Engine system

Abstract

To provide an engine system capable of improving combustion stability while preventing constant combustion.SOLUTION: A fuel injection device 11,12 that injects a main fuel, a first fuel having a combustion speed faster than that of the main fuel, and a second fuel having an octane number higher than that of the main fuel into the combustion chamber 5 as a fuel is provided, and when an engine load is less than a switching load Tx, the main fuel and the first fuel are injected into the combustion chamber 5; Further, the fuel injection device 11,12 is controlled so that the first fuel is injected after the main fuel is injected, and when the engine load is the switching load Tx or higher, the fuel injection device 11,12 is controlled so that the main fuel and the second fuel are injected into the combustion chamber 5 and the second fuel is injected after the main fuel is injected.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an engine system. [Background technology]

[0002] 2. Description of the Related Art Conventionally, in engines installed in vehicles and the like, it has been considered to improve engine performance by supplying a plurality of types of fuel to the combustion chamber.

[0003] For example, Patent Document 1 discloses an engine that is capable of injecting gasoline and hydrogen, which has a higher octane number than gasoline, into the combustion chamber, and that aims to suppress knocking by injecting hydrogen into the combustion chamber in addition to gasoline when the engine load is high. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-36538 Summary of the Invention [Problem to be solved by the invention]

[0005] In addition to preventing abnormal combustion such as knocking when the engine load is high as described above, the engine is also required to stably combust the air-fuel mixture when the engine load is low. The invention of Patent Document 1 does not sufficiently consider ensuring combustion stability when the engine load is low, and there is room for improvement in this regard.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide an engine system that can prevent abnormal combustion while improving combustion stability. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided an engine system including an engine body having a combustion chamber formed therein, and an intake passage and an exhaust passage connected to the engine body, the engine system including a fuel injection device that injects a main fuel, a first fuel having a faster combustion speed than the main fuel, and a second fuel having a higher octane number than the main fuel as fuel into the combustion chamber, an ignition plug that ignites a mixture of fuel and air in the combustion chamber, and a control device that controls the fuel injection device, wherein the control device controls the fuel injection device so that, when an engine load is less than a predetermined switching load, the main fuel and the first fuel are injected into the combustion chamber and the first fuel is injected after the main fuel is injected, and when the engine load is equal to or greater than the switching load, the control device controls the fuel injection device so that the main fuel and the second fuel are injected into the combustion chamber and the second fuel is injected after the main fuel is injected (claim 1).

[0008] According to the present invention, when the engine is operating in a high-load range where the engine load is equal to or greater than the switching load, a second fuel having a high octane rating is injected into the combustion chamber after the injection of the main fuel. This allows a mixture with a high concentration of the second fuel to be formed around the spark plug, i.e., a mixture that is difficult to self-ignite, and prevents the mixture from self-igniting due to a high-temperature spark plug, resulting in abnormal combustion. Furthermore, because the amount of the main fuel having a relatively low octane rating is kept small, the occurrence of knocking can be suppressed.

[0009] On the other hand, when the engine is operating in a low load range where the engine load is below the threshold load, the first fuel, which has a high combustion speed, is injected into the combustion chamber after the main fuel is injected. This allows a mixture with a high concentration of the first fuel, i.e., a mixture with a high combustion speed, to be formed around the spark plug, allowing the flame to grow quickly after ignition. This allows the main fuel to be reliably burned despite a temperature drop in the combustion chamber due to an increase in the combustion chamber volume. Therefore, according to the present invention, it is possible to ensure combustion stability in the low load range while suppressing the occurrence of abnormal combustion.

[0010] In the above configuration, the switching load is preferably set to a value greater when the engine water temperature, which is the temperature of the cooling water that cools the engine body, is low than when it is high (claim 2).

[0011] When the engine water temperature is low, combustion stability is likely to decrease, making it difficult to ensure combustion stability even in a region where the engine load is relatively high. In contrast, with this configuration, the switching load is set to a large value when the engine water temperature is low. That is, when the engine water temperature is low, control is implemented to improve combustion stability by injecting the main fuel and the first fuel, even in a region where the engine load is relatively high. Therefore, combustion stability can be ensured when the engine water temperature is low. Furthermore, when the engine water temperature is high, abnormal combustion is likely to occur even in a region where the engine load is relatively low. In contrast, with this configuration, when the engine water temperature is high, control is implemented to inject the main fuel and the second fuel, making it possible to suppress abnormal combustion, even in a region where the engine load is relatively low. Therefore, it is possible to reliably prevent abnormal combustion from occurring when the engine water temperature is high.

[0012] In the above configuration, the switching load is preferably set to a larger value when the intake air temperature, which is the temperature of the air flowing through the intake passage, is low than when it is high (claim 3).

[0013] When the intake air temperature is low, combustion stability is likely to decrease, and it is difficult to ensure combustion stability even in areas where the engine load is relatively high. In contrast, with this configuration, when the intake air temperature is low, the control that improves combustion stability is implemented even in areas where the engine load is relatively high, so combustion stability can be ensured when the engine water temperature is low. Furthermore, when the intake air temperature is high and knocking is likely to occur, the control that can suppress knocking is implemented even in areas where the engine load is relatively low, so knocking can be reliably prevented when the intake air temperature is high.

[0014] In the above configuration, preferably, the engine is provided with an EGR passage that connects the exhaust passage and the intake passage and recirculates EGR gas, which is part of the exhaust gas discharged from the engine body, to the intake passage; a first reforming catalyst that is provided in the EGR passage and reforms the main fuel to produce the first fuel; a first reforming fuel supply device that supplies the main fuel to the first reforming catalyst; a second reforming catalyst that is provided in the EGR passage and reforms the main fuel to produce the second fuel; and a second reforming fuel supply device that supplies the main fuel to the second reforming catalyst, and the fuel injection device injects the first fuel produced by the first reforming catalyst into the combustion chamber, and injects the second fuel produced by the second reforming catalyst into the combustion chamber (Claim 4).

[0015] According to this configuration, the activation of each reforming catalyst can be promoted by utilizing the high-temperature EGR gas.

[0016] In the above configuration, preferably, the EGR passage includes a first EGR passage and a second EGR passage through which the EGR gas flows independently of each other, and the first reforming catalyst is disposed in the first EGR passage, and the second reforming catalyst is disposed in the second EGR passage (claim 5).

[0017] According to this configuration, the EGR gas can be introduced to both the first reforming catalyst and the second reforming catalyst while still at a high temperature, thereby ensuring activation of both reforming catalysts.

[0018] In the above configuration, preferably, there is provided a first tank for storing the first fuel and a second tank for storing the second fuel, and the control device drives the first reforming fuel supply device when the amount of the first fuel stored in the first tank falls below a predetermined first judgment amount, and drives the second reforming fuel supply device when the amount of the second fuel stored in the second tank falls below a predetermined second judgment amount (claim 6).

[0019] According to this configuration, the storage amounts of the first fuel and the second fuel can be secured, and these fuels can be appropriately injected into the combustion chamber.

[0020] For example, the first fuel is hydrogen or ethane, and the second fuel is methane (claim 7).

[0021] According to another aspect of the present invention, there is provided an engine system including an engine body having a combustion chamber formed therein, and an intake passage and an exhaust passage connected to the engine body, the engine system including a fuel injection device that injects a main fuel, a first fuel having a faster combustion speed than the main fuel, and a second fuel having a higher octane number than the main fuel as fuel into the combustion chamber, an ignition plug that ignites a mixture of fuel and air in the combustion chamber, and a control device that controls the fuel injection device, wherein the control device controls the fuel injection device so that, when an engine water temperature that is a temperature of cooling water that cools the engine body is below a predetermined judgment water temperature, the main fuel and the first fuel are injected into the combustion chamber and the first fuel is injected after the main fuel is injected, and when the engine water temperature is equal to or higher than the judgment water temperature, the control device controls the fuel injection device so that the main fuel and the second fuel are injected into the combustion chamber and the second fuel is injected after the main fuel is injected (claim 8).

[0022] In this engine system, when the engine water temperature is equal to or higher than the threshold water temperature and knocking is likely to occur, the second fuel with a higher octane rating is injected into the combustion chamber after the injection of the main fuel. Therefore, as described above, knocking can be suppressed. On the other hand, when the engine water temperature is lower than the threshold water temperature and combustion stability is likely to decrease, the first fuel with a higher combustion speed is injected into the combustion chamber after the injection of the main fuel. Therefore, as described above, flame growth after ignition can be promoted, and the mixture containing the main fuel can be reliably combusted. Therefore, with this engine system, knocking can be suppressed while combustion stability is ensured.

[0023] According to another aspect of the present invention, there is provided an engine system including an engine body having a combustion chamber formed therein, and an intake passage and an exhaust passage connected to the engine body, the engine system including a fuel injection device that injects a main fuel, a first fuel having a faster combustion speed than the main fuel, and a second fuel having a higher octane number than the main fuel as fuel into the combustion chamber, an ignition plug that ignites a mixture of fuel and air in the combustion chamber, and a control device that controls the fuel injection device, wherein the control device controls the fuel injection device so that, when an intake temperature that is the temperature of air flowing through the intake passage is lower than a predetermined reference intake temperature, the main fuel and the first fuel are injected into the combustion chamber and the first fuel is injected after the main fuel is injected, and when the intake temperature is equal to or higher than the reference intake temperature, the control device controls the fuel injection device so that the main fuel and the second fuel are injected into the combustion chamber and the second fuel is injected after the main fuel is injected (claim 9).

