Two-cycle engine

Abstract

In this two-cycle engine, a cylinder is provided with: an intake hole that is in communication with a crank chamber through a bore part; an exhaust hole that is in communication with the bore part and that is disposed so as to oppose the intake hole in a radial direction of the bore part; at least one scavenging hole through which the bore part and the crank chamber are in communication with each other; and an injector that has an injection hole in communication with the bore part and that injects hydrogen-containing fuel into the bore part. The injector injects the fuel into the bore part in accordance with the timing when the exhaust hole is closed in a rising step in which the piston moves from the bottom dead center to the top dead center.

Description

two-stroke engine

[0001] The present disclosure relates to a two-stroke engine that operates on hydrogen as fuel.

[0002] As described in Patent Document 1, a two-stroke engine is known in which the hydrogen passage of a hydrogen injector is connected to the fuel passage of a fuel injector, and fuel and hydrogen are injected at a predetermined timing. In this engine, hydrogen is injected after the scavenging passage opens and ends before the scavenging passage closes. Fuel accumulated in the fuel passage is supplied to the combustion chamber through the scavenging passage by the injection of hydrogen. Mixing the fuel with hydrogen improves the ignition ability of the fuel.

[0003] Japanese Patent Application Publication No. 3-18664

[0004] In the above-mentioned two-stroke engine, a phenomenon called "pre-ignition" can occur, in which fuel containing hydrogen ignites before the spark (discharge) of the spark plug. Normally, the spark of the spark plug ignites the mixture at the appropriate time. However, when hydrogen fuel is included, the highly ignitable hydrogen fuel causes the mixture to spontaneously ignite (self-ignition phenomenon). This pre-ignition can lead to problems such as engine stalling, unstable or reverse rotation, or engine damage. It has been difficult to achieve stable operation in a two-stroke engine that runs on hydrogen fuel.

[0005] The present disclosure describes a two-stroke engine that can achieve stable operation even when fueled with hydrogen.

[0006] [1] One aspect of the present disclosure is a two-stroke engine (1) including: a cylinder (2) provided with a bore portion (3) and a combustion chamber (11) connected to one side of the bore portion (3) in the axial (L) direction; a crankcase (6) disposed on the other side of the cylinder (2) in the axial (L) direction and provided with a crank chamber (6a) connected to the other side of the bore portion (3); a piston (4) disposed in the bore portion (3) and capable of reciprocating along the axial (L) direction between the combustion chamber (11) and the crank chamber (6a); and a connecting rod (10) connecting the piston (4) to a crankshaft (7a) disposed in the crank chamber (6a), The piston (2) is provided with an intake hole (12) communicating with the crank chamber (6a) via the bore portion (3), an exhaust hole (13) communicating with the bore portion (3) and arranged so as to face the intake hole (12) in the radial direction of the bore portion (3), at least one scavenging hole (14, 16) communicating between the bore portion (3) and the crank chamber (6a), and an injector (30) having an injection hole (31) communicating with the bore portion (3) and for injecting fuel containing hydrogen into the bore portion (3), and the injector (30) injects fuel into the bore portion (3) in accordance with the timing at which the exhaust hole (13) is closed during the upward stroke of the piston (4) moving from the bottom dead center to the top dead center.

[0007] According to the two-stroke engine (1) of [1], fuel containing hydrogen is injected into the bore (3) by the injector (30) in synchronization with the closing of the exhaust port (13). During the ascending stroke of the piston (4), the scavenging stroke, which introduces fresh air, is completed, and then the exhaust port (13) is closed. High-temperature exhaust gas is discharged from the exhaust port (13), and fuel is injected in synchronization with the closing of the exhaust port (13) (i.e., the completion of the exhaust stroke). At this point, the exhaust of the high-temperature burned exhaust gas is completed, and the temperature inside the cylinder (2) has dropped due to the introduction of low-temperature fresh air (air) during the scavenging stroke. Therefore, fuel can be introduced into the combustion chamber (11) in an environment below the auto-ignition temperature of the fuel. As a result, auto-ignition can be prevented before the spark (discharge) of the spark plug, thereby achieving stable operation.

