Engine system

Abstract

To sufficiently suppress a hydrocarbon component contained in exhaust gas while improving durability and economical efficiency without using a catalyst requiring a noble metal when using fuel gas containing ammonia as a main component.SOLUTION: An engine system includes a control device 50 for causing at least a portion of a plurality of cylinders to act as a reforming cylinder 40d that causes a partial oxidation reaction of at least a portion of an air-fuel mixture including fuel N having ammonia as a main component and combustion air A to reform the air-fuel mixture into reformed gas K including combustion-promoting gas having a combustion rate faster than that of the fuel N, causes the remaining portion of the plurality of cylinders to act as normal cylinders 40a,40b,40c to which the reformed gas K reformed in the reforming cylinder 40d is guided, and executes air excess ratio control that controls an air excess ratio in the reforming cylinder 40d within a predetermined range in which the reformed gas K is generated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an engine system that uses an ammonia-based fuel. [Background technology]

[0002] Conventionally, various engine systems have been proposed as engine systems using ammonia as a main component. In view of the fact that ammonia is flame-retardant, an engine system is known in which part of the ammonia is reformed into hydrogen, which has high ignition properties, and the reformed hydrogen is used as fuel together with ammonia. As an example of such an engine system, as shown in Patent Document 1, there is known an engine system that includes a combustor that burns ammonia, a reformer that reforms the ammonia, and an engine that uses ammonia and hydrogen reformed by the reformer as fuel. In the engine system disclosed in Patent Document 1, the reforming reaction of ammonia is an endothermic reaction, so the reformer is heated by combustion gas obtained by burning ammonia in a combustor, and reforming in the reformer is carried out in such a manner that heat related to the reforming reaction in the reformer is supplied. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-92809 Summary of the Invention [Problem to be solved by the invention]

[0004] The engine system disclosed in Patent Document 1 required a combustor to promote the reforming reaction in the reformer, which required a relatively complicated configuration. Furthermore, it was necessary to burn part of the ammonia in the combustor to supply heat to promote the reforming reaction, which left room for improvement in terms of energy efficiency. Furthermore, the need to use a reformer to carry out the ammonia reforming reaction poses a problem in terms of durability, and the reformer uses relatively expensive precious metals, leaving room for improvement from an economical standpoint.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an engine system that can sufficiently suppress hydrocarbon components contained in exhaust gas while improving durability and economy without using a catalyst that requires a precious metal, when using a fuel gas containing ammonia as a main component. [Means for solving the problem]

[0006] The engine system to achieve the above object has the following characteristic configuration: at least some of the plurality of cylinders are operated as reforming cylinders that carry out a partial oxidation reaction of at least a portion of a mixture containing a fuel mainly composed of ammonia and combustion air to reform the mixture into a reformed gas containing a combustion-promoting gas that has a faster combustion speed than the fuel, and the remaining plurality of cylinders are operated as normal cylinders to which the reformed gas reformed in the reforming cylinders is introduced; The feature is that a control device is provided which executes excess air ratio control for controlling the excess air ratio in the reforming cylinder within a predetermined range in which the reformed gas is produced.

[0007] In an engine system having the above-described characteristic configuration, some of the engine's multiple cylinders are used as reforming cylinders that undergo a partial oxidation reaction of at least a portion of a mixture containing a fuel whose main component is ammonia and combustion air to reform it into a reformed gas containing a combustion-promoting gas that has a faster combustion speed than the fuel. Therefore, unlike conventional technology, no combustor for burning ammonia is required other than the engine, and the configuration can be simplified. In addition, since there is no need to burn ammonia in the combustor, improved energy efficiency can be expected. Furthermore, since there is no need to use a catalyst that requires a precious metal, durability and economy can be improved. Furthermore, excess air ratio control is performed to control the excess air ratio in the reformed cylinder within a predetermined range in which reformed gas is produced, and the reformed gas containing combustion-promoting gas produced in the reformed cylinder can be directed to the normal cylinder to operate the engine.This means that the reformed gas can be properly ignited in the normal cylinder to achieve stable combustion, and hydrocarbons used as fuel can be sufficiently reduced (or made zero), so the hydrocarbon components contained in exhaust gas can be sufficiently suppressed (or made zero), which can contribute to the realization of a carbon-free society. When using a fuel gas containing ammonia as a main component, an engine system can be realized that can sufficiently suppress hydrocarbon components contained in exhaust gas while improving durability and economy without using a catalyst that requires precious metals.

[0008] Further characteristic configurations of the engine system include: a fresh air temperature adjusting means for adjusting the temperature of fresh air supplied to the reforming cylinder; The control device When the combustion fluctuation rate of the reforming cylinder is equal to or greater than a predetermined stability determination threshold, the fresh air temperature adjustment means is activated to execute fresh air temperature increase control, which increases the temperature of the fresh air in the reforming cylinder.