[0024] In this engine system, when the intake air temperature is equal to or higher than the threshold water temperature, making knocking more likely to occur, the second fuel with a higher octane rating is injected into the combustion chamber after the injection of the main fuel. Therefore, as described above, knocking can be suppressed. On the other hand, when the intake air temperature is lower than the threshold water temperature, making combustion stability more likely to decrease, the first fuel with a higher combustion speed is injected into the combustion chamber after the injection of the main fuel. Therefore, as described above, flame growth after ignition is promoted, making it possible to reliably combust the air-fuel mixture containing the main fuel. Therefore, with this engine system, knocking can be suppressed while ensuring combustion stability. [Effects of the Invention]

[0025] As described above, the engine system of the present invention can improve combustion stability while preventing abnormal combustion. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a schematic configuration diagram of an engine system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view schematically showing a reforming catalyst. [Figure 3] FIG. 2 is a diagram showing a control block of the engine system. [Figure 4] FIG. 2 is a diagram showing the operating range of the engine body. [Figure 5] 4 is a flowchart showing control details related to fuel injection into a combustion chamber. [Figure 6] 4 is a graph showing the relationship between the engine water temperature and the intake air temperature and the switching load. [Figure 7] 4 is a graph showing the relationship between engine load and in-cylinder injection amount. [Figure 8] FIG. 4 is a diagram showing a schematic diagram of driving pulses of an injector and an ignition plug in a low load region. [Figure 9] FIG. 4 is a diagram showing a schematic diagram of driving pulses of an injector and an ignition plug in a high load region. [Figure 10] 4 is a flowchart showing control details regarding reforming of the main fuel. [Figure 11] FIG. 2 is a diagram showing a schematic view of the state inside the combustion chamber near the compression top dead center. [Figure 12] 10 is a flowchart showing control details relating to fuel injection into a combustion chamber in an engine system according to a second embodiment. [Figure 13] 10 is a flowchart showing control details relating to fuel injection into a combustion chamber in an engine system according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0027] (Overall configuration of the engine system) FIG. 1 is a schematic diagram showing a preferred embodiment of an engine system E according to the present invention. The engine system E includes an engine body 1 that is driven by a supply of fuel, and an intake passage 20 and an exhaust passage 30 that are connected to the engine body 1. The intake passage 20 is a passage through which intake air, which is air introduced into the engine body 1, flows. The exhaust passage 30 is a passage through which exhaust gas discharged from the engine body 1 flows. In the first embodiment, the engine system E is installed in a vehicle such as an automobile as a power source for driving the vehicle.

[0028] The engine body 1 is a multi-cylinder engine having a plurality of cylinders 2A (only one of which is shown in FIG. 1). In the first embodiment, the engine body 1 is a four-cylinder in-line engine, with the four cylinders 2A aligned in a direction perpendicular to the plane of the paper in FIG. 1. The engine body 1 includes a cylinder block 2 having the plurality of cylinders 2A formed therein, a cylinder head 3 attached to the upper surface of the cylinder block 2 so as to close the upper end openings of each cylinder 2A, and a plurality of pistons 4 housed in each cylinder 2A so as to be able to slide back and forth.

[0029] A combustion chamber 5 is defined above the piston 4 of each cylinder 2A. As will be described later, fuel is supplied to the combustion chamber 5. The mixture of the supplied fuel and air is burned in the combustion chamber 5, and the expansion force caused by the combustion causes the piston 4 to reciprocate up and down.

[0030] A crankshaft 13, which is the output shaft of the engine body 1, is provided at the bottom of the cylinder block 2 (below the pistons 4). The crankshaft 13 is connected to the pistons 4 of each cylinder 2A via connecting rods. The crankshaft 13 rotates around its central axis in response to the reciprocating motion (up and down movement) of the pistons 4. A crank angle sensor SN1 is attached to the cylinder block 2. The crank angle sensor SN1 detects the crank angle, which is the rotation angle of the crankshaft 13, and the engine speed, which is the rotation speed of the crankshaft 13.

[0031] A water jacket 15 through which coolant flows to cool the engine body 1 is formed in the cylinder block 2 and the cylinder head 3. A water temperature sensor SN2 is attached to the cylinder block 2. The engine water temperature sensor SN2 detects the temperature of the coolant flowing through the water jacket 15, i.e., the engine water temperature.

[0032] An intake port 6 and an exhaust port 7 that communicate with the combustion chamber 5 are formed in the cylinder head 3 for each cylinder 2A. The cylinder head 3 is also equipped with an intake valve 8 that opens and closes the opening of the intake port 6 on the combustion chamber 5 side, and an exhaust valve 9 that opens and closes the opening of the exhaust port 7 on the combustion chamber 5 side, for each cylinder 2A.

[0033] The cylinder head 3 is equipped with an ignition plug 10 for each cylinder 2A. One spark plug 19 is provided for each cylinder 2A. The spark plug 10 is an ignition device that ignites a mixture of fuel and air formed in the combustion chamber 5. In the first embodiment, the spark plug 10 is disposed so that its tip, including the spark plug, faces the interior of the combustion chamber 5 from near the center of the ceiling surface of the combustion chamber 5.

[0034] The cylinder head 3 is equipped with a main injector 11 and a sub-injector 12, one for each cylinder 2A. One main injector 11 and one sub-injector 12 are provided for each cylinder 2A. The main injector 11 and the sub-injector 12 are both fuel injection devices that inject fuel into the combustion chamber 5. In the first embodiment, the main injector 11 and the sub-injector 12 are both attached so that their respective tips face the combustion chamber 5 from near the center of the ceiling surface of the combustion chamber 5. The main injector 11 and the sub-injector 12 correspond to the "fuel injection device" in this invention.

[0035] Main fuel is injected from the main injector 11 into the combustion chamber 5. Specifically, the engine system E has a main fuel tank 60 that stores gasoline, and a main fuel supply pipe 71 that connects the main fuel tank 60 and the main injector 11. A main fuel pump 71P is provided in the main fuel supply pipe 71. The main injector 11 injects the main fuel that is pressure-fed from the main fuel tank 60 by the main fuel pump 71P into the combustion chamber 5. The main fuel is a hydrocarbon, and in the first embodiment, gasoline is used as the main fuel.

[0036] The sub-injector 12 injects into the combustion chamber 5 a first fuel having a faster burning speed than the main fuel and a second fuel having a higher octane number than the main fuel. As will be described later, the sub-injector 12 injects one of the first fuel and the second fuel depending on the engine load. In the first embodiment, hydrogen (H2), which has a faster burning speed than gasoline, the main fuel, is used as the first fuel. Furthermore, methane (CH4), which has a higher octane number than gasoline, the main fuel, is used as the second fuel. Note that hydrogen has a faster burning speed than methane.

[0037] Specifically, the engine system E has a first tank 61 that stores a first fuel and a second tank 62 that stores a second fuel. The engine system E has a first fuel supply pipe 76 connected to the first tank 61, a second fuel supply pipe 77 connected to the second tank 62, and a sub-fuel supply pipe 78 connected to the sub-injector 12. The engine system E has a three-way valve 79 to which an end of the first fuel supply pipe 76 opposite the first tank 61, an end of the second fuel supply pipe 77 opposite the second tank 62, and an end of the sub-fuel supply pipe 78 opposite the sub-injector 12 are connected. In the first embodiment, the three-way valve 79 is electromagnetic and has an actuator including a solenoid or the like that drives a valve body.

[0038] The three-way valve 79 includes a valve body that switches the pipe that communicates with the sub-fuel supply pipe 78 between the first fuel supply pipe 76 and the second fuel supply pipe 77. When the three-way valve 79 is in a state where the sub-fuel supply pipe 78 and the first fuel supply pipe 76 are in communication with each other, the first fuel in the first tank 61 is introduced into the sub-fuel supply pipe 78. On the other hand, when the three-way valve 79 is in a state where the sub-fuel supply pipe 78 and the second fuel supply pipe 77 are in communication with each other, the second fuel in the second tank 62 is introduced into the sub-fuel supply pipe 78. Hereinafter, the state where the three-way valve 79 is in a state where the sub-fuel supply pipe 78 and the first fuel supply pipe 76 are in communication with each other will be referred to as a "first tank communication state," and the state where the sub-fuel supply pipe 78 and the second fuel supply pipe 77 are in communication with each other will be referred to as a "second tank communication state."

[0039] A sub-fuel pump 78P is provided in the sub-fuel supply pipe 78. When the three-way valve 79 is in the first tank communication state, the sub-injector 12 injects the first fuel pressure-fed by the sub-fuel pump 78P into the combustion chamber 5. On the other hand, when the three-way valve 79 is in the second tank communication state, the sub-injector 12 injects the second fuel pressure-fed by the sub-fuel pump 78P into the combustion chamber 5.

