JP2022149420A - Combustion chamber structure and engine including the same - Google Patents

Abstract

To provide a combustion chamber structure and an engine including the same, the structure being capable of dispersing fuel to the whole combustion chamber and decreasing fuel loss by reducing influences of reverse squish flow by use of entrained flow generated by fuel injection.SOLUTION: A combustion chamber structure 10 according to the present invention includes a cylinder head 12 where a fuel injection valve 6 is located, a cylinder 11 and a piston 13. A combustion chamber 1 is configured with a space surrounded by a top face of the piston 13 including a cavity 19, the cylinder 11 and the cylinder head 12. An inner surface shape on a cross section of the cavity 19 including a cylinder center axis C has a bottom central protrusion 14 projected at a bottom of the cavity 19 in a direction getting closer to the fuel injection valve 6, and a first bottom face ramp 15 inclined to an opposite side of the top part of the piston 13 from the bottom central protrusion 14 in an outer diameter direction of the cavity 19. When the piston 13 is at a top dead center P1, an injection axis 22 showing an injection direction of fuel F injected from the fuel injection valve 6 intersects the first bottom face ramp 15.SELECTED DRAWING: Figure 2

Description

The present invention relates to a combustion chamber structure configured as a space surrounded by a cylinder, a piston having a cavity recessed in the top surface thereof, and a cylinder head, and an engine having the same.

As a combustion chamber structure of a diesel engine, Patent Literature 1 discloses a technique for providing a structure capable of suppressing emission of soot into the atmosphere. In this conventional combustion chamber structure, a cavity is recessed in the top surface of the piston against which fuel injected from a fuel injection valve arranged above the piston collides. The shape of the inner surface of the cavity on a cross section including the cylinder central axis includes a constricted portion around the cavity opening on the top surface of the piston, a central portion of the cavity bottom that protrudes in a direction approaching the fuel injection valve, and a constricted portion. and a peripheral portion that connects between the portion and the central portion using an arc centered on the cavity center side. In such a configuration, the fuel injection valve is set so that the direction of fuel injection is directed toward the vicinity of the boundary between the constricted portion and the peripheral portion.

JP 2010-121483 A

As an effect of the conventional technology, part of the combustion gas generated at the start of combustion rides on the reverse squish flow generated by the movement of the piston toward the bottom dead center, smoothly diffusing into the combustion chamber whose volume is expanding, It mixes with the air in the entire combustion chamber and efficiently generates power. On the other hand, however, the strong reverse squish flow causes the fuel and combustion gases to flow into the space surrounded by the piston, cylinder head, and cylinder liner wall surface, so that the fuel and combustion gases contact more areas of the combustion chamber. However, there is a detrimental effect of worsening the heat loss.

Therefore, the present invention has been made in consideration of such circumstances, and its object is to reduce the influence of the reverse squish flow by utilizing the entrain flow generated by fuel injection, thereby diffusing the fuel throughout the combustion chamber. To provide a combustion chamber structure capable of reducing heat loss while reducing heat loss, and an engine equipped with the same.

A combustion chamber structure according to one aspect of the present invention includes a cylinder head in which a fuel injection valve is arranged, a cylinder, and a piston that reciprocates inside the cylinder. A circular cavity is formed in the surface, the fuel injection valve is attached to the cylinder head, and injects fuel from the vicinity of the cylinder center axis passing through the center of the cavity, the top surface of the piston including the cavity, and the A combustion chamber structure in which a combustion chamber is formed by a space surrounded by a cylinder and the cylinder head, wherein an inner surface shape of the cavity on a cross section including the central axis of the cylinder is convex in a direction approaching the fuel injection valve. and a first bottom inclined portion inclined from the bottom central convex portion toward the outer diameter direction of the cavity to the side opposite to the piston top, and the piston is at the top dead center At the time, an injection axis representing an injection direction of the fuel injected from the fuel injection valve intersects the first bottom inclined portion.

In the combustion chamber structure according to one aspect of the present invention, the shape of the inner surface of the cavity on a cross section including the cylinder central axis is from the cavity opening at the top of the piston toward the center of the cavity on the side opposite to the top of the piston. It may have a second bottom slope portion that slopes, and a bottom arc portion that connects the first bottom slope portion and the second bottom slope portion using an arc.

