JP7800526B2 - internal combustion engine - Google Patents

Description

The present invention relates to an internal combustion engine that directly injects fuel into a cylinder, and in particular to an internal combustion engine that pre-injects a small amount of fuel prior to the main injection and is equipped with an ignition plug that ignites the pre-injected fuel.

Internal combustion engines are known in which a small amount of fuel is injected into a cylinder prior to the main injection, this prior fuel is spark-ignited, and then the fuel injected into the cylinder by the main injection is ignited. Patent Document 1 listed below shows an internal combustion engine in which a spark plug spark-ignites the prior fuel, increasing the temperature and pressure within the cylinder, and then the fuel injected into the cylinder by the main injection is self-ignited.

JP 2009-243366 A

A spark plug generates a spark by discharging electricity between the center electrode and the ground electrode. The ground electrode protrudes from the inner wall of the cylinder and is easily affected by the environment around the electrode, such as atomized fuel and ambient temperature.

The present invention aims to achieve at least one of the following: suppressing deformation or melting of the ground electrode, and suppressing the adhesion of soot to the surfaces of the center electrode and ground electrode.

The internal combustion engine of the present invention includes a cylinder; a piston that reciprocates within the cylinder along the axis of the cylinder and defines a cavity by a concave shape in the center of its top surface; a fuel injection nozzle that is located in the center of the upper part of the cylinder and injects fuel in multiple directions toward the periphery to form multiple fuel sprays; and an ignition plug that has a center electrode and a ground electrode located in the upper part of the cylinder corresponding to the outer periphery of the cavity and between adjacent fuel sprays, the spark plug being positioned so that the base of the ground electrode is located on a straight line passing through the center electrode and the fuel injection nozzle. The fuel injection nozzle performs at least one pre-injection to inject a small amount of fuel before the main injection in the latter half of the compression stroke, and the spark plug performs at least one spark ignition on the mixture formed in an annular shape around the outer periphery of the cylinder by the fuel spray from the pre-injection to form at least one spark. The main injection is performed near top dead center of the compression stroke, in which the fuel injection nozzle injects the required amount of fuel, and at least a portion of the main-injected fuel diffuses and burns from at least one spark.

This reduces exposure of the spark plug's center electrode and ground electrode to fuel spray.

In the above internal combustion engine, the opening of the cavity is circular and centered on the central axis of the cylinder, and the annular portion of the top surface of the piston outside the cavity is formed in a stepped shape with the outer periphery higher and the inner periphery lower , and the lower step surface of the stepped shape is annular and centered on the central axis of the cylinder, which allows the air-fuel mixture to collect near the outer periphery of the cavity.

In the above internal combustion engine, the center electrode of the spark plug may be located inside the outer periphery of the cavity. This prevents the center electrode and ground electrode from being exposed to flames flowing on the swirl generated on the outer periphery of the combustion chamber.

In the above internal combustion engine, the center electrode of the spark plug may be positioned corresponding to the lower step region of the stepped shape. This improves the reliability of ignition of the mixture on the outer periphery of the combustion chamber.

In the above internal combustion engine, the base of the ground electrode of the spark plug may be located between the center electrode of the spark plug and the fuel injection nozzle. This allows the ground electrode to be located away from the swirl-driven flame.

By reducing exposure of the spark plug's center electrode and ground electrode to fuel spray, it is possible to prevent at least one of deformation or melting of the ground electrode and the deposition of soot on the electrode surface.

1 is a diagram schematically illustrating a configuration of an internal combustion engine according to an embodiment of the present invention. FIG. 3 is a diagram showing fuel injection timing and ignition timing. FIG. 2 is a diagram schematically illustrating the state of fuel in a combustion chamber immediately after pre-injection. FIG. 2 is a diagram schematically illustrating the state of fuel in a combustion chamber immediately after spark ignition. FIG. 2 is a diagram schematically illustrating the state of fuel in a combustion chamber, and illustrates the state of diffusion of fuel burned by spark ignition. FIG. 2 is a diagram schematically showing the state of fuel in the combustion chamber, showing the state after main fuel injection. FIG. 10 is a diagram schematically illustrating the configuration of an internal combustion engine according to another embodiment of the present invention. 1 is a diagram schematically illustrating the configuration of an internal combustion engine related to the present invention.