[0040] The first tank 61 is provided with a first tank internal pressure sensor SN3. The first tank internal pressure sensor SN3 detects the first tank internal pressure, which is the pressure inside the first tank 61. The second tank 62 is provided with a second tank internal pressure sensor SN4. The second tank internal pressure sensor SN4 detects the second tank internal pressure, which is the pressure inside the second tank 62.

[0041] The intake passage 20 is connected to the cylinder head 3 so as to communicate with the intake port 6 of each cylinder 2A. In the intake passage 20, an air cleaner 21, a throttle valve 22, and a surge tank 23 are arranged in this order from the upstream side in the intake air flow direction.

[0042] The air cleaner 21 is a filter that removes foreign matter from the intake air. The throttle valve 22 is a valve that opens and closes the intake passage 20. The amount of intake air flowing through the intake passage 20, and therefore the amount of air introduced into the engine body 1, is changed depending on the opening degree of the throttle valve 22. The surge tank 23 is a tank that provides space for evenly distributing the intake air to each cylinder 2A.

[0043] An air flow sensor SN5 and an intake air temperature sensor SN6 are arranged in the intake passage 20. The air flow sensor SN5 detects the intake air volume, which is the flow rate of intake air flowing through the intake passage 20. The intake air temperature sensor SN6 detects the intake air temperature, which is the temperature of air flowing through the intake passage 20. The air flow sensor SN5 and the intake air temperature sensor SN6 are arranged near the air cleaner 21, and detect the flow rate and temperature of air passing through the intake passage 20 near the air cleaner 21, respectively.

[0044] The exhaust passage 30 is connected to the cylinder head 3 so as to communicate with the exhaust port 7 of each cylinder 2A.

[0045] The engine system E is provided with an EGR system 40. The EGR system 40 includes an EGR passage 41. The EGR passage 41 connects the exhaust passage 30 and the intake passage 20 and recirculates EGR gas, which is a part of the exhaust gas, to the intake passage 20. The EGR passage 41 connects the exhaust passage 30 and a portion of the intake passage 20 between the throttle valve 22 and the surge tank 23.

[0046] The EGR passage 41 branches into three passages along the way. That is, the EGR passage 41 has a main EGR passage 41A, a first EGR passage 41B, and a second EGR passage 41C, through which EGR gas flows independently of one another. Specifically, the EGR passage 41 has an exhaust-side EGR passage 41E extending from the exhaust passage 30, and an intake-side EGR passage 41F extending from the intake passage 20. The exhaust passage 30-side ends of the main EGR passage 41A, the first EGR passage 41B, and the second EGR passage 41C are each connected to the exhaust-side EGR passage 41E. The ends of the main EGR passage 41A, the first EGR passage 41B and the second EGR passage 41C on the intake passage 20 side are each connected to the intake side EGR passage 41F, and the main EGR passage 41A, the first EGR passage 41B and the second EGR passage 41C are connected in parallel to the exhaust side EGR passage 41E and the intake side EGR passage 41F.

[0047] The main EGR passage 41A is provided with a main EGR valve 42A that opens and closes the main EGR passage 41A. The first EGR passage 41B is provided with a first EGR valve 42B that opens and closes the first EGR passage 41B. The second EGR passage 41C is provided with a second EGR valve 42C that opens and closes the second EGR passage 41C. These EGR valves 42A, 42B, and 42C can be opened and closed independently. The EGR passage through which the EGR gas passes is switched by opening and closing these EGR valves 42A, 42B, and 42C, and the amount of EGR gas passing through each EGR passage 41A, 41B, and 41C is changed by the opening degrees of these EGR valves 42A, 42B, and 42C. For example, when the first EGR valve 42B and the second EGR valve 42C are open and the main EGR valve 42A is closed, the EGR gas flows separately into the first EGR passage 41B and the second EGR passage 41C, passes through these EGR passages 41B and 41C, joins together in the intake side EGR passage 41F, and then flows back into the intake passage 20.

[0048] An EGR cooler 43 is provided in the intake-side EGR passage 41F closer to the intake passage 20 than the intake passage 20-side ends of the main EGR passage 41A, the first EGR passage 41B, and the second EGR passage 41C, that is, downstream of the main EGR passage 41A, the first EGR passage 41B, and the second EGR passage 41C in the flow direction of the EGR gas. The EGR cooler 43 cools the EGR gas by heat exchange.

[0049] (Configuration related to fuel reforming) The first fuel (hydrogen) and the second fuel (methane) injected from the sub-injector 12 into the combustion chamber 5 are produced by reforming the main fuel (gasoline). The configuration related to the reforming of the main fuel will be described next.

[0050] The first EGR passage 41B is provided with a first reforming catalyst device 51 including a catalyst for reforming the main fuel into a first fuel, and a first reforming injector 53 for supplying the main fuel to the first reforming catalyst device 51. The first reforming catalyst device 51 is provided in the first EGR passage 41B closer to the intake passage 20 than the first EGR valve 42B (downstream in the flow direction of EGR gas). The first reforming injector 53 is provided in a portion of the first EGR passage 41B between the first reforming catalyst device 51 and the first EGR valve 42B (upstream of the first reforming catalyst device 51 and downstream of the first EGR valve 42B in the flow direction of EGR gas), and injects the main fuel into this portion. The first reforming catalyst device 51 corresponds to the "first reforming catalyst" in this invention. The first reforming injector 53 corresponds to the "first reforming fuel supply device" in this invention.

[0051] The engine system E has a first reforming fuel supply pipe 72 that connects the main fuel tank 60 and the first reforming injector 53, and a first reforming fuel pump 72P that is provided on the first reforming fuel supply pipe 72 and pressure-feeds the main fuel in the main fuel tank 60. The main fuel in the main fuel tank 60 is pressure-fed to the first reforming injector 53 by the first reforming fuel pump 72P, and the first reforming injector 53 injects the pressure-fed main fuel into the first EGR passage 41B.

[0052] The second EGR passage 41C is provided with a second reforming catalyst device 52 including a catalyst for reforming the main fuel into a second fuel, and a second reforming injector 54 for supplying the main fuel to the second reforming catalyst device 52. The second reforming catalyst device 52 is provided in the second EGR passage 41C closer to the intake passage 20 than the second EGR valve 42C. The second reforming injector 54 is provided in a portion of the second EGR passage 41C between the second reforming catalyst device 52 and the second EGR valve 42C (a portion upstream of the second reforming catalyst device 52 and downstream of the second EGR valve 42C in the flow direction of EGR gas), and injects the main fuel into this portion. The second reforming catalyst device 52 described above corresponds to the "second reforming catalyst" in this invention. The second reforming injector 54 described above corresponds to the "second reforming fuel supply device" in this invention.

[0053] The engine system E has a second reforming fuel supply pipe 73 that connects the main fuel tank 60 and the second reforming injector 54, and a second reforming fuel pump 73P that is provided on the second reforming fuel supply pipe 73 and pressure-feeds the main fuel in the main fuel tank 60. The main fuel in the main fuel tank 60 is pressure-fed to the second reforming injector 54 by the second reforming fuel pump 73P, and the second reforming injector 54 injects the pressure-fed main fuel into the second EGR passage 41C.

[0054] FIG. 2 is a schematic diagram illustrating the structure of the first reforming catalyst device 51. As shown in FIG. 2, the first reforming catalyst device 51 has an outer cylinder 150 that forms its outer shape, and a main body 151 that is arranged inside the outer cylinder 150. The outer cylinder 150 is generally cylindrical, and the main body 151 is generally columnar. The inner diameter of the outer cylinder 150 is larger than the outer diameter of the main body 151, and a space R is defined between the outer cylinder 150 and the main body 151. The outer cylinder 150 and the main body 151 are arranged generally coaxially, and the space R is defined over the entire circumferential direction of the main body 151. A communication port 157 that communicates the space R with the outside of the outer cylinder 150 is formed on the outer peripheral surface of the outer cylinder 150. The communication port 157 is connected to the first tank 61 via a first outlet pipe 74 (FIG. 1). The gap between the inner peripheral edge of one axial end of outer cylinder 150 and the outer peripheral edge of one axial end of main body 151 is closed by cover member 158. Similarly, the gap between the peripheral edges of the other axial ends of outer cylinder 150 and main body 151 is closed by cover member 159. As a result, space R communicates with the outside of outer cylinder 150 only via communication port 157.

[0055] One axial end of the main body 151 is connected to the upstream portion of the first EGR passage 41B, and the other axial end is connected to the downstream portion of the first EGR passage 41B. EGR gas flows into the main body 151 from one axial end, passes through the main body 151, and is then discharged from the other end to the downstream portion of the first EGR passage 41B.

[0056] The main body 151 of the first reforming catalytic device 51 includes a carrier 152 formed in a substantially cylindrical shape and a plurality of catalyst bodies 153 capable of reforming a first fuel into a second fuel. The carrier 152 has a porous shape. The catalyst bodies 153 are each granular and supported on the carrier 152. The carrier 152 is made of, for example, zirconia. In the first embodiment, the catalyst bodies 153 of the first reforming catalytic device 51 are capable of reforming gasoline to produce hydrogen, and in the first reforming catalytic device 51, the main fuel made of gasoline is reformed as described above to produce the first fuel made of hydrogen. For example, the catalyst bodies 153 of the first reforming catalytic device 51 include silica (SiO2) and nickel (Ni).