Further, in the combustion chamber structure according to one aspect of the present invention, the angle formed by the first inclined bottom surface portion and the cylinder central axis is larger than the angle formed by the second inclined bottom surface portion and the cylinder central axis. It can be big.

Further, in the combustion chamber structure according to one aspect and another aspect of the present invention, the fuel injection valve has a plurality of injection holes with an injection hole angle of 125° or more and 135° or less and spaced apart in the circumferential direction. may have.

Further, in the combustion chamber structure according to one aspect of the present invention, the diameter of the opening of the cavity may be 90% or more of the diameter of the cylinder.

Moreover, in the combustion chamber structure according to one aspect of the present invention, the fuel injection valve may have four or eight nozzle holes.

Further, in the combustion chamber structure according to one aspect of the present invention, a total of four intake/exhaust valves are arranged in one cylinder head, and valve recesses for avoiding contact with the intake/exhaust valves are formed in the piston. Four injection axes are provided on the top, and all the injection axes may be oriented so as to avoid the vicinity of the center of the valve recess when viewed in the direction of the cylinder center axis.

Further, in the combustion chamber structure according to one aspect of the present invention, four of the injection shafts may be oriented in a direction in which the valve recess does not exist.

Further, an engine according to one aspect of the present invention comprises the combustion chamber structure according to one aspect of the present invention, and the engine speed at maximum output excluding the instantaneous maximum speed is 2500 rpm or less. characterized by

According to the combustion chamber structure according to one aspect of the present invention, the entrain flow generated by fuel injection is utilized to weaken the effect of the reverse squish flow, thereby diffusing the fuel throughout the combustion chamber and reducing heat loss. It is possible to provide a combustion chamber structure and an engine including the same.

It is a mimetic diagram showing a schematic structure of engine E concerning an embodiment of the present invention. It is a schematic cross-sectional view showing a combustion chamber structure including a combustion chamber and a fuel injection valve. FIG. 3 is a schematic cross-sectional view showing a cross section taken along the line AA in FIG. 2; FIG. 4 is an explanatory diagram showing the flow of injected fuel in chronological order; FIG. 4 is an explanatory diagram showing the flow of injected fuel in chronological order; It is a schematic sectional drawing which shows the modification of the injection shaft in the axial direction view.

BEST MODE FOR CARRYING OUT THE INVENTION A combustion chamber structure and an engine having the same according to embodiments of the present invention will be described below with reference to the drawings. The engine according to the present embodiment is a cylinder direct injection diesel engine.

(Engine configuration)
First, the configuration of an engine having a combustion chamber structure according to an embodiment of the present invention will be described. FIG. 1 is a schematic diagram showing a schematic configuration of an engine E according to an embodiment of the invention. The engine E includes a combustion chamber 1, an air supply pipe 2, an intake valve 3, an exhaust pipe 4, an exhaust valve 5, a fuel injection valve 6, a crankshaft 7, a rotation speed sensor 8, and a control unit 9. , is equipped with

An air supply pipe 2 supplies air to the combustion chamber 1 . The intake valve 3 adjusts the amount of air supplied to the combustion chamber 1 . An exhaust pipe 4 discharges exhaust from the combustion chamber 1 . The exhaust valve 5 adjusts the amount of exhaust gas discharged from the combustion chamber 1 . The fuel injection valve 6 injects liquid fuel (hereinafter abbreviated as “fuel”) into the combustion chamber 1 . The crankshaft 7 is an output shaft of the engine E and is connected to a generator (not shown) or the like. A rotation speed sensor 8 is provided near the crankshaft 7 and detects the engine rotation speed. The control unit 9 controls the operation of each part of the engine E based on the engine speed and the like obtained from the speed sensor 8 .

(Construction of Combustion Chamber Structure)
FIG. 2 is a schematic sectional view showing a combustion chamber structure 10 including the combustion chamber 1 and the fuel injection valve 6. As shown in FIG. 3 is a schematic cross-sectional view showing a cross section taken along the line AA in FIG. 2. As shown in FIG. The combustion chamber structure 10 includes a cylindrical cylinder 11, a cylinder head 12 provided to close an opening of the cylinder 11, a piston 13 having a circular cross section provided inside the cylinder 11, the cylinder 11 and the cylinder head 12. and a piston 13 , and a fuel injection valve 6 attached to the cylinder head 12 .