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically illustrating one cylinder 12 of an internal combustion engine 10 and a piston 14 reciprocating along the central axis A of the cylinder 12. The internal combustion engine 10 may have multiple cylinders 12. Unless otherwise specified, in the following description, the direction along the central axis A will be referred to as the vertical direction, and the direction perpendicular to the vertical direction will be referred to as the horizontal direction. Additionally, the direction along the circumference of a circle centered on the central axis A will be referred to as the circumferential direction. In FIG. 1, (a) shows a cross section including the central axis A, and (b) shows the piston 14 as viewed from above in the direction along the central axis A.

The cylinder 12 is a roughly cylindrical space defined by the cylindrical inner wall surface 16a of the cylinder block 16 and the lower surface 18a of the cylinder head 18. The cylinder block 16 has a hole whose sides are defined by the cylindrical inner wall surface 16a and which is open upward and downward, with the cylinder head 18 positioned to cover this upper opening. A piston 14 is positioned below the cylinder 12, with the lower surface 18a of the cylinder head facing the top surface 14a of the piston. When the piston 14 is near top dead center, the space defined by the cylindrical inner wall surface 16a, the lower surface 18a of the cylinder head, and the top surface 14a of the piston is called the combustion chamber 20.

The cylinder head 18 is equipped with a fuel injection valve 22 that supplies fuel into the cylinder 12. The fuel injection valve 22 has a fuel injection nozzle 24 at its tip, which protrudes from the underside 18a of the cylinder head into the cylinder 12. The fuel injection nozzle 24, located in the center of the top of the cylinder 12, injects fuel radially into the cylinder 12. The fuel is injected in multiple directions, forming multiple fuel sprays 26. In this embodiment, the fuel injection nozzle 24 forms nine fuel sprays 26. The multiple fuel sprays 26 may be formed at equal intervals or at equal pitches in the circumferential direction. When the fuel injection valve 22 is attached to the cylinder head 18, the circumferential fuel injection direction is determined. This also determines the circumferential position of the fuel sprays 26. Fuel is injected from the fuel injection nozzle 24 slightly downward relative to the horizontal, and each fuel spray 26 is formed in a conical shape.

The center of the piston top surface 14a is formed with a concave shape, which defines a cavity 28. The concave peripheral wall surface that defines the cavity 28 is referred to as the peripheral wall surface 14b. The annular portion 30 of the piston top surface 14a, located outside the cavity 28, is formed with a stepped shape. The inner portion of the annular portion 30 is the low stage surface 32, and the outer portion is the high stage surface 34. The low stage surface 32 is located far from the top of the cylinder 12, i.e., at a low position, while the high stage surface 34 is located closer to the top of the cylinder 12 and at a high position. A surface perpendicular to the central axis A may be formed. An inclined surface 36 may be formed between the low stage surface 32 and the high stage surface 34, connecting them.

An ignition plug 38 is attached to the cylinder head 18. A threaded hole 18b is formed in a predetermined position in the cylinder head 18, and the spark plug 38 is threaded into this threaded hole to be threadedly connected to the cylinder head 18. The spark plug 38 has a center electrode 40 and a ground electrode 42 that are positioned within the cylinder 12 when installed. The center electrode 40 is located at the center of the end face of the spark plug 38. The ground electrode 42 has an overall L-shape and includes a base portion 42a erected on the end face near the periphery of the end face of the spark plug 38, and an opposing portion 42b that bends from the base portion 42a and extends to a position opposite the center electrode 40. The spark plug 38 ignites fuel in the cylinder 12 by electrical discharge generated between the center electrode 40 and the ground electrode 42. The spark plug 38, particularly the center electrode 40 and ground electrode 42, are positioned near the outer periphery of the cavity 28 of the piston 14, particularly inside the outer periphery of the cavity 28.

