Fuel injection device and reciprocation internal combustion engine

Abstract

To suppress vaporization of fuel remaining in a fuel supply passage and enable highly accurate fuel injection in a fuel injection device and a reciprocation internal combustion engine.SOLUTION: A fuel injection device includes: a first fuel supply passage for supplying first fuel with predetermined ignitability; a second fuel supply passage for supplying second fuel with ignitability lower than that of the first fuel; a fuel injection valve having a needle valve to which the second fuel supply passage is connected; a piston mechanism having a piston that is provided between the first fuel supply passage and the second fuel supply passage and moves by using differential pressure between first supply pressure of the first fuel and second supply pressure of the second fuel; and a discharge valve provided in the second fuel supply passage between the needle valve and the piston mechanism to inhibit a backflow of the second fuel from the needle valve to the piston mechanism side.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a fuel injection system and a reciprocating internal combustion engine. [Background technology]

[0002] A reciprocating internal combustion engine is equipped with a fuel injection device. The reciprocating internal combustion engine is driven by the combustion energy generated by injecting fuel into high-pressure air in a combustion chamber using the fuel injection device. In recent years, the use of carbon-free fuels that generate fewer harmful substances (such as carbon dioxide) has been considered as fuels to be used in fuel injection devices. However, some carbon-free fuels have poor ignition and combustion properties, and it has been proposed to use them in combination with fuels that have good ignition and combustion properties. An example of a fuel injection device that injects multiple types of fuel is described in Patent Document 1 below. The fuel injection device described in Patent Document 1 injects a fossil fuel as a first fuel and an alternative fuel as a second fuel in a stratified manner. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-180567 Summary of the Invention [Problem to be solved by the invention]

[0004] In a conventional fuel injection system, a fuel pump that pumps a first fuel is connected to a fuel injection valve via a fuel injection pipe, and an injection pump that pumps a second fuel is connected to the fuel injection valve via an injection pipe. In the conventional fuel injection system, when the pressure of the second fuel exceeds the valve-opening pressure of the fuel injection valve, the fuel injection valve opens to inject the second fuel. When the pressure of the second fuel subsequently falls below the valve-opening pressure of the fuel injection valve, the fuel injection valve closes to terminate injection of the second fuel. At this time, the fuel injection valve becomes hot due to combustion gas, and the heat of the fuel injection valve is transferred to the injection pipe, potentially vaporizing the second fuel remaining in the injection pipe. Because vaporized fuel is a compressible fluid, it may be difficult to properly compress and inject the partially vaporized second fuel at the time of the next fuel injection.

[0005] The present disclosure is intended to solve the above-mentioned problems, and aims to provide a fuel injection device and a reciprocating internal combustion engine that suppress vaporization of fuel remaining in the fuel supply path and enable highly accurate fuel injection. [Means for solving the problem]

[0006] In order to achieve the above object, the fuel injection device of the present disclosure includes a first fuel supply path that supplies a first fuel having a predetermined ignition quality, a second fuel supply path that supplies a second fuel having a lower ignition quality than the first fuel, a fuel injection valve having a needle valve to which the second fuel supply path is connected, a piston mechanism that is provided between the first fuel supply path and the second fuel supply path and has a piston that moves due to a pressure difference between a first supply pressure of the first fuel and a second supply pressure of the second fuel, and a discharge valve that is provided in the second fuel supply path between the needle valve and the piston mechanism and prevents backflow of the second fuel from the needle valve toward the piston mechanism.

[0007] The reciprocating internal combustion engine of the present disclosure includes an internal combustion engine body having a combustion chamber, and the fuel injection device that injects fuel into the combustion chamber. [Effects of the Invention]

[0008] According to the fuel injection device and reciprocating internal combustion engine of the present disclosure, it is possible to suppress vaporization of fuel remaining in the fuel supply path, thereby enabling highly accurate fuel injection. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing a marine diesel engine according to a first embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of the fuel injection device of the first embodiment. [Figure 3] FIG. 3 is a time chart showing the operation of the fuel injection device. [Figure 4] FIG. 4 is a graph showing the relationship between the temperature and the saturated vapor pressure of the second fuel. [Figure 5] FIG. 5 is a schematic diagram showing an example of the arrangement when the fuel injection device of the first embodiment is combined with another fuel injection device. [Figure 6] FIG. 6 is a schematic diagram showing the configuration of a fuel injection device according to the second embodiment. [Figure 7] FIG. 7 is a schematic diagram showing the configuration of a fuel injection device according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. Note that the present disclosure is not limited to these embodiments, and when there are multiple embodiments, the present disclosure also includes configurations that combine the embodiments. Furthermore, the components in the embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially identical, and those that are within the so-called equivalent range.

[0011] [First embodiment] <Marine diesel engine> Fig. 1 is a schematic diagram showing a marine diesel engine according to a first embodiment. In the first embodiment, a marine diesel engine will be described as a reciprocating internal combustion engine. However, the reciprocating internal combustion engine is not limited to a marine diesel engine.

[0012] As shown in FIG. 1, a marine diesel engine 10 is used, for example, as a main engine for propelling a ship, and is a two-stroke, one-cycle, uniflow scavenging crosshead internal combustion engine.

[0013] The marine diesel engine 10 has a diesel engine body (internal combustion engine body) 11. The diesel engine body 11 includes a cylinder liner 12, a piston 13, a scavenging trunk 14, an exhaust manifold 15, and an exhaust valve 16.

[0014] The cylinder liner 12 is cylindrical and is disposed inside a cylinder jacket (not shown), with a cylinder cover 21 fixed to the top. The piston 13 is cylindrical and is disposed inside the cylinder liner 12 and is supported so as to be freely movable in the axial direction. The lower end of the piston 13 is connected to the upper end of a piston rod 22. Although not shown, a crankshaft is rotatably supported at the bottom of the diesel engine body 11, and the lower end of a connecting rod is rotatably connected to the crank via a crank. The diesel engine body 11 supports a crosshead so as to be freely movable in the vertical direction, and the lower end of the piston rod 22 and the upper end of the connecting rod are rotatably connected to the crosshead.

[0015] The scavenging trunk 14 is connected to the lower part of the cylinder liner 12. The cylinder liner 12 communicates with the inside of the scavenging trunk 14 through a plurality of scavenging ports 23. Air is supplied to the scavenging trunk 14 through an intake pipe 24.

[0016] The cylinder liner 12 has an upper space to which a cylinder cover 21 is fixed, which is partitioned by the upper surface of the piston 13, thereby forming a combustion chamber 25. The cylinder cover 21 is connected to the exhaust manifold 15 via an exhaust pipe 26. That is, the combustion chamber 25 communicates with the exhaust manifold 15 via the exhaust pipe 26. The cylinder cover 21 is provided with an exhaust valve 16. The exhaust valve 16 is driven by a valve train 27 to open and close the exhaust pipe 26. When the exhaust valve 16 opens the exhaust pipe 26, the combustion chamber 25 communicates with the exhaust manifold 15 via the exhaust pipe 26.

[0017] The marine diesel engine 10 also includes a fuel injection device 17. The fuel injection device 17 has a fuel supply device 31, a fuel supply path 32, and a fuel injection valve 33. The fuel injection valve 33 is attached to the cylinder cover 21. The fuel injection valve 33 can inject fuel into the combustion chamber 25. The fuel supply device 31 is connected to the fuel injection valve 33 via the fuel supply path 32. The fuel supply device 31 can supply fuel stored in a fuel tank (not shown) to the fuel injection valve 33 via the fuel supply path 32.

[0018] First, when the piston 13 moves to the bottom dead center (the position indicated by the solid line in FIG. 1), the scavenging ports 23 open and the air in the scavenging trunk 14 is introduced through the scavenging ports 23 into the combustion chamber 25. Next, when the piston 13 moves up, the piston 13 blocks communication between the scavenging ports 23 and the combustion chamber 25. At this time, the exhaust valve 16 moves up by the valve train 27, the exhaust pipe 26 is closed, and the air in the combustion chamber 25 is compressed by the movement of the piston 13. Then, when the piston 13 moves to the top dead center (the position indicated by the two-dot chain line in FIG. 1), the pressure in the combustion chamber 25 reaches a predetermined compression pressure, and the fuel injection valve 33 is actuated to inject fuel into the combustion chamber 25. Then, the air and fuel mix and burn in the combustion chamber 25, and the combustion energy moves the piston 13 down. At this time, the exhaust valve 16 moves down by the valve train 27, opening the exhaust pipe 26. Then, exhaust gas generated by the combustion is pushed out from the combustion chamber 25 through the exhaust pipe 26 into the exhaust manifold 15 and discharged.

