A preheating unit and a biogas engine thereof

Abstract

The present application relates to the technical field of biogas engine, and discloses a preheating unit and a biogas engine thereof, wherein the preheating unit comprises a preheating sleeve cylinder, a spark plug and an oil injector; the preheating sleeve cylinder has a precombustion chamber inside; the precombustion chamber is divided into a transition cavity and a combustion cavity which are communicated with each other; the radial diameter of the transition cavity gradually increases along the direction close to the combustion cavity; the inner wall surface of the combustion cavity is a circular arc surface, the center Q of the circular arc surface and the center point P are located on the same straight line and have a spacing distance between them; and the preheating unit is built in the combustion cylinder body of the biogas engine; in the present application, the structure of the preheating sleeve cylinder is optimized, so that the preheating sleeve cylinder has better constraint on fuel, more uniform distribution effect and higher utilization rate, and the precombustion ignition effect of fuel can be greatly improved; then the fuel is ignited uniformly in the main combustion chamber of the engine, the fuel can be fully combusted, and the economy and output efficiency of the engine as a whole are improved.

Description

Technical Field

[0001] This invention relates to the field of biogas engine technology, and more particularly to a preheating unit and its biogas engine. Background Technology

[0002] Biogas is a combustible gas that can be used as fuel for internal combustion engines. The combustion gas in biogas is methane, and methane engines mostly use a premixed combustion mode. However, the performance of methane engines is limited by knocking, which in turn affects the engine's output. Biogas has a slow combustion speed and poor combustion isochoricity, resulting in high exhaust temperature and low thermal efficiency.

[0003] While existing methane engines employ pre-combustion chamber ignition technology, which pre-ignites the mixture within the chamber via spark plug electrodes, causing deflagration, the deflagration flame propagates through a small hole connecting the pre-combustion chamber and the main combustion chamber as a high-pressure jet. However, further research has revealed that the bottom of the preheating chamber in existing technologies is often spherical. Although this allows the combustion gases to be ejected radially from the pre-combustion chamber, it also makes it easy for the combustion gases to form vortices within the chamber, resulting in uneven distribution of the combustion gases and thus affecting the output performance of the biogas engine. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the current biogas engines, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to provide a preheating unit for a biogas engine, which aims to solve the problem of biogas combustion gas easily forming vortices in the pre-combustion chamber by setting an optimized structural design of the pre-combustion chamber.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a preheating unit, which includes a preheating cylinder, a spark plug and an injector, wherein the preheating cylinder has a pre-combustion chamber inside, the pre-combustion chamber is divided into a transition chamber and a combustion chamber that are interconnected, the radial diameter of the transition chamber gradually increases along the direction close to the combustion chamber, and the inner wall surface of the combustion chamber is a circular arc surface, the center Q of the circular arc surface and its center point P are located on the same straight line and there is a gap between them.

[0008] In a preferred embodiment of the preheating unit described in this invention, the interval distance satisfies the following relationship:

[0009] 0.1 ≤ L / (R+L) ≤ 0.4

[0010] Where R represents the radius of curvature of the circular arc surface.

[0011] In a preferred embodiment of the preheating unit of the present invention, the width of the connection between the transition chamber and the combustion chamber is K, and satisfies the following relationship:

[0012] 0.6≤(K / 2) / (R+L)≤0.75.

[0013] As a preferred embodiment of the preheating unit of the present invention, the preheating cylinder has at least three flame outlet holes on its bottom sidewall, and each flame outlet hole is located on the same plane and is arranged at equal intervals along the circumference of the combustion chamber.

[0014] In a preferred embodiment of the preheating unit of the present invention, the vertical distance between the plane enclosed by each of the flame outlet holes and the center point P of the combustion chamber is H, and satisfies the following relationship:

[0015] 0.5(R+L)≤H≤0.8(R+L).

[0016] As a preferred embodiment of the preheating unit of the present invention, it further includes a spark plug and an injector disposed on the top side wall of the preheating cylinder, wherein the ignition end of the spark plug and the oil outlet end of the injector are both located in the pre-combustion chamber; at least two injectors are symmetrically arranged along the central axis of the preheating cylinder; and the angle A between the axis of the injector and the central axis of the preheating cylinder is in the range of 30°≤A≤42°.

