An ultra-lean combustion system, zoned combustion control method and vehicle suitable for hydrogen fuel engines

Abstract

The present invention proposes an ultra-lean combustion system, a zoned combustion control method, and a vehicle suitable for a hydrogen fuel engine. Through a stratified lean combustion mode, a relatively rich mixture is formed near the spark plug, supplemented by a homogeneous mixture at the periphery to achieve high thermal efficiency and low nitrogen and oxygen emissions. The system includes: an intake duct, an exhaust duct, a piston, an intake valve, an exhaust valve, a spark plug, a high-pressure hydrogen nozzle, and a hydrogen injection shroud. The high-pressure hydrogen nozzle is arranged on the cylinder head between the two intake valves. The axis of the high-pressure hydrogen nozzle is located in the same plane as the cylinder centerline and forms an angle with the cylinder axis. The hydrogen injection shroud surrounds the hydrogen injection hole at the head of the high-pressure hydrogen nozzle and has a guide hole. The guide hole of the hydrogen injection shroud is located deep into the engine combustion chamber mounting surface, and the hydrogen injection shroud guides the hydrogen toward the spark plug ignition position.

Description

Technical Field

[0001] The present invention relates to the structural design and optimization of an automobile engine system, and in particular to an ultra-lean combustion system of a hydrogen fuel engine, a zoned combustion control method, and a vehicle. Background Art

[0002] As a zero-carbon fuel, hydrogen is an important component of the fuel structure to achieve net-zero emissions in the future. Currently, hydrogen fuel is mainly used in two ways: hydrogen fuel cells and hydrogen fuel engines. Among them, hydrogen fuel cells have a higher overall efficiency than hydrogen fuel engines, but they have higher requirements for hydrogen fuel purity. The efficient working area is in the low-load operating range, and the power output is lower than that of hydrogen fuel engines. The efficient working range of hydrogen fuel engines is in medium and high load conditions and can utilize crude hydrogen. Therefore, relying on the current mature engine manufacturing processes and technologies, hydrogen fuel engines can be used as the first choice during the transition period of hydrogen energy utilization.

[0003] From the perspective of physical and chemical properties, hydrogen has good diffusivity, low ignition energy, high auto-ignition temperature, wide ignition limit and fast combustion speed. In a spark-ignition engine, the heat release rate of hydrogen combustion is high and more concentrated, resulting in higher in-cylinder explosion pressure. It is often necessary to control the flame speed through lean combustion to improve the in-cylinder explosion pressure; in a compression-ignition engine, the mixture needs to be heated to meet the hydrogen auto-ignition temperature conditions. Currently, most hydrogen engines are spark-ignition-based. In order to improve the charging efficiency and avoid backfire and pre-ignition, the hydrogen injection method has developed from port injection to direct injection into the cylinder. Since hydrogen has a higher combustion temperature than gasoline and a shorter flame quenching distance, more heat transfer losses are generated in the medium and high speed regions, so the high thermal efficiency point shifts to low speed and high load; at the same time, the N2 oxidation time is sufficient under low speed conditions, so that the high thermal efficiency region corresponds to the high NOx region. Therefore, the current difficulty in the development of hydrogen fuel engines lies in expanding the overlapping range of the high efficiency region and the low NOx region, while achieving high thermal efficiency and low NOx emissions, such as Figure 1As shown. In this regard, the industry mostly adopts ultra-lean combustion mode, by increasing the excess air coefficient to avoid the high NOx area; at the same time, taking advantage of the wide ignition limit of hydrogen, it matches the high-pressure ratio supercharger to achieve higher thermal efficiency. This technical route faces some problems: 1. When the excess air coefficient of the hydrogen mixture is higher than 1.8, its premixed flame speed also decreases rapidly, thereby affecting the ignition stability; 2. The hydrogen density is low, and the combustion is concentrated at the bottom of the cylinder head, resulting in a large amount of heat transfer loss; 3. The exhaust energy generated by lean combustion is low, which often cannot meet the large intake volume requirements of hydrogen engines. In order to achieve stable combustion of the lean hydrogen mixture and meet the demand for high intake volume, the industry mostly adopts high compression ratio or pre-combustion chamber ignition solutions. Patent CN114183262A proposes a jet ignition direct injection solution based on the modification of a diesel engine with a pre-combustion chamber. The stable combustion of hydrogen is achieved through the pre-combustion chamber, but the pre-combustion chamber design is relatively complex and faces the problem of hydrogen embrittlement. Patent CN114109627A proposes a spark-assisted ignition + diffusion combustion (SI-CI) combustion control method for hydrogen direct injection combustion in a high-compression ratio diesel engine, but fails to optimize the combustion system structure. Patent CN114017178A proposes a two-stage hydrogen injection and ignition process to increase exhaust gas enthalpy and improve turbine performance. However, injecting hydrogen during the power stroke results in a certain amount of waste in hydrogen combustion energy. Summary of the Invention

[0004] In order to solve the above problems, the present invention proposes an ultra-lean combustion system, a zoned combustion control method and a vehicle suitable for hydrogen fuel engines. Through the stratified lean combustion mode, a relatively rich mixture is organized near the spark plug, and a homogeneous mixture is supplemented on the periphery to achieve high thermal efficiency and low nitrogen and oxygen emissions.

