Engine system

Abstract

This engine system is provided with: an engine including a cylinder and a piston housed in the cylinder; an air tank; an air supply system including a starting air line for guiding compressed air stored in the air tank into the cylinder as starting air of the engine; and a fuel gas supply system for supplying fuel gas into the cylinder. The engine further includes a crankshaft located below the piston for driving the piston, and a crankcase housing the crankshaft. The air supply system further includes a bleeding line for bleeding compressed air flowing through the starting air line and guiding the compressed air to the crank chamber in the crankcase.

Description

Engine System

[0001] This application claims priority to Japanese Patent Application No. 2023-140611, filed with the Japan Patent Office on August 31, 2023, the contents of which are incorporated herein by reference.

[0002] The engine system disclosed in Patent Document 1 includes a cylinder, a piston housed in the cylinder, a crankshaft located below the piston and for driving the piston, and a crankcase housing the crankshaft.

[0003] Japanese Patent Application Laid-Open No. 2017-031957

[0004] Fuel gas in the combustion chamber of a cylinder may leak between the cylinder and the piston into the crankcase (this fuel gas is sometimes called blow-by gas). If the concentration of unburned fuel gas in the crankcase is high, there is a risk of the fuel gas igniting. Measures to reduce this risk are preferably implemented without complicating the engine system configuration.

[0005] An object of the present disclosure is to provide an engine system that reduces the risk of ignition of unburned gas in the crankcase with a simple configuration.

[0006] An engine system according to at least one embodiment of the present disclosure comprises: an engine including a cylinder and a piston housed in the cylinder; an air supply system including an air tank and a starting air line for guiding compressed air stored in the air tank into the cylinder as starting air for the engine; and a fuel gas supply system for supplying fuel gas into the cylinder, wherein the engine further includes: a crankshaft located below the piston and for driving the piston; and a crankcase accommodating the crankshaft, and the air supply system further includes a bleed line for bleeding the compressed air flowing through the starting air line and guiding it to a crank chamber in the crankcase.

[0007] According to the present disclosure, it is possible to provide an engine system that reduces the risk of ignition of unburned gas in the crankcase with a simple configuration.

[0008] FIG. 1 is a schematic diagram of an engine system according to one embodiment. FIG. 2 is a schematic diagram of an engine according to one embodiment. FIG. 3 is a schematic diagram of an air supply system according to one embodiment. FIG. 4 is a schematic diagram of an engine system according to one embodiment. FIG. 5 is a flowchart of crankcase purge control according to one embodiment. FIG. 6 is a flowchart of engine control according to one embodiment. FIG. 7 is a schematic diagram of an engine system according to another embodiment. FIG. 8 is a schematic diagram of a crankcase according to a first embodiment. FIG. 9 is a schematic diagram of a crankcase according to a second embodiment. FIG. 10 is another schematic diagram of a crankcase according to the second embodiment. FIG. 11 is a schematic diagram of a crankcase according to a third embodiment. FIG. 12 is a schematic diagram of a crankcase according to a fourth embodiment. FIG. 13 is a schematic diagram of a crankcase according to a fifth embodiment. FIG. 14 is a schematic diagram of an engine system according to another embodiment.

[0009] Several embodiments of the present disclosure will be described below with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are not intended to limit the scope of the present disclosure and are merely illustrative examples. For example, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express relative displacements with a tolerance or angle or distance to the extent that the same function is achieved. For example, expressions expressing the equality of things, such as "same," "equal," and "homogeneous," not only express strict equality, but also express tolerance or differences to the extent that the same function is achieved. For example, expressions expressing shapes such as a square or cylindrical shape not only express shapes such as a square or cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is achieved. On the other hand, the expressions "comprise," "include," or "have" one component are not exclusive expressions that exclude the existence of other components. Note that similar components may be assigned the same reference numerals and descriptions thereof may be omitted.

[0010] 1 is a schematic diagram of an engine system 1 according to an embodiment of the present disclosure. The engine system 1, which may be incorporated into, for example, a power generation facility, includes an engine 5 having a combustion chamber 9 and a crankcase 18 formed therein, a fuel gas supply system 70 including a fuel gas line 11 for guiding fuel gas Fg to the combustion chamber 9, and a turbocharger 15 including a compressor wheel 12 for sending compressed air Ca to the combustion chamber 9. The engine 5 in this example is a stationary engine.

[0011] The fuel gas Fg in this example includes a first fuel gas fg1 and a second fuel gas fg2. More specifically, the fuel gas line 11 of the fuel gas supply system 70 includes a first fuel gas line 11a for supplying the first fuel gas fg1 to the combustion chamber 9 and a second fuel gas line 11b for supplying the second fuel gas fg2 to the combustion chamber 9. The fuel gas supply system 70 also includes a fuel gas flow regulation valve 73 and a fuel on-off valve 77 arranged on the fuel gas line 11 (see FIG. 4 ). The fuel gas flow regulation valve 73 includes a first fuel flow regulation valve 73a arranged on the first fuel gas line 11a and a second fuel flow regulation valve 73b arranged on the second fuel gas line 11b. The fuel on-off valve 77 includes a first fuel on-off valve 77a arranged on the first fuel gas line 11a and a second fuel on-off valve 77b arranged on the second fuel gas line 11b. By adopting this configuration, the combustion chamber 9 shown in FIG. 1 can selectively perform combustion of the first fuel gas fg1, the second fuel gas fg2, or a combination of both fuel gases.

[0012] The first fuel gas fg1 and the second fuel gas fg2 may be any gas, but the lower explosive limit concentration of the second fuel gas fg2 is lower than the lower explosive limit concentration of the first fuel gas fg1. The first fuel gas fg1 is, for example, a fossil fuel gas, and a more specific example is natural gas. The second fuel gas fg2 is a non-fossil fuel gas, and a more specific example includes at least one of hydrogen gas, biofuel gas, and ammonia gas. However, the second fuel gas fg2 may be, for example, a fossil fuel gas such as propane gas. As described above, various fuel gases can be used for the first fuel gas fg1 and the second fuel gas fg2. However, the following describes an embodiment in which the first fuel gas fg1 is natural gas and the second fuel gas fg2 is hydrogen gas.

[0013] When either natural gas or hydrogen gas is supplied exclusively, the combustion of that gas occurs in the combustion chamber 9. For example, when hydrogen gas is supplied exclusively, the first fuel on-off valve 77a is closed and the second fuel on-off valve 77b is open. On the other hand, when a mixed gas is supplied to the combustion chamber 9, the mixed combustion of hydrogen gas and natural gas occurs in the combustion chamber 9. At this time, both the first fuel on-off valve 77a and the second fuel on-off valve 77b are open. In this example, the controller 90 is configured to control the ratio between the supply amounts of natural gas and hydrogen gas. More specifically, the controller 90 can adjust the mixed combustion ratio in the combustion chamber 9 by controlling the opening degrees of the first fuel flow regulation valve 73a (see FIG. 4) and the second fuel flow regulation valve 73b (see FIG. 4).

[0014] 1 further includes a turbine wheel 14 and a rotor shaft 13 connected to the turbine wheel 14 and the compressor wheel 12. The engine system 1 also includes an exhaust gas line 89 for guiding exhaust gas Eg discharged from the combustion chamber 9 to the turbine wheel 14. The exhaust gas Eg drives the rotor shaft 13 via the turbine wheel 14, thereby driving the compressor wheel 12. As a result, the compressor wheel 12 generates compressed air Ca.

[0015] The engine system 1 further includes an air intake line 25 for guiding the compressed air Ca delivered by the compressor wheel 12 to the combustion chamber 9, and an air cooler 28 arranged on the air intake line 25. The air cooler 28 is a device for cooling the compressed air Ca. The air cooler 28 may be an air-cooled air cooler or a water-cooled air cooler.

[0016] The air intake line 25 has a first air intake line 251 for guiding the compressed air Ca to the air cooler 28, and a second air intake line 252 for guiding the cooled compressed air Ca discharged from the air cooler 28 to the combustion chamber 9. The cooled compressed air Ca flowing through the second air intake line 252 is guided to the combustion chamber 9 via an air intake pipe 102 (see FIG. 2) and an air intake pipe 103 (see FIG. 2). The air intake pipe 102 and the air intake pipe 103 will be described later.

[0017] 2 is a schematic diagram of an engine 5 according to one embodiment of the present disclosure, showing a cross section perpendicular to the axis of a crankshaft 16 of the engine 5. The engine 5 includes a cylinder 6, a piston 7 housed in the cylinder 6, a crankshaft 16 located below the piston 7, and a crankcase 20 that houses the crankshaft 16. A crankpin 81 configured to rotate in conjunction with the crankshaft 16 is connected to the piston 7 via a connecting rod 19. In this way, the crankshaft 16 is driven by the piston 7. In the following description, the axial direction of the crankshaft 16 may be abbreviated as the "axial direction."

[0018] The illustrated engine 5 is, as an example, a V-type multi-cylinder engine. More specifically, two axially adjacent pistons 7 are arranged in a generally V-shape at a predetermined bank angle when viewed in the axial direction. The number of cylinder units 8, each including a cylinder 6 and a piston 7, arranged in the axial direction (the number of cylinders) is, for example, 12, 14, 16, 18, 20, or 24. The crankcase 20 in this example is long in the axial direction (see FIG. 8 ). Note that the engine 5 in another example may be an in-line multi-cylinder engine. There are no particular restrictions on the number of cylinders, and the number of cylinders may be, for example, 2, 4, 6, or 8.

