Fuel reforming system for vehicle

Abstract

To produce and supply a large amount of high-purity hydrogen gas as fuel.SOLUTION: A fuel reforming system 1 for a vehicle mounted with an engine 3 includes a decomposition device 6 that decomposes hydrocarbon fuel into carbon and hydrogen gas, a hydrogen gas supply section 5 and the like. The decomposition device 6 separates hydrogen gas by using a hydrogen permeation film 63. The hydrogen gas supply section 5 includes: a reforming tank 8 that enables any of first high-purity hydrogen gas and second low-purity hydrogen gas to be taken out by using hydrogen storage alloy MH; a first hydrogen gas supply line 51 for supplying the first hydrogen gas from the reforming tank 8 to a combustion chamber 3a; and a second hydrogen gas supply line 52 for supplying the second hydrogen gas from the reforming tank 8 to the combustion chamber 3a. The hydrogen gas with different purity can be supplied to the combustion chamber 3a in different routes.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The disclosed technology relates to a fuel reforming system for a vehicle equipped with a reciprocating engine. [Background technology]

[0002] Patent Document 1 describes an apparatus (cracker) that directly decomposes hydrocarbons into carbon and hydrogen. This decomposition apparatus includes a reactor that houses a catalyst. When a raw material gas containing hydrocarbons is supplied to the reactor, carbon produced by a catalytic reaction adheres to the catalyst. A reaction gas containing hydrogen passes through the reactor.

[0003] Patent Document 1 also describes the installation of a hydrogen purification device downstream of the reactor, if necessary. By installing a hydrogen purification device, the hydrogen in the reaction gas can be purified and the hydrogen concentration of the reaction gas can be increased. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-104521 Summary of the Invention [Problem to be solved by the invention]

[0005] Carbon neutral initiatives are being sought in the field of vehicle technology (for example, four-wheeled automobiles). To achieve carbon neutrality in vehicles equipped with engines that use hydrocarbon fuels (including gasoline and / or diesel), new technologies for recovering carbon (C) or carbon dioxide (CO2) from hydrocarbon fuels are required, in addition to improving the thermal efficiency of the engine and / or improving exhaust emission performance.

[0006] If you want to capture carbon or carbon dioxide in a vehicle equipped with an engine that uses hydrocarbon fuel, (1) capturing carbon dioxide after the combustion of hydrocarbon fuels; or (2) Decomposing the hydrocarbon fuel into carbon and hydrogen gas before combustion of the hydrocarbon fuel, and recovering the carbon; It is possible that...

[0007] Considering that the captured carbon dioxide or carbon will be stored in the vehicle, option (2) is more advantageous in terms of fuel efficiency because carbon dioxide is heavier than carbon. Also, option (2) allows hydrogen gas to be used as engine fuel. Combustion of hydrogen gas has the added advantage of not producing carbon oxides due to combustion.

[0008] Therefore, it is conceivable to mount the above-mentioned cracking device on a vehicle. The cracking device is equipped with a heating device for raising the temperature of the catalyst. Therefore, when the cracking device is mounted on a vehicle, it is possible to use the heat of the engine to raise the temperature of the catalyst.

[0009] However, when using hydrogen gas as engine fuel, high-concentration hydrogen gas is required. In contrast, the cracking device described above requires the installation of a hydrogen purification device using a method such as PSA (Pressure Swing Adsorption) to obtain high-concentration hydrogen gas. Installing such a hydrogen purification device on a vehicle increases the vehicle's weight. Therefore, conventional cracking devices are not suitable for installation on vehicles.

[0010] The technology disclosed herein provides a fuel reforming system suitable for installation in a vehicle. [Means for solving the problem]

[0011] The disclosed technology relates to a fuel reforming system for a vehicle equipped with a reciprocating engine in which a combustion chamber in which combustion takes place is defined inside a cylinder in which a piston reciprocates.

[0012] The fuel reforming system includes a cracker that decomposes hydrocarbon fuel into carbon and hydrogen gas and stores the carbon, a hydrocarbon fuel supply unit that supplies the hydrocarbon fuel to the cracker, and a hydrogen gas supply unit that supplies the hydrogen gas produced by the cracker as fuel to the combustion chamber.

[0013] The cracker is configured to use the heat and pressure of the combustion gas generated in the combustion chamber to decompose the hydrocarbon fuel into the carbon and the hydrogen gas, and to separate the hydrogen gas by allowing it to permeate a hydrogen-permeable membrane.

[0014] The hydrogen gas supply unit includes a reforming tank that stores the hydrogen gas separated in the decomposer and is capable of extracting either a relatively high-purity first hydrogen gas or a relatively low-purity second hydrogen gas using a built-in hydrogen storage alloy, a first hydrogen gas supply line that supplies the first hydrogen gas from the reforming tank to the combustion chamber, and a second hydrogen gas supply line that supplies the second hydrogen gas from the reforming tank to the combustion chamber, and is configured to be able to supply hydrogen gases of different purities to the combustion chamber via different routes.

[0015] That is, this fuel reforming system is equipped with a cracker that uses the heat and pressure of the combustion gas generated in the combustion chamber to decompose hydrocarbon fuel into carbon and hydrogen gas and store the carbon. Therefore, of the hydrocarbon fuel, the carbon is recovered in the cracker, and the hydrogen gas can be used as fuel. Moreover, the heat and pressure of the combustion gas generated in the combustion chamber are used for the decomposition and separation. Therefore, combustion energy can be effectively utilized and energy loss can be suppressed.

[0016] However, there is a limit to the purity of hydrogen gas that can be separated using a hydrogen-permeable membrane. It is difficult to separate hydrogen to a high degree of purity suitable for use as fuel. In response to this, this fuel reforming system uses a hydrogen storage alloy built into the reforming tank that stores the hydrogen gas.

[0017] The hydrogen storage alloy adsorbs hydrogen gas. By adjusting the pressure and temperature of the hydrogen storage alloy, the hydrogen gas can be absorbed or released. Furthermore, the pressure and temperature at which the hydrogen storage alloy efficiently absorbs hydrogen gas are within a range that can be controlled in a vehicle. Therefore, even a reforming tank mounted on a vehicle can effectively absorb or release a large amount of hydrogen gas. As a result, the reforming tank can extract either a relatively high-purity first hydrogen gas or a relatively low-purity second hydrogen gas.

[0018] The hydrogen gas supply unit is equipped with a first hydrogen gas supply line that supplies the first hydrogen gas to the combustion chamber and a second hydrogen gas supply line that supplies the second hydrogen gas to the combustion chamber, and is configured to be able to supply hydrogen gases of different purities to the combustion chamber via different routes.

[0019] For example, if a large amount of hydrogen gas is adsorbed into the hydrogen storage alloy in the reforming tank, impure gas will also accumulate in the reforming tank. Therefore, while most of the hydrogen gas is adsorbed into the hydrogen storage alloy, hydrogen gas containing a large amount of impure gas, i.e., low-purity second hydrogen gas, is released through the second hydrogen gas supply line. In this way, the high-purity first hydrogen gas adsorbed into the hydrogen storage alloy can be released from the reforming tank through the first hydrogen gas supply line.

[0020] The second hydrogen gas is also supplied to the combustion chamber. Therefore, the second hydrogen gas can also be used as fuel. This fuel reforming system has a relatively simple structure and can use high-purity hydrogen gas as fuel. Low-purity hydrogen gas can also be used as fuel. Since it is supplied through different routes, it can be used according to the purity of the hydrogen gas. A fuel reforming system that applies the disclosed technology is suitable as a fuel reforming system to be installed in a vehicle.

[0021] The combustion chamber may further include a hydrocarbon fuel supply line that supplies the hydrocarbon fuel as fuel from the hydrocarbon fuel supply unit to the combustion chamber, and may be configured to be able to supply the hydrocarbon fuel when the first hydrogen gas or the second hydrogen gas is supplied to the combustion chamber.

[0022] Combustion of hydrogen gas alone may not be able to achieve the required load for a reciprocating engine. However, with this configuration, the shortfall in combustion energy can be compensated for by hydrocarbon fuel. Therefore, even high required loads can be met, improving vehicle performance.

[0023] The hydrogen gas supply unit may be configured to include two reforming tanks consisting of a first reforming tank and a second reforming tank arranged in parallel, and to be able to store the hydrogen gas separated in the cracker by switching between the first reforming tank and the second reforming tank.

[0024] If there is only one reforming tank, when the storage amount of hydrogen gas becomes low, the hydrogen gas cannot be used as fuel unless the storage amount is increased. In contrast, with this configuration, when the storage amount of one reforming tank is low, hydrogen gas can be stored in that reforming tank while hydrogen gas is released from the other reforming tank, and the hydrogen gas can be used as fuel. This increases the opportunities for using hydrogen gas as fuel. Hydrogen gas can be generated and used as fuel more efficiently.

[0025] The reciprocating engine may be configured in a variety of ways to be used with the disclosed reforming system.

[0026] For example, the reciprocating engine may be configured to execute a six-stroke cycle consisting of an intake stroke in which at least intake air is introduced into the combustion chamber through an intake port as the piston descends, a compression stroke in which the mixture containing the hydrogen gas supplied to the combustion chamber is compressed as the piston rises, an expansion stroke in which the piston descends as the mixture is burned, a re-compression stroke in which the combustion gas is compressed as the piston rises, a re-expansion stroke in which the piston descends, and an exhaust stroke in which exhaust gas is discharged through an exhaust port as the piston rises.

[0027] The reciprocating engine may also be configured to execute an irregular four-stroke cycle consisting of a compression stroke in which the mixture containing the hydrogen gas supplied to the combustion chamber is compressed as the piston rises, an expansion stroke in which the piston descends as the mixture is burned, a recompression stroke in which the combustion gas is compressed as the piston rises, and a scavenging stroke in which exhaust gas from the combustion chamber is discharged through an exhaust port while at least intake air is introduced into the cylinder through an intake port as the piston descends. [Effects of the Invention]

[0028] The disclosed technology makes it possible to generate large amounts of high-purity hydrogen gas and supply it as fuel with a relatively simple configuration, thereby realizing a fuel reforming system suitable for installation in a vehicle. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic diagram of a fuel reforming system. [Figure 2] FIG. 1 is a schematic diagram of a decomposer. [Figure 3] FIG. 2 is a block diagram of a control system. [Figure 4] FIG. 2 is a diagram for explaining a special combustion cycle (six-stroke cycle). [Figure 5] FIG. 1 is a schematic diagram showing the structure of an MH tank. [Figure 6] 1 is an example of a PCT diagram of a hydrogen storage alloy. [Figure 7] 10 is a time chart relating to the occlusion and release operations of the MH tank. [Figure 8] This is an engine control map. [Figure 9] 3 is a flowchart that serves as a basis for control by the fuel reforming system. [Figure 10A] 3 is a flowchart showing key points of control by the fuel reforming system. [Figure 10B] 3 is a flowchart showing key points of control by the fuel reforming system. [Figure 11] FIG. 2 is a diagram showing main processing states corresponding to the control of the fuel reforming system. [Figure 12] FIG. 1 is a schematic diagram of a fuel reforming system (application system) of an application example. [Figure 13] FIG. 2 is a block diagram of a control system in an application system. [Figure 14A] 1 is a flowchart in an application system. [Figure 14B] 1 is a flowchart in an application system. [Figure 14C] 1 is a flowchart in an application system. [Figure 15A] FIG. 10 is a diagram showing the main processing states corresponding to the control of the application system. [Figure 15B] FIG. 10 is a diagram showing the main processing states corresponding to the control of the application system. [Figure 15C] FIG. 10 is a diagram showing the main processing states corresponding to the control of the application system. [Figure 16] FIG. 10 is a diagram for explaining a modified example of the special combustion cycle. DETAILED DESCRIPTION OF THE INVENTION

[0030] The disclosed technology will be described below, however, the following description is merely exemplary in nature.

