Liquid ammonia in-cylinder direct injection engine combustion system with active pre-combustion chamber and method

Abstract

The invention provides a liquid ammonia in-cylinder direct injection engine combustion system and method with an active pre-combustion chamber, and relates to the technical field of internal combustion engines, the liquid ammonia in-cylinder direct injection engine combustion system comprises a cylinder cover and a cylinder sleeve arranged below the cylinder cover, the pre-combustion chamber is vertically arranged in the center of the cylinder cover, a liquid ammonia injector is arranged on one side of the pre-combustion chamber, and the active pre-combustion chamber is arranged in the cylinder sleeve. A hydrogen ejector and a spark plug are arranged on the pre-combustion chamber; and spraying holes are formed in the pre-combustion chamber and located in the bottom of the pre-combustion chamber, and the spraying holes of the pre-combustion chamber face one side of the liquid ammonia ejector. According to the liquid ammonia in-cylinder direct injection engine combustion system and method with the active pre-combustion chamber, the effect that diffusion combustion is promoted through premixed combustion of ammonia fuel is achieved, accurate control over the combustion initial point and the heat release rate is achieved, and the requirements for the low hydrogen energy ratio, high ignition efficiency and high heat efficiency of an ammonia fuel engine in the full working condition range are met.

Description

Technical Field

[0001] The present 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 Art

[0002] Traditional resources such as oil are gradually becoming depleted, while the environmental impacts of traditional fuel combustion are increasingly receiving global attention. The search for new alternative energy sources is imperative. Hydrogen, as a zero-carbon fuel, is considered an ideal clean energy source. However, the storage and transportation conditions and costs of hydrogen are currently high, and it is prone to explosion, requires high safety storage requirements, and is difficult to liquefy. These issues hinder its large-scale application at this stage. Ammonia is a promising hydrogen-carrying fuel, with a high hydrogen mass fraction of 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 widespread adoption in the fuel sector. Pre-combustion chamber ignition and the addition of a hydrogen combustion aid are effective solutions to address ammonia's ignition difficulties and increase the flame propagation speed. Active pre-combustion chamber jet ignition can achieve stable ammonia ignition. The concept of ammonia-hydrogen fusion fuel involves using ammonia as an onboard fuel. A portion of the ammonia is catalytically converted into hydrogen, which is then used to ignite the ammonia for combustion, achieving efficient, near-zero-emission combustion.

[0003] Currently, pre-chamber jet ignition for ammonia combustion primarily involves injecting ammonia into the intake duct, but this presents challenges such as low charging efficiency, low thermal efficiency, and high unburned ammonia emissions. Some existing inventions employ pre-chamber jet ignition to ignite premixed ammonia mixtures or injected ammonia fuel, achieving premixed or diffusion combustion. However, these ignition methods suffer from excessive engine pressure rise or high hydrogen energy requirements. Summary of the Invention

[0004] The present invention aims to provide a combustion system and method for a liquid ammonia direct injection engine with an active precombustion chamber. By designing and adjusting parameters such as liquid ammonia injection timing, hydrogen ratio, injection pattern, spark plug ignition timing, and precombustion chamber nozzle holes and liquid ammonia injector nozzle holes, a reasonable concentration of mixed gas and high energy jet flame can be formed in the precombustion chamber under different operating conditions, effectively igniting a portion of the premixed ammonia fuel in the main combustion chamber, forming a premixed combustion flame in the main combustion chamber, and then injecting the remaining liquid ammonia fuel into the premixed combustion flame in the main combustion chamber. The premixed combustion flame ignites the liquid ammonia fuel stream, forming a combination of liquid ammonia fuel premixed combustion and diffusion combustion, realizing a combined combustion mode of premixed combustion promoting diffusion combustion, thereby achieving enhanced ignition of liquid ammonia fuel with a low hydrogen energy ratio. A combustion method for a liquid ammonia direct injection engine with an active precombustion chamber is also proposed. On this basis, a precombustion chamber nozzle hole arrangement and liquid ammonia injector nozzle hole arrangement adapted to the precombustion chamber installation position are proposed to achieve low hydrogen energy demand, 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 starting point and heat release rate can be achieved, meeting the high ammonia replacement rate and high thermal efficiency of the ammonia fuel engine over the entire operating range.