[0019] 2 is an OHV (Over Head Valve) engine in which each cylinder unit 8 includes a cylinder head and a valve mechanism provided in the cylinder head. More specifically, the engine 5 includes a camshaft 85 extending in the axial direction, a cam (not shown) provided on the camshaft 85, a push rod 87 configured to be displaced up and down by rotation of the cam, a rocker arm 86 configured to swing in response to displacement of the push rod 87, and an intake valve 82 and an exhaust valve 83 connected to one end of the rocker arm 86. When the rocker arm 86 swings about an axis parallel to the axial direction, the intake valve 82 and the exhaust valve 83 included in the valve mechanism open and close the ports of the cylinder 6.

[0020] A combustion chamber 9 of the engine 5 is defined by various components such as the inner circumferential surface of the cylinder 6 and the upper end surface of the piston 7. The engine 5 includes an intake pipe 102 and an intake pipe 103, and compressed air Ca supplied to the intake pipe 102 from the intake line 25 (see FIG. 1 ) flows into the combustion chamber 9 via the intake pipe 103.

[0021] The type of engine 5 of the present disclosure is not particularly limited, and for example, a pre-combustion chamber gas engine may be employed. More specifically, the combustion chamber 9 includes a pre-combustion chamber to which fuel gas Fg is supplied and a main combustion chamber in which fuel gas Fg supplied from a separate line is combusted using a combustion flame ignited in the pre-combustion chamber. In the pre-combustion chamber, pre-combustion (pre-combustion) of the fuel gas Fg is primarily caused by the ignition operation of a spark plug 45 (see FIG. 4), and combustion of the fuel gas Fg is completed in the main combustion chamber. Exhaust gas Eg generated by the combustion is discharged into an exhaust gas line 89 (see FIG. 1) via an exhaust pipe 105, which is a component of the engine 5.

[0022] A crank chamber 18 is formed inside the crankcase 20. A portion of the fuel gas Fg supplied to the combustion chamber 9 leaks into the crank chamber 18 as blow-by gas through the gap between the piston 7 and the cylinder 6. The occurrence of an unburned gas explosion in the crank chamber 18 can be suppressed by keeping the concentration of unburned gas, which is the unburned fuel gas Fg in the crank chamber 18, below the lower explosive limit. If the concentration exceeds the lower explosive limit, the risk of an explosion of the unburned gas in the crank chamber 18 increases. The lower explosive limit varies depending on the type of fuel gas Fg, the proportion of hydrogen gas contained in the fuel gas Fg, and the like.

[0023] 1 , the engine system 1 further includes an air supply system 120 for supplying starting air for the engine 5 to the combustion chambers 9 (more specifically, the auxiliary and main combustion chambers) in the cylinders 6. The starting air is air that is sent into the cylinders 6 when the engine 5 starts operating from a stopped state. When the starting air is supplied into the cylinders 6, the crankshaft 16, which had been stopped, starts to rotate.

[0024] The air supply system 120 includes a compressor 129, an air tank 126 that stores compressed air Cb discharged from the compressor 129, and a starting air line 125 for directing the compressed air Cb in the air tank 126 to the combustion chamber 9 as starting air.

[0025] The air supply system 120 of this example further includes an air pressure sensor 128 for measuring the pressure in the air tank 126, a compressed air supply line 127 for guiding compressed air Cb from a compressor 129 to the air tank 126, and a control valve 124 arranged on the compressed air supply line 127. When the measurement value of the air pressure sensor 128 falls below a specified value, the control valve 124 switches from a closed state to an open state, and the compressed air Cb is supplied from the compressor 129 to the air tank 126. Such control of the supply of compressed air Cb may be executed by a controller 90 constituting the engine system 1.

[0026] The air supply system 120 further includes a bleed line 30 for bleeding the compressed air Cb flowing through the starting air line 125 and directing the air to the crank chamber 18 in the crankcase 20. The supply of the compressed air Cb (i.e., starting air) from the starting air line 125 to the combustion chamber 9 ends upon completion of the start of the engine 5. On the other hand, the supply of the compressed air Cb from the bleed line 30 to the crank chamber 18 is performed during steady operation of the engine 5. As a more specific example, when it is determined that the concentration of unburned gas in the crank chamber 18 exceeds the allowable concentration, the compressed air Cb is supplied from the bleed line 30 to the crank chamber 18. Here, the concentration of unburned gas (hereinafter also referred to as unburned gas concentration) may be the concentration of natural gas or the concentration of hydrogen gas, but it is preferable to monitor the concentration of hydrogen gas, which has a low lower explosion limit.

[0027] Even if unburned gas leaks from the combustion chamber 9 into the crank chamber 18, the compressed air Cb flowing into the crank chamber 18 from the bleed line 30 mixes with the unburned gas, and the compressed air Cb is purged. In other words, the unburned gas concentration in the crank chamber 18 is reduced by the compressed air Cb guided to the crank chamber 18 by the bleed line 30. This reduces the risk of unburned gas ignition in the crank chamber 18. Furthermore, because the compressed air Cb flowing through the starting air line 125 provided for starting the engine 5 is used to reduce the unburned gas concentration in the crank chamber 18, the configuration of the engine system 1 can be simplified. As described above, an engine system 1 is realized that reduces the risk of unburned gas ignition in the crank chamber 18 with a simple configuration.

[0028] 1, the engine system 1 will be further described. The engine system 1 further includes a discharge line 60 for guiding a discharge object Eo to the outside. The discharge object Eo is a fluid including fuel gas Fg (i.e., unburned gas) leaking into the crank chamber 18 and compressed air Cb supplied to the crank chamber 18 from the bleed line 30.

[0029] In this example, the discharge target Eo further includes oil mist. Oil mist can be generated when lubricating oil adhering to moving parts such as the shafts, cams, gears, or pistons 7 that make up the engine 5 is scattered. Alternatively, an oil tank (not shown) that stores lubricating oil is located below the crankcase 18, and oil mist can be generated when a portion of the stored lubricating oil in the form of a liquid pool evaporates. Oil mist also floats within the crankcase 18.

[0030] <Outline of Air Supply System 120> Figure 3 is a schematic diagram showing an air supply system 120 according to one embodiment of the present disclosure. The air supply system 120 includes a starting air line 125 for guiding compressed air Cb from an air tank 126 to the combustion chamber 9 in the cylinder 6. In the starting air line 125, an air control valve 203 and an on-off valve 110 are arranged in this order from the upstream side. A bleed line 30 is connected to the starting air line 125 between the air control valve 203 and the on-off valve 110, and a bleed on-off valve 3 is arranged in the bleed line 30.

[0031] When starting the engine system 1, the on-off valve 110 is opened to supply starting air to the combustion chamber 9. When combustion in the combustion chamber 9 resumes normal operation, the on-off valve 110 is closed.

[0032] <Purge Control of Crankcase 18 According to One Embodiment> Fig. 4 is a schematic diagram showing an engine system 1A (1) according to one embodiment. The engine system 1A includes a concentration sensor 51 for measuring a gas concentration correlated with the unburned gas concentration in the crankcase 18. The concentration sensor 51 is configured to measure at least one of the concentration of natural gas or the concentration of hydrogen gas. When the concentrations of both gases are measured, the concentration sensor 51 may be configured with two sensors.

[0033] In this example, the concentration sensor 51 is configured to measure only the concentration of hydrogen gas. More specifically, the concentration sensor 51 is disposed in the crankcase 20 and configured to directly measure the hydrogen gas concentration in the crank chamber 18. That is, in this example, the measurement value of the concentration sensor 51 is treated as the hydrogen gas concentration in the crank chamber 18.

[0034] As another example, the concentration sensor 51 may be configured to measure the concentration of hydrogen gas in any one of the intake pipe 103, the combustion chamber 9, or the exhaust line 60. In this case, the concentration of hydrogen gas in the crankcase 18 is obtained as an estimated value through the measurement by the concentration sensor 51. As a more specific example, a physical model or statistical model that correlates the measurement value of the concentration sensor 51 with the hydrogen gas concentration in the crankcase 18 is used. The physical model is a model based on a static equilibrium equation, a state equation, or the like derived from physical knowledge. The statistical model is a model that uses a neural network, multiple regression analysis, or the like. An example of a statistical model is a machine learning model.

[0035] 4, the bleed air on-off valve 3A (3) of the engine system 1A is controlled in accordance with the measurement result of the concentration sensor 51. More specifically, a bleed air on-off control unit 911, which is a component of the controller 90A (90) of the engine system 1A, controls the bleed air on-off valve 3A. When the unburned gas concentration (hydrogen gas concentration in this example) in the crank chamber 18 determined from the measurement value of the concentration sensor 51 exceeds the allowable concentration, the bleed air on-off control unit 911 controls the bleed air on-off valve 3A so that the bleed air on-off valve 3A switches from a closed state to an open state.

[0036] According to the above configuration, when it is necessary to reduce the unburned gas concentration (hydrogen gas concentration in this example) in the crank chamber 18, the bleed on-off valve 3A switches from a closed state to an open state. This makes it possible to reduce the amount of compressed air Cb bled from the starting air line 125, and to effectively use the compressed air Cb stored in the air tank 126.