[0031] (Configuration of fuel reforming system) FIG. 1 shows a fuel reforming system 1 mounted on a vehicle. A hydrocarbon fuel is stored in a fuel tank mounted on the vehicle. The hydrocarbon fuel is, for example, gasoline. The hydrocarbon fuel is not limited to gasoline. The fuel reforming system 1 decomposes the hydrocarbon fuel into carbon and hydrogen gas. The carbon is stored in a decomposer 6, which will be described later. The hydrogen gas is used as fuel for a reciprocating engine 3. The fuel reforming system 1 achieves carbon neutrality for vehicles that are equipped with hydrocarbon fuel.

[0032] The fuel reforming system 1 includes a reciprocating engine 3 (hereinafter simply referred to as the engine 3). The engine 3 includes a cylinder 31 and a piston 32 that reciprocates within the cylinder 31. A combustion chamber 3a is formed at the upper end of the cylinder 31, the lower surface of which is partitioned by the piston 32. The engine 3 includes a plurality of cylinders 31.

[0033] The multiple cylinders 31 are aligned, for example, in the direction in which the crankshaft of the engine 3 extends. The pistons 32 of each cylinder 31 are connected to the crankshaft via connecting rods. The connecting rods convert the reciprocating motion of the pistons 32 into rotation of the crankshaft. The crankshaft is connected to the drive wheels via a transmission. The engine 3 outputs driving force for running the vehicle.

[0034] The engine 3 has an intake port 33. The intake port 33 is connected to the upper part of the cylinder 31, i.e., to the combustion chamber 3a. Each cylinder 31 has one or more intake ports 33. Each cylinder 31 may have, for example, two intake ports 33. The intake port 33 is connected to an intake pipe. As will be described later, intake air is introduced into the combustion chamber 3a through the intake port 33. The intake air includes at least fresh air (outside air). The intake air may also include EGR (Exhaust Gas Recirculation) gas.

[0035] The engine 3 has an intake valve 34. The intake valve 34 is a poppet valve that opens and closes the intake port 33. When the intake valve 34 opens, intake air is introduced into the combustion chamber 3a. An intake valve train 41 shown in FIG. 3 opens and closes the intake valve 34. The intake valve train 41 has, for example, an intake camshaft mechanically connected to the intake valve 34.

[0036] The intake valve train 41 can continuously change the valve timing of the intake valve 34 (so-called S-VT (Sequential-Valve Timing)). The intake valve train 41 can also continuously change the valve lift of the intake valve 34 (so-called CVVL (Continuously Variable Valve Lift)). The intake valve train 41 can employ a known hydraulic or electric mechanism. The intake valve train 41 changes the valve timing and / or valve lift depending on the operating state of the engine 3.

[0037] The engine 3 has an exhaust port 35. The exhaust port 35 is connected to the combustion chamber 3a. Each cylinder 31 has one or more exhaust ports 35. Each cylinder 31 may have, for example, one exhaust port 35. The exhaust port 35 is connected to an exhaust pipe. As will be described later, exhaust gas is discharged from the combustion chamber 3a through the exhaust port 35.

[0038] The engine 3 has an exhaust valve 36. The exhaust valve 36 is a poppet valve that opens and closes the exhaust port 35. When the exhaust valve 36 opens, exhaust gas is discharged to the outside of the cylinder 31. An exhaust valve train 42 shown in FIG. 3 opens and closes the exhaust valve 36. The exhaust valve train 42 has, for example, an exhaust camshaft mechanically connected to the exhaust valve 36.

[0039] The exhaust valve train 42 can continuously change the valve timing of the exhaust valve 36 (so-called S-VT). The exhaust valve train 42 can also continuously change the valve lift of the exhaust valve 36 (so-called CVVL). A known hydraulic or electric mechanism can be used for the exhaust valve train 42. The exhaust valve train 42 changes the valve timing and / or valve lift according to the operating state of the engine 3.

[0040] The engine 3 has a third port 37. The third port 37 is connected to the combustion chamber 3a. Each cylinder 31 has at least one third port 37. Each cylinder 31 may have, for example, one third port 37.

[0041] A typical engine 3 has two intake ports and two exhaust ports per cylinder. One of the two exhaust ports may be converted into a third port 37. The engine 3 in FIG. 1 has two intake ports 33, one exhaust port 35, and one third port 37 per cylinder 31. For ease of understanding, the exhaust port 35 and the third port 37 are depicted in offset positions in FIG. 1.

[0042] One of the two intake ports 33 may be converted into the third port 37. However, two intake ports 33 have the advantage of being able to introduce a large amount of fresh air into the combustion chamber 3a. If an exhaust port or an intake port is converted into the third port 37, a general engine 3 can be used as the engine 3 of the fuel reforming system 1. The engine 3 may have two intake ports 33, two exhaust ports 35, and one third port 37 per cylinder 31.

[0043] The engine 3 has an on-off valve 38. The on-off valve 38 is a poppet valve that opens and closes a third port 37. A third valve train 43 shown in FIG. 3 opens and closes the on-off valve 38. The third valve train 43 has, for example, a third camshaft mechanically connected to the on-off valve 38. The third valve train 43 opens the on-off valve 38 twice during one cycle.

[0044] The third valve train 43 can also stop the opening and closing of the on-off valve 38. A known hydraulic or electric mechanism can be used as the valve stopping mechanism that stops the opening and closing of the on-off valve 38. The valve stopping mechanism may be incorporated, for example, into a rocker arm interposed between the third camshaft and the on-off valve 38. The valve stopping mechanism may also be incorporated into a lash adjuster that supports the rocker arm. The on-off valve 38 may be mechanically connected to the intake camshaft or the exhaust camshaft.

[0045] An intake port injector 44 is attached to the engine 3. An injection hole of the intake port injector 44 faces the inside of the intake port 33. The intake port injector 44 injects hydrocarbon fuel into the intake port 33. A hydrocarbon fuel supply unit 45 is connected to the intake port injector 44 via a hydrocarbon fuel supply line 45a. The hydrocarbon fuel supply unit 45 has a fuel tank that stores hydrocarbon fuel and a fuel pump that pressure-feeds the hydrocarbon fuel.

[0046] A third port injector 46 is attached to the engine 3. An injection hole of the third port injector 46 faces the inside of the third port 37. The third port injector 46 injects hydrocarbon fuel into the third port 37. The hydrocarbon fuel supply unit 45 is also connected to the third port injector 46 via a reformed fuel supply line 45b.

[0047] As a result, the hydrocarbon fuel supply unit 45 supplies hydrocarbon fuel to the intake port injector 44 and the third port injector 46 through the hydrocarbon fuel supply line 45a and the reformed fuel supply line 45b.

[0048] A hydrogen injector 47 is attached to the engine 3. An injection hole of the hydrogen injector 47 faces the combustion chamber 3a. The hydrogen injector 47 injects hydrogen gas (high-purity hydrogen gas: first hydrogen gas, which will be described later) into the combustion chamber 3a.

[0049] It is also possible to attach an injector that injects hydrocarbon fuel to the engine 3 so as to face the combustion chamber 3 a, and attach a hydrogen injector that injects hydrogen gas to the engine 3 so as to face the inside of the intake port 33 .

[0050] A hydrogen injector 48 is attached to the engine 3. The hydrogen injector 48 is a valve (anti-flash valve) that prevents flames from flowing backward even if they are generated by injection. The injection hole of the hydrogen injector 48 faces the inside of the third port 37. The hydrogen injector 48 injects hydrogen gas (low-purity hydrogen gas: second hydrogen gas, described later) into the third port 37.

[0051] (decomposer) The cracker 6 is connected to the third port 37. The cracker 6 cracks the hydrocarbon fuel into carbon and hydrogen gas. The cracker 6 is attached to each cylinder 31. The cracker 6 may be common to multiple cylinders 31.

[0052] Figure 2 shows the structure of the cracker 6. The cracker 6 uses a catalyst to decompose the hydrocarbon fuel into carbon and hydrogen gas, and separates the hydrogen gas by passing it through a hydrogen-permeable membrane 63. The cracker 6 is a so-called membrane reactor. The decomposition of a hydrocarbon fuel, for example, isooctane, is represented by the following chemical reaction formula:

[0053] iC8H18(g) = 8C(s) + 9H2

[0054] The recovery of solid carbon prevents the weight of the vehicle from increasing. The fuel reforming system 1 is suitable for use as an in-vehicle system.

[0055] The cracker 6 has a support 61. The support 61 is, for example, a cylindrical body. The support 61 is made of, for example, porous ceramic. The porous ceramic is, for example, zirconia. The support 61 has the function of accommodating a catalyst support 62, which will be described later, and the function of supporting a hydrogen-permeable membrane 63 and allowing the generated hydrogen gas to pass through. The support 61 can have various structures as long as it has the two functions described above.

[0056] The cracker 6 has a catalyst support 62. A catalyst that can be used to crack hydrocarbon fuel is, for example, a Ni-Al-Fe alloy. Various catalysts can be used as long as they can be used to crack hydrocarbon fuel.

[0057] The support 62 may be, for example, an aluminum oxide ball. The catalyst is applied to the surface of the ball. A large number of the support 62 are packed inside the support 61. The use of balls as the support 62 increases the surface area of ​​the catalyst and improves the cracking efficiency of the cracker 6. The shape of the support 62 is not limited to a specific shape.

[0058] Carbon produced by the decomposition of hydrocarbon fuel adheres to the surface of the support 62. The cracker 6 also stores carbon. The use of balls increases the amount of carbon stored in the cracker 6 and also maintains the cracking capacity of the cracker 6 even when the amount of carbon stored increases. The use of balls also facilitates the separation of hydrogen gas that is cracked from the hydrocarbon fuel. As will be described later, efficient separation of hydrogen gas also prevents a decrease in the cracking capacity of the cracker 6.