As shown in the cross section including the cylinder center axis C in FIG. 18 and . A groove-shaped cavity 19 is formed on the top surface of the piston 13 by the second bottom slope portion 17 , the bottom arc portion 18 , the first bottom slope portion 15 , and the bottom center convex portion 14 . This cavity 19 has a circular opening as viewed in the axial direction as shown in FIG. 3, and the diameter D1 of the opening as shown in FIG. ing.

As shown in FIG. 2 , the bottom central convex portion 14 is a projection formed so that the radial central portion of the top surface of the piston 13 projects toward the fuel injection valve 6 side.

The first bottom inclined portion 15 is an inclined surface forming an angle θ1 with respect to the cylinder central axis C, as shown in FIG. The first bottom surface inclined portion 15 extends radially outward from the base end portion of the bottom central protrusion 14 and is inclined so as to separate from the cylinder head 12 as it extends radially outward. In the present invention, "forming an angle" means a smaller crossing angle.

As shown in FIG. 2, the peripheral edge portion 16 is an end surface that is formed on the radially outer portion of the top surface of the piston 13 and extends perpendicularly to the cylinder central axis C. As shown in FIG. A valve recess 20 is formed in a radially inner portion of the peripheral edge portion 16 so as to be one step lower than the periphery. As shown in FIG. 3, the valve recesses 20 have an arc-shaped outer shape when viewed in the axial direction of the cylinder (hereinafter abbreviated as "axial view"). It is These valve recesses 20 prevent the intake valves 3 and exhaust valves 5 shown in FIG. playing a role.

The second bottom inclined portion 17 is an inclined surface forming an angle θ2 with respect to the cylinder central axis C, as shown in FIG. The second bottom inclined portion 17 extends radially inward from the inner edge portion of the peripheral edge portion 16 and is inclined away from the cylinder head 12 as it extends radially inward. Note that the angle θ2 is set to be smaller than the angle θ1. In other words, the angle θ1 is set larger than the angle θ2. Further, the angle θ3 formed between the second bottom surface inclined portion 17 and the first bottom surface inclined portion 15, that is, the value obtained by subtracting the sum of the angles θ1 and θ2 from 180° is set to 50° or more.

As shown in FIG. 2 , the arcuate bottom surface 18 is a curved surface that is formed to be convex toward the side opposite to the fuel injection valve 6 and curved in an arc shape. The arcuate bottom surface portion 18 has one end connected to the lower end portion of the first inclined bottom surface portion 15 and the other end connected to the lower end portion of the second inclined bottom surface portion 17 . Thereby, the first bottom slope portion 15 and the second bottom slope portion 17 are connected to each other by the bottom arc portion 18 .

The piston 13 configured in this manner is housed inside the cylinder 11 and reciprocates between a so-called top dead center P1 indicated by a solid line in FIG. 2 and a so-called bottom dead center P2 indicated by a two-dot chain line in FIG. It is movable.

As shown in FIG. 2, the fuel injection valve 6 has a plurality of injection holes 21 that are capable of injecting the fuel F at an injection hole angle .theta.4. Here, the "injection hole angle θ4" in the present invention is also called the "head angle", and is formed by the injection axis 22 representing the injection direction of the fuel F and the cylinder center axis C in a cross section including the cylinder center axis C. It means an angle that is double the angle. In this embodiment, the nozzle hole angle θ4 is set to 125° or more and 135° or less. Further, as indicated by a two-dot chain line in FIG. 3, the fuel injection valve 6 of this embodiment is provided with a total of eight injection holes 21 at intervals of 45° in the circumferential direction.