[0057] A separation membrane 156 that allows only the first fuel to pass through is provided on the outer peripheral surface of the main body 151. In detail, the separation membrane 156 is configured to allow only the first fuel to pass through among the components contained in the EGR gas and the components contained in the gas generated by reforming the main fuel in the first reforming catalyst device 51. The separation membrane 156 is provided on almost the entire outer peripheral surface of the main body 151. As described above, in the first embodiment, the first fuel is hydrogen, and the separation membrane 156 of the first reforming catalyst device 51 allows only hydrogen to pass through.

[0058] With the above configuration, when the main fuel (gasoline, F1) is injected from the first reforming injector 53 into the first EGR passage 41B while EGR gas is flowing through the first EGR passage 41B, as shown by arrow Y1 in FIG. 2, the main fuel (gasoline) is introduced into the main body 151 of the first reforming catalyst device 51. Furthermore, when high-temperature EGR gas is introduced into the main body 151 of the first reforming catalyst device 51 via the first EGR passage 41B, the first reforming catalyst device 51 is heated and activated (more specifically, the catalyst main body 153 is activated). Then, when the main fuel (gasoline) is introduced into the main body 151 while the first reforming catalyst device 51 is activated, the main fuel (gasoline) is reformed by the action of the catalyst main body 153 to generate a first fuel (hydrogen). The generated first fuel (hydrogen) is discharged into the space R through the separation membrane 156, as shown by arrow Y2. The first fuel (hydrogen) discharged into the space R flows from the communication port 157 into the first discharge pipe 74, as shown by the arrow Y3, and is introduced into the first tank 61 via the first discharge pipe 74 and stored in the first tank 61.

[0059] The structure of the second reforming catalyst device 52 is similar to that of the first reforming catalyst device 51, and will be briefly described here. Also, in FIG. 2, the reference numerals of the respective elements of the second reforming catalyst device 52 are shown in parentheses. Specifically, the second reforming catalyst device 52 has an outer casing 250 that forms its outer shape, and a main body 251 arranged inside the outer casing 250. The main body 251 includes a carrier 252 and a plurality of catalyst bodies 253 that are supported on the carrier 252, each of which is granular and capable of reforming the main fuel into a second fuel. A separation membrane 256 that allows only the second fuel to pass through is provided on the outer peripheral surface of the main body 251 of the second reforming catalyst device 52, among the components contained in the EGR gas and the gas generated in the second reforming catalyst device 52. In the first embodiment, the catalyst body 253 used in the second reforming catalyst device 52 is capable of reforming gasoline to produce methane, and in the second reforming catalyst device 52, the main fuel made of gasoline is reformed as described above to produce the second fuel made of methane. For example, the catalyst body 253 of the second reforming catalyst device 52 contains alumina (Al2O3) and iron (Fe). Furthermore, the separation membrane 256 used in the second reforming catalyst device 52 is one that is permeable only to methane. Furthermore, the carrier 252 of the second reforming catalyst device 52 is made of, for example, zirconia and has a porous shape, similar to the carrier 152 of the first reforming catalyst device 51.

[0060] With the above-described configuration, when the main fuel (gasoline) is injected from the second reforming injector 54 into the second EGR passage 41C while EGR gas is flowing through the second EGR passage 41C, the main fuel (gasoline) is introduced into the main body 251 of the second reforming catalyst device 52. Furthermore, when high-temperature EGR gas is introduced into the main body 251 via the second EGR passage 41C, the second reforming catalyst device 52 is heated and activated (more specifically, the catalyst main body 253 is activated). Then, when the main fuel (gasoline) is introduced into the main body 251 while the second reforming catalyst device 52 is activated, the main fuel (gasoline) is reformed by the action of the catalyst main body 253 to produce the second fuel (methane). The produced second fuel passes through the separation membrane 256 and is discharged into the space R. The second fuel (methane) discharged into the space R flows into the second discharge pipe 75 from the communication port 257, and is introduced into the second tank 62 via the second discharge pipe 75 and stored in the second tank 62.

[0061] In addition, in the first reforming catalyst device 51 and the second reforming catalyst device 52, carbon is generated when the main fuel (gasoline) is reformed, and solid carbon is precipitated around the catalyst body 153, 253 as the main fuel (gasoline) is reformed.

[0062] (Control system) FIG. 3 is a functional block diagram showing the control system of the engine system E. The PCM 80 shown in this diagram is a device for overall control of the engine system E. The PCM 80 is composed of a microcomputer including a processor (CPU) that performs various arithmetic processing, memories such as ROM and RAM, and various input / output buses. The PCM 80 corresponds to the "control device" in this invention.

[0063] The PCM80 is electrically connected to the crank angle sensor SN1, engine water temperature sensor SN2, first tank internal pressure sensor SN3, second tank internal pressure sensor SN4, air flow sensor SN5, and intake air temperature sensor SN6. A vehicle equipped with the engine system E is equipped with an accelerator sensor SN7 that detects the accelerator position, which is the opening of an accelerator pedal provided on the vehicle. The PCM80 is also electrically connected to the accelerator sensor SN7. Information detected by each sensor SN1 to SN7, namely, information on the crank angle, engine speed, engine water temperature, first tank internal pressure, second tank internal pressure, intake air volume, intake air temperature, and accelerator position, is sequentially input to the PCM80.

[0064] The PCM 80 controls each part of the engine system E while executing various determinations and calculations based on input information from each of the sensors SN1 to SN7. The PCM 80 is electrically connected to the spark plug 10, the main injector 11, the sub-injector 12, the throttle valve 22, the three-way valve 79, the main EGR valve 42A, the first EGR valve 42B, the second EGR valve 42C, the first reforming injector 53, and the second reforming injector 54, and outputs control signals to each of these devices based on the results of the above calculations, etc.

[0065] (Fuel injection control) The control of fuel injection, which is a feature of the present invention, will now be described.

[0066] FIG. 4 is a control map with the horizontal axis representing engine speed and the vertical axis representing engine load. The operating range of the engine body 1 is divided into two regions according to the control content. Specifically, the operating range of the engine system E is divided into a low load region A1 where the engine load is less than a predetermined switching load Tx, and a high load region A2 where the engine load is equal to or greater than the switching load Tx. As will be described later, the switching load Tx is changed according to the engine water temperature and intake air temperature.

[0067] The type of fuel injected from the sub-injector 12 differs between the low load range A1 and the high load range A2. In the low load range A1, a first fuel is injected from the sub-injector 12, and in the high load range A2, a second fuel is injected from the sub-injector 12.

[0068] 5 is a flowchart showing the contents of the control relating to fuel injection into the combustion chamber 5, i.e., in-cylinder fuel injection, performed by the PCM 80. Steps S1 to S11 shown in FIG. 5 are repeatedly performed at predetermined intervals while the engine body 1 is running.

[0069] First, the PCM 80 reads various information detected by the sensors SN1 to SN7 etc. (Step S1) In Step S1, the PCM 80 reads at least the engine speed, engine water temperature, intake air amount, intake air temperature and accelerator opening.

[0070] Next, the PCM 80 determines whether or not a fuel cut is being performed to stop the supply of fuel into the combustion chamber 5 (step S2). This determination is made based on the engine speed, accelerator opening, and the like read in step S1.

[0071] If the determination in step S2 is YES and fuel cut is in progress, the process ends without performing the processes in step S3 and thereafter (return to step S1).

[0072] On the other hand, if the determination in step S2 is NO and fuel cut is not in progress, the PCM 80 sets the switching load Tx (step S3). The PCM 80 sets the switching load Tx based on the engine load, the engine water temperature read in step S1 (i.e., the current engine water temperature), and the intake air temperature read in step S1 (i.e., the current intake air temperature). FIG. 6 is a graph showing the relationship between the engine water temperature, the intake air temperature, and the switching load Tx. As shown in FIG. 6, the PCM 80 sets the switching load Tx to a smaller value as the engine water temperature increases. Also, the PCM 80 sets the switching load Tx to a smaller value as the intake air temperature increases. Also, as shown in FIG. 4, the PCM 80 sets the switching load Tx to a higher value as the engine load increases. In the first embodiment, the switching load Tx is preset to satisfy the above-mentioned relationships between the engine load, engine water temperature, and intake air temperature and is stored in the PCM 80 in a map or the like. The PCM 80 extracts a value corresponding to the current engine load, engine water temperature, and intake air temperature and sets it as the switching load Tx. As described above, the switching load Tx is the engine load that separates the low load region A1 and the high load region A2. Therefore, as shown in FIG. 4, when the switching load Tx is set to a small value in response to a high engine water temperature or intake air temperature, the high load region A2 extends further toward the low load side. Furthermore, when the switching load Tx is set to a large value in response to a low engine water temperature or intake air temperature, the low load region A1 extends further toward the high load side. The PCM 80 separately calculates the current engine load based on the engine speed and the accelerator pedal position.

[0073] After step S3, the PCM 80 determines whether the engine body 1 is operating within the low load range A1, that is, whether the engine load is less than the switching load Tx (step S4).