[0037] The engine system 1A illustrated in FIG. 4 includes a pressure sensor 52 for measuring the pressure in the crankcase 18. The bleed air on-off valve 3A in this example is a flow rate regulating valve that can adjust the flow rate of compressed air Cb in the bleed air line 30. The bleed air on-off control unit 911 is configured to control the opening degree of the bleed air on-off valve 3A so that the measurement value of the pressure sensor 52 is equal to or less than the allowable pressure. For example, if it is determined that the measurement value of the pressure sensor 52 exceeds the allowable pressure, the bleed air on-off control unit 911 executes control to decrease the opening degree of the bleed air on-off valve 3A. This control may be executed after the measurement value exceeds the allowable pressure or before the measurement value exceeds the allowable pressure. Note that if it is determined that the measurement value of the pressure sensor 52 does not exceed the allowable pressure, the bleed air on-off control unit 911 may execute control to further increase the opening degree of the bleed air on-off valve 3A.

[0038] According to the above-described configuration, the opening degree of the bleed on-off valve 3A is controlled so that the pressure in the crank chamber 18 is equal to or lower than the allowable pressure. This makes it possible to prevent unburned gas, including hydrogen gas, in the crank chamber 18 from leaking from the crankcase 20 via an unintended route other than the exhaust line 60.

[0039] If the bleed air on-off valve 3A is opened through the control of the bleed air on-off control unit 911, thereby allowing compressed air Cb to flow into the crank chamber 18, it is basically possible to reduce the unburned gas concentration (hydrogen gas concentration in this example) in the crank chamber 18 to a permissible concentration or lower. However, even if compressed air Cb is allowed to flow into the crank chamber 18, the unburned gas concentration determined from the measurement value of the concentration sensor 51 may still exceed the permissible concentration. In this case, control is performed to change the combustion environment of the engine 5. Specifically, control is performed to change the ignition timing of the spark plug 45, control the flow rate of compressed air Ca flowing into the combustion chamber 9 from the air intake line 25, and control the supply amount of fuel gas Fg. Specific configurations for performing these controls will be described below.

[0040] The control for changing the ignition timing will now be described. The engine system 1A includes a phase sensor 53 (see FIG. 2) for measuring the rotational angle phase of the crankshaft 16. The controller 90A (see FIG. 4) further includes an ignition control unit 913 for controlling the spark plug 45 based on the rotational angle phase measured by the phase sensor 53. Through the control of the ignition control unit 913, the spark plug 45 periodically performs an ignition operation.

[0041] If the unburned gas concentration (in this example, the hydrogen gas concentration) still does not fall below the allowable concentration even after compressed air Cb has flowed into the crank chamber 18, the ignition control unit 913 is configured to advance the ignition timing of the spark plug 45 compared to when the unburned gas concentration is below the allowable concentration.

[0042] In this example, if the unburned gas concentration (hydrogen gas concentration in this example) is below the permissible concentration while the engine 5 is running, the first ignition control unit controls the spark plug 45. Furthermore, even after the unburned gas concentration exceeds the permissible concentration, the first ignition control unit continues to control the spark plug 45 as long as it is determined that the unburned gas concentration will not fall below the permissible concentration even if compressed air Cb is supplied to the crank chamber 18. On the other hand, if it is determined that the unburned gas concentration will not fall below the permissible concentration, the second ignition control unit controls the spark plug 45 instead of the first ignition control unit.

[0043] According to the above configuration, if the unburned gas concentration (hydrogen gas concentration in this example) in the crank chamber 18 still does not reach or exceed the permissible concentration even after the bleed air on-off valve 3A is opened through the control of the bleed air on-off control unit 911, the ignition timing of the spark plug 45 is advanced. As a result, the fuel gas Fg in the combustion chamber 9 changes to exhaust gas Eg at an earlier timing, reducing the concentration of unburned gas leaking into the crank chamber 18. Therefore, the unburned gas concentration in the crank chamber 18 can be reduced to or below the permissible concentration.

[0044] Continuing to refer to FIG. 4 , the flow rate control of the compressed air Ca flowing into the combustion chamber 9 will be described. The engine system 1A further includes an intake flow control valve 253 arranged on the second intake line 252 of the intake line 25. The controller 90A also includes an intake air amount control unit 914 for controlling the intake air flow control valve 253. The intake air amount control unit 914 is configured to control the intake air flow control valve 253 so as to increase the flow rate of the compressed air Ca in the intake line 25 if the unburned gas concentration (hydrogen gas concentration in this example) remains above the permissible concentration even after the compressed air Cb flows into the crank chamber 18. Note that the intake air flow control valve 253 may be arranged on the first intake line 251 instead of the second intake line 252.

[0045] According to the above configuration, if the unburned gas concentration (hydrogen gas concentration in this example) in the crank chamber 18 still does not reach or fall below the permissible concentration even after the bleed on-off valve 3A is opened through the control of the bleed on-off control unit 911, the flow rate of the compressed air Ca supplied to the combustion chamber 9 increases, thereby reducing the concentration of unburned gas leaking from the combustion chamber 9 to the crank chamber 18. This makes it possible to reduce the unburned gas concentration in the crank chamber 18 to or below the permissible concentration.

[0046] Continuing to refer to FIG. 4 , the control of the supply amount of fuel gas Fg will be described. The controller 90A further includes a fuel gas amount control unit 915 for controlling the fuel gas flow regulation valve 73. The fuel gas amount control unit 915 is configured to control the fuel gas flow regulation valve 73 so as to reduce the flow rate of fuel gas Fg in the fuel gas line 11 if the unburned gas concentration (hydrogen gas concentration in this example) does not fall below the allowable concentration even after compressed air Cb flows into the crank chamber 18. Several specific examples of control of the fuel gas flow regulation valve 73 are described below.

[0047] For example, when co-combustion of natural gas and hydrogen gas occurs in the combustion chamber 9, it is preferable to reduce the supply amount of hydrogen gas, which has a relatively low lower explosion limit concentration. The fuel gas quantity control unit 915 controls the second fuel flow regulation valve 73b so as to reduce the aperture of the second fuel flow regulation valve 73b (at this time, the second fuel flow regulation valve 73b may not be closed, and the second fuel flow regulation valve 73b may be maintained in an open state). Alternatively, control to reduce the supply amount of natural gas may also be executed at the same time. That is, the fuel gas quantity control unit 915 may control the first fuel flow regulation valve 73a so as to reduce the aperture of the first fuel flow regulation valve 73a.

[0048] As another example, when the mono-combustion of the second fuel gas fg2 occurs in the combustion chamber 9, the fuel gas quantity control unit 915 may execute control to reduce the opening degree of only the second fuel flow regulating valve 73b out of the first fuel flow regulating valve 73a and the second fuel flow regulating valve 73b.

[0049] According to the above configuration, if the unburned gas concentration (hydrogen gas concentration in this example) in the crank chamber 18 still does not fall below the permissible concentration even after the bleed on-off valve 3A is opened through the control of the bleed on-off control unit 911, the flow rate of the fuel gas Fg supplied to the combustion chamber 9 is reduced, and the ratio of the amount of fuel gas Fg supplied to the amount of compressed air Ca supplied to the combustion chamber 9 decreases. Therefore, the concentration of unburned gas leaking from the combustion chamber 9 to the crank chamber 18 is reduced. This makes it possible to reduce the unburned gas concentration in the crank chamber 18 to the permissible concentration or below.

[0050] Note that if the unburned gas concentration (hydrogen gas concentration in this example) does not fall below the allowable concentration even after the fuel gas quantity control unit 915 has executed control of the fuel gas flow adjustment valve 73, the supply of hydrogen gas may be stopped by the fuel valve control unit 916, a component of the controller 90A. For example, when mixed combustion of natural gas and hydrogen gas is occurring in the combustion chamber 9, the fuel valve control unit 916 may control the second fuel on-off valve 77b so that the second fuel on-off valve 77b changes from an open state to a closed state. As a result, while the first fuel on-off valve 77a remains open, the second fuel on-off valve 77b changes from an open state to a closed state. In other words, combustion in the combustion chamber 9 changes from mixed combustion of natural gas and hydrogen gas to mono-combustion of natural gas.

[0051] According to the above configuration, if the unburned gas concentration (hydrogen gas concentration in this example) in the crank chamber 18 still does not fall below the permissible concentration even after the flow rate of the fuel gas Fg is reduced through the control of the fuel gas amount control unit 915, the second fuel on-off valve 77b switches from the open state to the closed state. This reduces the amount of hydrogen gas contained in the unburned gas leaking from the combustion chamber 9 to the crank chamber 18, thereby reducing the risk of the unburned gas igniting in the crank chamber 18.

[0052] 5 and 6, the crankcase purge control executed by the controller 90A will be described. The crankcase purge control is a control for reducing the unburned gas concentration in the crankcase 18 to an allowable concentration or less by purging the unburned gas in the crankcase 18 with compressed air Cb. This control is periodically started, for example, while the engine 5 is performing steady operation. Here, it is assumed that natural gas and hydrogen gas are being mixed and burned in the combustion chamber 9 during steady operation of the engine 5. Before the crankcase purge control is started, the air control valve 203, the first pilot control valve 201, and the second pilot control valve 202 are all in a closed state.