The fuel injection valve 6 configured in this manner is attached to a position near the cylinder center axis C in the cylinder head 12 . As a result, as shown in FIG. 2, in a cross section including the cylinder center axis C, the injection axis 22 of each injection hole 21 intersects the first bottom inclined portion 15 of the piston 13 when positioned at the top dead center P1. is oriented to Further, as shown in FIG. 3 , all of the injection shafts 22 of the eight injection holes 21 are oriented so as to avoid the center 23 of the valve recess 20 when viewed in the axial direction. More specifically, four of the eight injection shafts 22 are oriented in a direction in which no valve recesses 20 exist, that is, to areas between adjacent valve recesses 20 when viewed in the axial direction. In addition, the remaining four injection shafts 22 are oriented in the direction in which the valve recess 20 exists in an axial view, and are oriented in a region other than the center 23 .

(Action and effect of combustion chamber structure)
Next, the effects of the combustion chamber structure 10 according to this embodiment will be described. 4 and 5 are explanatory diagrams showing the flow of the injected fuel F in chronological order. In the combustion chamber structure 10 described above, the fuel F is injected from the fuel injection valve 6 when the piston 13 is positioned at the top dead center P1 as shown in FIG. 4(a). At this time, the injection axis 22 of the injected fuel F is oriented so as to intersect the first bottom inclined portion 15 of the piston 13 as described above. Therefore, the injected fuel F collides with a predetermined portion of the first bottom surface inclined portion 15 and flows downward along the first bottom surface inclined portion 15 .

Thereafter, as shown in FIG. 4(b), the fuel F flows in an arc along the bottom arc portion 18, thereby changing its flow direction upward. Furthermore, the fuel F reaches the radially outer edge of the cavity 19 by flowing upward along the second bottom inclined portion 17 from the bottom arc portion 18 .

By the way, the fuel F injected from the fuel injection valve 6 develops so as to take in the surrounding gas into itself, so that the flow of gas substantially perpendicular to the injection axis 22 of itself, that is, the entrain flow, flows around. known to cause In particular, in the fuel injection valve 6 having a plurality of injection holes 21 as in the present embodiment, the fuel F injected from adjacent injection holes 21 interferes with each other, causing the injected fuel F to travel forward in the injection direction. Since the gas is taken in from the side, an entrain flow 24 is generated in a direction opposite to the injection direction of the fuel F, as shown in FIG. 5(a).

Therefore, the fuel F that has reached the radially outer edge of the cavity 19 is attracted by the entrain flow 24, and its flow direction is directed toward the radially central portion of the combustion chamber 1, as shown in FIG. 5(a). change as you go. As a result, mixing of the fuel F and air is promoted in the radial center portion of the combustion chamber 1 where air is abundantly present, and the air utilization rate is improved, so the fuel consumption of the engine E can be reduced.

Furthermore, in this embodiment, as shown in FIG. 2, the angle θ2 formed by the second bottom surface inclined portion 17 with respect to the cylinder central axis C is less than or equal to the angle θ1 formed by the first bottom surface inclined portion 15 with respect to the cylinder central axis C. is set to the size of That is, the second bottom surface inclined portion 17 is formed to be steeper than the first bottom surface inclined portion 15 . Therefore, the fuel F flowing along the steep second bottom surface inclined portion 17 tends to form a vortex at the radially outer edge of the cavity 19 . It is easy to change to the center part in the radial direction. Due to such a swirling effect, the fuel F that has reached the radially outer edge of the cavity 19 is more likely to flow toward the radially central portion of the combustion chamber 1, so that the fuel consumption of the engine E can be further reduced. . Numerical simulation confirmed that such a vortex formation effect becomes remarkable when the angle formed by the second bottom surface inclined portion 17 and the first bottom surface inclined portion 15 is 50° or more.

After that, the piston 13 starts moving from the top dead center P1 toward the bottom dead center P2. Then, a reverse squish flow 25 is generated inside the combustion chamber 1 as shown in FIG. 5(b). More specifically, a space called a squish 26 is formed at the radially outer edge of the combustion chamber 1 by the peripheral edge 16 of the piston 13 , the wall surface of the cylinder 11 and the bottom surface of the cylinder head 12 . When the volume of the combustion chamber 1 increases as the piston 13 descends, gas flows from the inside of the cavity 19 toward the squish 26, that is, a reverse squish flow 25 is generated. When the fuel F flows into the squish 26 under the influence of the reverse squish flow 25 and burns, the generated combustion gas may come into contact with the cylinder 11, increasing heat loss.

