Combustion System, Gas Engine and Combustion System Design Method

Abstract

This invention relates to the field of engine technology and discloses a combustion system, a gas engine, and a combustion system design method. The method utilizes a fuel mist jet injected from a second fuel injection hole to ignite the natural gas jets located on both sides of a reference line of the natural gas injector. This ensures that all natural gas jets on either side of the reference line are ignited by the fuel mist jet injected from the second fuel injection hole on the same side of the reference line. The projection of the central axis of the first fuel injection hole onto a first preset plane coincides with the reference line, and β > θ1. This prevents the fuel mist jet injected from the first fuel injection hole from touching the bottom surface of the natural gas injector and the top surface of the piston. Furthermore, the fuel mist jet injected from the first fuel injection hole ignites the natural gas jet located between the natural gas injector and the fuel injector and near the reference line, as well as the natural gas jet located on the side of the fuel injector opposite to the natural gas injector and near the reference line, thus improving the combustion uniformity within the combustion chamber.

Description

Technical Field

[0001] This invention relates to the field of engine technology, and in particular to a combustion system, a gas engine, and a combustion system design method. Background Technology

[0002] High-pressure direct injection compression ignition (HPDI) natural gas engines use 5% diesel fuel injected into the cylinder before the compression reaches top dead center for ignition, while 95% natural gas is injected into the flame at a pressure of 300 bar to become the primary fuel for combustion and power generation. HPDI engines maintain the same power and torque as traditional diesel engines, offering identical performance, but with 20% higher power and torque compared to spark-ignition natural gas engines.

[0003] In existing technologies, some HPDI engines use coupled injectors, meaning that diesel injection and natural gas injection are performed by the same injector, and their arrangement is as follows: Figure 1 and Figure 2 As shown, the injector adopts a dual-row orifice design, in which the lower layer of injection orifices is for diesel fuel and the upper layer is for natural gas fuel. Multiple natural gas injection orifices and multiple diesel injection orifices are arranged at intervals along the circumference of the injector. The multiple natural gas injection orifices and multiple diesel injection orifices are distributed in a one-to-one correspondence. The central axis of the natural gas injection orifice and the central axis of the corresponding diesel injection orifice are located on the same plane and are parallel. The diesel fuel jet injected by the diesel injection orifice is shorter than the natural gas jet injected by the natural gas injection orifice.

[0004] In the HPDI engine using coupled injectors, the natural gas passage in the injector needs to be sealed with diesel fuel, and the pressure of the gas rail determines the injection pressure of both diesel and natural gas. Due to the difficulty in manufacturing the gas rail, the current gas rail pressure is relatively low. Although the diesel fuel consumption is lower, the overall injection duration is longer, and diesel atomization is poor.

[0005] To address this, existing technologies have proposed a dual-injector combustion system, such as... Figure 3 As shown, a natural gas injector 1000' is arranged in the center of the combustion chamber, and a fuel injector 2000' is arranged at the edge. This separates diesel injection and natural gas injection to solve the problem of diesel injection pressure being affected by natural gas rail pressure, thereby increasing diesel injection pressure, shortening injection duration, and improving fuel atomization effect.

[0006] The aforementioned combustion system employing dual injectors has limitations. Because the fuel injectors are positioned at the edge, diesel injection holes can only be installed on the side facing the natural gas. Installing diesel injection holes on the side away from the natural gas would not only fail to ignite the gas but would also cause diesel to be sprayed onto the cylinder liners. If a smaller diesel jet ignites a larger natural gas jet, the natural gas jet on the side away from the fuel injectors will inevitably be difficult to ignite, resulting in lower heat exchange efficiency and poor emissions performance.

[0007] Therefore, a combustion system is urgently needed to solve the above-mentioned technical problems. Summary of the Invention

[0008] The purpose of this invention is to propose a combustion system, a gas engine, and a combustion system design method that can achieve the effect of better igniting multiple natural gas mists with the least amount of fuel mist, shorten the combustion duration, and improve the combustion efficiency of the gas engine.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] A combustion system includes a piston, a cylinder head, a natural gas injector, and a fuel injector, wherein a combustion chamber is formed between the piston and the cylinder head; the natural gas injector is arranged coaxially with the piston and has a plurality of circumferentially spaced natural gas injection holes.

[0011] The central axis of the fuel injector is parallel to the central axis of the natural gas injector. The fuel injector is provided with a first fuel injection hole and two second fuel injection holes. Along the circumference of the fuel injector, the first fuel injection hole is located between the two second fuel injection holes, and the diameter of the second fuel injection hole is larger than the diameter of the first fuel injection hole.

