Combustion system and method for liquid ammonia direct injection engine with active pre-combustion chamber

Abstract

This invention provides a liquid ammonia direct injection engine combustion system and method with an active pre-combustion chamber, relating to the field of internal combustion engine technology. It includes a cylinder head and a cylinder liner located below the cylinder head. A pre-combustion chamber is vertically disposed at the center of the cylinder head. A liquid ammonia injector is disposed on one side of the pre-combustion chamber. A hydrogen injector and a spark plug are disposed on the pre-combustion chamber. Injection holes are disposed on the pre-combustion chamber, all located at the bottom of the chamber, facing the side with the liquid ammonia injector. This invention, employing the aforementioned liquid ammonia direct injection engine combustion system and method with an active pre-combustion chamber, achieves the effect of premixed combustion of ammonia fuel to promote diffusion combustion, realizing precise control of the combustion initiation point and heat release rate, and meeting the requirements of low hydrogen energy ratio, high ignition efficiency, and high thermal efficiency across the entire operating range of ammonia fuel engines.

Description

Technical Field

[0001] This invention relates to the field of internal combustion engines, and in particular to a liquid ammonia direct injection engine combustion system and method with an active pre-combustion chamber. Background Technology

[0002] Hydrogen, as a zero-carbon fuel, is considered an ideal clean energy source. However, the conditions and costs for hydrogen storage and transportation are currently high, it is prone to explosion, has high safety storage requirements, and is not easily liquefied. These problems hinder its large-scale application at present. Ammonia, as a good hydrogen-carrying fuel, has a hydrogen mass fraction as high as 17.6% and is easier to transport and store. However, ammonia's low combustion rate, narrow combustion limits, and difficulty in ignition limit its application and promotion in the fuel field. Pre-combustion chamber ignition, with the addition of hydrogen as a combustion aid, is an effective solution to the problem of ammonia ignition difficulties and to improve the flame propagation speed of ammonia. Active pre-combustion chamber jet ignition can achieve stable ammonia ignition. The concept of ammonia-hydrogen fusion fuel is to use ammonia as on-board storage fuel, with a portion of the ammonia being catalytically converted into hydrogen online, and then using this hydrogen to ignite the ammonia for combustion, achieving efficient near-zero emission combustion of ammonia-hydrogen fusion.

[0003] Currently, the main technology for igniting ammonia combustion using pre-combustion chamber jet ignition employs ammonia injection through the intake manifold. However, this approach suffers from low charging efficiency, low thermal efficiency, and high unburned ammonia emissions. Some existing inventions utilize pre-combustion chamber jet ignition to ignite premixed ammonia mixtures or injected ammonia fuel, achieving premixed or diffusion combustion. However, these ignition methods suffer from excessively high engine pressure rise rates or high hydrogen energy requirements. Summary of the Invention

[0004] The purpose of this invention is to provide a combustion system and method for a liquid ammonia direct injection engine with an active pre-combustion chamber. By designing and adjusting parameters such as liquid ammonia injection timing, hydrogen ratio, injection pattern, spark plug ignition timing, and pre-combustion chamber nozzle and liquid ammonia injector nozzle, it ensures that a reasonably concentrated mixture and a high-energy jet flame are formed in the pre-combustion chamber under different operating conditions. This effectively ignites a portion of the premixed ammonia fuel in the main combustion chamber, forming a premixed combustion flame. The remaining liquid ammonia fuel is then injected into the premixed combustion flame in the main combustion chamber, igniting the liquid ammonia fuel jet. This combines premixed combustion and diffusion combustion, achieving a combined combustion mode that promotes diffusion combustion. This method enables enhanced ignition of liquid ammonia fuel with a low hydrogen energy ratio in a liquid ammonia direct injection engine with an active pre-combustion chamber. Furthermore, it proposes a pre-combustion chamber nozzle arrangement and a liquid ammonia injector nozzle arrangement adapted to the pre-combustion chamber installation location, achieving low hydrogen energy requirements, high space utilization, and low wall heat transfer loss, thereby improving the engine's indicated thermal efficiency. By adjusting the liquid ammonia injection timing and spark plug ignition timing, precise control of the combustion start point and heat release rate can be achieved, meeting the requirements of high ammonia substitution rate and high thermal efficiency of ammonia fuel engines across the entire operating range.

