Engine System

Abstract

To provide an engine system capable of shortening a start time of an engine.SOLUTION: An engine system 1 includes: a main throttle valve 6 controlling a flow rate of air to be supplied to an ammonia engine 2; a main injector 5 supplying ammonia gas to the ammonia engine 2; a reformer 12 generating reformed gas; a reforming throttle valve 14 controlling a flow rate of air to be supplied to the reformer 12; a reforming injector 15 supplying ammonia gas to the reformer 12; a combustor 30 generating combustion gas for heating a reforming catalyst 22 of the reformer 12; a combustion injector 33 supplying ammonia gas to the combustor 30; and a controller 40 controlling the combustion injector 33 so that ammonia gas is supplied to the combustor 30 and the ammonia gas is burned with an air-fuel ratio rich in the combustor 30 at start of the ammonia engine 2.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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-211155 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-mentioned conventional technology has the following problems. That is, the catalyst in the cracker is heated by an electric heater, and the temperature of the catalyst rises. Then, when the temperature of the catalyst reaches a reformable temperature (activation temperature), hydrogen is generated by the cracker. Then, in the engine body, ammonia is mixed with hydrogen and burned. As such, it takes time for the temperature of the cracker catalyst to reach the activation temperature, so it takes a long time for hydrogen to be generated from the cracker. As a result, the engine start-up time is long.

[0005] An object of the present invention is to provide an engine system capable of shortening the engine start time. [Means for solving the problem]

[0006] An engine system according to one aspect of the present invention includes an engine in which fuel is burned together with hydrogen, an intake passage through which air supplied to the engine flows, a first flow control valve disposed in the intake passage and configured to control the flow rate of the air supplied to the engine, a first fuel 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 configured to control the flow rate of the air supplied to the reformer, a second fuel supply valve that supplies fuel to the reformer, and a fuel supply valve for the reformer. the first flow control valve, the first fuel supply valve, the second flow control valve, the second fuel supply valve, and the third fuel supply valve when the engine is started. The combustion system includes a reformed gas flow path through which the reformed gas generated by the reformer flows toward the engine, a combustor connected to the reformer and generating combustion gas for heating the catalyst, a branch flow path connecting the air flow path and the combustor and through which air supplied to the combustor flows, a third fuel supply valve which supplies fuel to the combustor, and a start control unit which controls the first flow control valve, the first fuel supply valve, the second flow control valve, the second fuel supply valve, and the third fuel supply valve when the engine is started, and the start control unit controls the third fuel supply valve so that fuel is supplied to the combustor and is burned in the combustor with a rich air-fuel ratio.

[0007] In such an engine system, first, air flows from the air passage through a branch passage and is supplied to the combustor, and the third fuel supply valve supplies fuel to the combustor, whereby the fuel is burned in the combustor. At this time, the third fuel supply valve is controlled so that the fuel is burned in the combustor in a rich air-fuel ratio state, whereby the fuel is thermally decomposed and hydrogen is generated. The hydrogen generated by the combustor flows through the reformer and the reformed gas passage and is supplied to the engine. Then, the catalyst of the reformer is heated by the combustion gas generated in the combustor, whereby the temperature of the catalyst rises, and fuel and air are supplied to the reformer by the second fuel supply valve and the second flow control valve. Then, when the temperature of the catalyst reaches a reformable temperature (activation temperature), a reformed gas containing hydrogen is generated in the reformer, and the reformed gas flows through the reformed gas passage and is supplied to the engine. Also, the first fuel supply valve and the first flow control valve supply fuel and air to the engine, whereby the fuel is mixed with hydrogen and burned. By producing hydrogen in the combustor before producing hydrogen in the reformer in this way, the amount of hydrogen required to start the engine can be obtained earlier, thereby shortening the engine start time.

[0008] The startup control unit may, while controlling the third fuel supply valve so that fuel is supplied to the combustor and the fuel is burned in the combustor with a rich air-fuel ratio, control the second flow control valve so that the flow rate of air supplied to the reformer is equal to or less than a specified value, and thereafter control the second flow control valve so that the flow rate of air supplied to the reformer is greater than the specified value.

[0009] In this configuration, while fuel is being burned in the combustor with a rich air-fuel ratio, the flow rate of air supplied to the reformer is suppressed, so that even if the temperature of the catalyst in the reformer rises due to the combustion gas, the hydrogen generated by the combustor is less likely to be burned in the reformer. Therefore, the hydrogen generated by the combustor is less likely to be consumed, further shortening the engine start-up time.