[0012] The intersection point of the central axis of the first fuel injection hole and the central axis of the fuel injector is Q. The tangent line passing through point Q and tangent to the end of the natural gas injector away from the cylinder head is a preset straight line. The angle between the preset straight line and the central axis of the fuel injector is β. The angle between the central axis of the first fuel injection hole and the central axis of the fuel injector is θ1, where β > θ1.

[0013] The projection of the central axis of the fuel injector onto the first preset plane is the first projection point, and the projection of the central axis of the natural gas injector onto the first preset plane is the second projection point. The first preset plane is perpendicular to the central axis of the piston. The line connecting the first projection point and the second projection point is the baseline. The projection of the central axis of the first fuel injection hole onto the first preset plane coincides with the baseline.

[0014] As a preferred technical solution of the above-mentioned combustion system, the baseline is coplanar with the central axis of the natural gas injector and both are located in the second preset plane, and the central axes of the two second fuel injection holes are symmetrically arranged about the second preset plane.

[0015] As a preferred technical solution of the above-mentioned combustion system, the included angle between the central axes of the two second fuel injection holes is α, where 30°≤α≤60°.

[0016] As a preferred technical solution of the above-mentioned combustion system, the angle between the central axis of the second fuel injection hole and the central axis of the fuel injector is the second injection cone angle θ2, where θ1 < θ2 ≤ 90°.

[0017] As a preferred technical solution of the above-mentioned combustion system, the distance between the central axis of the fuel injector and the central axis of the natural gas injector is L, 30mm≤L≤70mm.

[0018] As a preferred technical solution of the above-mentioned combustion system, the combustion chamber includes a combustion chamber recess provided on the top surface of the piston, a central boss is provided at the bottom of the combustion chamber recess, an annular boss is provided around the circumferential sidewall of the central boss, and a first recess is formed between the annular boss and the bottom of the combustion chamber recess.

[0019] The central axis of the natural gas injection hole intersects the inner wall of the combustion chamber recess at a preset position, which is located at the junction of the first recess and the annular boss.

[0020] As a preferred technical solution of the above-mentioned combustion system, the cross-section of the combustion chamber in any third preset plane is symmetrically arranged about the central axis of the combustion chamber, and the central axis of the combustion chamber is located in the third preset plane.

[0021] As a preferred technical solution of the above-mentioned combustion system, the natural gas injection holes are provided with eight holes, which are evenly distributed circumferentially along the central axis of the natural gas injector.

[0022] To achieve the above objectives, the present invention also provides a gas engine, including a cylinder and a combustion system as described in any of the above embodiments, wherein the cylinder is provided with a piston bore, and the piston is axially movably disposed within the piston bore.

[0023] To achieve the above objectives, the present invention also provides a combustion system design method, applicable to the combustion system described in any of the above embodiments, the combustion system design method comprising the following steps:

[0024] Construct a three-dimensional model of the combustion system and perform three-dimensional combustion simulation based on the three-dimensional model of the combustion system;

[0025] If the fuel mist jet from the first fuel injection orifice can reach the bottom surface of the natural gas injector and / or the top surface of the piston, then reduce the angle between the central axis of the first fuel injection orifice and the central axis of the fuel injector.

[0026] If the fuel mist jet from the first fuel injection orifice cannot ignite the natural gas jet on the side of the natural gas injector opposite to the fuel injector, then the diameter of the first fuel injection orifice should be increased.

[0027] If the fuel mist jet from the second fuel injection hole can hit the side of the natural gas injector, then increase the included angle between the central axes of the two first fuel injection holes.

[0028] If the fuel mist jet from the second fuel injection orifice cannot ignite the natural gas jet located on the same side of the baseline, then adjust the angle between the central axis of the second fuel injection orifice and the central axis of the fuel injector, and increase the diameter of the second fuel injection orifice.

[0029] The beneficial effects of this invention are as follows: The combustion system and gas engine provided by this invention utilize fuel mist jets injected from two second fuel injection holes to ignite the natural gas jets located on both sides of the baseline of the natural gas injector. Because the diameter of the second fuel injection holes is larger than that of the first fuel injection holes, the natural gas jets on either side of the baseline can be completely ignited by the fuel mist jets injected from the second fuel injection holes located on the same side of the baseline. By limiting the projection of the central axis of the first fuel injection hole onto the first preset plane to coincide with the baseline and β > θ1, the fuel mist jets injected from the first fuel injection holes will not touch the bottom surface of the natural gas injector or the top surface of the piston. Furthermore, the fuel mist jets injected from the first fuel injection holes can ignite the natural gas jets located between the natural gas injector and the fuel injector and near the baseline, as well as the natural gas jets located on the side of the fuel injector opposite to the natural gas injector and near the baseline. This improves the combustion uniformity within the combustion chamber, shortens the combustion duration, and is more conducive to improving thermal efficiency and reducing emissions.