[0005] To achieve the above objectives, the present invention provides a combustion method for a liquid ammonia direct injection engine with an active pre-combustion chamber, comprising the following steps:

[0006] During the intake stroke, the pressure in the pre-combustion chamber is higher than that in the main combustion chamber, and the exhaust gas formed in the previous cycle in the pre-combustion chamber is forced out of the pre-combustion chamber.

[0007] During the compression stroke, fresh air is forced into the pre-combustion chamber because the pressure in the pre-combustion chamber is lower than that in the main combustion chamber.

[0008] In the later stage of the compression stroke, according to the amount of air in the pre-combustion chamber, the corresponding hydrogen is injected into the pre-combustion chamber through the hydrogen injector at the top of the pre-combustion chamber. The hydrogen mixes with the fresh air that is compressed into the pre-combustion chamber to form a combustible mixture that is rich at the top and lean at the bottom.

[0009] Near the top dead center of the compressor, a portion of liquid ammonia oil jet is first injected into the main combustion chamber through the liquid ammonia injector to form a premixed ammonia mixture in the main combustion chamber.

[0010] The concentration of the premixed hydrogen mixture in the pre-combustion chamber has reached the ignition requirements. Energy is released through the spark plug to ignite the premixed hydrogen mixture in the pre-combustion chamber. The premixed hydrogen mixture burns rapidly in layers from top to bottom. The resulting high-temperature and high-pressure combustion flame will be rapidly injected through the pre-combustion chamber and spread into the main combustion chamber, forming a strong turbulent flame in the main combustion chamber and igniting the premixed ammonia mixture in the main combustion chamber, thus forming ammonia premixed combustion in the main combustion chamber.

[0011] Then, the remaining liquid ammonia oil jet is injected into the main combustion chamber using a liquid ammonia injector. The liquid ammonia oil jet is ignited by a premixed combustion flame, forming a diffusion combustion of the subsequent liquid ammonia oil jet, thus achieving a combined combustion mode that promotes diffusion combustion through premixed combustion.

[0012] Preferably, the first injection of liquid ammonia begins within 30-50°CA before top dead center, the liquid ammonia injection amount is 30%-50% of the total fuel mass, the hydrogen injector in the pre-combustion chamber begins within 130-50°CA before top dead center, and the spark plug ignition time in the pre-combustion chamber is within 6-18°CA before top dead center.

[0013] Preferably, the diameter of the left nozzle of the liquid ammonia injector is larger than that of the right nozzle, the spray penetration distance on the left side is greater than that on the right side, and the angle between the left nozzle and the central axis of the cylinder is greater than that between the right nozzle and the central axis of the cylinder.

[0014] Preferably, the angle between the central axis of the liquid ammonia injector and the central axis of the cylinder liner is in the range of 10°-20°, and the distance between the nozzle head of the liquid ammonia injector and the central axis of the pre-combustion chamber is 20mm.

[0015] Preferably, the liquid ammonia injector is used to supply liquid ammonia with a pressure range of 40-60 MPa to the main combustion chamber, and the hydrogen injector is used to supply hydrogen with a pressure range of 0.8-2.0 MPa.

[0016] A liquid ammonia direct injection engine combustion system with an active pre-combustion chamber includes a cylinder head and a cylinder liner disposed below the cylinder head. A pre-combustion chamber is vertically disposed at the center of the cylinder head. A liquid ammonia injector is disposed on one side of the pre-combustion chamber. A hydrogen injector and a spark plug are disposed on the pre-combustion chamber.

[0017] The pre-combustion chamber is provided with spray holes, all of which are located at the bottom of the pre-combustion chamber. The spray holes of the pre-combustion chamber face the side of the liquid ammonia injector, and the angle between the spray holes of the pre-combustion chamber and the central axis of the pre-combustion chamber is in the range of 70°-82°.

