Multistage pre-combustion chamber coupling system of hydrogen-diesel dual-fuel engine and control method

Abstract

The invention provides a multi-stage pre-combustion chamber coupling system of a hydrogen-diesel dual-fuel engine and a control method. The multi-stage pre-combustion chamber coupling system comprises a stepped pre-combustion chamber, and the top of the stepped pre-combustion chamber communicates with a hydrogen injector, a diesel injector and a spark plug; the stepped pre-combustion chamber is composed of three stages of cylindrical cavities with the diameters decreasing progressively, the diameter gradient of each stage is 10%-15%, the height difference is 5 mm, the ratio of the total length of the cavity to the diameter of the main combustion chamber is 1: 3-1: 5, and the volume of the stepped pre-combustion chamber is 3% of the volume of the main combustion chamber. The method comprises the following steps: step 1, a hydrogen injection stage:-20 DEG C to-10 DEG C ; step 2, a hydrogen combustion stage, namely-6 DEG C CA; step 3, a diesel oil injection stage:-5 DEG CA to 0 DEG CA; and step 4, a jet ignition stage: 0-degree CA to + 15-degree CA. Through structural coupling of the hydrogen-diesel engine and the multi-stage pre-combustion chamber, combustion is more sufficient and efficient, the turbulence intensity is more beneficial to combustion, engine energy is fully utilized and combusted, and efficient utilization of the multi-stage pre-combustion chamber on the engine is promoted.

Description

Technical Field

[0001] The present invention relates to a multi-stage pre-chamber coupling system and control method for a hydrogen-diesel dual-fuel engine, belonging to the field of internal combustion engine combustion technology. Background Art

[0002] In the prior art, the combustion efficiency of hydrogen-diesel engines is limited by problems such as uneven fuel mixing, low combustion rate, and knocking tendency. Although the traditional single-stage pre-chamber design (such as patent CN217421343U) can improve the ignition energy through hydrogen pre-combustion, it still has the following defects: insufficient fuel stratification control: a single injection timing leads to premature mixing of hydrogen and diesel, incomplete combustion, and limited improvement in thermal efficiency (such as patent CN115126592A); insufficient turbulence intensity: the single-stage pre-chamber structure cannot generate stepped turbulence through staged combustion, and the flame propagation speed is limited; carbon deposition and injector blockage: diesel is directly exposed to the high-temperature pre-chamber environment, easily forming an oil film attachment, which affects the injection accuracy (such as patent 202110525858.X).

[0003] In response to the above problems, existing improvement solutions (such as patent CN202111368728.6) enhance the mixture tumble through an eccentric pre-chamber design, but still do not solve the core problems of time-sharing fuel control and thermodynamics coupling optimization. Therefore, there is an urgent need for a multi-stage pre-chamber system that can achieve staged injection and combustion co-control of hydrogen and diesel. Summary of the Invention

[0004] Object of the Invention: Aiming at the deficiencies in the prior art, the present invention provides a multi-stage pre-chamber coupling system and control method for a hydrogen-diesel dual-fuel engine, aiming to solve the problems of uneven fuel mixing, low combustion efficiency, and large thermodynamic losses in the existing pre-chamber technology of hydrogen-diesel engines, and provide a pre-chamber jet ignition system with time-sharing injection and multi-stage combustion, which improves the in-cylinder turbulence intensity and flame propagation stability through the stepped combustion of hydrogen and diesel.

[0005] Technical Solution: A multi-stage pre-chamber coupling system for a hydrogen-diesel dual-fuel engine includes a stepped pre-chamber communicated with the top of the engine main combustion chamber. The stepped pre-chamber is communicated with the main combustion chamber through a tapered flow channel jet nozzle opened at the lower end. A hydrogen injector, a diesel injector, and a spark plug are communicated with the top of the stepped pre-chamber.

[0006] The stepped pre-chamber is composed of three cylindrical cavities with decreasing diameters. The diameter gradient of each stage is 10%-15%, the height difference is 5 mm, the ratio of the total length of the cavity to the diameter of the main combustion chamber is 1:3 - 1:5, and the volume of the stepped pre-chamber is 3% of the volume of the main combustion chamber.