[0030] The combustion system design method provided by this invention enables rapid design of combustion systems required for different engine models. It achieves optimized design of the combustion system through three-dimensional combustion simulation, which is faster and less costly than experimental selection. By optimizing the combustion system design, uniform mixing of natural gas and air within the combustion chamber and uniform ignition by the fuel injector can be achieved, shortening the combustion duration and improving the engine's thermal efficiency. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the content of the embodiments of the present invention and these drawings without creative effort.

[0032] Figure 1This is a schematic diagram of a combustion system using coupled injectors in the prior art. Figure 1 ;

[0033] Figure 2 This is a schematic diagram of a combustion system using coupled injectors in the prior art. Figure 2 ;

[0034] Figure 3 This is a schematic diagram of a combustion system using dual injectors in the prior art;

[0035] Figure 4 This is a cross-sectional schematic diagram of the combustion system provided in an embodiment of the present invention on a second predetermined plane;

[0036] Figure 5 This is a cross-sectional schematic diagram of the combustion system provided in an embodiment of the present invention on a first preset plane;

[0037] Figure 6 This is a cross-sectional schematic diagram of the fuel injector provided in an embodiment of the present invention on a first preset plane;

[0038] Figure 7 This is a schematic cross-section of the fuel injector provided in the embodiment of the present invention on the second preset plane. Figure 1 ;

[0039] Figure 8 This is a schematic cross-section of the fuel injector provided in the embodiment of the present invention on the second preset plane. Figure 2

[0040] Figure 9 This is a detailed flowchart of the design method for the combustion system provided in the embodiments of the present invention.

[0041] In the picture:

[0042] 1000' Natural gas injector; 2000' Fuel injector;

[0043] 1. Fuel injector; 11. First fuel injection hole; 12. Second fuel injection hole; 2. Natural gas injector; 3. Piston; 31. Central boss; 32. Annular boss; 33. First recess; 4. Cylinder head; 100. First preset plane; 200. Second preset plane; 300. Baseline. Detailed Implementation

[0044] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0045] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0046] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0047] In the description of this embodiment, the terms "upper," "lower," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0048] like Figures 4 to 8 As shown, an embodiment of the present invention provides a combustion system including a piston 3, a cylinder head 4, a natural gas injector 2 and a fuel injector 1, wherein a combustion chamber is formed between the piston 3 and the cylinder head 4; the natural gas injector 2 is coaxially arranged with the piston 3, and the natural gas injector 2 is provided with a plurality of natural gas injection holes arranged circumferentially at intervals.

[0049] The central axis of the fuel injector 1 is parallel to the central axis of the natural gas injector 2. The fuel injector 1 is provided with a first fuel injection hole 11 and two second fuel injection holes 12. Along the circumference of the fuel injector 1, the first fuel injection hole 11 is located between the two second fuel injection holes 12, and the diameter of the second fuel injection hole 12 is larger than the diameter of the first fuel injection hole 11.

[0050] The intersection point of the central axis of the first fuel injection hole 11 and the central axis of the fuel injector 1 is Q. The tangent line passing through point Q and tangent to the end of the natural gas injector 2 away from the cylinder head 4 is a preset straight line. The angle between the preset straight line and the central axis of the fuel injector 1 is β. The angle between the central axis of the first fuel injection hole 11 and the central axis of the fuel injector 1 is θ1, where β > θ1.

[0051] The projection of the central axis of the fuel injector 1 onto the first preset plane 100 is the first projection point, and the projection of the central axis of the natural gas injector 2 onto the first preset plane 100 is the second projection point. The first preset plane 100 is perpendicular to the central axis of the piston 3. The line connecting the first projection point and the second projection point is the reference line 300. The projection of the central axis of the first fuel injection hole 11 onto the first preset plane 100 coincides with the reference line 300.

