Engine

Abstract

To provide an engine capable of suppressing occurrence of abnormal combustion by avoiding remaining of gas fuel.SOLUTION: The engine includes a cylinder head, an intake port formed in the cylinder head, a surge tank disposed on one side in an up-down direction with respect to an inlet portion of the intake port, a communication passage that allows the surge tank and the intake port to communicate with each other, and a gaseous fuel injector that injects gaseous fuel. The injection port of the gaseous fuel injector is disposed in the communication passage only on the other side in the vertical direction with respect to the central axis of the communication passage.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Patent document 1 discloses an engine including a cylinder head, an intake pipe connected to an intake port of the cylinder head, and a fuel gas supply device provided in the intake pipe for injecting fuel gas into air flowing through an intake passage of the intake pipe. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-25117 Summary of the Invention [Problem to be solved by the invention]

[0004] If fuel gas (gaseous fuel) injected from a fuel gas supply device (gaseous fuel injector) remains in the intake passage, there is a risk of abnormal combustion due to unintended ignition of the fuel gas. For this reason, it is desirable to configure the engine so that fuel gas is quickly discharged from the intake passage. However, Patent Document 1 does not consider this point.

[0005] The present invention has been made to solve the above problems, and its object is to provide an engine that can prevent gaseous fuel from remaining and suppress the occurrence of abnormal combustion. [Means for solving the problem]

[0006] An engine according to one aspect of the present invention comprises a cylinder head, an intake port formed in the cylinder head, a surge tank arranged on one side in the vertical direction relative to the inlet of the intake port, a communication passage connecting the surge tank and the intake port, and a gas fuel injector that injects gas fuel, wherein the nozzle of the gas fuel injector is arranged in the communication passage only on the other side in the vertical direction relative to the central axis of the communication passage. [Effects of the Invention]

[0007] According to the above configuration, it is possible to prevent gaseous fuel from remaining and suppress the occurrence of abnormal combustion. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an explanatory diagram schematically illustrating a general configuration of an engine according to an embodiment of the present invention; [Figure 2] FIG. 2 is a perspective view showing a schematic configuration of the engine, as seen from the left front. [Figure 3] FIG. 4 is a side view showing a configuration of an adapter provided in the engine. [Figure 4] FIG. 2 is a cross-sectional view of the adapter. [Figure 5] FIG. 2 is an explanatory diagram schematically illustrating the configuration of a combustion chamber of the engine. [Figure 6] FIG. 2 is an explanatory diagram illustrating the opening and closing timing of an intake valve and an exhaust valve provided in the engine. [Figure 7] FIG. 2 is a bottom view showing the configuration of a tip portion of a liquid fuel injector provided in the engine. [Figure 8] 4 is a flowchart showing a process for switching the engine from a liquid fuel mode to a gas fuel mode. [Figure 9] 10 is an explanatory diagram illustrating the injection amount of liquid fuel per unit time and the injection amount of gas fuel per unit time when switching from the liquid fuel mode to the gas fuel mode. FIG. [Figure 10]4 is a graph showing a change in pressure of the liquid fuel injected from the liquid fuel injector. DETAILED DESCRIPTION OF THE INVENTION

[0009] The following describes an embodiment of the present invention with reference to the drawings.

[0010] [1. Engine Overview] Fig. 1 is an explanatory diagram showing a schematic configuration of an engine 1 according to an embodiment of the present invention. Fig. 2 is a perspective view showing the schematic configuration of the engine 1 from the left front. The engine 1 is mounted on, for example, a tractor TR. In addition to the tractor TR, the engine 1 may also be mounted on agricultural machinery such as a combine harvester, construction machinery such as a hydraulic excavator, a ship, etc.

[0011] The engine 1 of this embodiment has a liquid fuel mode and a gas fuel mode. In the liquid fuel mode, the engine 1 compresses air drawn in from the outside (also called intake air), injects liquid fuel into the heated air, and burns (auto-ignites) the liquid fuel to generate power. In this embodiment, the liquid fuel is diesel oil, but is not limited to this. For example, the liquid fuel may be heavy oil, biofuel, or the like. In other words, the liquid fuel mode is a mode in which the engine 1 functions as, for example, a diesel engine.

[0012] In the gaseous fuel mode, the engine 1 generates power by injecting gaseous fuel into the intake air to generate a mixture, compressing the mixture, and injecting liquid fuel into the heated mixture to combust the gaseous fuel (in the mixture). More specifically, the gaseous fuel is ignited and burned by the self-ignition of the liquid fuel injected into the heated mixture. That is, in the gaseous fuel mode, the liquid fuel functions as an ignition fuel. In this embodiment, the gaseous fuel is hydrogen, but is not limited to this. For example, the gaseous fuel may be ammonia, natural gas, or the like.

[0013] The engine 1 includes an engine body 2, an intake pipe 3, an intake manifold 4, an adapter 5, an exhaust manifold 6, an exhaust pipe 7, and a turbocharger 8. The engine body 2 has a cylinder block 21, an oil pan 22, a piston 23, and a cylinder head 24. That is, the engine 1 includes the cylinder block 21, the oil pan 22, the piston 23, and the cylinder head 24.

[0014] Here, directions in this embodiment are defined as follows. As shown in FIG. 2 in particular, the direction in which the cylinder block 21 and the oil pan 22 are aligned is the up-down direction. The direction in which the oil pan 22 is located relative to the cylinder block 21 is the "downward" direction, and the opposite direction (the direction in which the cylinder head 24 is located) is the "upward" direction. Furthermore, the direction in which the intake manifold 4 is located relative to the cylinder block 21, from bottom to top, is the "leftward" direction, and the opposite direction (the direction in which the exhaust manifold 6 is located) is the "rightward" direction. Furthermore, the direction perpendicular to the up-down and left-right directions is the front-rear direction. The side where a compressor 81 (described later) included in the turbocharger 8 is located is the "front," and the side where a turbine 82 (described later) included in the turbocharger 8 is located is the "rearward" direction. In the drawings, the front is indicated by the symbol "F," the rear by the symbol "B," the right by the symbol "R," the left by the symbol "L," the top by the symbol "U," and the bottom by the symbol "D," as necessary. It should be noted that these directions are names used merely for the purpose of explanation and are not intended to limit the actual positional relationship and direction.

[0015] The cylinder block 21 is made of a rectangular parallelepiped metal member extending in the front-rear direction, with its longitudinal direction aligned along the front-rear direction. An oil pan 22 that stores lubricating oil is connected to the bottom of the cylinder block 21.