[0005] The present invention provides an ultra-lean combustion system suitable for a hydrogen fuel engine, comprising:

[0006] Intake duct, exhaust duct, piston, intake valve, exhaust valve, spark plug, high-pressure hydrogen injection nozzle, and hydrogen injection guide cover;

[0007] The high-pressure hydrogen nozzle is arranged on the cylinder head between the two intake valves;

[0008] The axis of the high-pressure hydrogen nozzle is located in the same plane as the center line of the cylinder and forms an angle with the cylinder axis;

[0009] The hydrogen injection guide cover wraps the hydrogen injection hole of the high-pressure hydrogen injection nozzle head. The hydrogen injection guide cover has a guide hole. The guide hole of the hydrogen injection guide cover is located deep into the installation surface of the engine combustion chamber. The guide direction of the hydrogen injection guide cover is the ignition position of the spark plug.

[0010] Preferably, the top surface of the piston is an exhaust side recess, and the exhaust side recess is composed of two connected cylindrical surfaces, and the center position of the intersection arc of the two cylindrical surfaces is the deepest part of the exhaust side recess.

[0011] Preferably, the lower surface of the cylinder head, the bottom surface of the intake valve and the bottom surface of the exhaust valve are respectively coated with a thermal barrier coating made of a high-temperature resistant heat-insulating material.

[0012] Preferably, the jet pressure of the high-pressure hydrogen nozzle is ≥4 MPa, and the hydrogen beam flow rate is 1.5-8 g / s;

[0013] The diameter of the guide hole is 11.5 times that of the hydrogen injection hole. The depth of the hydrogen injection hole into the engine combustion chamber mounting surface is 0-5mm. The angle formed by the axial direction of the high-pressure hydrogen injection nozzle and the cylinder axis is 65°-70°.

[0014] Preferably, the horizontal distance between the center position of the exhaust side recess and the center position of the exhaust valve is between 8-10 mm;

[0015] The depth of the exhaust side pit is 4%-6% of the cylinder diameter;

[0016] The chord length of the intersection arc of the two cylindrical surfaces is 2-3 times the edge chord length of the hyperbolic cylindrical surfaces.

[0017] Preferably, the thermal barrier coating includes a ceramic surface layer and an adhesive layer. The adhesive layer is used between the metal surface and the ceramic surface layer. The ceramic surface layer is made of yttria-stabilized zirconia ceramic, and the adhesive layer is made of nickel-chromium-aluminum alloy NiCrAl. The thickness ratio of the ceramic surface layer and the adhesive layer is 3:1, and the porosity of the thermal barrier coating is 5%-30%.

[0018] Preferably, the air intake duct is a tangential air intake duct, and the angle between the air intake duct and the horizontal plane of the cylinder head is between 20° and 26°;

[0019] The exhaust duct includes a first straight pipe section, a curved pipe section and a second straight pipe section connected in sequence from the exhaust valve seat position. The outer edge curvature radius R1 of the curved pipe section is 1.2-1.25 times the diameter D2 of the exhaust valve, and the maximum pipe diameter D3 of the second straight pipe section is 11.2 times the diameter D2 of the exhaust valve.

[0020] Preferably, the excess air coefficient of the hydrogen mixture is between 1.8 and 3.0 in the entire operating range, wherein the excess air coefficient in the external characteristic range is 1.8, the excess air coefficient at the highest thermal efficiency point is 2.3, and the excess air coefficient in other operating ranges is between 1.8 and 3.0.

[0021] The present invention further provides a zoned combustion control method for a hydrogen fuel engine, which is applied to the above-mentioned ultra-lean combustion system for a hydrogen fuel engine. The method comprises:

[0022] When the hydrogen fuel engine operates in a preset low-load operating range, the excess air coefficient of the hydrogen fuel engine is controlled to be 1.8, and the high-pressure hydrogen nozzle 8 is controlled to perform closed-valve injection after the intake valve is closed and before the piston reaches top dead center. The hydrogen gas beam is guided through the guide holes of the hydrogen injection guide cover to form a mixture with a concentration exceeding a preset concentration at the ignition position of the spark plug; the high-pressure hydrogen nozzle 8 is controlled to inject hydrogen at 50°-70°CA BTDC, and the spark plug is controlled to ignite 1°-5°CA before the piston reaches top dead center;

[0023] When the hydrogen fuel engine operates within a preset rated operating range, the high-pressure hydrogen nozzle is controlled to spray hydrogen at 70°-100° CA BTDC, and the hydrogen mixture is guided to the spark plug ignition position through the guide hole 92 of the hydrogen injection guide cover to form a stratified mixture. The spark plug is controlled to ignite 5°-10° CA before the piston reaches the top dead center.