[0019] <Configuration of fuel injection system> FIG. 2 is a schematic diagram showing the configuration of the fuel injection device of the first embodiment.

[0020] 2, the fuel injection device 17 includes a fuel supply device 31, a fuel supply path 32, and a fuel injection valve 33. The fuel supply device 31 includes a first fuel supply source 40, a supply pump 41, and a second fuel supply source 42. The fuel supply path 32 includes a first fuel supply path 43 and a second fuel supply path 44. The fuel injection valve 33 includes a needle valve 45 and a piston mechanism 47.

[0021] The fuel injection device 17 can inject a second fuel having lower (worse) ignitability than a first fuel having a predetermined ignitability. Here, ignitability refers to the ease with which the first fuel and the second fuel can be ignited. The first fuel is a fossil fuel (e.g., diesel fuel such as light oil or heavy oil), and the second fuel is, for example, ammonia, methanol, liquefied petroleum gas (LPG), etc. However, the first fuel and the second fuel are not limited to the fuels mentioned above.

[0022] A first fuel supply source 40 and a supply pump 41 are connected to the first fuel supply path 43 at an upstream end in the supply direction of the first fuel. The first fuel supply source 40 is composed of, for example, a pressure accumulator for the first fuel and a pressure pump that pressurizes the first fuel. The first fuel supply source 40 supplies low-pressure first fuel to the upstream side of the first fuel supply path 43. The supply pump 41 is connected to the first fuel supply path 43 downstream of the first fuel supply source 40. The supply pump 41 pressurizes the first fuel on the upstream side of the first fuel supply path 43 to high pressure and supplies it to the downstream side of the first fuel supply path 43.

[0023] The supply pump 41 has a piston 51 and a plunger 52. The piston 51 and the plunger 52 are connected to each other, and the plunger 52 is connected to the first fuel supply path 43. The piston 51 is connected to a working fluid source 54 by a first working oil supply path 53, and a first solenoid valve 55 is provided on the first working oil supply path 53. The working fluid source 54 supplies working fluid at a predetermined pressure to the first working oil supply path 53. The supply pump 41 functions as a booster pump, with the pressure-receiving area of ​​the plunger 52 set smaller than the pressure-receiving area of ​​the piston 51. The first solenoid valve 55 is connected to a control unit 56 and opens and closes in response to commands from the control unit 56.

[0024] When the first solenoid valve 55 is opened, the working fluid from the working fluid source 54 is supplied to the piston 51 through the first working oil supply path 53. The piston 51 is actuated by the supply of working fluid, and operates the plunger 52. Then, the supply pump 41 pressurizes the first fuel in the first fuel supply path 43. At this time, the supply pump 41 operates by increasing the pressure of the working fluid, and therefore pressurizes the first fuel to a high pressure.

[0025] The second fuel supply path 44 has an upstream end in the supply direction of the second fuel connected to a second fuel supply source 42. The second fuel supply source 42 is configured, for example, with a pressure accumulator for the second fuel and a pressure pump that pressurizes the second fuel. The second fuel supply source 42 supplies the second fuel to the upstream side of the second fuel supply path 44.

[0026] The downstream end of second fuel supply path 44 is connected to needle valve 45. Needle valve 45 has a valve element 45a, a biasing spring 45b, a chamber 45c, a fuel supply path 45d, a nozzle hole 45e, and a sliding seal portion 45f. Second fuel supply path 44 is connected to chamber 45c. Chamber 45c is connected to fuel supply path 45d, and fuel supply path 45d has nozzle hole 45e formed at its tip. Valve element 45a is seated by the biasing force of biasing spring 45b, thereby blocking communication between chamber 45c and fuel supply path 45d. When second fuel having a pressure higher than the second injection pressure is supplied to chamber 45c from second fuel supply path 44, valve element 45a rises against the biasing force of biasing spring 45b, thereby connecting chamber 45c and fuel supply path 45d. Then, the second fuel supplied to the chamber 45c flows into the fuel supply passage 45d and is injected from the injection holes 45e.

[0027] The piston mechanism 47 is provided between the first fuel supply path 43 and the second fuel supply path 44. Specifically, the first fuel supply path 43 has an upstream end connected to the first fuel supply source 40 and the supply pump 41, and a downstream end connected to the piston mechanism 47. The second fuel supply path 44 has an upstream path 61 and a downstream path 62. The upstream end of the upstream path 61 is connected to the second fuel supply source 42, and a downstream end connected to the piston mechanism 47. The downstream path 62 has an upstream end connected to the piston mechanism 47 and a downstream end connected to the needle valve 45. One end of the piston mechanism 47 in the piston movement direction is connected to the downstream end of the first fuel supply path 43, and the other end of the piston movement direction is connected to a midpoint of the second fuel supply path 44, i.e., the downstream end of the upstream path 61 and the upstream end of the downstream path 62.

[0028] The piston mechanism 47 has a cylindrical cylinder 71 and a columnar piston 72. The piston 72 is disposed inside the cylinder 71 and supported so as to be freely movable in the axial direction. One end of the cylinder 71 in the movement direction of the piston 72 communicates with the downstream end of the first fuel supply path 43, and the other end of the cylinder 71 in the movement direction of the piston 72 communicates with a midway portion of the second fuel supply path 44. The piston 72 is a rod-equipped piston and has a rod portion 73 with a small diameter and a main body portion 74 with a larger diameter than the rod portion 73. The main body portion 74 of the piston 72 is disposed inside the cylinder 71 and supported so as to be freely movable in the axial direction. The rod portion 73 of the piston 72 is integrally provided with the main body portion 74, and the tip portion of the rod portion 73 extends outside the cylinder 71.

[0029] The piston 72 has a first pressure-receiving surface 72a formed on the first fuel supply path 43 side and a second pressure-receiving surface 72b formed on the second fuel supply path 44 side. The first supply pressure of the first fuel supply path 43 acts on the first pressure-receiving surface 72a of the piston 72, and the second supply pressure of the second fuel supply path 44 acts on the second pressure-receiving surface 72b. The piston mechanism 47 reciprocates the piston 72 due to the pressure difference between the first supply pressure of the first fuel and the second supply pressure of the second fuel.

[0030] In the piston mechanism 47, the axial length of the main body 74 is shorter than the axial length of the cylinder 71. Therefore, the piston mechanism 47 is provided with a first reservoir 75 on the first pressure-receiving surface 72a side and a second reservoir 76 on the second pressure-receiving surface 72b side. The first reservoir 75 communicates with the first fuel supply path 43 and stores the first fuel. The second reservoir 76 communicates with the second fuel supply path 44 and stores the second fuel. The piston 72 is movable within the cylinder 71, but the amount of reciprocating movement is limited by a stopper (not shown). That is, when the piston 72 moves furthest toward the first fuel supply path 43, a gap is secured between the first pressure-receiving surface 72a and one end of the cylinder 71, and the first reservoir 75 including this gap is secured. On the other hand, when the piston 72 moves closest to the second fuel supply path 44, a gap is created between the second pressure-receiving surface 72b and the other end of the cylinder 71, and a second storage section 76 including this gap is created.

[0031] As described above, the piston 72 is a rod-equipped piston, and the first pressure-receiving surface 72a is formed on one side of the main body 74, and the second pressure-receiving surface 72b is formed on the other side. Because the rod 73 is provided on one side of the main body 74, the area of ​​the first pressure-receiving surface 72a is smaller than the area of ​​the second pressure-receiving surface 72b. The piston mechanism 47 is provided with a first reservoir 75 communicating with the first fuel supply path 43 on the side of the first pressure-receiving surface 72a, and a second reservoir 76 communicating with the second fuel supply path 44 on the side of the second pressure-receiving surface 72b. Therefore, due to the difference in area between the first pressure-receiving surface 72a and the second pressure-receiving surface 72b, the piston mechanism 47 has a first supply pressure acting on the first fuel supply path 43 via the first reservoir 75 that is higher than the second supply pressure acting on the second fuel supply path 44 via the second reservoir 76.