[0008] [2] In the two-stroke engine (1) described above in [1], the injection hole (31) of the injector (30) may open into the bore portion (3) at a position equal to or slightly higher than one edge of the exhaust hole (13) in the axial direction (L). Although the temperature of fresh air increases due to compression, this configuration allows the fuel injection position to be as close as possible to the exhaust hole (13) in the axial direction (L), thereby enabling a low-temperature environment to be established at the same time as the fresh air begins to be compressed. In other words, the fuel injection position can be moved away from a position close to the combustion chamber (11), which is subject to high pressure and high temperature. This allows low-temperature hydrogen to be introduced into the bore portion (3), which is in a low-temperature environment, thereby preventing the temperature from increasing due to compression and more reliably preventing auto-ignition.

[0009] [3] In the two-stroke engine (1) of [1] or [2] above, the injector (30) may be attached to the cylinder (2) at a position adjacent to one side of the intake hole (12) in the axial direction (L). With this configuration, the injector (30) can be attached at a position far from the combustion chamber (11) (i.e., a position in the bore portion (3) at the start of compression where pressure has not yet risen), making it possible to use an inexpensive low-pressure injector (30). While injectors designed to withstand high pressure and high temperature are expensive, the above configuration can suppress this increase in cost.

[0010] [4] In the two-stroke engine (1) of any one of [1] to [3] above, the connection position (C) of the piston (4) with the connecting rod (10) may be offset toward the intake port (12) with respect to a line (A1) that passes through the rotation center (R) of the crankshaft (7a) and is parallel to the reciprocating direction of the piston (4). By offsetting the connection position (C), the exhaust port (13) can be opened at an earlier crank angle. The earlier opening timing of the exhaust port (13) allows high-temperature exhaust gas to be discharged early, so high-temperature burned gas can be reliably discharged with high exhaust efficiency, and auto-ignition can be more reliably prevented.

[0011] According to the present disclosure, even when hydrogen fuel is used, the self-ignition phenomenon can be prevented and stable operation can be achieved.

[0012] Fig. 1 is a side view of a two-stroke engine according to an embodiment of the present disclosure. Fig. 2 is a longitudinal cross-sectional view taken along line II-II in Fig. 1. Fig. 3 is a block diagram showing a schematic configuration related to fuel injection control. Fig. 4 is a longitudinal cross-sectional view showing a state in which the piston is positioned at bottom dead center. Fig. 5 is a longitudinal cross-sectional view taken along line VV in Fig. 4. Fig. 6 is a longitudinal cross-sectional view showing a state in which the exhaust port is closed during the ascending stroke (at the completion timing of the exhaust stroke). Fig. 7 is a cross-sectional view showing an enlarged portion of Fig. 6. Fig. 8 is a longitudinal cross-sectional view taken along line VIII-VIII in Fig. 4.

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated descriptions will be omitted. In the following description, when "upper and lower" are used, it is based on the case where the cylinder body 2a is erected so that the bore portion 3 of the cylinder 2 extends vertically, with the opening into which the piston 4 is inserted facing downward. "Up" corresponds to one side in the direction of the axis L of the bore portion 3, and "lower" corresponds to the lower side in the direction of the axis L.

[0014] As shown in Figures 1 and 2, engine (two-stroke engine) 1 is a two-stroke engine that uses a scavenging system and is installed in, for example, a brush cutter or a backpack power sprayer. Engine 1 includes a cylinder 2, a piston 4 that reciprocates within a bore 3 within cylinder 2, a crankcase 6 connected below cylinder 2 and having a crank chamber 6a that connects to bore 3, and a crank mechanism 7 disposed within crank chamber 6a of crankcase 6. A piston pin 8 disposed within piston 4 is connected to a crank pin 9 of crank mechanism 7 disposed within crankcase 6 by a connecting rod 10. Thus, connecting rod 10 connects piston 4 to a crankshaft 7a disposed within crank chamber 6a. Piston 4 is disposed within bore 3 and is reciprocable along axis L between combustion chamber 11 and crank chamber 6a. In the following description, the connecting rod 10 will be referred to as a connecting rod 10.

[0015] The cylinder 2 is formed with a combustion chamber 11, a cylindrical bore portion 3 connected to the combustion chamber 11 and into which the piston 4 is inserted, an intake port 12 and an exhaust port 13 communicating with the bore portion 3, a pair of intake-side scavenging ports 14, and a pair of exhaust-side scavenging ports 16. The cylinder 2 has a cylinder main body 2a and a pair of scavenging cassettes 2b fitted into a lower portion of the cylinder main body 2a. The pair of scavenging cassettes 2b are fitted and fixed in two openings formed in the bore portion 3 so as to face each other in the radial direction. The pair of intake-side scavenging ports 14 and the pair of exhaust-side scavenging ports 16 are formed, for example, by the cylinder main body 2a and the pair of scavenging cassettes 2b (see FIG. 2 ).