[0017] Another objective of this invention is to provide a biogas engine that addresses the problem of turbulent formation of biogas combustion gases within the pre-combustion chamber, as well as the issue of high temperatures and slow cooling at the valves of the engine combustion cylinder, which leads to short valve lifespan, by incorporating a novel pre-combustion chamber structural design.

[0018] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a biogas engine, which includes a preheating unit, a combustion cylinder and a valve unit, wherein the combustion cylinder has a main combustion chamber inside the cylinder, the preheating unit is embedded in the middle side wall of the combustion cylinder, and the preheating cylinder and the main combustion chamber are kept in communication through the flame outlet.

[0019] As a preferred embodiment of the biogas engine of the present invention, it further includes: a valve unit disposed on the side wall of the combustion cylinder, the valve unit including an intake assembly and an outlet assembly, the intake assembly and the outlet assembly being symmetrically distributed on both sides of the preheating unit and communicating with the main combustion chamber; an intake port and an outlet port communicating with the main combustion chamber are provided on the side wall of the combustion cylinder, and the intake assembly and the outlet assembly are respectively installed at the intake port and the outlet port; the intake assembly and the outlet assembly have the same structure.

[0020] In a preferred embodiment of the biogas engine of the present invention, the intake assembly includes an intake valve seat, an intake valve movably disposed within the intake valve seat, and a sealing ring fitted onto the outer wall of the intake valve seat; the intake valve seat has an annular cooling channel inside, and its side wall has an inlet and an outlet communicating with the cooling channel; its circumferential side wall has a through hole; the inner annular side wall of the sealing ring has an air ring groove, which communicates with the cooling channel through the through hole; the side wall of the intake valve has a cooling channel, and its side wall has an inlet and an outlet communicating with the cooling channel.

[0021] In a preferred embodiment of the biogas engine of the present invention, a pressure sensor is provided on the side wall of the intake valve seat, and its monitoring end is located in the cooling channel; a temperature sensor is provided at the outlet of the cooling channel.

[0022] The beneficial effects of this invention are:

[0023] The preheating unit in this invention optimizes the structural design of the preheating cylinder, giving it better constraint on the fuel, a more uniform distribution effect, and a higher utilization rate, which can significantly improve the pre-combustion effect of the fuel; thus, the fuel is evenly ignited in the main combustion chamber of the engine, allowing for complete combustion and improving the overall economy and output efficiency of the engine. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0025] Figure 1 This is a schematic diagram of the overall structure of the preheating unit of the present invention.

[0026] Figure 2 This is a three-dimensional cross-sectional view of the preheating cylinder of the preheating unit of the present invention.

[0027] Figure 3This is a schematic diagram of the internal plan of the preheating cylinder of the preheating unit of the present invention.

[0028] Figure 4 This is a schematic diagram of the gas flow in the pre-combustion chamber of the preheating unit of the present invention.

[0029] Figure 5 This is a schematic diagram of the overall structure of the biogas engine of the present invention.

[0030] Figure 6 This is a schematic diagram of the intake valve seat connection structure of the biogas engine of the present invention.

[0031] Figure 7 This is a cross-sectional planar structural diagram of the intake valve seat of the biogas engine of the present invention.

[0032] Figure 8 This is a schematic diagram of the air intake valve structure of the biogas engine of the present invention. Detailed Implementation

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0034] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0035] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0036] Secondly, the present invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not according to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0037] Example 1

[0038] Reference Figures 1-4The first embodiment of the present invention provides a preheating unit, including a preheating cylinder 100, a spark plug 200, and an injector 300. The preheating cylinder 100 is used for preheating and mixing fuel. It is hollow inside and forms a pre-combustion chamber, namely the pre-combustion chamber M. The pre-combustion chamber M is divided into two parts along its axial direction, namely a transition chamber 101 and a combustion chamber 102 that are interconnected. The transition chamber 101 is configured with a variable diameter, and its radial diameter gradually increases along the direction near the end of the combustion chamber 102, forming a funnel shape with a gradually increasing opening. The inner wall surface of the combustion chamber 102 is a circular arc surface, and the center Q of the circular arc surface and the center point P of the chamber are located on the same straight line and there is a distance L between the two points.