[0032] Piston 72 has a bulge 77 between rod portion 73 and main body portion 74. Meanwhile, cylinder 71 has a seat portion 78 formed by reducing the inner diameter at the end on the side of first fuel supply path 43. When piston 72 moves inside cylinder 71 toward first fuel supply path 43, piston mechanism 47 has bulge 77 abut against seat portion 78, thereby blocking communication between first fuel supply path 43 and first reservoir 75.

[0033] In the piston mechanism 47, a sliding portion 79 is formed between the cylinder 71 and the rod portion 73 of the piston 72. One end of a drain path 80 is in communication with the sliding portion 79. The sliding portion 79 is in communication with the first storage portion 75, so the first fuel leaks. The drain path 80 discharges and recovers the first fuel leaked at the sliding portion 79 to the outside. Here, because the pressure of the first fuel in the first fuel supply path 43 is higher than the pressure of the second fuel in the second fuel supply path 44, the second fuel in the second fuel supply path 44 is prevented from flowing from the second storage portion 76 through the sliding portion between the cylinder 71 and the piston 72, and from the first storage portion 75 to the first fuel supply path 43, thereby preventing mixing with the first fuel. Therefore, the first fuel recovered from the drain path 80 does not contain the second fuel, making it easier to process.

[0034] The needle valve 45 is also provided with a seal path 81 that prevents the second fuel from flowing to the drain. The seal path 81 has a first seal path 82, a second seal path 83, and a third seal path 84. The upstream end of the first seal path 82 is connected to the first fuel supply path 43, and the first fuel from the first fuel supply path 43 is supplied to the first seal path 82. The upstream end of the second seal path 83 is connected to a first fuel supply source 85, and the first fuel is supplied to the second seal path 83. The first fuel supply source 85 supplies the first fuel at a higher pressure than the second fuel supplied from the second fuel supply source 42. The downstream ends of the first seal path 82 and the second seal path 83 join together and are connected to the upstream end of the third seal path 84. The downstream end of the third seal path 84 is connected to the sliding seal portion 45f of the valve body 45a of the needle valve 45.

[0035] The first seal passage 82 is provided with a check valve 86 that prevents the first fuel from flowing back from the needle valve 45 toward the first fuel supply passage 43. The second seal passage 83 is provided with a check valve 87 that prevents the first fuel from flowing back from the needle valve 45 toward the first fuel supply source 85. The third seal passage 84 applies the pressure of the first fuel in the first fuel supply passage 43 or the pressure of the first fuel in the first fuel supply source 85 to the sliding seal portion 45f of the needle valve 45. Therefore, the seal passage 81 applies the pressure of the first fuel in the first fuel supply passage 43 or the pressure of the first fuel in the first fuel supply source 85 to the sliding seal portion 45f of the needle valve 45, thereby maintaining the lubricity of the sliding seal portion 45f of the valve body 45a and suppressing the outflow of the second fuel to the drain.

[0036] In the piston mechanism 47, a first supply pressure of the first fuel from the first fuel supply path 43 acts on a first pressure-receiving surface 72a side of the piston 72 via a first reservoir 75, and a second supply pressure of the second fuel from the second fuel supply path 44 acts on a second pressure-receiving surface 72b side of the piston 72 via a second reservoir 76. When the supply pump 41 is in a stopped state, the second supply pressure of the second fuel in the second fuel supply path 44 is lower than the first supply pressure of the first fuel in the first fuel supply path 43. Therefore, a small amount of the first fuel in the first reservoir 75 leaks into the sliding portions between the cylinder 71 and the piston 72, enabling lubrication of the sliding portions and sealing for the second fuel.

[0037] In addition, because the area of ​​the first pressure-receiving surface 72a of the piston mechanism 47 is smaller than the area of ​​the second pressure-receiving surface 72b, the pressure balance acting on the piston 72 is upward. Therefore, in the piston mechanism 47, the piston 72 moves toward the first fuel supply path 43, and a predetermined amount of the second fuel is stored in the second storage portion 76. Meanwhile, when the supply pump 41 is operated, the first supply pressure of the first fuel in the first fuel supply path 43 increases and becomes higher than the second supply pressure of the second fuel in the second fuel supply path 44. Therefore, in the piston mechanism 47, the piston 72 moves toward the second fuel supply path 44, and supplies the second fuel in the second storage portion 76 to the needle valve 45. When the second supply pressure exceeds the second injection pressure, the needle valve 45 injects the second fuel. In addition, in the needle valve 45, the first fuel in the first fuel supply path 43 is supplied to the sliding seal portion 45f through the seal path 81, and a small amount of the first fuel flows toward the chamber 45c, thereby ensuring the lubrication of the valve body 45a and suppressing the outflow of the second fuel to the drain.

[0038] The first fuel supply path 43 is provided with a check valve 91 between the connection portion of the supply pump 41 and the connection portion of the piston mechanism 47. The check valve 91 prevents the first fuel from flowing back from the piston mechanism 47 side to the supply pump 41 side. The first fuel supply path 43 is also provided with a check valve 92 between the connection portion of the supply pump 41 and the first fuel supply source 40. The check valve 92 prevents the first fuel from flowing back from the connection portion of the supply pump 41 side to the first fuel supply source 40 side. The first fuel supply path 43 is also provided with a return path 93 that branches off from the path between the piston mechanism 47 and the check valve 91. The return path 93 bypasses the check valves 91, 92 and the supply pump 41. The return path 93 is provided with a check valve 94. When the supply pump 41 stops, the pressure downstream of the check valve 91 (for example, the second supply pressure of the second fuel in the second fuel supply path 44) is released by the pressure obtained by adding the spring force of the check valve 94 to the pressure upstream of the check valve 91, and the first fuel in the first fuel supply path 43 on the piston mechanism 47 side is returned, bypassing the check valve 91.

[0039] A second fuel supply valve 111 is provided in the second fuel supply path 44 between the connection portion of the second fuel supply source 42 and the piston mechanism 47. The second fuel supply valve 111 is an electromagnetic valve, is connected to the control unit 56, and opens and closes in response to commands from the control unit 56. When the second fuel supply valve 111 is opened, the second fuel is supplied from the second fuel supply source 42 to the second fuel supply path 44. A nitrogen supply source 112 is also connected to the second fuel supply path 44 via the second fuel supply valve 111. The second fuel supply valve 111 switches between the supply of the second fuel from the second fuel supply source 42 and the supply of nitrogen (N2) from the nitrogen supply source 112 to the second fuel supply path 44. In this case, the pressure of the nitrogen from the nitrogen supply source 112 is lower than the pressure of the second fuel from the second fuel supply source 42.

[0040] In the fuel injection valve 33, a discharge valve 121 is provided in the second fuel supply path 44 between the needle valve 45 and the piston mechanism 47, to prevent the second fuel from flowing back from the needle valve 45 toward the piston mechanism 47. Specifically, the discharge valve 121 is provided in the downstream path 62 that connects the needle valve 45 and the second reservoir 76 of the piston mechanism 47.

[0041] The discharge valve 121 is a check valve in which a closing force acting on a ball by the biasing force of a spring closes the downstream path 62. The biasing force of the spring is a valve closing force, and the discharge valve 121 opens when a valve opening force greater than the valve closing force acts. The valve opening pressure of the discharge valve 121 is preferably higher than the second supply pressure of the second fuel supplied from the second fuel supply source 42 to the second fuel supply path 44. The downstream path 62 in the second fuel supply path 44 is divided by the discharge valve 121 into an upstream first path 62a and a downstream second path 62b, and when the discharge valve 121 is closed, the flow of the second fuel from the second path 62b to the first path 62a is blocked.

[0042] The fuel injection valve 33 has a first purge path 122 provided in the second fuel supply path 44, and the first purge path 122 is provided with a first purge valve 123. One end of the first purge path 122 is connected to the downstream path 62 between the second storage portion 76 of the piston mechanism 47 and the discharge valve 121, and the other end is connected to a second fuel recovery system (not shown). The first purge valve 123 can be operated by an opening / closing control valve (purge control portion) 124.