[0053] The crankcase purge control is executed by a processor (hereinafter, sometimes simply referred to as the "processor") that constitutes the controller 90A. Hereinafter, "step" may be abbreviated as "S."

[0054] First, the processor determines whether the unburned gas concentration (hydrogen gas concentration in this example) in the crank chamber 18 obtained from the measurement value of the concentration sensor 51 is equal to or lower than the allowable concentration (S11). If it is determined that the unburned gas concentration is equal to or lower than the allowable concentration (S11: YES), the processor ends the crank chamber purge control.

[0055] On the other hand, if it is determined that the unburned gas concentration exceeds the allowable concentration (S11: NO), the processor executes control to switch the bleed air on-off valve 3A from the closed state to the open state (S13). In S13, the processor may control the opening degree of the bleed air on-off valve 3A so that the measurement value of the pressure sensor 52 becomes equal to or less than the allowable pressure. The processor that executes S13 is an example of the bleed air on-off control unit 911.

[0056] Next, the processor again determines whether the unburned gas concentration in the crank chamber 18 is equal to or lower than the permissible concentration (S15). S15 is the same process as S11. If the unburned gas concentration is equal to or lower than the permissible concentration (S15: YES), the processor ends the crank chamber purge control. On the other hand, if the unburned gas concentration still exceeds the permissible concentration (S15: NO), the processor executes engine control to change the combustion environment of the engine 5 (S17).

[0057] The engine control will be described with reference to Figure 6. The processor switches the ignition timing of the spark plug 45 from the first ignition timing to the second ignition timing (S31). Next, the processor controls the intake air flow control valve 253 to increase the flow rate of compressed air Ca in the intake line 25 (S33). Thereafter, the processor controls the fuel gas flow control valve 73 to decrease the flow rate of fuel gas Fg in the fuel gas line 11 (S35). The processor that executes S31 is an example of the ignition control unit 913, the processor that executes S33 is an example of the intake air amount control unit 914, and the processor that executes S35 is an example of the fuel gas amount control unit 915.

[0058] Next, the processor determines whether the unburned gas concentration has fallen below the allowable concentration (S37). S37 is the same process as S11. If the unburned gas concentration has fallen below the allowable concentration (S37: YES), the processor returns to the crankcase purge control and ends the process. On the other hand, if the unburned gas concentration still exceeds the allowable concentration (S37: NO), the processor executes control to switch the second fuel on-off valve 77b from the open state to the closed state (S39). This switches the combustion in the combustion chamber 9 from a mixed combustion of natural gas and hydrogen gas to a single combustion of natural gas. Because hydrogen gas is no longer supplied to the combustion chamber 9, the unburned gas concentration falls below the allowable concentration. The processor returns to the crankcase purge control and ends the process. The processor executing S39 is an example of the fuel valve control unit 916.

[0059] In engine control, at least one of S31, S33, and S35 may be executed. For example, S31 and S33 may be executed without S35 being executed. Alternatively, even if S31, S33, and S35 are all executed, a determination process similar to S11 may be executed after each step is executed. For example, after S31 is executed and before S33 is executed, it may be determined whether the unburned gas concentration is equal to or lower than the permissible concentration. If it is determined that the unburned gas concentration is equal to or lower than the permissible concentration, the processor may return to crank chamber purge control and end the process without executing the processes from S33 onward.

[0060] <Purge control of crank chamber 18 according to another embodiment> Fig. 7 is a schematic diagram showing an engine system 1B (1) according to another embodiment. In Fig. 7, the same components as those in engine system 1A (see Fig. 4) are given the same reference numerals, and the description thereof will be omitted or simplified below.

[0061] The bleed air on-off valve 3B (3) of the engine system 1B is an on-off valve and does not have the function of continuously adjusting the flow rate of the compressed air Cb. The flow rate of the compressed air Cb is adjusted by a flow rate adjustment valve 4 arranged on the bleed air line 30. The controller 90B (90) of the engine system 1B has a flow rate adjustment control unit 912 for controlling the aperture of the flow rate adjustment valve 4. The flow rate adjustment control unit 912 is configured to control the aperture of the flow rate adjustment valve 4 so that the measurement value of the pressure sensor 52 is equal to or less than the allowable pressure. The flow rate adjustment control unit 912 is realized by a processor controlling the flow rate adjustment valve 4 (a detailed description of the control flow will be omitted).

[0062] The controller 90B may include at least one of the ignition control unit 913, the air supply amount control unit 914, the fuel gas amount control unit 915, and the fuel valve control unit 916 described with reference to FIG.

[0063] <Crankcase 20 (First Embodiment)> Figure 8 is a schematic diagram showing the crankcase 20A (20) of the engine 5A (5) according to the first embodiment. In the example of Figure 8, the bleed on-off valve 3 arranged on the bleed line 30 is omitted (the same applies to Figures 9, 11, and 12).

[0064] The crankcase 20A has a first side wall portion 21A (21) which is an end portion on one side in the axial direction, and a second side wall portion 22A (22) which is an end portion opposite to the first side wall portion 21. A first side inlet 37A (37) to which the extraction line 30A is connected is formed in the first side wall portion 21A (21), and a second side outlet 68 is formed in the second side wall portion 22A (22).

[0065] According to the above configuration, the compressed air Cb that has passed through the one-side inlet 37A flows axially through the crank chamber 18, and then flows through the other-side outlet 68 and into the discharge line 60. Because the unburned gas and the compressed air Cb tend to mix axially within the crank chamber 18, the compressed air Cb is likely to be discharged together with the unburned gas into the discharge line 60. This makes it possible to uniformly reduce the concentration of unburned gas within the crank chamber 18.

[0066] In the example of FIG. 8 , at least a portion of the one-side inlet 37A (37) is disposed at the same height as the other-side outlet 68. In the example shown, both the one-side inlet 37A and the other-side outlet 68 are disposed at positions higher than the crankshaft 16, but the present disclosure is not limited to this. For example, the one-side inlet 37A may be disposed at a lower position than the crankshaft 16, or at least a portion of the one-side inlet 37A may be disposed at the same height as the crankshaft 16. Alternatively, both the one-side inlet 37A and the other-side outlet 68 may be disposed at positions lower than the crankshaft 16.

[0067] With the configuration in which the one-side inlet 37A is positioned lower than the other-side outlet 68, the compressed air Cb flowing through the crank chamber 18 also moves upward as it flows toward the other-side outlet 68. This allows the compressed air Cb to be distributed throughout the crank chamber 18, making it easier for both the compressed air Cb and unburned gas to be discharged into the discharge line 60. This allows the concentration of unburned gas to be uniformly reduced within the crank chamber 18.

[0068] <Crankcase 20 (Second Embodiment)> Figure 9 is a schematic diagram showing a crankcase 20B (20) of an engine 5B (5) according to a second embodiment. In Figure 9, the same components as those in the engine 5A (see Figure 8) are given the same reference numerals, and their descriptions will be omitted or simplified below.

[0069] The bleed line 30B of the engine 5B has a first bleed line 31 and a second bleed line 32. The first bleed line 31 is connected to the starting air line 125 and one side wall portion 21B (21) of the crankcase 20B. That is, the first bleed line 31 is configured to guide the compressed air Cb bled from the starting air line 125 to the one side wall portion 21B. The second bleed line 32 branches off from the first bleed line 31 and connects to the other side wall portion 22B (22) of the crankcase 20B. That is, the second bleed line 32 is configured to guide the compressed air Cb bled from the first bleed line 31 to the other side wall portion 22B.

[0070] A one-side inlet 37B (37) to which the one-side bleed line 31 is connected is formed in the one-side wall portion 21B, and a other-side inlet 38 to which the other-side bleed line 32 is connected is formed in the other-side wall portion 22B. In the illustrated example, at least a portion of the one-side inlet 37B (37) is disposed at the same height as the other-side inlet 38.

[0071] 9 , both the first inlet 37B and the second inlet 38 are positioned higher than the crankshaft 16, but the present disclosure is not limited to this. The first inlet 37B may be positioned lower than the crankshaft 16, or at least a portion of the first inlet 37B may be positioned at the same height as the crankshaft 16. Alternatively, both the first inlet 37B and the second inlet 38 may be positioned lower than the crankshaft 16.

[0072] According to the above configuration, the compressed air Cb flows into the crank chamber 18 from both sides in the axial direction, and therefore the compressed air Cb can be distributed throughout the crank chamber 18. This makes it possible to uniformly reduce the concentration of unburned gas within the crank chamber 18.

[0073] Continuing with the description of the configuration of the engine 5B, the discharge line 60 illustrated in Fig. 9 includes a first discharge line 61 connected to the first side wall portion 21B and a second discharge line 62 connected to the second side wall portion 22B. A first discharge port 67 to which the first discharge line 61 is connected is formed in the first side wall portion 21B, and a second discharge port 68 to which the second discharge line 62 is connected is formed in the second side wall portion 22B.

[0074] In this example, at least a portion of the one-side discharge port 67 is disposed at a higher position than the other-side discharge port 68, more specifically, the entire one-side discharge port 67 is disposed at a higher position than the other-side discharge port 68. Also, at least a portion of the one-side discharge port 67 is disposed at a higher position than the one-side inlet 37B (37), more specifically, the entire one-side discharge port 67 is disposed at a higher position than the one-side inlet 37B. Also, in this example, at least a portion of the other-side discharge port 68 is disposed at the same height as the other-side inlet 38.