[0039] Since the cross-section of the transition cavity 101 gradually increases from top to bottom, that is, its inner wall surface is inclined, when the fuel injected by the injector 300 hits the inner wall surface of the transition cavity 101, the transition cavity 101 guides the fuel, thereby ensuring that the fuel can smoothly enter the combustion chamber 102.

[0040] Furthermore, since there is a distance L between the center Q of the arc surface of the combustion chamber 102 and the center point P, that is, the center Q of the inner wall of the combustion chamber 102 is eccentrically arranged with respect to the central axis of the transition chamber 101, this arrangement can make the fuel flow distribution within the combustion chamber 102 more uniform. Specifically, see attached... Figure 3 and Figure 4 As shown, fuel enters the combustion chamber 102 from the transition chamber 101, forming an annular fuel flow under the influence of the curved surfaces around the edges. This annular fuel flow directs the fuel flow, reducing or eliminating collisions between fuel streams, and significantly reducing or eliminating vortices formed in the center of the fuel chamber. This results in a more uniform fuel distribution within the pre-combustion chamber M, improving preheating efficiency and indirectly increasing the output efficiency of the biogas engine. Furthermore, the annular fuel flow also creates a downward concave shape in the central region of the combustion chamber 102, ensuring that fuel overflows from the combustion chamber while promoting a more uniform fuel distribution across all layers of the combustion chamber 102.

[0041] Furthermore, since the combustion chamber 102 is not a cylindrical chamber with a single diameter, its internal variable-diameter chamber space is larger, which can increase the amount of fuel and solvent in the pre-combustion chamber M, accommodate more fuel, and increase the combustion output.

[0042] Furthermore, the center Q of the arc surface of the combustion chamber 102 and the center point P of the chamber are on the same straight line and there is a distance L between them. The distance L satisfies the following relationship:

[0043] 0.1 ≤ L / (R+L) ≤ 0.4

[0044] Where R represents the radius of curvature of the circular arc surface.

[0045] For details, see attached. Figure 3 As shown, the radius of the combustion chamber 102 is R+L. The ratio of L to R+L is the eccentricity of the inner wall of the combustion chamber 102. When the ratio of L / (R+L) is too small, i.e. less than 0.1, the eccentricity between the inner wall of the combustion chamber 102 and the center of the combustion chamber 102 will be too small, almost similar to a sphere in the prior art, which will cause vortices to form in the middle of the combustion chamber 102. Conversely, when the ratio of R+L is too large, i.e. greater than 0.4, the outward bulge of the inner wall of the combustion chamber 102 will increase, similar to an ellipse. This will not only occupy too much internal space of the preheating cylinder 100, but also affect the distribution of fuel. Therefore, the interval distance L within this range can make the fuel form the best convection effect in the combustion chamber 102.

[0046] Furthermore, the width of the connection between the transition cavity 101 and the combustion cavity 102 is K, and satisfies the following relationship:

[0047] 0.6≤(K / 2) / (R+L)≤0.75.

[0048] Specifically, such as Figure 3 As shown, the connection between the transition chamber 101 and the combustion chamber 102 is the top opening of the combustion chamber 102, and the width at this point is K. The ratio of K to R+L is called the narrowing ratio of the combustion chamber 102. The smaller the narrowing ratio, the greater the narrowing degree, which can better constrain the fuel overflow in the combustion chamber 102, ensure the amount of fuel in the combustion chamber 102, improve the pre-combustion effect of the fuel, and thus improve the engine output efficiency.

[0049] However, when the narrowing ratio is too small, i.e. (K / 2) / (R+L) is less than 0.6, the fuel in the transition chamber 101 cannot smoothly enter the combustion chamber 102, causing the fuel to accumulate in the transition chamber 101. This not only increases the risk of carbon deposits in the pre-combustion chamber M, but also leads to fuel waste. When the narrowing ratio is too large, i.e. (K / 2) / (R+L) is greater than 0.75, the fuel in the combustion chamber 102 will overflow into the transition chamber 101, which will still lead to fuel waste.

[0050] At least three flame outlet holes 103 are provided on the bottom side wall of the preheating cylinder 100. These flame outlet holes 103 are located on the same plane and are arranged at equal intervals along the circumference of the combustion chamber 102. The vertical distance H between the plane enclosed by the flame outlet holes 103 and the center point P of the combustion chamber 102 satisfies the following relationship:

[0051] 0.5(R+L)≤H≤0.8(R+L).