[0009] As explained above, ammonia is flame-retardant, which can cause misfires in the reforming cylinder. If such misfires occur frequently, the reformed gas may not be properly generated in the reforming cylinder, which may result in a decrease in efficiency. According to the above characteristic configuration, when the combustion variation rate of the reforming cylinder is equal to or greater than a predetermined stability determination threshold, i.e., when it is determined that the non-flammable ammonia is not properly ignited in the reforming cylinder, the fresh air temperature adjustment means executes fresh air temperature increase control to increase the temperature of the fresh air in the reforming cylinder, thereby promoting the ignition and combustion of the non-flammable ammonia in the reforming cylinder and appropriately promoting the endothermic reforming reaction of ammonia. This allows the reformed gas to be stably generated in the reforming cylinder and the reformed gas to be introduced into the normal cylinder, allowing the engine system to operate efficiently. Here, raising the temperature of the fresh air in the reforming cylinder includes not only raising the temperature of the fresh air before it is led to the reforming cylinder, but also raising the temperature of the fresh air after it has been led to the reforming cylinder.

[0010] Further characteristic configurations of the engine system include: the fresh air temperature adjusting means includes an actual compression ratio adjusting means for adjusting the pressure in the reforming cylinder to adjust the actual compression ratio of the reforming cylinder, The control device When the stability determination threshold value is equal to or greater than the stability determination threshold value, the actual compression ratio adjusting means is operated to execute actual compression ratio increasing control for increasing the actual compression ratio of the reformed cylinder.

[0011] As an example of the temperature adjusting means, an actual compression ratio adjusting means for adjusting the actual compression ratio of the reforming cylinder can be provided. According to the above characteristic configuration, when the combustion fluctuation rate of the reformed cylinder is equal to or greater than a predetermined stability judgment threshold, the control device executes actual compression ratio increase control using the actual compression ratio adjustment means to increase the actual compression ratio of the reformed cylinder.Therefore, when ammonia combustion in the reformed cylinder becomes unstable, the actual compression ratio in the reformed cylinder can be increased to increase the combustion peak temperature in the compression process in the reformed cylinder and promote the ignition of ammonia. In the above-described actual compression ratio increase control, the in-cylinder pressure at the peak combustion temperature in the compression stroke of the reforming cylinder also increases, so that the ignition of ammonia in the reforming cylinder can be increased more satisfactorily.

[0012] Further characteristic configurations of the engine system include: The fresh air temperature adjusting means includes an exhaust gas recirculation amount adjusting means for adjusting the amount of exhaust gas recirculated to the reforming cylinder, The control device When the value is equal to or greater than the reforming cylinder stability determination threshold, the exhaust gas recirculation amount adjusting means is activated to execute exhaust gas recirculation amount increase control for increasing the amount of exhaust gas recirculated to the reforming cylinder.

[0013] As an example of the fresh air temperature adjusting means, an exhaust gas recirculation amount adjusting means for adjusting the amount of exhaust gas recirculated to the reforming cylinder can be provided. According to the above characteristic configuration, when the combustion fluctuation rate of the reforming cylinder is equal to or greater than a predetermined stability judgment threshold, the control device activates the exhaust gas recirculation amount adjustment means to execute exhaust gas recirculation amount increase control, which increases the amount of exhaust gas recirculated to the reforming cylinder.Therefore, the exhaust gas guided to the reforming cylinder increases the combustion peak temperature in the compression process in the reforming cylinder, thereby promoting the ignition of ammonia.

[0014] Further characteristic configurations of the engine system include: a three-way catalyst is provided in an exhaust passage through which exhaust gas from the normal cylinder flows; The control device executes the excess air ratio control to set the excess air ratio of the reforming cylinder to a fuel-rich region less than 1, and The excess air ratio of the normal cylinder is set to 1.

[0015] When ammonia is burned, the exhaust gas contains nitrogen oxide components. However, in a configuration in which a three-way catalyst is provided in the exhaust passage through which exhaust gas from the normal cylinder flows, as in the characteristic configuration described above, the control device performs excess air ratio control, setting the excess air ratio of the reforming cylinder to a fuel-rich region less than 1, and setting the excess air ratio of the normal cylinder to 1. This allows reformed gas to be produced well in the reforming cylinder, and efficient combustion to be carried out in the normal cylinder using the produced reformed gas as fuel, while the three-way catalyst can effectively remove the nitrogen oxide components contained in the exhaust gas exhausted from the normal cylinder performing stoichiometric combustion.

[0016] Further characteristic configurations of the engine system include: a memory unit that stores a reforming ratio map relating to the reforming ratio of ammonia using the temperature, pressure, and oxygen concentration in the reforming cylinder as parameters; The control device operates at least the fresh air temperature adjusting means based on the reforming ratio map stored in the storage unit.