The center electrode 40 and the ground electrode 42 are positioned between adjacent fuel sprays 26A, 26B in the circumferential direction. The center electrode 40 may be positioned equidistant from the center lines of adjacent fuel sprays 26A, 26B. Positioning the center electrode 40 and the ground electrode 42 between the fuel sprays 26 reduces exposure of the center electrode 40 and the ground electrode 42 to the flame of the fuel spray 26 that has ignited and is in a burning state, thereby reducing melting damage. Furthermore, when the fuel spray 26 is not ignited, adhesion of unburned fuel to the center electrode 40 and the ground electrode 42 is reduced. This reduces contamination by soot that occurs when fuel adheres to the electrodes and then burns. This also reduces poor discharge of the spark plug 38.

Furthermore, when viewed in a direction along the central axis A, the base 42a of the ground electrode may be located on a straight line L passing through the fuel injection nozzle 24 and the center electrode 40. This reduces the projected area of the ground electrode 42 relative to the fuel spray 26, thereby suppressing contact of the fuel spray 26 with the ground electrode 42.

Furthermore, the base 42a of the ground electrode may be located between the fuel injection nozzle 24 and the center electrode 40. This reduces exposure of the base 42a of the ground electrode to flames that spread circumferentially due to swirls formed on the outer periphery of the combustion chamber 20, thereby suppressing melting damage.

To position the ground electrode 42 on line L, the alignment mark 44 on the circumference of the spark plug 38 is oriented in a predetermined direction. For example, it is aligned with a reference mark (not shown) on the cylinder head 18. The alignment mark 44 is positioned so that it can be seen by the worker installing the spark plug 38. Specifically, the spark plug 38 is screwed into the cylinder head 18 with a washer 46 of a predetermined thickness between them, and the position of the alignment mark 44 is confirmed. If the alignment mark 44 is aligned in the predetermined direction, for example, facing the reference mark, the work is complete. If the alignment mark 44 is not aligned in the predetermined direction, a washer 46 of a different thickness from the washer currently being used is selected based on the deviation from the predetermined direction, the washer 46 is replaced, and the spark plug 38 is screwed in again.

Figure 2 shows the fuel injection timing and injection amount. Figures 3 to 6 are schematic diagrams illustrating the fuel injected into the cylinder 12 and the fuel combustion state. Figures 3 to 6 (a) show a cross section including the center axis A of the cylinder 12, and (b) show the combustion chamber 20 as viewed from above. Fuel is pre-injected prior to the main injection at a timing such that the fuel injected at the end of the compression stroke does not directly collide with the cylindrical inner wall surface 16a of the cylinder block. Pre-injection occurs, for example, after 40° before top dead center. In the example shown in Figure 2, pre-injection Ip occurs approximately 30° before top dead center, and main injection Im occurs during the period including top dead center. The fuel supplied by pre-injection Ip may be 15 to 25% of the total injection amount. Pre-injection Ip may be performed once or multiple times. In the example shown, two pre-injections Ip are performed with the centers of the injection periods at 31.5° and 27.5° before top dead center. The main injection Im is performed between 5° before top dead center and 4° after top dead center. Furthermore, ignition by the spark plug 38 occurs at 20° before top dead center, as indicated by F in the figure.

Figure 3 is a schematic diagram showing the state inside the combustion chamber 20 at approximately 30° before top dead center when pre-injection Ip is performed. The pre-injected fuel forms a radial fuel spray 26. The fuel spray 26 avoids the spark plug 38, preventing liquid fuel from adhering to the center electrode 40 and ground electrode 42. Furthermore, the piston 14 has not yet reached top dead center, and the fuel spray 26 deviates from the peripheral wall surface 14b that defines the cavity 28, preventing collision. A swirl S is generated inside the combustion chamber 20. The swirl S is created by, for example, forming the intake port 48 (see Figure 1) so that the intake air flow drawn into the cylinder 12 has a swirling component.