[0016] The bore 3 has a cylindrical bore surface 3a and extends along the axis L within the cylinder 2. The bore 3 is open on its bottom dead center side (the lower side in FIG. 2 ) and communicates with the crank chamber 6a. A recessed combustion chamber 11 is formed at the end of the bore 3 on the top dead center side, and a discharge electrode 18a of an ignition plug 18 is disposed inside the combustion chamber 11. A spark plug mounting hole 19 into which the spark plug 18 is mounted is provided near the combustion chamber 11 in the cylinder body 2a.

[0017] The intake holes 12 and the exhaust holes 13 are each connected to the bore portion 3, and the exhaust holes 13 are positioned slightly closer to the top dead center than the intake holes 12 in the direction of the axis L. The intake holes 12 and the exhaust holes 13 are positioned to face each other in the radial direction of the bore portion 3. In other words, the intake holes 12 and the exhaust holes 13 are positioned so as to be offset from each other by approximately 180° in the circumferential direction of the bore portion 3.

[0018] The intake-side scavenging holes 14 are used to introduce fresh air into the bore 3 and the combustion chamber 11 during the scavenging stroke, and extend along the axial line L inside the sidewall of the cylinder 2. In this embodiment, the fresh air is only air drawn in via an air cleaner (not shown). The ends of the intake-side scavenging holes 14 on the top dead center side communicate with the bore 3 at positions substantially similar to the positions of the exhaust holes 13 in the axial line L. The intake-side scavenging holes 14 are spaced apart from each other in the circumferential direction of the bore 3. More specifically, the intake-side scavenging holes 14 are arranged substantially symmetrically with respect to an imaginary line connecting the intake hole 12 and the exhaust hole 13 in the radial direction. The intake-side scavenging holes 14 are arranged so that the fresh air introduced into the bore 3 is directed toward the intake hole 12. The ends of the intake-side scavenging holes 14 on the bottom dead center side communicate with the crank chamber 6a.

[0019] As shown in FIG. 2 , the crank mechanism 7 includes a crankshaft 7a, a pair of crank webs 7b connected to the crankshaft 7a, and a pair of connecting portions 7c (see also FIG. 5 ) provided on radially opposite sides of the crank webs 7b. The connecting rod 10 includes a small end 21 located in the bore 3, a big end 22 located in the crank chamber 6a, and a rod body 23 connecting the small end 21 and the big end 22. A piston pin 8 is inserted into the small end 21 of the connecting rod 10, and the small end 21 is rotatably connected to the piston 4 via the piston pin 8. A crank pin 9 is inserted into the big end 22 of the connecting rod 10, and the big end 22 is rotatably connected to the connecting portion 7c of the crank mechanism 7 via the crank pin 9. When the crankshaft 7a rotates about the center of rotation R, the connecting center P of the connecting rod 10 relative to the crankshaft 7a moves circularly around the center of rotation R of the crankshaft 7a.

[0020] Next, the position of the piston 4 will be described in detail with reference to FIG. 6 . FIG. 6 is a longitudinal cross-sectional view showing a state in which the exhaust hole 13 is closed (i.e., a closed hole state) during the ascending stroke of the piston 4. As shown in FIG. 6 , the connection position C of the piston 4 with the connecting rod 10 is offset toward the intake hole 12 with respect to a line A1 that passes through the rotation center R of the crankshaft 7a (see FIG. 8 ) and is parallel to the reciprocating direction of the piston 4 (i.e., parallel to the axis L of the bore 3) (see offset distance D shown in the figure). From another perspective, the connection position C is on the central axis A2 of the piston 4, and the exhaust hole 13 is located on the opposite side of the line A1 from the offset side of the connection position C. The central axis A2 of the piston 4 coincides with the axis L of the bore 3. Note that the axis L of the bore 3 may be located anywhere in the circumferential direction (anywhere within a 360° range) as long as the height position of the exhaust hole 13 is maintained.