[0017] As a result of extensive research, the inventors have obtained a reforming rate map relating to the reforming rate of ammonia, using the temperature, pressure and oxygen concentration in the reforming cylinder as parameters, by performing an equilibrium calculation of the reforming reaction of ammonia. According to the above characteristic configuration, the control device activates at least the fresh air temperature adjustment means based on the reforming ratio map obtained in this manner, and for example, when ignition performance in the reforming cylinder is deteriorating, the control device controls the new temperature adjustment means to increase the ammonia reforming ratio and increase the hydrogen component contained in the reformed gas, thereby realizing stable operation of the entire engine system.

[0018] Further characteristic configurations of the engine system include: a storage unit that stores an ignition map relating to the ignition of ammonia using the temperature, pressure, and excess air ratio in the reforming cylinder as parameters; The control device operates at least the fresh air temperature adjusting means based on the ignition map stored in the memory unit, and controls the excess air ratio of the reforming cylinder by the excess air ratio control.

[0019] As a result of extensive research, the inventors obtained an ignition map relating to the ignition of ammonia by performing calculations relating to the combustibility of ammonia, using the temperature, pressure and excess air ratio in the reforming cylinder as parameters. According to the above characteristic configuration, the control device controls the excess air ratio of at least the reforming cylinder based on the ignition map obtained in this manner, thereby, for example, adjusting the temperature and pressure of the reforming cylinder to predetermined values ​​and adjusting the excess air ratio of the reforming cylinder to an extent that ammonia can be ignited on the fuel-rich side, thereby realizing an operating state in which misfires in the reforming cylinder can be appropriately suppressed while the efficiency of generating reformed gas can be appropriately increased.

[0020] Further characteristic configurations of the engine system include: a first fuel supply unit that supplies fuel to be introduced to at least the normal cylinder, and a second fuel supply unit that supplies fuel to be introduced to the reforming cylinder; The control device is characterized in that, while performing the air excess ratio control that adjusts the fuel supply amount by the second fuel supply unit to control the air excess ratio in the reformed cylinder within a predetermined range in which the reformed gas is produced, the control device performs fuel ratio reduction control that reduces the fuel ratio, which is the ratio of the total fuel supply amount to all of the normal cylinders by the first fuel supply unit to the total fuel supply amount to all of the reformed cylinders by the second fuel supply unit.

[0021] As described above, by lowering the fuel ratio, which is the ratio of the total fuel supply to all normal cylinders to the total fuel supply to the reformed cylinders, i.e., by increasing the amount of fuel derived from the reformed gas used in the normal cylinders, the net thermal efficiency of the engine can be improved.

[0022] Further characteristic configurations of the engine system include: The control device executes a reformed gas operation in which only the reformed gas is introduced as the fuel to the normal cylinders while the excess air ratio control is being executed.

[0023] As described above, by increasing the proportion of reformed gas (combustion-promoting gas) as fuel for the normal cylinders, it is possible to expect an improvement in the net thermal efficiency of the normal cylinders. Therefore, by performing reformed gas operation in which only reformed gas is introduced as fuel to the normal cylinders, as in the above characteristic configuration, it is possible to improve the net thermal efficiency.

[0024] Further characteristic configurations of the engine system include: The engine is characterized by comprising a reformed engine having at least one reformed cylinder as the plurality of cylinders, and an external power engine having the normal cylinders as the plurality of cylinders.

[0025] The engine system of the present invention, as in the above-described characteristic configuration, can effectively exhibit the effects described so far even when it is configured to have a separate reformed engine with a reformed cylinder and an external output engine with a normal cylinder to which reformed gas is guided from the reformed cylinder. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a schematic configuration diagram of an engine system according to a first embodiment. [Figure 2] 1 is a schematic configuration diagram of a reformed cylinder of an engine system according to a first embodiment. [Figure 3] FIG. 10 is a schematic configuration diagram of an engine system according to a second embodiment. [Figure 4] FIG. 10 is a schematic configuration diagram of an engine system according to a third embodiment. [Figure 5] 1 is a reforming rate map relating to the reforming rate of ammonia using temperature, pressure, and oxygen concentration as parameters, and is a reforming rate map at a predetermined temperature and a predetermined pressure. [Figure 6] FIG. 1 is a graph showing equilibrium calculation results for each predetermined equivalence ratio at 700 K and 40 atm. [Figure 7] FIG. 1 is a graph showing equilibrium calculation results for each predetermined equivalence ratio at 1000 K and 40 atm. DETAILED DESCRIPTION OF THE INVENTION

[0027] The engine system 100 according to the embodiment of the present invention relates to an engine system that, when using a fuel gas containing ammonia as a main component, can sufficiently suppress hydrocarbon components contained in exhaust gas while improving durability and economy without using a catalyst that requires a precious metal. The engine system 100 will be described below with reference to the drawings.