[0059] The decomposer 6 has a hydrogen-permeable membrane 63. The hydrogen-permeable membrane 63 is, for example, a Pd alloy membrane. The hydrogen-permeable membrane 63 is attached to the inner surface of the support 61. The hydrogen-permeable membrane 63 may also be attached to the outer surface of the support 61.

[0060] The hydrogen-permeable membrane 63 has molecular-sized pores and has the function of selectively allowing hydrogen gas to permeate. However, this selectivity is not perfect, and the hydrogen gas that permeates the hydrogen-permeable membrane 63 contains impurity gases such as nitrogen gas. The hydrogen gas permeability of the hydrogen-permeable membrane 63 is inversely related to the amount of hydrogen gas that permeates.

[0061] In other words, increasing the purity of the permeating hydrogen gas reduces the amount of hydrogen gas that permeates. Furthermore, when the purity exceeds 95%, the amount of hydrogen gas that permeates reaches a plateau. Therefore, considering the practically acceptable permeation amount, the purity of hydrogen gas that can be separated by hydrogen-permeable membrane 63 is generally about 80%. Hydrogen gas containing impurities (also called crude hydrogen gas) that permeates hydrogen-permeable membrane 63 passes through support 61 and reaches the outside of support 61 (see the white arrow in Figure 2).

[0062] The cracker 6 has a case 64. The support 61 is housed in the case 64. A space is formed between the outer peripheral surface of the support 61 and the inner peripheral surface of the case 64. The case 64 has the function of collecting the crude hydrogen gas and guiding it to the hydrogen gas receiving line 50 described below.

[0063] A third port 37 is connected to an end of the case 64. More specifically, the third port 37 is connected to the inside of the cylindrical support 61. The combustion gas and hydrocarbon fuel are introduced through the third port 37 into the inside of the support 61 and the hydrogen-permeable membrane 63. Inside the support 61 and the hydrogen-permeable membrane 63, the hydrocarbon fuel is decomposed into carbon and hydrogen gas.

[0064] A hydrogen gas receiving line 50 is connected to the side of the case 64. The hydrogen gas produced inside the support 61, together with a small amount of impure gas, passes through the hydrogen permeable membrane 63 and the support 61 to reach the outside of the support 61. The crude hydrogen gas passes through the hydrogen gas receiving line 50 and is sent to the hydrogen gas supply unit 5.

[0065] (Hydrogen gas supply unit) As shown in FIG. 1 , the hydrogen gas supply unit 5 is connected to a hydrogen injector 47 and a hydrogen injection valve 48. The hydrogen gas supply unit 5 supplies hydrogen gases of different purities (first hydrogen gas and second hydrogen gas) to the hydrogen injector 47 and the hydrogen injection valve 48. As described above, these hydrogen gases are obtained from hydrogen gas decomposed from a hydrocarbon fuel. The hydrogen gas supply unit 5 may be common to multiple cylinders 31. Alternatively, a hydrogen gas supply unit 5 may be provided for each cylinder 31.

[0066] The hydrogen gas supply unit 5 is composed of a hydrogen gas receiving line 50, a first hydrogen gas supply line 51, a second hydrogen gas supply line 52, an MH tank 8 (an example of a reforming tank), a switching valve 57, a storage valve 58, a gas pump 59, and the like.

[0067] The upstream end of the hydrogen gas receiving line 50 is connected to the decomposer 6 as described above. The downstream end of the hydrogen gas receiving line 50 is connected to the MH tank 8. A check valve 55 is installed on the upstream side of the hydrogen gas receiving line 50. The check valve 55 prevents hydrogen gas from flowing from the downstream side to the upstream side of the hydrogen gas receiving line 50.

[0068] A storage valve 58 is installed downstream of the hydrogen gas receiving line 50. The storage valve 58 opens and closes the passage of the hydrogen gas receiving line 50 in response to a control signal from a controller 21, which will be described later. The hydrogen gas receiving line 50 has a bypass passage 54 that bypasses the check valve 55. A gas pump 59 is installed in the bypass passage 54.

[0069] When the gas pump 59 is activated, the pressure downstream of the hydrogen gas receiving line 50 increases. However, as will be described later, the pressurization performance of the gas pump 59 does not need to be high. Even when the gas pump 59 is activated, the pressure downstream of the hydrogen gas receiving line 50 is less than 1 MPa. This does not involve handling high-pressure gas, and is easy to handle.

[0070] When gas pump 59 is activated, the pressure on the upstream side decreases. As a result, the pressure difference (the pressure difference between the primary side and the secondary side) across hydrogen-permeable membrane 63 increases. As a result, the amount of hydrogen gas permeating increases. Because the hydrogen gas generated inside support 61 permeates out of support 61 more quickly, the decomposition reaction of the hydrocarbon fuel inside support 61 is accelerated.

[0071] The MH tank 8 stores the crude hydrogen gas separated in the cracker 6. The MH tank 8 contains a hydrogen storage alloy (Metal Hydrid: MH). The MH tank 8 is configured to be able to extract either a relatively high-purity first hydrogen gas or a relatively low-purity second hydrogen gas by utilizing the hydrogen storage alloy.

[0072] The MH tank 8 is equipped with a temperature adjustment unit 71 and a heater 72. The temperature adjustment unit 71 adjusts the temperature of the MH tank 8 by circulating and supplying a liquid medium made of water or oil to the MH tank 8. The temperature adjustment unit 71 may utilize the cooling water of the engine 3 or the like. The heater 72 is preferably provided because it has excellent heating response, but is not essential. The MH tank 8 will be described in detail later.

[0073] One end of a hydrogen gas extraction line 53 is connected to the downstream side of the MH tank 8. A switching valve 57 is provided at the other end of the hydrogen gas extraction line 53. A first hydrogen gas supply line 51 and a second hydrogen gas supply line 52 are connected to the two downstream sides of the switching valve 57.

[0074] The switching valve 57 receives a control signal from the controller 21, which will be described later, and switches the hydrogen gas flow path between the first hydrogen gas supply line 51 side and the second hydrogen gas supply line 52 side. The switching valve 57 also receives a control signal from the controller 21, which will be described later, and closes the hydrogen gas passage.

[0075] A pressure regulating valve 51a is installed in the first hydrogen gas supply line 51. The pressure regulating valve 51a increases the pressure of the hydrogen gas flowing to the hydrogen injector 47. When the hydrogen injector 47 is opened, relatively high-pressure hydrogen gas is supplied directly to the combustion chamber 3a through the first hydrogen gas supply line 51.

[0076] On the other hand, the second hydrogen gas supply line 52 does not have a pressure adjustment valve 51a or the like. By switching the selector valve 57 to the second hydrogen gas supply line 52, the inside of the MH tank 8 is connected to the intake port 33 via the second hydrogen gas supply line 52. Therefore, hydrogen gas flows in the second hydrogen gas supply line 52 in accordance with the pressure difference between the MH tank 8 and the intake port 33. The second hydrogen gas supply line 52 indirectly supplies relatively low-pressure hydrogen gas to the combustion chamber 3a via the intake port 33.

[0077] (Controller) Figure 3 shows a block diagram of the control system 2 installed in the vehicle. The fuel reforming system 1 cooperates with this control system 2. The fuel reforming system 1 and the control system 2 share devices as necessary. The control system 2 has a controller 21. The controller 21 is composed of hardware such as a processor, memory, and interface, and software such as a database and control program.

[0078] The rotation speed sensor 22 is electrically connected to the controller 21. The rotation speed sensor 22 is attached to the engine 3. The rotation speed sensor 22 outputs a measurement signal corresponding to the rotation speed of the crankshaft to the controller 21. The controller 21 obtains the rotation speed of the engine 3 based on the measurement signal of the rotation speed sensor 22.

[0079] The accelerator sensor 23 is electrically connected to the controller 21. The accelerator sensor 23 is attached to an accelerator pedal. The accelerator sensor 23 outputs a signal corresponding to the depression amount of the accelerator pedal to the controller 21. The controller 21 obtains the required load of the engine 3 based on the measurement signal of the accelerator sensor 23.

[0080] The MH tank temperature sensor 24 is electrically connected to the controller 21. The MH tank temperature sensor 24 is attached to the MH tank 8. The MH tank temperature sensor 24 outputs a signal corresponding to the temperature of the MH tank 8 to the controller 21. The controller 21 obtains the required temperature of the MH tank 8 based on the signal from the MH tank temperature sensor 24 and controls the temperature adjustment unit 71 or the heater 72.

[0081] The MH tank pressure sensor 25 is electrically connected to the controller 21. The MH tank pressure sensor 25 is attached to the MH tank 8. The MH tank pressure sensor 25 outputs a signal corresponding to the internal pressure of the MH tank 8 to the controller 21. Based on the signal from the MH tank pressure sensor 25, the controller 21 determines whether the gas pump 59 needs to be operated, the amount of hydrogen gas stored in the MH tank 8, etc.

[0082] The hydrogen operation switch 26 is electrically connected to the controller 21. The hydrogen operation switch 26 is mounted near the driver's seat of the vehicle. The hydrogen operation switch 26 outputs a signal corresponding to the driver's on / off operation to the controller 21. Based on the signal from the hydrogen operation switch 26, the controller 21 determines the need for hydrogen gas mono-fuel operation (operation by burning only hydrogen gas).

[0083] The intake valve train 41, exhaust valve train 42, and third valve train 43 described above are each electrically connected to the controller 21. The controller 21 outputs a control signal to each of the intake valve train 41, exhaust valve train 42, and third valve train 43 depending on the operating state of the engine 3. The intake valve train 41 changes the valve timing and / or valve lift of the intake valve 34 based on the control signal from the controller 21. The exhaust valve train 42 changes the valve timing and / or valve lift of the exhaust valve 36 based on the control signal from the controller 21. The third valve train 43 switches the on-off valve 38 between open and closed states based on the control signal from the controller 21.

[0084] The intake port injector 44, the third port injector 46, and the hydrogen injector 47 are each electrically connected to the controller 21. The controller 21 outputs a control signal to each of the intake port injector 44, the third port injector 46, and the hydrogen injector 47. The intake port injector 44 injects a predetermined amount of hydrocarbon fuel into the intake port 33 at a predetermined timing based on the control signal from the controller 21. The third port injector 46 injects a predetermined amount of hydrocarbon fuel into the third port 37 at a predetermined timing based on the control signal from the controller 21. The hydrogen injector 47 injects a predetermined amount of hydrogen gas into the combustion chamber 3a at a predetermined timing based on the control signal from the controller 21.

[0085] The control system 2 has an ignition plug 27. The ignition plug 27 is attached to the engine 3 and faces the combustion chamber 3a. The ignition plug 27 is electrically connected to the controller 21. The controller 21 outputs a control signal to the ignition plug 27. The ignition plug 27 ignites the air-fuel mixture in the combustion chamber 3a at a predetermined timing based on the control signal from the controller 21.