[0007] The ratio of the inlet diameter to the outlet diameter of the tapered flow channel jet nozzle is 2:1, the number of spray holes is 6 - 8, the inner surface is provided with spiral guide grooves, and a tungsten carbide coating is provided, and the groove depth is 0.2 - 0.3 mm.

[0008] The hydrogen injector selects a multi-hole electromagnetic injection valve. The injection holes of the multi-hole electromagnetic injection valve are set to at least 6 spray holes and are symmetrically arranged. The hole diameter is set to 0.2 mm, and the injection axis forms a 60° angle with the center line of the stepped pre-chamber.

[0009] The diesel injector is configured with a piezoelectric high-pressure common rail injector. The injection holes of the configured piezoelectric high-pressure common rail injector are set to at least 6 spray holes and are evenly distributed. The hole diameter is set to 0.15 mm, and the injection cone angle is set to 90°.

[0010] The control method of the hydrogen-diesel dual-fuel engine multi-stage pre-chamber coupling system includes the following steps:

[0011] Step 1, hydrogen injection stage, -20°CA to -10°CA;

[0012] Inject hydrogen with an equivalence ratio of 0.8 - 1.2 into the pre-chamber through the hydrogen injector;

[0013] Step 2, hydrogen combustion stage, -6°CA;

[0014] The spark plug ignites the hydrogen, so that the temperature in the pre-chamber reaches 800 - 1000 °C, and the turbulent flame intensity is increased to 5 - 8 m / s;

[0015] Step 3, diesel injection stage, -5°CA to 0°CA;

[0016] The diesel injector injects diesel with a pulse width of 2 - 3 ms, and uses the high-temperature environment of the pre-chamber to achieve atomization ignition;

[0017] Step 4, jet ignition stage, 0°CA to +15°CA;

[0018] The high-temperature gas forms a flame jet through the tapered flow channel jet nozzle, and the jet velocity is 200 - 250 m / s, igniting the lean mixture in the main combustion chamber.

[0019] The specific content of Step 1 is as follows:

[0020] The injection pressure is set to 8 Mpa to 12 MPa, corresponding to the injection pressures under low-load conditions and high-load conditions. The hydrogen flow rate is adjusted to 0.3 g / cycle to 0.8 g / cycle through PID closed-loop control;

[0021] The injection pulse width is set to 10°CA, corresponding to an injection duration of 1.67 ms @ 3000 rpm. The equivalence ratio Φ ranges from 0.9 to 1.1 to ensure the formation of a uniform hydrogen - air mixture layer in the pre - combustion chamber;

[0022] Introduce the calculation formula for the hydrogen injection timing matching

[0023]

[0024] Based on the law of conservation of mass in fluid mechanics, calculate the hydrogen mass flow rate, C d is the flow coefficient obtained through CFD (Computational Fluid Dynamics); is the hydrogen mass flow rate, determined by the engine speed and the hydrogen injection quantity per cycle. ΔP is the pressure change value, which can be measured through simulation experiments.

[0025] The specific content of step 2 is as follows:

[0026] The ignition energy is set to 80 mJ, and a dual - pulse ignition strategy is adopted. The energy of the first discharge is 50 mJ, and after an interval of 0.5 ms, the second discharge is 30 mJ. The spark duration is 2.5 ms to ensure stable ignition of hydrogen in the turbulent flow field;

[0027] During ignition, combustion monitoring is carried out. The combustion state is real - time feedback through the ion - current sensor integrated in the spark plug. If misfire is detected, that is, the ion current < 0.1 mA, the ECU is triggered to perform supplementary ignition at - 4°CA;

[0028] The calculation method of the turbulent flame intensity is as follows:

[0029]

[0030] In the formula, S T is the turbulent flame speed, which determines the combustion duration. S L is the laminar flame speed, which is affected by temperature after hydrogen addition. α is the turbulence intensification coefficient, k is the turbulent kinetic energy, is the turbulent pulsation speed.

[0031] The specific content of step 3 is as follows:

[0032] The injection pressure is set to 25 MPa to 30 MPa, corresponding to the first injection stage and the second injection stage. The injection quantity in the first injection stage accounts for 60% - 70% of the total injection quantity, which is used to establish the basic combustion; the injection quantity in the second injection stage accounts for 40% - 30% of the total injection quantity, which is used to maintain combustion stability.