[0018] Preferably, the pre-combustion chamber has a structure that is wider at the top and narrower at the bottom, and the pre-combustion chamber also includes a cylindrical top, a trapezoidal transition area, and a cylindrical throat from top to bottom.

[0019] Preferably, a piston is disposed inside the cylinder liner, and the cylinder liner, cylinder head and piston constitute an ω-shaped main combustion chamber, and the injection port of the pre-combustion chamber is located inside the main combustion chamber.

[0020] Preferably, the angle between the liquid ammonia injector nozzle and the central axis of the cylinder liner is in the range of 40°-76°.

[0021] Preferably, the nozzle diameter of the pre-combustion chamber is determined according to the volume of the pre-combustion chamber, and the nozzle diameter range of the pre-combustion chamber is 1.0-3.0 mm.

[0022] Therefore, the present invention employs the above-mentioned liquid ammonia direct injection engine combustion system and method with an active pre-combustion chamber, and the technical effects are as follows:

[0023] The combustion organization method of liquid ammonia direct injection engine with active pre-combustion chamber only requires the addition of a pre-combustion chamber and side-mounted injectors to the cylinder head, without affecting the original engine valves and other structures. The engine structure does not require major modifications, and the operating and production costs are both low.

[0024] By setting the pre-combustion chamber nozzles only on the side facing the liquid ammonia injector and adjusting the circumferential and axial angles of the nozzles, the ignition efficiency of ammonia fuel was effectively improved, the amount of hydrogen energy used was reduced, and the demand for hydrogen front-end supply was decreased.

[0025] By matching the nozzle diameter, angle, and injection strategy of the liquid ammonia injector with the shape of the main combustion chamber and the position of the liquid ammonia injector, the nozzle diameter of the nozzle facing the pre-combustion chamber and the liquid ammonia oil jet penetration distance are increased. This ensures that the liquid ammonia oil jet can cover the side of the main combustion chamber away from the liquid ammonia injector, ensuring that the air in all positions of the main combustion chamber is fully utilized. This ensures that the flame distribution in the main combustion chamber is uniform, reduces the problem of excessively high temperature in some areas, and reduces the problem of high heat loss from the wall.

[0026] The combustion organization method of a liquid ammonia direct injection engine with an active pre-combustion chamber combines premixed combustion and diffusion combustion of liquid ammonia fuel. This effectively solves the problem of difficult ignition of liquid ammonia fuel jets when the hydrogen energy content is low, and improves the combustion rate of the liquid ammonia fuel jets, achieving premixed combustion to promote diffusion combustion. It also effectively reduces the problem of excessively high cylinder pressure rise caused by premixed combustion, lowering the strength requirements for engine materials. This combustion method effectively improves the combustion stability and efficiency of liquid ammonia engines under low hydrogen energy requirements. When the minimum hydrogen energy content is only 5%, the combustion efficiency reaches over 99%; at a compression ratio of 16, the maximum indicated thermal efficiency reaches 50%. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a liquid ammonia direct injection engine combustion system with an active pre-combustion chamber according to the present invention.

[0028] Figure 2 This is a schematic diagram of the pre-combustion chamber;

[0029] Figure 3 Schematic diagram of the pre-combustion chamber nozzle arrangement;

[0030] Figure 4 A schematic diagram of the nozzle arrangement for a liquid ammonia injector;

[0031] Figure 5 This is a schematic diagram of the efficient combustion process of liquid ammonia. Figure 5 (a) is a schematic diagram of the hydrogen injector needle valve being pulled up, where hydrogen mixes with fresh air that has been forced into the pre-combustion chamber to form a combustible mixture. Figure 5 (b) is a schematic diagram of the liquid ammonia injector being turned on to inject liquid ammonia into the main combustion chamber, and the liquid ammonia mixing with air to form an ammonia mixture. Figure 5 (c) The spark plug ignites the mixture in the pre-combustion chamber, a flame is formed in the pre-combustion chamber, and the jet flame ignites part of the premixed ammonia mixture to form premixed combustion; Figure 5 (d) is a schematic diagram of the liquid ammonia injector being turned on again to inject the remaining liquid ammonia into the main combustion chamber, and the premixed combustion flame igniting the liquid ammonia oil jet to form diffusion combustion.