[0086] The control system 2 has an inverter 28. The vehicle has a drive motor (assist motor) that outputs driving force for running the vehicle. The inverter 28 controls the drive motor. The inverter 28 is electrically connected to the controller 21. The controller 21 outputs a control signal to the inverter 28 when the output of the engine 3 is insufficient. This activates the drive motor to assist the operation of the engine 3.

[0087] The control system 2 has a temperature adjustment unit 71. The temperature adjustment unit 71 is electrically connected to the controller 21. The controller 21 outputs a control signal to the temperature adjustment unit 71. Based on the control signal from the controller 21, the temperature adjustment unit 71 circulates the liquid medium and adjusts the temperature of the circulating liquid medium.

[0088] The control system 2 includes a gas pump 59. The gas pump 59 is electrically connected to the controller 21. The controller 21 outputs a control signal to the gas pump 59, which causes the gas pump 59 to operate or stop.

[0089] The control system 2 has a heater 72. The heater 72 is electrically connected to the controller 21. The controller 21 outputs a control signal to the heater 72. This causes the heater 72 to generate heat.

[0090] The control system 2 has a storage valve 58 and a switching valve 57. The storage valve 58 and the switching valve 57 are electrically connected to the controller 21. The controller 21 outputs control signals to the storage valve 58 and the switching valve 57. The storage valve 58 opens and closes based on the control signal from the controller 21. The switching valve 57 switches the downstream flow path to the first hydrogen gas supply line 51 or the second hydrogen gas supply line 52, or closes these flow paths, based on the control signal from the controller 21.

[0091] (Reciprocating engine operation) The engine 3 of this embodiment operates in a six-stroke cycle (an example of a special combustion cycle) so that the cracker 6 can crack hydrocarbon fuel. Here, the combustion cycle for the aforementioned hydrogen gas-only combustion operation (operation using only hydrogen gas combustion) is illustrated as an example of the six-stroke cycle. Figure 4 shows each stroke of the cycle.

[0092] S1 is the intake stroke. During the intake stroke S1, the engine 3 introduces intake air into the combustion chamber 3a as the piston 32 descends. During the intake stroke S1, the intake valve 34 opens. The intake air is introduced into the combustion chamber 3a through the intake port 33. The intake air includes at least fresh air.

[0093] The intake air may contain EGR gas. This EGR gas is so-called external EGR gas that has been recirculated to the intake pipe through the EGR passage. During the intake stroke S1, the exhaust valve 36 may open. When the exhaust valve 36 opens, exhaust gas is introduced into the combustion chamber 3a through the exhaust port 35. The exhaust gas introduced into the combustion chamber 3a is so-called internal EGR gas. Note that the opening / closing valve 38 of the third port 37 is closed.

[0094] 4, the hydrogen injector 47 injects hydrogen gas into the combustion chamber 3a during the intake stroke S1. The hydrogen injector 47 may inject hydrogen gas during the compression stroke S2 ​​following the intake stroke S1. The hydrogen injector 47 may inject hydrogen gas during the period from the intake stroke S1 to the compression stroke S2.

[0095] If there is a shortage of hydrogen gas, the intake port injector 44 may inject hydrocarbon fuel into the intake port 33 during the intake stroke S1 to make up for the shortage. Also, if there is no hydrogen gas, the intake port injector 44 may inject hydrocarbon fuel into the intake port 33 during the intake stroke S1 instead of the hydrogen injector 47.

[0096] When there is a shortage of hydrogen gas supplied to the combustion chamber 3a, the intake port injector 44 injects hydrocarbon fuel to ensure the required amount of fuel for the engine 3. The engine 3 can be operated using hydrocarbon fuel or both hydrocarbon fuel and hydrogen gas.

[0097] S2 is the compression stroke. During the compression stroke S2, the engine 3 compresses the air-fuel mixture in the combustion chamber 3a by the upward movement of the piston 32. The intake valve 34, the exhaust valve 36, and the on-off valve 38 are all closed.

[0098] The spark plug 27 ignites the air-fuel mixture in the combustion chamber 3a near the top dead center of the compression stroke. The air-fuel mixture begins to burn. S3 is the expansion stroke. During the expansion stroke S3, the piston 32 descends due to the combustion of the air-fuel mixture. The intake valve 34, exhaust valve 36, and on-off valve 38 are all closed.

[0099] S4 is a recompression stroke. In the recompression stroke S4, the engine 3 compresses the combustion gas in the combustion chamber 3a by raising the piston 32. In the recompression stroke S4, the on-off valve 38 opens. The compressed combustion gas is introduced into the cracker 6 through the third port 37. In addition, in the recompression stroke S4, the third port injector 46 injects hydrocarbon fuel into the third port 37. The hydrocarbon fuel is introduced into the cracker 6 together with the combustion gas.

[0100] As described above, in the cracker 6, the hydrocarbon fuel is decomposed into carbon and hydrogen gas by the heat of the combustion gas and the catalyst. The carbon is stored in the cracker 6. The hydrogen gas (crude hydrogen gas) permeates the hydrogen permeable membrane 63 due to the pressure of the combustion gas and is sent to the hydrogen gas supply unit 5.

[0101] Because the high pressure of the combustion gas in the recompression stroke is applied to the inside of the cracker 6, the hydrogen gas generated inside the cracker 6 quickly permeates the hydrogen-permeable membrane 63. Because the amount of hydrogen gas inside the cracker 6 is reduced, the cracking reaction of the hydrocarbon fuel is promoted. The cracker 6, which utilizes the pressure of the recompression stroke S4 of the engine 3, can generate a relatively large amount of crude hydrogen gas even though it is small.

[0102] S5 is a re-expansion stroke. In the re-expansion stroke S5, the piston 32 descends. The on-off valve 38 may be opened in the re-expansion stroke S5. When the on-off valve 38 is opened, the combustion gas from which carbon and hydrogen gas have been removed is introduced from the cracker 6 into the combustion chamber 3a. Opening the on-off valve 38 in the re-expansion stroke S5 is advantageous in reducing pumping loss of the engine 3.

[0103] S6 is the exhaust stroke. During the exhaust stroke S6, the engine 3 discharges the combustion gas in the combustion chamber 3a through the exhaust port 35 as the piston 32 rises. During the exhaust stroke S6, the exhaust valve 36 opens. The combustion gas in the combustion chamber 3a is discharged to the exhaust port 35. During the exhaust stroke S6, the intake valve 34 and the on-off valve 38 are closed.

[0104] After the exhaust stroke S6, the engine 3 returns to the intake stroke S1.

[0105] Instead of or together with opening the on-off valve 38 in the re-expansion stroke S5, the on-off valve 38 may be opened in the intake stroke S1. If the on-off valve 38 is opened in the intake stroke S1, the combustion gas from which carbon and hydrogen gas have been removed is introduced from the cracker 6 into the cylinder 31. This combustion gas becomes EGR gas.

[0106] If the on-off valve 38 does not open in the re-expansion stroke S5, the hydrocarbon fuel introduced into the cracker 6 in the re-compression stroke S4 will remain in the cracker 6 for a long time, which has the advantage of promoting the cracking reaction of the hydrocarbon fuel.

[0107] The fuel reforming system 1 stores the carbon produced by the decomposition of hydrocarbon fuel in the cracker 6. The engine 3 then burns the hydrogen gas produced by the decomposition of hydrocarbon fuel, so no carbon oxides are produced by combustion. The fuel reforming system 1 can achieve carbon neutrality.

[0108] The fuel reforming system 1 also decomposes hydrocarbon fuel using the heat and pressure generated by the engine 3. Therefore, no separate dedicated device is required. The fuel reforming system 1 is useful as an in-vehicle system.

[0109] If the amount of carbon stored in the cracker 6 increases, the carbon is recovered from the cracker 6. For example, when a vehicle is brought in for maintenance, the support 62 with the carbon attached thereto is taken out from the cracker 6, and the carbon is removed from the support 62 using, for example, a mill. The recovered carbon can be used as industrial carbon. The support 62 from which the carbon has been removed can be re-coated with a catalyst as necessary and then re-filled into the cracker 6.

[0110] <High-purity hydrogen gas> The fuel reforming system 1 uses hydrogen gas as fuel. The purity of hydrogen gas is directly linked to combustion energy, so a high purity is preferable. However, as mentioned above, in reality, the purity of hydrogen gas obtained in the cracker 6 is about 80%.

[0111] Therefore, the present inventors have devised a device that uses a hydrogen storage alloy MH to enable the use of high purity hydrogen gas, for example 90% or more, as fuel with a relatively simple configuration.

[0112] (MH Tank) Figure 5 shows an example of the structure of the MH tank 8. In Figure 5, the left is the upstream side. The MH tank 8 is composed of multiple tank elements 80 connected in parallel. Each tank element 80 has a housing 81 that is a long, thin cylinder with both ends closed and sealed with lids. An inlet pipe 82 and an inlet gas pipe 83 are attached to the upstream lid, and an outlet pipe 84 and an outlet gas pipe 85 are attached to the downstream lid.

[0113] Two temperature control pipes 86 are housed inside the housing 81 and extend along the longitudinal direction. Ends of these temperature control pipes 86 are connected to an inlet pipe 82 and an outlet pipe 84. The inlet pipe 82 and the outlet pipe 84 of each tank element 80 are connected to a circulation path through which the liquid medium in the temperature adjustment unit 71 circulates.

[0114] The interior of the housing 81 is partitioned along the longitudinal direction into a plurality of (six in the illustrated example) charging chambers 81a. Each charging chamber 81a communicates with an inlet gas pipe 83. The inlet gas pipe 83 of each tank element 80 is connected to the hydrogen gas receiving line 50. Therefore, the crude hydrogen gas obtained in the cracker 6 flows into each charging chamber 81a.

[0115] Each filling chamber 81a is filled with particulate hydrogen storage alloy MH. Hydrogen storage alloy MH is well known. There are various types of hydrogen storage alloy MH. A hydrogen storage alloy MH suitable for the specifications can be selected from these and used.

[0116] Each filling chamber 81a also contains a tube filter 88. One end of each tube filter 88 is sealed, and the other end is connected to an outlet gas pipe 85. The tube filter 88 does not allow the hydrogen storage alloy MH to pass through, but only allows gases such as hydrogen gas to pass through. The outlet pipe 84 of each tank element 80 is connected to the hydrogen gas extraction line 53.

[0117] The hydrogen storage alloy MH adsorbs hydrogen gas. Therefore, of the crude hydrogen gas that flows into each filling chamber 81a, only the hydrogen gas is adsorbed by the hydrogen storage alloy MH. The MH tank 8 stores the hydrogen gas in a state in which it is adsorbed by the hydrogen storage alloy MH. Impure gases are stored in the gaps between the hydrogen storage alloys MH. Therefore, the impure gases are separated from the hydrogen gas and stored in the MH tank 8 in a concentrated state.