[0043] The first purge valve 123 has a cylinder 123a, a piston 123b, a first port portion 123c, and a second port portion 123d. The piston 123b is supported axially movably relative to the cylinder 123a. The first port portion 123c is provided on a side portion of the cylinder 123a on the tip end side of the piston 123b. The second port portion 123d is provided on the tip end of the piston 123b in the cylinder 123a. The first purge path 122 has a first path 122a and a second path 122b. One end of the first path 122a is connected to the first path 62a of the downstream path 62, and the other end is connected to the second port portion 123d. One end of the second path 122b is connected to the first port portion 123c.

[0044] Furthermore, the first purge valve 123 has a cylinder 123a connected to a hydraulic oil source 126 via a communication path 125, and an on / off control valve 124 is provided in the communication path 125. The on / off control valve 124 is an electromagnetic valve, and the first purge valve 123 is operated by the on / off control valve 124. That is, when the on / off control valve 124 is open, hydraulic oil from the hydraulic oil source 126 is supplied to the first purge valve 123 via the communication path 125, and when the on / off control valve 124 is closed, the hydraulic oil pressure in the communication path 125 decreases.

[0045] When piston 123b contacts the seat portion of cylinder 123a, first port portion 123c and second port portion 123d are blocked, and first purge path 122 is blocked between first path 122a and second path 122b. When piston 123b moves away from the seat portion of cylinder 123a, first purge valve 123 communicates between first port portion 123c and second port portion 123d, and first purge path 122 communicates between first path 122a and second path 122b. When the tip of piston 123b contacts the seat portion to close first purge path 122, the contact position between the tip and the seat becomes annular. The seat portion separates the first port portion 123c and the second port portion 123d, and when hydraulic oil is supplied to the first purge valve 123 from the communication path 125, the piston 123b is actuated.

[0046] Furthermore, the fuel injection valve 33 has a second purge path 127 provided in the needle valve 45, and the second purge path 127 is provided with a second purge valve 128. One end of the second purge path 127 is connected to the chamber 45c of the needle valve 45, and the other end joins the first purge path 122 and is connected to a second fuel recovery system (not shown). Similar to the first purge valve 123, the second purge valve 128 can be operated by the on / off control valve 124.

[0047] The second purge valve 128 has a cylinder 128a, a piston 128b, a first port 128c, and a second port 128d. The piston 128b is supported axially movably relative to the cylinder 128a. The first port 128c is provided on a side of the cylinder 128a on the tip side of the piston 128b. The second port 128d is provided on the tip of the piston 128b in the cylinder 128a. The second purge path 127 has a first path 127a and a second path 127b. One end of the first path 127a is connected to the chamber 45c and the other end is connected to the second port 128d. One end of the second path 127b is connected to the first port 128c.

[0048] Further, the second purge valve 128 has a cylinder 128a connected to the hydraulic oil source 126 via a communication path 129, and an on / off control valve 124 is provided in the communication path 129. That is, the first purge valve 123 and the second purge valve 128 are controlled to open and close by the same on / off control valve 124.

[0049] When piston 128b contacts the seat portion of cylinder 128a, second purge valve 128 blocks first port 128c from second port 128d, and second purge path 127 blocks first path 127a from second path 127b. When piston 128b moves away from the seat portion of cylinder 128a, second purge valve 128 connects first port 128c to second port 128d, and second purge path 127 connects first path 127a to second path 127b. When piston 128b contacts the seat portion of cylinder 128a to close second purge path 127, the contact position between the tip and the seat becomes annular. The seat portion separates the first port portion 128c and the second port portion 128d, and when hydraulic oil (first fuel) is supplied to the second purge valve 128 from the communication path 129, the piston 128b is actuated.

[0050] <Fuel injection system operation> FIG. 3 is a time chart showing the operation of the fuel injection device.

[0051] 2 and 3, when the supply pump 41 operates at crank angle a1, the first supply pressure of the first fuel in the first fuel supply path 43 increases, and the first supply pressure acts on the piston 72, causing the piston 72 to descend and decrease in lift (upper solid line in FIG. 3). Then, the bulge 77 of the piston 72 moves away from the seat 78, and the first fuel supply path 43 communicates with the first storage portion 75. When the first fuel in the first fuel supply path 43 is supplied to the first storage portion 75, the pressure P1 (middle solid line in FIG. 3) increases, the piston 72 further descends, and the second fuel in the second storage portion 76 is pressurized, causing the pressure P2 (upper dotted line in FIG. 3) to increase. At this time, the first fuel in the first fuel supply path 43, whose pressure has increased, flows from the first sealing path 82 to open the check valve 86, and the sealing pressure P3 of the needle valve 45 (two-dot chain line in FIG. 3) increases.

[0052] From crank angle a2 to crank angle a3, the lift amount of needle valve 45 increases, and when second supply pressure P2 of the second fuel in second reservoir 76 exceeds the injection pressure of needle valve 45, needle valve 45 is opened and the second fuel is sprayed from nozzle hole 45e of needle valve 45. When supply pump 41 subsequently stops, pressures P1 and P2 decrease, and from crank angle a4 to crank angle a5, needle valve 45 closes and injection ends. Then, from crank angle a5 to crank angle a6, the pressure of the first fuel in first fuel supply path 43 is increased due to the area difference between second pressure-receiving surface 72b and first pressure-receiving surface 72a of piston mechanism 47, check valve 91 closes and check valve 94 opens, and the first fuel is returned through return path 93, while piston 72 of piston mechanism 47 moves toward first fuel supply path 43. The seal pressure P3 of the needle valve 45 is always maintained at a pressure higher than the pressure of the second fuel, and is supplied to the sliding seal portion 45f of the needle valve 45, thereby maintaining the lubricity of the sliding seal portion 45f of the needle valve 45 and preventing the second fuel from leaking into the drain.

[0053] In the piston mechanism 47, when the piston 72 moves from the second fuel supply path 44 side to the first fuel supply path 43 side, the volume of the second storage portion 76 increases, and a predetermined amount of the second fuel is stored in the second storage portion 76. When the piston 72 reaches the first fuel supply path 43 side at crank angle a6, the bulge portion 77 of the piston 72 abuts against the seat portion 78, and communication between the first fuel supply path 43 and the first storage portion 75 is blocked. Then, the first supply pressure P1 of the first fuel in the first storage portion 75 (the solid line in the middle of FIG. 3 ) and the pressure P2 of the second fuel in the second storage portion 76 (the dotted line in the middle of FIG. 3 ) are maintained slightly higher than the first fuel pressure P4 of the first fuel in the first fuel supply path 43 (the dashed-dotted line in FIG. 3 ).

[0054] When the second fuel supply valve 111 is opened, the second fuel from the second fuel supply source 42 is supplied to the second storage portion 76 of the piston mechanism 47 through the second fuel supply path 44. When the piston 72 of the piston mechanism 47 moves downward, the second fuel in the second storage portion 76 is pressurized, and the pressure increases. When the pressure exceeds the valve opening pressure of the discharge valve 121, the second fuel is supplied to the needle valve 45. When the injection of the second fuel through the needle valve 45 ends, the pressure of the second fuel in the downstream path 62 of the second fuel supply path 44 decreases, but the pressure of the second fuel in the second path 62b partitioned by the discharge valve 121 becomes the sum of the second supply pressure of the second fuel and the valve opening pressure of the discharge valve 121. In other words, the pressure P5 downstream of the discharge valve 121 is maintained higher than the pressure P2 of the second storage portion 76. Therefore, the second fuel in the second passage 62b of the downstream passage 62 is prevented from vaporizing and is maintained in a liquid state.

[0055] 4 is a graph showing the relationship between the temperature and saturated vapor pressure of the second fuel. Note that in FIG. 4, ammonia is used as the second fuel for explanation.

[0056] 4 is a graph showing the change in saturated vapor pressure of the second fuel as the temperature of the second fuel increases, with the liquid state above the solid line and the gas state below the solid line. This shows that the more the pressure of the second fuel is increased or the more the pressure drop is suppressed, the higher the saturated temperature becomes, i.e., the more vaporization can be suppressed. In this embodiment, a discharge valve 121 is provided in the downstream path 62. Therefore, by separating the second path 62b with the discharge valve 121, the pressure drop of the second fuel in the second path 62b is suppressed, vaporization of the second fuel in the second path 62b is suppressed, and the liquid state of the second fuel is maintained.