[0032] Figure Labels

[0033] 1. Piston; 2. Cylinder liner; 3. Cylinder head; 4. Intake manifold; 5. Intake valve; 6. Exhaust manifold; 7. Exhaust valve; 8. Liquid ammonia injector; 9. Pre-combustion chamber; 91. Top; 92. Transition zone; 93. Throat; 94. Nozzle; 10. Hydrogen injector; 11. Spark plug; 12. Main combustion chamber. Detailed Implementation

[0034] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0036] Example 1

[0037] like Figure 1-5 As shown, the combustion system of a liquid ammonia direct injection engine with an active pre-combustion chamber includes a cylinder liner 2, a cylinder head 3 mounted on the cylinder liner 2, and intake manifolds 4 and exhaust manifolds 6 on both sides of the cylinder head 3. The intake manifolds 4 and 6 are connected to the ω-shaped main combustion chamber 12, and intake valves 5 and exhaust valves 7 are located at the intake manifolds 4 and 6, respectively. A piston 1 is located inside the cylinder liner 2 below the cylinder head 3. The cylinder liner 2, cylinder head 3, and piston 1 constitute the ω-shaped main combustion chamber 12, which adopts a symmetrical design.

[0038] A pre-combustion chamber 9 is provided on the cylinder head 3, and a hydrogen injector 10 is provided on the pre-combustion chamber 9. A spark plug 11 is provided on one side of the hydrogen injector 10 and on the other side of the pre-combustion chamber 9. The liquid ammonia injector 8 is provided on the cylinder head 3. The spark plug 11 is installed obliquely on the upper left of the pre-combustion chamber 9. The hydrogen injector 10 is installed vertically on the right side of the top 91 of the pre-combustion chamber 9. The hydrogen injector 10 is used to provide hydrogen with a pressure range of 0.8-2.0 MPa. The maximum injection pressure of the hydrogen injector 10 can reach 60 bar.

[0039] The liquid ammonia injector 8 is installed obliquely inside the cylinder head 3. The angle between the axis of the liquid ammonia injector 8 and the central axis of the cylinder liner 2 ranges from 10° to 20°. In this embodiment, the angle between the axis of the liquid ammonia injector 8 and the central axis of the cylinder liner 2 is 13°. The liquid ammonia injection pressure is in the range of 400 bar to 600 bar. The nozzle of the liquid ammonia injector 8 adopts a 10-hole structure. The nozzle 94 of the pre-combustion chamber 9 is located inside the main combustion chamber 12. The nozzle of the liquid ammonia injector 8 is asymmetrically arranged. The angle between the nozzle of the liquid ammonia injector 8 and the central axis of the cylinder liner 2 ranges from 40° to 76°. In this embodiment, the angle is 72°. The nozzle head of the liquid ammonia injector 8 extends into the main combustion chamber 12, and there is a 20 mm distance between the nozzle head of the liquid ammonia injector 8 and the central axis of the pre-combustion chamber 9. The diameter of the left nozzle of the liquid ammonia injector 8 is larger than that of the right nozzle, and the spray penetration distance on the left is greater than that on the right. Ensure that the liquid ammonia oil jet covers the side of the main combustion chamber 12 away from the liquid ammonia injector 8, thereby ensuring uniform flame distribution in the main combustion chamber 12 and avoiding excessive local temperature and excessive heat loss from the wall.

[0040] Specific parameters of the liquid ammonia injector nozzle are as follows: Figure 4 As shown, the angle α1 between nozzles (1) and (2) and the central axis of the cylinder is 74.5°, and the nozzle diameter D1 is 0.32mm; the angle α2 between nozzles (3) and (4) and the central axis of the cylinder is 74.5°, and the nozzle diameter D2 is 0.28mm; the angle α3 between nozzles (5), (6), (7), (8), (9) and (10) and the central axis of the cylinder is 67.5°, and the nozzle diameter D3 is 0.20mm.

