EP4782669A1

EP4782669A1 - Gas engine

Info

Publication number: EP4782669A1
Application number: EP24868357.5A
Authority: EP
Inventors: Nobuhiro SHIMMURA; Masakuni OIKAWA; Yasuo Takagi; Yuji Mihara
Original assignee: Kawasaki Heavy Industries Ltd; Kawasaki Jukogyo KK; Gotoh Educational Corp
Current assignee: Kawasaki Heavy Industries Ltd; Gotoh Educational Corp; Kawasaki Motors Ltd
Priority date: 2023-09-20
Filing date: 2024-09-20
Publication date: 2026-07-29
Also published as: WO2025063280A1; JPWO2025063280A1

Abstract

A gas engine (100) according to one aspect of the present disclosure includes: a cylinder (11); a piston (12) that reciprocates in the cylinder (11) and includes a cavity (32) formed in a range including a central portion of a top surface of the piston (12); a fuel injector (18) that injects gas fuel directly to the central portion of the top surface of the piston (12); and an igniter (17) that ignites a fuel-air mixture containing the gas fuel and air.

Description

Technical Field

The present disclosure relates to a gas engine.

Background Art

PTL 1 below describes a gas fuel direct injection engine in which a top surface of a piston includes a cavity. Since the cavity described in PTL 1 is offset toward an intake port, gas fuel can be guided to the vicinity of an ignition plug, and a combustible fuel-air mixture can be formed in the vicinity of the ignition plug. According to the gas fuel direct injection engine described in PTL 1, it is thought that since the cavity is offset toward the intake port, the gas fuel is injected toward a portion of the top surface of the piston which is closer to the intake port than a central portion of the top surface.

Citation List

Patent Literature

PTL 1: Japanese Laid-Open Patent Application Publication No. 2005-337073

Summary of Invention

Technical Problem

According to the above gas engine, the gas fuel whose direction has been changed by guiding of a wall surface of the cavity is "directly" supplied to the ignition plug. Therefore, the gas fuel is not adequately mixed with air, and the gas fuel becomes locally rich in a combustion chamber. As a result, the amount of NOx generated may increase.
An object of the present disclosure is to provide a gas engine which can suppress the generation of NOx.

Solution to Problem

A gas engine according to one aspect of the present disclosure includes: a cylinder; a piston that reciprocates in the cylinder and includes a cavity located in a range including a central portion of a top surface of the piston; a fuel injector that injects gas fuel directly to the central portion of the top surface of the piston; and an igniter that ignites a fuel-air mixture containing the gas fuel and air.

Advantageous Effects of Invention

The gas engine according to one aspect of the present disclosure can suppress the generation of NOx.

Brief Description of Drawings

FIG. 1 is a schematic diagram showing a gas engine according to Embodiment 1.
FIG. 2 is a sectional view taken along line II-II of FIG. 1.
FIG. 3 is a diagram showing the gas engine according to Embodiment 2 and corresponding to FIG. 2.

Description of Embodiments

Embodiment 1

First, a gas engine 100 according to Embodiment 1 will be described. FIG. 1 is a schematic diagram showing the gas engine 100 according to Embodiment 1. FIG. 2 is a sectional view taken along line II-II of FIG. 1. In the gas engine 100, gas fuel, such as hydrogen gas or natural gas, is used as fuel.
As shown in FIG. 1, the gas engine 100 includes a cylinder 11, a piston 12, an intake port 13, an exhaust port 14, an intake valve 15, an exhaust valve 16, and an igniter 17. Moreover, as shown in FIG. 2, the gas engine 100 includes a fuel injector 18. Hereinafter, these components will be described in order.