[0024] When the hydrogen fuel engine operates in a preset high-load operating range, after the intake valve is closed, the high-pressure hydrogen nozzle is controlled to spray hydrogen at an injection ratio of 30%-50% to produce a homogeneous mixture with an excess air coefficient of 3.6-6; at 70°-100°CA BTDC, the high-pressure hydrogen nozzle is controlled again to spray hydrogen, and the hydrogen is guided through the guide holes of the hydrogen injection guide cover to form a stratified mixture at the ignition position of the spark plug, and the spark plug is controlled to ignite 5°-10°CA before the piston reaches the top dead center.

[0025] The present invention also provides a vehicle comprising the ultra-lean combustion system suitable for a hydrogen fuel engine.

[0026] The present invention provides the following beneficial effects: a dedicated combustion system designed for a zero-carbon emission hydrogen fuel hybrid system. This hydrogen fuel engine combustion system is designed for ultra-lean hydrogen mixture combustion (1.8 < λ < 3). A hydrogen injector and deflector are used to organize the hydrogen beam and form a stratified mixture, addressing ignition stability issues. A thermal barrier coating on the cylinder head bottom, combined with the low density of hydrogen, which tends to concentrate at the top of the combustion chamber, provides thermal insulation for the hydrogen mixture combustion, reducing heat transfer losses and increasing thermal efficiency. By combining a single-stage electric turbocharger or a two-stage electric supercharger and turbocharger, the system meets the high intake flow requirements of the lean combustion mode of hydrogen fuel engines. The exhaust-side dimple design enhances tumble mixing and assists in deflecting the hydrogen beam toward the spark plug. Optimizing intake and exhaust gases improves flow resistance, increases exhaust gas enthalpy, and assists the electric turbine in generating electricity, achieving maximum energy utilization. Furthermore, the use of closed-valve injection and injection late in the compression stroke (70-90° CA BTDC) effectively prevents backfire and pre-ignition, reducing in-cylinder explosion pressure. Furthermore, the present invention proposes a hydrogen ultra-lean combustion control method for a hydrogen-electric hybrid system, which achieves high-efficiency and low-emission combustion under the premise of meeting the dynamic performance under different load conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Shown is a schematic diagram of the optimization target of the present invention;

[0028] Figure 2 Shown is a schematic diagram of the powertrain structure matched with the combustion system of the present invention;

[0029] Figure 3 Shown is a schematic diagram of the combustion system of the present invention A - intake and exhaust ducts, thermal barrier coating (corresponding to Figure 6 Section AA);

[0030] Figure 4 Shown is a schematic diagram of the combustion system of the present invention B - hydrogen injection, piston top surface (corresponding to Figure 6 Section BB);

[0031] Figure 5 Shown is a schematic diagram of the top surface shape of the piston of the present invention;

[0032] Figure 6 Shown is a schematic diagram of the thermal barrier coating of the present invention;

[0033] Figure 7 Shown is a schematic diagram of the hydrogen deflector of the present invention;

[0034] Figure 8 The figure shows a schematic diagram of the zone control of hydrogen ultra-lean combustion according to the present invention;

[0035] Figure 9The figure shows the distribution of velocity, turbulent kinetic energy and equivalence ratio after hydrogen injection at -60° CA ATDC under the rated operating conditions of a certain engine according to the present invention.

[0036] 1. Piston; 11. Piston top surface A curved surface; 12. Piston top surface B curved surface; 2. Exhaust duct; 3. Exhaust valve; 4. Intake valve; 5. Intake duct; 6. Thermal barrier coating; 61. Exhaust valve bottom surface coating; 62. Cylinder head bottom coating; 63. Intake valve bottom coating; 7. Spark plug; 8. High-pressure hydrogen nozzle; 9. Hydrogen injection shroud; 91. Lower end surface of shroud; 92. Diversion hole;

[0037] D1: Hydrogen fuel engine cylinder diameter

[0038] D2: Exhaust duct inlet diameter

[0039] D3: Exhaust duct outlet diameter

[0040] L1: Diameter of the first straight pipe section at the exhaust duct inlet

[0041] L2: Diameter of the second straight pipe section of the exhaust duct

[0042] R1: The outer radius of the exhaust duct bend

[0043] R2: Inner radius of the exhaust duct bend

[0044] S1: Length of outer edge of piston top surface B

[0045] S2: The chord length of the intersection arc between the piston top surface A and the piston top surface B

[0046] S3: Length of outer edge of piston top surface A

[0047] M: The lowest point of the pit on the top of the piston

[0048] W: Horizontal distance between the lowest point of the piston top pit and the center of the exhaust valve

[0049] d1: Hydrogen injection guide hole diameter

[0050] d2: Hydrogen injection shroud diameter. DETAILED DESCRIPTION

[0051] The present invention will be further described below with reference to the accompanying drawings.