Figure 4 is a schematic diagram showing the state inside the combustion chamber 20 at 20° before top dead center, immediately after spark ignition. As the injected fuel swirls, adjacent sprays connect and some vaporize, forming an annularly distributed mixture 50. The mixture 50 is distributed around the outer periphery of the cavity 28 and the annular portion 30 of the piston top surface 14a. Furthermore, because the annular portion 30 has a stepped shape, an airflow is generated from the high-stage surface 34 toward the low-stage surface 32 as the piston 14 rises, forcing the mixture 50 inward. This increases the fuel concentration of the mixture near the spark plug 38. When spark ignition occurs from the spark plug 38, the mixture at the spark plug 38 burns, forming a flame 52.

Figure 5 is a diagram showing the state inside the combustion chamber 20 at 10° before top dead center. The figure shows the flame 52 formed by spark ignition spreading and being swirled by the swirl S.

Figure 6 is a schematic diagram showing the state inside the combustion chamber 20 at top dead center. A main injection Im is performed, forming a fuel spray 26. The fuel spray 26 ignites using a flame 52 as a spark to form an injection flame 54. The flame 52 spreads in both clockwise and counterclockwise directions in the figure. The injection flame 54, i.e., the burning fuel spray 26, avoids the spark plug 38, thereby suppressing melting damage to the ground electrode 42 and other components. Furthermore, some of the pre-injected and main-injected fuel may ignite and burn due to the temperature increase inside the combustion chamber 20 caused by the rise of the piston 14.

Figure 7 is a schematic diagram showing the configuration of an internal combustion engine 60 of another embodiment. Components similar to those in the previously described internal combustion engine 10 are assigned the same reference numerals and will not be described again. As with Figure 1, (a) shows a cross section including the central axis A, and (b) shows the piston 14 as viewed from above in a direction along the central axis A. The internal combustion engine 60 differs from the previously described internal combustion engine 10 in part of the configuration of the cylinder head. The cylinder head 62 of the internal combustion engine 60 has a lower surface 62a that, together with the cylindrical inner wall surface 16a of the cylinder block, defines the cylinder 12. In this respect, the lower surface 62a of the cylinder head is common to the lower surface 18a of the cylinder head of the internal combustion engine 10. The cylinder head 62 differs from the previously described cylinder head 18 in the position of the screw hole 62b for connecting the spark plug 38. The position of the threaded hole 62b in the internal combustion engine 60 is determined so that the center electrode 40 of the inserted spark plug 38 faces the lower stage surface 32 of the annular portion 30 of the piston top surface 14a. Similar to the internal combustion engine 10, the center electrode 40 and ground electrode 42 are positioned between adjacent fuel sprays 26A, 26B. Furthermore, the base 42a of the ground electrode may be located on a straight line L passing through the fuel injection nozzle 24 and the center electrode 40. In particular, the base 42a of the ground electrode may be located inside the center electrode 40, that is, on the fuel injection nozzle 24 side, to avoid a strong swirl flow on the outer periphery of the combustion chamber 20. The combustion process in the internal combustion engine 60 is similar to that in the internal combustion engine 10.

8 is a diagram schematically illustrating the configuration of an internal combustion engine 70 related to the present invention . Components similar to those in the internal combustion engine 10 described above are assigned the same reference numerals, and a description thereof will be omitted. Similar to FIG. 1 , (a) illustrates a cross section including the central axis A, and (b) illustrates a piston 76 viewed from above in a direction along the central axis A. The internal combustion engine 70 uses the collision of fuel sprays with the piston wall surface to form an annularly distributed mixture formed by pre-injected fuel.

The intake port 74 of the cylinder head 72 is formed so that the swirling component of the intake air flow sent from the intake port 74 into the cylinder 12 is less than that of the aforementioned internal combustion engines 10 and 60. Specifically, the intake port 74 is formed so that the direction of the portion adjacent to the cylinder 12 is approximately parallel to the central axis A or approximately facing the central axis A.