Cylinder

The cylinder 11 includes a cylinder block 21 and a cylinder head 22. The cylinder block 21 serves as an inner side surface of the cylinder 11, and the cylinder head 22 serves as an upper surface of the cylinder 11. Although FIG. 1 shows one cylinder 11, the gas engine 100 according to the present embodiment includes the cylinders 11. An upper-lower direction on the plane of FIG. 1 corresponds to a central axis direction of the cylinder 11. Hereinafter, the central axis direction of the cylinder 11 is simply referred to as an "axial direction." Moreover, hereinafter, a direction orthogonal to a central axis 23 of the cylinder 11 is referred to as a "radial direction."

Piston

The piston 12 is a member that reciprocates in the cylinder 11. The piston 12 is coupled to a crankshaft through a connecting rod 24. The piston 12 defines a combustion chamber 25 together with the cylinder 11. Moreover, the piston 12 includes a cavity 32 located on a top surface 31 of the piston 12. The cavity 32 of the present embodiment is located in a range including a central portion of the top surface 31 of the piston 12. More specifically, the cavity 32 is circular when viewed in the axial direction, and a central portion of a bottom surface 33 of the cavity 32 is located on the central axis 23 of the cylinder 11. However, the shape and the position of the cavity 32 are not limited to the above.
The above-described "central portion of the top surface 31" of the piston 12 includes not only a point of the top surface 31 which is located on the central axis 23 of the cylinder 11 (hereinafter referred to as a "center point") but also a portion that can be regarded as a substantially center point, i.e., a portion that is slightly offset in the radial direction from the center point. For example, a portion in which an offset from the center point in the radial direction is within 20% of the diameter of the cylinder 11 is included in the "central portion of the top surface 31."
Moreover, the area of a section of the cavity 32 which is perpendicular to the axial direction (hereinafter referred to as a "sectional area") is 25% or more and 80% or less of the sectional area of the cylinder 11. The section of the cavity 32 of the present embodiment which is perpendicular to the axial direction is circular. In such a case, when the diameter of the cavity 32 is 50% of the inner diameter of the cylinder 11, the sectional area of the cavity 32 is 25% of the sectional area of the cylinder 11. Moreover, when the diameter of the cavity 32 is about 90% of the inner diameter of the cylinder 11, the sectional area of the cavity 32 is 80% of the sectional area of the cylinder 11. When the sectional area of the cavity 32 varies depending on a position along the axial direction, the phrase "the sectional area of the cavity 32" in "the sectional area of the cavity 32 is 25% or more and 80% or less of the sectional area of the cylinder 11" denotes the largest sectional area among the sectional areas of the cavity 32.

Intake Port

The intake port 13 is a port through which air is supplied to the combustion chamber 25. The intake port 13 is located in the cylinder head 22. In the present embodiment, one intake port 13 is located in one cylinder 11. However, the intake ports 13 may be located in one cylinder 11.

Exhaust Port

The exhaust port 14 is a port through which exhaust gas is discharged from the combustion chamber 25. The exhaust port 14 is located in the cylinder head 22. In the present embodiment, one exhaust port 14 is located in one cylinder 11. However, the exhaust ports 14 may be located in one cylinder 11.

Intake Valve

The intake valve 15 is a valve that opens and closes the intake port 13. The intake valve 15 may be configured to be able to change a timing at which the intake port 13 is opened and closed, or may be configured such that the timing at which the intake port 13 is opened and closed is constant.

Exhaust Valve

The exhaust valve 16 is a valve that opens and closes the exhaust port 14. The exhaust valve 16 may be configured to be able to change a timing at which the exhaust port 14 is opened and closed, or may be configured such that the timing at which the exhaust port 14 is opened and closed is constant.