[0052] like Figure 3 and Figure 4 As shown, the ultra-lean combustion system of the hydrogen direct injection engine described in the present invention includes a piston 1, an intake duct 5, an exhaust duct 2, an intake valve 4, an exhaust valve 3, a thermal barrier coating 6, a spark plug 7, a high-pressure hydrogen nozzle 8, and a hydrogen injection guide cover 9.

[0053] Furthermore, the engine matched with the hydrogen fuel engine ultra-lean combustion system is a spark-ignition direct injection engine with a compression ratio range of 10-13, and the matched system is an extended-range hydrogen-electric hybrid powertrain system ( Figure 2 ), the hydrogen fuel engine works as a range extender in the high-efficiency and low-emission operating range.

[0054] Furthermore, the hydrogen fuel engine combustion system is equipped with an electric turbocharger for single-stage supercharging or an electric supercharger + turbocharger for two-stage supercharging. The excess air ratio of the hydrogen mixture is 1.8-3.0, producing stratified ultra-lean combustion.

[0055] Furthermore, the injection pressure of the high-pressure hydrogen nozzle 8 is ≥4MPa, and the hydrogen beam flow rate generated is 1.5-8g / s. The high-pressure hydrogen nozzle 8 is arranged on the cylinder head between the two intake valves 4, facing the spark plug 7, and its axis is located in the same plane as the cylinder centerline, and the angle between the axis and the cylinder axis is 65-70°.

[0056] Furthermore, the hydrogen injection guide cover 9 wraps the hydrogen injection hole at the head of the high-pressure hydrogen injection nozzle 8. The diameter d2 of the lower end surface 91 of the guide cover is 4-6 mm. The upper part of the hydrogen injection guide cover 9 is a single guide hole 92. The diversion direction is the ignition position of the spark plug 7. The aperture of the guide hole 92 is 11.5 times the aperture of the hydrogen injection nozzle. The reference range d1 is 1.0-1.8 mm. The hydrogen injection guide cover 9 is located 0-4 mm deep into the installation surface of the combustion chamber.

[0057] Furthermore, the top surface of the piston 1 is an exhaust-side recess. The recess is composed of two cylindrical surfaces: cylindrical curved surface A 11 and cylindrical curved surface B 12. The deepest point of the recess is at the center M of the arc where curved surfaces A 11 and B 12 intersect. The horizontal distance W between the center M and the center of the exhaust valve 3 is 8-10 mm, and the recess depth H is 4%-6% of the cylinder diameter D1. The chord length S2 corresponding to the intersection of curved surfaces A and B is 2-3 times that of the curved surface edges S1 and S3, where S1 = S3.

[0058] Furthermore, the thermal barrier coating 6 includes a cylinder head lower surface coating 62, an intake valve bottom surface coating 63 and an exhaust valve bottom surface coating 61, which respectively cover the lower surface of the cylinder head and the lower surfaces of the intake valve 4 and the exhaust valve 3, and are used for surface thermal insulation. The coating ceramic surface layer adopts high-temperature resistant thermal insulation material, and the coating bonding layer adopts alloy. The total coating thickness is 100-300μm, and is achieved by high-temperature flame spraying or plasma spraying. The thickness ratio of the ceramic surface layer and the bonding layer is 3:1, and the coating porosity is 5%-30%.

[0059] Furthermore, the air intake duct 5 is a tangential air intake duct, and the angle between the air intake duct 5 and the horizontal plane of the cylinder head is 20-26 degrees.

[0060] Furthermore, the exhaust duct 2 comprises a first straight section, a curved section, and a second straight section, starting from the exhaust valve seat. The first straight section has a length L1 of 8-10 mm. The outer radius of curvature R1 of the curved section is 1.2-1.5 times the diameter D2 of the exhaust valve 3, while the inner radius of curvature R2 is 4-5 mm. The second straight section has a length L2 of 30-40 mm and a maximum diameter D3 of 11.2 times the diameter D2 of the exhaust valve 3.