[0052] Specifically, such as Figure 3As shown, when H is too small, i.e. less than 0.5(R+L), the flame outlet 103 will be too close to the center of the combustion chamber 102, and the flame stream generated by the fuel below the flame outlet 103 will be too far from the flame outlet 103 and cannot be discharged smoothly, which reduces the utilization rate of the flame stream and the utilization rate of fuel, and is not conducive to fuel economy.

[0053] Conversely, when H is too large, i.e. greater than 0.8(R+L), since the wall of the pre-combustion chamber M is curved and the width of the curved surface becomes narrower towards the bottom, the spacing between multiple flame outlets 103 will decrease as the flame outlet 103 gets closer to the bottom, thus affecting the uniformity of the flame flow and also adversely affecting the utilization of the flame flow, reducing the utilization rate of the flame flow, reducing the utilization rate of fuel, and being detrimental to fuel economy.

[0054] It should be noted that the multiple flame outlets 103 are located on the same plane and are arranged at intervals along the circumference of the combustion chamber 102. That is, in the vertical projection, the flame outlets 103 are in the same plane, and the multiple flame outlets 103 are evenly spaced along the circumference of the combustion chamber 102, which ensures the uniformity of flame output. This allows the flame to enter the main combustion chamber 401 evenly, thereby allowing the fuel in the main combustion chamber 401 to be ignited evenly. This not only achieves better flame flow utilization but also promotes the complete combustion of fuel in the main combustion chamber 401, improving combustion efficiency and thus improving the engine's economy and efficiency.

[0055] In addition, the preheating unit 100 also includes a spark plug 200 and an injector 300 disposed on the top side wall of the preheating cylinder 100. The ignition end of the spark plug 200 and the oil outlet end of the injector 300 are both located in the pre-combustion chamber M. There are at least two injectors 300 symmetrically arranged along the central axis of the preheating cylinder 100. The included angle A between the axis of the injector 300 and the central axis of the preheating cylinder 100 is in the range of 30°≤A≤42°.

[0056] Specifically, such as Figure 1As shown in the illustration, in this embodiment, two injectors 300 are used as an example. The two injectors 300 are arranged symmetrically. The angle between the axis of the injector 300 and the axis of the spark plug 200 is A, and A can be 30°, 35°, 40°, or 42°. It should be noted that when the angle A between the injector 300 and the spark plug 200 is too large, the fuel is easily sprayed onto the inner wall of the preheating cylinder 100, affecting the fuel entering the combustion chamber 102. Conversely, when the angle between the injector 300 and the spark plug 200 is too small, although the fuel is directly injected into the pre-combustion chamber M, the fuel will not pass through the ignition head of the spark plug 200. Setting the included angle A between 30°≤A≤42° is an optimal range obtained after repeated verification. Within this optimal range, not only can the fuel be smoothly injected into the combustion chamber 102, but the fuel can also pass through the ignition head of the spark plug 200 during the injection process, using the fuel to clean the spark plug 200, reducing carbon deposits on the spark plug 200 and improving the service life of the spark plug 200.

[0057] Example 2

[0058] Reference Figures 5-8 The second embodiment of the present invention provides a biogas engine, which includes the preheating unit in embodiment 1, and also includes a combustion cylinder 400 and a valve unit 500. The combustion cylinder has a main combustion chamber 401 inside, and the preheating unit is embedded in the middle side wall of the combustion cylinder 400. The preheating sleeve cylinder 100 and the main combustion chamber 401 are kept in communication through the fire outlet 103.

[0059] The side wall of the combustion cylinder 400 also has a valve unit 500 for the input and output of gas in the main combustion chamber 401; combined with the attached... Figure 5 As shown, the valve unit 500 includes an intake assembly 501 and an exhaust assembly 502, which are symmetrically distributed on both sides of the preheating unit and communicate with the main combustion chamber 401. The intake assembly 501 is used to supply a mixture of fuel and air into the main combustion chamber 401, while the exhaust assembly 502 is used to discharge the exhaust gas after combustion in the main combustion chamber 401.

[0060] The side wall of the combustion cylinder 400 is provided with an air inlet 402 and an air outlet 403 that connect to the main combustion chamber 401. The air inlet assembly 501 and the air outlet assembly 502 are respectively installed at the air inlet 402 and the air outlet 403.