[0057] Furthermore, when the second fuel is being injected, the high-pressure first fuel from the first fuel supply path 43 acts on the sliding seal portion 45f of the needle valve 45 through the first seal path 82 and the third seal path 84. On the other hand, when the second fuel is not being injected, the high-pressure first fuel from the first fuel supply source 85 acts on the sliding seal portion 45f of the needle valve 45 through the second seal path 83 and the third seal path 84. This makes it possible to prevent the second fuel from leaking to the drain while maintaining the lubricity of the sliding seal portion 45f of the valve body 45a.

[0058] Furthermore, needle valve 45 blocks communication between chamber 45c and fuel supply path 45d by seating valve element 45a on its seat due to the biasing force of biasing spring 45b. If the seat of needle valve 45 becomes defective or damaged, combustion gas (second fuel) from the combustion chamber may pass through needle valve 45 and enter second fuel supply path 44. Even in this case, discharge valve 121 is provided in downstream path 62, preventing combustion gas (second fuel) from the combustion chamber from entering second fuel supply path 44 upstream of discharge valve 121 and also preventing it from entering seal path 81. Furthermore, because the opening pressure of discharge valve 121 is higher than the supply pressure of the second fuel, discharge valve 121 is not opened by the pressure of the second fuel in second reservoir 76, preventing the outflow of the second fuel.

[0059] After the fuel injection valve 33 is stopped, it is necessary to discharge the second fuel remaining in the second fuel supply path 44 and the like. That is, when the first purge valve 123 and the second purge valve 128 are opened by the on-off control valve 124 and the purge gas supply valve 115 is opened, purge gas is supplied from the purge gas supply path 114 to the second fuel supply path 44. At this time, the second fuel supply valve 111 is in a closed state. Since the first purge valve 123 and the second purge valve 128 are opened, the first purge path 122 and the second purge path 127 are opened. Then, the purge gas supplied to the second fuel supply path 44 pushes out the second fuel remaining in the second reservoir 76 and the first path 62a of the downstream path 62, and the second fuel is discharged from the first purge path 122. Furthermore, the discharge valve 121 is opened by the purge gas supplied to the second fuel supply path 44 , and the second fuel remaining in the second path 62 b of the downstream path 62 is pushed out and discharged from the second purge path 127 .

[0060] FIG. 5 is a schematic diagram showing an example of the arrangement when the fuel injection device of the first embodiment is combined with another fuel injection device.

[0061] In the fuel injection device 17 of the first embodiment, the fuel injection valve 33 can inject only the second fuel. Therefore, it is useful to combine and apply another fuel injection device 18 that can inject only the first fuel with the fuel injection device 17 of the first embodiment. That is, as shown in FIG. 5 , the fuel injection device 17 includes a fuel supply device 31, a fuel supply path 32, and a fuel injection valve 33, and the fuel injection valve 33 injects the second fuel. The fuel injection device 18 includes a fuel supply device 18a, a fuel supply path 18b, and a fuel injection valve 18c, and the fuel injection valve 18c injects the first fuel. With this configuration, the fuel injection valve 18c can inject only the first fuel, and the fuel injection valve 33 can inject only the second fuel. Furthermore, the fuel injection valve 18c and the fuel injection valve 33 can inject both the first fuel and the second fuel. When only the second fuel is injected by the fuel injection valve 33, the first fuel injected from the fuel injection valve 18c can be used as the ignition fuel.

[0062] [Second embodiment] 6 is a schematic diagram showing the configuration of a fuel injection device according to a second embodiment. Members having the same functions as those in the first embodiment described above are given the same reference numerals, and detailed explanations thereof will be omitted.

[0063] 6, the fuel injection device 17A includes a fuel supply device 31, a fuel supply path 32, and a fuel injection valve 33A. The fuel supply device 31 has a first fuel supply source 40, a supply pump 41, and a second fuel supply source 42. The fuel supply path 32 has a first fuel supply path 43 and a second fuel supply path 44. The fuel injection valve 33A includes a needle valve 45 and a piston mechanism 47. The fuel injection valve 33A differs from the fuel injection valve 33 of the first embodiment in the configuration of the discharge valve.

[0064] The fuel injection valve 33A is provided with a second fuel supply valve 111 and a check valve 118 in an upstream path 61 of the second fuel supply path 44. The check valve 118 has a cylinder 118a, a piston 118b, and a communication path 118c. The piston 118b is supported so as to be movable axially relative to the cylinder 118a. The piston 118b moves in a direction along the upstream path 61. The communication path 118c is provided inside the piston 118b. The upstream path 61 is connected to the tip and base ends of the piston 118b in the cylinder 118a. When the check valve 118 moves toward the second fuel supply valve 111 and closes, the communication path 118c is closed and the upstream path 61 is shut off.

[0065] Furthermore, fuel injection valve 33A is provided with a discharge valve 131 in second fuel supply path 44 between needle valve 45 and piston mechanism 47, which prevents the second fuel from flowing back from needle valve 45 toward piston mechanism 47. Specifically, discharge valve 131 is provided in downstream path 62 connecting needle valve 45 and second reservoir 76 of piston mechanism 47.

[0066] The discharge valve 131 is a control valve that operates by a control oil pressure (pressure of the first fuel). The opening and closing of the discharge valve 131 can be controlled by an on-off control valve (discharge control unit) 132. That is, a hydraulic oil supply source 133 is connected to a pressure regulating valve 135 via a supply pump 134, and an on-off valve 137 and an on-off control valve 132 are connected in parallel to the pressure regulating valve 135 via a branch path 136. The on-off control valve 132 is then connected to the discharge valve 131 via a control path 138. The pressure regulating valve 135 regulates the pressure of the first fuel from the hydraulic oil supply source 133 to a predetermined pressure and supplies the pressure to the on-off valve 137 and the on-off control valve 132. Note that the pressure is preferably higher than the pressure of the second fuel in the second path 62b when injection of the second fuel is completed, but is not limited to this.

[0067] The discharge valve 131 has a cylinder 131a, a piston 131b, a first port portion 131c, a second port portion 131d, and a third port portion 131e. The piston 131b is supported axially movably relative to the cylinder 131a. The first port portion 131c is provided on a side portion of the cylinder 131a on the tip end side of the piston 131b. The second port portion 131d is provided in an intermediate portion of the piston 131b in the cylinder 131a. The third port portion 131e is provided at the base end of the piston 131b in the cylinder 131a. The first path 62a is connected to the tip end of the piston 131b in the cylinder 131a. The second path 62b is connected to the first port portion 131c. The control path 138 is connected to the third port portion 131e.

[0068] The on-off control valve 132 controls the opening and closing of the downstream path 62 in the second fuel supply path 44 by adjusting the control oil pressure (pressure of the first fuel) acting on the discharge valve 131, which is a control valve. The on-off control valve 132 has substantially the same function as, for example, the on-off control valve 124 of the first embodiment (see FIG. 2). The discharge valve 131 closes the first port portion 131c when a control oil pressure of a predetermined pressure is applied from the on-off control valve 132, thereby closing the downstream path 62. As a result, when the second fuel is injected, the discharge valve 131 opens and injection is performed when the pressure of the second fuel becomes higher than the control oil pressure, and the discharge valve closes at the end of injection, thereby maintaining the pressure in the second path 62b higher than the pressure in the first path 62a. The downstream path 62 in the second fuel supply path 44 is divided by the discharge valve 131 into an upstream first path 62a and a downstream second path 62b, and when the discharge valve 131 is closed, the first path 62a and the second path 62b are blocked, preventing the flow of the second fuel from the second path 62b to the first path 62a.