[0028] [First embodiment] As shown in FIG. 1, the engine system 100 according to the first embodiment has at least some of the multiple cylinders 40a, 40b, 40c, and 40d (four in this embodiment) functioning as reforming cylinders 40d that carry out a partial oxidation reaction of at least part of a mixture M containing a fuel N (ammonia in this embodiment) mainly composed of ammonia and combustion air A in an engine body 40 to reform it into a reformed gas K containing a combustion-promoting gas having a faster combustion speed than the fuel N, and the remaining multiple cylinders 40a, 40b, 40c, and 40d functioning as normal cylinders 40a, 40b, and 40c to which the reformed gas K reformed in the reforming cylinder 40d is introduced. The engine is provided with a first fuel supply unit that supplies fuel N to be led to the normal cylinders 40a, 40b, and 40c, and a second fuel supply unit that supplies fuel N to be led to the reforming cylinder 40d, and the reformed gas K reformed in the reforming cylinder 40d is led to at least the normal cylinders 40a, 40b, and 40c (in this embodiment, it is led only to the normal cylinders 40a, 40b, and 40c).

[0029] In the reforming cylinder 40d, ammonia and oxygen contained in the combustion air undergo a chemical reaction as shown in the following formula 1, producing high-temperature combustion gas (exothermic reaction).

[0030] NH3+3 / 4O2→1 / 2N2+3 / 2H2O... [Formula 1]

[0031] Furthermore, when the temperature of the reforming cylinder 40d reaches a predetermined reaction temperature, an ammonia reforming reaction occurs. Specifically, as shown in the following formula 2, an ammonia decomposition reaction (endothermic reaction) occurs, and reformed gas K containing hydrogen as a combustion promoting gas is generated.

[0032] NH3→3 / 2H2+1 / 2N2... [Formula 2]

[0033] The engine system 100 of the first embodiment is configured as a turbocharged engine and includes at least one (three in this embodiment) normal cylinders 40a, 40b, 40c and at least one (one in this embodiment) reformed cylinder 40d. Furthermore, the engine system includes an engine control unit (hereinafter referred to as a control device 50) that receives measurement results from sensors that detect the operating state of the engine and is composed of a group of hardware and software that controls the operation of the turbocharged engine based on the input signals.

[0034] Although detailed illustration is omitted for this type of engine system 100, combustion air A is supplied from the main air intake pipe 20 to the combustion chambers (not shown) of the normal cylinders 40a, 40b, and 40c, and fuel N is supplied to the combustion chambers (not shown) by the first injectors IJa, IJb, and IJc via the first fuel supply passage 11. These fuels are compressed as the pistons rise, and are then spark-ignited by spark plugs (not shown), causing the fuel to burn and expand, pushing the pistons down and outputting rotational power from the rotating shaft (not shown). Exhaust gas E generated by the combustion is pushed out of the combustion chambers of the normal cylinders 40a, 40b, and 40c through exhaust valves (not shown) into the exhaust passage 27 and discharged to the outside. As will be described in detail later, the combustion air A supplied from the main air intake pipe 20 is also supplied to the reforming cylinder 40d through the reforming cylinder intake branch pipe 20d, and the piston in the reforming cylinder 40d is also pushed down, outputting rotational power from the rotary shaft. However, the reformed gas K generated as exhaust gas in the reforming cylinder 40d is not discharged to the outside, but is returned to the main air intake pipe 20 via the reformed gas passage 28 and is guided to the normal cylinders 40a, 40b, and 40c.

[0035] The main air intake pipe 20 is provided with an air cleaner 21 that purifies the combustion air A, and a throttle valve 23 for normal cylinders that can adjust the amount of combustion air A supplied to the normal cylinders 40a, 40b, and 40c by adjusting the opening, in the order listed from the upstream side.

[0036] The reforming cylinder intake branch pipe 20d branches off from the main intake pipe 20 upstream of the normal cylinder throttle valve 23 and is provided with the following in the order listed from the upstream side: a compressor 31 as a supercharger 30 that compresses the combustion air A; an intercooler 22 that cools the combustion air A that has been heated by the compressor 31; and a reforming cylinder throttle valve 25 whose opening can be adjusted to adjust the amount of fresh air supplied to the reforming cylinder 40d.

[0037] The first fuel supply passage 11 that introduces the fuel N to the normal cylinders 40a, 40b, and 40c is provided with a vaporizer 70 that vaporizes ammonia as the fuel N, and first injectors IJa, IJb, and IJc that inject the fuel N while adjusting the amount of fuel supplied to the combustion chambers of the normal cylinders 40a, 40b, and 40c. That is, the first fuel supply passage 11 and the first injectors IJa, IJb, and IJc function as a first fuel supply unit.