[0118] FIG. 6 shows an example of a PCT diagram (pressure composition isotherm diagram) for the hydrogen storage alloy MH. The PCT diagram shows the absorption and desorption behavior of the hydrogen storage alloy MH. C60 is the isothermal absorption curve at 60°C, and D60 is the isothermal desorption curve at 60°C. Similarly, C20 is the isothermal absorption curve at 20°C, and D20 is the isothermal desorption curve at 20°C. 20°C and 60°C are temperatures that can be controlled by a general temperature control device. These are also the main temperatures of the cooling water that regulates the temperature of the engine 3.

[0119] At all of these temperatures, there is a region (plateau region) in the pressure range of 0.1 MPa to 1 MPa where the storage capacity increases without increasing the pressure. This means that hydrogen gas can be effectively stored at pressures below 1 MPa. Compressed gases above 1 MPa are considered high-pressure gases and are subject to legal restrictions.

[0120] Even if the pressure of the MH tank 8 is set to less than 1 MPa, hydrogen gas can be effectively stored, so it can be excluded from the handling of high-pressure gas. Moreover, since a high-performance gas pump 59 is not required, the equipment can be simplified. Therefore, it is suitable for installation in a vehicle.

[0121] The hydrogen storage alloy MH adsorbs hydrogen gas when the pressure is increased and releases it when the pressure is reduced. The hydrogen storage alloy MH generates heat when adsorbing hydrogen gas. On the other hand, the hydrogen storage alloy MH absorbs heat when releasing hydrogen gas. Therefore, it is preferable to cool the MH tank 8 when storing hydrogen gas. Cooling promotes the adsorption of hydrogen gas into the hydrogen storage alloy MH. It is preferable to heat the MH tank 8 when releasing hydrogen gas. Heating promotes the separation of hydrogen gas from the hydrogen storage alloy MH.

[0122] By controlling the temperature and / or pressure of the MH tank 8, it is possible to adjust the adsorption and separation of hydrogen gas onto the hydrogen storage alloy MH. This makes it possible to increase the purity of the hydrogen gas extracted from the MH tank 8 compared to crude hydrogen gas. High-purity hydrogen gas is an excellent fuel for the engine 3. This can improve the performance of the vehicle.

[0123] (MH tank operation) Figure 7 shows an example of a time chart relating to the occlusion and release operations of the MH tank 8. The top row shows the change in gas mass inside the MH tank 8. The middle row shows the change in internal temperature of the MH tank 8. The bottom row shows the change in internal pressure of the MH tank 8.

[0124] When the storage valve 58 is opened, crude hydrogen gas flows into the MH tank 8, which is in an unused state here (time t0). As a result, the internal pressure rises suddenly. The hydrogen storage alloy MH begins to adsorb hydrogen gas, causing the internal temperature to rise. When the temperature adjustment unit 71 starts cooling (time t1), the internal temperature is maintained at an appropriate temperature. As a result, hydrogen gas is gradually adsorbed into the hydrogen storage alloy MH. As a result, the amount of stored impure gas also increases.

[0125] When the storage valve 58 is closed (at time t2), the inflow of crude hydrogen gas stops, and the adsorption of hydrogen gas by the hydrogen storage alloy MH also stops. After this, the switching valve 57 is switched to the second hydrogen gas supply line 52. As a result, the internal pressure drops to normal pressure in one go (at time t3).

[0126] Most of the hydrogen gas is adsorbed by the hydrogen storage alloy MH and therefore remains in the MH tank 8. On the other hand, the small amount of hydrogen gas that is not adsorbed by the hydrogen storage alloy MH and the impure gases that accumulate in the gaps between the hydrogen storage alloy MH are released from the MH tank 8. In other words, hydrogen gas containing a large amount of impure gas, that is, low-purity hydrogen gas (an example of the second hydrogen gas), is released from the MH tank 8. This corresponds to the tank purging mode, which will be described later.

[0127] After that, the switching valve 57 is closed or switched to the first hydrogen gas supply line 51 (timing t4), which prevents hydrogen gas from flowing out of the MH tank 8. Because the internal temperature has been lowered by cooling, hydrogen gas gradually separates from the hydrogen storage alloy MH, and the internal pressure increases.

[0128] Next, in preparation for the release of hydrogen gas from the MH tank 8, cooling is stopped and instead heating by the heater 72 is started (timing t5). Heating by circulating hot water may be used instead of the heater 72. This causes a sudden rise in the internal temperature. This promotes the separation of hydrogen gas from the hydrogen storage alloy MH, and so the internal pressure also rises suddenly.

[0129] Then, the hydrogen injector 47 is opened (at timing t6). The switching valve 57 may be switched to the second hydrogen gas supply line 52. This allows hydrogen gas to flow out of the MH tank 8. The hydrogen gas separated from the hydrogen storage alloy MH is released from the MH tank 8. Since impurity gases have been removed, this hydrogen gas is high-purity hydrogen gas (first hydrogen gas). Accordingly, the mass of hydrogen gas in the MH tank 8 decreases. The internal pressure and internal temperature also decrease.

[0130] In this way, it is possible to adjust the adsorption and separation of hydrogen gas onto the hydrogen storage alloy MH by controlling the temperature and / or pressure of the MH tank 8. This makes it possible to remove impure gases from the crude hydrogen gas in the MH tank 8, and to supply hydrogen gas of higher purity to the combustion chamber 3a.

[0131] Although high purity hydrogen gas is preferable as fuel, it is not necessary to completely remove impurities from the crude hydrogen gas. In practice, a purity of 90% or more is sufficient. Therefore, the relatively high purity hydrogen gas (first hydrogen gas) referred to here also aims for such a purity.

[0132] In contrast, the relatively low-purity hydrogen gas (second hydrogen gas) is hydrogen gas that contains a large amount of impurity gas and has a lower purity than the first hydrogen gas, as described above. In this fuel reforming system 1, such low-purity second hydrogen gas is removed from the MH tank 8 by tank scavenging operation. This produces high-purity first hydrogen gas, which is used as fuel to be directly injected into the combustion chamber 3a. The second hydrogen gas is injected into the intake port 33 and is also used as fuel.

[0133] (Switching of combustion cycles as the vehicle moves) The operating state of the engine 3 varies greatly from low load to high load and from low rotation to high rotation depending on the running of the vehicle. When the rotation speed of the engine 3 is low, the time per cycle is relatively long, so the cracker 6 can efficiently decompose the hydrocarbon fuel into carbon and hydrogen gas. However, when the rotation speed of the engine 3 is high, the time per cycle is short, so it becomes difficult to ensure time for the decomposition reaction of the hydrocarbon fuel.

[0134] Therefore, this control system 2 switches between a six-stroke cycle (special combustion cycle) that decomposes hydrocarbon fuel and a four-stroke cycle (normal combustion cycle) that does not decompose hydrocarbon fuel depending on the operating conditions related to the engine 3 speed and required load.

[0135] 8 shows a control map of the engine 3. The control map corresponds to an operating region of the engine 3 defined by the rotation speed and required load of the engine 3. The controller 21 operates the engine 3 in accordance with the control map.

[0136] The control map is divided into a first region (1) and a second region (2). The first region (1) is a region where the rotation speed is lower than a first rotation speed N1. The second region (2) is a region where the rotation speed is equal to or higher than the first rotation speed N1. The first rotation speed N1 may be a rotation speed included in the medium rotation speed region when the operating region of the engine 3 is divided into three regions in the rotation speed direction: a low rotation speed region, a medium rotation speed region, and a high rotation speed region.

[0137] The first region (1) is further divided into a first high load region (1H) and a first low-medium load region (1L). The first high load region (1H) is a region where the load is equal to or greater than Te1, and the first low-medium load region (1L) is a region where the load is less than Te1. The load Te1 may be a load included in the high load region when the operating region of the engine 3 is divided into three equal regions in the load direction: low load, medium load, and high load.

[0138] The first high load region (1H) is further divided into a first high load upper region (1Ha) and a first high load lower region (1Hb). The first high load upper region (1Ha) is a region where the load is equal to or greater than the load Te2, and the first high load lower region (1Hb) is a region where the load is less than the load Te2. The load Te2 is a load on the higher load side than the load Te1, and may be a load included in the middle region when the first high load region (1H) is divided into thirds.

[0139] In the first region (1), the controller 21 causes the engine 3 to execute a six-stroke cycle.

[0140] When the engine 3 is operating in the first low-medium load range (1L), as described above, the controller 21 performs operation using hydrogen gas as fuel (hydrogen gas mono-fuel operation). Specifically, the first hydrogen gas is injected from the hydrogen injector 47 via the first hydrogen gas supply line 51 from the MH tank 8, thereby supplying high-purity hydrogen gas directly to the combustion chamber 3a and causing it to burn.

[0141] A six-stroke cycle has two more strokes per cycle than a four-stroke cycle. Therefore, the output of a six-stroke cycle is smaller than that of a four-stroke cycle. Therefore, when the load increases, the output of the engine 3 becomes insufficient.

[0142] Therefore, in order to eliminate this shortage of output, when the engine 3 is operating in the first high load lower region (1Hb), the controller 21 port-injects hydrocarbon fuel from the intake port injector 44 via the hydrocarbon fuel supply line 45a, thereby supplying the hydrocarbon fuel to the combustion chamber 3a and causing it to burn.

[0143] When the load on the engine 3 is high, the heat of the combustion gas generated in the combustion chamber 3a increases. The pressure in the combustion chamber 3a also increases. Therefore, in this case, the decomposition of hydrogen gas in the cracker 6 is promoted compared to when the load on the engine 3 is low. This is advantageous for the generation of hydrogen gas. Operation at high load with port injection in a six-stroke cycle can effectively utilize this advantage. As a result, hydrogen gas can be effectively generated in the cracker 6.

[0144] When the engine 3 operates in the first high-load upper range (1Ha), the controller 21 also controls the inverter 28 to drive the drive motor. In this way, by combining the combustion of hydrogen gas and hydrocarbon fuel, and further by combining it with motor assist, the engine 3 can cope with a wide operating range in the load direction.

[0145] In the second region (2), the controller 21 causes the engine 3 to execute a four-stroke cycle.

[0146] That is, the controller 21 controls the third valve train 43 to stop the opening of the on-off valve 38. Then, the controller 21 controls the intake valve train 41 and the exhaust valve train 42 to open the intake valve 34 and the exhaust valve 36 at predetermined timing. The controller 21 also port-injects hydrocarbon fuel from the intake port injector 44 via the hydrocarbon fuel supply line 45a at predetermined timing. This supplies the hydrocarbon fuel to the combustion chamber 3a and causes it to burn.

[0147] In the second region (2), the controller 21 executes a combustion cycle using such hydrocarbon fuel. The engine 3 has a mechanism for changing the speed ratio between the crankshaft and the camshaft. When switching between the six-stroke cycle and the four-stroke cycle, the controller 21 changes the speed ratio.

[0148] (Example of control by fuel reforming system) Fig. 9 shows the flow of processing that forms the basis of control by the fuel reforming system 1. Fig. 10A and Fig. 10B show an example of the flow that forms the key points of control by the fuel reforming system 1. Fig. 11 shows the main processing states corresponding to the control by the fuel reforming system 1.