[0075] FIG. 10 is a conceptual perspective view of the crankcase 20B (the crankshaft 16 is not shown). In an axial view, the first inlet 37B and the second outlet 68 are positioned offset from each other in the horizontal direction (hereinafter sometimes referred to as the width direction). In an axial view, the second inlet 38 and the first outlet 67 are positioned offset from each other in the width direction. In the illustrated example, the first inlet 37B and the second inlet 38 are positioned on a first widthwise side relative to the center of the crankcase 20. The first outlet 67 and the second outlet 68 are positioned on a second widthwise side opposite the first widthwise side relative to the center of the crankcase 20. The width direction is a horizontal direction perpendicular to the axial direction.

[0076] In this example, at least a portion of the compressed air Cb introduced from the one-side inlet 37B to the crank chamber 18 passes through the other-side outlet 68 as the discharge object Eo. The discharge object Eo that passes through the other-side outlet 68 is discharged to the outside via the other-side discharge line 62. Similarly, at least a portion of the compressed air Cb introduced from the other-side inlet 38 to the crank chamber 18 passes through the one-side outlet 67 as the discharge object Eo. The discharge object Eo that passes through the one-side discharge port 67 is discharged to the outside via the one-side discharge line 61.

[0077] According to the above configuration, the compressed air Cb flowing into the crank chamber 18 from the one-side inlet 37 is likely to spread horizontally within the crank chamber 18 as it flows toward the other-side outlet 68. Similarly, the compressed air Cb flowing into the crank chamber 18 from the other-side inlet 38 is likely to spread horizontally within the crank chamber 18 as it flows toward the one-side outlet 67. This makes it easier for unburned gas within the crank chamber 18 to be discharged from the one-side outlet 67 and the other-side outlet 68, thereby making it possible to uniformly reduce the concentration of unburned gas within the crank chamber 18.

[0078] <Crankcase 20 (Third Embodiment)> Figure 11 is a schematic diagram of an engine 5C (5) according to a third embodiment, showing a plan view of the engine 5C. The engine 5C has a first side wall portion 21C (21) at one end in the axial direction, a second side wall portion 22C (22) at the end opposite the first side wall portion 21C, and a side wall portion 23 connected to the first side wall portion 21C and the second side wall portion 22C. The side wall portion 23 is an end of the crankcase 20C on a first side in the width direction.

[0079] The bleed air line 30C (30) according to the third embodiment has a side bleed air line 33 that connects to the starting air line 125 and the side wall portion 23. A side inlet port 39 to which the side bleed air line 33 connects is formed in the central portion 24 of the side wall portion 23 in the axial direction. The side bleed air line 33 is configured to guide compressed air Cb bled from the starting air line 125 to the side inlet port 39.

[0080] 11 includes a one-side discharge line 61 connected to one side wall portion 21C (21) and a second-side discharge line 62 connected to the other side wall portion 22C (22). A one-side discharge port 67 and a second-side discharge port 68 are formed in one side wall portion 21C and the other side wall portion 22C, respectively.

[0081] According to the above configuration, the compressed air Cb that flows into the crank chamber 18 from the side inlet port 39 formed in the central portion 24 of the side wall portion 23 can flow toward one side and the other side in the axial direction. This allows the compressed air Cb to be distributed throughout the crank chamber 18, making it easier for unburned gas in the crank chamber 18 to be discharged from the one-side discharge port 67 and the other-side discharge port 68. This makes it possible to uniformly reduce the concentration of unburned gas in the crank chamber 18. Note that the bleed line 30C may further include, in addition to the side bleed line 33, at least one of a plurality of connecting bleed lines 35 (see FIG. 12 ) according to a fourth embodiment described below. Even in this case, the above-described technical advantages can be obtained.

[0082] <Crankcase 20 (Fourth Embodiment)> Figure 12 is a schematic diagram of an engine 5D (5) according to the fourth embodiment, showing a plan view of the engine 5D. The engine 5D is a V-type multi-cylinder engine in which a plurality of cylinder units 8 are arranged along the axial direction. The cylinder units 8 of the engine 5D include a plurality of cylinder units 8A arranged on a first side in the width direction from the axis of the crankshaft 16, and a plurality of cylinder units 8B arranged on a second side in the width direction from the axis. The number of cylinder units 8A is the same as the number of cylinder units 8B.

[0083] The crankcase 20D (20) of the engine 5D has one side wall portion 21D (21) which is an end portion on one side in the axial direction, the other side wall portion 22D (22) which is an end portion opposite the one side wall portion 21D, a first side wall portion 27 which is an end portion on the first side in the width direction, and a second side wall portion 26 which is an end portion opposite the first side wall portion 27.

[0084] The engine 5D further has at least one partition wall 29. The partition wall 29 extends in the width direction and connects to the first side wall 27 and the second side wall 26. Furthermore, the partition wall 29 separates one or more of the plurality of cylinder units 8 from the other cylinder units 8 in a plan view.

[0085] As a more specific example, the cylinder unit 8 shown in FIG. 12 includes multiple pairs of cylinder units 8, each pair being axially adjacent cylinder units 8A, 8B. Each of the multiple partition walls 29 is arranged to separate each pair of cylinder units 8 from the other pairs of cylinder units 8. In the crank chamber 18, the multiple partition walls 29 form spaces 17, the number of which is half the number of cylinders of the engine 5D. A pair of cylinder units 8 is arranged in each space 17 in plan view. For example, if the engine 5D has 18 cylinders, the crank chamber 18 is divided into nine spaces 17 (the number of partition walls 29 is eight). However, the partition walls 29 of the present disclosure are not limited to the above embodiment. The number of partition walls 29 may be two (not shown). In this case, the crank chamber 18 is divided into three spaces 17, and three pairs of cylinder units 8 are arranged in each space 17. As yet another example, the number of partition wall portions 29 may be one (not shown).

[0086] The bleed line 30D of the engine 5D includes a plurality of connecting bleed lines 35 that connect to the first side wall portion 27 so as to communicate with each of the plurality of spaces 17. In addition, the exhaust line 60 of the engine 5D includes a plurality of connecting exhaust lines 65 that connect to the second side wall portion 26 so as to communicate with each of the plurality of spaces 17.

[0087] The first side wall portion 27 is formed with a plurality of side inlets 41 to which the plurality of connecting bleed lines 35 are respectively connected, and the second side wall portion 26 is formed with a plurality of side outlets 42 to which the plurality of connecting exhaust lines 65 are respectively connected. In each space 17, the side inlets 41 may be arranged at a lower position than the side outlets 42. However, the present disclosure is not limited to this, and the side inlets 41 may be arranged at a higher position than the side outlets 42, or the side inlets 41 and the side outlets 42 may be arranged at the same height.

[0088] According to the above configuration, one or more cylinder units 8 are arranged in each of the multiple spaces 17 separated by the partition wall portions 29 in a plan view, which may result in leakage of unburned gas into each space 17. However, compressed air Cb flows into each space 17 from each connecting bleed line 35, and in each space 17, a discharge target Eo containing compressed air Cb and unburned gas is discharged via each connecting discharge line 65. Since it is possible to more reliably dilute the unburned gas in each space 17 with compressed air Cb, the risk of ignition of unburned gas in the crank chamber 18 can be reduced. Note that the above technical advantages can be obtained even if the engine 5D is an in-line multi-cylinder engine.

[0089] <Crankcase 20 (Fifth Embodiment)> Figure 13 is a schematic diagram of an engine 5E (5) according to a fifth embodiment. In this figure, the same components as those in the engine 5D are assigned the same reference numerals. The discharge line 60 shown in this figure includes a first discharge line 61 connected to a first discharge port 67 formed in the first side wall portion 21D, and a second discharge line 62 connected to a second discharge port 68 in the second side wall portion 22D. The first discharge line 61 is configured to guide the discharge objects Eo discharged from the first discharge port 67 to the outside. The second discharge line 62 is configured to guide the discharge objects Eo discharged from the second discharge port 68 to the outside.

[0090] According to the above configuration, the compressed air that flows into the crank chamber 20E (20) from the side inlet 41 can flow toward both sides in the axial direction, thereby allowing the compressed air to be distributed throughout the crank chamber 20E, thereby uniformly reducing the concentration of unburned gas within the crank chamber 20E.

[0091] <Another embodiment> An engine system 1C(1) according to another embodiment will be described with reference to Fig. 14. The engine system 1C includes an exhaust gas line 990 for guiding exhaust gas Eg discharged from the combustion chamber 9 to the turbine wheel 14, a bypass exhaust gas line 991 for extracting the exhaust gas flowing through the exhaust gas line 990 and discharging the exhaust gas to the outside while bypassing the turbine wheel 14, and a bypass flow adjustment valve 993 for controlling the flow rate of exhaust gas flowing through the bypass exhaust gas line.

[0092] The controller 90C (90) includes a bypass exhaust gas amount control unit 917. If the unburned gas concentration determined from the measurement value of the concentration sensor 51 does not become equal to or lower than the permissible concentration even after the bleed air on-off valve 3 is opened through the control of the bleed air on-off control unit 911, the bypass exhaust gas amount control unit 917 controls the bypass flow adjustment valve 993 so as to reduce the flow rate of exhaust gas flowing through the bypass exhaust gas line 991.