[0069] The needle valve 45 is provided with a seal path 81 that prevents the second fuel from flowing to the drain. The seal path 81 has a first seal path 82, a second seal path 83, and a third seal path 84. The upstream end of the first seal path 82 is connected to the first fuel supply path 43, and the first fuel is supplied from the first fuel supply path 43. The upstream end of the second seal path 83 is connected to the hydraulic oil supply source 133 via an on-off valve 137 or the like, and the first fuel is supplied. The downstream ends of the first seal path 82 and the second seal path 83 join together and are connected to the upstream end of the third seal path 84. The downstream end of the third seal path 84 is connected to the sliding seal portion 45f of the valve body 45a of the needle valve 45.

[0070] The first sealing passage 82 is provided with a sealing piston 141 that prevents the first fuel from flowing back from the needle valve 45 toward the first fuel supply passage 43. The sealing piston 141 has a cylinder 141a, a piston 141b, a first port portion 141c, and a second port portion 141d. The piston 141b is supported axially movably relative to the cylinder 141a. The first port portion 141c is provided on a side portion of the cylinder 141a near the tip end of the piston 141b. The second port portion 141d is provided on the base end of the piston 141b in the cylinder 141a and functions as a reservoir for the first fuel. An end of the upstream passage of the first sealing passage 82 is connected to the tip end of the piston 141b in the cylinder 141a. An end of the downstream passage of the first sealing passage 82, i.e., an upstream end of the third sealing passage 84, is connected to the second port portion 141d. When the seal piston 141 moves to the first fuel supply path 43 side and closes, the first port portion 141c is closed and the first seal path 82 is blocked.

[0071] The second sealing passage 83 is provided with a check valve 142 that prevents backflow of the first fuel from the needle valve 45 toward the hydraulic oil supply source 133. The check valve 142 has a cylinder 142a, a piston 142b, and a communication passage 142c. The piston 142b is supported so as to be axially movable relative to the cylinder 142a. The communication passage 142c is provided inside the piston 142b. An end of the upstream passage of the second sealing passage 83 is connected to the tip end of the piston 142b in the cylinder 142a. An end of the downstream passage of the second sealing passage 83, i.e., the upstream end of the third sealing passage 84, is connected to the base end of the piston 142b in the cylinder 142a. When the check valve 142 moves toward the on-off valve 137 and is closed, the communication passage 142c is closed and the second sealing passage 83 is shut off.

[0072] The third sealing path 84 is connected to the confluence of the first sealing path 82 and the second sealing path 83, and causes the pressure of the first fuel in the first fuel supply path 43 or the pressure of the first fuel adjusted by the pressure regulating valve 135 to act on the sliding seal portion 45f of the needle valve 45. Therefore, the sealing path 81 causes the pressure of the first fuel in the first fuel supply path 43 adjusted by the pressure regulating valve 135 to act on the sliding seal portion 45f of the needle valve 45, thereby maintaining the lubricity of the sliding seal portion 45f of the valve body 45a and suppressing the outflow of the second fuel to the drain.

[0073] The fuel injection valve 33A has a purge path 151 provided in the second fuel supply path 44, and the purge path 151 is provided with a purge valve 152. One end of the purge path 151 is connected to the second reservoir 76 of the piston mechanism 47, and the other end is connected to a second fuel recovery system (not shown). The purge valve 152 can be operated by an opening / closing control valve (purge control section) 132.

[0074] The purge valve 152 has a cylinder 152a, a piston 152b, a first port portion 152c, a second port portion 152d, and a third port portion 152e. The piston 152b is supported in the cylinder 152a so as to be freely movable in the axial direction. The first port portion 152c is provided on a side portion of the cylinder 152a on the tip end side of the piston 152b. The second port portion 152d is provided in an intermediate portion of the piston 152b in the cylinder 152a. The third port portion 152e is provided at the base end of the piston 152b in the cylinder 152a. The purge path 151 has an upstream path end leading to the second reservoir 67 connected to the first port portion 152c, and a downstream path end leading to the second fuel recovery system connected to the tip end of the piston 152b in the cylinder 152a. The control path 139 connected to the third port 131e of the discharge valve 131 is connected to the third port 152e.

[0075] When the piston 152b contacts the seat portion of the cylinder 152a, the first port portion 152c of the purge valve 152 is closed, blocking the purge path 151. When the piston 152b separates from the seat portion of the cylinder 152a, the first port portion 152c of the purge valve 152 is opened, opening the purge path 151.

[0076] In the fuel injection device 17A of the second embodiment, a discharge valve 131 is provided in the downstream path 62 of the second fuel supply path 44 as a control valve that is operated by a control oil pressure (pressure of the first fuel) supplied from an opening / closing control valve 132. The discharge valve 131 is operated by the control oil pressure, eliminating the need for a biasing member such as a spring, and thus simplifying the structure.

[0077] Furthermore, in the seal passage 81, a seal piston 141 is provided in the first seal passage 82, and a check valve 142 is provided in the first seal passage 82. The seal piston 141 has an area ratio of one end to the other end of a piston 142b of the seal piston 141 of 1:1. That is, the area ratio is set so that, during injection of the second fuel, the pressure of the first fuel in the first seal passage 82 can be maintained higher than the pressure of the second fuel in the second passage 62b downstream of the discharge valve 131. During injection of the second fuel, the pressure of the high-pressure first fuel in the first fuel supply passage 43 acts on the sliding seal portion 45f of the needle valve 45 through the first seal passage 82 (seal piston 141) and the third seal passage 84. On the other hand, when the second fuel is not being injected, the pressure of the first fuel adjusted by the pressure adjustment valve 135 acts on the sliding seal portion 45f of the needle valve 45 through the second seal path 83 (check valve 142) and the third seal path 84. At this time, the seal piston 141 moves to open and close the first seal path 82, allowing smooth switching of the hydraulic pressure source for the sliding seal portion 45f. This makes it possible to prevent the second fuel from leaking to the drain while maintaining the lubricity of the sliding seal portion 45f of the valve body 45a.

[0078] Furthermore, if the seat portion of needle valve 45 becomes defective or damaged, there is a risk that combustion gas from the combustion chamber will pass through needle valve 45 and enter first fuel supply path 43 or second fuel supply path 44. Even in this case, the provision of discharge valve 131 and seal piston 141 prevents combustion gas from the combustion chamber from entering second fuel supply path 44 upstream of discharge valve 131, and also prevents the combustion gas from entering the seal path 81 side.

[0079] After the fuel injection valve 33A is stopped, it is necessary to discharge the second fuel remaining in the second fuel supply path 44 and the like. That is, when the on-off control valve 132 opens the discharge valve 131 and the purge valve 152, purge gas is supplied to the second fuel supply path 44. At this time, when the second fuel supply valve 111 is opened, the purge gas supplied to the second fuel supply path 44 pushes out the second fuel remaining in the second reservoir 76 and the downstream path 62, and the second fuel is discharged from the purge path 151.

[0080] [Third embodiment] 7 is a schematic diagram showing the configuration of a fuel injection device according to a third embodiment. Members having the same functions as those in the second embodiment described above are given the same reference numerals, and detailed explanations thereof will be omitted.

[0081] 7, the fuel injection device 17B includes a fuel supply device 31, a fuel supply path 32, and a fuel injection valve 33B. The fuel supply device 31 has a first fuel supply source 40, a supply pump 41, and a second fuel supply source 42. The fuel supply path 32 has a first fuel supply path 43 and a second fuel supply path 44. The fuel injection valve 33B includes a needle valve 45 and a piston mechanism 47. The fuel injection valve 33B differs from the fuel injection valve 33A of the second embodiment in the configuration of the purge mechanism.

[0082] The piston mechanism 47 has a cylinder 71 and a piston 72. The piston 72 is supported inside the cylinder 71 so as to be freely movable in the axial direction. The piston mechanism 47 is provided with a first storage section 75 on the side of the first pressure-receiving surface 72a, and a second storage section 76 on the side of the second pressure-receiving surface 72b. The first storage section 75 communicates with the first fuel supply path 43 and stores the first fuel. The second storage section 76 communicates with the second fuel supply path 44 and stores the second fuel. In the piston mechanism 47, when the piston 72 moves most toward the first fuel supply path 43, the volume of the second storage section 76 is maximized, and when the piston 72 moves most toward the second fuel supply path 44, the volume of the first storage section 75 is maximized.