[0010] The start control unit may control the third fuel supply valve so that fuel is supplied to the combustor and the fuel is burned in the combustor with a rich air-fuel ratio, and then control the third fuel supply valve so that the supply of fuel to the combustor is stopped.

[0011] In such a configuration, after the catalyst in the reformer is heated to the desired temperature by the combustion gas generated in the combustor, the third fuel supply valve is closed, thereby preventing the third fuel supply valve from wasting fuel to the combustor.

[0012] The engine system may further include a third flow control valve disposed in the branch passage and controlling the flow rate of air supplied to the reformer, the branch passage connecting the combustor with a side of the air passage upstream of the second flow control valve, and the starting control unit may control the third fuel supply valve and the third flow control valve so that fuel and air are supplied to the combustor and fuel is burned in the combustor with a rich air-fuel ratio, and then control the third fuel supply valve and the third flow control valve so that the supply of fuel and air to the combustor is stopped.

[0013] In this configuration, the flow rate of air supplied to the combustor can be precisely controlled by the third flow control valve, and therefore, a control operation for making the air-fuel ratio in the combustor rich can be easily performed.

[0014] The start control unit may determine whether or not a specified time has elapsed since fuel is supplied to the combustor and control of the third fuel supply valve is started so that the fuel is burned in the combustor with a rich air-fuel ratio, and when the specified time has elapsed, control the third fuel supply valve so that the supply of fuel to the combustor is stopped.

[0015] In this configuration, even without using a particular sensor or the like, when the temperature of the catalyst in the reformer is raised to a desired temperature by the combustion gas generated in the combustor, the third fuel supply valve can be closed. Effect of the Invention

[0016] According to the present invention, the engine start time can be reduced. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic configuration diagram showing an engine system according to an embodiment of the present invention. [Diagram 2] 4 is a flowchart showing a procedure of a control process executed by a controller shown in FIG. 1. [Diagram 3] 4 is a graph showing an example of the relationship between the air-fuel ratio and the amount of H2 produced, the amount of NO produced, and the amount of remaining NH3. [Figure 4] FIG. 2 is a timing diagram illustrating the operation of the engine system shown in FIG. [Diagram 5] FIG. 2 is a diagram showing a comparison of the timing at which combustion gas and hydrogen are generated when ammonia gas is burned in a combustor with a lean air-fuel ratio and a rich air-fuel ratio. [Figure 6] 1 is a graph showing a comparison of changes over time in the temperature of combustion gas and the rotation speed of an ammonia engine when ammonia gas is burned in a combustor with a lean and rich air-fuel ratio. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0019] Fig. 1 is a schematic diagram showing an engine system according to an embodiment of the present invention. In Fig. 1, an engine system 1 according to the present embodiment is mounted on a vehicle (not shown). The engine system 1 includes an ammonia engine 2, an intake passage 3, an exhaust passage 4, a main injector 5, and a main throttle valve 6.

[0020] The ammonia engine 2 is an engine that uses ammonia gas (NH3 gas) as fuel. In the ammonia engine 2, hydrogen (H2) is mixed with the ammonia gas as a combustion aid to facilitate combustion of the flame-retardant ammonia gas. The ammonia engine 2 has a combustion chamber (not shown) in which the ammonia gas is burned together with the hydrogen to generate exhaust gas. The ammonia engine 2 is, for example, a four-cylinder engine.

[0021] The intake passage 3 is connected to the combustion chamber of the ammonia engine 2. The intake passage 3 is a passage through which air flows to be supplied to 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.

[0022] The exhaust passage 4 is connected to the combustion chamber of the ammonia engine 2. The exhaust passage 4 is a passage through which exhaust gas generated by the ammonia engine 2 flows. In the exhaust passage 4, 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.

[0023] The main injector 5 is an electromagnetic fuel injection valve that injects ammonia gas toward the combustion chamber of the ammonia engine 2. The main injector 5 constitutes a first fuel supply valve that supplies ammonia gas to the ammonia engine 2. The number of main injectors 5 is the same as the number of cylinders of the ammonia engine 2.

[0024] 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.

[0025] The engine system 1 also includes an ammonia cylinder 10, a vaporizer 11, a reformer 12, an air passage 13, a reforming throttle valve 14, a reforming injector 15, a reformed gas passage 16, a cooler 17, and a flow control valve 18.