[0149] (A1) in Figure 11 shows the operating state when the amount of hydrogen gas stored in the MH tank 8 is small. Similarly, (A2) shows the operating state when the amount of hydrogen gas stored in the MH tank 8 is large. (A3) shows the operating state during deceleration.

[0150] (B) shows the state when the engine is operating in a hydrogen-only combustion mode. (C) shows the state when the engine 3 is operating in the first high load range (1H). (D) shows the state when the engine is operating in a tank scavenging mode.

[0151] 9, the controller 21 reads various signals input from the accelerator sensor 23 and the like (step S1). The controller 21 calculates the required output of the engine 3 based on the read signals (step S2). The controller 21 refers to a control map and determines whether the required output is in the first region (1) (step S3).

[0152] As a result, if the required output is in the first region (1), the controller 21 executes operation using a six-stroke cycle, i.e., operation using a special combustion cycle capable of producing hydrogen gas (step S4). On the other hand, if the required output is not in the first region (1), i.e., is in the second region (2), the controller 21 executes operation using a four-stroke cycle, i.e., operation using a normal combustion cycle fueled by hydrocarbon fuel (step S5).

[0153] 10A shows the flow of main processes during operation using the special combustion cycle. The controller 21 determines whether or not tank scavenging operation is necessary (step S11). That is, the controller 21 determines whether or not it is necessary to remove impure gas from the MH tank 8. As a result, if it is determined that tank scavenging operation is necessary, the controller 21 executes processing in the tank scavenging mode (step S12).

[0154] Figure 10B shows an example of the processing flow in tank purging mode. As shown by the thick solid line in Figure 11(D), controller 21 switches switching valve 57 to second hydrogen gas supply line 52 (step S51). As a result, the downstream side of MH tank 8 is opened through intake port 33. Accordingly, the internal pressure of MH tank 8 is reduced to a low pressure.

[0155] As a result, impure gas in the MH tank 8 and hydrogen gas that has not been adsorbed by the hydrogen storage alloy MH (most of the hydrogen gas is adsorbed by the hydrogen storage alloy MH), i.e., low-purity hydrogen gas (second hydrogen gas), are discharged into the intake port 33.

[0156] The controller 21 determines whether the vehicle is decelerating (step S52). During deceleration, the engine 3 does not need to output power, so fuel does not need to be supplied to the combustion chamber 3a. The controller 21 stops the supply of fuel (fuel cut).

[0157] However, the second hydrogen gas discharged into the intake port 33 may be burned in the combustion chamber 3a, and the combustion heat can be used to decompose the hydrogen gas.

[0158] If it is determined that deceleration is occurring, the controller 21 determines whether or not impure gas has been sufficiently removed from the MH tank 8. Specifically, it determines whether or not a predetermined time t1 set based on the degree of deceleration, the internal pressure of the MH tank 8, etc. has elapsed (step S53). As a result, if it is determined that the predetermined time t1 has elapsed, the controller 21 ends the tank scavenging operation. Then, the process returns to that of FIG. 10A.

[0159] On the other hand, if it is determined that the engine 3 is not decelerating, that is, that the engine 3 needs to output power, the controller 21 port-injects hydrocarbon fuel from the intake port injector 44 via the hydrocarbon fuel supply line 45a (step S54), as shown by the thick dashed line in Figure 11 (D). This supplies the hydrocarbon fuel to the combustion chamber 3a and causes it to burn. The second hydrogen gas discharged into the intake port 33 is also used as fuel.

[0160] Controller 21 then determines whether or not impure gas has been sufficiently removed from MH tank 8. Specifically, it determines whether or not a predetermined time t2 set based on the degree of acceleration, the internal pressure of MH tank 8, etc. has elapsed (step S55). As a result, if it is determined that predetermined time t2 has elapsed, controller 21 ends the tank scavenging operation. Then, the process returns to FIG. 10A.

[0161] On the other hand, if it is determined that scavenging is not necessary (No in step S11), the controller 21 switches the switching valve 57 to the first hydrogen gas supply line 51 (step S13). As a result, the downstream side of the MH tank 8 is closed by the hydrogen injector 47. Unless the predetermined pressure is reached and the hydrogen injector 47 is opened, hydrogen gas will not flow. As a result, the MH tank 8 is maintained at the predetermined internal pressure.

[0162] As shown by the thick solid line La in (A2) of Figure 11, the controller 21 supplies the hydrocarbon fuel to the third port injector 46 through the reformed fuel supply line 45b. Then, the third port injector 46 is opened to inject the hydrocarbon fuel into the third port 37 (step S14).

[0163] This causes decomposition of hydrogen gas and carbon and separation of hydrogen gas in the decomposer 6. As a result, crude hydrogen gas is supplied to the MH tank 8, as shown by the thick solid line Lb in (A2) of Figure 11 and the like.

[0164] The controller 21 determines the amount of hydrogen gas stored in the MH tank 8. Specifically, it determines whether the internal pressure Pt of the MH tank 8 is equal to or greater than a predetermined reference pressure Ps (step S15). As a result, if the internal pressure Pt of the MH tank 8 is less than the reference pressure Ps (i.e., if the amount of hydrogen gas stored is small), the controller 21 does not operate the gas pump 59 (No in step S15). Crude hydrogen gas is supplied to the MH tank 8 by utilizing the pressure generated in the combustion chamber 3a.

[0165] On the other hand, if the internal pressure Pt of the MH tank 8 is equal to or greater than the reference pressure Ps (that is, if the amount of stored hydrogen gas is large), the controller 21 activates the gas pump 59 (step S16).

[0166] 11(A2), crude hydrogen gas is pressurized by the gas pump 59 and supplied to the MH tank 8. Even if the internal pressure of the MH tank 8 is high, crude hydrogen gas can be stored.

[0167] At this time, the MH tank 8 is cooled by the temperature adjusting unit 71. As a result, the MH tank 8 is maintained at a temperature optimum for adsorption of the internal pressure hydrogen storage alloy MH.

[0168] After step S13, the controller 21 also determines whether the hydrogen operation switch 26 is on (step S17). If it determines that the hydrogen operation switch 26 is on, the controller 21 controls the hydrogen injector 47 to inject the first hydrogen gas directly into the combustion chamber 3a, as shown by the thick solid line Ld in (A2) of Figure 11 (step S18).

[0169] This allows the first hydrogen gas to be burned as fuel. Because it is highly pure hydrogen gas, high output can be obtained. However, depending on the load on the engine 3, the output may be insufficient. In that case, port injection using hydrocarbon fuel may be performed, as shown by the thick dashed line Le in (A2) of FIG. 11, etc.

[0170] In hydrogen gas mono-fuel operation (operation using only hydrogen gas combustion), as shown in FIG. 11(B), cooling by the temperature adjustment unit 71 may be stopped and the MH tank 8 may be heated by the heater 72. This will promote separation of hydrogen gas from the hydrogen storage alloy MH. The internal pressure of the MH tank 8 can be increased, and the amount of first hydrogen gas released from the MH tank 8 can be increased. Stable injection from the hydrogen injector 47 can be ensured, and the range in which hydrogen gas mono-fuel operation is possible can be expanded.

[0171] On the other hand, if it is determined that the hydrogen operation switch 26 is off (No in step S17), the controller 21 determines whether the operation of the engine 3 is in the first high load region (1H). Specifically, it determines whether the required load Te of the engine 3 is equal to or greater than the load Te1 (step S19).

[0172] As a result, if it is determined that the engine 3 is not operating in the first high load range (1H), that is, in the first low-medium load range (1L), the controller 21 directly injects the first hydrogen gas as fuel into the combustion chamber 3a (step S18). Because the load on the engine 3 is not high, small combustion energy is sufficient. Therefore, hydrogen gas mono-fuel operation can be performed.

[0173] On the other hand, when it is determined that the engine 3 is operating in the first high load range (1H), the controller 21 performs port injection of hydrocarbon fuel as fuel (step S20), as shown in FIG. 11(C). Since a large amount of combustion energy is obtained, it can handle a high load on the engine 3. The heat and pressure in the combustion chamber 3a also increase, which promotes the production of hydrogen gas in the cracker 6.

[0174] Next, the controller 21 determines whether the operation of the engine 3 is in the first high-load upper region (1Ha). Specifically, it determines whether the required load Te of the engine 3 is equal to or greater than the load Te2 (step S21). As a result, if it is determined that the operation of the engine 3 is in the first high-load upper region (1Ha), the controller 21 executes motor assist (step S22). That is, the controller 21 controls the inverter 28 to drive the drive motor.

[0175] This makes it possible to cope with a load that exceeds the output of the engine 3. The operating range of the engine 3 can be expanded to the first high load upper range (1Ha).

[0176] As described above in the processing of the tank scavenging mode, the engine 3 does not need to output power during deceleration. Therefore, fuel does not need to be supplied to the combustion chamber 3a. The controller 21 stops the supply of fuel (fuel cut) during deceleration, even during normal operation using a six-stroke cycle.

[0177] Even in this case, the controller 21 continues to generate hydrogen gas, as shown in (A3) of Fig. 11. That is, the controller 21 supplies hydrocarbon fuel to the third port injector 46 through the reformed fuel supply line 45b, and opens the third port injector 46 to inject the hydrocarbon fuel into the third port 37.

[0178] The heat and pressure in the combustion chamber 3a can be utilized even during deceleration, so hydrogen gas can be generated efficiently. At this time, the engine 3 obtains mechanical resistance through pumping, so deceleration energy can also be secured.

[0179] <Application example of fuel reforming system> Fig. 12 shows an application example of the fuel reforming system 1 (also referred to as application system 1A). Fig. 13 shows a block diagram of the control system 2 in application system 1A. The basic configuration of application system 1A is the same as that of the above-described fuel reforming system 1. Therefore, the same components are designated by the same reference numerals, and their description will be simplified or omitted.

[0180] The application system 1A is equipped with two of the above-mentioned MH tanks 8. That is, the hydrogen gas supply unit 5 is equipped with two MH tanks 8 (a first MH tank 8A and a second MH tank 8B) arranged in parallel. The hydrogen gas separated in the cracker 6 can be stored in either the first MH tank 8A or the second MH tank 8B by switching between them.

[0181] Accordingly, in the hydrogen gas supply unit 5 of the application system 1A, switching storage valves 58a are installed in the hydrogen gas receiving line 50 corresponding to the first MH tank 8A and the second MH tank 8B, instead of the storage valves 58. The switching storage valves 58a cause the downstream side of the hydrogen gas receiving line 50 to branch into two.

[0182] Similarly, a first switching valve 57A and a second switching valve 57B are installed in each hydrogen gas extraction line 53. The first switching valve 57A and the second switching valve 57B cause the upstream sides of the first hydrogen gas supply line 51 and the second hydrogen gas supply line 52 to branch into two.