[0083] In fuel injection device 17B, one end of purge path 151 constituting the purge mechanism is connected to second storage portion 76. Fuel injection device 17B differs from fuel injection device 17A (see FIG. 6) in that purge valve 152 (see FIG. 6) is not provided in purge path 151. Although one end of purge path 151 is connected to second storage portion 76, purge path 151 and second storage portion 76 communicate with each other when piston 72 moves furthest toward first fuel supply path 43 and second storage portion 76 reaches its maximum volume.

[0084] Therefore, after the fuel injection valve 33B is stopped, the on-off control valve 132 opens the discharge valve 131, and purge gas is supplied to the second fuel supply path 44. At this time, when the second fuel supply valve 111 is opened, the purge gas supplied to the second fuel supply path 44 is supplied to the second storage portion 76, and the pressure in the second storage portion 76 increases. When the pressure in the second storage portion 76 increases, the piston 72 moves toward the first fuel supply path 43. Then, when the second storage portion 76 reaches its maximum volume, the purge path 151 communicates with the second storage portion 76. Then, the purge gas supplied to the second fuel supply path 44 pushes out the second fuel remaining in the second storage portion 76 and the downstream path 62, and the second fuel is discharged from the purge path 151.

[0085] The fuel injection device 17B of the third embodiment is provided with a purge path 151 that communicates with the second storage portion 76 when the piston moves and the second storage portion 76 reaches its maximum volume. When the piston moves away from the first fuel supply path 43 and the second storage portion 76 does not reach its maximum volume, the second storage portion 76 does not communicate with the purge path 151. This allows the piston 72 to appropriately pressurize the second fuel in the second storage portion 76. On the other hand, when purge gas at a predetermined pressure is supplied from the second fuel supply path 44 to the second storage portion 76, the piston 72 moves toward the first fuel supply path 43, the second storage portion 76 reaches its maximum volume, and the purge path 151 communicates with the second storage portion 76. This allows the second fuel remaining in the second fuel supply path 44, the second storage portion 76, and the like to be appropriately discharged. Furthermore, the purge mechanism does not require a purge valve, which simplifies the structure.

[0086] [Effects of this embodiment] The fuel injection device according to the first aspect includes a first fuel supply path (43) that supplies a first fuel having a predetermined ignition quality, a second fuel supply path (44) that supplies a second fuel having a lower ignition quality than the first fuel, fuel injection valves (33, 33A, 33B) having a needle valve (45) to which the second fuel supply path (44) is connected, a piston mechanism (47) that is provided between the first fuel supply path (43) and the second fuel supply path (44) and has a piston (72) that moves due to a pressure difference between a first supply pressure of the first fuel and a second supply pressure of the second fuel, and discharge valves (121, 131) that are provided in the second fuel supply path (44) between the needle valve (45) and the piston mechanism (47) and that prevent backflow of the second fuel from the needle valve (45) toward the piston mechanism (47).

[0087] According to the fuel injection device of the first aspect, piston 72 is moved by the pressure difference between the first supply pressure of the first fuel and the second supply pressure of the second fuel, thereby alternately performing a storage stroke of the second fuel and an injection stroke of the second fuel by fuel injection valves 33, 33A, 33B. That is, the first fuel and the second fuel are pressurized and supplied to piston mechanism 47 without being mixed together along the way. As a result, by suppressing mixing of the first fuel and the second fuel, highly accurate fuel injection is possible, and harmful substances contained in exhaust gas can be reduced.

[0088] Furthermore, the fuel injection device according to the first aspect is provided with discharge valves 121, 131 that prevent backflow of the second fuel from the needle valve 45 toward the piston mechanism 47. After injection of the second fuel by the needle valve 45 is completed, the discharge valves 121, 131 separate the second passage 62b between the needle valve 45 and the discharge valves 121, 131, thereby suppressing a drop in pressure. Therefore, the second fuel in the second passage 62b in the downstream passage 62 of the second fuel supply passage 44 is suppressed from vaporizing and maintained in a fluid state. As a result, vaporization of the second fuel remaining in the second fuel supply passage 44 can be suppressed, enabling highly accurate fuel injection.

[0089] The fuel injection device according to the second aspect is the fuel injection device according to the first aspect, further comprising: second fuel supply path 44 having an upstream path 61 connecting second fuel supply source 42 and second storage portion 76; and downstream path 62 connecting second storage portion 76 and needle valve 45; and discharge valves 121, 131 are provided in downstream path 62. This suppresses a pressure drop in second path 62b between discharge valves 121, 131 and needle valve 45, thereby suppressing vaporization of the second fuel.

[0090] The fuel injection device according to the third aspect is the fuel injection device according to the first or second aspect, and further, the discharge valves 121 and 131 are check valves, which simplifies the structure.

[0091] A fuel injection device according to a fourth aspect is the fuel injection device according to any one of the first to third aspects, and further, the valve opening pressure of discharge valves 121, 131 is higher than the second supply pressure of the second fuel supplied from second fuel supply source 42 to second fuel supply path 44. This prevents discharge valve 121 from being opened by the pressure of the second fuel in second reservoir 76, and makes it possible to suppress outflow of the second fuel.

[0092] A fuel injection device according to a fifth aspect is the fuel injection device according to any one of the first to fourth aspects, and further includes an opening / closing control valve (discharge control section) 132 that is a control valve and opens / closes the second fuel supply path 44 by controlling the control oil pressure acting on the discharge valve (control valve) 1312. As a result, the discharge valve 131 is operated by the control oil pressure, so that an urging member such as a spring is not required, and the structure can be simplified.

[0093] A fuel injection device according to a sixth aspect is the fuel injection device according to any one of the first to fifth aspects, further comprising a seal path 81 for supplying the first fuel to the sliding seal portion 45f of the needle valve 45. This makes it possible to maintain the lubricity of the sliding seal portion 45f of the valve body 45a of the needle valve 45 and to prevent the second fuel from flowing out to the drain.

[0094] A fuel injection device according to a seventh aspect is the fuel injection device according to the sixth aspect, and further includes a first seal path 82 that supplies the first fuel in the first fuel supply path 43 to the sliding seal portion 45f, and a second seal path 83 that supplies the first fuel at a higher pressure than the second fuel in the second fuel supply path 44 between the needle valve 45 and the piston mechanism 47 after the second fuel is injected. This makes it possible to apply the pressure of the high-pressure first fuel to the sliding seal portion 45f regardless of the injection of the second fuel.

[0095] The fuel injection device according to an eighth aspect is the fuel injection device according to the seventh aspect, further comprising: a seal piston 141 that prevents backflow of the first fuel from the needle valve 45 and is provided movably along the first seal passage 82; and a check valve 142 that prevents backflow of the first fuel from the needle valve 45 is provided in the second seal passage 83. As a result, when the second fuel is injected, the high-pressure first fuel in the first fuel supply passage 43 acts on the sliding seal portion 45f through the first seal passage 82 (seal piston 141). When the second fuel is not injected, the pressure of the first fuel adjusted by the pressure adjustment valve 135 acts on the sliding seal portion 45f through the second seal passage 83 (check valve 142). The seal piston 141 moves to open and close the first seal passage 82, allowing smooth switching of the hydraulic pressure source for the sliding seal portion 45f.

[0096] A fuel injection device according to a ninth aspect is the fuel injection device according to any one of the first to eighth aspects, and further includes a first purge path 122 connected to the second storage portion 76 to discharge the second fuel, a first purge valve 123 that opens and closes the first purge path 122, and an opening / closing control valve (purge control portion) 124 that controls the opening and closing of the first purge valve 123. As a result, the opening / closing control valve 124 controls the opening and closing of the first purge valve 123, so that the second fuel remaining in the second fuel supply path 44 and the second storage portion 76 can be discharged to the outside.

[0097] A fuel injection device according to a tenth aspect is the fuel injection device according to any one of the first to eighth aspects, and further includes a second purge path 127 connected to chamber 45c of needle valve 45 to discharge the second fuel, a second purge valve 128 that opens and closes second purge path 127, and an opening / closing control valve (purge control section) 124 that controls the opening and closing of second purge valve 128. As a result, by controlling the opening and closing of second purge valve 128 with opening / closing control valve 124, the second fuel remaining in second fuel supply path 44 and needle valve 45 can be discharged to the outside.