[0026] The ammonia cylinder 10 is a container for storing ammonia in a liquid state. That is, the ammonia cylinder 10 stores liquid ammonia.

[0027] The vaporizer 11 vaporizes the liquid ammonia stored in the ammonia cylinder 10 to generate ammonia gas. The ammonia gas generated in the vaporizer 11 flows through an ammonia flow path 19 and is supplied to the main injector 5, and also flows through an ammonia flow path 20 and is supplied to the reforming injector 15.

[0028] The reformer 12 generates reformed gas containing hydrogen by reforming ammonia gas using heat generated by burning ammonia gas. The reformer 12 has a cylindrical housing 21 and a reforming catalyst 22 housed in the housing 21. The housing 21 is made of a metal material such as stainless steel that is resistant to corrosion by ammonia gas.

[0029] The reforming catalyst 22 has, for example, a honeycomb structure. The reforming catalyst 22 is a catalyst that burns ammonia gas and decomposes the ammonia gas into hydrogen. The reforming catalyst 22 is, for example, an ATR (Autothermal Reformer) type ammonia reforming catalyst. As the reforming catalyst 22, for example, a cobalt-based catalyst, a rhodium-based catalyst, a ruthenium-based catalyst, a palladium-based catalyst, or the like is used.

[0030] The air flow path 13 connects the intake passage 3 and the reformer 12. One end of the air flow path 13 branches off and is connected to a portion of the intake passage 3 between the air cleaner 7 and the main throttle valve 6. The other end of the air flow path 13 is connected to an inlet portion of a housing 21 of the reformer 12. The air flow path 13 is a flow path through which air supplied to the reformer 12 flows.

[0031] The reforming throttle valve 14 is disposed in the air flow passage 13. The reforming throttle valve 14 is an electromagnetic second flow control valve that controls the flow rate of air supplied to the reformer 12.

[0032] The reforming injector 15 is an electromagnetic fuel injection valve that injects ammonia gas into the air flow path 13. The reforming injector 15 injects ammonia gas between the reforming throttle valve 14 and the reformer 12 in the air flow path 13. The reforming injector 15 constitutes a second fuel supply valve that supplies ammonia gas to the reformer 12. The number of reforming injectors 15 may be multiple (two in this case) or may be one.

[0033] The reformed gas flow passage 16 connects the reformer 12 and the intake passage 3. One end of the reformed gas flow passage 16 is connected to an outlet portion of the housing 21 of the reformer 12. The other end of the reformed gas flow passage 16 is connected to a portion of the intake passage 3 between the main throttle valve 6 and the ammonia engine 2. The reformed gas flow passage 16 is a flow passage through which the reformed gas generated by the reformer 12 flows toward the ammonia engine 2.

[0034] The cooler 17 is disposed in the reformed gas passage 16. The cooler 17 cools the reformed gas flowing through the reformed gas passage 16, for example, by using engine cooling water that cools the ammonia engine 2.

[0035] The flow rate regulating valve 18 is disposed downstream of the cooler 17 in the reformed gas flow passage 16. The flow rate regulating valve 18 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 18, an opening / closing valve (ON / OFF valve) may be used.

[0036] The engine system 1 also includes a combustor 30 , a branch passage 31 , a combustion throttle valve 32 , and a combustion injector 33 .

[0037] The combustor 30 is connected to the reformer 12. The combustor 30 generates a combustion gas for heating the reforming catalyst 22 of the reformer 12. The combustor 30 is, for example, a tubular flame burner that ignites and burns ammonia gas in a swirling flow state.

[0038] The combustor 30 has a cylindrical housing 34 and an ignition plug 35. The housing 34 is connected to an upstream portion of the housing 21 of the reformer 12 via a connection portion 36. The housing 34 and the connection portion 36 are formed of the same material as the housing 21. The connection portion 36 is provided in a downstream portion of the housing 34. The ignition plug 35 ignites ammonia gas in the housing 34. The ignition plug 35 is disposed at the upstream end of the housing 34.

[0039] The branch flow passage 31 connects the air flow passage 13 and the combustor 30. One end of the branch flow passage 31 branches off and is connected to the air flow passage 13 upstream of the reforming throttle valve 14. The other end of the branch flow passage 31 is connected to an upstream portion of a housing 34 of the combustor 30. The branch flow passage 31 is a flow passage through which air supplied to the combustor 30 flows.