[0061] Furthermore, the present invention proposes a partitioned combustion control method for a hydrogen fuel engine to achieve ultra-lean combustion, such as Figure 8 As a range extender in a hydrogen-electric hybrid system, the engine's typical operating range is smaller than that of a traditional engine. Its high-efficiency range primarily covers medium-to-low speeds and medium-to-high loads. However, the operating strategy of a hydrogen fuel engine at high speeds and high loads in low-battery mode still needs to be considered.

[0062] When the hydrogen fuel engine operates in the low-load range (0 ≤ speed ≤ 3500, torque ≤ 60Nm), the exhaust gas energy cannot meet the intake boost pressure requirements. At this time, the electronic supercharger or electric turbocharger operates in the electric assist mode. Figure 2 The power battery drives the electronic supercharger or electric turbocharger to achieve a high boost ratio, meet the intake requirements of the hydrogen fuel engine, and achieve an excess air coefficient of 1.8. In terms of combustion control, after the intake valve 4 is closed and before the top dead center, the high-pressure hydrogen nozzle 8 performs closed-valve injection, and the hydrogen gas beam is guided through the hydrogen injection guide hole 92, forming a richer mixture near the spark plug 7 to achieve stratified lean combustion. Due to the low hydrogen injection amount under low load conditions, the hydrogen injection timing can be delayed, and hydrogen can be injected at 50°-70°CA BTDC, and ignited at 1°-5°CA before the top dead center. Using this patented structure and strategy in this operating range can achieve stable combustion. Since the excess air coefficient is controlled to be no less than 1.8, the original NOx emissions of the engine are less than 1500ppm, and the lean burn low-load thermal efficiency can reach more than 39%.

[0063] When the hydrogen engine operates within the rated operating range (rpm ≤ 3500 rpm, torque ≤ 60 Nm ≤ 80 Nm), the engine maintains an excess air ratio between 2.3 and 3. This excess air ratio requires a high boost pressure. If a single-stage electric turbocharger is used, the electric turbocharger operates in both electric-assist and balanced modes depending on the engine's operating conditions. If a two-stage electric supercharger and turbocharger are used, the electric supercharger operates in electric-assist mode depending on the operating conditions to meet intake boost pressure and flow requirements. Hydrogen injection occurs between 70° and 100° CA BTDC, generating a stratified mixture guided by guide holes 92. Spark plug 7 ignition occurs between 5° and 10° CA before top dead center. Implementing this control strategy within this operating range keeps engine raw NOx emissions below 1000 ppm. When the excess air ratio reaches 2.5 or higher at rated operating conditions, raw NOx emissions can be controlled below 200 ppm. Under this operating condition, the thermal efficiency of the hydrogen fuel engine can be improved by more than 41% in the low speed range (around 2000rpm).

[0064] When the engine operates in the high-load range (other regions within the external characteristics), the mixture must be appropriately enriched to meet power requirements, achieving an engine excess air ratio of 1.8. Due to the high hydrogen injection volume and the short injection window in the high-speed range, a closed-valve double injection is employed. The first injection occurs after the intake valve 4 closes, with an injection ratio of 30%-50%, producing a homogeneous mixture with an excess air ratio of 3.6-6. The second injection occurs between 70° and 100° CA BTDC, guiding the flow guide holes 92 to produce a stratified mixture. Spark plug 7 ignites 5°-10° CA before top dead center. Thermal barrier coating 6 on the cylinder head bottom and the bottoms of the intake and exhaust valves 4 and 3 reduces heat transfer losses in the hydrogen mixture, increasing power generation after top dead center. Combined with optimized piston top surfaces and intake and exhaust ports 5 and 2, the mixed flow ratio is enhanced, improving exhaust gas enthalpy, driving electric turbocharger power generation or turbine power generation, and maximizing energy utilization. Implementation of this control strategy in this operating range keeps the excess air coefficient at least 1.8, keeping the engine's raw NOx emissions below 1500 ppm while maintaining a thermal efficiency of at least 40%. By reducing the excess air coefficient to 1.5, the hydrogen fuel cell engine achieves a maximum thermal efficiency of 43% under low-speed, externally characteristic operating conditions. However, maintaining the excess air coefficient above 1.8 to ensure low NOx emissions results in a loss of thermal efficiency.

[0065] Below, the technical solution of the present invention is further described through preferred embodiments.

[0066] The hydrogen combustion system is applied to a 1.5L 4-cylinder direct injection hydrogen engine with a cylinder diameter of 73mm and a stroke of 88mm.

[0067] like Figure 3 and Figure 4 As shown, the ultra-lean combustion system of the hydrogen direct injection engine described in the present invention includes a piston 1, an intake duct 5, an exhaust duct 2, an intake valve 4, an exhaust valve 3, a thermal barrier coating 6, a spark plug 7, a high-pressure hydrogen nozzle 8, and a hydrogen injection guide cover 9.