[0016] A cylindrical cylinder 21a extending in the vertical direction is formed in the cylinder block 21. The cylinders 21a extend downward from the upper surface of the cylinder block 21, and a plurality of cylinders 21a (six in this embodiment) are provided lined up in the front-rear direction. In other words, the engine 1 of this embodiment is equipped with a plurality of cylinders 21a (six in this embodiment).

[0017] A piston 23 is housed in each cylinder 21a so as to be slidable up and down within the cylinder 21a (see also FIG. 5, which will be described later). That is, the piston 23 reciprocates within the cylinder 21a. Each piston 23 is made of a cylindrical metal member.

[0018] Each piston 23 is connected to a crankshaft (not shown) via a connecting rod (not shown). The crankshaft is supported at the bottom of the cylinder block 21 so as to be rotatable relative to the cylinder block 21. When each piston 23 reciprocates within each cylinder 21a, the crankshaft rotates, and power (also referred to as rotational power) can be extracted from the engine 1 (crankshaft) to the outside.

[0019] The cylinder head 24 is made of a metal member having a substantially rectangular parallelepiped shape and is connected to the upper part of the cylinder block 21. A cylinder head 24 is provided corresponding to each cylinder 21a of the cylinder block 21. That is, in this embodiment, six cylinder heads 24 are provided. Each cylinder head 24 is disposed above a corresponding cylinder 21a. The space enclosed by the inner circumferential surface of the cylinder 21a, the top surface 23a of the piston 23 (see FIG. 5 described later), and the lower surface of the cylinder head 24 is called the combustion chamber 2a.

[0020] An intake port 24a is formed in each cylinder head 24. That is, the engine 1 is provided with a plurality of intake ports 24a (six in this embodiment). More specifically, the intake port 24a extends downward from the left side surface of each cylinder head 24 toward the right, and is connected to each combustion chamber 2a (each cylinder 21a). That is, the cylinder 21a is connected to the intake port 24a.

[0021] A plurality of (six in this embodiment) liquid fuel injectors 10 are provided in the cylinder head 24, one for each combustion chamber 2a (each cylinder 21a). That is, the engine 1 includes the liquid fuel injectors 10 attached to the cylinder head 24.

[0022] Each liquid fuel injector 10 injects liquid fuel stored at high pressure in a common rail 11 into each combustion chamber 2a at a predetermined timing. The liquid fuel is pumped to the common rail 11 by a supply pump 12 driven by power supplied from the crankshaft via a belt (not shown) or the like.

[0023] The intake pipe 3 draws in air from the outside and supplies it to the intake manifold 4. The intake manifold 4 supplies the air supplied from the intake pipe 3 to each combustion chamber 2a (each cylinder 21a) via the adapter 5 and each intake port 24a. Therefore, the air supplied from the intake manifold 4 flows through each intake port 24a.

[0024] The intake manifold 4 is made of a metal member integrally having a surge tank 41 connected to the intake pipe 3 and a plurality of branch pipes 42 extending from the surge tank 41. In other words, the engine 1 is equipped with the surge tank 41. The surge tank 41 is provided to suppress pulsation of air (intake pulsation) supplied to each combustion chamber 2a. The plurality of branch pipes 42 are connected to an adapter 5.

[0025] The adapter 5 is connected to each branch pipe 42 and each intake port 24a (cylinder head 24). In this embodiment, the adapter 5 enables connection between two adjacent branch pipes 42 and two adjacent intake ports 24a. For this reason, three adapters 5 are provided in this embodiment. The configuration of the adapters 5 will be described later.

[0026] Each adapter 5 is provided with two gaseous fuel injectors 15 corresponding to adjacent combustion chambers 2a (each cylinder 21a). That is, the engine 1 is provided with a plurality of gaseous fuel injectors 15 (six in this embodiment) corresponding to each cylinder 21a.

[0027] Each gaseous fuel injector 15 injects, at a predetermined timing, gaseous fuel stored in a gaseous fuel supply pipe 16. The gaseous fuel supply pipe 16 is connected to a gaseous fuel tank TR2 that stores gaseous fuel via a pressure regulating valve 17 and a valve unit TR1.

[0028] The pressure regulating valve 17 is capable of adjusting the pressure of the gaseous fuel stored in the gaseous fuel supply pipe 16. The valve unit TR1 is configured to include various control valves. The various control valves include an on / off valve that can switch on / off communication between the gaseous fuel supply pipe 16 and the gaseous fuel tank TR2, a bleed valve that is used when discharging the gaseous fuel from the gaseous fuel supply pipe 16 or the gaseous fuel tank TR2, and the like.

[0029] The valve unit TR1 and the gas fuel tank TR2 are provided in the tractor TR separately from the engine 1. The valve unit TR1 and the gas fuel tank TR2 are not limited to the above configuration, and may be provided integrally with the engine 1, for example.

[0030] In this embodiment, the gaseous fuel injectors 15, the gaseous fuel supply pipe 16, the pressure regulating valve 17, the valve unit TR1, and the gaseous fuel tank TR2 are collectively referred to as a gaseous fuel supply unit GS.

[0031] The exhaust manifold 6 collects exhaust gases discharged from each combustion chamber 2a and discharges the collected exhaust gases into an exhaust pipe 7. The exhaust pipe 7 discharges the exhaust gases collected by the exhaust manifold 6 to the outside.

[0032] The turbocharger 8 has a compressor 81 provided in the intake pipe 3, a turbine 82 provided in the exhaust pipe 7, and a connecting shaft 83 connecting the compressor 81 and the turbine 82. The turbine 82 rotates when exposed to exhaust gas flowing through the exhaust pipe 7. The compressor 81 is driven by the rotational power of the turbine 82 transmitted via the connecting shaft 83, and compresses air taken in from the outside. Therefore, the turbocharger 8 can increase the amount of air supplied to each combustion chamber 2a (each cylinder 21a).

[0033] Furthermore, the intake pipe 3 and the exhaust pipe 7 are configured to be able to communicate with each other via a bypass pipe 9. More specifically, one end of the bypass pipe 9 is connected to the intake pipe 3, and the other end is connected to the exhaust pipe 7. The bypass pipe 9 is provided with a bypass valve 91 that enables on / off switching of the communication between the intake pipe 3 and the exhaust pipe 7. When the bypass valve 91 is operated to connect the intake pipe 3 and the exhaust pipe 7, a portion of the intake air is discharged directly to the exhaust pipe 7 (without passing through the engine body 2). This adjusts the air-fuel ratio during combustion in each combustion chamber 2a. The air-fuel ratio refers to the mixture ratio of air and fuel (liquid fuel or gaseous fuel).

[0034] The tractor TR on which the engine 1 is mounted is provided with a control device TR3 in addition to the engine 1, a valve unit TR1, and a gas fuel tank TR2. The control device TR3 is composed of an electronic control unit also called an ECU (Electronic Control Unit). The control device TR3 electrically controls each part of the tractor TR, including the engine 1. A sensor TR4 is connected to the control device TR3.