[0038] The supercharger 30 is configured as a turbo-type supercharger 30 that supplies exhaust gas E discharged from the normal cylinders 40a, 40b, 40c to a turbine 32 provided in the exhaust passage 27 connected to the normal cylinders 40a, 40b, 40c, and compresses fresh air supplied to the combustion chamber of the reforming cylinder 40d by a compressor 31 provided in the reforming cylinder air intake duct 20d while being connected to the turbine 32. That is, the supercharger 30 rotates the turbine 32 by the kinetic energy of the exhaust gas E flowing through the exhaust passage 27, compresses combustion air A flowing through the reforming cylinder air intake duct 20d by the rotational force of the turbine 32, and supplies it to the combustion chamber of the reforming cylinder 40d, thereby performing so-called supercharging. That is, in this embodiment, the supercharger 30 supercharges only the combustion air A that is led to the reforming cylinder 40d.

[0039] In addition, downstream of the turbine 32 in the exhaust passage 27, there are provided a three-way catalyst CT1 that purifies the harmful components contained in the exhaust gas E, such as carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NOx), and an SCR catalyst CT2 that removes NOx contained in the exhaust gas E. Furthermore, the control device 50 sets the excess air ratios of the normal cylinders 40a, 40b, and 40c to 1. Note that, as will be described in detail later, the control device 50 executes excess air ratio control, which will be described later, and sets the excess air ratio of the reforming cylinder 40d to a fuel-rich region that is less than 1.

[0040] Downstream of the air cleaner 21, the main air intake pipe 20 branches into a plurality of normal cylinder air intake branch pipes 20a, 20b, and 20c that lead combustion air A to the normal cylinders 40a, 40b, and 40c, respectively, and a reforming cylinder air intake branch pipe 20d that leads combustion air A to the reforming cylinder 40d. The reforming cylinder 40d is configured to partially oxidize a portion of the fresh air in its combustion chamber to generate a reformed gas K containing hydrogen as a combustion-promoting gas having a faster combustion speed than the fuel N (ammonia in this embodiment). It is known that when ammonia and combustion air are mixed and burned, the amount of hydrogen generated peaks in a fuel-rich region where the excess air ratio is less than 1. Therefore, in this embodiment, in order to burn the mixture in a fuel-rich state in the fuel chamber of the reforming cylinder 40d, a second fuel supply passage 29 is connected to the reforming cylinder intake pipe 20d, which supplies fresh air to the reforming cylinder 40d, and the second fuel supply passage 29 is provided with a carburetor 71 that vaporizes the fuel N. Furthermore, a reformed gas passage 28, which passes the reformed gas K reformed in the reforming cylinder 40d, is connected to the reforming cylinder 40d, and the downstream end of the reformed gas passage 28 is connected to the downstream side of the throttle valve 23 for normal cylinders of the main intake pipe 20. That is, in this embodiment, the reformed gas K is entirely guided to the normal cylinders 40a, 40b, 40c. An intercooler 42, which cools the reformed gas K, is provided in the reformed gas passage 28. The control device 50 executes excess air ratio control to control the excess air ratio in the reforming cylinder 40d within a predetermined range in which the reformed gas K is produced. More preferably, in the excess air ratio control, the control device 50 controls the second injector IJd so that the excess air ratio of the fresh air to the reforming cylinder 40d is smaller than 1.

[0041] That is, the second fuel supply passage 29 and the second injector IJd function as a second fuel supply unit.

[0042] A rotation speed sensor that measures the rotation speed of the rotation shaft (not shown) is provided as an operating state detection unit 41 on the rotation shaft (not shown) of the engine body 40. Furthermore, a torque measurement sensor that measures the torque of the rotating shaft (not shown) of the engine body 40 is provided as an operating state detection unit 41 on the rotating shaft of the engine body 40, and the control device 50 controls the opening of the first injectors IJa, IJb, IJc, the second injector IJd, the throttle valve 23 for the normal cylinder, and the throttle valve 25 for the reformed cylinder so that the engine output calculated based on the engine speed measured by the speed sensor and the torque measured by the torque measurement sensor becomes a target output.