[0061] Furthermore, in this embodiment, the intake assembly 501 and the exhaust assembly 502 adopt the same structural design. The structure of the intake assembly 501 will be described in detail below, and the structure of the exhaust assembly 502 will not be described in detail.

[0062] For details, see attached. Figure 6 and Figure 7 As shown, the intake assembly 501 includes an intake valve seat 501a, an intake valve 501b movably disposed within the intake valve seat 501a, and a sealing ring 501c fitted onto the outer wall of the intake valve seat 501a. The intake valve seat 501a is annular in shape, with an annular cooling channel 501a-1 inside its annular body. An inlet 501a-2 and an outlet 501a-3 communicating with the cooling channel 501a-1 are provided on its side wall. An external cooling pipe G can introduce cooling medium into the cooling channel 501a-1 through the inlet 501a-2 and discharge it through the outlet 501a-3. It should be noted that the cooling medium can be air, coolant, or other liquids or gases. The introduced cooling medium can cool the entire intake valve seat 501a, improving the working performance and service life of the intake valve seat 501a and the entire intake assembly.

[0063] The sealing ring 501c is annular and tightly fitted onto the circumferential sidewall of the intake valve seat 501a, serving to seal the intake valve seat 501a at the intake port 402. A ring groove 501c-1 is formed on the inner ring sidewall of the sealing ring 501c, communicating with the cooling channel 501a-1 through a through hole T. It should be noted that the through hole T is radially formed on the circumferential sidewall of the intake valve seat 501a, and multiple sets can be formed at equal intervals. This allows the cooling medium in the cooling channel 501a-1 to enter the ring groove 501c-1. The cooling medium entering the ring groove 501c-1 not only reduces the temperature of the sealing ring 501c but also utilizes the pressure of the cooling medium to generate external tension in the sealing ring 501c, thereby improving the sealing performance of the intake valve seat 501a.

[0064] Similarly, it can be understood that the cooling channel 501b-1 provided in the side wall of the intake valve 501b, and the inlet 501b-2 and outlet 501b-3 on the side wall communicating with the cooling channel 501b-1, are used to cool the intake valve 501b, which will not be described again here.

[0065] Furthermore, in conjunction with the appendix Figure 6As shown, a pressure sensor Y is installed on the side wall of the intake valve seat 501a, with its monitoring end located inside the cooling channel 501a-1. In this embodiment, the pressure sensor Y is installed on the top side wall of the intake valve seat 501a as an example. The specific installation position is not required and depends on the actual installation. The monitoring end of the pressure sensor Y needs to extend into the cooling channel 501a-1. By collecting the pressure in the cooling channel 501a-1, the wear condition of the intake valve seat 501a can be determined. For example, since the bottom of the intake valve seat 501a is in contact with the intake valve 501b, the bottom of the intake valve seat 501a also has the largest wear surface. When the bottom of the intake valve seat 501a is worn through, the cooling channel 321 leaks, causing the pressure inside the cooling channel 501a-1 to decrease or become unbalanced. After the pressure sensor Y detects the decrease in pressure inside the cooling channel 501a-1, it sends the monitoring data to the external central control system to remind the user, thereby realizing real-time monitoring of valve seat wear and improving the safety of use.

[0066] There can be multiple pressure sensors Y, which are arranged circumferentially at intervals on the valve seat to monitor the air pressure at different locations and improve the accuracy of valve seat wear monitoring.

[0067] A temperature sensor W is installed at the outlet 501b-3 of the cooling channel 501b-1 to monitor the outlet air temperature. The cooling efficiency is determined by the outlet air temperature. When the outlet air temperature is high, it means that the cooling effect is reduced. The intake speed can be increased to remove more heat, or the temperature of the cooling medium can be reduced to remove more heat, thereby reducing the valve temperature and improving the valve life.