[0040] Combustion throttle valve 32 is disposed in branch passage 31. Combustion throttle valve 32 is an electromagnetic third flow control valve that controls the flow rate of air supplied to combustor 30.

[0041] The combustion injector 33 is connected to the ammonia flow path 19 via an ammonia flow path 37. The ammonia flow path 37 is a flow path through which the ammonia gas generated in the vaporizer 11 flows.

[0042] Combustion injector 33 is an electromagnetic fuel injection valve that injects ammonia gas into branch passage 31. Combustion injector 33 injects ammonia gas into branch passage 31 between combustion throttle valve 32 and combustor 30. Combustion injector 33 constitutes a third fuel supply valve that supplies ammonia gas to combustor 30. The number of combustion injectors 33 may be multiple (two in this case) or may be one.

[0043] The engine system 1 also includes a controller 40. The controller 40 is composed of a CPU, a RAM, a ROM, an input / output interface, etc. The controller 40 constitutes a start control unit that controls the main injector 5, the main throttle valve 6, the reforming throttle valve 14, the reforming injector 15, the flow control valve 18, the combustion throttle valve 32, the combustion injector 33, and the ignition plug 35 of the combustor 30 when the ammonia engine 2 is started.

[0044] The controller 40 controls the combustion injector 33 so that ammonia gas is supplied to the combustor 30 and combusted in the combustor 30 with a rich air-fuel ratio.

[0045] At this time, the controller 40 controls the combustion injector 33 and the combustion throttle valve 32 so that ammonia gas and air are supplied to the combustor 30 and the ammonia gas is burned in the combustor 30 with the air-fuel ratio rich, and then controls the combustion injector 33 and the combustion throttle valve 32 so that the supply of ammonia gas and air to the combustor 30 is stopped.

[0046] In addition, while the controller 40 is supplying ammonia gas to the combustor 30 and controlling the combustion injector 33 so that the ammonia gas is burned in the combustor 30 with a rich air-fuel ratio, the controller 40 controls the reforming throttle valve 14 so that the flow rate of air supplied to the reformer 12 is equal to or less than a specified value, and then controls the reforming throttle valve 14 so that the flow rate of air supplied to the reformer 12 is greater than the specified value.

[0047] Specifically, while the controller 40 controls the combustion injector 33 so that ammonia gas is supplied to the combustor 30 and the ammonia gas is burned in the combustor 30 with a rich air-fuel ratio, the controller 40 controls the reforming throttle valve 14 so that the flow rate of air supplied to the reformer 12 is zero, and then controls the reforming throttle valve 14 so that air is supplied to the reformer 12.

[0048] 2 is a flowchart showing the procedure of the control process executed by the controller 40. This process is executed when an ignition switch (not shown) of the vehicle is turned ON.

[0049] Before this process is executed, the main injector 5, main throttle valve 6, reforming throttle valve 14, reforming injector 15, flow control valve 18, combustion throttle valve 32, and combustion injector 33 are all in a closed state.

[0050] 2, the controller 40 first controls the flow rate control valve 18 to open (step S101). The controller 40 also controls the main throttle valve 6 to open (step S102). This causes air to be supplied to the ammonia engine 2. The controller 40 also controls the reforming injector 15 to open (step S103). This causes ammonia gas to be supplied to the reformer 12.

[0051] In addition, the controller 40 controls the combustion throttle valve 32 and the combustion injector 33 to open (step S104). As a result, air and ammonia gas are supplied to the combustor 30.

[0052] At this time, the controller 40 controls the combustion throttle valve 32 and the combustion injector 33 so that the ammonia gas is burned in the combustor 30 with the air-fuel ratio in a rich state. The rich air-fuel ratio state is a state in which the ratio of ammonia gas is higher than the theoretical air-fuel ratio (stoichiometric: λ=1.0) as shown in Fig. 3. The lean air-fuel ratio state is a state in which the ratio of ammonia gas is lower than the theoretical air-fuel ratio.

[0053] In the graph shown in Figure 3, the horizontal axis indicates the air-fuel ratio (λ) and the vertical axis indicates the amount of gas. The solid line P indicates the amount of H2 produced, the dashed line Q indicates the amount of NO produced, and the dashed line R indicates the amount of unburned NH3 remaining. On the richer side of the theoretical air-fuel ratio, the amount of H2 produced becomes greater than the amount of NO produced, and the amount of unburned NH3 remaining increases rapidly. Note that Figure 3 shows calculated values ​​when ammonia gas is burned at normal temperature and pressure.