[0033] In step 1:

[0034] The hydrogen injection amount is dynamically adjusted according to the engine load. During low-load conditions, hydrogen injection with an equivalence ratio of 0.8 to 1.0 is adopted; during high-load conditions, hydrogen injection with an equivalence ratio of 1.0 to 1.2 is adopted.

[0035] Beneficial effects:

[0036] Improvement in thermal efficiency: The pre-chamber temperature and turbulent kinetic energy are increased through hydrogen pre-ignition. The diesel secondary combustion forms a stable jet. The indicated thermal efficiency is increased by 7.6% compared with the traditional system without a pre-chamber and by 4.7% compared with a single-stage pre-chamber system. The fuel indicated consumption is decreased by 23.4% compared with the engine with a single-stage hydrogen pre-chamber and by 26.4% compared with the hydrogen spark ignition without a pre-chamber, saving fuel and energy.

[0037] Knock suppression: The staged combustion of hydrogen and diesel reduces the peak pressure fluctuation in the cylinder, and the knock tendency is reduced by 40%-60%;

[0038] Emission optimization: The NOx generation amount is reduced by 25%-30%, and the soot emission is reduced by more than 90%. Description of the drawings

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0040] Figure 1 It is a structural diagram of the stepped pre-chamber and the cylinder block with a stepped pre-chamber of the present invention.

[0041] Figure 2 It is a multi-stage pre-chamber model established by the present invention based on converge3.0.

[0042] Figure 3 It is a comparison diagram of the change in turbulent kinetic energy of the present invention.

[0043] Figure 4 It is a comparison diagram of the indicated thermal efficiency under four working conditions of the present invention.

[0044] Figure 5 It is a comparison diagram of the temperature cloud map and flame propagation of the present invention. Detailed implementation manners

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0046] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0047] In the present invention, unless otherwise clearly defined and limited, the first feature being "above" or "below" the second feature may include direct contact between the first and second features, or may include indirect contact between the first and second features through additional features therebetween. Moreover, the first feature being "above", "over" and "on" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the horizontal height of the first feature is higher than that of the second feature. The first feature being "below", "under" and "beneath" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the horizontal height of the first feature is lower than that of the second feature.

[0048] As Figure 1 shown, a multi-stage pre-chamber coupling system for a hydrogen-diesel dual-fuel engine includes a stepped pre-chamber communicating with the top of the engine main combustion chamber. The stepped pre-chamber communicates with the main combustion chamber through a tapered flow channel jet nozzle opened at the lower end. A hydrogen injector, a diesel injector, and a spark plug are connected to the top of the stepped pre-chamber.

[0049] The stepped pre-chamber is composed of three cylindrical cavities with decreasing diameters. The diameter gradient of each stage decreases by 10%-15% from top to bottom, the height difference is 5 mm, the ratio of the total length of the cavity to the diameter of the main combustion chamber is 1:3 - 1:5, and the volume of the stepped pre-chamber is 3% of the volume of the main combustion chamber. In this embodiment, the diameter gradient of each stage decreases by 12.5% from top to bottom, and the ratio of the total length of the cavity to the diameter of the main combustion chamber is 1:4.

[0050] The volume of the stepped pre-chamber is obtained according to the following formula:

[0051]

[0052] Q ignis the minimum ignition energy released by the combustion of hydrogen in the pre - combustion chamber, and LHV H is the lower heating value of hydrogen, and ρ H is the density of hydrogen under standard conditions, and φ pre is the equivalence ratio of the pre - combustion chamber;

[0053] The ratio of the inlet diameter to the outlet diameter of the converging - type flow - channel jet nozzle is 2:1, the number of injection holes is 6 - 8, the inner surface is provided with spiral flow - guiding grooves, and a tungsten carbide coating is provided, and the groove depth is 0.2 - 0.3 mm. In this embodiment, the number of injection holes is set to 6, and the groove depth is set to 0.2 mm.

[0054] The hydrogen injector selects a multi - hole electromagnetic injection valve. The injection holes of the multi - hole electromagnetic injection valve are set to at least 6 injection holes and are symmetrically arranged. The hole diameter is set to 0.2 mm, and the injection axis forms an angle of 60° with the center line of the stepped pre - combustion chamber.