[0021] The engine 1 is a piston valve type two-stroke engine in which an intake port 12 is opened and closed by a piston 4 reciprocating within a bore portion 3. In the engine 1, air taken in through the intake port 12 passes through a crank chamber 6a and is introduced into the bore portion 3 through a pair of intake-side scavenging ports 14 and a pair of exhaust-side scavenging ports 16. The engine 1 of this embodiment uses hydrogen fuel. The hydrogen fuel is injected (introduced) into the bore portion 3 from a fuel source F (see FIG. 3 ). That is, the hydrogen fuel is injected directly into the bore portion 3 without passing through the crank chamber 6a, the pair of intake-side scavenging ports 14, or the pair of exhaust-side scavenging ports 16.

[0022] As shown in Figures 1 and 2, the cylinder 2 is provided with an injector 30 that injects hydrogen fuel into the bore 3. The injector 30 is attached to the cylinder 2 at a position adjacent to the upper side (one side) of the intake port 12 in the direction of the axis L. The injector 30 is fixed to the cylinder 2 by an appropriate fastening member or the like. The injector 30 has an injection hole 31 that communicates with the bore 3. The center line 31L (see Figure 7) of the injection hole 31 is oriented, for example, at a position and in a direction perpendicular to the axis L of the bore 3 (i.e., in the radial direction). The injector 30 has a built-in valve, such as a coil-type solenoid valve (not shown). The valve opens and closes the fuel flow path connected to the injection hole 31.

[0023] As shown in FIG. 7 , the injection hole 31 extends toward the center (axis L) of the bore portion 3. The injection hole 31 opens into the bore portion 3 at a position slightly higher in the axial direction than the upper end (edge) 13b of the opening 13a of the exhaust hole 13. More specifically, the center line 31L of the injection hole 31 is located slightly higher than the upper end 13b of the opening 13a. To explain the phrase "located in a slightly higher position" in more detail, for example, it is preferable that the difference in position (distance) in the axial direction between the upper end 13b of the opening 13a and the center line 31L of the injection hole 31 is within 20% or less of the distance from the closed position of the exhaust hole 13 (i.e., the upper end 13b) to top dead center. The injection hole 31 may also open into the bore portion 3 at the same position in the axial direction as the upper end (edge) 13b of the opening 13a of the exhaust hole 13. In this case, the center line 31L of the injection hole 31 may coincide with the position of the upper end 13b of the opening 13a.

[0024] In this embodiment, hydrogen fuel is used. The hydrogen fuel is filled in a compressed gas state in a fuel source F constituted by a pressure tank or the like. Note that the engine 1 may also use a mixed gas of hydrogen and other fuels. In this specification, "fuel containing hydrogen" includes both hydrogen fuel consisting of only hydrogen (100% hydrogen) and mixed fuels of hydrogen and other fuels. The engine 1 of this embodiment, which solves the problem of auto-ignition (pre-ignition) when using hydrogen fuel, easily solves the problem of auto-ignition and enables normal operation even when using a mixed fuel containing hydrogen.

[0025] FIG. 3 is a block diagram showing a schematic configuration related to fuel injection control. As shown in FIG. 3, in the engine 1, only air containing no hydrogen fuel is taken in through the intake port 12. An engine control unit (ECU) 40 controls the engine 1. The ECU 40 controls the amount of air by adjusting the opening of a throttle valve (not shown), and also controls the injector 30. The ECU 40 controls the timing at which hydrogen fuel is injected by the injector 30. A pressure control valve (regulator) (not shown) is provided between the fuel source F and the injector 30. The pressure control valve keeps the pressure of hydrogen fuel applied to the injector 30 constant. The ECU 40 can precisely control the timing and injection time of fuel injection by the injector 30 (the opening time of the injector 30). This allows precise control of the amount of hydrogen supplied. The exhaust gas discharged from the exhaust port 13 is released into the atmosphere through a muffler 5.

[0026] In this embodiment, the injector 30 is controlled by the ECU 40 to inject hydrogen fuel into the bore 3 at the timing when the exhaust port 13 is closed during the upward stroke of the piston 4, when the piston 4 moves from bottom dead center to top dead center. The injector 30 needs to be able to inject fuel at a pressure higher than the internal pressure of the bore 3. However, since the internal pressure of the bore 3 is approximately the same as atmospheric pressure at the timing when the exhaust port 13 is closed, it is sufficient for the injector 30 to inject hydrogen fuel at a low pressure. A general-purpose injector 30 can be used.