[0005] To achieve the above object, 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 pressed out of the pre-combustion chamber;

[0007] During the compression stroke, fresh air is pressed into the pre-combustion chamber because the pre-combustion chamber pressure is lower than the main combustion chamber pressure;

[0008] At the end of the compression stroke, hydrogen is injected into the pre-combustion chamber through the hydrogen injector at the top of the pre-combustion chamber according to the amount of air in the pre-combustion chamber. The hydrogen mixes with the fresh air 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 compression, a portion of the liquid ammonia oil beam 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 precombustion chamber has reached the ignition requirement. The spark plug releases energy to ignite the premixed hydrogen mixture in the precombustion chamber. The premixed hydrogen mixture burns rapidly in layers from top to bottom. The high-temperature and high-pressure combustion flame generated will quickly propagate through the precombustion chamber 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, forming ammonia premixed combustion in the main combustion chamber.

[0011] Then, the remaining liquid ammonia oil beam is injected into the main combustion chamber using a liquid ammonia injector, and the liquid ammonia oil beam is ignited by a premixed combustion flame to form subsequent diffusion combustion of the liquid ammonia oil beam, realizing a combined combustion mode of premixed combustion promoting diffusion combustion.

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

[0013] Preferably, the aperture of the left spray hole of the liquid ammonia injector is larger than that of the right spray hole, the left spray penetration distance is larger than that of the right spray penetration distance, and the angle between the left spray hole and the central axis of the cylinder is larger than the angle between the right spray hole and the central axis of the cylinder.

[0014] Preferably, the angle formed by 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 20 mm.

[0015] Preferably, the liquid ammonia injector is used to provide liquid ammonia with a pressure range of 40-60 MPa into the main combustion chamber, and the hydrogen injector is used to provide 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 comprises 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, and a hydrogen injector and a spark plug are disposed on the pre-combustion chamber.

[0017] The pre-combustion chamber is provided with spray holes, which are all located at the bottom of the pre-combustion chamber. The spray holes of the pre-combustion chamber face one 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 interior of the pre-combustion chamber is a structure that is wide at the top and narrow at the bottom, and the pre-combustion chamber further includes a cylindrical top, a terraced transition zone, and a cylindrical throat from top to bottom.

[0019] Preferably, a piston is provided in the cylinder liner, and the cylinder liner, cylinder head and piston constitute an ω-shaped main combustion chamber, and the spray hole of the pre-combustion chamber is located in 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 diameter of the nozzle hole of the pre-combustion chamber is determined according to the volume of the pre-combustion chamber, and the diameter range of the nozzle hole of the pre-combustion chamber is 1.0-3.0 mm.

[0022] Therefore, the present invention adopts 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 the liquid ammonia direct injection engine with an active pre-combustion chamber only requires the installation of a set of pre-combustion chambers and side-mounted fuel injectors on the cylinder head. It has no impact on the original valve structures of the engine, and the engine structure does not require major changes. The use cost and production cost are both low.

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

[0025] By matching the liquid ammonia injector's spray hole diameter, angle and injection strategy with the main combustion chamber shape and liquid ammonia injector position, the spray hole diameter of the liquid ammonia injector on the side facing the pre-combustion chamber and the liquid ammonia oil beam penetration distance are increased, ensuring that the liquid ammonia oil beam can cover the side of the main combustion chamber away from the liquid ammonia injector, ensuring that the air at various positions in the main combustion chamber is fully utilized, thereby ensuring uniform flame distribution in the main combustion chamber, reducing excessive temperatures in some areas, and reducing the problem of high wall heat transfer losses.