However, in the present invention, the injection axis 22 of the fuel F is oriented so as to intersect the first bottom inclined portion 15 of the piston 13, and an entrain flow 24 is generated inside the combustion chamber 1 in the opposite direction. The entrain flow 24 weakens the influence of the reverse squish flow 25 on the fuel F, thereby suppressing the inflow of the fuel F into the squish 26 . As a result, the fuel F is diffused and burned throughout the combustion chamber 1, and contact between the combustion gas and the cylinder 11 is reduced, so that heat loss can be reduced. The effect of the entrain flow 24 weakening the influence of the reverse squish flow 25 in this way is obtained when the nozzle hole angle θ4 of the fuel injection valve 6 is 125° or more and 135° or less. It becomes noticeable because it becomes easier to be

Furthermore, in this embodiment, the diameter D1 of the opening of the cavity 19 is set relatively wide. This is because the flow velocity of the reverse squish flow 25 is inversely proportional to the size of the diameter D1 of the opening of the cavity 19 . If the diameter D1 of the opening of the cavity 19 is set relatively wide to reduce the flow velocity of the reverse squish flow 25 as in this embodiment, the influence of the reverse squish flow 25 on the fuel F can be weakened. , the inflow of the fuel F into the squish 26 is further suppressed. This makes it possible to further reduce heat loss. By setting the diameter D1 of the opening of the cavity 19 to 90% or more of the inner diameter D2 of the cylinder 11, the reverse squish flow can be greatly weakened, so that a more remarkable heat loss reduction effect can be obtained.

Further, when the diameter D1 of the opening of the cavity 19 is set relatively wide, the axial depth of the cavity 19 is set shallow in order to keep the volume of the combustion chamber 1 constant. Accordingly, the injection hole angle θ4 of the fuel injection valve 6 is set relatively narrow. As a result, the fuel F injected from the fuel injection valve 6 collides with the first bottom inclined portion 15 at an early stage, and the amount of air introduced into the fuel F is restricted, thereby slowing down the initial combustion. As a result, an increase in combustion temperature is suppressed, so that it is possible to reduce the amount of nitrogen oxide (NOx) emissions.

Furthermore, in this embodiment, all the injection axes 22 of the eight nozzle holes 21 of the fuel injection valve 6 are oriented so as to avoid the center 23 of the valve recess 20 when viewed in the axial direction. This is because when the fuel F is injected into the valve recess 20, the fuel F tends to reach and stay in the cylinder 11, and the mixture with the air existing inside the combustion chamber 1 becomes insufficient. This is because incomplete combustion occurs, leading to deterioration of exhaust gas. Therefore, by orienting all the injection axes 22 so as to avoid the center 23 of the valve recess 20, the injected fuel F is less likely to be adversely affected by the valve recess 20. FIG. Furthermore, in this embodiment, four of the eight injection shafts 22 are oriented in directions in which the valve recesses 20 do not exist when viewed in the axial direction. Therefore, the fuel F injected in these four directions can be less likely to be adversely affected by the valve recess 20 .

Furthermore, in this embodiment, the engine speed at maximum output is set relatively low. As the engine speed increases, although details are not shown in the figure, swirl flow (swirling flow generated during intake) and squish flow (flow from squish 26 generated when piston 13 rises to cavity 19) occur inside combustion chamber 1. The air flow, such as the direction of flow), becomes faster. As a result, the effect of the entrain flow 24, that is, the effect of weakening the influence of the reverse squish flow 25 on the fuel F, is relatively weakened. Therefore, it is preferable to set the engine speed relatively low in order to sufficiently obtain the heat loss reduction effect and the exhaust improvement effect of the present invention. Numerical simulations have confirmed that the effects of the present invention as described above are remarkably obtained when the engine speed at maximum output is set to 2500 rpm or less, excluding the instantaneous maximum speed.

(Modification)
The number of injection holes 21 of the fuel injection valve 6 is not limited to eight in the present embodiment, and can be arbitrarily changed according to the number of valve recesses 20 and the like. For example, the number of injection holes 21 can be four. In this case, all four injection shafts 22 avoid the center 23 of the valve recess 20. 20 may be set so as to point in a nonexistent direction.