[0052] The combustion system coaxializes the natural gas injector 2 with the piston 3 and positions the fuel injector 1 on one side of the natural gas injector 2. Since the projection of the central axis of the first fuel injection orifice 11 onto the first preset plane 100 coincides with the reference line 300, and along the axial direction of the fuel injector 1, the first fuel injection orifice 11 is located between two second fuel injection orifices 12. The fuel mist sprayed from the two second fuel injection orifices 12 ignites the natural gas jets on both sides of the reference line 300 of the natural gas injector 2. By limiting the diameter of the second fuel injection orifice 12 to be larger than that of the first fuel injection orifice 11, the penetration distance of the second fuel injection orifice 12 is made greater than that of the first fuel injection orifice 11, thus ensuring that the natural gas jets on either side of the reference line 300 are completely ignited by the fuel mist sprayed from the two second fuel injection orifices 12. The fuel mist injected by the second fuel injection hole 12 on the same side of the line 300 is ignited; by limiting the projection of the central axis of the first fuel injection hole 11 onto the first preset plane 100 to coincide with the reference line 300 and β>θ1, the fuel mist injected by the first fuel injection hole 11 can be prevented from touching the bottom surface of the natural gas injector 2 and the top surface of the piston 3, and the fuel mist injected by the first fuel injection hole 11 can ignite the natural gas stream located between the natural gas injector 2 and the fuel injector 1 and near the reference line 300, as well as the natural gas stream located on the side of the fuel injector 1 opposite to the natural gas injector 2 and near the reference line 300, thereby improving the combustion uniformity in the combustion chamber, shortening the combustion duration, and further improving thermal efficiency and reducing emissions.

[0053] In some embodiments, the baseline 300 is coplanar with the central axis of the natural gas injector 2 and both lie on the second preset plane 200, and the central axes of the two second fuel injection holes 12 are symmetrically arranged about the second preset plane 200. This can improve the consistency of natural gas and fuel on both sides of the baseline 300.

[0054] The included angle between the central axes of the two second fuel injection holes 12 is α. The design principle for α is to be as small as possible without the fuel flame touching the side of the natural gas injector 2. In some embodiments, 30°≤α≤60°. This can further improve the uniformity of natural gas and fuel on both sides of the baseline 300. It should be noted that α can take any value between 30° and 60°, such as any value of 30°, 35°, 40°, 45°, 50°, 55°, or 60°.

[0055] In some embodiments, the angle between the central axis of the second fuel injection hole 12 and the central axis of the fuel injector 1 is the second injection cone angle θ2, where θ1 < θ2 ≤ 90°. This configuration ensures effective fuel ignition while allowing the fuel mist jets from the two second fuel injection holes 12 to ignite all natural gas jets on both sides of the reference line 300.

[0056] In some embodiments, the distance between the central axis of the fuel injector 1 and the central axis of the natural gas injector 2 is L, where 30mm ≤ L ≤ 70mm.

[0057] It should be noted that the diameter of the second fuel injection orifice 12 is D1, and the diameter of the first fuel injection orifice 11 is D2. The sizes of D1 and D2 depend on the diameter of the combustion chamber and the size of L to ensure that the fuel mist can ignite all the natural gas jets. The specific values ​​of D1 and D2 are not specified here. As for L, it can be any value between 30mm and 70mm, such as any value of 30mm, 35mm, 40mm, 45mm, 50mm, 55mm, 60mm, 65mm, or 70mm.

[0058] In some embodiments, the combustion chamber includes a combustion chamber recess located on the top surface of the piston 3. A central boss 31 is provided at the bottom of the combustion chamber recess, and an annular boss 32 is provided around the circumferential sidewall of the central boss 31. A first recess 33 is formed between the annular boss 32 and the bottom of the combustion chamber recess. The central axis of the natural gas injection orifice intersects the inner wall of the combustion chamber recess at a predetermined position, located at the junction of the first recess 33 and the annular boss 32. This allows the natural gas mist to be injected to the junction of the first recess 33 and the annular boss 32, thereby causing the natural gas to form a swirling flow under the guiding effect of the first recess 33, improving the uniformity of the natural gas within the first recess 33.

[0059] In some embodiments, the cross-section of the combustion chamber in any third preset plane is symmetrically arranged about the central axis of the combustion chamber, and the central axis of the combustion chamber is located in the third preset plane. This makes the entire combustion chamber a symmetrical structure.

[0060] In some embodiments, eight natural gas injection holes are provided, which are evenly distributed circumferentially along the central axis of the natural gas injector 2. By using eight natural gas injection holes evenly distributed circumferentially along the natural gas injector 2, in conjunction with a symmetrically arranged combustion chamber, the uniformity of natural gas within the combustion chamber can be improved.