[0041] The pre-combustion chamber 9 has a structure that is wider at the top and narrower at the bottom. From top to bottom, it is divided into a cylindrical top 91, a trapezoidal transition area 92, a cylindrical throat 93, and an injection hole 94 located at the bottom of the throat 93. The central axis of the pre-combustion chamber 9 coincides with the central axis of the cylinder liner 2.

[0042] Multiple nozzles 94 are provided on the pre-combustion chamber 9, all located at the bottom of the pre-combustion chamber 9 and within the main combustion chamber 12. Based on the spatial distribution characteristics of the liquid ammonia fuel jet within the main combustion chamber 12, in this embodiment, four nozzles 94 are provided, each with a diameter of 1.8 mm. The nozzles 94 in the pre-combustion chamber 9 are arranged on the side facing the liquid ammonia injector 8, and the circumferential and axial angles of the nozzles 94 in the pre-combustion chamber 9 are adjusted. The angle between the nozzles 94 and the central axis of the pre-combustion chamber 9 ranges from 70° to 82°, and in this embodiment, the angle is 74°. This enhances the spatial path overlap between the flame in the pre-combustion chamber 9 and the ammonia fuel, thereby achieving an effective ignition ratio of ≥99% for the premixed ammonia mixture and the subsequent liquid ammonia fuel jet, provided that the hydrogen energy percentage is ≤5%.

[0043] A combustion method for a liquid ammonia direct injection engine with an active pre-combustion chamber includes the following steps:

[0044] During the intake stroke, piston 1 moves downward, the pressure inside the cylinder decreases, the pressure inside the main combustion chamber 12 is less than the pressure inside the pre-combustion chamber 9, and the exhaust gas generated in the previous cycle in the pre-combustion chamber 9 is discharged.

[0045] During the compression stroke, piston 1 moves upward, and fresh air from the main combustion chamber 12 is forced into the pre-combustion chamber 9 through the nozzle 94, causing the pressure in the pre-combustion chamber 9 to gradually increase. The hydrogen injector 10 injects at a pressure of 1.0 MPa. After the needle valve of the hydrogen injector 10 is pulled up, hydrogen can be injected into the pre-combustion chamber 9 when the injection pressure is greater than the pressure in the pre-combustion chamber 9. The injection duration is 82-51°CA before top dead center, and the total energy proportion of the hydrogen injected into the pre-combustion chamber 9 is 5%. Fresh air continuously forms a tumble within the nozzle 94 of the pre-combustion chamber 9 and flows towards the top 91 of the pre-combustion chamber 9, continuously mixing with the hydrogen entering the pre-combustion chamber 9 during the compression stroke. Because the upper part of the pre-combustion chamber 9 is wider, the tumble gradually weakens during its upward movement, resulting in a heterogeneous hydrogen distribution in the pre-combustion chamber 9, richer at the top and leaner at the bottom. By adjusting the hydrogen injection pressure and injection timing, a mixture distribution favorable for combustion can be formed in the pre-combustion chamber 9.

[0046] Near the top dead center of the compression stroke, the liquid ammonia injector 8 in the main combustion chamber 12 begins to operate, with an injection pressure of 50 MPa. Since the ω-type main combustion chamber 12 is a symmetrical design, and the liquid ammonia injector 8 is located on the right side of the main combustion chamber 12, to ensure that the air on the left side of the main combustion chamber 12 is fully utilized, the nozzle arrangement of the liquid ammonia injector 8 needs to be matched, increasing the nozzle diameter of the left nozzle and the liquid ammonia jet penetration distance, resulting in a jet shape as shown in the image. Figure 4 As shown, this allows the ammonia mixture to cover the left side of the main combustion chamber 12, thereby ensuring a uniform flame distribution within the main combustion chamber 12 and preventing excessively high temperatures in certain areas of the wall.