[0068] Furthermore, the engine matched with the hydrogen fuel engine ultra-lean combustion system is an inline 4-cylinder spark-ignition direct injection engine with a geometric compression ratio of 10.5, and the matched system is an extended-range hydrogen-electric hybrid powertrain system, such as Figure 2 As shown, the hydrogen fuel engine works as a range extender in the high-efficiency and low-emission operating range.

[0069] Furthermore, the hydrogen fuel engine combustion system is matched with an electric turbocharger for single-stage supercharging or an electronic supercharger + turbocharger for two-stage supercharging, and the excess air coefficient of the hydrogen mixture is between 1.8 and 3.0 in the full operating range, of which the excess air coefficient in the external characteristic range is 1.8, the excess air coefficient at the highest thermal efficiency point is 2.3, and the excess air coefficient in other operating ranges is between 1.8 and 3.0.

[0070] Furthermore, the injection pressure of the high-pressure hydrogen nozzle 8 under high-load conditions is 18 MPa, and the hydrogen beam flow rate generated is 7 g / s; the low-load condition is 10 MPa, and the hydrogen beam flow rate generated is 3.9 g / s. The high-pressure hydrogen nozzle 8 is arranged between the intake valves 4, facing the spark plug 7, and its axis is in the same plane as the cylinder centerline, and the angle between them and the cylinder axis is 65°.

[0071] Furthermore, the hydrogen injection guide cover 9 wraps the hydrogen injection hole at the head of the high-pressure hydrogen injection nozzle 8. The diameter d2 of the lower end surface 91 of the guide cover is 6 mm. A single guide hole 92 is designed on the upper part of the hydrogen injection guide cover 9. The diversion direction is the ignition position of the spark plug 7. The aperture d1 of the guide hole 92 is 1.8 mm. The guide hole of the hydrogen injection guide cover 9 is located 2 mm deep into the installation surface of the combustion chamber.

[0072] Furthermore, the top surface of the piston 1 is an exhaust-side recess, formed from two cylindrical surfaces: cylindrical curved surface A 11 and cylindrical curved surface B 12. The deepest point of the recess is located at the center M of the arc where curved surfaces A 11 and B 12 intersect. The horizontal distance W between the center M and the center of the exhaust valve 3 is 8.5 mm, and the recess depth H is 5% of the cylinder diameter D1. The chord length S2 corresponding to the intersection of curved surfaces A and B is 69 mm, which is three times the length of the curved surface edge arcs S1 and S3.

[0073] Furthermore, the thermal barrier coating 6 includes a cylinder head lower surface coating 62, an intake valve bottom surface coating 63 and an exhaust valve bottom surface coating 61, which respectively cover the lower surface of the cylinder head and the lower surfaces of the intake valve 4 and the exhaust valve 3, and are used for surface thermal insulation. The coating ceramic surface layer adopts yttria-stabilized zirconia (8YSG), the coating bonding layer material is NiCrAl, the total coating thickness is 300μm, the ceramic surface layer and the bonding layer thickness ratio is 3:1, and the coating porosity is 10%.

[0074] Furthermore, the air intake duct 5 is a tangential air intake duct, and the angle between the air intake duct 5 and the horizontal plane of the cylinder head is 26°.

[0075] Furthermore, the exhaust duct 2 includes a first straight section, a curved section, and a second straight section, sequentially connected from the exhaust valve seat. The length L1 of the first straight section is 8.1 mm. The outer radius of curvature R1 of the curved section is 1.25 times the diameter D2 of the exhaust valve 3, and the inner radius of curvature R2 is 4.65 mm. The length L2 of the second straight section is 37 mm, and the maximum diameter D3 of the second straight section is 1.17 times the diameter D2 of the exhaust valve 3.

[0076] Furthermore, the present invention proposes a method for controlling ultra-lean combustion zones of a hydrogen fuel engine, such as Figure 8 As a range extender for a hydrogen-electric hybrid system, the engine's operating range is smaller than that of a traditional engine. Its high-efficiency range primarily covers low to medium speeds and medium to high loads. Through zone control, efficient use of hydrogen fuel can be achieved.