[0035] The sensor TR4 detects information related to the engine 1 and outputs the detected information to the control device TR3. In this embodiment, the sensor TR4 includes multiple types of sensors. Each of the multiple types of sensors is connected to the control device TR3 so that it can input a signal thereto. The multiple types of sensors include, for example, a pressure sensor that detects the pressure in the combustion chamber 2a, a leak sensor that detects leakage of gaseous fuel, and the like. Note that the control device TR3 is not limited to the above configuration and may be, for example, integrally provided with the engine 1.

[0036] [2. Adapter configuration] The configuration of the adapter 5 will be described with reference to Figures 3 and 4. Figure 3 is a side view showing the configuration of the adapter 5. Figure 4 is a cross-sectional view of the adapter 5 taken in the left-right direction at the position along line A-A' in Figure 3. The adapter 5 includes a flow path portion 51 and a cover 52.

[0037] The flow path section 51 is made of a metal member integrally including a pair of blocks 51a aligned in the front-rear direction and a flat plate 51b extending horizontally and connecting the upper parts of the blocks 51a. A passage 51a1 penetrating in the left-right direction is formed in each block 51a. That is, a plurality of passages 51a1 are integrally provided in the adapter 5. Each passage 51a1 is formed rectangular in side view. Note that the shape of the passage 51a1 is not limited to the above and may be, for example, circular, elliptical, or a polygon other than a rectangle. In addition, a through-hole 51H penetrating (the upper part of) the block 51a and the flat plate 51b is provided in the upper part of the adapter 5 from the upper surface of each passage 51a1 upward.

[0038] The gas fuel injectors 15 are attached to the flow passage portions 51. In this embodiment, a gas fuel injector 15 is attached to each passage 51a1. Specifically, two gas fuel injectors 15 are provided for one flow passage portion 51.

[0039] The gas fuel injector 15 has a main body 15a and a nozzle 15b that protrudes downward from the bottom surface of the main body 15a. That is, the nozzle 15b protrudes toward the other side in the vertical direction (downward in this embodiment). The main body 15a includes an electromagnetic valve and the like. Note that, for convenience, the interior of the main body 15a is not shown in FIG. 4.

[0040] An injection port 15b1 is provided on the right side (opposing the intake port 24a) of the tip (lower end) of the nozzle 15b. The injection port 15b1 is formed in a circular shape in side view. The shape of the injection port 15b1 is not limited to the above and may be, for example, an ellipse, a rectangle, a polygon other than a rectangle, or the like. When the gaseous fuel injector 15 injects gaseous fuel, the gaseous fuel is injected from the injection port 15b1.

[0041] The nozzle 15b may be configured such that the tip thereof is bent to the right (toward the intake port 24a). In this case, the injection port 15b1 is preferably provided at the bent tip thereof so as to face the intake port 24a.

[0042] When attaching the gaseous fuel injector 15 to the flow path portion 51, the gaseous fuel injector 15 is moved from above to below the flow path portion 51 while aligning the nozzle 15b with the through-hole 51H. Then, the nozzle 15b is inserted into the through-hole 51H, and the gaseous fuel injector 15 can be disposed in the flow path portion 51.

[0043] A distribution pipe 16a extending from the gaseous fuel supply pipe 16 (see FIGS. 1 and 2) is connected to each gaseous fuel injector 15 attached to the flow path portion 51. The distribution pipe 16a is configured by branching the lower end of a vertically extending metal tubular member to the front and rear. The gaseous fuel injectors 15 are connected to the front and rear branches of the branched lower end of the distribution pipe 16a. The upper end of the distribution pipe 16a is connected to the gaseous fuel supply pipe 16.

[0044] A part of the gas fuel injector 15 attached to the flow path portion 51 is covered by a cover 52. The cover 52 protects the gas fuel injector 15 (particularly the main body portion 15a).

[0045] As shown in FIG. 4 in particular, one end (the left end) of the passage 51a1 of the flow path portion 51 is connected to the conduit 42a of the branch pipe 42, and the other end (the right end) is connected to the inlet 24a1 of the intake port 24a. In this embodiment, the inlet 24a1 of the intake port 24a refers to the left end of the intake port 24a. Therefore, air supplied from the intake pipe 3 (see FIG. 1) to the surge tank 41 flows through the conduit 42a of the branch pipe 42 and the passage 51a1 of the flow path portion 51, and is supplied to the intake port 24a. In other words, the surge tank 41 and the intake port 24a are connected by the conduit 42a of the branch pipe 42 and the passage 51a1 of the flow path portion 51.

[0046] In this embodiment, the pipe 42a of the branch pipe 42 and the passage 51a1 of the flow path portion 51 are collectively referred to as a communication passage 100. That is, the engine 1 of this embodiment is provided with the communication passage 100, which communicates between the surge tank 41 and the intake port 24a.

[0047] In particular, the pipe 42a of the branch pipe 42 is referred to as a first communication passage 101, and the passage 51a1 of the flow path portion 51 is referred to as a second communication passage 102. That is, the communication passage 100 has the first communication passage 101 connected to the surge tank 41, and the second communication passage 102 connected to the first communication passage 101 and the intake port 24a.

[0048] In this embodiment, the surge tank 41 is disposed above the inlet portion 24a1 of the intake port 24a. That is, the surge tank 41 is disposed on one side (above in this embodiment) of the inlet portion 24a1 of the intake port 24a in the up-down direction. The branch pipe 42 extending from the surge tank 41 extends while sloping downward as it moves from left to right, and is connected to the adapter 5 (particularly the flow path portion 51). Therefore, the pipe 42a of the branch pipe 42 also extends while sloping downward as it moves from left to right. That is, the first communication passage 101 (the pipe 42a of the branch pipe 42 in this embodiment) slopes toward the other side (down in this embodiment) in the up-down direction as it moves from the surge tank 41 side (left in this embodiment) toward the second communication passage 102 side (right in this embodiment).

[0049] More specifically, a first wall surface 101a is located on the upper side of the first communication passage 101, and a second wall surface 102a is located on the lower side of the second communication passage 102. That is, the first communication passage 101 includes the first wall surface 101a located on one side in the vertical direction (upper in this embodiment), and the second communication passage 102 includes the second wall surface 102a located on the other side in the vertical direction (lower in this embodiment). In addition, the injection port 15b1 of the gas fuel injector 15 is located on the lower side of the second communication passage 102 (between the center axis C1 of the second communication passage 102 and the second wall surface 102a in the vertical direction). In detail, the injection port 15b1 is located on the lower side of the second communication passage 102, out of the lower side of the second communication passage 102 and the upper side of the second communication passage 102 (between the central axis C1 of the second communication passage 102 and the wall surface of the second communication passage 102 that faces the second wall surface 102a in the up-down direction). That is, the injection port 15b1 is arranged only on the other side (lower in this embodiment) of the central axis C1 of the communication passage 100 in the up-down direction in the communication passage 100 (the second communication passage 102 in this embodiment).