Igniter

The igniter 17 is a device that ignites a fuel-air mixture in the combustion chamber 25. The igniter 17 of the present embodiment is located in the cylinder block 21 so as to face the combustion chamber 25. The igniter 17 is located on the central axis 23 of the cylinder 11. Examples of the igniter 17 include: an ignition plug; a prechamber igniter; and a device that injects pilot fuel that is more easily ignitable than main fuel, and performs ignition by auto-ignition of the pilot fuel. The gas fuel is injected into the combustion chamber 25 from the below-described fuel injector 18 and is then mixed with the air supplied through the intake port 13. Thus, the fuel-air mixture containing the gas fuel and the air is formed. When the proportion of the gas fuel in the fuel-air mixture (hereinafter referred to as "the concentration of the fuel-air mixture") is increased in the vicinity of the igniter 17, the ignition by the igniter 17 is facilitated.
On the other hand, depending on a method of increasing the concentration of the fuel-air mixture in the vicinity of the igniter 17, the concentration of the fuel-air mixture may vary in the combustion chamber 25, and the locally rich fuel-air mixture may be formed. In this case, in a zone where the rich fuel-air mixture exists, the combustion temperature becomes high, and NOx is easily generated. To be specific, in order to suppress the generation of NOx, it is desirable that the variation of the concentration of the fuel-air mixture in the combustion chamber 25 be suppressed, and the concentration of the fuel-air mixture be made uniform. Therefore, as described below, the gas engine 100 according to the present embodiment is configured such that the concentration of the fuel-air mixture in the combustion chamber 25 is made uniform.

Fuel Injector

The fuel injector 18 is a device that injects the gas fuel into the combustion chamber 25. As shown in FIG. 2, the fuel injector 18 is located in the cylinder block 21 so as to face the combustion chamber 25. The fuel injector 18 is located outside the central axis 23 of the cylinder 11 in the radial direction. The fuel injector 18 of the present embodiment injects the gas fuel directly to the central portion of the top surface 31 of the piston 12. However, since the piston 12 moves in the cylinder 11, continuously injecting the gas fuel directly to the central portion of the top surface 31 of the piston 12 by the fuel injector 18 is substantially impossible. Therefore, the fuel injector 18 may inject the gas fuel directly to the central portion of the top surface 31 of the piston 12 at a certain time point during the injection of the gas fuel.
As above, in the present embodiment, since the fuel injector 18 injects the gas fuel directly to the central portion of the top surface 31 of the piston 12, the gas fuel injected from the fuel injector 18 impinges on the bottom surface 33 of the cavity 32. Mixing of the gas fuel that has impinged on the bottom surface 33 of the cavity 32 with the air is promoted by the roll-up of a vortex in the vicinity of a side surface 35 of the cavity 32. Thus, the fuel-air mixture whose concentration is uniform is formed and spreads in an area extending from an upper portion of the cavity 32 to the igniter 17. Therefore, according to the gas engine 100 of the present embodiment, the concentration of the fuel-air mixture can be made uniform, and the generation of NOx can be suppressed. Moreover, since the concentration of the fuel-air mixture is made uniform, abnormal combustion can also be suppressed.