[0077] When the hydrogen fuel engine operates in the low-load range (0 ≤ speed ≤ 3500, torque ≤ 60Nm), the exhaust gas energy cannot meet the intake boost pressure requirements. At this time, the electronic supercharger or electric turbocharger operates in the electric assist mode. Figure 2 The power battery drives the supercharger to achieve a high boost ratio, meeting the intake requirements of the hydrogen-fueled engine and achieving an excess air coefficient of 1.8. Regarding combustion control, the high-pressure hydrogen nozzle 8 is controlled to perform closed-valve injection between the closing of the intake valve 4 and the arrival of the piston 1 at top dead center. The hydrogen gas stream is directed through the guide holes 92 of the hydrogen injection shroud 9 to form a richer mixture near the ignition position of the spark plug 7, achieving stratified lean combustion. Due to the low hydrogen injection volume under low-load conditions, the injection timing can be delayed, with the high-pressure hydrogen nozzle 8 controlling hydrogen injection between 50° and 70° CABTDC. Spark plug 7 is controlled to ignite 1° to 5° CA before the piston reaches top dead center, achieving stable combustion while simultaneously achieving high combustion efficiency and low NOx emissions. Under these operating conditions, the preferred embodiment engine can achieve an effective thermal efficiency of ≥39% and raw engine NOx emissions below 1500 ppm.

[0078] When the hydrogen fuel engine operates within the rated operating range (rpm ≤ 3500, torque ≤ 60 Nm ≤ 80 Nm), the engine excess air ratio is maintained between 2.3 and 3. Under these excess air ratios, the engine requires a high boost pressure. If a single-stage electric turbocharger is used, the electric turbocharger operates in electric-assist and balanced modes depending on the engine operating conditions. If a two-stage electric supercharger and turbocharger are used, the electric supercharger operates in electric-assist mode depending on the operating conditions, thereby meeting intake boost pressure and flow requirements. High-pressure hydrogen nozzle 8 injects hydrogen between 70° and 100° CA BTDC, guiding guide holes 92 to produce a stratified mixture. Spark plug 7 ignites 5° to 10° CA before the piston reaches top dead center. Within this operating range, the hydrogen fuel engine achieves high thermal efficiency with low emissions. Under these operating conditions, the preferred embodiment engine's raw NOx emissions are below 1000 ppm, and the engine can achieve an effective thermal efficiency of ≥ 41%. When the excess air coefficient at the rated operating point reaches above 2.5, the original NOx emission can be controlled below 200ppm, and the effective thermal efficiency is about 40%.

[0079] When the engine operates in the high-load range (other regions within the external characteristics), the mixture must be appropriately enriched to meet power requirements, achieving an excess air ratio of 1.8. Due to the high hydrogen injection volume and the short injection window in the high-speed range, a closed-valve double injection method is employed. The first injection occurs after the intake valve 4 closes, with an injection ratio of 30%-50%, producing a homogeneous mixture with an excess air ratio of 3.6-6. The second injection occurs between 70° and 100° CA BTDC, guiding the flow guide holes 92 to produce a stratified mixture. Spark plug 7 ignites 5°-10° CA before top dead center. Thermal barrier coating 6 on the cylinder head bottom and the bottoms of the intake and exhaust valves 4 and 3 reduces heat transfer losses in the hydrogen mixture, thereby increasing power generation after top dead center. Combined with optimized piston top surfaces and intake and exhaust ports 5 and 2, the mixed flow ratio is enhanced, improving exhaust gas enthalpy, driving electric turbocharger power generation or turbine power generation, and achieving maximum energy utilization. Under this operating condition, the preferred embodiment engine controls the excess air coefficient to be no less than 1.8, the original NOx emission of the engine is less than 1500ppm, and the effective thermal efficiency is ≥40%.

[0080] Furthermore, according to the numerical simulation results, the combustion system under rated operating conditions has the following distributions of in-cylinder velocity, turbulent kinetic energy and equivalence ratio after ignition: Figure 9 As shown in the figure, the hydrogen beam can form concentration stratification under the guidance of clockwise airflow, producing a rich hydrogen mixture near the spark plug and generating high turbulent kinetic energy in the center of the combustion chamber. This is conducive to the stable combustion of the lean mixture and improves thermal efficiency.

