode, the amount of nitrogen oxides acquired in the nitrogen oxide amount acquisition step and the amount of ammonia acquired in the ammonia amount acquisition step do not exceed threshold values.

[0102] According to the method of 13), the combustion state and the like change when environmental conditions change, and therefore the relationship between the excess air ratio and the amount of nitrogen oxide emissions and the amount of ammonia emissions is constantly changing. In the above control method, the amount of nitrogen oxides acquired in the nitrogen oxide amount acquisition step and the amount of ammonia acquired in the ammonia amount acquisition step are used as control parameters for adjusting the flow rate of the combustion gas introduced into the internal combustion engine (2), rather than the excess air ratio. This control method makes it possible to adjust the flow rate of the combustion gas so that the amount of nitrogen oxides and ammonia emissions meet their limit values ​​even when environmental conditions change.

[0103] REFERENCE SIGNS LIST 1 Internal combustion engine system 2 Internal combustion engine 3 Control device 4 Liquid fuel introduction line 5 Combustion gas introduction line 6 Ammonia gas introduction line 7 Exhaust gas discharge line 8 Liquid fuel side injector 9 Ammonia side injector 10 Flow rate adjustment device 11 Turbocharger 12 Nitrogen oxide sensor 13 Ammonia sensor 14 Temperature sensor 15 Selection device 21 Cylinder 22 Combustion chamber 30 Memory unit 31 Nitrogen oxide amount acquisition unit 32 Ammonia amount acquisition unit 33 Flow rate control unit 34 First operation mode control unit 35 Exhaust gas temperature acquisition unit 36 ​​Parameter acquisition unit 37 Association information acquisition unit 38 Operation condition determination unit 39 Second operation mode control unit 41 Common rail 42 Branch pipe 43 Liquid fuel supply source 44 Liquid fuel pipe 45 Pressure booster 51 Compressor 52 First combustion gas pipe 53 Second combustion gas pipe 54 Intake side branch pipe 55 Throttle valve 56 Intercooler 61 Ammonia gas supply source 62 Ammonia gas pipe 63 Ammonia gas side branch pipe 71 Exhaust gas pipe 72 Exhaust gas side branch pipe 73 Turbine 74 Rotating shaft 75 Generator 76 Exhaust gas connection pipe 77 Denitrification catalyst 78 Ammonia decomposition catalyst 79 Exhaust gas discharge pipe AA Ammonia amount ANO Nitrogen oxide amount AT Ammonia threshold GT Exhaust gas temperature NOT1 First nitrogen oxide threshold NOT2 Second nitrogen oxide threshold TT1 First temperature threshold TT2 Second temperature threshold

Claims

1. A control device for an internal combustion engine for controlling operation of an internal combustion engine configured to be able to switch between a plurality of operating modes, the plurality of operating modes including a mono-fuel operation mode in which liquid fuel is used as the fuel used, and a multi-fuel operation mode in which both the liquid fuel and ammonia gas are used as the fuel used, the control device for the internal combustion engine comprising: a nitrogen oxide amount acquisition unit configured to acquire an amount of nitrogen oxides in exhaust gas discharged from the internal combustion engine; an ammonia amount acquisition unit configured to acquire an amount of ammonia in the exhaust gas discharged from the internal combustion engine; and a flow rate control unit configured to give a flow rate adjustment instruction to adjust the flow rate of the combustion gas introduced to the internal combustion engine, to a flow rate adjustment device configured to adjust the flow rate of the combustion gas introduced to the internal combustion engine, so that each of the amount of nitrogen oxide acquired by the nitrogen oxide amount acquisition unit and the amount of ammonia acquired by the ammonia amount acquisition unit does not exceed a threshold value when the internal combustion engine is operated in the multi-fuel operation mode.

2. A control device for an internal combustion engine as described in claim 1, wherein the flow control unit is configured to, when the internal combustion engine is operated in the multi-fuel operation mode, issue a flow reduction instruction to the flow control device to reduce the flow rate of the combustion gas guided to the internal combustion engine when the amount of nitrogen oxides acquired by the nitrogen oxide amount acquisition unit satisfies a flow reduction condition including at least a judgment condition that the amount of nitrogen oxides acquired by the nitrogen oxide amount acquisition unit is equal to or less than a first nitrogen oxide threshold value.

3. A control device for an internal combustion engine as described in claim 2, wherein the flow rate control unit is configured to issue a flow rate increase instruction to the flow rate control device to increase the flow rate of the combustion gas guided to the internal combustion engine when a flow rate increase condition is satisfied, the flow rate increase condition including both a determination condition that the amount of ammonia acquired by the ammonia amount acquisition unit is equal to or less than the ammonia threshold value and a determination condition that the amount of nitrogen oxides acquired by the nitrogen oxide amount acquisition unit exceeds a second nitrogen oxide threshold value that is equal to the first nitrogen oxide threshold value or is greater than the first nitrogen oxide threshold value, when the internal combustion engine is operated in the multi-fuel operation mode.