In addition, the gas fuel is mixed with the air in the cavity 32. Therefore, the inflow of the fuel-air mixture into a squish area 26 can be suppressed. The squish area 26 is a gap between a portion of the top surface 31 of the piston 12 which is located outside the cavity 32 in the radial direction and a lower surface of the cylinder block 21. By suppressing the inflow of the fuel-air mixture into the squish area 26, various effects can be achieved, such as the suppression of excessive leaning of the formed fuel-air mixture, the reduction of blowby gas, the suppression of cooling loss, and the suppression of the abnormal combustion caused by high-temperature particles derived from lubricating oil and generated at the piston ring. Among these, the reduction of the blowby gas and the suppression of the cooling loss contribute to the improvement of the heat efficiency of the engine.
Moreover, the fuel injector 18 of the present embodiment includes only one injection opening portion 34 that injects the gas fuel. Therefore, according to the present embodiment, the directivity of the gas fuel injected from the fuel injector 18 improves, and the gas fuel injected toward the central portion of the top surface 31 of the piston 12 can accurately reach the central portion of the top surface 31 of the piston 12. The shape (not the arrangement) of the injection opening portion 34 is not limited and may be a circular shape, a rectangular shape, or an annular shape.
Moreover, the pressure of the gas fuel injected by the fuel injector 18 of the present embodiment is less than 10 MPa. Typically, the pressure of the gas fuel injected is classified into "low pressure" that is 0.1 MPa or more and less than 3 MPa, "medium pressure" that is 3 MPa or more and less than 10 MPa, and "high pressure" that is 10 MPa or more. To be specific, the pressure of the gas fuel injected by the fuel injector 18 of the present embodiment is the low pressure or the medium pressure.
As above, by suppressing the pressure of the gas fuel injected by the fuel injector 18, the gas fuel can be prevented from being discharged from the cavity 32 before being mixed with the air. To be specific, the concentration of the fuel-air mixture can be made more uniform. Moreover, the inflow of the fuel-air mixture into the squish area 26 can also be suppressed. Furthermore, in the present embodiment, since the pressure of the gas fuel injected is relatively low, the cost of auxiliary equipment, such as a compressor that pressurizes the gas fuel and a tank that stores the pressurized gas fuel, can be suppressed more than when the pressure of the gas fuel injected is the high pressure.
As described above, in the present embodiment, the area of the bottom surface of the cavity 32 is 25% or more and 80% or less of the sectional area of the cylinder 11. When the area of the bottom surface of the cavity 32 is set to 25% or more of the sectional area of the cylinder 11, an excessive increase in the concentration of the fuel-air mixture in the cavity 32 can be suppressed. Moreover, when the area of the bottom surface of the cavity 32 is set to 80% or less of the sectional area of the cylinder 11, the diffusibility of the gas fuel can be maintained.
Moreover, when a crank angle of the piston 12 is between 90° before bottom dead center (BBDC) and 140° after bottom dead center (ABDC), and after the intake valve 15 closes the intake port 13, the fuel injector 18 of the present embodiment starts injecting the gas fuel. In the present embodiment, since the fuel injector 18 injects the gas fuel at a relatively early timing, i.e., when the crank angle of the piston 12 is between 90° before bottom dead center and 140° after bottom dead center, a time for the formation of the fuel-air mixture can be adequately secured, and the concentration of the fuel-air mixture can be made more uniform. Moreover, since the fuel injector 18 injects the gas fuel after the intake valve 15 closes the intake port 13, it is possible to prevent the backflow of the gas fuel to the intake port 13.