[0043] As explained above, since non-flammable ammonia is used as the fuel N, combustion in the combustion chambers of the cylinders 40a, 40b, 40c, and 40d may become unstable. Therefore, in the engine system 100 according to the first embodiment, when combustion in a combustion chamber becomes unstable, in order to increase the pressure and temperature of the combustion chamber and stabilize the combustion (improve ignition), as shown in Fig. 2, the reforming cylinder 40d is provided with an opening / closing timing setting mechanism 61 that sets the opening / closing timing of an intake valve 63 that opens and closes the intake port 20f to which the reforming cylinder intake branch pipe 20d is connected, and an exhaust valve 64 that opens and closes the exhaust port 28b to which the reformed gas passage 28 is connected. When the combustion fluctuation rate of the reforming cylinder 40d detected by the combustion fluctuation rate detection unit serving as the operating state detection unit 41 is equal to or greater than a predetermined stability determination threshold, the control device 50 adjusts (increases) the pressure in the combustion chamber of the reforming cylinder 40d before ignition by, for example, changing and adjusting the closing timing of the intake valve 63 during the compression stroke using the opening / closing timing setting mechanism 61, or by adjusting the boost pressure of the fresh air using the above-mentioned supercharger 30, thereby setting the actual compression ratio in the combustion chamber to a desired actual compression ratio (an example of actual compression ratio increase control).The control device 50, the opening / closing timing setting mechanism 61, the intake valve 63, the supercharger 30, etc. then function as actual compression ratio setting means (an example of fresh air temperature adjustment means) that adjusts the temperature of the fresh air supplied to the reforming cylinder 40d. The above-mentioned actual compression ratio setting means may be configured to be able to adjust the actual compression ratio of not only the reformed cylinder 40d but also the normal cylinders 40a, 40b, and 40c.

[0044] Furthermore, the control device 50 includes a memory unit 50a that stores a reforming ratio map relating to the reforming ratio of ammonia using the temperature, pressure, and oxygen concentration in the reforming cylinder 40d as parameters, and is configured to operate an actual compression ratio setting means (an example of a fresh air temperature adjusting means) based on the reforming ratio map stored in the memory unit 50a. More specifically, the inventors have found that the reforming ratio of ammonia, in other words, the amount of hydrogen produced as the reformed gas K, varies depending on the temperature, pressure, and oxygen concentration in the reforming cylinder 40d, and that in the example shown in FIG. 5, for example, the peak production amount occurs at a predetermined temperature (1 atm), a predetermined pressure (473.15 K), and a predetermined oxygen concentration α. Therefore, the inventors operate an actual compression ratio adjustment means to maximize the amount of hydrogen produced in the reforming cylinder 40d based on the peak combustion temperature (temperature measured by an in-cylinder temperature sensor), in-cylinder pressure (pressure measured by an in-cylinder pressure sensor), oxygen concentration (oxygen concentration of exhaust gas immediately after the outlet of the reforming cylinder 40d), and a reforming ratio map (reformation ratio map as shown in Figure 5 for various temperatures and pressures). This makes it possible to maximize the net thermal efficiency of the engine system 100.

[0045] Furthermore, the inventors performed equilibrium calculations regarding the reforming rate of ammonia for each equivalence ratio. The results for 700 K and 40 atm are shown in Figure 6 and Table 1, and the results for 1000 K and 40 atm are shown in Figure 7 and Table 2. Note that these results are equilibrium calculation results after a sufficient amount of time has passed in the reaction formulas shown in the above-mentioned [Equation 1] and [Equation 2]. From the calculation results, the inventors have found that the equilibrium shifts in the direction of increasing hydrogen through thermal decomposition of ammonia as the oxygen-rich conditions become lower (the higher the equivalence ratio), and that the equilibrium shifts in the direction of increasing hydrogen through thermal decomposition of ammonia by increasing the temperature. Therefore, in the engine system 100 according to this embodiment, when increasing the combustion-promoting gas (particularly hydrogen) in the reformed gas K, the control device 50 performs control such that the equivalence ratio of the reformed cylinder 40d increases as the target amount of combustion-promoting gas increases. Furthermore, when increasing the combustion promoting gas (particularly hydrogen) in the reformed gas K, the control device 50 performs control such that the temperature of the reforming cylinder 40d increases as the target amount of combustion promoting gas increases.

[0046] [Table 1]

[0047] [Table 2]

[0048] Furthermore, the inventors of the present application have found that when the control device 50 is performing the above-mentioned excess air ratio control, the net thermal efficiency of the engine body 40 improves as the fuel ratio, which is the ratio of the total fuel supply amount to all normal cylinders 40a, 40b, 40c to the total fuel supply amount to all reformed cylinders 40d, is reduced. Therefore, while the control device 50 is adjusting the amount of fuel supplied by the second fuel supply unit to perform excess air ratio control in the reformed cylinder 40d, it executes fuel ratio reduction control to reduce the fuel ratio, which is the ratio of the total amount of fuel supplied by the first fuel supply unit to all normal cylinders 40a, 40b, 40c to the total amount of fuel supplied by the second fuel supply unit to all reformed cylinders 40d.

[0049] [Another embodiment] (1) In the above embodiment, the fuel N is ammonia. However, in view of the fact that ammonia is flame-retardant, a configuration may be adopted in which a combustion-promoting gas such as hydrogen is mixed with the ammonia, for example, at the time of starting. Also, for example, a configuration may be adopted in which the temperature is raised using a glow plug or the like at the time of starting, so that the reforming cylinder 40d can be operated while the reforming reaction occurs stably inside the reforming cylinder 40d.