[0068] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A preheating unit, characterized in that: The system includes a preheating cylinder (100) with a pre-combustion chamber (M) inside. The pre-combustion chamber (M) is divided into a transition chamber (101) and a combustion chamber (102) that are interconnected. The radial diameter of the transition chamber (101) gradually increases in the direction close to the combustion chamber (102). The inner wall of the combustion chamber (102) is a curved surface with the center (Q) of the curved surface and its center point (P) on the same straight line and separated by a distance (L). The pre-combustion chamber (M) is used for fuel to enter from the transition chamber (101). The fuel enters the combustion chamber (102) and forms an annular fuel flow under the action of the arc surface around the edge. The annular fuel flow is used to direct the fuel flow, reduce or eliminate the collision between fuel flows, reduce or eliminate the vortex formed in the middle of the fuel chamber, make the fuel distribution in the pre-combustion chamber (M) more uniform and improve the preheating efficiency, and make the central area of ​​the combustion chamber (102) concave downward, ensuring that the fuel overflows from the combustion chamber while promoting a more uniform fuel distribution in the upper and lower layers of the combustion chamber (102). The interval distance (L) satisfies the following relationship: 0.1≤L / (R+L)≤0.4, where R represents the radius of curvature of the arc surface; The width of the connection between the transition cavity (101) and the combustion cavity (102) is K, and satisfies the following relationship: 0.6≤(K / 2) / (R+L)≤0.

75.

2. The preheating unit according to claim 1, characterized in that: The preheating cylinder (100) has at least three flame outlet holes (103) on its bottom side wall, and each flame outlet hole (103) is located on the same plane and is arranged at equal intervals along the circumference of the combustion chamber (102).

3. The preheating unit according to claim 2, characterized in that: The vertical distance between the plane enclosed by each of the flame outlet holes (103) and the center point (P) of the combustion chamber (102) is H, and satisfies the following relationship: 0.5(R+L)≤H≤0.8(R+L).

4. The preheating unit according to claim 3, characterized in that: It also includes a spark plug (200) and an injector (300) disposed on the top side wall of the preheating cylinder (100), wherein the ignition end of the spark plug (200) and the oil outlet end of the injector (300) are both located in the pre-combustion chamber (M); the spark plug (200) is disposed along the central axis of the preheating cylinder (100), and there are at least two injectors (300) symmetrically disposed along the central axis of the preheating cylinder (100); and the included angle A between the axis of the injector (300) and the central axis of the preheating cylinder (100) is in the range of 30°≤A≤42°.

5. A biogas engine, characterized in that: Including the preheating unit as described in claim 3 or 4, it further includes a combustion cylinder (400) having a main combustion chamber (401) inside the cylinder, the preheating unit being embedded in the middle side wall of the combustion cylinder (400), and the preheating sleeve cylinder (100) and the main combustion chamber (401) being kept in communication through the flame outlet (103).

6. The biogas engine according to claim 5, characterized in that: It also includes a valve unit (500) disposed on the side wall of the combustion cylinder (400). The valve unit (500) includes an intake assembly (501) and an exhaust assembly (502). The intake assembly (501) and the exhaust assembly (502) are symmetrically distributed on both sides of the preheating unit and communicate with the main combustion chamber (401). An intake port (402) and an exhaust port (403) communicating with the main combustion chamber (401) are provided on the side wall of the combustion cylinder (400). The intake assembly (501) and the exhaust assembly (502) are respectively installed at the intake port (402) and the exhaust port (403). The intake assembly (501) and the exhaust assembly (502) have the same structure.

7. The biogas engine according to claim 6, characterized in that: The intake assembly (501) includes an intake valve seat (501a), an intake valve (501b) movably disposed within the intake valve seat (501a), and a sealing ring (501c) fitted onto the outer wall of the intake valve seat (501a). The intake valve seat (501a) has an annular cooling channel (501a-1) inside, and its sidewall has an inlet (501a-2) and an outlet (501a-3) communicating with the cooling channel (501a-1). A through hole (T) is provided on its circumferential sidewall. The sealing ring (501c) has an air ring groove (501c-1) on its inner ring sidewall, and the air ring groove (501c-1) communicates with the cooling channel (501a-1) through the through hole (T); the air inlet valve (501b) has a cooling channel (501b-1) in its sidewall, and its sidewall has an inlet (501b-2) and an outlet (501b-3) communicating with the cooling channel (501b-1).

8. The biogas engine according to claim 7, characterized in that: A pressure sensor (Y) is installed on the side wall of the intake valve seat (501a), and its monitoring end is located in the cooling channel (501a-1); a temperature sensor (W) is installed at the outlet (501b-3) of the cooling channel (501b-1).

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