[0050] The first wall surface 101a is inclined so that a first intersection P1 between a straight line L1 extending along the first wall surface 101a toward the second wall surface 102a and the second wall surface 102a is positioned to the left of the injection port 15b1. That is, the straight line L1 intersects with the second wall surface 102a at a position shifted toward the first communication passage 101 (to the left in this embodiment) with respect to the injection port 15b1. As a result, air flowing near the first wall surface 101a in the first communication passage 101 flows along the first wall surface 101a and toward the second wall surface 102a. Therefore, the air flowing through the second communication passage 102 flows faster on the lower side of the second communication passage 102 than on the upper side of the second communication passage 102. In other words, the flow velocity of the air flowing through the second communication passage 102 is greater on the lower side than on the upper side (see the dashed arrow in FIG. 4).

[0051] According to the above configuration, for example, compared to a configuration in which the injection port 15b1 is disposed on one side (upper side in this embodiment) in the up-down direction with respect to the central axis C1 of the communication passage 100, the gaseous fuel injected from the injection port 15b1 can be supplied to the intake port 24a more quickly. That is, the gaseous fuel can be quickly discharged from the communication passage 100. This makes it possible to prevent the gaseous fuel from remaining, for example, near the injection port 15b1. Therefore, it is possible to prevent the remaining gaseous fuel from unintentionally igniting and causing abnormal combustion. As a result, it is possible to prevent the gaseous fuel from remaining and to suppress the occurrence of abnormal combustion.

[0052] The following configuration is desirable from the viewpoint of improving the dischargeability of the gaseous fuel from the communication passage 100 while increasing the degree of freedom in the layout of the gaseous fuel injector 15. That is, in a configuration like this embodiment in which the gaseous fuel injector 15 has a nozzle 15b that protrudes toward the other side in the up-down direction (downward in this embodiment), the injection port 15b1 is desirably provided in the nozzle 15b.

[0053] From the viewpoint of reliably realizing a configuration in which the flow velocity of air flowing through the second communication passage 102 in which the injection port 15b1 is arranged is made higher on the lower side than on the upper side, the following configuration is desirable: That is, as in this embodiment, it is desirable that the first communication passage 101 connected to the second communication passage 102 be inclined to the other side in the up-down direction (downward in this embodiment) as it moves from the surge tank 41 side toward the second communication passage 102 side.

[0054] In a configuration in which first communication passage 101 includes a first wall surface 101a on the upper side and second communication passage 102 includes a second wall surface 102a on the lower side, the following configuration is desirable from the viewpoint of making first wall surface 101a function as an air guide plate that guides air flowing near first wall surface 101a to second wall surface 102a. That is, as in this embodiment, it is desirable that straight line L1 extending along first wall surface 101a toward second wall surface 102a intersects with second wall surface 102a at a position shifted toward first communication passage 101 (to the left in this embodiment) with respect to injection port 15b1.

[0055] As described above, in this embodiment, three adapters 5 are provided, each having two passages 51a1 (second communication passages 102) integrally formed therein. That is, the engine 1 of this embodiment is provided with a plurality of communication passages 100 (particularly the second communication passages 102). In particular, in one adapter 5, the intake ports 24a connected to the plurality of passages 51a1 formed in this adapter 5 are adjacent to each other. That is, in this embodiment, the communication passages 100 (second communication passages 102) corresponding to adjacent intake ports 24a are integrally formed.

[0056] If the communication passages 100 corresponding to adjacent intake ports 24a are integrally formed, the number of parts can be reduced compared to, for example, a configuration in which the communication passages 100 are provided separately. This facilitates compact arrangement of the gaseous fuel injector 15 and makes it easy to realize a configuration in which the injection port 15b1 of the gaseous fuel injector 15 is disposed close to the intake port 24a. Therefore, even in a configuration in which a plurality of intake ports 24a and communication passages 100 are provided, the following configuration is desirable from the viewpoint of reliably improving the discharge of gaseous fuel from the communication passage 100 and reliably suppressing abnormal combustion by disposing the injection port 15b1 closer to the intake port 24a. That is, as shown in FIG. 3, it is desirable that the communication passages 100 corresponding to adjacent intake ports 24a (second communication passages 102 in this embodiment) be integrally formed.

[0057] From the viewpoint of easily increasing the displacement of the engine 1 (while suppressing abnormal combustion), it is desirable to provide multiple cylinders 21a connected to each intake port 24a, as shown in Figure 1. The displacement of the engine 1 refers to the difference in volume between the combustion chamber 2a when the piston 23 is located at bottom dead center and the combustion chamber 2a when the piston 23 is located at top dead center.

[0058] [3. Combustion chamber configuration] The configuration of the combustion chamber 2a will be described with reference to Fig. 5. Fig. 5 is an explanatory diagram that schematically shows the configuration of the combustion chamber 2a. In Fig. 5, the piston 23 is shown by a solid line when it is at top dead center, and the piston 23 is shown by a dashed line when it is at bottom dead center. As described above, the combustion chamber 2a refers to the space enclosed by the inner circumferential surface of the cylinder 21a, the top surface 23a of the piston 23, and the underside of the cylinder head 24.

[0059] A recess 23a1 is formed in the top surface 23a of the piston 23. That is, the piston 23 has the recess 23a1 in the top surface 23a. The recess 23a1 includes a bottom surface portion 23a2 and a side surface portion 23a3. The bottom surface portion 23a2 constitutes the bottom surface of the recess 23a1, and a portion near the center in the horizontal direction protrudes upward. The side surface portion 23a3 constitutes the side surface of the recess 23a1 and is formed in a substantially annular shape in a plan view. More specifically, the side surface portion 23a3 slopes downward from the outside to the inside, and its lower edge is connected to the outer periphery of the bottom surface portion 23a2. Note that the bottom surface portion 23a2 is not limited to the above configuration. For example, the bottom surface portion 23a2 may be flat. That is, a portion near the center in the horizontal direction of the bottom surface portion 23a2 does not have to protrude upward.

[0060] As described above, the liquid fuel injector 10 is attached to the cylinder head 24. The liquid fuel injector 10 is disposed so that its tip (lower end) slightly protrudes from the lower surface of the cylinder head 24.