[0061] Embodiments of the present invention also provide a gas engine, including a cylinder block and a combustion system as described in any of the above embodiments. The cylinder block has a piston hole, and a piston 3 is axially movably disposed within the piston hole. This gas engine has the same technical effects as the combustion system described above, and will not be described in detail here. It should be noted that the fuel injector 1 of this gas engine can be a diesel injector, and the natural gas injected by the natural gas injector 2 can be methanol, methane, etc., and will not be specifically limited here.

[0062] Figure 9 This is a detailed flowchart of the combustion system design method provided in the embodiments of the present invention, such as... Figure 9 As shown, embodiments of the present invention also provide a method for designing a combustion system, the method comprising the following steps:

[0063] S1. Construct a three-dimensional model of the combustion system;

[0064] S2. Perform three-dimensional combustion simulation based on the three-dimensional model of the combustion system;

[0065] S3. Determine whether the fuel mist sprayed from the first fuel injection hole 11 can reach the bottom surface of the natural gas injector 2 and / or the top surface of the piston 3. If yes, reduce the angle between the central axis of the first fuel injection hole 11 and the central axis of the fuel injector 1 to update the three-dimensional model of the combustion system, and then execute S2; if no, execute S4.

[0066] S4. Determine whether the fuel mist jet injected by the first fuel injection hole 11 can ignite the natural gas jet on the side of the natural gas injector 2 opposite to the fuel injector 1. If yes, execute S5. If no, increase the aperture of the first fuel injection hole 11 to update the three-dimensional model of the combustion system, and then execute S2.

[0067] S5. Determine whether the fuel mist jet injected by the second fuel injection hole 12 can hit the side of the natural gas injector 2. If yes, increase the included angle between the central axes of the two first fuel injection holes 11 to update the three-dimensional model of the combustion system, and then execute S2; if no, execute S6.

[0068] S6. Determine whether the fuel mist jet injected by the second fuel injection hole 12 can ignite the natural gas jet located on the same side of the reference line 300 as the second fuel injection hole 12; if yes, the fuel system design is completed; if no, adjust the angle between the central axis of the second fuel injection hole 12 and the central axis of the fuel injector 1 and / or increase the diameter of the second fuel injection hole 12.

[0069] In step S6, if the fuel mist sprayed by the second fuel injection hole 12 cannot ignite the natural gas jet located on the same side of the reference line 300 as the second fuel injection hole 12, it may be because the angle between the central axis of the second fuel injection hole 12 and the central axis of the fuel injector 1 is too large or too small, resulting in less natural gas jet that the fuel sprayed by the second fuel injection hole 12 can contact, or it may be because the penetration distance of the fuel mist sprayed by the second fuel injection hole 12 is insufficient. Therefore, based on the simulation results, it is determined whether to adjust the angle between the central axis of the second fuel injection hole 12 and the central axis of the fuel injector 1, or to increase the diameter of the second fuel injection hole 12.

[0070] It should be noted that in step S3, the combustion simulation results are used to determine whether the fuel mist sprayed from the first fuel injection hole 11 can reach the bottom surface of the natural gas injector 2 and / or the top surface of the piston 3. In step S4, the combustion simulation results are used to determine whether the fuel mist sprayed from the first fuel injection hole 11 can ignite the natural gas stream on the side of the natural gas injector 2 opposite to the fuel injector 1. In step S5, the combustion simulation results are used to determine whether the fuel mist sprayed from the second fuel injection hole 12 can touch the side of the natural gas injector 2. In step S6, the combustion simulation results are used to determine whether the fuel mist sprayed from the second fuel injection hole 12 can ignite the natural gas stream located on the same side as the second fuel injection hole 12 on the baseline 300. How to make the above judgments based on the combustion simulation results can be done by visual observation, and will not be described in detail here.

[0071] The combustion system design method provided in this embodiment can quickly design combustion systems according to the requirements of different engine models. It achieves optimized design of the combustion system through three-dimensional combustion simulation, which is faster and less costly than experimental selection. By optimizing the combustion system design, natural gas and air can be uniformly mixed in the combustion chamber and uniformly ignited by the fuel injector 1, shortening the combustion duration and improving the engine's thermal efficiency.