Similar to the piston 14 described above, the piston 76 has a concave shape formed in the center of the top surface 76a, which defines the cavity 28. The peripheral wall surface of this concave shape is referred to as the peripheral wall surface 76b. The annular portion 78 of the piston's top surface 76a, located outside the cavity 28, is formed in a flat shape. The annular portion 78 is a plane perpendicular to the central axis A.

The cylinder 12 is defined by the lower surface 72a of the cylinder head and the cylindrical inner wall surface 16a of the cylinder block. A threaded hole 72b is formed in the cylinder head 72 for connecting the ignition plug 38. The ignition plug 38 connected to the cylinder head 72, particularly the center electrode 40 and ground electrode 42, is located near the outer periphery of the cavity 28, particularly inside the outer periphery.

The fuel injection valve 80 is fixed to the cylinder head 72 so that the fuel injection nozzle 82 is positioned at the center of the top of the cylinder 12. Fuel is injected radially from the fuel injection nozzle 82. The injected fuel forms multiple fuel sprays 84; in this embodiment, the fuel injection nozzle 82 forms nine fuel sprays 84. The multiple fuel sprays 84 may be formed at equal intervals or equal pitch in the circumferential direction. The fuel injection valve 80 is configured so that the circumferential fuel injection direction is determined when the fuel injection valve 80 is attached to the cylinder head 72. This also determines the position of the fuel sprays 84. The fuel is injected slightly downward relative to the horizontal, and each fuel spray 84 is formed in a cone shape.

The center electrode 40 and ground electrode 42 of the spark plug 38 are positioned between adjacent fuel sprays 84A, 84B in the circumferential direction. The center electrode 40 may be positioned equidistant from the center lines of the two fuel sprays 84A, 84B. By positioning the center electrode 40 and ground electrode 42 between the fuel sprays 84, exposure of the center electrode 40 and ground electrode 42 to the flame of the ignited and combusted fuel spray 84 is reduced, thereby suppressing melting damage. Furthermore, when the fuel spray 84 is not ignited, adhesion of unburned fuel to the center electrode 40 and ground electrode 42 is suppressed. This prevents poor discharge of the spark plug 38 due to soot, which is generated when fuel adheres to the electrodes and then burns.

Furthermore, the base 42a of the ground electrode may be located on a straight line L passing through the fuel injection nozzle 82 and the center electrode 40. This reduces the projected area of the ground electrode 42 relative to the fuel spray 84, thereby preventing the fuel spray 84 from contacting the ground electrode 42.

Furthermore, the base 42a of the ground electrode may be located between the fuel injection nozzle 82 and the center electrode 40. By separating the base 42a of the ground electrode from the annular mixture 86 formed near the outer periphery of the cavity 28, exposure to flames spreading circumferentially along the annular mixture 86 is reduced, thereby suppressing melting damage.

Fuel is injected toward the circumferential wall surface 76b of the ascending piston 76, which defines the cavity 28, particularly toward its upper portion. For this reason, fuel may be injected further downward than in the internal combustion engines 10 and 60 described above, or may be injected at a later injection timing than in the internal combustion engines 10 and 60, when the piston 76 is closer to top dead center. When the fuel spray 84 collides with the circumferential wall surface 76b, it spreads circumferentially to the left and right, forming an annular mixture 86. Thereafter, as in the internal combustion engines 10 and 60, the spark plug 38 ignites the annular mixture to form a flame, and fuel is supplied by the main injection and burns with the pre-injected fuel.

Methanol can be used as fuel in the internal combustion engines 10, 60, and 70.