[0027] Next, the operation of the engine 1 will be described. As shown in Figure 2, when the piston 4 reaches near top dead center, the air-fuel mixture explodes in the combustion chamber 11, and the piston 4 descends toward bottom dead center. As the piston 4 continues to descend, the exhaust port 13 opens, and the combustion gas is exhausted. Then, slightly after the exhaust port 13 opens, the intake-side scavenging port 14 and the exhaust-side scavenging port 16 become exposed in the bore portion 3, and the scavenging stroke begins (see Figures 4 and 5).

[0028] Next, as the piston 4 rises from bottom dead center to top dead center, the intake-side scavenging port 14 and the exhaust-side scavenging port 16 are closed by the piston 4. The exhaust port 13 is also closed by the piston 4. As shown in FIGS. 6 and 8, at the timing when the exhaust port 13 is closed during the piston 4's upward stroke, the injector 30 is controlled by the ECU 40 to inject hydrogen fuel into the bore 3. This causes air and hydrogen fuel to mix, generating an air-fuel mixture. As shown in FIGS. 6, 7, and 8, when hydrogen fuel is injected, the opening 13a of the exhaust port 13 is closed, but the opening 31a of the injection hole 31 is open. The top 4a of the piston 4 is slightly raised above the peripheral end 4b of the piston 4. At this time, as shown in FIG. 8, when viewed from a direction perpendicular to the axis L (a direction facing the injector 30), the opening 31 a of the injection hole 31 appears to protrude slightly from the top 4 a of the piston 4, or is hidden by the top 4 a of the piston 4.

[0029] The injection timing of the hydrogen fuel may be when the upper end 13b of the opening 13a of the exhaust hole 13 is closed by the piston 4, or may be slightly before or after that. Specifically, the timing "before" the exhaust hole 13 is closed is, for example, a timing that does not cause "blow-by," in which hydrogen fuel introduced into the bore portion 3 escapes directly into the exhaust hole 13. The timing "after" the exhaust hole 13 is closed is, for example, a timing when the internal pressure of the bore portion 3 begins to increase due to compression after the exhaust hole 13 is closed. In this way, the injector 30 injects the hydrogen fuel into the bore portion 3 in accordance with the timing when the exhaust hole 13 is closed during the upward stroke of the piston 4. From another perspective, the injector 30 injects the hydrogen fuel into the bore portion 3 at least before the peripheral end 4b of the piston 4 completely closes the opening 31a of the injection hole 31.

[0030] As the piston 4 moves further upward, the air-fuel mixture in the combustion chamber 11 is compressed. As the piston 4 moves further upward, the intake port 12 communicates with the crank chamber 6a via the bore portion 3, and fresh air is introduced into the crank chamber 6a (see FIG. 2).

[0031] In the engine 1 of this embodiment, fuel containing hydrogen is injected into the bore 3 by the injector 30 in synchronization with the closing of the exhaust port 13. During the ascending stroke of the piston 4, the scavenging stroke, which introduces fresh air, is completed, and then the exhaust port 13 is closed. High-temperature exhaust gas is discharged from the exhaust port 13, and fuel is injected in synchronization with the closing of the exhaust port 13 (i.e., the completion of the exhaust stroke). At this point, the exhaust of high-temperature burned exhaust gas is completed, and the temperature inside the cylinder 2 has dropped due to the introduction of low-temperature fresh air during the scavenging stroke. Therefore, fuel can be introduced into the combustion chamber 11 in an environment below the auto-ignition temperature of the fuel. As a result, auto-ignition can be prevented before the spark (discharge) of the spark plug, achieving stable operation.

[0032] The injection hole 31 of the injector 30 opens into the bore 3 at a position that is the same as or slightly higher than the edge on one side of the exhaust hole 13 in the direction of the axis L. This allows the fuel injection position to be as close as possible to the position of the exhaust hole 13 in the direction of the axis L. In other words, the fuel injection position can be moved away from a position close to the combustion chamber 11, which becomes high-pressure and high-temperature. This allows low-temperature hydrogen to be introduced into the bore 3, which has a low-temperature environment, preventing the hydrogen from becoming too hot due to compression and more reliably preventing auto-ignition.

[0033] The injector 30 is attached to the cylinder 2 at a position adjacent to one side of the intake hole 12 in the direction of the axis L. This allows the injector 30 to be attached at a position far from the combustion chamber 11 (i.e., a position in the bore 3 at the start of compression where pressure has not yet risen), making it possible to use a low-cost, standard-spec low-pressure injector 30. While an injector designed to withstand high pressure and high temperature would be expensive, the above-described configuration makes it possible to suppress this increase in cost.