[0183] As for heaters 72, first heaters 72A and 72B are provided corresponding to the first MH tank 8A and the second MH tank 8B, respectively. A switching flow path valve 71a is provided in the circulation path through which the liquid medium circulates in temperature adjustment unit 71. By switching switching flow path valve 71a, the circulation path of the liquid medium can be switched to the first MH tank 8A and / or the second MH tank 8B.

[0184] An MH tank temperature sensor 24 and an MH tank pressure sensor 25 are also installed corresponding to the first MH tank 8A and the second MH tank 8B, respectively. Specifically, as shown in Fig. 13, a first MH tank temperature sensor 24A, a first MH tank pressure sensor 25A, a second MH tank temperature sensor 24B, and a second MH tank pressure sensor 25B are installed.

[0185] In the control system 2 of the application system 1A, similar to the fuel reforming system 1, various devices corresponding to the first MH tank 8A and the second MH tank 8B, such as the second MH tank pressure sensor 25B, are electrically connected to the controller 21. The functions of these devices are similar to those of the corresponding devices in the control system 2 described above, and therefore a description thereof will be omitted.

[0186] However, the switching storage valve 58a has a different function from the storage valve 58. The switching storage valve 58a switches the downstream flow path of the hydrogen gas receiving line 50 based on a control signal from the controller 21.

[0187] (Example of control by application systems) 14A, 14B, and 14C show an example of the operation flow of the special combustion cycle by the application system 1A. Note that the processing flow that forms the basis of control is the same in the case of the application system 1A as in the fuel reforming system 1 shown in FIG.

[0188] 15A, 15B, and 15C show the main processing states corresponding to the control by application system 1 A. Controller 21 switches between using first MH tank 8A and second MH tank 8B depending on the operating state of engine 3 and the storage states of first MH tank 8A and second MH tank 8B.

[0189] 15A shows the operating state when the amount of hydrogen gas stored in one of the first MH tank 8A and the second MH tank 8B is small. (A1-1) shows the case where hydrogen gas is stored in the first MH tank 8A and released from the second MH tank 8B. (A1-2) shows the case where hydrogen gas is stored in the second MH tank 8B and released from the first MH tank 8A.

[0190] (A2-1) in Figure 15B shows the operating state when the first MH tank 8A has a large amount of stored hydrogen gas. (D-1) in Figure 15B shows the operating state in the two-tank scavenging mode, which will be described later. (C2) in Figure 15C shows the operating state when hydrogen gas is stored in the second MH tank 8B and the engine 3 is operating in the first high load range (1H). (B) in Figure 15C shows hydrogen gas mono-fuel operation, in which hydrogen gas is released from the second MH tank 8B.

[0191] 14A, controller 21 switches selector valve 57 (first selector valve 57A or second selector valve 57B) of MH tank 8 that is discharging (also referred to as discharging MH tank 8) of first MH tank 8A or second MH tank 8B to first hydrogen gas supply line 51 (step S61).

[0192] Then, the controller 21 determines whether or not tank scavenging operation is necessary for the MH tank 8 on the non-discharge side (also referred to as the occluded MH tank 8) (step S62). As a result, if it is determined that tank scavenging operation is necessary, the controller 21 executes processing in the two-tank scavenging mode (step S63).

[0193] Figure 14C shows the flow of processing in the two-tank scavenging mode. An example is shown in Figure 15B (D-1). Note that here, the first MH tank 8A is the stored MH tank 8, and the second MH tank 8B is the released MH tank 8.

[0194] Controller 21 switches first switching valve 57A of first MH tank 8A to second hydrogen gas supply line 52 (step S81). As a result, the downstream side of first MH tank 8A is opened through intake port 33. Accordingly, the internal pressure of first MH tank 8A is reduced to a low pressure.

[0195] As a result, the impure gas in the first MH tank 8A and the hydrogen gas not adsorbed by the hydrogen storage alloy MH, that is, the low-purity hydrogen gas (second hydrogen gas), are discharged into the intake port 33.

[0196] At this time, the temperature adjustment unit 71 switches the switching flow path valve 71a to stop the circulation of the liquid medium to the first MH tank 8A. Then, the first heater 72A heats the first MH tank 8A. This promotes scavenging of the first MH tank 8A, enabling processing to be completed in a short time.

[0197] Controller 21 determines whether the vehicle is decelerating (step S82). During deceleration, controller 21 stops the supply of fuel (fuel cut). If it determines that the vehicle is decelerating, controller 21 determines whether impure gases have been sufficiently removed from first MH tank 8A. Specifically, it determines whether a predetermined time t1, which is set based on the degree of deceleration, the internal pressure of first MH tank 8A, etc., has elapsed (step S83).

[0198] As a result, when it is determined that the predetermined time t1 has elapsed, the controller 21 closes the first switching valve 57A (step S84). Then, the controller 21 ends the tank scavenging operation. The process returns to the process in FIG. 14A.

[0199] On the other hand, if it is determined that the vehicle is not decelerating, as shown in (D-1) of Figure 15B, the controller 21 activates the hydrogen injector 47 to directly inject the first hydrogen gas from the second MH tank 8B into the combustion chamber 3a (step S85). This supplies high-purity hydrogen gas to the combustion chamber 3a and causes it to be burned. The second hydrogen gas discharged into the intake port 33 is also used as fuel.

[0200] At this time, the hydrocarbon fuel may be port-injected from the intake port injector 44 via the hydrocarbon fuel supply line 45a. In this way, the hydrocarbon fuel can be supplied to the combustion chamber 3a and burned. This can be used even if the output of the engine 3 is large.

[0201] Controller 21 then determines whether or not impure gas has been sufficiently removed from first MH tank 8A. Specifically, it determines whether or not a predetermined time t2, which is set based on the degree of acceleration, the internal pressure of first MH tank 8A, etc., has elapsed (step S86). As a result, if it is determined that predetermined time t2 has elapsed, controller 21 closes first switching valve 57A (step S84). Controller 21 then ends the tank scavenging operation. The process returns to that of FIG. 14A.

[0202] If it is determined in step S62 that the tank scavenging operation is not required, the controller 21 supplies hydrocarbon fuel to the third port injector 46 through the reformed fuel supply line 45b, as shown in (A1-1) of Fig. 15. Then, the third port injector 46 is opened to inject the hydrocarbon fuel into the third port 37 (step S64).

[0203] As a result, decomposition of hydrogen gas and carbon and separation of hydrogen gas are carried out in the decomposer 6. Then, the produced crude hydrogen gas is supplied to the occluded MH tank 8 by utilizing the pressure generated in the combustion chamber 3a.

[0204] Subsequently, the controller 21 determines whether the storage amount of hydrogen gas in the occluding MH tank 8 is appropriate. Specifically, based on the internal pressure of the occluding MH tank 8 or the like, it is determined whether the storage amount Vtc of hydrogen gas in the occluding MH tank 8 is equal to or greater than a predetermined storage amount (the upper limit set value V1) (step S65).

[0205] As a result, if it is determined that the storage amount of hydrogen gas in the occluding MH tank 8 is full (Vtc≥V1), the controller 21 changes the occluding MH tank 8 (step S66). This is because hydrogen gas cannot be stored even if it is generated. Then, it returns to before step S61.

[0206] On the other hand, if it is determined that the storage amount of hydrogen gas in the occluding MH tank 8 is not full (Vtc<V1), the controller 21 determines the amount of hydrogen gas stored in the occluding MH tank 8. Specifically, it is determined whether the internal pressure Ptc of the occluding MH tank 8 is equal to or greater than a predetermined reference pressure Ps (step S67).

[0207] As a result, if the internal pressure Ptc of the occluding MH tank 8 is less than the reference pressure Ps (that is, when the storage amount of hydrogen gas is small), the controller 21 does not operate the gas pump 59 (No in step S67). As shown in FIG. 15A, the raw hydrogen gas is supplied to the MH tank 8 by using the pressure generated in the combustion chamber 3a.

[0208] On the other hand, if the internal pressure Ptc of the MH tank 8 is equal to or greater than the reference pressure Ps (that is, when the storage amount of hydrogen gas is large), the controller 21 operates the gas pump 59 as shown in (A2-1) of FIG. 15B (step S68). Thereby, the raw hydrogen gas is pressurized by the gas pump 59 and supplied to the occluding MH tank 8. The raw hydrogen gas can be stored even if the internal pressure of the occluding MH tank 8 is high.

[0209] In step S62, if it is determined that the tank scavenging operation is unnecessary, the controller 21 also determines whether the storage amount of hydrogen gas in the discharging MH tank 8 is sufficient. Specifically, based on the internal pressure of the discharging MH tank 8 or the like, it is determined whether the storage amount of hydrogen gas in the discharging MH tank 8 is less than a predetermined storage amount (the lower limit set value V2) (step S69).

[0210] As a result, when it is determined that the hydrogen gas storage amount in the discharge MH tank 8 is below the lower limit (Vtd < V2), the controller 21 changes the discharge MH tank 8 (step S70). This is because the hydrogen gas cannot be appropriately discharged. Then, it returns to before step S61.

[0211] On the other hand, when it is determined that the hydrogen gas storage amount in the discharge MH tank 8 is not below the lower limit (Vtd ≥ V2), the controller 21 determines whether the hydrogen operation switch 26 is on or not as shown in FIG. 14B (step S71).

[0212] As a result, when it is determined that the hydrogen operation switch 26 is on, the controller 21 controls the hydrogen injector 47 and directly injects the first hydrogen gas into the combustion chamber 3a as shown in FIGS. 15A etc. (step S72). When the output is insufficient depending on the load of the engine 3, port injection with hydrocarbon fuel may be performed.

[0213] In the hydrogen gas dedicated combustion operation, as shown in (B) of FIG. 15C, in the discharge MH tank 8, cooling by the temperature adjustment unit 71 may be stopped and heating may be performed with the heater 72. The discharge amount of the first hydrogen gas can be increased. Stable injection of the hydrogen injector 47 can be ensured, and the region where the hydrogen gas dedicated combustion operation can be performed can be expanded.

[0214] In the hydrogen gas dedicated combustion operation, the discharge MH tank 8 and the absorption MH tank 8 may be the same. That is, hydrogen gas is discharged while being absorbed into the MH tank. In the hydrogen gas dedicated combustion operation, the discharge MH tank 8 may be switched. Also, as shown by the broken line in (B) of FIG. 15C, the first hydrogen gas may be discharged from both the first MH tank 8A and the second MH tank 8B.

[0215] On the other hand, when it is determined that the hydrogen operation switch 26 is off (No in step S71), the controller 21 determines whether the operation of the engine 3 is in the first high load region (1H) or not. Specifically, it determines whether the load Te of the engine 3 is greater than or equal to the load Te1 or not (step S73).

[0216] As a result, if it is determined that the engine 3 is not operating in the first high load range (1H), that is, in the first low-medium load range (1L), the controller 21 injects the first hydrogen gas directly from the discharge MH tank 8 into the combustion chamber 3a as fuel (step S72). Because the load on the engine 3 is not high, small combustion energy is sufficient. Therefore, hydrogen gas mono-fuel operation can be performed.