[0093] According to the above configuration, if the unburned gas concentration in the crank chamber 18 does not become equal to or lower than the permissible concentration even after the bleed air on-off valve 3 is opened through the control of the bleed air on-off control unit 911, the bypass exhaust gas amount control unit 917 controls the bypass flow adjustment valve 993 to increase the flow rate of the exhaust gas Eg supplied to the turbine wheel 14. This increases the rotation speed of the compressor wheel 12 and increases the flow rate of the compressed air Ca supplied to the combustion chamber 9, thereby reducing the concentration of unburned gas leaking from the combustion chamber 9 to the crank chamber 18. This makes it possible to reduce the unburned gas concentration in the crank chamber 18 to the permissible concentration or lower.

[0094] <Others> The supercharger 15 does not have to include the turbine wheel 14. The supercharger 15 may be an electric compressor including a rotor shaft 13 and a compressor wheel 12 connected to the rotor shaft 13.

[0095] The controller 90 described above is configured by a computer and includes a processor, a memory (storage medium), and an external communication interface. The processor may be a CPU, a GPU, an MPU, a DSP, or a combination thereof. The processor according to other embodiments may be implemented by an integrated circuit such as a PLD, an ASIC, an FPGA, or an MCU. The memory is configured to temporarily or non-temporarily store various data and may be implemented by at least one of a RAM, a ROM, or a flash memory, for example. The processor executes various control processes according to instructions from a program loaded into the memory.

[0096] <Summary> The contents described in the above-described embodiments can be understood, for example, as follows.

[0097] 1) An engine system (1) according to at least one embodiment of the present disclosure comprises: an engine (5) including a cylinder (6) and a piston (7) housed in the cylinder; an air supply system (120) including an air tank (126) and a starting air line (125) for guiding compressed air (Cb) stored in the air tank into the cylinder as starting air for the engine; and a fuel gas supply system (70) for supplying fuel gas (Fg) into the cylinder, wherein the engine further includes: a crankshaft (16) positioned below the piston and configured to be driven by the piston; and a crankcase (20) accommodating the crankshaft; and the air supply system further includes a bleed line (30) for bleeding the compressed air flowing through the starting air line and guiding the compressed air to a crank chamber in the crankcase.

[0098] According to the configuration of 1) above, even if unburned gas, which is unburned fuel gas, leaks from the combustion chamber to the crankcase, the concentration of unburned gas in the crankcase is reduced by the compressed air led to the crankcase by the bleed line. This reduces the risk of unburned gas ignition in the crankcase. Furthermore, because the compressed air flowing through the starting air line provided for starting the engine is used to reduce the concentration of unburned gas in the crankcase, the configuration of the engine system can be simplified. As described above, an engine system is realized that reduces the risk of unburned gas ignition in the crankcase with a simple configuration.

[0099] 2) In some embodiments, in the engine system described in 1) above, the air supply system further includes a bleed air on-off valve (3) arranged on the bleed line, and the engine system further includes: a concentration sensor (51) for measuring a gas concentration correlated with an unburned gas concentration, which is the concentration of the fuel gas in an unburned state in the crankcase; and a bleed air on-off control unit (911) for controlling the bleed air on-off valve so that the bleed air on-off valve switches from a closed state to an open state when the unburned gas concentration in the crankcase, which is determined from the measurement value of the concentration sensor, exceeds an allowable concentration.

[0100] According to the configuration of 2) above, when it is necessary to reduce the concentration of unburned gas in the crankcase, the bleed valve switches from a closed state to an open state, thereby reducing the amount of compressed air bled from the starting air line and allowing for effective use of the compressed air stored in the air tank.

[0101] 3) In some embodiments, the engine system described in 2) above, further includes a pressure sensor (52) for measuring the pressure in the crankcase, and the bleed air opening / closing control unit is configured to control the opening of the bleed air opening / closing valve so that the measurement value of the pressure sensor is equal to or less than an allowable pressure.

[0102] According to the configuration of 3), the opening of the bleed valve is controlled so that the pressure in the crankcase is equal to or lower than the allowable pressure, thereby preventing unburned gas in the crankcase from leaking to the outside via an unintended route.

[0103] 4) In some embodiments, in the engine system described in 2) above, the air supply system further includes a flow control valve (4) arranged on the bleed line, and the engine system further includes a pressure sensor (52) for measuring the pressure in the crankcase, and a flow control unit (912) for controlling the opening of the flow control valve so that the measurement value of the pressure sensor is equal to or less than an allowable pressure.

[0104] According to the configuration of 4), the opening of the flow control valve is controlled so that the pressure in the crank chamber is equal to or lower than the allowable pressure, thereby preventing unburned gas in the crank chamber from leaking to the outside via an unintended route.

[0105] 5) In some embodiments, the engine system is the engine system described in any one of 2) to 4) above, wherein the engine further includes an ignition plug (45) disposed in the combustion chamber (9), and the engine system further includes: a phase sensor (53) for measuring a rotational angle phase of the crankshaft; and an ignition control unit (913) for controlling the spark plug based on the rotational angle phase measured by the phase sensor, and the ignition control unit is configured to advance the ignition timing of the spark plug when the unburned gas concentration in the crank chamber, which is determined from the measurement value of the concentration sensor, does not become equal to or lower than the permissible concentration even after the bleed air opening / closing valve is set to the open state through control of the bleed air opening / closing control unit, compared to when the unburned gas concentration is equal to or lower than the permissible concentration.

[0106] According to the configuration of 5) above, if the unburned gas concentration in the crankcase does not fall below the permissible concentration even after the bleed air on-off valve is opened through the control of the bleed air on-off control unit, the ignition timing of the spark plug is advanced. This reduces the concentration of unburned gas leaking from the combustion chamber to the crankcase, making it possible to keep the unburned gas concentration in the crankcase below the permissible concentration.

[0107] 6) In some embodiments, the engine system according to any one of 2) to 5) above further comprises: a turbocharger (15) including a compressor wheel (12) for delivering compressed air; an air intake line (25) for guiding the compressed air from the compressor wheel into the cylinder; an air intake flow control valve (253) arranged on the air intake line; and an air intake amount control unit (914) for controlling the air intake flow control valve so as to increase the flow rate of the compressed air in the air intake line when the unburned gas concentration calculated from the measurement value of the concentration sensor does not become equal to or lower than the permissible concentration even after the bleed air opening / closing valve is set to the open state through the control of the bleed air opening / closing control unit.

[0108] According to the configuration of 6) above, if the unburned gas concentration in the crankcase does not fall below the permissible concentration even after the bleed on-off valve is opened through the control of the bleed on-off control unit, the flow rate of compressed air supplied to the combustion chamber increases, thereby reducing the concentration of unburned gas leaking from the combustion chamber to the crankcase, thereby making it possible to keep the unburned gas concentration in the crankcase below the permissible concentration.

[0109] 7) In some embodiments, the engine system described in 2) above further includes: a turbocharger (15) including a compressor wheel (12) and a turbine wheel (13) for driving the compressor wheel; an exhaust gas line (990) for guiding exhaust gas (Eg) discharged from the engine to the turbine wheel; a bypass exhaust gas line (991) for bleeding the exhaust gas flowing through the exhaust gas line and discharging the exhaust gas to the outside, bypassing the turbine wheel; a bypass flow adjustment valve (993) for controlling the flow rate of the exhaust gas flowing through the bypass exhaust gas line; and a bypass exhaust gas amount control unit (917) for controlling the bypass flow adjustment valve so as to reduce the flow rate of the exhaust gas flowing through the bypass exhaust gas line when the unburned gas concentration calculated from the measurement value of the concentration sensor does not become equal to or lower than the allowable concentration even after the bleeding open / close valve is set to the open state through the control of the bleeding open / close control unit.

[0110] According to the configuration of 7) above, if the unburned gas concentration in the crankcase does not fall below the permissible concentration even after the bleed air on-off valve is opened through the control of the bleed air on-off control unit, the bypass flow adjustment valve is controlled by the bypass exhaust gas amount control unit to increase the flow rate of exhaust gas supplied to the turbine wheel. This increases the rotation speed of the compressor wheel and the flow rate of compressed air supplied to the combustion chamber, thereby reducing the concentration of unburned gas leaking from the combustion chamber to the crankcase. This makes it possible to reduce the unburned gas concentration in the crankcase to the permissible concentration or below.

[0111] 8) In some embodiments, in the engine system described in any one of 2) to 7) above, the fuel gas supply system further includes a fuel gas line (11) for guiding the fuel gas into the cylinder, a fuel gas flow regulating valve (73) arranged on the fuel gas line, and a fuel gas amount control unit (915) for controlling the fuel gas flow regulating valve so as to reduce the flow rate of the fuel gas in the fuel gas line when the unburned gas concentration calculated from the measurement value of the concentration sensor does not become equal to or lower than the allowable concentration even after the bleeding opening / closing valve is set to the open state through the control of the bleeding opening / closing control unit.