[0034] The connection position C of the piston 4 with the connecting rod 10 is offset toward the intake port 12 with respect to a line A1 that passes through the rotation center R of the crankshaft 7a and is parallel to the reciprocating direction of the piston 4. The offset of the connection position C allows the exhaust port 13 to be opened at an earlier crank angle. The earlier opening of the exhaust port 13 allows high-temperature exhaust gas to be discharged earlier, more reliably preventing auto-ignition. Furthermore, because the exhaust port 13 is closed at an earlier crank angle due to the offset, a decrease in the compression ratio can be prevented by the earlier closing of the exhaust port 13 while maintaining high exhaust efficiency due to the earlier opening of the exhaust port 13. This prevents a decrease in power output due to a decrease in the compression ratio.

[0035] Although the embodiment of the present disclosure has been described above, the present invention is not limited to the above embodiment. For example, the injector 30 may be attached at a position away from the cylinder 2. The injection hole 31 may be positioned closer to the combustion chamber 11 than the injection hole 31 in the above embodiment.

[0036] The piston 4 may not be offset, and the coupling position C may be located on the straight line A1.

[0037] The present invention is not limited to a configuration in which four scavenging holes, i.e., a pair of intake-side scavenging holes 14 and a pair of exhaust-side scavenging holes 16, are provided in the cylinder 2, but may also be configured with one intake-side scavenging hole 14 and one exhaust-side scavenging hole 16. The present invention is also applicable to a stratified scavenging engine that uses air. Also, only a pair of scavenging holes that are radially opposed to each other may be provided between the intake hole 12 and the exhaust hole 13. Only one scavenging hole may be provided in the cylinder 2.

[0038] 1...engine (two-stroke engine), 2...cylinder, 3...bore portion, 4...piston, 6...crankcase, 6a...crank chamber, 7...crank mechanism, 11...combustion chamber, 12...intake port, 13...exhaust port, 13a...opening, 13b...upper end, 14...intake side scavenging port (scavenging port), 16...exhaust side scavenging port (scavenging port), 30...injector, 31...injection hole, A1...straight line, A2...central axis, C...connection position, D...offset distance, L...axis (of bore portion), P...connection center, R...center of rotation.

Claims

1. A two-stroke engine (1) comprising: a cylinder (2) provided with a bore portion (3) and a combustion chamber (11) connected to one side of the bore portion (3) in the axial (L) direction; a crankcase (6) disposed on the other side of the cylinder (2) in the axial (L) direction and provided with a crank chamber (6a) connected to the other side of the bore portion (3); a piston (4) disposed in the bore portion (3) and capable of reciprocating along the axial (L) direction between the combustion chamber (11) and the crank chamber (6a); and a connecting rod (10) connecting the piston (4) to a crankshaft (7a) disposed in the crank chamber (6a), wherein the cylinder (2) has an intake hole (12) communicating with the crank chamber (6a) via the bore portion (3); a two-stroke engine including: an exhaust hole (13) communicating with the bore portion (3) and arranged to face the intake hole (12) in the radial direction of the bore portion (3); at least one scavenging hole (14, 16) communicating the bore portion (3) with the crank chamber (6a); and an injector (30) having an injection hole (31) communicating with the bore portion (3) and injecting fuel containing hydrogen into the bore portion (3), wherein the injector (30) injects the fuel into the bore portion (3) in accordance with a timing at which the exhaust hole (13) is closed during an upward stroke in which the piston (4) moves from bottom dead center to top dead center.

2. The two-stroke engine according to claim 1, wherein the injection hole (31) of the injector (30) opens into the bore portion (3) at a position equal to or slightly higher than an edge on one side of the exhaust hole (13) in the axial direction (L).

3. The two-stroke engine according to claim 1 or 2, wherein the injector (30) is attached to the cylinder (2) at a position adjacent to one side of the intake hole (12) in the direction of the axis (L).

4. A two-stroke engine as set forth in any one of claims 1 to 3, wherein a connecting position (C) of the piston (4) with the connecting rod (10) is offset toward the intake hole (12) with respect to a straight line (A1) that passes through the rotation center (R) of the crankshaft (7a) and is parallel to the reciprocating direction of the piston (4).

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