[0026] The combustion organization method for a liquid ammonia direct-injection engine with an active precombustion chamber combines premixed and diffusion combustion of the liquid ammonia fuel. This effectively addresses the difficulty in igniting the liquid ammonia fuel beam when the hydrogen energy content is low, increases its combustion rate, and achieves the effect of premixed combustion promoting diffusion combustion. It also effectively reduces the excessive rate of rise in engine cylinder pressure caused by premixed combustion and lowers the demand for engine material strength. This combustion method effectively improves the combustion stability and efficiency of liquid ammonia engines with low hydrogen energy requirements. The combustion efficiency reaches over 99% when the hydrogen energy content is as low as 5%, and the maximum indicated thermal efficiency reaches 50% at a compression ratio of 16. BRIEF DESCRIPTION OF THE DRAWINGS

[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 is a schematic diagram of the pre-combustion chamber;

[0029] Figure 3 This is a schematic diagram of the nozzle arrangement of the pre-combustion chamber;

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

[0031] Figure 5 This is a schematic diagram of the liquid ammonia efficient combustion process; Figure 5 (a) Schematic diagram of the hydrogen injector needle valve being pulled up, and hydrogen mixing with fresh air compressed into the pre-combustion chamber to form a combustible mixture; Figure 5 (b) is a schematic diagram showing the liquid ammonia injector being opened to inject liquid ammonia into the main combustion chamber, where the liquid ammonia mixes 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 pre-mixed ammonia mixture, forming pre-mixed combustion; Figure 5 (d) is a schematic diagram of the liquid ammonia injector being opened again to inject the remaining liquid ammonia into the main combustion chamber. The premixed combustion flame ignites the liquid ammonia oil beam to form diffusion combustion.

[0032] Reference numerals

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

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

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

[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 an intake duct 4 and an exhaust duct 6 on either side of the cylinder head 3. The intake duct 4 and the exhaust duct are connected to an ω-shaped main combustion chamber 12. The intake duct 4 and the exhaust duct 6 are provided with an intake valve 5 and an exhaust valve 7. A piston 1 is disposed below the cylinder head 3 and is located within the cylinder liner 2. The cylinder liner 2, cylinder head 3, and piston 1 form an ω-shaped main combustion chamber 12, which has a symmetrical design.

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

[0039] The liquid ammonia injector 8 is installed at an angle within the cylinder head 3. The angle formed 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 formed 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 ranges from 400 bar to 600 bar. The nozzle of the liquid ammonia injector 8 adopts a 10-hole structure. The spray holes 94 of the precombustion chamber 9 are located within the main combustion chamber 12. The nozzles of the liquid ammonia injector 8 are arranged asymmetrically. 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. There is a distance of 20 mm between the nozzle head of the liquid ammonia injector 8 and the central axis of the precombustion chamber 9. The left nozzle of the liquid ammonia injector 8 has a larger diameter than the right nozzle, and the spray penetration distance on the left is greater than that on the right. Ensure that the liquid ammonia oil beam 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 wall heat transfer loss.

[0040] Liquid ammonia injector nozzle specific parameters such as Figure 4 As shown, the angle α1 between the nozzle holes (1) and (2) and the cylinder center axis is 74.5°, and the nozzle hole diameter D1 is 0.32 mm; the angle α2 between the nozzle holes (3) and (4) and the cylinder center axis is 74.5°, and the nozzle hole diameter D2 is 0.28 mm; the angle α3 between the nozzle holes (5) (6) (7) (8) (9) and (10) and the cylinder center axis is 67.5°, and the nozzle hole diameter D3 is 0.20 mm.

[0041] The interior of the pre-combustion chamber 9 is a structure that is wide at the top and narrow at the bottom. From top to bottom, it is divided into a cylindrical top 91, a stepped transition zone 92, a cylindrical throat 93, and a spray hole 94 at the bottom end of the throat 93. The central axis of the pre-combustion chamber 9 coincides with the central axis of the cylinder liner 2.