[0112] According to the configuration of 8) above, if the unburned gas concentration in the crankcase does not become equal to or less than the permissible concentration even after the bleed on-off valve is opened through the control of the bleed on-off control unit, the flow rate of fuel gas supplied to the combustion chamber is reduced, thereby reducing the concentration of unburned gas leaking from the combustion chamber to the crankcase, thereby making it possible to make the unburned gas concentration in the crankcase equal to or less than the permissible concentration.

[0113] 9) In some embodiments, in the engine system described in 8) above, the fuel gas supply system includes: a first fuel gas line (11a) for guiding a first fuel gas to a combustion chamber (9) of the engine; a first fuel on-off valve (77a) arranged on the first fuel gas line; a second fuel gas line (11b) for guiding a second fuel gas having a lower explosion limit concentration than the first fuel gas to the combustion chamber; and a second fuel on-off valve (77b) arranged on the second fuel gas line; when the bleeding on-off control unit controls the bleeding on-off valve, at least the second fuel on-off valve of the first fuel on-off valve or the second fuel on-off valve is in an open state; and the engine system further includes a fuel valve control unit (916) for controlling the second fuel on-off valve so that the second fuel on-off valve changes from the open state to a closed state when the unburned gas concentration calculated from the measurement value of the concentration sensor does not become equal to or lower than the allowable concentration even after the flow rate of the fuel gas is reduced through the control of the fuel gas quantity control unit.

[0114] According to the configuration of 9) above, if the unburned gas concentration in the crank chamber does not become equal to or lower than the permissible concentration even after the flow rate of the fuel gas is reduced through the control of the fuel gas amount control unit, the second fuel on-off valve is switched from the open state to the closed state. This reduces the proportion of the second fuel gas contained in the unburned gas leaking from the combustion chamber to the crank chamber, thereby reducing the risk of ignition of the unburned gas in the crank chamber.

[0115] 10) In some embodiments, the engine system is one of the engine systems described in any one of 1) to 9) above, wherein the engine is a multi-cylinder engine in which a plurality of cylinder units (8), each including the cylinder and the piston, are arranged along the axial direction of the crankshaft, and the engine system further includes a discharge line (60) for guiding a discharge object (Eo), which is a fluid including the compressed air in the crank chamber, to the outside, and the crankcase has a one side wall portion (21) which is an end portion on one side in the axial direction, and a other side wall portion (22) which is an end portion opposite to the one side wall portion, and a one side inlet (37) to which the bleed line is connected is formed in the one side wall portion, and a other side outlet (68) to which the discharge line is connected is formed in the other side wall portion.

[0116] According to the configuration of 10), the compressed air that has passed through the inlet on one side flows in the axial direction through the crank chamber, and then flows through the outlet on the other side and into the discharge line. Since the unburned gas and compressed air tend to mix in the axial direction within the crank chamber, the concentration of unburned gas can be uniformly reduced within the crank chamber.

[0117] 11) In some embodiments, in the engine system described in 10), the one-side inlet is positioned lower than the other-side outlet.

[0118] According to the configuration of 11), the compressed air flowing through the crank chamber also moves upward as it flows toward the other exhaust port, thereby enabling the compressed air to be distributed throughout the crank chamber, thereby uniformly reducing the concentration of unburned gas within the crank chamber.

[0119] 12) In some embodiments, the engine system according to 10) or 11) above further comprises: a one-side discharge line (61) connected to the one side wall portion and for guiding the discharge object to the outside; and a other-side discharge line (62) connected to the other side wall portion and for guiding the discharge object to the outside; wherein the bleed line has: a one-side bleed line (30) for guiding the compressed air bled from the air supply line to the one side wall portion; and a other-side bleed line (30) branching from the one-side bleed line and connecting to the other side wall portion; wherein the one side wall portion is further formed with a one-side discharge port (67) to which the one-side discharge line is connected; and the other side wall portion is further formed with a other-side inlet (38) to which the other side bleed line is connected; When viewed in the axial direction of the crankshaft, the one-side inlet and the other-side outlet are arranged at positions horizontally offset from each other, and the other-side inlet and the one-side outlet are arranged at positions horizontally offset from each other.

[0120] According to the configuration of 12), the compressed air flowing into the crankcase from the inlet on one side is likely to spread horizontally throughout the crankcase as it flows toward the outlet on the other side. Similarly, the compressed air flowing into the crankcase from the inlet on the other side is likely to spread horizontally throughout the crankcase as it flows toward the outlet on one side. This allows the concentration of unburned gas to be uniformly reduced within the crankcase.

[0121] 13) In some embodiments, the engine system is the engine system described in any one of 1) to 9) above, wherein the engine is a multi-cylinder engine in which a plurality of cylinder units (8), each including the cylinder and the piston, are arranged along the axial direction of the crankshaft, the crankcase has: one side wall portion (21) at one end in the axial direction; another side wall portion (22) at the opposite end from the one side wall portion; a first side wall portion (27) at a first end in a horizontal direction (width direction) perpendicular to the axial direction; and a second side wall portion (26) at the opposite end from the first side wall portion; and at least one partition wall portion (29) connected to the first side wall portion and the second side wall portion so as to separate one or more of the plurality of cylinder units from the other cylinder units in a plan view, and the bleed line is The crankcase includes a plurality of connecting bleed lines (35) connected to the first side wall portion so as to communicate with each of a plurality of spaces (17) of the crankcase partitioned by the at least one partition wall portion, and the discharge line includes a plurality of connecting discharge lines (65) connected to the second side wall portion so as to communicate with each of the plurality of spaces of the crankcase.

[0122] According to the configuration of 13), since one or more cylinder units are arranged in each of the multiple spaces separated by the partition wall portions in a plan view, unburned gas leaks into each space. However, compressed air flows into each space from each connecting bleed line, and the compressed air and unburned gas in each space are discharged via each connecting exhaust line. Since the unburned gas in each space can be more reliably diluted with compressed air, the risk of ignition of unburned gas in the crankcase can be reduced.

[0123] 14) In some embodiments, the engine system is one described in any one of 1) to 9) above, wherein the engine is a multi-cylinder engine in which a plurality of cylinder units (8), each including the cylinder and the piston, are arranged along the axial direction of the crankshaft, the crankcase has one side wall portion (21) at one end in the axial direction, another side wall portion (22) at the opposite end from the one side wall portion, and a side wall portion (23) connecting the one side wall portion and the other side wall portion, the bleed line has a side bleed line (30) connecting the compressed air return line and the side wall portion, and a side inlet (39) to which the side bleed line is connected is formed in a central portion (24) of the side wall portion in the axial direction of the crankshaft.

[0124] According to the configuration of 14) above, the compressed air that flows into the crank chamber from the side inlet port formed in the center of the side wall can flow toward both sides in the axial direction, thereby distributing the compressed air throughout the crank chamber and uniformly reducing the concentration of unburned gas within the crank chamber.

[0125] 15) In some embodiments, the engine system is the one described in any one of 1) to 9) above, further comprising a discharge line (60) for guiding the discharge object, which is a fluid including the compressed air in the crankcase, to the outside, and the discharge line has: a one-side discharge line (61) connected to a one-side discharge port (67) formed in the one side wall portion and for guiding the discharge object discharged from the one-side discharge port to the outside; and a other-side discharge line (62) connected to a other-side discharge port (68) formed in the other side wall portion and for guiding the discharge object discharged from the other-side discharge port to the outside.

[0126] According to the configuration of 15) above, the compressed air that flows into the crankcase from the side inlet can flow toward both sides in the axial direction, thereby distributing the compressed air throughout the crankcase, thereby uniformly reducing the concentration of unburned gas within the crankcase.

[0127] REFERENCE SIGNS LIST 1: Engine system 3: Bleed on-off valve 4: Flow rate control valve 5: Engine 6: Cylinder 7: Piston 8: Cylinder unit 9: Combustion chamber 11: Fuel gas line 11a: First fuel gas line 11b: Second fuel gas line 12: Compressor wheel 13: Rotor shaft 14: Turbine wheel 15: Supercharger 16: Crankshaft 17: Space 18: Crankcase 19: Connecting rod 20: Crankcase 21: One side wall portion 23: Side wall portion 24: Central portion 25: Air supply line 26: Second side wall portion 27: First side wall portion 28: Air cooler 29: Partition wall portion 30: Bleed line 31: One side bleed line 32: Other side bleed line 33: Side bleed line 35: Connecting bleed line 37: One side inlet 38: Other side inlet 39: Side inlet 41: Side inlet 42: Side outlet 45: Spark plug 51: Concentration sensor 52: Pressure sensor 53: Phase sensor 60: Discharge line 61: One side outlet line 62: Other side outlet line 65: Connecting discharge line 67: One side outlet 68: Other side outlet 70: Fuel gas supply system 73: Fuel gas flow adjustment valve 73a: First fuel flow adjustment valve 73b: Second fuel flow adjustment valve 77: Fuel on / off valve 77a: First fuel on / off valve 77b: Second fuel on / off valve 81: Crank pin 82: Air intake valve 83: Exhaust valve 85 : Camshaft 86 : Rocker arm 87 : Push rod 89 : Exhaust gas line 90 : Controller 102,103: Air intake pipe 105: Exhaust pipe 110: Pilot valve 111: First pilot valve 112: Second pilot valve 116: Pilot air line 117: First pilot air line 118: Second pilot air line 119: Upstream main air line 120: Air supply system 121: First main air line 122: Second main air line 123: Main air line 124: Control valve 125: Starting air line 126: Air tank 127: Compressed air supply line 128: Air pressure sensor 129: Compressor 201: First pilot control valve 202: Second pilot control valve 203: Air control valve 251: First air intake line 252: Second air intake line 253: Air intake flow adjustment valve 911: Extraction opening / closing control unit 912: Flow rate adjustment control unit 913: Ignition control unit 914: Air supply amount control unit 915: Fuel gas amount control unit 916: Fuel valve control unit 917: Bypass exhaust gas amount control unit 990: Exhaust gas line 991: Bypass exhaust gas line 993: Bypass flow adjustment valve Ca, Cb: Compressed air Eg: Exhaust gas Eo: Emission object Fg: Fuel gas P1: Connection point fg1: First fuel gas fg2: Second fuel gas

Claims

1. An engine system comprising: an engine including a cylinder and a piston housed in the cylinder; an air supply system including an air tank and a starting air line for directing compressed air stored in the air tank into the cylinder as starting air for the engine; and a fuel gas supply system for supplying fuel gas into the cylinder, wherein the engine further includes: a crankshaft located below the piston and configured to be driven by the piston; and a crankcase housing the crankshaft, and the air supply system further includes an air bleed line for bleeding the compressed air flowing through the starting air line and directing it to a crank chamber in the crankcase.