[0072] Furthermore, the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A combustion system, characterized in that, It includes a piston (3), a cylinder head (4), a natural gas injector (2) and a fuel injector (1). A combustion chamber is formed between the piston (3) and the cylinder head (4). The natural gas injector (2) is arranged coaxially with the piston (3). The natural gas injector (2) is provided with a plurality of natural gas injection holes arranged circumferentially. The central axis of the fuel injector (1) is parallel to the central axis of the natural gas injector (2). The fuel injector (1) is provided with a first fuel injection hole (11) and two second fuel injection holes (12). Along the circumference of the fuel injector (1), the first fuel injection hole (11) is located between the two second fuel injection holes (12). The diameter of the second fuel injection holes (12) is larger than the diameter of the first fuel injection hole (11). The intersection point of the central axis of the first fuel injection hole (11) and the central axis of the fuel injector (1) is Q. The tangent line passing through point Q and tangent to the end of the natural gas injector (2) away from the cylinder head (4) is a preset straight line. The angle between the preset straight line and the central axis of the fuel injector (1) is β. The angle between the central axis of the first fuel injection hole (11) and the central axis of the fuel injector (1) is θ1, where β > θ1. The projection of the central axis of the fuel injector (1) onto the first preset plane (100) is the first projection point, and the projection of the central axis of the natural gas injector (2) onto the first preset plane (100) is the second projection point. The first preset plane (100) is perpendicular to the central axis of the piston (3). The line connecting the first projection point and the second projection point is the reference line (300). The projection of the central axis of the first fuel injection hole (11) onto the first preset plane (100) coincides with the reference line (300).

2. The combustion system according to claim 1, characterized in that, The baseline (300) is coplanar with the central axis of the natural gas injector (2) and both are located on the second preset plane (200). The central axes of the two second fuel injection holes (12) are arranged symmetrically about the second preset plane (200).

3. The combustion system according to claim 2, characterized in that, The included angle between the central axes of the two second fuel injection holes (12) is α, where 30°≤α≤60°.

4. The combustion system according to claim 1, characterized in that, The angle between the central axis of the second fuel injection hole (12) and the central axis of the fuel injector (1) is the second injection cone angle θ2, where θ1 < θ2 ≤ 90°.

5. The combustion system according to claim 1, characterized in that, The distance between the central axis of the fuel injector (1) and the central axis of the natural gas injector (2) is L, 30mm≤L≤70mm.

6. The combustion system according to any one of claims 1 to 5, characterized in that, The combustion chamber includes a combustion chamber recess on the top surface of the piston (3), a central boss (31) is provided at the bottom of the combustion chamber recess, and an annular boss (32) is provided around the circumferential sidewall of the central boss (31) of the combustion chamber recess, and a first recess (33) is formed between the annular boss (32) and the bottom of the combustion chamber recess. The central axis of the natural gas injection hole intersects the inner wall of the combustion chamber recess at a preset position, which is located at the junction of the first recess (33) and the annular boss (32).

7. The combustion system according to claim 6, characterized in that, The cross-section of the combustion chamber in any third preset plane is symmetrically arranged about the central axis of the combustion chamber, and the central axis of the combustion chamber is located in the third preset plane.

8. The combustion system according to any one of claims 1 to 5, characterized in that, The natural gas injection holes are provided in eight parts, and the eight natural gas injection holes are evenly distributed circumferentially along the central axis of the natural gas injector (2).

9. A gas engine, characterized in that, The system includes a cylinder block and a combustion system as described in any one of claims 1 to 8, wherein the cylinder block is provided with a piston bore and the piston (3) is axially movably disposed within the piston bore.

10. A combustion system design method, characterized in that, The combustion system design method, applied to any one of claims 1 to 8, comprises the following steps: Construct a three-dimensional model of the combustion system and perform three-dimensional combustion simulation based on the three-dimensional model of the combustion system; If the fuel mist jet injected by the first fuel injection hole (11) can reach the bottom surface of the natural gas injector (2) and / or the top surface of the piston (3), then the angle between the central axis of the first fuel injection hole (11) and the central axis of the fuel injector (1) is reduced. If the fuel mist jet injected by the first fuel injection hole (11) cannot ignite the natural gas jet on the side of the natural gas injector (2) opposite to the fuel injector (1), then the diameter of the first fuel injection hole (11) is increased. If the fuel mist jet from the second fuel injection hole (12) can hit the side of the natural gas injector (2), then the included angle between the central axes of the two first fuel injection holes (11) is increased. If the fuel mist sprayed by the second fuel injection hole (12) cannot ignite the natural gas jet that is located on the same side of the reference line (300) as the second fuel injection hole (12), then adjust the angle between the central axis of the second fuel injection hole (12) and the central axis of the fuel injector (1) and increase the diameter of the second fuel injection hole (12).

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