[0042] The pre-combustion chamber 9 is provided with a plurality of spray holes 94, all of which are located at the bottom of the pre-combustion chamber 9 and in the main combustion chamber 12. According to the spatial distribution characteristics of the liquid ammonia oil beam in the main combustion chamber 12, in this embodiment, four spray holes 94 are provided, and the diameter of the spray holes 94 is 1.8 mm. The spray holes 94 of the pre-combustion chamber 9 are arranged on the side facing the liquid ammonia injector 8, and the circumferential and axial angles of the spray holes 94 of the pre-combustion chamber 9 are adjusted. The angle between the spray holes 94 of the pre-combustion chamber 9 and the central axis of the pre-combustion chamber 9 ranges from 70° to 82°. In this embodiment, the angle is 74°, so as to enhance the degree of overlap between the spatial paths of the flame in the pre-combustion chamber 9 and the ammonia fuel, thereby achieving an effective ignition ratio of ≥99% of the premixed ammonia mixture and the subsequent liquid ammonia oil beam under the condition that the hydrogen energy proportion is ≤5%.

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

[0044] During the intake stroke, the piston 1 moves downward, the pressure in the cylinder decreases, the pressure in the main combustion chamber 12 is lower than the pressure in 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, the piston 1 moves upward, and the fresh air in the main combustion chamber 12 is pressed into the precombustion chamber 9 through the spray hole 94 of the precombustion chamber 9, and the pressure in the precombustion chamber 9 gradually increases. The injection pressure of the hydrogen injector 10 is 1.0 MPa. After the needle valve of the hydrogen injector 10 is pulled up, hydrogen can be sprayed into the precombustion chamber 9 when the injection pressure is greater than the pressure of the precombustion chamber 9. The injection duration is 82-51°CA before the top dead center, and the total energy of the hydrogen injected into the precombustion chamber 9 accounts for 5%. The fresh air will continuously form a tumble flow in the spray hole 94 of the precombustion chamber 9 and flow to the top 91 of the precombustion chamber 9, and continuously mix with the hydrogen entering the precombustion chamber 9 during the compression stroke. Since the upper half of the precombustion chamber 9 is wider, the tumble flow will gradually weaken during the upward movement, so the hydrogen in the precombustion chamber 9 will present a non-homogeneous distribution state with a thick top and a thin bottom. By adjusting the hydrogen injection pressure and injection time, a mixture distribution state that is conducive to combustion can be formed in the precombustion chamber 9.

[0046] Near the compression top dead center, the liquid ammonia injector 8 in the main combustion chamber 12 starts working, and the injection pressure of the liquid ammonia injector 8 is 50MPa. Since the ω-shaped main combustion chamber 12 is symmetrically designed, and the liquid ammonia injector 8 is arranged on the right side of the main combustion chamber 12. In order to ensure that the air on the left side of the main combustion chamber 12 is fully utilized, it is necessary to match the nozzle layout of the liquid ammonia injector 8. The nozzle diameter and liquid ammonia oil beam penetration distance of the left nozzle of the liquid ammonia injector 8 are increased, and the jet shape is as follows: Figure 4 As shown, the ammonia mixture can cover the left side of the main combustion chamber 12, thereby ensuring that the flame in the main combustion chamber 12 is evenly distributed and the temperature of some areas of the wall is too high.

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

[0048] The first injection of liquid ammonia injector 8 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 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 appropriate concentration has formed in the main combustion chamber 12 before the flame propagates in the pre-combustion chamber 9. The jet flame generated by the combustion of hydrogen in the pre-combustion chamber 9 ignites the ammonia mixture mixed with air in the main combustion chamber 12, forming a strong premixed combustion in the main combustion chamber 12. The remaining liquid ammonia oil stream is then injected into the premixed combustion flame using the high-pressure liquid ammonia injector 8, forming diffusion combustion. This achieves a combination of premixed combustion and diffusion combustion of the liquid ammonia fuel, and uses premixed combustion to promote diffusion combustion, thereby significantly reducing hydrogen usage. 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 to the left area. This mixed combustion mode of liquid ammonia premixed combustion combined with diffusion combustion effectively reduces the problem of excessive engine cylinder pressure rise rate caused by premixed combustion, reduces the higher hydrogen energy required for direct ignition of the liquid ammonia oil beam, improves the ignition stability of the liquid ammonia oil beam, and achieves 99% combustion efficiency and 50% indicated thermal efficiency of the liquid ammonia engine.