[0054] Then, the controller 40 controls the ignition plug 35 of the combustor 30 to be ON (step S105). As a result, the ammonia gas is ignited and burned in the combustor 30, generating combustion gas, and the reforming catalyst 22 of the reformer 12 is heated by the combustion gas.

[0055] Thereafter, the controller 40 determines whether or not a specified time has elapsed since the combustion throttle valve 32 and the combustion injector 33 were controlled to open in step S104 (step S106). The specified time is, for example, the time it takes for the reforming catalyst 22 of the reformer 12 to reach a combustible temperature, and is set in advance through experiments or the like. The combustible temperature is the temperature at which the reforming catalyst 22 can combust ammonia gas.

[0056] When the controller 40 determines that the specified time has elapsed, it controls the ignition plug 35 of the combustor 30 to turn OFF (step S107). This causes the generation of combustion gas in the combustor 30 to stop.

[0057] Then, the controller 40 controls the combustion throttle valve 32 and the combustion injector 33 to close (step S108). As a result, the supply of air and ammonia gas to the combustor 30 is stopped.

[0058] The controller 40 also controls the reforming throttle valve 14 to open (step S109). This causes air to be supplied to the reformer 12. Then, the controller 40 controls the main injector 5 to open (step S110). This causes ammonia gas to be supplied to the ammonia engine 2.

[0059] In the engine system 1 as described above, when the vehicle ignition switch (not shown) is turned ON, the flow rate adjustment valve 18 opens to a specified opening degree (see FIG. 4(a)).

[0060] Then, the main throttle valve 6 opens to a specified opening (see FIG. 4(b)), and air is supplied to the ammonia engine 2. Also, the reforming injector 15 opens so as to inject a specified amount of ammonia gas (see FIG. 4(h)), and ammonia gas is supplied to the reformer 12.

[0061] Furthermore, combustion throttle valve 32 opens to a specified opening degree (see FIG. 4(d)), and combustion injector 33 opens to inject a specified amount of ammonia gas (see FIG. 4(e)), thereby supplying air and ammonia gas to combustor 30. At this time, combustion throttle valve 32 and combustion injector 33 open so that the air-fuel ratio in combustor 30 becomes rich.

[0062] In addition, when the ignition plug 35 of the combustor 30 is turned on (see FIG. 4(f)), the ammonia gas is ignited and combusted. Specifically, as shown in the following formula, ammonia reacts with oxygen in the air to generate high-temperature combustion gas (exothermic reaction). NH3+3 / 4O2→1 / 2N2+3 / 2H2O …(A)

[0063] The combustion gas is supplied from the combustor 30 through the connection part 36 to the reformer 12. The heat of the combustion gas heats the reforming catalyst 22 of the reformer 12, thereby increasing the temperature of the reforming catalyst 22. When a specified time T has elapsed since the combustion throttle valve 32 and the combustion injector 33 were opened, the temperature of the reforming catalyst 22 reaches a combustible temperature.

[0064] When the temperature of the reforming catalyst 22 reaches a combustion temperature, the ignition plug 35 is turned OFF (see FIG. 4(f)). Also, the combustion throttle valve 32 and the combustion injector 33 are closed (see FIGS. 4(d) and (e)), thereby stopping the supply of air and ammonia gas to the combustor 30. This ends the combustion of ammonia gas in the combustor 30.

[0065] Then, the reforming throttle valve 14 opens to a specified degree (see FIG. 4(g)), and air is supplied to the reformer 12. Then, the reforming catalyst 22 burns the ammonia gas, causing the exothermic reaction of formula (A) above, and the temperature of the reforming catalyst 22 further rises due to the self-heat of the reforming catalyst 22. Then, when the temperature of the reforming catalyst 22 reaches an activation temperature (reformable temperature), the ammonia gas is reformed by the reforming catalyst 22. Specifically, as shown in the following formula, a decomposition reaction of ammonia occurs (endothermic reaction), and a reformed gas containing hydrogen is produced. NH3→3 / 2H2+1 / 2N2…(B)

[0066] The reformed gas flows through the reformed gas flow passage 16 and the intake passage 3 and is supplied to the ammonia engine 2. The main injector 5 opens so that a specified amount of ammonia gas is injected from the main injector 5 (see FIG. 4(c)), and thus ammonia gas is supplied to the ammonia engine 2. Then, in the ammonia engine 2, the ammonia gas is combusted 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.