Claims

1. A zoned combustion control method for a hydrogen fuel engine, applied to an ultra-lean combustion system for a hydrogen fuel engine, characterized in that: The ultra-lean burn system for a hydrogen fuel engine comprises: Intake duct (5), exhaust duct (2), piston (1), intake valve (4), exhaust valve (3), spark plug (7), high-pressure hydrogen injection nozzle (8), and hydrogen injection guide cover (9); The high-pressure hydrogen injection nozzle (8) is arranged on the cylinder head between the two intake valves (4); The axis of the high-pressure hydrogen nozzle (8) is located in the same plane as the center line of the cylinder and forms an angle with the axis of the cylinder; The hydrogen injection guide cover (9) wraps the hydrogen injection hole of the head of the high-pressure hydrogen injection nozzle (8), and the hydrogen injection guide cover (9) has a guide hole. The guide hole of the hydrogen injection guide cover (9) is located deep into the installation surface of the engine combustion chamber, and the guide direction of the hydrogen injection guide cover (9) is the ignition position of the spark plug (7); The method comprises: When the hydrogen fuel engine operates in a preset low-load operating range, the excess air coefficient of the hydrogen fuel engine is controlled to be 1.8, and the high-pressure hydrogen nozzle (8) is controlled to perform closed-valve injection after the intake valve (4) is closed and before the piston (1) reaches the top dead center, and the hydrogen gas beam is guided through the guide hole (92) of the hydrogen injection guide cover (9) to form a mixed gas with a concentration exceeding the preset concentration at the ignition position of the spark plug (7); the high-pressure hydrogen nozzle (8) is controlled to spray hydrogen at 50°-70°CA BTDC, and the spark plug (7) is controlled to ignite 1°-5°CA before the piston reaches the top dead center; When the hydrogen fuel engine operates in a preset rated operating range, the high-pressure hydrogen nozzle (8) is controlled to spray hydrogen at 70°-100°CA BTDC, and the hydrogen is guided to form a stratified mixture at the ignition position of the spark plug (7) through the guide hole (92) of the hydrogen injection guide cover (9), and the spark plug (7) is controlled to ignite 5°-10°CA before the piston reaches the top dead center; When the hydrogen fuel engine operates in a preset high-load operating range, after the intake valve is closed, the high-pressure hydrogen nozzle (8) is controlled to spray hydrogen at an injection ratio of 30%-50% to generate a homogeneous mixture with an excess air coefficient of 3.6-6; at 70°-100°CA BTDC, the high-pressure hydrogen nozzle (8) is controlled again to spray hydrogen, and the hydrogen is guided to form a stratified mixture at the ignition position of the spark plug (7) through the guide hole (92) of the hydrogen injection guide cover (9), and the spark plug (7) is controlled to ignite 5°-10°CA before the piston reaches the top dead center.

2. The zoned combustion control method for a hydrogen fuel engine according to claim 1, characterized in that: The top surface of the piston is an exhaust side pit, which is composed of two connected cylindrical surfaces. The center position of the intersection arc of the two cylindrical surfaces is the deepest part of the exhaust side pit.

3. The zoned combustion control method for a hydrogen fuel engine according to claim 1 or 2, characterized in that: The lower surface of the cylinder head, the bottom surface of the intake valve, and the bottom surface of the exhaust valve are respectively coated with a thermal barrier coating (6) made of a high-temperature resistant heat-insulating material.

4. The zoned combustion control method for a hydrogen fuel engine according to claim 1, characterized in that: The jet pressure of the high-pressure hydrogen nozzle is ≥4MPa, and the hydrogen beam flow rate is 1.5-8g / s; The diameter of the guide hole is 11.5 times that of the hydrogen injection hole. The depth of the hydrogen injection hole into the engine combustion chamber mounting surface is 0-5 mm. The angle formed by the axial direction of the high-pressure hydrogen injection nozzle (8) and the cylinder axis is 65°-70°.

5. The zoned combustion control method for a hydrogen fuel engine according to claim 2, characterized in that: The horizontal distance between the center position of the exhaust side recess and the center position of the exhaust valve (3) is between 8 and 10 mm; The depth of the exhaust side pit is 4%-6% of the cylinder diameter; The chord length of the intersection arc of the two cylindrical surfaces is 2-3 times the chord length of the edge of the two cylindrical surfaces.

6. The zoned combustion control method for a hydrogen fuel engine according to claim 3, characterized in that: The thermal barrier coating includes a ceramic surface layer and a bonding layer. The bonding layer is used between the metal surface and the ceramic surface layer. The ceramic surface layer is made of yttria-stabilized zirconia ceramic, and the bonding layer is made of nickel-chromium-aluminum alloy NiCrAl. The thickness ratio of the ceramic surface layer and the bonding layer is 3:1, and the porosity of the thermal barrier coating is 5%-30%.

7. The zoned combustion control method for a hydrogen fuel engine according to claim 1, characterized in that: The air intake duct (5) is a tangential air intake duct, and the angle between the air intake duct (5) and the horizontal plane of the cylinder head is between 20° and 26°; The exhaust duct (2) includes a first straight pipe section, a curved pipe section, and a second straight pipe section connected in sequence from the exhaust valve seat position, the outer edge curvature radius R1 of the curved pipe section is 1.2-1.25 times the diameter D2 of the exhaust valve (3), and the maximum pipe diameter D3 of the second straight pipe section is 11.2 times the diameter D2 of the exhaust valve (3).

8. The zoned combustion control method for a hydrogen fuel engine according to claim 1, characterized in that: The excess air coefficient of the hydrogen mixture ranges from 1.8 to 3.0 under all operating conditions, of which the excess air coefficient in the external characteristic range is 1.8, the excess air coefficient at the highest thermal efficiency point is 2.3, and the excess air coefficient in other operating ranges is between 1.8 and 3.0.

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