[0047] Near the top dead center of the compressor, the mixture concentration in the pre-combustion chamber 9 has reached the ignition requirement. The mixture in the pre-combustion chamber 9 is ignited by releasing energy through the spark plug 11. The mixture burns rapidly in layers from top to bottom, and the resulting high-temperature and high-pressure combustion flame is quickly injected into the main combustion chamber 12 through the pre-combustion chamber 9.

[0048] The first injection by the liquid ammonia injector 8 begins within 30-50°CA before top dead center, with the liquid ammonia injection amount being 30%-50% of the total fuel mass. The spark plug 11 in the pre-combustion chamber 9 ignites within 6-18°CA before top dead center, ensuring that a premixed ammonia mixture of suitable concentration has formed in the main combustion chamber 12 before flame propagation in the pre-combustion chamber 9. The jet flame generated by hydrogen combustion in the pre-combustion chamber 9 ignites the ammonia mixture mixed with air in the main combustion chamber 12, forming a strong premixed combustion within the main combustion chamber 12. Then, the remaining liquid ammonia jet is injected into the premixed combustion flame using the high-pressure liquid ammonia injector 8, forming diffusion combustion. This combines premixed combustion and diffusion combustion of the liquid ammonia fuel, using premixed combustion to promote diffusion combustion and significantly reduce hydrogen consumption. Because the liquid ammonia injector 8 is located on the right side of the cylinder head 3, the high-temperature combustion flame in the main combustion chamber 12 propagates from the right side to the left. This hybrid combustion mode, which combines premixed combustion of liquid ammonia with diffusion combustion, effectively reduces the problem of excessive cylinder pressure rise caused by premixed combustion. It also reduces the high hydrogen energy required to directly ignite the liquid ammonia fuel jet, improves the ignition stability of the liquid ammonia fuel jet, and achieves a combustion efficiency of 99% and an indicated thermal efficiency of 50% for the liquid ammonia engine.

[0049] Therefore, this invention employs the aforementioned combustion system and method for a liquid ammonia direct injection engine with an active pre-combustion chamber. By designing and adjusting parameters such as the pre-combustion chamber structure, nozzle parameters, hydrogen ratio, injection pattern, and spark plug ignition timing, it ensures that a reasonably concentrated mixture and a high-energy jet flame are formed in the pre-combustion chamber under different operating conditions. This effectively ignites a portion of the premixed ammonia fuel in the main combustion chamber, forming ammonia premixed combustion. The premixed combustion flame then ignites the subsequent liquid ammonia fuel jet, leading to the diffusion combustion of the remaining liquid ammonia. This invention achieves a combustion organization method for a liquid ammonia direct injection engine with an active pre-combustion chamber that promotes diffusion combustion through premixed combustion and enhances ignition energy at low hydrogen ratios. It also achieves precise control of the combustion initiation point and heat release rate, satisfying the requirements of low hydrogen ratio, high ammonia combustion stability, and high thermal efficiency across the entire operating range of ammonia fuel engines.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. 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 still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A combustion method for a liquid ammonia direct injection engine with an active pre-combustion chamber, the method being based on a liquid ammonia direct injection engine combustion system with an active pre-combustion chamber, characterized in that, The system includes a cylinder head and a cylinder liner located below the cylinder head. A pre-combustion chamber is vertically arranged at the center of the cylinder head. A liquid ammonia injector is arranged on one side of the pre-combustion chamber. The liquid ammonia injector is obliquely installed inside the cylinder head. A hydrogen injector and a spark plug are arranged on the pre-combustion chamber. The pre-combustion chamber is provided with spray holes, all of which are located at the bottom of the pre-combustion chamber. The spray holes of the pre-combustion chamber face the liquid ammonia injector side, and the angle between the spray holes of the pre-combustion chamber and the central axis of the pre-combustion chamber is in the range of 70°-82°. The method includes the following steps: During the intake stroke, the pressure in the pre-combustion chamber is higher than that in the main combustion chamber, and the exhaust gas formed in the previous cycle in the pre-combustion chamber is forced out of the pre-combustion chamber. During the compression stroke, fresh air is forced into the pre-combustion chamber because the pressure in the pre-combustion chamber is lower than that in the main combustion chamber. In the later stage of the compression stroke, according to the amount of air in the pre-combustion chamber, the corresponding hydrogen is injected into the pre-combustion chamber through the hydrogen injector at the top of the pre-combustion chamber. The hydrogen mixes with the fresh air that is compressed into the pre-combustion chamber to form a combustible mixture that is rich at the top and lean at the bottom. Near the top dead center of the compressor, a portion of liquid ammonia oil jet is first injected into the main combustion chamber through the liquid ammonia injector to form a premixed ammonia mixture in the main combustion chamber. The concentration of the premixed hydrogen mixture in the pre-combustion chamber has reached the ignition requirements. Energy is released through the spark plug to ignite the premixed hydrogen mixture in the pre-combustion chamber. The premixed hydrogen mixture burns rapidly in layers from top to bottom. The resulting high-temperature and high-pressure combustion flame will be rapidly injected through the pre-combustion chamber and spread into the main combustion chamber, forming a strong turbulent flame in the main combustion chamber and igniting the premixed ammonia mixture in the main combustion chamber, thus forming ammonia premixed combustion in the main combustion chamber. Then, the remaining liquid ammonia oil jet is injected into the main combustion chamber using a liquid ammonia injector. The liquid ammonia oil jet is ignited by a premixed combustion flame, forming the diffusion combustion of the subsequent liquid ammonia oil jet, thus realizing a combined combustion mode that promotes diffusion combustion through premixed combustion. The first injection of liquid ammonia begins within 30-50°CA before top dead center, and the amount of liquid ammonia injected is 30%-50% of the total fuel mass. The hydrogen injector in the pre-combustion chamber begins within 130-50°CA before top dead center, and the spark plug ignition time in the pre-combustion chamber is within 6-18°CA before top dead center.