[0074] If the determination in step S4 is YES, the engine load is less than the switching load Tx, and the engine body 1 is operating within the low load range A1, the PCM 80 sets the injection amount of the main injector 11, that is, the amount of fuel injected from the main injector 11 into the combustion chamber 5 (step S5). Also in step S5, the PCM 80 sets the injection timing, which is the timing at which the main injector 11 injects fuel. Main fuel is injected from the main injector 11. Thus, in step S5, the injection amount and injection timing of the main fuel are set.

[0075] After step S5, the PCM 80 sets the injection amount of the sub-injector 12, that is, the amount of fuel injected from the sub-injector 12 into the combustion chamber 5 (step S6). Also, in step S6, the PCM 80 sets the injection timing, which is the timing at which the sub-injector 12 injects fuel. As described above, in the low load range A1, the first fuel is injected from the sub-injector 12. Thus, in step S6, the injection amount and injection timing of the first fuel are set.

[0076] After step S6, the PCM 80 sets the state of the three-way valve 79 to the first tank communication state (step S7), which connects the sub-fuel supply pipe 78 and the first fuel supply pipe 76, and introduces the first fuel from the first tank 61 into the sub-fuel supply pipe 78 and, ultimately, the sub-injector 12.

[0077] After step S7, the PCM 80 drives the main injector 11 and the sub-injector 12 (step S8). In step S8, which follows step S7, the main fuel is injected from the main injector 11, and the first fuel is injected from the sub-injector 12. At this time, the PCM 80 drives the main injector 11 so that the main injector 11 injects the main fuel at the injection timing set in step S5, and the amount of main fuel set in step S5 is injected from the main injector 11. The PCM 80 also drives the sub-injector 12 so that the sub-injector 12 injects the first fuel at the injection timing set in step S6, and the amount of first fuel set in step S6 is injected from the sub-injector 12. After step S8, the process ends (returns to step S1).

[0078] FIG. 7 is a graph showing the relationship between the in-cylinder injection amount, which is the amount of fuel injected into the combustion chamber 5, and the engine load. As shown in FIG. 7, in the first embodiment, in the low load region A1, the total amount of in-cylinder injection, which is the sum of the injection amount of the main fuel (gasoline) and the injection amount of the first fuel (hydrogen), increases as the engine load increases. Furthermore, the injection amount of the main fuel increases as the engine load increases. On the other hand, the injection amount of the first fuel decreases as the engine load increases. Note that the unit of the in-cylinder injection amount on the vertical axis of FIG. 7 is the weight of fuel injected into one cylinder 2A per combustion cycle. In steps S5 and S6 described above, the injection amounts of the main fuel and the first fuel are set so that the relationship between the engine load and the injection amount satisfies the above relationship. In the first embodiment, the injection amounts of the main fuel and the first fuel are set in advance so as to satisfy the above-described relationships for the engine speed and the engine load, and are stored in the PCM 80 as maps. In steps S5 and S6, the PCM 80 extracts values ​​corresponding to the engine speed and the engine load read in step S1 from these maps and sets them as the injection amounts.

[0079] FIG. 8 is a diagram schematically illustrating the drive pulse Qm1 of the main injector 11, the drive pulse Qs1 of the sub-injector 12, and the drive pulse SP1 of the spark plug 10 when the engine body 1 is operating in the low load range A1. As shown in FIG. 8, in the low load range A1, the main injector 11 is driven from the early to middle stages of the compression stroke and injects main fuel into the combustion chamber 5 during this period. The sub-injector 12 is driven after the drive of the main injector 11 has finished and injects the first fuel into the combustion chamber 5 after the injection of the main fuel has finished. In the example of FIG. 8, the injection start time T1 of the main injector 11 is set to the early stage of the compression stroke, and the injection end time T2 is set to the middle stage of the compression stroke. Also, in the example of FIG. 8, the injection start time T3 and injection end time T4 of the sub-injector 12 are both set near the compression top dead center TDC, and the sub-injector 12 injects the first fuel near the compression top dead center TDC. The ignition timing Ts1 at which the spark plug 10 ignites is set immediately after the injection end timing T4 of the sub-injector 12, and the spark plug 10 ignites the air-fuel mixture in the combustion chamber 5 immediately after the injection of the first fuel ends. Note that the initial and middle periods of the compression stroke refer to the first and second periods when the compression stroke is divided into thirds.

[0080] 5, if the determination in step S4 is NO, the engine load is equal to or greater than the switching load Tx, and the engine body 1 is operating within the high load range A2, the PCM 80 proceeds to step S9. In step S9, similar to step S5, the PCM 80 sets the injection amount and injection timing of the main fuel (main injector 11).

[0081] After step S9, the PCM 80 sets the injection amount of the sub-injector 12 (step S10). Also, in step S10, the PCM 80 sets the injection timing of the sub-injector 12. As described above, in the high load range A2, the second fuel is injected from the sub-injector 12. Thus, in step S10, the injection amount and injection timing of the second fuel are set.

[0082] After step S10, the PCM 80 switches the three-way valve 79 to the second tank communication state (step S11). This connects the sub-fuel supply pipe 78 and the second fuel supply pipe 77, and the second fuel in the second tank 62 is introduced into the sub-fuel supply pipe 78 and, ultimately, the sub-injector 12.

[0083] After step S11, the PCM 80 proceeds to step S8, where it drives the main injector 11 and the sub-injector 12. In step S8, which is performed after step S11, the main injector 11 injects the main fuel, and the sub-injector 12 injects the second fuel. At this time, the PCM 80 drives the main injector 11 so that the main injector 11 injects the main fuel at the injection timing set in step S9, and the amount of main fuel set in step S9 is injected from the main injector 11. The PCM 80 also drives the sub-injector 12 so that the sub-injector 12 injects the second fuel at the injection timing set in step S10, and the amount of second fuel set in step S10 is injected from the sub-injector 12. After step S8, the process ends (returns to step S1).

[0084] As shown in FIG. 7, in the first embodiment, in the high load range A2, the total in-cylinder injection amount, which is the sum of the injection amount of the main fuel (gasoline) and the injection amount of the second fuel (methane), increases as the engine load increases. Furthermore, in the high load range A2, both the injection amount of the main fuel and the injection amount of the second fuel increase as the engine load increases. In steps S9 and S10, the injection amounts of the main fuel and the second fuel are set so that the relationship between the engine load and the injection amount satisfies the above relationship. In the first embodiment, these injection amounts are preset to satisfy the above relationship for each engine speed and engine load and are stored in the PCM 80 as maps. In steps S9 and S10, the PCM 80 extracts values ​​corresponding to the engine speed and engine load read in step S1 from these maps and sets them as the injection amounts. Note that the calorific value per unit weight of methane is smaller than the calorific value per unit weight of hydrogen. Therefore, when the engine load increases from the low side (low load region A1 side) to the high side (high load region A2 side) across the switching load Tx, the total amount of in-cylinder injection increases rapidly.

[0085] 9 is a diagram schematically showing the drive pulse Qm2 of the main injector 11, the drive pulse Qs2 of the sub-injector 12, and the ignition (SP2) by the spark plug 10 when the engine body 1 is operating in the high load range A2. As shown in FIG. 9, in the high load range A2 as well, the main injector 11 is driven for a period from the early to middle stages of the compression stroke, and injects main fuel into the combustion chamber 5 during this period, as in the low load range A1. Also in the high load range A2, the sub-injector 12 is driven after the drive of the main injector 11 has finished, and injects the second fuel into the combustion chamber 5 after the injection of the main fuel has finished. In the example of FIG. 9, the injection start timing T11 of the main injector 11 is set to the early stage of the compression stroke, and the injection end timing T12 is set to the middle stage of the compression stroke. 9, the injection start timing T13 and injection end timing T14 of the sub-injector 12 are both set near compression top dead center TDC, and the sub-injector 12 injects the second fuel near compression top dead center TDC. Also in the high load range A2, the ignition timing Ts2 at which the spark plug 10 performs ignition is set immediately after the injection end timing T14 of the sub-injector 12, and the spark plug 10 ignites the air-fuel mixture in the combustion chamber 5 immediately after the injection of the second fuel ends.

[0086] Next, control relating to reforming of the main fuel will be described. Fig. 10 is a flowchart showing the contents of control relating to reforming of the main fuel carried out by the PCM 80. Steps S21 to S40 shown in Fig. 10 are repeatedly carried out at predetermined intervals while the engine body 1 is running.

[0087] First, the PCM 80 reads various information detected by the sensors SN1 to SN7, etc. (step S21). In step S21, the PCM 80 reads at least the engine speed, the first tank internal pressure, the second tank internal pressure, the intake air amount, the intake temperature, and the accelerator opening.

[0088] Next, the PCM 80 determines whether or not the reforming permission condition is satisfied (step S22). The reforming permission condition is satisfied when fuel cut is not being performed and EGR is being performed, which recirculates EGR gas to the intake passage 20. The PCM 80 separately determines whether or not to perform EGR based on the engine speed, engine load, etc., and determines whether or not EGR is being performed based on this determination, and also determines whether or not fuel cut is being performed based on the engine speed, accelerator opening, etc. read in step S1.