[0061] The cylinder head 24 is further provided with an intake valve 24b that allows air to be supplied to the combustion chamber 2a, and an exhaust valve 24c that allows exhaust gas to be discharged from the combustion chamber 2a. The intake valve 24b and the exhaust valve 24c are each provided on the cylinder head 24 so as to be movable up and down.

[0062] When the intake valve 24b is in the uppermost position, it turns off communication between the intake port 24a and the combustion chamber 2a, blocking the supply of air from the intake port 24a to the combustion chamber 2a. As the intake valve 24b moves downward from the uppermost position, it turns on communication between the intake port 24a and the combustion chamber 2a, and air is supplied from the intake port 24a to the combustion chamber 2a. The amount of air supplied from the intake port 24a to the combustion chamber 2a is adjusted according to the downward movement amount (also referred to as the lift amount) of the intake valve 24b. Hereinafter, the state in which the intake valve 24b is in the uppermost position will be referred to as the closed state of the intake valve 24b, and the state in which the intake valve 24b is moved downward from the uppermost position (a state other than the uppermost position) will be referred to as the open state of the intake valve 24b.

[0063] When the exhaust valve 24c is in the upper end position, it turns off communication between the combustion chamber 2a and the exhaust manifold 6 (see FIGS. 1 and 2) and blocks the discharge of exhaust gas from the combustion chamber 2a to the exhaust manifold 6. As the exhaust valve 24c moves downward from the upper end position, it turns on communication between the combustion chamber 2a and the exhaust manifold 6 and discharges exhaust gas from the combustion chamber 2a to the exhaust manifold 6. The amount of exhaust gas discharged from the combustion chamber 2a to the exhaust manifold 6 is adjusted according to the downward movement amount (also referred to as the lift amount) of the exhaust valve 24c. Hereinafter, the state in which the exhaust valve 24c is in the upper end position will be referred to as the closed state of the exhaust valve 24c, and the state in which the exhaust valve 24c is moved downward from the upper end position (a state other than the upper end position) will be referred to as the open state of the exhaust valve 24c.

[0064] The opening and closing timing of the intake valve 24b and the exhaust valve 24c will now be described with reference to Figure 6. Figure 6 is an explanatory diagram illustrating the opening and closing timing of the intake valve 24b and the exhaust valve 24c. Figure 6 also illustrates the lift amounts of the intake valve 24b and the exhaust valve 24c relative to the position of the piston 23 in the cylinder 21a. In Figure 6, the lift amount of the intake valve 24b is indicated by a solid line, and the lift amount of the exhaust valve 24c is indicated by a dashed line.

[0065] During the exhaust stroke, the piston 23 moves from bottom dead center toward top dead center. At this time, the exhaust valve 24c is moved downward from its upper end position and opens, and exhaust gas generated in the combustion chamber 2a by the immediately preceding combustion is discharged from the combustion chamber 2a into the exhaust manifold 6. When the piston 23 reaches the exhaust top dead center and moves a predetermined distance toward the intake bottom dead center, the exhaust valve 24c is returned to its upper end position and closes.

[0066] Shortly before the piston 23 reaches the exhaust top dead center, the intake valve 24b is moved downward from its upper end position to an open state, and the supply of air from the intake port 24a to the combustion chamber 2a begins. Furthermore, when the supply of air from the intake port 24a to the combustion chamber 2a begins, the gaseous fuel injector 15 injects gaseous fuel. The gaseous fuel injector 15 may inject gaseous fuel constantly during the gaseous fuel injection period shown in FIG. 6, or may inject the gaseous fuel at a predetermined timing during the gaseous fuel injection period. The predetermined timing may occur once or multiple times during the gaseous fuel injection period.

[0067] In addition, in this embodiment, the gas fuel injection period is a portion of the period during which the intake valve 24b is open, but is not limited to this and may be, for example, the entire period during which the intake valve 24b is open.

[0068] When the piston 23 reaches the vicinity of the intake bottom dead center, the intake valve 24b is returned to its upper end position and closed. During the compression stroke, the piston 23 moves from the bottom dead center toward the top dead center. At this time, both the intake valve 24b and the exhaust valve 24c are maintained in a closed state.

[0069] When the piston 23 reaches near the top dead center of compression, the liquid fuel injector 10 injects liquid fuel. That is, the liquid fuel injector 10 injects liquid fuel when the piston 23 is located near the top dead center of compression. The liquid fuel injector 10 injects liquid fuel multiple times at predetermined timings during the liquid fuel injection period shown in FIG. 6. Note that the liquid fuel may be injected only once during the liquid fuel injection period. As a result, the injected liquid fuel functions as ignition fuel (self-ignites), and the gaseous fuel mixed with the air is burned.

[0070] In this embodiment, the vicinity of the compression top dead center of the piston 23 means the following. That is, it means the range between the position of the piston 23 corresponding to the crankshaft being rotated 15 degrees counterclockwise when the piston 23 is at the compression top dead center and the position of the piston 23 corresponding to the crankshaft being rotated 15 degrees clockwise. The counterclockwise and clockwise directions are directions when the engine 1 is viewed from the front. However, they are not limited to 15 degrees and may be, for example, 10 degrees or 20 degrees. Furthermore, the angle of the crankshaft corresponding to the position of the piston 23 may be different between the clockwise side and the counterclockwise side.

[0071] The liquid fuel injector 10 injects liquid fuel from a tip portion of the liquid fuel injector 10. More details are as follows. FIG. 7 is a bottom view showing the configuration of the tip portion of the liquid fuel injector 10. When viewed from below the combustion chamber 2a, the tip portion of the liquid fuel injector 10 is disposed so as to overlap with the central portion 21a1 of the cylinder 21a (see also FIG. 5). A plurality of (eight in this embodiment) injection holes 10a are formed in the tip portion of the liquid fuel injector 10. That is, the liquid fuel injector 10 has a plurality of injection holes 10a disposed so as to overlap with the central portion 21a1 of the cylinder 21a when viewed from one side (upper in this embodiment) or the other side (lower in this embodiment) in the up-down direction. The number of injection holes 10a is not limited to the above and may be, for example, one or a number other than eight (four, five, etc.).

[0072] When the liquid fuel injector 10 injects liquid fuel, the liquid fuel is injected radially from each injection hole 10a in the radial direction of the combustion chamber 2a. More specifically, the axis 10a1 of each injection hole 10a extends from the injection hole 10a in the radial direction of the cylinder 21a when viewing the combustion chamber 2a from below.