[0050] (2) The reformed gas flow passage 28 may be configured to be connected to the exhaust port 28a of the reformed cylinder 40d and at least one of the normal cylinder air intake pipes 20a, 20b, and 20c that supply fresh air to the normal cylinders 40a, 40b, and 40c. Furthermore, the first fuel supply unit may be configured to supply fuel not only to the normal cylinders 40a, 40b, and 40c, but also to the reforming cylinder 40d.

[0051] (3) In the above embodiment, an example was shown in which the engine system 100 includes the supercharger 30. However, even if the engine system 100 does not include the supercharger 30, the object of the present invention can be satisfactorily achieved. Furthermore, in the above embodiment, an example in which a turbo type is provided as the supercharger 30 has been shown, but a supercharger type may also be used. Furthermore, in the above embodiment, an example of so-called single-stage supercharging, in which the supercharger 30 includes a single compressor 31 and a single turbine 32, has been shown, but it may alternatively be a multi-stage supercharger having two or more stages.

[0052] (4) In the above embodiment, each of the cylinders 40a, 40b, 40c, and 40d is configured to ignite ammonia as fuel N by spark ignition. However, a configuration in which self-ignition combustion is performed may be adopted in all or any of the cylinders 40a, 40b, 40c, and 40d.

[0053] (5) The engine system 100 may be provided with a fresh air temperature adjustment means capable of adjusting the temperature of fresh air supplied to the reforming cylinder 40d, and the control device 50 may be configured to activate the fresh air temperature adjustment means to perform fresh air temperature increase control to increase the temperature of the fresh air in the reforming cylinder 40d when the combustion fluctuation rate of the reforming cylinder 40d is equal to or greater than a predetermined stability determination threshold. For example, a heat exchanger (not shown) may be provided as fresh air temperature adjustment means between the reforming cylinder throttle valve 25 of the reforming cylinder intake pipe 20d and the reforming cylinder 40d, for exchanging heat between the fresh air flowing through the reforming cylinder intake pipe 20d and a portion of the exhaust gas E flowing through the exhaust passage 27, and the fresh air temperature may be adjusted by adjusting the flow rate of the exhaust gas E flowing through the heat exchanger. Alternatively, instead of the heat exchanger, a heater capable of heating fresh air with thermal energy from various heating sources may be provided.

[0054] (6) Furthermore, as the fresh air temperature adjusting means, a configuration may be adopted in which an exhaust gas recirculation amount adjusting means is provided for adjusting the amount of exhaust gas recirculated to the reforming cylinder 40d. To provide further explanation, as shown in FIG. 3, the engine system 100 includes an exhaust branch pipe 27a that guides a portion of the exhaust gas E flowing through the exhaust passage 27 of the normal cylinders 40a, 40b, and 40c to the reforming cylinder intake branch pipe 20d, and an exhaust gas flow rate control valve 27b (an example of an exhaust gas recirculation amount adjustment means) that adjusts the flow rate of the exhaust gas E flowing through the exhaust branch pipe 27a, and the control device 50 may be configured to operate the exhaust gas flow rate control valve 27b when the combustion fluctuation rate of the reforming cylinder 40d is equal to or greater than a predetermined stability determination threshold value, thereby performing exhaust gas recirculation amount increase control to increase the amount of exhaust gas recirculated to the reforming cylinder 40d. As another configuration, as shown in FIG. 4, the engine system 100 may include a reformed gas flow branch pipe 28d that guides a portion of the reformed gas K (an example of exhaust gas) flowing through the reformed gas flow path 28 to the reformed cylinder intake branch pipe 20d, and a reformed gas flow rate control valve 28c (an example of an exhaust gas recirculation amount adjustment means) that adjusts the flow rate of the reformed gas K flowing through the reformed gas flow branch pipe 28d, and the control device 50 may operate the reformed gas flow rate control valve 28c when the combustion fluctuation rate of the reformed cylinder 40d is equal to or greater than a predetermined stability determination threshold, thereby performing exhaust gas recirculation amount increase control to increase the amount of exhaust gas recirculated to the reformed cylinder 40d.

[0055] (7) The control device 50 may be configured to perform a reformed gas operation in which only the reformed gas K is introduced as fuel into the normal cylinders 40a, 40b, and 40c while excess air ratio control is being performed.

[0056] (8) Although not shown, the engine system 100 may be configured to include a reformed engine having at least one reformed cylinder as its multiple cylinders, and an external power engine having normal cylinders as its multiple cylinders.

[0057] (9) Although not shown in the figures, the engine system 100 may be provided with a memory unit 50a that stores an ignition map relating to the ignition of ammonia, with the temperature, pressure, and excess air ratio in the reforming cylinder 40d as parameters, and the control device 50 may be configured to operate at least the fresh air temperature adjustment means and control the excess air ratio of the reforming cylinder by excess air ratio control based on the ignition map stored in the memory unit 50a.