[0089] If the determination in step S22 is NO and the reforming permission condition is not satisfied, the PCM 80 proceeds to step S40. In step S40, the PCM 80 stops the first reforming injector 53 and the second reforming injector 54 and prohibits injection of main fuel from these injectors. The PCM 80 also closes the first EGR valve 42B and the second EGR valve 42C. In the first embodiment, if the determination in step S22 is NO and a fuel cut is being performed or EGR is not being implemented, the main EGR valve 42A is also closed. After step S40, the PCM 80 ends the processing (returns to step S1). Here, in the processing of opening (or closing) the valves in step S40 and steps S24, S27, S30, and S33 (described later), if the valves are already open (or closed), they are maintained open (or closed). Furthermore, in the process of driving (or stopping) the injectors in step S40 and steps S26, S28, S32, and S34 described below, if the injectors are already driven (or stopped), they are maintained in that state.

[0090] If the determination in step S22 is YES and the reforming permission condition is met, the PCM 80 determines whether the first tank storage amount, which is the weight of the first fuel stored in the first tank 61, is less than a first determination amount (step S23). The PCM 80 estimates the first tank storage amount based on the intake air temperature, the first tank internal pressure, etc. read in step S1, and compares this estimated value with the first determination amount. The first determination amount is set in advance and stored in the PCM 80.

[0091] If the determination in step S23 is NO and the first tank storage amount is equal to or greater than the first determination amount, the PCM 80 closes the first EGR valve 42B (step S27). In addition, the PCM 80 stops driving the first reforming injector 53 (step S28). After step S28, the PCM 80 proceeds to step S29.

[0092] On the other hand, if the determination in step S23 is YES, that is, the amount of gas stored in the first tank is less than the first determination amount, the PCM 80 opens the first EGR valve 42B (step S24). When the first EGR valve 42B opens, the EGR gas is introduced into the first EGR passage 41B and passes through the first reforming catalyst device 51.

[0093] Next, the PCM 80 determines whether the first reforming catalyst device 51 is activated (step S25). The PCM 80 estimates the temperature of the first reforming catalyst device 51 based on the engine speed, intake air volume, intake air temperature, etc., and makes this determination based on the estimated temperature. If the determination in step S25 is NO, meaning the first reforming catalyst device 51 is not activated, the PCM 80 proceeds to step S28 and stops the first reforming injector 53. After step S28, the PCM 80 proceeds to step S29.

[0094] On the other hand, if the determination in step S25 is YES and the first reforming catalyst device 51 is activated, the PCM 80 drives the first reforming injector 53 (step S26). At this time, the PCM 80 estimates the flow rate of EGR gas flowing through the first EGR passage 41B based on the engine speed, the intake air amount, the opening degrees of the EGR valves 42A, 42B, 42C, etc., and adjusts the injection amount of the first reforming injector 53 based on this estimated amount. In the first embodiment, the PCM 80 increases the injection amount of the first reforming injector 53 as the estimated flow rate of EGR gas increases and the first reforming catalyst device 51 is therefore more likely to reach a high temperature. After step S26, the PCM 80 proceeds to step S29.

[0095] In step S29, the PCM 80 determines whether the second tank storage amount, which is the weight of the second fuel stored in the second tank 62, is less than a second determination amount. The PCM 80 estimates the second tank storage amount based on the intake air temperature, the second tank internal pressure, etc. read in step S1, and compares this estimated value with the second determination amount. The second determination amount is set in advance and stored in the PCM 80.

[0096] If the determination in step S29 is NO and the second tank storage amount is equal to or greater than the second determination amount, the PCM 80 closes the second EGR valve 42C (step S33). In addition, the PCM 80 stops driving the second reforming injector 54 (step S34). After step S34, the PCM 80 ends the processing (returns to step S1).

[0097] On the other hand, if the determination in step S29 is YES, that is, the second tank storage amount is less than the second determination amount, the PCM 80 opens the second EGR valve 42C (step S30). When the second EGR valve 42C opens, the EGR gas is introduced into the second EGR passage 41C and passes through the second reforming catalyst device 52.

[0098] Next, the PCM 80 determines whether the second reforming catalyst device 52 is activated (step S31). As in step S25, the PCM 80 estimates the temperature of the second reforming catalyst device 52 based on the engine speed, intake air volume, intake air temperature, etc., and makes this determination based on the estimated temperature. If the determination in step S31 is NO, meaning the second reforming catalyst device 52 is not activated, the PCM 80 proceeds to step S34 and stops the second reforming injector 54. Thereafter, the PCM 80 ends the processing (returns to step S1).

[0099] On the other hand, if the determination in step S31 is YES and the second reforming catalyst device 52 is active, the PCM 80 drives the second reforming injector 54 (step S32). At this time, the PCM 80 estimates the flow rate of EGR gas flowing through the second EGR passage 41C based on the engine speed, the intake air amount, the opening degrees of the EGR valves 42A, 42B, 42C, etc., and adjusts the injection amount of the second reforming injector 54 based on this estimated amount. In the first embodiment, the PCM 80 increases the injection amount of the second reforming injector 54 as the flow rate of EGR gas flowing through the second EGR passage 41C increases.

[0100] Although not shown in the figures, in the first embodiment, if the determination in step S22 is YES, when at least one of the first EGR valve 42B and the second EGR valve 42C is open, the main EGR valve 42A is closed, and the main EGR valve 42A is opened only when both the first EGR valve 42B and the second EGR valve 42C are closed.

[0101] As described above, in the first embodiment, basically, when the first tank storage amount falls below the first determination amount while the first reforming catalyst device 51 is active, the main fuel is injected from the first reforming injector 53, thereby producing the first fuel. Also, when the second tank storage amount falls below the second determination amount while the second reforming catalyst device 52 is active, the main fuel is injected from the second reforming injector 54, thereby producing the second fuel.

[0102] (effect, etc.) FIG. 11 is a schematic diagram showing the state inside the combustion chamber 5 near the top dead center of the compression stroke. In the above embodiment, the first fuel or the second fuel is injected after the main fuel is injected (F2). Therefore, as shown in FIG. 11, the state of the combustion chamber 5 at the ignition timing can be such that the mixture F11 of the main fuel and air is unevenly distributed on the outer periphery and the mixture F12 of the first fuel and air or the second fuel and air is unevenly distributed in the center of the combustion chamber 5. In particular, in the first embodiment, the main fuel is injected during the compression stroke, where the gas flow in the combustion chamber 5 is relatively weak, rather than during the intake stroke, where the gas flow is strong. This prevents the main fuel from diffusing throughout the combustion chamber 5, and ensures that the mixture F11 with a high concentration of the main fuel is formed on the outer periphery of the combustion chamber 5. Furthermore, in the first embodiment, the first fuel or the second fuel is injected near the top dead center of the compression stroke, and ignition is performed immediately thereafter. Therefore, the mixture F21 having a high concentration of the first fuel or the second fuel can be reliably formed in the center of the combustion chamber 5 in the region around the spark plug 10.

[0103] In the above embodiment, in the low load range A1, the first fuel, which has a faster combustion speed than the main fuel, is injected into the combustion chamber 5. Therefore, in the low load range A1, a flame kernel can be formed in the mixture region where the combustion speed is fast by ignition by the spark plug 10. As a result, according to the first embodiment, in the low load range A1, the flame kernel can be rapidly grown and the flame can be propagated early to the mixture of the main fuel and air present on the outer periphery of the combustion chamber 5. Therefore, even if the volume of the combustion chamber 5 increases as the piston 4 descends and the temperature inside the combustion chamber 5 decreases as the volume increases, it is possible to avoid stagnation of flame propagation and ensure combustion stability.

[0104] Furthermore, in the first embodiment, in the high load range A2, the second fuel, which has a higher octane rating than the main fuel, is injected after the injection of the main fuel. This makes it possible to suppress knocking in the high load range A2. Specifically, the vicinity of the spark plug of the ignition plug 10 is prone to high temperatures, making the air-fuel mixture prone to self-ignition around the spark plug. In contrast, in the above embodiment, an air-fuel mixture with a high octane rating that is difficult to self-ignite is formed around the spark plug 10, making it possible to suppress self-ignition of the air-fuel mixture around the spark plug 10. In other words, it is possible to suppress pre-ignition of the air-fuel mixture and abnormal combustion resulting from pre-ignition. Furthermore, by using the second fuel as part of the fuel supplied to the combustion chamber 5, it is possible to reduce the amount of main fuel with a low octane rating. This makes it possible to suppress knocking caused by self-ignition of the air-fuel mixture.

[0105] As described above, knocking can be suppressed by using a fuel with a high octane rating as the second fuel. However, if a fuel with a high octane rating but a fast combustion speed is used as the second fuel, the combustion of the mixture of the second fuel and air may proceed excessively quickly, which may reduce the effect of suppressing knocking. In contrast, in the first embodiment, a fuel with a higher octane rating than the main fuel and a combustion speed similar to that of the main fuel is used as the second fuel. This ensures that knocking can be suppressed.

[0106] Furthermore, in the first embodiment, the switching load Tx is set to a larger value when the engine water temperature is low than when it is high, thereby more reliably improving combustion stability. Specifically, combustion stability is more likely to decrease when the engine water temperature is low than when it is high, and when the engine water temperature is low, it is difficult to ensure combustion stability even in a relatively high engine load range. In contrast, in the first embodiment, when the engine water temperature is low, the switching load Tx is set to a larger value, and the first fuel, which has a higher combustion speed, is injected instead of the second fuel up to a higher load range. Therefore, combustion stability can be ensured when the engine water temperature is low.