<Additional Notes>
[1]
Cylinder and
a piston that reciprocates within the cylinder along an axis of the cylinder, the piston having a recessed shape at the center of a top surface that defines a cavity;
a fuel injection nozzle disposed in a central portion of an upper portion of the cylinder and configured to inject fuel in a plurality of directions toward the periphery to form a plurality of fuel sprays;
an ignition plug having a center electrode and a ground electrode disposed in an upper portion of the cylinder corresponding to the vicinity of the outer periphery of the cavity and between adjacent fuel sprays, the ignition plug being positioned so that a base of the ground electrode is located on a straight line passing through the center electrode and the fuel injection nozzle;
Including,
the fuel injection nozzle performs at least one pre-injection in which a small amount of fuel is injected before a main injection in the latter half of the compression stroke,
The ignition plug generates at least one spark by spark igniting at least one air-fuel mixture formed in an annular shape on the outer periphery of the cylinder by fuel spray from the pre-injection,
a main injection in which the fuel injection nozzle injects a required amount of fuel near the compression top dead center, and at least a part of the main injected fuel undergoes diffusion combustion starting from the at least one spark;
Internal combustion engine.
[2]
The internal combustion engine according to the above item [1], wherein an annular portion of the top surface of the piston that is outside the cavity is formed in a stepped shape with an outer circumferential side higher than an inner circumferential side.
[3]
The internal combustion engine according to the above item [1] or [2], wherein the center electrode of the spark plug is located inside the outer circumferential edge of the cavity.
[4]
The internal combustion engine according to the above item [2], wherein the center electrode of the spark plug is located in a region corresponding to a lower step of the stepped shape.
[5]
The internal combustion engine according to any one of the above items [1] to [4], wherein a base of the ground electrode of the spark plug is located between the center electrode of the spark plug and the fuel injection nozzle.

10, 60, 70 Internal combustion engine, 12 Cylinder, 14, 76 Piston, 16 Cylinder block, 18, 62, 72 Cylinder head, 18b, 62b, 72b Cylinder head threaded hole, 20 Combustion chamber, 22, 80 Fuel injection valve, 24, 82 Fuel injection nozzle, 26, 84 Fuel spray, 28 Cavity, 30, 78 Annular portion, 32 Lower stage surface, 34 Upper stage surface, 36 Inclined surface, 38 Spark plug, 40 Center electrode, 42 Ground electrode, 42a Base of ground electrode, 42b Opposing portion of ground electrode, 44 Alignment mark, 46 Washer, 50, 86 Air-fuel mixture, 52 Flame, 54 Injection flame.

Claims (4)

Cylinder and
a piston that reciprocates within the cylinder along an axis of the cylinder, the piston having a recessed shape at the center of a top surface that defines a cavity;
a fuel injection nozzle disposed in a central portion of an upper portion of the cylinder and configured to inject fuel in a plurality of directions toward the periphery to form a plurality of fuel sprays;
an ignition plug having a center electrode and a ground electrode disposed in an upper portion of the cylinder corresponding to the vicinity of the outer periphery of the cavity and between adjacent fuel sprays, the ignition plug being positioned so that a base of the ground electrode is located on a straight line passing through the center electrode and the fuel injection nozzle;
Including,
the fuel injection nozzle performs at least one pre-injection in which a small amount of fuel is injected before a main injection in the latter half of the compression stroke,
The ignition plug generates at least one spark by spark igniting at least one air-fuel mixture formed in an annular shape on the outer periphery of the cylinder by fuel spray from the pre-injection,
a main injection in which the fuel injection nozzle injects a required amount of fuel near the compression top dead center, and at least a portion of the main injected fuel undergoes diffusion combustion starting from the at least one spark;
The opening of the cavity has a circular shape centered on the central axis of the cylinder,
The annular portion of the top surface of the piston outside the cavity is formed in a stepped shape with the outer circumferential side being higher and the inner circumferential side being lower, and the lower step surface of the stepped shape is annular in shape with the center on the central axis of the cylinder.
Internal combustion engine. An internal combustion engine as described in claim 1, wherein the center electrode of the spark plug is located inside the outer periphery of the cavity. 2. The internal combustion engine according to claim 1 , wherein the center electrode of the spark plug is located in a region corresponding to a lower step of the stepped shape. 4. The internal combustion engine according to claim 1, wherein a base of the ground electrode of the spark plug is located between the center electrode of the spark plug and the fuel injection nozzle.