Embodiment 2

Next, a gas engine 200 according to Embodiment 1 will be described. FIG. 3 is a diagram showing the gas engine 200 according to Embodiment 2 and corresponding to FIG. 2. The shape of the cavity 32 of the gas engine 200 according to Embodiment 2 is different from that of the gas engine 100 according to Embodiment 1. Except for this, the gas engine 200 according to Embodiment 2 includes the same components as the gas engine 100 according to Embodiment 1. Therefore, the following will mainly describe the shape of the cavity 32 of the gas engine 200 according to Embodiment 2, and other descriptions are omitted.
The cavity 32 of the present embodiment includes a protrusion 41. The protrusion 41 is located on the bottom surface 33 of the cavity 32. Moreover, the protrusion 41 is convex toward an opening of the cavity 32, i.e., toward the outside in the axial direction (toward the upper side on the plane of FIG. 3). The protrusion 41 of the present embodiment has a substantially conical shape, and a tip of the protrusion 41 has a hemispherical shape. Moreover, a top portion of the protrusion 41 is located at the central portion of the top surface 31 of the piston 12. Therefore, the gas fuel injected from the fuel injector 18 toward the central portion of the top surface 31 of the piston 12 impinges on the vicinity of the top portion of the protrusion 41.
Therefore, according to the present embodiment, the gas fuel injected from the fuel injector 18 impinges on the vicinity of the top portion of the protrusion 41, diffuses, and spreads to the outside in the radial direction along the surface of the protrusion 41 to further diffuse. Then, the diffused gas fuel is mixed with the air by the roll-up of the vortex in the vicinity of the side surface 35, and this forms the fuel-air mixture whose concentration is uniform. Therefore, according to the gas engine 200 of the present embodiment, the generation of NOx can be further suppressed.
Moreover, the volume of the cavity 32 is set to an appropriate value in accordance with design conditions, such as an engine compression ratio and valve lifts of the intake valve 15 and the exhaust valve 16. Therefore, under the same design conditions, the cavity 32 including the protrusion 41 as in the present embodiment becomes deeper than the cavity 32 that does not include the protrusion 41. Thus, in the gas engine 200 according to the present embodiment, the fuel-air mixture is easily retained in the cavity 32 and is less likely to flow into the squish area 26.
Furthermore, the cavity 32 of the present embodiment includes a return portion 42. The return portion 42 is located at an opening portion of the cavity 32 and is inclined inward. To be specific, an axially outer end portion of the side surface 35 of the cavity 32 corresponds to the return portion 42, and this portion is formed such that an inner diameter thereof decreases toward the outside in the axial direction.
As described above, since the cavity 32 of the present embodiment includes the return portion 42, the inflow of the fuel-air mixture, formed in the cavity 32, into the squish area 26 can be suppressed. In addition, in the present embodiment, a boundary portion between the bottom surface 33 and the side surface 35 of the cavity 32 curves in a sectional view. Therefore, the fuel-air mixture formed in the cavity 32 easily flows along the side surface 35. In addition, the cavity 32 includes the return portion 42, and therefore, the inflow of the fuel-air mixture into the squish area 26 can be further suppressed.
The cavity 32 of the present embodiment includes both of the protrusion 41 and the return portion 42 but may include only one of them.

Modified Example

Each of the above-described gas engines 100 and 200 may include a swirl flow generator that generates a swirl flow in the cylinder 11. Herein, the swirl flow denotes the flow of the fuel gas and the air about a rotation axis coinciding with the central axis of the cylinder 11. The fuel gas is lower in density than the air. Therefore, when the swirl flow is generated in the cylinder 11, the fuel gas moves to a radially inner portion of the cylinder 11. As a result, the fuel-air mixture containing the fuel gas is less likely to be formed in the vicinity of the squish area 26, and therefore, the inflow of the fuel-air mixture into the squish area 26 can be further suppressed.
Moreover, as described above, according to the gas engines 100 and 200, the concentration of the fuel-air mixture in the cavity 32 can be made uniform. Since each of the gas engines 100 and 200 includes the swirl flow generator that generates the swirl flow in the cylinder 11, the inflow of the fuel-air mixture into the squish area 26 is suppressed. Therefore, the concentration of the fuel-air mixture in the cavity 32 is made further uniform, and thus, the generation of NOx can be further suppressed.
For example, the above-described swirl flow generator is the intake port 13, which is of a helical type. The helical intake port 13 includes an intake passage having a spiral shape, and the air that has passed through the intake passage generates the swirl flow in the cylinder 11. Moreover, the swirl flow generator may be the intake port 13 that guides the air into the cylinder 11 along a tangential direction of the cylinder 11. In this case, the air guided by the intake port 13 rotates along the inner side surface of the cylinder 11 to generate the swirl flow. The swirl flow generator is not limited to the above configuration and may have a configuration other than the intake port 13.