[0049] Therefore, the present invention adopts the above-mentioned liquid ammonia direct injection engine combustion system and method 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 is ensured that a mixture with a reasonable concentration and a jet flame with high energy can be formed in the pre-combustion chamber under different working conditions, effectively igniting part of the ammonia fuel premixed in the main combustion chamber to form ammonia premixed combustion, and using the premixed combustion flame to ignite the subsequent liquid ammonia oil beam to form subsequent liquid ammonia diffusion combustion. A combustion organization method for a liquid ammonia direct injection engine with an active pre-combustion chamber is provided to achieve premixed combustion to promote diffusion combustion and enhance ignition energy under low hydrogen energy ratio. Accurate control of the combustion starting point and heat release rate is achieved to meet the low hydrogen energy ratio, high ammonia combustion stability and high thermal efficiency of the ammonia fuel engine in the full working range.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements 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, characterized in that: The following steps are involved: 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 pressed out of the pre-combustion chamber; During the compression stroke, fresh air is pressed into the pre-combustion chamber because the pre-combustion chamber pressure is lower than the main combustion chamber pressure; At the end of the compression stroke, hydrogen is injected into the pre-combustion chamber through the hydrogen injector at the top of the pre-combustion chamber according to the amount of air in the pre-combustion chamber. The hydrogen mixes with the fresh air 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 compression, a portion of the liquid ammonia oil beam 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 precombustion chamber has reached the ignition requirement. The spark plug releases energy to ignite the premixed hydrogen mixture in the precombustion chamber. The premixed hydrogen mixture burns rapidly in layers from top to bottom. The high-temperature and high-pressure combustion flame generated will quickly propagate through the precombustion chamber 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, forming ammonia premixed combustion in the main combustion chamber. Then, the remaining liquid ammonia oil beam is injected into the main combustion chamber using a liquid ammonia injector, and the liquid ammonia oil beam is ignited by a premixed combustion flame to form subsequent diffusion combustion of the liquid ammonia oil beam, realizing a combined combustion mode of premixed combustion promoting diffusion combustion.

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

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 aperture of the left spray hole of the liquid ammonia injector is larger than that of the right spray hole, the left spray penetration distance is larger than that of the right spray penetration distance, and the angle between the left spray hole and the central axis of the cylinder is larger than the angle between the right spray hole and the central axis of the cylinder.

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 angle formed by 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 20 mm.

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 liquid ammonia injector is used to provide liquid ammonia with a pressure range of 40-60MPa into the main combustion chamber, and the hydrogen injector is used to provide hydrogen with a pressure range of 0.8-2.0MPa.

6. A liquid ammonia direct injection engine combustion system with an active pre-combustion chamber, characterized in that: The ignition system comprises a cylinder head and a cylinder liner arranged below the cylinder head, wherein 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, and a hydrogen injector and a spark plug are arranged on the pre-combustion chamber; The pre-combustion chamber is provided with spray holes, which are all located at the bottom of the pre-combustion chamber. The spray holes of the pre-combustion chamber face one 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°.

7. The liquid ammonia direct injection engine combustion system with an active pre-combustion chamber according to claim 6, characterized in that: The interior of the pre-combustion chamber is a structure that is wide at the top and narrow at the bottom. The pre-combustion chamber further comprises a cylindrical top, a terraced transition zone, and a cylindrical throat from top to bottom.

8. The liquid ammonia direct injection engine combustion system with an active pre-combustion chamber according to claim 6, characterized in that: A piston is arranged in the cylinder liner, and the cylinder liner, cylinder head and piston form an ω-shaped main combustion chamber. The spray hole of the pre-combustion chamber is located in the main combustion chamber.

9. The liquid ammonia direct injection engine combustion system with an active pre-combustion chamber according to claim 6, characterized in that: The angle between the liquid ammonia injector nozzle and the central axis of the cylinder liner is in the range of 40°-76°.

10. The liquid ammonia direct injection engine combustion system with an active pre-combustion chamber according to claim 6, characterized in that: The diameter of the spray hole of the pre-combustion chamber is determined according to the volume of the pre-combustion chamber, and the diameter range of the spray hole of the pre-combustion chamber is 1.0-3.0 mm.

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