In the present embodiment, the injection shafts 22 are oriented so as to avoid the center 23 of the valve recess 20 from the viewpoint of preventing deterioration of the exhaust gas. As a result, as shown in FIG. is oriented. However, in the case of a high-output engine, etc., where the combustion temperature is high, the piston 13 is likely to crack at the periphery of the valve recess 20, so it is not preferable that the injection shaft 22 is oriented in the direction of the periphery. Therefore, when giving priority to such a point of view, as shown in FIG. It is preferable to set the injection axis 22 so as to point in a direction in which the valve recess 20 does not exist. It should be noted that when the total number of injection shafts 27 is four, all the injection shafts 27 may be set to point in the direction in which the valve recess 20 does not exist.

The combustion chamber structure according to the present invention can also be applied to an in-cylinder injection gasoline engine.

1 Combustion Chamber 2 Air Supply Pipe 3 Intake Valve 4 Exhaust Pipe 5 Exhaust Valve 6 Fuel Injection Valve 7 Crankshaft 8 Revolution Sensor 9 Control Part 10 Combustion Chamber Structure 11 Cylinder 12 Cylinder Head 13 Piston 14 Bottom Center Projection 15 First Bottom Inclination Part 16 Peripheral Edge 17 Second Bottom Inclined Part 18 Bottom Circular Part 19 Cavity 20 Valve Recess 21 Injection Hole 22 Injection Axis 23 Center 24 Entrain Flow 25 Reverse Squish Flow 26 Squish 27 Injection Axis C Cylinder Central Axis D1 Diameter D2 Inside Diameter E Engine F Fuel P1 Top dead center P2 Bottom dead center θ1 angle θ2 angle θ3 angle θ4 injection hole angle

Claims (9)

A cylinder head in which a fuel injection valve is arranged, a cylinder, and a piston that reciprocates inside the cylinder,
A circular cavity is formed on the top surface of the piston on the side of the cylinder head,
The fuel injection valve is attached to the cylinder head and injects fuel from the vicinity of a cylinder central axis passing through the center of the cavity,
A combustion chamber structure in which a combustion chamber is configured by a space surrounded by the top surface of the piston including the cavity, the cylinder, and the cylinder head,
A center projection of the bottom surface of the cavity bottom, the inner surface of which is convex in a direction approaching the fuel injection valve, and a piston top portion extending from the center projection of the bottom surface toward the outer diameter of the cavity. and a first bottom sloped portion that slopes on the opposite side,
When the piston is at the top dead center, an injection axis representing an injection direction of the fuel injected from the fuel injection valve intersects the first bottom inclined portion.
A combustion chamber structure characterized by: A second bottom surface inclined portion in which the inner surface shape of the cavity on a cross section including the cylinder central axis is inclined from the cavity opening of the piston top portion toward the center portion of the cavity toward the opposite side of the piston top portion, and the first bottom surface inclined portion. a bottom arc portion connecting the second bottom slope portion with an arc;
The combustion chamber structure according to claim 1, characterized in that: an angle formed by the first bottom inclined portion and the cylinder central axis is larger than an angle formed by the second bottom inclined portion and the cylinder central axis;
3. The combustion chamber structure according to claim 2, characterized by: The fuel injection valve has an injection hole angle of 125° or more and 135° or less, and has a plurality of injection holes spaced apart in the circumferential direction.
The combustion chamber structure according to any one of claims 1 to 3, characterized in that: The diameter of the opening of the cavity is 90% or more of the diameter of the cylinder,
The combustion chamber structure according to any one of claims 1 to 4, characterized in that: In the fuel injection valve, the number of the injection holes is 4 or 8,
5. The combustion chamber structure according to claim 4, characterized in that: A total of four intake/exhaust valves are arranged in one cylinder head, and four valve recesses are provided at the top of the piston for avoiding contact with the intake/exhaust valves. all the injection axes are oriented to avoid near the center of the valve recess;
The combustion chamber structure according to claim 6, characterized in that: Four of the injection axes are oriented in a direction in which the valve recess does not exist.
The combustion chamber structure according to claim 7, characterized by: 9. An engine comprising the combustion chamber structure according to any one of claims 1 to 8, wherein the engine speed at maximum output excluding the instantaneous maximum speed is 2500 rpm or less.
An engine characterized by:

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