2. The combustion method of a liquid ammonia direct injection engine with an active pre-combustion chamber according to claim 1, characterized in that, The liquid ammonia injector is located on the right side of the main combustion chamber. The diameter of the left nozzle of the liquid ammonia injector is larger than that of the right nozzle, the spray penetration distance on the left side is greater than that on the right side, and the angle between the left nozzle and the cylinder center axis is greater than that between the right nozzle and the cylinder center axis.

3. The combustion method of a liquid ammonia direct injection engine with an active pre-combustion chamber according to claim 1, characterized in that, The angle between the central axis of the liquid ammonia injector and the central axis of the cylinder liner is in the range of 10°-20°, and the distance between the nozzle head of the liquid ammonia injector and the central axis of the pre-combustion chamber is 20mm.

4. The combustion method of a liquid ammonia direct injection engine with an active pre-combustion chamber according to claim 1, characterized in that, The liquid ammonia injector is used to supply liquid ammonia with a pressure range of 40-60 MPa into the main combustion chamber, and the hydrogen injector is used to supply hydrogen with a pressure range of 0.8-2.0 MPa.

5. The combustion method of a liquid ammonia direct injection engine with an active pre-combustion chamber according to claim 1, characterized in that, The pre-combustion chamber has a structure that is wider at the top and narrower at the bottom. From top to bottom, the pre-combustion chamber also includes a cylindrical top, a trapezoidal transition area, and a cylindrical throat.

6. The combustion method of a liquid ammonia direct injection engine with an active pre-combustion chamber according to claim 1, characterized in that, A piston is installed inside the cylinder liner. The cylinder liner, cylinder head, and piston form an ω-shaped main combustion chamber. The nozzle of the pre-combustion chamber is located inside the main combustion chamber.

7. The combustion method of a liquid ammonia direct injection engine with an active pre-combustion chamber according to claim 1, characterized in that, The angle between the liquid ammonia injector nozzle and the cylinder liner center axis ranges from 40° to 76°.

8. The combustion method of a liquid ammonia direct injection engine with an active pre-combustion chamber according to claim 1, characterized in that, The nozzle diameter of the pre-combustion chamber is determined according to the volume of the pre-combustion chamber, and the nozzle diameter range is 1.0-3.0 mm.

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