[0098] A fuel injection device according to an eleventh aspect is the fuel injection device according to any one of the first to eighth aspects, and further includes a purge path 151 having one end connected to the second reservoir 76 and discharging the second fuel, a purge valve 152 that opens and closes the purge path 151, and an on-off control valve (purge control unit) 132 that controls the opening and closing of the second purge valve 128. As a result, the on-off control valve 132 controls the opening and closing of the purge valve 152, so that the second fuel remaining in the second fuel supply path 44 and the needle valve 45 can be discharged to the outside. Furthermore, by providing only one set of the purge path 151 and the purge valve 152, the structure can be simplified.

[0099] A fuel injection device according to a twelfth aspect is the fuel injection device according to any one of the first to eighth aspects, further including a purge path 151 connected to the second storage portion 76 and discharging the second fuel when the piston 72 moves and the second storage portion 76 reaches its maximum volume. As a result, when purge gas of a predetermined pressure is supplied from the second fuel supply path 44 to the second storage portion 76, the piston 72 moves and the second storage portion 76 reaches its maximum volume, and the purge path 151 comes into communication with the second storage portion 76, so that the second fuel remaining in the second fuel supply path 44, the second storage portion 76, etc. can be appropriately discharged. Furthermore, there is no need to provide a purge valve in the purge path 151, which simplifies the structure.

[0100] A fuel injection device according to a thirteenth aspect is the fuel injection device according to any one of the first to twelfth aspects, further comprising: a piston mechanism 47 including a cylinder 71 provided between the first fuel supply path 43 and the second fuel supply path 44; and a piston 72 movably supported by the cylinder 71, wherein the piston 72 has a first pressure-receiving surface 72a at one end thereof on which a first supply pressure acts and a second pressure-receiving surface 72b at the other end thereof on which a second supply pressure acts, the area of ​​the first pressure-receiving surface 72a being smaller than the area of ​​the second pressure-receiving surface 72b. This makes the pressure of the first fuel in the first fuel supply path 43 higher than the pressure of the second fuel in the second fuel supply path 44, and therefore the second fuel in the second fuel supply path 44 does not flow toward the first fuel supply path 43 and mix with the first fuel. The recovered first fuel does not contain the second fuel, making it easier to process.

[0101] A reciprocating internal combustion engine according to a fourteenth aspect includes a diesel engine body 11 having a combustion chamber 25, and a fuel injection device 17, 17A, 17B according to any one of the first to seventeenth aspects that injects fuel into the combustion chamber 25. This makes it possible to suppress vaporization of the second fuel remaining in the second fuel supply path 44, thereby enabling highly accurate fuel injection. [Explanation of symbols]

[0102] 10 Marine diesel engines (reciprocating internal combustion engines) 11 Diesel engine body (internal combustion engine body) 12 Cylinder liner 13 Piston 14 Scavenging trunk 15 Exhaust manifold 16 Exhaust valve 17,17A,17B Fuel injection device 31 Fuel supply system 32 Fuel supply route 33, 33A, 33B fuel injection valve 40 Primary fuel source 41 Supply Pump 42 Secondary fuel source 43 First fuel supply route 44 Second fuel supply line 45 Needle valve 47 Piston mechanism 51 Piston 52 Plunger 53 First hydraulic oil supply line 54 Working fluid source 55 First solenoid valve 56 Control Unit 61 Upstream Route 62 Downstream Route 71 cylinders 72 Piston 72a First pressure surface 72b Second pressure surface 73 Rod section 74 Main body 75 First storage section 76 Second storage section 77 Bulge 78 Seat section 79 Sliding part 80 Drain path 81 Seal Path 82 First seal path 83 Second seal path 84 Third Seal Route 85 1st fuel source 86,87 Check valve 91,92 Check valve 93 Return Route 94 Check valve 111 Second fuel supply valve 112 Nitrogen Sources 121 Discharge valve (check valve) 122 First Purge Path 123 First purge valve 124 Opening and closing control valve (purge control section) 125 Connecting Route 126 Hydraulic oil source 127 Second Purge Path 128 Second purge valve 131 Discharge valve (control valve) 132 Opening and closing control valve (discharge control section, purge control section) 133 Hydraulic oil supply source 134 Supply Pump 135 Pressure Regulating Valve 136 Branching Routes 137 On-off valve 138,139 Control Path 141 Sealed Piston 142 Check valve 151 Purge Route

Claims

1. a first fuel supply path for supplying a first fuel having a predetermined ignition property; a second fuel supply path for supplying a second fuel having lower ignition ability than the first fuel; a fuel injection valve having a needle valve to which the second fuel supply path is connected; a piston mechanism provided between the first fuel supply path and the second fuel supply path, the piston moving in response to a pressure difference between a first supply pressure of the first fuel and a second supply pressure of the second fuel; a discharge valve provided in the second fuel supply path between the needle valve and the piston mechanism to prevent backflow of the second fuel from the needle valve toward the piston mechanism; A fuel injection device comprising:

2. the piston mechanism has a first storage portion to which the first fuel supply path is connected and a second storage portion to which the second fuel supply path is connected, the second fuel supply path has an upstream path connecting a second fuel supply source and the second storage portion and a downstream path connecting the second storage portion and the needle valve, and the discharge valve is provided in the downstream path.

2. The fuel injection system of claim 1.

3. The discharge valve is a check valve.

3. A fuel injection device according to claim 1 or 2.

4. a valve opening pressure of the check valve that is higher than a second supply pressure of the second fuel that is supplied from a second fuel supply source to the second fuel supply path; 4. The fuel injection system of claim 3.

5. the discharge valve is a control valve and has a discharge control section that opens and closes the second fuel supply path by controlling a control oil pressure acting on the control valve.

2. The fuel injection system of claim 1.

6. the needle valve is connected to the second fuel supply path downstream of the piston mechanism, and a seal path is provided to supply the first fuel to a sliding seal portion of the needle valve.

2. The fuel injection system of claim 1.

7. the seal path includes a first seal path that supplies the first fuel in the first fuel supply path to the sliding seal portion, and a second seal path that supplies the first fuel at a pressure higher than that of the second fuel in the second fuel supply path between the needle valve and the piston mechanism after injecting the second fuel.

7. The fuel injection system of claim 6.

8. a seal piston that prevents backflow of the first fuel from the needle valve is provided movably along the first seal path, and a check valve that prevents backflow of the first fuel from the needle valve is provided in the second seal path.

8. A fuel injection system according to claim 7.

9. the piston mechanism has a first storage portion to which the first fuel supply path is connected and a second storage portion to which the second fuel supply path is connected, a first purge path connected to the second storage portion and discharging the second fuel, a first purge valve that opens and closes the first purge path, and a purge control portion that controls the opening and closing of the first purge valve.

2. The fuel injection system of claim 1.

10. the needle valve is connected to the second fuel supply path downstream of the piston mechanism, and includes a second purge path connected to a chamber of the needle valve to discharge the second fuel, a second purge valve that opens and closes the second purge path, and a purge control unit that controls the opening and closing of the second purge valve.

10. The fuel injection system of claim 9.

11. the piston mechanism has a first storage portion to which the first fuel supply path is connected and a second storage portion to which the second fuel supply path is connected, a purge path having one end connected to the second storage portion and discharging the second fuel, a purge valve that opens and closes the purge path, and a purge control portion that controls the opening and closing of the purge valve.

2. The fuel injection system of claim 1.

12. the piston mechanism has a first storage portion to which the first fuel supply path is connected and a second storage portion to which the second fuel supply path is connected, and a purge path connected to the second storage portion and discharging the second fuel when the piston moves and the second storage portion reaches a maximum volume; 2. The fuel injection system of claim 1.

13. the piston mechanism includes a cylinder provided between the first fuel supply path and the second fuel supply path, and the piston movably supported by the cylinder, the piston having a first pressure-receiving surface on which the first supply pressure acts at one end and a second pressure-receiving surface on which the second supply pressure acts at the other end, the area of ​​the first pressure-receiving surface being smaller than the area of ​​the second pressure-receiving surface; 2. The fuel injection system of claim 1.

14. an internal combustion engine body having a combustion chamber; a fuel injection device according to claim 1 for injecting fuel into the combustion chamber; A reciprocating internal combustion engine comprising:

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