[0073] In a configuration in which the engine 1 includes a cylinder 21a connected to an intake port 24a and a piston 23 that reciprocates within the cylinder 21a, the following configuration is desirable for injecting liquid fuel into a high-temperature mixture (of air and gaseous fuel). That is, the engine 1 is desirably provided with a liquid fuel injector 10 that injects liquid fuel when the piston 23 is located near top dead center of compression. Furthermore, if the flame propagates evenly within the cylinder 21a (combustion chamber 2a), the liquid fuel burns quickly and the generation of particulate matter such as soot is suppressed, so it is desirable to ignite the liquid fuel at the horizontal center 21a1 of the cylinder 21a. From this perspective, in a configuration in which the engine 1 includes a liquid fuel injector 10 attached to the cylinder head 24, as in this embodiment, the following configuration is desirable. That is, as shown in FIG. 7, it is desirable that the liquid fuel injector 10 has a plurality of injection holes 10a that are arranged in a stacked manner in the central portion 21a1 of the cylinder 21a when viewed from the top-bottom direction, and that the axis 10a1 of each injection hole 10a extends in the radial direction of the cylinder 21a.

[0074] In particular, when the piston 23 is positioned at the top dead center of the compression stroke, a second intersection P2 between the axis 10a1 of each injection hole 10a and the piston 23 is located on the side surface 23a3 of the recess 23a1 (see FIG. 5). That is, when the piston 23 is positioned at the top dead center of the compression stroke, the axis 10a1 intersects with the side surface 23a3 of the recess 23a1.

[0075] When the piston 23 is positioned at top dead center of compression stroke, if the axis 10a1 intersects with the side surface 23a3 of the recessed portion 23a1, the distance (time) it takes for the injected liquid fuel to reach the piston 23 is longer than when the axis 10a1 intersects with the bottom surface 23a2 of the recessed portion 23a1, for example. This allows the liquid fuel to ignite before it reaches the piston 23, ensuring rapid combustion of the liquid fuel. Therefore, from the perspective of ensuring rapid combustion of the liquid fuel and suppressing the generation of particulate matter such as soot, the following configuration is desirable. That is, as shown in FIG. 5, in a configuration in which the piston 23 has the recessed portion 23a1 on the top surface 23a, it is desirable that the axis 10a1 of the injection hole 10a intersects with the side surface 23a3 of the recessed portion 23a1 when the piston 23 is positioned at top dead center of compression stroke.

[0076] [4. Switching from liquid fuel mode to gas fuel mode] The flow of switching from the liquid fuel mode to the gas fuel mode will be described with reference to Fig. 8. Fig. 8 is a flowchart showing the flow of switching from the liquid fuel mode to the gas fuel mode. In step S0, it is assumed that the engine 1 is in the liquid fuel mode.

[0077] In step S1, the control device TR3 (see FIG. 1) acquires information about the engine 1. The acquisition of the information is realized by a sensor TR4 (see FIG. 1) connected to the control device TR3 detecting information about the engine 1 and outputting the detected information to the control device TR3. Once the control device TR3 acquires the information about the engine 1, the process proceeds to the next step S2.

[0078] In step S2, the control device TR3 determines whether the engine 1 is in the liquid fuel mode. If the engine 1 is in the liquid fuel mode (Yes in step S2), the process proceeds to the next step S3. If the engine 1 is not in the liquid fuel mode (No in step S2), this flowchart ends.

[0079] In step S3, the control device TR3 sets the pressure of the liquid fuel injected from the liquid fuel injector 10 to the liquid fuel mode injection pressure. That is, the liquid fuel injector 10 injects the liquid fuel at the liquid fuel mode injection pressure in the liquid fuel mode. In this embodiment, the above setting is achieved by the control device TR3 controlling the supply pump 12 (see FIG. 1) to change the pressure of the liquid fuel stored in the common rail 11 (see FIG. 1).

[0080] In step S4, the control device TR3 determines whether or not a mode switching command has been issued. In this embodiment, the mode switching command is issued by the operator of the tractor TR operating a switching unit (not shown) provided on the tractor TR. The switching unit is, for example, a switching switch. If a mode switching command has been issued (Yes in step S4), the process proceeds to the next step S5. If a mode switching command has not been issued (No in step S4), the control device TR3 continues to determine whether or not a mode switching command has been issued.

[0081] In step S5, the control device TR3 executes a self-diagnosis of the engine 1. The self-diagnosis includes, for example, determining whether or not a gaseous fuel leak has occurred in the gaseous fuel supply unit GS (see FIG. 1). The determination is made based on information detected by the leak sensor included in the sensor TR4. After the self-diagnosis is executed, the process proceeds to the next step S6.

[0082] In step S6, the control device TR3 determines whether or not there is an abnormality in the engine 1. In this embodiment, the above determination is made based on the results of self-diagnosis. For example, if the results of self-diagnosis include the occurrence of a gas fuel leak, the control device TR3 determines that there is an abnormality in the engine 1. If there is an abnormality in the engine 1 (Yes in step S6), this flowchart ends (without switching from the liquid fuel mode to the gas fuel mode). If there is no abnormality in the engine 1 (No in step S6), the process proceeds to step S7.

[0083] In step S7, the control device TR3 switches the mode of the engine 1 from the liquid fuel mode to the gas fuel mode. Once the mode has been switched from the liquid fuel mode to the gas fuel mode, the process proceeds to the next step S8.

[0084] In step S8, the control device TR3 sets the pressure of the liquid fuel injected from the liquid fuel injector 10 to the gas fuel mode injection pressure. That is, the liquid fuel injector 10 injects liquid fuel at the gas fuel mode injection pressure in the gas fuel mode. In this embodiment, the gas fuel mode injection pressure is set to a pressure lower than the liquid fuel mode injection pressure. More specifically, the control device TR3 controls the supply pump 12 to reduce the pressure of the liquid fuel stored in the common rail 11, thereby reducing the pressure of the liquid fuel injected from the liquid fuel injector 10. That is, the pressure of the liquid fuel injected from the liquid fuel injector 10 is lower in the gas fuel mode (i.e., the gas fuel mode injection pressure) than in the liquid fuel mode (i.e., the liquid fuel mode injection pressure).

[0085] In a configuration in which the engine 1 has a liquid fuel mode and a gas fuel mode, and particularly in the gas fuel mode, from the viewpoint of suppressing the generation of particulate matter such as soot resulting from incomplete combustion of liquid fuel due to an excessive supply of liquid fuel as ignition fuel, the following configuration is desirable: That is, as in this embodiment, it is desirable that the pressure of the liquid fuel injected from the liquid fuel injector 10 be smaller (lower pressure) in the gas fuel mode than in the liquid fuel mode.