[0058] (10) Although not shown in the drawings, the engine system 100 may be configured to supply, as the fuel N, a combustion-promoting gas such as hydrogen in addition to the flame-retardant ammonia.

[0059] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, as long as no contradictions arise. Furthermore, the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these, and can be modified as appropriate within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0060] The engine system of the present invention can be effectively used as an engine system that can sufficiently suppress hydrocarbon components contained in exhaust gases while improving durability and economy without using a catalyst that requires a precious metal, when using a fuel gas containing ammonia as a main component. [Explanation of symbols]

[0061] 11: 1st fuel supply path 27: Exhaust duct 27b: Exhaust gas flow control valve 28c: Reformed gas flow control valve 29:Second fuel supply path 40d: Modified cylinder 41: Driving state detection unit 50: Control device 50a: Storage section 61: Opening and closing timing setting mechanism 100: Engine system A: Combustion air CT1: Three-way catalyst K: Reformed gas N: fuel

Claims

1. at least some of the plurality of cylinders are operated as reforming cylinders that carry out a partial oxidation reaction of at least a portion of a mixture containing a fuel mainly composed of ammonia and combustion air to reform the mixture into a reformed gas containing a combustion-promoting gas that has a faster combustion speed than the fuel, and the remaining plurality of cylinders are operated as normal cylinders to which the reformed gas reformed in the reforming cylinders is introduced; An engine system including a control device that controls an excess air ratio in the reforming cylinder within a predetermined range in which the reformed gas is produced.

2. a fresh air temperature adjusting means for adjusting the temperature of fresh air supplied to the reforming cylinder; The control device 2. The engine system according to claim 1, wherein when the combustion fluctuation rate of the reforming cylinder is equal to or greater than a predetermined stability determination threshold, the fresh air temperature adjustment means is activated to perform fresh air temperature increase control to increase the temperature of the fresh air in the reforming cylinder.

3. the fresh air temperature adjusting means includes an actual compression ratio adjusting means for adjusting the pressure in the reforming cylinder to adjust the actual compression ratio of the reforming cylinder, The control device 3. The engine system according to claim 2, wherein when the stability determination threshold is met or higher, the actual compression ratio adjusting means is operated to execute actual compression ratio increasing control for increasing the actual compression ratio of the reformed cylinder.

4. The fresh air temperature adjusting means includes an exhaust gas recirculation amount adjusting means for adjusting the amount of exhaust gas recirculated to the reforming cylinder, The control device 3. The engine system according to claim 2, wherein when the stability determination threshold is exceeded, the exhaust gas recirculation amount adjusting means is activated to execute exhaust gas recirculation amount increase control, which increases the amount of exhaust gas recirculated to the reforming cylinder.

5. a three-way catalyst is provided in an exhaust passage through which exhaust gas from the normal cylinder flows; The control device executes the excess air ratio control to set the excess air ratio of the reforming cylinder to a fuel-rich region less than 1, and 3. The engine system according to claim 1, wherein the excess air ratio of the normal cylinder is set to 1.

6. a memory unit that stores a reforming ratio map relating to the reforming ratio of ammonia using the temperature, pressure, and oxygen concentration in the reforming cylinder as parameters; 3. The engine system according to claim 2, wherein the control device operates at least the fresh air temperature adjusting means based on the reforming ratio map stored in the storage unit.

7. a storage unit that stores an ignition map relating to the ignition of ammonia using the temperature, pressure, and excess air ratio in the reforming cylinder as parameters; 3. The engine system according to claim 2, wherein the control device activates at least the fresh air temperature adjustment means and controls the excess air ratio of the reformed cylinder by the excess air ratio control based on the ignition property map stored in the memory unit.

8. a first fuel supply unit that supplies fuel to be introduced to at least the normal cylinder, and a second fuel supply unit that supplies fuel to be introduced to the reforming cylinder, 3. The engine system according to claim 1, wherein the control device executes a fuel ratio reduction control to reduce a fuel ratio, which is the ratio of the total fuel supply amount to all of the normal cylinders by the first fuel supply unit to the total fuel supply amount to all of the reformed cylinders by the second fuel supply unit, while executing the air excess ratio control to adjust the fuel supply amount by the second fuel supply unit to control the air excess ratio in the reformed cylinder within a predetermined range in which the reformed gas is generated.

9. 3. The engine system according to claim 1, wherein the control device executes a reformed gas operation in which only the reformed gas is introduced as the fuel into the normal cylinders while the excess air ratio control is being executed.

10. 3. The engine system according to claim 1, further comprising: a reformed engine having at least one reformed cylinder as the plurality of cylinders; and an external power engine having the normal cylinders as the plurality of cylinders.

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