[0067] Here, when ammonia gas is burned in the combustor 30 with the air-fuel ratio in a lean state (see FIG. 3), combustion gas is generated as shown in FIG. 5(a), but hydrogen is not easily generated because thermal decomposition of ammonia is unlikely to occur. Therefore, hydrogen is not generated until the temperature of the reforming catalyst 22 of the reformer 12 reaches the activation temperature.

[0068] Therefore, at time t1 after the temperature of the reforming catalyst 22 reaches the activation temperature, hydrogen begins to be generated by the reformer 12. The hydrogen generated by the reformer 12 flows through the reformed gas flow passage 16 and the intake passage 3 and is supplied to the ammonia engine 2. Then, at a subsequent time t2, the amount of hydrogen required to start the ammonia engine 2 is reached.

[0069] On the other hand, when ammonia gas is burned in the combustor 30 with the air-fuel ratio being rich (see FIG. 3), as shown in FIG. 5(b), at time t0, combustion gas is generated and hydrogen is produced by thermal decomposition of the ammonia gas. The hydrogen produced by the combustor 30 flows through the reformer 12, the reformed gas passage 16, and the intake passage 3 and is supplied to the ammonia engine 2.

[0070] Thereafter, the combustion of the ammonia gas is completed in the combustor 30, but at time t1 after the temperature of the reforming catalyst 22 reaches the activation temperature, hydrogen begins to be generated by the reformer 12. The hydrogen generated by the reformer 12 flows through the reformed gas flow passage 16 and the intake passage 3 and is supplied to the ammonia engine 2. Then, at time t* earlier than the above-mentioned time t2, the amount of hydrogen required to start the ammonia engine 2 is reached.

[0071] In this way, hydrogen is produced by the combustor 30, and then produced by the reformer 12, so that the amount of hydrogen required to start the ammonia engine 2 is quickly obtained. This shortens the start-up time of the ammonia engine 2 (see time t2→t* in FIG. 5).

[0072] FIG. 6 is a graph showing a comparison of the temperature of the combustion gas and the change over time in the rotation speed of the ammonia engine 2 when ammonia gas is combusted in the combustor 30 with a lean and rich air-fuel ratio.

[0073] Fig. 6(a) shows experimental data when ammonia gas is burned in the combustor 30 with a lean air-fuel ratio (λ=1.13). In Fig. 6(a), the dashed line Ma indicates the temperature of the combustion gas, and the solid line Na indicates the rotation speed of the ammonia engine 2. The time ta is the time when the first combustion (first explosion) occurs in the ammonia engine 2.

[0074] Fig. 6(b) shows experimental data when ammonia gas is burned in the combustor 30 with the air-fuel ratio being rich (λ=0.84). In Fig. 6(b), the dashed line Mb indicates the temperature of the combustion gas, and the solid line Nb indicates the rotation speed of the ammonia engine 2. Time tb is the time when the first combustion (initial explosion) occurs in the ammonia engine 2.

[0075] As can be seen from FIG. 6, when ammonia gas is burned in the combustor 30 with the air-fuel ratio being rich, the initial explosion timing of the ammonia engine 2 is earlier by (ta-tb) seconds than when ammonia gas is burned in the combustor 30 with the air-fuel ratio being lean.

[0076] As described above, according to this embodiment, first, air flows from the air passage 13 through the branch passage 31 and is supplied to the combustor 30, and ammonia gas is supplied to the combustor 30 by the combustion injector 33, so that the ammonia gas is burned in the combustor 30. At this time, the combustion injector 33 is controlled so that the ammonia gas is burned in the combustor 30 in a rich air-fuel ratio state, whereby the ammonia gas is thermally decomposed and hydrogen is generated. The hydrogen generated by the combustor 30 flows through the reformer 12 and the reformed gas passage 16 and is supplied to the ammonia engine 2. Then, the reforming catalyst 22 of the reformer 12 is heated by the combustion gas generated in the combustor 30, so that the temperature of the reforming catalyst 22 increases, and ammonia gas and air are supplied to the reformer 12 by the reforming injector 15 and the reforming throttle valve 14. Then, when the temperature of the reforming catalyst 22 reaches a reformable temperature (activation temperature), a reformed gas containing hydrogen is generated in the reformer 12, and the reformed gas flows through the reformed gas passage 16 and is supplied to the ammonia engine 2. Furthermore, ammonia gas and air are supplied to the ammonia engine 2 by the main injector 5 and the main throttle valve 6, whereby the ammonia gas is mixed with hydrogen and burned in the ammonia engine 2. By producing hydrogen in the combustor 30 before producing hydrogen in the reformer 12 in this way, the amount of hydrogen required to start the ammonia engine 2 can be obtained quickly. This shortens the start-up time of the ammonia engine 2.