[0107] Furthermore, when the engine water temperature is high, abnormal combustion is likely to occur even in a region where the engine load is relatively low. In contrast, in the first embodiment, when the engine water temperature is high, the switching load Tx is set to a relatively small value, and control is performed to suppress abnormal combustion by injecting the main fuel and the second fuel even in a region where the engine load is relatively low. This makes it possible to more reliably prevent abnormal combustion from occurring.

[0108] Similarly, combustion stability is more likely to decrease and abnormal combustion to occur when the intake temperature is low than when it is high. In contrast, in the first embodiment, the switch load Tx is set to a larger value when the intake temperature is low than when it is high, and the first fuel, not the second fuel, is injected up to the higher load range. Therefore, combustion stability can be ensured when the intake temperature is low. Furthermore, when the intake temperature is high, abnormal combustion is more likely to occur even in a range where the engine load is relatively low. In contrast, in the above embodiment, when the intake temperature is high, the switch load Tx is set to a relatively small value, and the second fuel, not the first fuel, is injected even in a range where the engine load is relatively low. Therefore, abnormal combustion can be more reliably prevented.

[0109] Furthermore, in the above embodiment, a first reforming catalyst device 51 that reforms the main fuel to produce a first fuel, and a second reforming catalyst device 52 that reforms the main fuel to produce a second fuel are provided in the EGR passage 41. Also provided are a first reforming injector 53 that supplies the main fuel to the first reforming catalyst device 51, and a second reforming injector 54 that supplies the main fuel to the second reforming catalyst device 52. The first fuel produced by the first reforming catalyst device 51 is injected into the combustion chamber 5, and the second fuel produced by the second reforming catalyst device 52 is injected into the combustion chamber. Therefore, the high-temperature EGR gas flowing through the EGR passage 41 can be used to activate the reforming catalyst devices 51, 52.

[0110] If the first reforming catalyst device 51 and the second reforming catalyst device 52 were arranged side by side in the EGR gas flow direction in a common passage, the downstream reforming catalyst device in the EGR gas flow direction would be introduced with EGR gas that has been cooled after warming the upstream reforming catalyst device. This could reduce the activation promotion effect of the downstream reforming catalyst device by the EGR gas. In contrast, in the first embodiment, the EGR passage 41 is provided with a first EGR passage 41B and a second EGR passage 41C through which EGR gas flows independently. The first reforming catalyst device 51 is disposed in the first EGR passage 41B, and the second reforming catalyst device 52 is disposed in the second EGR passage 41C. This allows EGR gas to be introduced into each reforming catalyst device 51, 52 at a high temperature, thereby reliably promoting the activation of both reforming catalyst devices 51, 52.

[0111] Furthermore, in the first embodiment described above, when the first tank storage amount, which is the weight of the first fuel stored in the first tank 61, falls below a first determination amount, the first reforming injector 53 is driven to produce the first fuel, and when the second tank storage amount, which is the weight of the second fuel stored in the second tank 62, falls below a second determination amount, the second reforming injector 54 is driven to produce the second fuel. Therefore, the storage amounts of the first fuel and the second fuel in each tank 61, 62 can be ensured, and these fuels can be appropriately injected into the combustion chamber 5.

[0112] (Second embodiment) Next, an engine system according to a second embodiment will be described. In the first embodiment described above, the pattern of injecting the first fuel into the combustion chamber 5 and the pattern of injecting the second fuel into the combustion chamber 5 were switched depending on the engine load. In contrast, in the engine system according to the second embodiment, the above two patterns are switched depending on the engine water temperature. The configuration other than the control related to this switching is the same as in the first embodiment, and the control related to this switching will be described below.

[0113] Fig. 12 is a flowchart corresponding to Fig. 5, showing the control content related to fuel injection according to the second embodiment. In Fig. 12, the same steps as in Fig. 5 are given the same reference numerals. Also, detailed explanations of the same steps as in Fig. 5 will be omitted.

[0114] In the second embodiment as well, first, the PCM 80 reads various information detected by the sensors SN1 to SN7, etc. (step S1). Next, in the second embodiment as well, the PCM 80 determines whether or not a fuel cut is in progress, which stops the supply of fuel to the combustion chamber 5 (step S2). If the determination in step S2 is YES, meaning that a fuel cut is in progress, the PCM 80 ends the process without performing the processes in and after step S3 (return to step S1).

[0115] On the other hand, in the second embodiment, unlike the first embodiment, if the determination in step S2 is NO and fuel cut is not in progress, the PCM 80 does not perform step S3 described above, and performs step S104 instead of step S4. In step S104, the PCM 80 determines whether the current engine water temperature read in step S1 is lower than a predetermined determination water temperature. The determination water temperature is preset and stored in the PCM 80.

[0116] In the second embodiment, the PCM 80 proceeds to step S5 when the determination in step S104 is YES and the engine water temperature is lower than the determination water temperature. The processing in step S5 and the processing after step S5 are the same as those in the first embodiment, and in the second embodiment, when the engine water temperature is lower than the determination water temperature, the main fuel is injected from the main injector 11 and the first fuel is injected from the sub-injector 12. In the second embodiment, the PCM 80 proceeds to step S9 when the determination in step S104 is NO and the engine water temperature is equal to or higher than the determination water temperature. The processing in step S9 and the processing after step S9 are the same as those in the first embodiment, and in the second embodiment, when the engine water temperature is equal to or higher than the determination water temperature, the main fuel is injected from the main injector 11 and the second fuel is injected from the sub-injector 12.

[0117] As described above, in the second embodiment, when the engine water temperature is below the threshold water temperature, the first fuel, which has a faster combustion speed than the main fuel, is injected after the main fuel. Therefore, when the engine water temperature is below the threshold water temperature and the engine body 1 has not been sufficiently warmed up, making it easy for combustion stability to decrease, it is possible to suppress a decrease in combustion stability. Furthermore, when the engine water temperature is equal to or higher than the threshold water temperature, the second fuel, which has a higher octane number than the main fuel, is injected after the main fuel. Therefore, when the engine water temperature is equal to or higher than the threshold water temperature and the temperature of the wall surface of the combustion chamber 5 is high, making it easy for abnormal combustion to occur, it is possible to suppress the occurrence of abnormal combustion. Note that, among the effects and advantages described for the first embodiment, the effects and advantages realized by the components provided in both the first and second embodiments can also be obtained in the second embodiment.

[0118] (Third embodiment) Next, an engine system according to a third embodiment will be described. In the first embodiment, the pattern of injecting the first fuel into the combustion chamber 5 and the pattern of injecting the second fuel into the combustion chamber 5 were switched depending on the engine load. In contrast, in the engine system according to the third embodiment, the above two patterns are switched depending on the intake air temperature. The configuration other than the control related to this switching is the same as in the first embodiment, and the control related to this switching will be described below.

[0119] Fig. 13 is a flowchart corresponding to Fig. 5, showing the control content related to fuel injection according to the third embodiment. In Fig. 13, the same steps as in Fig. 5 are given the same reference numerals. Also, detailed description of the same steps as in Fig. 5 will be omitted.

[0120] In the third embodiment as well, first, the PCM 80 reads various information detected by the sensors SN1 to SN7, etc. (step S1). Next, in the third embodiment as well, the PCM 80 determines whether or not a fuel cut is being performed, which stops the supply of fuel to the combustion chamber 5 (step S2). If the determination in step S2 is YES, meaning that a fuel cut is being performed, the PCM 80 ends the process without performing the processes in and after step S3 (returning to step S1).

[0121] On the other hand, in the third embodiment, unlike the first embodiment, when the determination in step S2 is NO and fuel cut is not in progress, the PCM 80 does not perform the above-mentioned step S3, and performs step S204 instead of step S4. In step S204, the PCM 80 determines whether the current intake air temperature read in step S1 is less than a predetermined first intake air temperature. The determined intake air temperature is set in advance and stored in the PCM 80.

[0122] In the third embodiment, the PCM 80 proceeds to step S5 when the determination in step S204 is YES and the intake air temperature is less than the determination intake air temperature. The processing in step S5 and the processing after step S5 are the same as those in the first embodiment, and in the third embodiment, when the intake air temperature is less than the determination intake air temperature, the main fuel is injected from the main injector 11 and the first fuel is injected from the sub-injector 12. In the third embodiment, the PCM 80 proceeds to step S9 when the determination in step S204 is NO and the intake air temperature is equal to or greater than the determination intake air temperature. The processing in step S9 and the processing after step S9 are the same as those in the first embodiment, and in the third embodiment, when the intake air temperature is equal to or greater than the determination intake air temperature, the main fuel is injected from the main injector 11 and the second fuel is injected from the sub-injector 12.