[0086] Here, the injection amount of liquid fuel per unit time (e.g., 1 second) and the injection amount of gas fuel per unit time (e.g., 1 second) when switching from the liquid fuel mode to the gas fuel mode will be described with reference to FIG. 9. FIG. 9 is an explanatory diagram illustrating the injection amount of liquid fuel per unit time and the injection amount of gas fuel per unit time when switching from the liquid fuel mode to the gas fuel mode. In FIG. 9, the injection amount of liquid fuel per unit time is indicated by a dashed line, and the injection amount of gas fuel per unit time is indicated by a solid line. In the following, the injection amount of liquid fuel per unit time will sometimes be referred to as the liquid fuel injection amount 10Q, and the injection amount of gas fuel per unit time will sometimes be referred to as the gas fuel injection amount 15Q.

[0087] At time t0, the engine 1 is started. In this embodiment, when the engine 1 is started, the mode of the engine 1 is set to the liquid fuel mode. Immediately after the engine 1 is started, the liquid fuel injector 10 injects liquid fuel at a constant first liquid fuel injection amount 10Q1 in order to stabilize the output of the engine 1. Once the output of the engine 1 has stabilized, the liquid fuel injection amount 10Q is reduced to less than the first liquid fuel injection amount 10Q1 and is adjusted (controlled) so as to obtain a predetermined output (for example, rated output) (see the period from time t1 to time t2).

[0088] At time t2, the operator inputs the above-mentioned mode switching command, and the above-mentioned self-diagnosis is performed from time t2 to time t3. During the self-diagnosis (the period from time t2 to time t3), the liquid fuel injector 10 injects liquid fuel at a constant second liquid fuel injection amount 10Q2. If the self-diagnosis determines that there is no abnormality in the engine 1, the mode of the engine 1 is switched from the liquid fuel mode to the gas fuel mode, and the gas fuel injector 15 starts injecting gas fuel (see time t3).

[0089] The gas fuel mode is provided with a trial period (the period from time t3 to time t4) and a transition period (the period from time t4 to time t5). The trial period is provided to determine whether combustion in the gas fuel mode can be performed normally. During the trial period, the gas fuel injector 15 injects gas fuel at a constant first gas fuel injection amount 15Q1. Once gas fuel injection begins, the liquid fuel injection amount 10Q naturally decreases.

[0090] The transition period is set to prevent the output (combustion of gaseous fuel and liquid fuel) of the engine 1 from becoming unstable due to an increase in gaseous fuel injection quantity 15Q and a decrease in liquid fuel injection quantity 10Q. The transition period includes a first transition period (the period from time t4 to time t4A) and a second transition period (the period from time t4A to time t5). During the first transition period, gaseous fuel injection quantity 15Q increases at a constant rate from first gaseous fuel injection quantity 15Q1, while liquid fuel injection quantity 10Q gradually decreases. During the second transition period, liquid fuel injection quantity 10Q decreases at a constant rate, while gaseous fuel injection quantity 15Q gradually increases.

[0091] When the second transition period ends, the gas fuel injection amount 15Q is adjusted (controlled) so that a predetermined output (for example, rated output) is obtained from the engine 1, and the liquid fuel injection amount 10Q is set to a constant third liquid fuel injection amount 10Q3 (see the period after time t5). Below, a description will be given of changes in the pressure of the liquid fuel injected from the liquid fuel injector 10 during the period after time t5.

[0092] 5. Change in pressure of liquid fuel injected from the liquid fuel injector 10 10 is a graph showing the change in the pressure of the liquid fuel injected from the liquid fuel injector 10 (liquid fuel injection pressure 10P) versus the mixed combustion ratio R. The mixed combustion ratio R means the proportion of the heat value of the gaseous fuel to the total heat value (the sum of the heat value of the gaseous fuel and the heat value of the liquid fuel) in one combustion.

[0093] The liquid fuel injection pressure 10P decreases (becomes lower) as the fuel-combustion ratio R increases. For example, the liquid fuel injection pressure 10P when the fuel-combustion ratio R is a first fuel-combustion ratio R1 (e.g., 90%) is defined as a first injection pressure 10P1. That is, when the fuel-combustion ratio R is the first fuel-combustion ratio R1, the liquid fuel injector 10 injects liquid fuel at the first injection pressure 10P1. Also, when the fuel-combustion ratio R is a second fuel-combustion ratio R2 (e.g., 95%) that is higher than the first fuel-combustion ratio R1, the liquid fuel injection pressure 10P is defined as a second injection pressure 10P2. Comparing the first injection pressure 10P1 and the second injection pressure 10P2, the second injection pressure 10P2 is smaller (lower) than the first injection pressure 10P1. That is, when the second fuel mixture ratio R2 is higher than the first fuel mixture ratio R1, the liquid fuel injector 10 injects the liquid fuel at a second injection pressure 10P2 lower than the first injection pressure 10P1.

[0094] As the liquid fuel injection pressure 10P increases, the liquid fuel injection quantity 10Q (the amount of liquid fuel injected per unit time) increases. For example, the liquid fuel injection quantity 10Q at the first injection pressure 10P1 is greater than the liquid fuel injection quantity 10Q at the second injection pressure 10P2 (which is lower than the first injection pressure 10P1). Therefore, assuming that a second mixing ratio R2, which is higher than the first mixing ratio R1, is achieved at the first injection pressure 10P1, the gas fuel injection quantity 15Q (the amount of gas fuel injected per unit time) must be increased compared to when the second injection pressure 10P2 is used. In other words, when the liquid fuel injection pressure 10P is maintained at a high pressure, it is difficult to increase the mixing ratio R. Therefore, in order to easily achieve a higher combustion ratio R (than the first combustion ratio R1) in a configuration in which the liquid fuel injector 10 injects liquid fuel at a first injection pressure 10P1 when the combustion ratio is first R1, as in this embodiment, the following configuration is desirable: When the combustion ratio is a second combustion ratio R2 that is higher than the first combustion ratio R1, it is desirable for the liquid fuel injector 10 to inject liquid fuel at a second injection pressure 10P2 that is lower than the first injection pressure 10P1.

[0095] [6. Supplementary Information] In the present embodiment, the case where the upper side is defined as "one side in the vertical direction" and the lower side is defined as "the other side in the vertical direction" has been described, but this is not limiting. For example, the lower side may be defined as "one side in the vertical direction" and the upper side may be defined as "the other side in the vertical direction." In other words, the up and down may be reversed. Specifically, the surge tank 41 may be disposed below the inlet portion 24a1 of the intake port 24a. In this case, the effect of this embodiment can be obtained as long as the injection port 15b1 of the gas fuel injector 15 is disposed above the central axis C1 of the communication passage 100.

[0096] In this embodiment, a configuration in which six cylinders 21a are provided has been described, but the present invention is not limited to this. For example, the number of cylinders 21a may be one. That is, the engine 1 may be a single-cylinder engine. Furthermore, the number of cylinders 21a may be a number other than six (two, three, etc.).