[0077] In this embodiment, while ammonia gas is supplied to the combustor 30 and the combustion injector 33 is controlled so that the ammonia gas is burned in the combustor 30 with the air-fuel ratio rich, the reforming throttle valve 14 is controlled so that the flow rate of air supplied to the reformer 12 is equal to or less than a specified value, and then the reforming throttle valve 14 is controlled so that the flow rate of air supplied to the reformer 12 is greater than the specified value. In this case, while ammonia gas is burned in the combustor 30 with the air-fuel ratio rich, the flow rate of air supplied to the reformer 12 is suppressed, so that even if the temperature of the reforming catalyst 22 of the reformer 12 is increased by the combustion gas, the hydrogen generated by the combustor 30 is less likely to be burned in the reformer 12. Therefore, the hydrogen generated by the combustor 30 is less likely to be consumed, and the start-up time of the ammonia engine 2 is further shortened.

[0078] Furthermore, in this embodiment, ammonia gas is supplied to the combustor 30 and the combustion injector 33 is controlled so that the ammonia gas is burned in the combustor 30 with the air-fuel ratio rich, and then the combustion injector 33 is controlled so that the supply of ammonia gas to the combustor 30 is stopped. In this case, after the reforming catalyst 22 of the reformer 12 is heated to a desired temperature by the combustion gas generated in the combustor 30, the combustion injector 33 is closed, thereby preventing ammonia gas from being needlessly supplied to the combustor 30 from the combustion injector 33.

[0079] Furthermore, in this embodiment, ammonia gas and air are supplied to the combustor 30, and the combustion injector 33 and the combustion throttle valve 32 are controlled so that the ammonia gas is burned in the combustor 30 with the air-fuel ratio rich, and then the combustion injector 33 and the combustion throttle valve 32 are controlled so that the supply of ammonia gas and air to the combustor 30 is stopped. In this case, the flow rate of air supplied to the combustor 30 can be precisely controlled by the combustion throttle valve 32. Therefore, a control operation for making the air-fuel ratio rich in the combustor 30 can be easily performed.

[0080] Furthermore, in this embodiment, a determination is made as to whether a specified time has elapsed since ammonia gas is supplied to the combustor 30 and control of the combustion injector 33 is started so that the ammonia gas is burned in the combustor 30 with a rich air-fuel ratio, and when the specified time has elapsed, the combustion injector 33 is controlled so that the supply of fuel to the combustor 30 is stopped. In this case, even without using a particular sensor or the like, the combustion injector 33 can be closed when the reforming catalyst 22 of the reformer 12 is heated to a desired temperature by the combustion gas generated in the combustor 30.

[0081] The present invention is not limited to the above embodiment. For example, in the above embodiment, while ammonia gas is combusted in the combustor 30 with a rich air-fuel ratio, the flow rate of air supplied to the reformer 12 becomes zero, and then air is supplied to the reformer 12, but the present invention is not particularly limited to such a form. While ammonia gas is combusted in the combustor 30 with a rich air-fuel ratio, a small amount of air may be supplied to the reformer 12, and then the flow rate of air supplied to the reformer 12 may be increased.

[0082] In the above embodiment, after a specified time has elapsed since the combustion throttle valve 32 and the combustion injector 33 are controlled to open, when reformed gas containing hydrogen is generated by the reformer 12, the main injector 5 is opened to supply ammonia gas to the ammonia engine 2, but the present invention is not limited to this embodiment. For example, the main injector 5 may be opened when hydrogen is generated by the combustor 30.