[0217] On the other hand, when it is determined that the engine 3 is operating in the first high load range (1H), the controller 21 performs port injection of hydrocarbon fuel as fuel (step S74), as shown in (C2) of FIG. 15C. Since a large amount of combustion energy is obtained, the engine 3 can cope with a high load. The heat and pressure in the combustion chamber 3a also increase, which promotes the production of hydrogen gas in the cracker 6.

[0218] Next, the controller 21 determines whether the operation of the engine 3 is in the first high-load upper region (1Ha). Specifically, it determines whether the load Te of the engine 3 is equal to or greater than the load Te2 (step S75). As a result, if it is determined that the operation of the engine 3 is in the first high-load upper region (1Ha), the controller 21 executes motor assist (step S76). That is, the controller 21 controls the inverter 28 to drive the drive motor.

[0219] This allows the engine 3 to cope with a large load being requested, and expands the operating range of the engine 3 to the first high load upper range (1Ha).

[0220] <Special combustion cycle variant> In the above-described embodiment, the engine 3 is illustrated as executing a six-stroke cycle. However, the special combustion cycle is not limited to a six-stroke cycle. In this modification, the engine 3 is illustrated as executing an irregular four-stroke cycle as the special combustion cycle.

[0221] Figure 16 shows the steps involved in a modified four-stroke cycle.

[0222] S1 is the compression stroke. During the compression stroke S1, the engine 3 compresses the air-fuel mixture in the combustion chamber 3a by the upward movement of the piston 32. The intake valve 34, the exhaust valve 36, and the on-off valve 38 are all closed.

[0223] The hydrogen injector 47 injects hydrogen gas into the combustion chamber 3a during the compression stroke S1. If there is a shortage of hydrogen gas, the intake port injector 44 may inject hydrocarbon fuel into the intake port 33 during the scavenging stroke S4 described below to make up for the shortage. If there is no hydrogen gas, the intake port injector 44 may inject hydrocarbon fuel into the intake port 33 during the scavenging stroke S4 instead of the hydrogen injector 47.

[0224] When there is a shortage of hydrogen gas supplied to the combustion chamber 3a, the intake port injector 44 injects hydrocarbon fuel to ensure the required amount of fuel for the engine 3. The engine 3 can be operated using hydrocarbon fuel or both hydrocarbon fuel and hydrogen gas.

[0225] The spark plug 27 ignites the air-fuel mixture in the combustion chamber 3a near the top dead center of the compression stroke. The air-fuel mixture begins to burn. S2 is the expansion stroke. During the expansion stroke S2, the piston 32 descends due to the combustion of the air-fuel mixture. The intake valve 34, exhaust valve 36, and on-off valve 38 are all closed.

[0226] S3 is a recompression stroke. During the recompression stroke S3, the engine 3 compresses the combustion gas in the combustion chamber 3a by moving the piston 32 upward. During the recompression stroke S3, the on-off valve 38 opens. The compressed combustion gas is introduced into the cracker 6 through the third port 37. During the recompression stroke S3, the third port injector 46 injects hydrocarbon fuel into the third port 37.

[0227] The hydrocarbon fuel is introduced into the cracker 6 together with the combustion gas. As described above, in the cracker 6, the hydrocarbon fuel is decomposed into carbon and hydrogen gas by the heat of the combustion gas and the catalyst. The carbon is stored in the cracker 6. The hydrogen gas permeates the hydrogen permeable membrane 63 of the cracker 6 due to the pressure of the combustion gas and is sent to the hydrogen gas supply unit 5.

[0228] Because the high pressure of the combustion gas in the recompression stroke is applied to the inside of the cracker 6, the hydrogen gas generated inside the cracker 6 quickly permeates the hydrogen-permeable membrane 63. Because the amount of hydrogen gas inside the cracker 6 is reduced, the cracking reaction of the hydrocarbon fuel is promoted. The cracker 6, which utilizes the pressure of the recompression stroke S3 of the engine 3, can generate the amount of hydrogen gas required to operate the engine 3, even though it is small.

[0229] S4 is a scavenging stroke. In the scavenging stroke S4, the piston 32 descends. The on-off valve 38 opens in the scavenging stroke S4. When the on-off valve 38 opens, residual gas is introduced from the cracker 6 into the combustion chamber 3a.

[0230] In the scavenging stroke S6, the exhaust valve 36 opens. Combustion gas in the combustion chamber 3a is discharged to the exhaust port 35. In the scavenging stroke S6, the intake valve 34 also opens. Intake air is introduced into the combustion chamber 3a through the intake port 33. The intake air includes at least fresh air. The intake air may also include EGR gas. This EGR gas is so-called external EGR gas that has been recirculated to the intake pipe through the EGR passage. The engine 3 performs gas exchange in the combustion chamber 3a in the scavenging stroke S6.

[0231] The chart shown at the bottom of FIG. 16 shows the lift curves of the intake valve 34, the exhaust valve 36, and the on-off valve 38 when the irregular four-stroke cycle is being executed.

[0232] The on-off valve 38 opens during the recompression stroke and also opens during the scavenging stroke. During the recompression stroke, combustion gas in the combustion chamber 3a is introduced into the third port 37, and during the scavenging stroke, combustion gas flows from the cracker 6 into the combustion chamber 3a. The on-off valve 38 opens twice per cycle.

[0233] During the scavenging stroke, the exhaust valve 36 also opens. The exhaust valve 36 opens after the on-off valve 38 opens. The timing of opening the exhaust valve 36 may be the early period when the scavenging stroke is divided into three equal periods: early, middle, and late. During the early period of the scavenging stroke, the pressure in the combustion chamber 3a is high. When the exhaust valve 36 opens, the high pressure in the combustion chamber 3a efficiently discharges exhaust gas from the cylinder 31 to the exhaust port 35.

[0234] During the scavenging stroke, the intake valve 34 also opens. The intake valve 34 opens after the exhaust valve 36 opens. The timing at which the intake valve 34 opens may be in the middle of the scavenging stroke. As the piston 32 descends at a relatively high speed, intake air is introduced into the combustion chamber 3a through the intake port 33.

[0235] The disclosed technology is not limited to the above-described embodiment, but also includes various other configurations. For example, the method of using the first hydrogen gas and the second hydrogen gas can be changed as appropriate depending on the specifications of the vehicle and engine 3. The structure of the cracker 6 is also one example.

[0236] The second hydrogen gas is not limited to the hydrogen gas released during the scavenging operation, and the second hydrogen gas (relatively low purity hydrogen gas) may also be actively used as fuel. [Explanation of symbols]

[0237] 1 Fuel reforming system 2. Control System 3 Reciprocating engine 3a Combustion chamber 5 Hydrogen gas supply unit 6 Decomposer 8 MH tank (an example of a reforming tank) 21 Controller 22 RPM sensor 23 Accelerator sensor 24 MH Tank Temperature Sensor 25 MH Tank Pressure Sensor 26 Hydrogen operation switch 27 Spark plug 28 Inverter 31 cylinders 32 piston 33 Intake port 34 Intake valve 35 exhaust port 36 Exhaust valve 37 Third Port 38 On-off valve 44 Intake port injector 45 Hydrocarbon fuel supply unit 45a Hydrocarbon fuel supply line 45b Reformed fuel supply line 46 Third port injector 47 Hydrogen Injector 48 Hydrogen injector 50 Hydrogen gas receiving line 51 First hydrogen gas supply line 51a Pressure regulating valve 52 Second hydrogen gas supply line 53 Hydrogen gas extraction line 54 Bypass Passage 55 Check valve 57 Switching valve 58 Storage valve 58a Switching storage valve 59 Gas Pump 63 Hydrogen permeable membrane 71 Temperature control section MH Hydrogen storage alloy

Claims

1. A fuel reforming system for a vehicle equipped with a reciprocating engine in which a combustion chamber in which combustion occurs is defined inside a cylinder in which a piston reciprocates, a cracker for cracking a hydrocarbon fuel into carbon and hydrogen gas and storing the carbon; a hydrocarbon fuel supply unit that supplies the hydrocarbon fuel to the cracker; a hydrogen gas supply unit that supplies the hydrogen gas generated by the cracker to the combustion chamber as fuel; Equipped with the cracker is configured to use heat and pressure of combustion gas generated in the combustion chamber to decompose the hydrocarbon fuel into the carbon and the hydrogen gas, and separate the hydrogen gas by allowing it to permeate through a hydrogen-permeable membrane; The hydrogen gas supply unit a reforming tank that stores the hydrogen gas separated in the cracker and that can extract either a relatively high-purity first hydrogen gas or a relatively low-purity second hydrogen gas by utilizing a hydrogen storage alloy contained therein; a first hydrogen gas supply line that supplies the first hydrogen gas from the reforming tank to the combustion chamber; a second hydrogen gas supply line that supplies the second hydrogen gas from the reforming tank to the combustion chamber; Equipped with A fuel reforming system configured to allow hydrogen gas of different purity to be supplied to the combustion chamber through different routes.

2. 2. The fuel reforming system of claim 1, a hydrocarbon fuel supply line that supplies the hydrocarbon fuel as fuel from the hydrocarbon fuel supply unit to the combustion chamber; A fuel reforming system configured to be able to supply the hydrocarbon fuel when supplying the first hydrogen gas or the second hydrogen gas to the combustion chamber.

3. 2. The fuel reforming system of claim 1, the hydrogen gas supply unit includes two reforming tanks, a first reforming tank and a second reforming tank, which are arranged in parallel; The fuel reforming system is configured so that the hydrogen gas separated in the cracker can be stored in either the first reforming tank or the second reforming tank by switching between them.

4. The fuel reforming system according to any one of claims 1 to 3, The reciprocating engine, an intake stroke in which at least intake air is introduced into the combustion chamber through an intake port as the piston descends; a compression stroke in which the mixture containing the hydrogen gas supplied to the combustion chamber is compressed by the rise of the piston; an expansion stroke in which the piston descends due to combustion of the air-fuel mixture; a recompression stroke in which the combustion gas is compressed by the rise of the piston; a re-expansion stroke in which the piston descends; and an exhaust stroke in which exhaust gas is discharged through the exhaust port as the piston rises; A fuel reforming system configured to perform a six-stroke cycle consisting of:

5. The fuel reforming system according to any one of claims 1 to 3, The reciprocating engine, a compression stroke in which the mixture containing the hydrogen gas supplied to the combustion chamber is compressed by the rise of the piston; an expansion stroke in which the piston descends due to combustion of the air-fuel mixture; a recompression stroke in which the combustion gas is compressed by the rising of the piston; and a scavenging stroke in which exhaust gas from the combustion chamber is discharged through an exhaust port while at least intake air is introduced into the cylinder through an intake port as the piston descends; A fuel reforming system configured to perform a modified four-stroke cycle comprising:

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