2. The engine system according to claim 1, wherein the air supply system further includes an air bleed valve arranged on the bleed line, and the engine system further comprises: a concentration sensor for measuring a gas concentration that correlates with an unburned gas concentration, which is the concentration of the fuel gas in an unburned state in the crank chamber; and a bleed open / close control unit for controlling the bleed open / close valve so that the bleed open / close valve is switched from a closed state to an open state when the unburned gas concentration in the crank chamber obtained from the measurement value of the concentration sensor exceeds an allowable concentration.

3. The engine system according to claim 2, further comprising a pressure sensor for measuring pressure in the crankcase, and the bleed air opening / closing control section is configured to control the opening of the bleed air opening / closing valve so that the measurement value of the pressure sensor is equal to or lower than an allowable pressure.

4. An engine system as described in claim 2, wherein the air supply system further includes a flow control valve arranged on the bleed line, and the engine system further includes: a pressure sensor for measuring the pressure in the crankcase; and a flow control control unit for controlling the opening of the flow control valve so that the measurement value of the pressure sensor is equal to or lower than an allowable pressure.

5. The engine system according to claim 2, wherein the engine further includes an ignition plug disposed in the combustion chamber, and the engine system further includes: a phase sensor for measuring a rotational angle phase of the crankshaft; and an ignition control unit for controlling the ignition plug based on the rotational angle phase measured by the phase sensor, and the ignition control unit is configured to advance the ignition timing of the spark plug when the unburned gas concentration in the crank chamber determined from the measurement value of the concentration sensor does not fall below the permissible concentration even after the bleed opening / closing valve is opened through the control of the bleed opening / closing control unit, compared to when the unburned gas concentration is below the permissible concentration.

6. The engine system of claim 2, further comprising: an intake air line for guiding the compressed air from a compressor wheel into the cylinder; an intake air flow control valve arranged on the intake air line; and an intake air volume control unit for controlling the intake air flow control valve so as to increase the flow rate of the compressed air in the intake air line when the unburned gas concentration obtained from the measurement value of the concentration sensor does not become equal to or lower than the permissible concentration even after the bleed air opening / closing valve is opened through the control of the bleed air opening / closing control unit.

7. The engine system according to claim 2, further comprising: a turbocharger including a compressor wheel and a turbine wheel for driving the compressor wheel; an exhaust gas line for guiding exhaust gas discharged from the engine to the turbine wheel; a bypass exhaust gas line for bleeding the exhaust gas flowing through the exhaust gas line and discharging the exhaust gas to the outside by bypassing the turbine wheel; a bypass flow regulating valve for controlling the flow rate of the exhaust gas flowing through the bypass exhaust gas line; and a bypass exhaust gas amount control unit for controlling the bypass flow regulating valve so as to reduce the flow rate of the exhaust gas flowing through the bypass exhaust gas line when the unburned gas concentration obtained from the measurement value of the concentration sensor does not become equal to or lower than the permissible concentration even after the bleeding opening / closing valve is opened through the control of the bleeding opening / closing control unit.

8. The engine system of claim 2, wherein the fuel gas supply system further comprises: a fuel gas line for directing the fuel gas into the cylinder; a fuel gas flow regulating valve arranged on the fuel gas line; and a fuel gas quantity control unit for controlling the fuel gas flow regulating valve so as to reduce the flow rate of the fuel gas in the fuel gas line when the unburned gas concentration calculated from the measurement value of the concentration sensor does not become equal to or lower than the permissible concentration even after the extraction opening / closing valve is opened through the control of the extraction opening / closing control unit.

9. The engine system according to claim 8, wherein the fuel gas supply system includes: a first fuel gas line for guiding a first fuel gas to a combustion chamber of the engine; a first fuel on-off valve arranged on the first fuel gas line; a second fuel gas line for guiding a second fuel gas having a lower explosion limit concentration than the first fuel gas to the combustion chamber; and a second fuel on-off valve arranged on the second fuel gas line; when the bleeding on-off control unit controls the bleeding on-off valve, at least the second fuel on-off valve of the first fuel on-off valve or the second fuel on-off valve is in an open state, and the engine system further includes a fuel valve control unit for controlling the second fuel on-off valve to change from the open state to a closed state when the unburned gas concentration calculated from the measurement value of the concentration sensor does not become equal to or lower than the permissible concentration even after the flow rate of the fuel gas is reduced through the control of the fuel gas quantity control unit.

10. The engine system according to claim 1, wherein the engine is a multi-cylinder engine in which a plurality of cylinder units, each including the cylinder and the piston, are arranged along the axial direction of the crankshaft, the engine system further comprises an exhaust line for guiding an object to be exhausted, which is a fluid including the compressed air in the crank chamber, to the outside, the crankcase having a first side wall portion which is an end portion on one side in the axial direction, and a second side wall portion which is an end portion opposite to the first side wall portion, the first side wall portion having a first side inlet port to which the bleed line is connected, and the second side wall portion having a second side outlet port to which the exhaust line is connected.

11. The engine system according to claim 10, wherein the one-side inlet is disposed at a lower position than the other-side outlet.

12. The engine system according to claim 10, wherein the exhaust line comprises: a one-side exhaust line connected to the one-side wall portion and for guiding the object to be exhausted to the outside; and a other-side exhaust line connected to the other-side exhaust port of the other-side wall portion and for guiding the object to be exhausted to the outside; the bleed line comprises: a one-side bleed line connected to the one-side inlet of the one-side wall portion and for guiding the compressed air bled from the starting air line to the one-side inlet; and a other-side bleed line branching off from the one-side bleed line and connecting to the other-side wall portion; the one-side wall portion is further formed with a one-side exhaust port to which the one-side exhaust line is connected; and the other-side wall portion is further formed with a other-side inlet to which the other-side bleed line is connected; and when viewed in the axial direction of the crankshaft, the one-side inlet and the other-side exhaust port are arranged at positions horizontally offset from each other, and the other-side inlet and the one-side exhaust port are arranged at positions horizontally offset from each other.

13. The engine is a multi-cylinder engine in which a plurality of cylinder units, each including the cylinder and the piston, are arranged along the axial direction of the crankshaft, the crankcase has: one side wall portion which is an end portion on one side of the axial direction; the other side wall portion which is an end portion opposite to the one side wall portion; a first side wall portion which is an end portion on a first side in a horizontal direction perpendicular to the axial direction; a second side wall portion which is an end portion opposite to the first side wall portion; and at least one partition wall portion connected to the first side wall portion and the second side wall portion so as to separate one or more of the plurality of cylinder units from the other cylinder units in a plan view, the bleed line includes a plurality of connecting bleed lines connected to the first side wall portion so as to communicate with each of a plurality of spaces of the crank chamber partitioned by the at least one partition wall portion, the engine system further includes a discharge line for guiding a discharge object, which is a fluid including the compressed air in the crank chamber, to the outside, the discharge line being The engine system of claim 1 , further comprising a plurality of connecting exhaust lines connected to the second sidewall portion so as to communicate with each of the plurality of spaces of the crankcase.

14. The engine system according to claim 1, wherein the engine is a multi-cylinder engine in which a plurality of cylinder units, each including the cylinder and the piston, are arranged along the axial direction of the crankshaft, the crankcase has one side wall portion which is an end portion on one side in the axial direction, the other side wall portion which is an end portion opposite to the one side wall portion, and a side wall portion connecting the one side wall portion and the other side wall portion, the bleed line has a side bleed line connecting the starting air line and the side wall portion, and a side inlet to which the side bleed line is connected is formed in a central portion of the side wall portion in the axial direction of the crankshaft.

15. The engine system according to claim 14, further comprising a discharge line for guiding a discharge object which is a fluid including the compressed air in the crank chamber to the outside, the discharge line comprising: a one-side discharge port v connected to the one-side discharge port formed in the one-side wall portion and for guiding the discharge object discharged from the one-side discharge port to the outside; and a other-side discharge line connected to the other-side discharge port formed in the other-side wall portion and for guiding the discharge object discharged from the other-side discharge port to the outside.

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