[0097] In this embodiment, the in-line engine 1 in which the cylinders 21a are arranged in a line in the front-rear direction has been described, but the engine 1 is not limited to the in-line type and may be, for example, a V-type.

[0098] [7. Notes] The engine 1 described in this embodiment can also be expressed as an engine described in the following supplementary notes.

[0099] The engine in Appendix (1) is A cylinder head, an intake port formed in the cylinder head; a surge tank disposed on one side in the up-down direction with respect to an inlet portion of the intake port; a communication passage that communicates the surge tank with the intake port; a gas fuel injector that injects gas fuel, The injection port of the gas fuel injector is disposed in the communication passage only on the other side in the up-down direction with respect to the central axis of the communication passage.

[0100] The engine of appendix (2) is the engine of appendix (1), the gas fuel injector has a nozzle protruding toward the other side in the up-down direction, The injection port is provided in the nozzle.

[0101] The engine of supplementary note (3) is the engine according to supplementary note (1) or (2), The communication passage is a first communication passage connected to the surge tank; a second communication passage connected to the first communication passage and the intake port, the injection port is disposed in the second communication passage, The first communication passage is inclined toward the other side in the up-down direction from the surge tank side toward the second communication passage side.

[0102] The engine of supplementary note (4) is the engine of supplementary note (3), the first communication passage includes a first wall surface located on one side in the up-down direction, the second communication passage includes a second wall surface located on the other side in the up-down direction, A straight line extending along the first wall surface toward the second wall surface intersects with the second wall surface at a position shifted toward the first communication passage with respect to the injection port.

[0103] The engine of supplementary note (5) is the engine according to any one of supplementary notes (1) to (4), a plurality of the intake ports and the communication passages; The communication passages corresponding to the adjacent intake ports are integrally formed.

[0104] The engine of appendix (6) is the engine of appendix (5), A plurality of cylinders are connected to the intake ports.

[0105] The engine of supplementary note (7) is the engine according to any one of supplementary notes (1) to (5), a cylinder connected to the intake port; a piston that reciprocates within the cylinder; a liquid fuel injector attached to the cylinder head and configured to inject liquid fuel when the piston is positioned near a compression top dead center, the liquid fuel injector has a plurality of injection holes arranged in a stacked manner in a center portion of the cylinder when viewed from the up-down direction, The axis of each injection hole extends in the radial direction of the cylinder.

[0106] The engine of supplementary note (8) is the engine according to supplementary note (7), The piston has a recess on its top surface, The axis intersects with a side surface of the recess when the piston is positioned at the compression top dead center.

[0107] The engine of supplementary note (9) is the engine according to supplementary note (7) or (8), a liquid fuel mode in which the liquid fuel is burned; a gas fuel mode in which the gas fuel is burned using the liquid fuel as an ignition fuel, The pressure of the liquid fuel injected from the liquid fuel injector is lower in the gas fuel mode than in the liquid fuel mode.

[0108] The engine of supplementary note (10) is the engine according to any one of supplementary notes (7) to (9), The liquid fuel injector includes: In the case of a first mixing ratio, the liquid fuel is injected at a first injection pressure; When a second fuel-combustion ratio is higher than the first fuel-combustion ratio, the liquid fuel is injected at a second injection pressure lower than the first injection pressure.

[0109] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these, and the invention can be expanded or modified without departing from the spirit of the invention. [Industrial Applicability]

[0110] The present invention can be used in, for example, work machines (agricultural machines, construction machines, etc.) and ships. [Explanation of symbols]

[0111] 1 engine 10 Liquid fuel injector 10P1 First injection pressure 10P2 Second injection pressure 10a injection hole 10a1 axis 15 Gaseous fuel injector 15b nozzle 15b1 Nozzle 21a Cylinder 21a1 central part 23 Piston 23a Top 23a1 recess 23a3 Side part 24 Cylinder head 24a intake port 24a1 Entrance 41 Surge Tank 100 communication path 101 1st communication passage 101a 1st wall 102 2nd communication passage 102a Second wall C1 center axis L1 straight line R1 First mixed combustion ratio R2 2nd co-firing rate

Claims

1. A cylinder head, an intake port formed in the cylinder head; a surge tank disposed on one side in the up-down direction with respect to an inlet portion of the intake port; a communication passage that communicates the surge tank with the intake port; a gas fuel injector that injects gas fuel, an injection port of the gaseous fuel injector is disposed in the communication passage only on the other side in the up-down direction with respect to a central axis of the communication passage.

2. the gas fuel injector has a nozzle protruding toward the other side in the up-down direction, The engine of claim 1 , wherein the injection port is provided in the nozzle.

3. The communication passage is a first communication passage connected to the surge tank; a second communication passage connected to the first communication passage and the intake port, the injection port is disposed in the second communication passage, The engine according to claim 1 , wherein the first communication passage is inclined toward the other side in the up-down direction from the surge tank side toward the second communication passage side.

4. the first communication passage includes a first wall surface located on one side in the up-down direction, the second communication passage includes a second wall surface located on the other side in the up-down direction, The engine according to claim 3 , wherein the straight line extending along the first wall surface toward the second wall surface intersects with the second wall surface at a position shifted toward the first communication passage with respect to the injection port.

5. a plurality of the intake ports and the communication passages; The engine according to claim 1 , wherein the communication passages corresponding to adjacent intake ports are integrally formed.

6. 6. The engine of claim 5, comprising a plurality of cylinders connected to each of said intake ports.

7. a cylinder connected to the intake port; a piston that reciprocates within the cylinder; a liquid fuel injector attached to the cylinder head and configured to inject liquid fuel when the piston is positioned near a compression top dead center, the liquid fuel injector has a plurality of injection holes arranged in a stacked manner in a center portion of the cylinder when viewed from the up-down direction, The engine according to claim 1 , wherein an axis of each of the injection holes extends in a radial direction of the cylinder.

8. The piston has a recess on its top surface, The engine of claim 7 , wherein the axis intersects with a side surface of the recess when the piston is at top dead center of compression.

9. a liquid fuel mode in which the liquid fuel is burned; a gas fuel mode in which the gas fuel is burned using the liquid fuel as an ignition fuel, 8. The engine of claim 7, wherein the pressure of the liquid fuel injected from the liquid fuel injector is less in the gas fuel mode than in the liquid fuel mode.

10. The liquid fuel injector includes: In the case of a first mixed-combustion ratio, the liquid fuel is injected at a first injection pressure; 10. The engine according to claim 7, wherein when a second fuel-fuel mixture ratio is higher than the first fuel-fuel mixture ratio, the liquid fuel is injected at a second injection pressure lower than the first injection pressure.

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