4. The control device for an internal combustion engine according to any one of claims 1 to 3, further comprising a first operation mode control unit configured to switch the operation mode of the internal combustion engine to the exclusive combustion operation mode when a multi-combustion operation stop condition is satisfied, the multi-combustion operation stop condition including both a determination condition that the amount of nitrogen oxides acquired by the nitrogen oxide amount acquisition unit exceeds a first nitrogen oxide threshold value and a determination condition that the amount of ammonia acquired by the ammonia amount acquisition unit exceeds an ammonia threshold value, while the internal combustion engine is operated in the multi-combustion operation mode.

5. A control device for an internal combustion engine as described in claim 2 or 3, further comprising an exhaust gas temperature acquisition unit configured to acquire the temperature of the exhaust gas, and the flow rate reduction condition further includes a determination condition that the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition unit is equal to or lower than a first temperature threshold value.

6. A control device for an internal combustion engine as described in claim 5, configured to issue a flow rate increase instruction to the flow control device to increase the flow rate of the combustion gas guided to the internal combustion engine when a flow rate increase condition is satisfied, the flow rate increase condition including both a determination condition that the amount of ammonia acquired by the ammonia amount acquisition unit is equal to or less than an ammonia threshold value and a determination condition that the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition unit exceeds a second temperature threshold value that is equal to or greater than the first temperature threshold value, while the internal combustion engine is operating in the multi-fuel operation mode.

7. A control device for an internal combustion engine as claimed in any one of claims 1 to 3, further comprising: a parameter acquisition unit that acquires a plurality of parameters relating to an operating state of the internal combustion engine; an association information acquisition unit that acquires association information that associates the plurality of parameters with operating conditions under which the multi-fuel operation mode is possible; and an operating condition determination unit that determines whether or not the plurality of parameters acquired by the parameter acquisition unit satisfy the operating conditions based on the association information acquired by the association information acquisition unit when the internal combustion engine is operating in the exclusive combustion operation mode.

8. The control device for an internal combustion engine according to claim 7, further comprising a second operation mode control unit configured to switch the operation mode of the internal combustion engine to the multi-combustion operation mode when a multi-combustion operation enabling condition is satisfied, the multi-combustion operation enabling condition including a determination condition that the plurality of parameters satisfy the operating condition, while the internal combustion engine is operated in the exclusive combustion operation mode.

9. The control device for an internal combustion engine according to claim 7, wherein the association information includes a control map indicating the relationship between the plurality of parameters and the operating conditions, the control map being configured based on the plurality of parameters and setting an area in which the multi-fuel operation mode is possible.

10. A control device for an internal combustion engine as described in any one of claims 1 to 3, wherein the nitrogen oxide amount acquisition unit is configured to acquire the amount of nitrogen oxides in the exhaust gas flowing downstream of a denitrification catalyst for removing the nitrogen oxides in an exhaust gas discharge line through which the exhaust gas discharged from the internal combustion engine flows.

11. The control device for an internal combustion engine according to any one of claims 1 to 3, wherein the ammonia amount acquisition unit is configured to acquire the amount of ammonia in the exhaust gas flowing downstream of an ammonia decomposition catalyst for removing the ammonia in an exhaust gas discharge line through which the exhaust gas discharged from the internal combustion engine flows.

12. The control device for an internal combustion engine according to claim 5, wherein the exhaust gas temperature acquisition unit is configured to acquire the temperature of the exhaust gas flowing upstream of a turbine in an exhaust gas discharge line through which the exhaust gas discharged from the internal combustion engine flows.

13. A control method for an internal combustion engine for controlling operation of an internal combustion engine configured to be able to switch between a plurality of operating modes, the plurality of operating modes including a mono-fuel operation mode in which liquid fuel is used as the fuel used, and a multi-fuel operation mode in which both the liquid fuel and ammonia gas are used as the fuel used, the control method for the internal combustion engine comprising: a nitrogen oxide amount acquisition step of acquiring an amount of nitrogen oxides in exhaust gas discharged from the internal combustion engine; an ammonia amount acquisition step of acquiring an amount of ammonia in the exhaust gas discharged from the internal combustion engine; and a flow rate control step of issuing a flow rate adjustment instruction to a flow rate adjustment device configured to adjust the flow rate of the combustion gas introduced to the internal combustion engine so that each of the amount of nitrogen oxides acquired in the nitrogen oxide amount acquisition step and the amount of ammonia acquired in the ammonia amount acquisition step does not exceed a threshold value while the internal combustion engine is operated in the multi-fuel operation mode.

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