Conclusion

A first aspect disclosed in the present specification is a gas engine including: a cylinder; a piston that reciprocates in the cylinder and includes a cavity located in a range including a central portion of a top surface of the piston; a fuel injector that injects gas fuel directly to the central portion of the top surface of the piston; and an igniter that ignites a fuel-air mixture containing the gas fuel and air.
According to this configuration, since the gas fuel is diffused in the cavity, the concentration of the fuel-air mixture can be made uniform, and the generation of NOx can be suppressed.
A second aspect disclosed in the present specification is the gas engine according to the first aspect, wherein when a crank angle of the piston is between 90° before bottom dead center and 140° after bottom dead center, and after an intake valve closes an intake port, the fuel injector starts injecting the gas fuel.
According to this configuration, the concentration of the fuel-air mixture can be made further uniform, and the backflow of the gas fuel to the intake port can be prevented.
A third aspect disclosed in the present specification is the gas engine according to the first or second aspect, wherein a sectional area of the cavity is 25% or more and 80% or less of a sectional area of the cylinder.
According to this configuration, an excessive increase in the concentration of the fuel-air mixture in the cavity can be suppressed, and the diffusibility of the gas fuel can be maintained.
A fourth aspect disclosed in the present specification is the gas engine according to any one of the first to third aspects, wherein a central portion of a bottom surface of the cavity is located on a central axis of the cylinder.
According to this configuration, the gas fuel can be efficiently diffused in the cavity.
A fifth aspect disclosed in the present specification is the gas engine according to any one of the first to fourth aspects, wherein the fuel injector includes one injection opening portion through which the gas fuel is injected.
According to this configuration, the gas fuel injected from the fuel injector can accurately reach the central portion of the top surface of the piston.
A sixth aspect disclosed in the present specification is the gas engine according to any one of the first to fifth aspects, wherein pressure of the gas fuel injected by the fuel injector is less than 10 MPa.
According to this configuration, the concentration of the fuel-air mixture can be made further uniform.
A seventh aspect disclosed in the present specification is the gas engine according to any one of the first to sixth aspects, wherein the cavity includes a protrusion that is located on a bottom surface of the cavity and is convex toward an opening of the cavity.
According to this configuration, the concentration of the fuel-air mixture can be made further uniform.
An eighth aspect disclosed in the present specification is the gas engine according to any one of the first to seventh aspects, wherein the cavity includes a return portion that is located at an opening portion of the cavity and is inclined inward.
According to this configuration, the inflow of the fuel-air mixture into the squish area can be suppressed.
A ninth aspect disclosed in the present specification is the gas engine according to any one of the first to eighth aspects, including a swirl flow generator that generates a swirl flow in the cylinder.
According to this configuration, the inflow of the fuel-air mixture into the squish area can be further suppressed.

Reference Signs List

11: cylinder
12: piston
13: intake port (swirl flow generator)
15: intake valve
17: igniter
18: fuel injector
23: central axis
31: top surface
32: cavity
33: bottom surface
34: injection opening portion
41: protrusion
42: return portion
100: gas engine
200: gas engine

Claims

A gas engine comprising:
a cylinder;

a piston that reciprocates in the cylinder and includes a cavity located in a range including a central portion of a top surface of the piston;

a fuel injector that injects gas fuel directly to the central portion of the top surface of the piston; and

an igniter that ignites a fuel-air mixture containing the gas fuel and air.
The gas engine according to claim 1, wherein when a crank angle of the piston is between 90° before bottom dead center and 140° after bottom dead center, and after an intake valve closes an intake port, the fuel injector starts injecting the gas fuel.
The gas engine according to claim 1, wherein a sectional area of the cavity is 25% or more and 80% or less of a sectional area of the cylinder.
The gas engine according to claim 1, wherein a central portion of a bottom surface of the cavity is located on a central axis of the cylinder.
The gas engine according to claim 1, wherein the fuel injector includes one injection opening portion through which the gas fuel is injected.
The gas engine according to claim 1, wherein pressure of the gas fuel injected by the fuel injector is less than 10 MPa.
The gas engine according to claim 1, wherein the cavity includes a protrusion that is located on a bottom surface of the cavity and is convex toward an opening of the cavity.
The gas engine according to claim 1, wherein the cavity includes a return portion that is located at an opening portion of the cavity and is inclined inward.
The gas engine according to claim 1, comprising a swirl flow generator that generates a swirl flow in the cylinder.