[0083] In addition, in the above embodiment, the combustion throttle valve 32 and the combustion injector 33 are closed when a specified time has elapsed since the combustion throttle valve 32 and the combustion injector 33 were controlled to open, but this is not particularly limited to the embodiment. After the combustion throttle valve 32 and the combustion injector 33 are controlled to open, the combustion throttle valve 32 and the combustion injector 33 may be closed when a temperature sensor or the like detects that the temperature of the reformer 12 has reached a specified temperature (e.g., a combustible temperature).

[0084] In the above embodiment, the combustion throttle valve 32 and the combustion injector 33 are opened so that ammonia gas is combusted in a rich air-fuel ratio state in the combustor 30, and then the combustion throttle valve 32 and the combustion injector 33 are closed, but the present invention is not limited to such an embodiment. For example, the combustion throttle valve 32 and the combustion injector 33 may be left open even after the reformed gas is produced by the reformer 12.

[0085] In the above embodiment, the combustion throttle valve 32 is disposed in the branch passage 31 that connects the air passage 13 and the combustor 30, but such a combustion throttle valve 32 may not be provided.

[0086] In the above embodiment, the reformer 12 has the reforming catalyst 22 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 12 may have a combustion catalyst that burns ammonia gas and a reforming catalyst that decomposes the ammonia gas into hydrogen separately.

[0087] In addition, in the above embodiment, the combustor 30 is a tubular flame burner that ignites ammonia gas in a swirling flow state, but the combustor 30 is not limited to a tubular flame burner as long as it ignites and burns ammonia gas.

[0088] 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]

[0089] 1...engine system, 2...ammonia engine (engine), 3...intake passage, 5...main injector (first fuel supply valve), 6...main throttle valve (first flow control valve), 12...reformer, 13...air flow path, 14...reforming throttle valve (second flow control valve), 15...reforming injector (second fuel supply valve), 16...reformed gas flow path, 22...reforming catalyst (catalyst), 30...combustor, 31...branch flow path, 32...combustion throttle valve (third flow control valve), 33...combustion injector (third fuel supply valve), 40...controller (start control section).

Claims

1. An engine in which ammonia is combusted with hydrogen; an intake passage through which air supplied to the engine flows; a first flow control valve disposed in the intake passage and configured to control a flow rate of air supplied to the engine; a first fuel supply valve that supplies the ammonia to the engine; a reformer having a catalyst for decomposing the ammonia into the hydrogen and for reforming the ammonia 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 ammonia to the reformer; a reformed gas flow path through which the reformed gas generated by the reformer flows toward the engine; a combustor connected to the reformer and configured to generate a combustion gas for heating the catalyst; a branch flow passage connecting the air flow passage and the combustor, through which air supplied to the combustor flows; a third fuel supply valve for supplying the ammonia to the combustor; a start control unit that controls the first flow control valve, the first fuel supply valve, the second flow control valve, the second fuel supply valve, and the third fuel supply valve at a start of the engine, The engine system, wherein the starting control unit controls the third fuel supply valve so that the ammonia is supplied to the combustor and the ammonia is burned in the combustor in a rich air-fuel ratio state.

2. 2. The engine system according to claim 1, wherein the starting control unit controls the second flow control valve so that a flow rate of air supplied to the reformer is equal to or less than a specified value while the ammonia is supplied to the combustor and the third fuel supply valve is controlled so that the ammonia is burned in the combustor in a state where the air-fuel ratio is rich.

3. 3. The engine system according to claim 1, wherein the starting control unit controls the third fuel supply valve so that the ammonia is supplied to the combustor and the ammonia is burned in the combustor in a state where the air-fuel ratio is rich, and then controls the third fuel supply valve so that supply of the ammonia to the combustor is stopped.

4. a third flow control valve arranged in the branch passage and configured to control a flow rate of air supplied to the reformer; the branch passage connects a portion of the air passage upstream of the second flow control valve to the combustor, 4. The engine system according to claim 3, wherein the starting control unit controls the third fuel supply valve and the third flow control valve so that the ammonia and the air are supplied to the combustor and the ammonia is burned in the combustor in a state where the air-fuel ratio is rich, and then controls the third fuel supply valve and the third flow control valve so that supply of the ammonia and the air to the combustor is stopped.

5. 5. The engine system according to claim 3 or 4, wherein the starting control unit determines whether or not a specified time has elapsed since starting control of the third fuel supply valve so that the ammonia is supplied to the combustor and the ammonia is burned in the combustor in a state where the air-fuel ratio is rich, and controls the third fuel supply valve so that supply of the ammonia to the combustor is stopped when the specified time has elapsed.

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