[0123] As described above, in the third embodiment, when the intake air temperature is lower than the threshold intake air temperature, the first fuel, which has a faster combustion speed than the main fuel, is injected after the main fuel. Therefore, when the intake air temperature is lower than the threshold intake air temperature and the temperature of the intake air introduced into the combustion chamber 5, and therefore the temperature of the air-fuel mixture in the combustion chamber 5, is low, which tends to reduce combustion stability, it is possible to suppress a decrease in combustion stability. Furthermore, when the intake air temperature is equal to or higher than the threshold intake air temperature, the second fuel, which has a higher octane number than the main fuel, is injected after the main fuel. Therefore, when the intake air temperature is equal to or higher than the threshold intake air temperature and the temperature of the intake air introduced into the combustion chamber 5, and therefore the temperature of the air-fuel mixture in the combustion chamber 5, is high, which tends to reduce abnormal combustion, it is possible to suppress the occurrence of abnormal combustion. Note that, among the effects and advantages described for the first embodiment, the effects and advantages achieved by the components provided in both the first and third embodiments can also be obtained in the third embodiment.

[0124] (Variation) In the above embodiment, the main fuel is gasoline, but the main fuel is not limited to gasoline. Furthermore, the first fuel may be any fuel that has a faster combustion speed than the main fuel, and the first fuel is not limited to hydrogen. For example, the first fuel may be ethane (C2H6). Furthermore, the second fuel may be any fuel that has a higher octane rating than the main fuel, and the second fuel is not limited to methane.

[0125] In the above embodiment, the catalyst provided in the first reforming catalytic device 51 is described as being made of silica and nickel, but the catalyst provided in the first reforming catalytic device 51 is not limited to this. For example, instead of the above, a catalyst made of alumina or a carbon material and nickel may be built into the first reforming catalytic device 51. Also, a catalyst made of silica, alumina or a carbon material and iron (Fe) may be built into the first reforming catalytic device 51. Also, a catalyst made of titania (TiO2) and a ruthenium-nickel alloy (RuNi alloy), a catalyst made of a metal oxide or a carbon material and platinum (Pt), a catalyst made of a metal oxide or a carbon material and ruthenium (Ru), or a catalyst made of a metal oxide or a carbon material and rhodium (Rh) may be built into the first reforming catalytic device 51.

[0126] In the above embodiment, the case where the catalyst provided in the second reforming catalytic device 52 is made of alumina and iron has been described, but the catalyst provided in the second reforming catalytic device 52 is not limited to this. For example, instead of the above, the second reforming catalytic device 52 may incorporate a catalyst made of manganese oxide (MnO2) and iron, a catalyst made of alumina and nickel, a catalyst made of zeolite and nickel, a catalyst made of zeolite and cobalt (Co), or a catalyst made of activated carbon and cobalt (Co).

[0127] In the first embodiment, the switching load Tx is changed according to the engine water temperature, and in the second embodiment, the switching load Tx is changed according to the intake air temperature. However, the switching load Tx may be changed according to both the engine water temperature and the intake air temperature. Furthermore, the switching load Tx may be set to a constant value regardless of the engine water temperature and the intake air temperature.

[0128] In the above embodiment, the first fuel and the second fuel are generated by reforming the main fuel, but the first fuel and the second fuel may be generated by a method other than reforming the main fuel. Also, the first fuel and the second fuel may be supplied from outside the engine system E.

[0129] In the above embodiment, the fuel supplied to the sub-injector 12, and therefore the fuel injected into the combustion chamber 5, is switched between the first fuel and the second fuel by the three-way valve 79. However, the specific configuration for performing this switching is not limited to this. For example, a device capable of individually injecting two fluids may be used as the sub-injector 12, and the fuel to be injected into the combustion chamber 5 may be switched by the sub-injector 12 itself. Alternatively, an injector that injects the first fuel and an injector that injects the second fuel may be separately attached to the engine body 1, and the fuel switching may be performed by switching which of these two injectors is driven. Furthermore, with regard to the configuration for injecting the main fuel and the other fuel, a device capable of individually injecting a plurality of fluids may be used, and the main fuel and the other fuel may be injected from this device, respectively.

[0130] In the above embodiment, the main fuel is injected from the early to middle stages of the compression stroke, and the first fuel and the second fuel are injected near the compression top dead center (TDC). However, the injection timing of each fuel is not limited to this.

[0131] In the above embodiment, the engine system E is described as being mounted on a vehicle, but the engine system E is not limited to being mounted on a vehicle and may be stationary for purposes such as power generation.

[0132] Furthermore, the specific structure of the engine body 1, such as the number of cylinders, is not limited to that described above. [Explanation of symbols]

[0133] 1 Engine body 5 Combustion chamber 10 Spark plugs 11 Main injector (fuel injection device) 12 Sub-injector (fuel injection device) 20 Intake passage 30 Exhaust passage 41 EGR passage 41A First EGR passage 41B 2nd EGR passage 51 First reforming catalyst device (first reforming catalyst) 52 Second reforming catalyst device (second reforming catalyst) 53 First reforming injector (first reforming fuel supply device) 54 Second reforming injector (second reforming fuel supply device) 61 First Tank 62 Second Tank 80 PCM (controller)

Claims

1. An engine system including an engine body having a combustion chamber formed therein, and an intake passage and an exhaust passage connected to the engine body, a fuel injection device that injects, into the combustion chamber, a main fuel, a first fuel having a faster combustion speed than the main fuel, and a second fuel having a higher octane number than the main fuel; a spark plug that ignites a mixture of fuel and air in the combustion chamber; a control device for controlling the fuel injection device, The control device controlling the fuel injection device so that, when an engine load is less than a predetermined switching load, the main fuel and the first fuel are injected into the combustion chamber, and the first fuel is injected after the main fuel is injected; and controlling the fuel injection device so that, when an engine load is equal to or greater than the switching load, the main fuel and the second fuel are injected into the combustion chamber, and the second fuel is injected after the main fuel is injected.

2. 2. The engine system according to claim 1, An engine system characterized in that the switching load is set to a larger value when the engine water temperature, which is the temperature of the cooling water that cools the engine body, is low than when it is high.

3. 2. The engine system according to claim 1, An engine system characterized in that the switching load is set to a larger value when the intake air temperature, which is the temperature of the air flowing through the intake passage, is low than when it is high.

4. 2. The engine system according to claim 1, an EGR passage that connects the exhaust passage and the intake passage and recirculates EGR gas, which is a part of the exhaust gas discharged from the engine body, to the intake passage; a first reforming catalyst provided in the EGR passage and configured to reform the main fuel to produce the first fuel; a first reforming fuel supply device that supplies the main fuel to the first reforming catalyst; a second reforming catalyst provided in the EGR passage and configured to reform the main fuel to produce the second fuel; a second reforming fuel supply device that supplies the main fuel to the second reforming catalyst, The engine system is characterized in that the fuel injection device injects the first fuel produced by the first reforming catalyst into the combustion chamber, and injects the second fuel produced by the second reforming catalyst into the combustion chamber.

5. 5. The engine system according to claim 4, the EGR passage includes a first EGR passage and a second EGR passage through which the EGR gas flows independently of each other, the first reforming catalyst is disposed in the first EGR passage; The engine system is characterized in that the second reforming catalyst is disposed in the second EGR passage.

6. 5. The engine system according to claim 4, a first tank for storing the first fuel; a second tank for storing the second fuel; The control device drives the first reforming fuel supply device when the amount of the first fuel stored in the first tank becomes equal to or less than a predetermined first judgment amount, and drives the second reforming fuel supply device when the amount of the second fuel stored in the second tank becomes equal to or less than a predetermined second judgment amount.

7. The engine system according to any one of claims 1 to 6, the first fuel is hydrogen or ethane; 10. An engine system, wherein the second fuel is methane.

8. An engine system including an engine body having a combustion chamber formed therein, and an intake passage and an exhaust passage connected to the engine body, a fuel injection device that injects, into the combustion chamber, a main fuel, a first fuel having a faster combustion speed than the main fuel, and a second fuel having a higher octane number than the main fuel; a spark plug that ignites a mixture of fuel and air in the combustion chamber; a control device for controlling the fuel injection device, The control device when an engine water temperature, which is a temperature of cooling water that cools the engine body, is lower than a predetermined judgment water temperature, the fuel injection device is controlled so that the main fuel and the first fuel are injected into the combustion chamber, and the first fuel is injected after the main fuel is injected; and controlling the fuel injection device so that, when the engine water temperature is equal to or higher than the determination water temperature, the main fuel and the second fuel are injected into the combustion chamber, and the second fuel is injected after the main fuel is injected.

9. An engine system including an engine body having a combustion chamber formed therein, and an intake passage and an exhaust passage connected to the engine body, a fuel injection device that injects, into the combustion chamber, a main fuel, a first fuel having a faster combustion speed than the main fuel, and a second fuel having a higher octane number than the main fuel; a spark plug that ignites a mixture of fuel and air in the combustion chamber; a control device for controlling the fuel injection device, The control device when an intake air temperature, which is a temperature of air flowing through the intake passage, is lower than a predetermined determined intake air temperature, the fuel injection device is controlled so that the main fuel and the first fuel are injected into the combustion chamber, and the first fuel is injected after the main fuel is injected; and controlling the fuel injection device so that, when the intake air temperature is equal to or higher than the determined intake air temperature, the main fuel and the second fuel are injected into the combustion chamber, and the second fuel is injected after the main fuel is injected.

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