[0055] In this embodiment, the number of injection holes of the multi - hole electromagnetic injection valve is set to 6;

[0056] The diesel injector is configured with a piezoelectric high - pressure common - rail injector. The injection holes of the configured piezoelectric high - pressure common - rail injector are set to at least 6 injection holes and are evenly distributed. The hole diameter is set to 0.15 mm, and the injection cone angle is set to 90°.

[0057] In this embodiment, the number of injection holes of the piezoelectric high - pressure common - rail injector is set to 6;

[0058] The control method of the hydrogen - diesel dual - fuel engine multi - stage pre - combustion chamber coupling system includes the following steps:

[0059] Step 1, hydrogen injection stage, - 20°CA to - 10°CA;

[0060] Inject hydrogen with an equivalence ratio of 0.8 - 1.2 into the pre - combustion chamber through the hydrogen injector;

[0061] In this embodiment, the equivalence ratio of hydrogen injection is 0.8

[0062] Step 2, hydrogen combustion stage, - 6°CA;

[0063] The spark plug ignites the hydrogen, so that the temperature in the pre - combustion chamber reaches 800 - 1000 °C, and the turbulent flame speed increases to 5 - 8 m / s; In this embodiment, the temperature threshold in the pre - combustion chamber is set to 1000 °C, and the turbulent flame speed threshold is set to 8 m / s

[0064] Step 3, diesel injection stage, - 5°CA to 0°CA;

[0065] The diesel injector injects diesel with a pulse width of 2 - 3 ms, and uses the high - temperature environment in the pre - combustion chamber to achieve atomization ignition;

[0066] In this embodiment, the diesel injector injects diesel with a pulse width of 5 ms;

[0067] Step 4: Jet ignition stage, 0°CA to +15°CA;

[0068] The high-temperature gas forms a flame jet through the jet injection of the converging flow channel, with a jet velocity of 200 - 250 m / s, igniting the lean mixture in the main combustion chamber.

[0069] Specifically, step 1 is as follows:

[0070] The injection pressure is set to 8 Mpa to 12 MPa, corresponding to the injection pressures under low-load and high-load conditions. The hydrogen flow rate is adjusted to 0.3 g / cycle to 0.8 g / cycle through PID closed-loop control;

[0071] The injection pulse width is set to 10°CA, corresponding to an injection duration of 1.67 ms @ 3000 rpm, and the equivalence ratio Φ is taken as 0.9 to 1.1 to ensure the formation of a uniform mixture layer of hydrogen in the pre-chamber;

[0072] Introduce the calculation formula for the hydrogen injection timing matching

[0073]

[0074] Based on the law of conservation of mass in fluid mechanics, calculate the hydrogen mass flow rate C corresponding to the injection pulse width d is the flow coefficient obtained through CFD computational fluid dynamics is the hydrogen mass flow rate, determined by the engine speed and the hydrogen injection amount per cycle. ΔP is the pressure change value, which can be measured through simulation experiments.

[0075] Specifically, step 2 is as follows:

[0076] The ignition energy is set to 80 mJ, and a dual-pulse ignition strategy is adopted. The first discharge energy is 50 mJ, and the second discharge is 30 mJ after an interval of 0.5 ms. The spark duration is 2.5 ms to ensure stable ignition of hydrogen in the turbulent flow field;

[0077] During ignition, combustion monitoring is carried out. The combustion state is real-time feedback through the ion current sensor integrated in the spark plug. If misfire is detected, that is, the ion current < 0.1 mA, the ECU is triggered to perform supplementary ignition at -4°CA;

[0078] Among them, the calculation method of the turbulent flame intensity is as follows:

[0079]

[0080] In the formula, S T is the turbulent flame speed, which determines the combustion duration, S Lis the laminar flame speed, which is affected by temperature after hydrogen addition, α is the turbulence intensification coefficient, k is the turbulent kinetic energy, is the turbulent pulsation velocity.

[0081] The specific steps of step 3 are as follows:

[0082] The injection pressure is set to 25 MPa to 30 MPa, corresponding to the first injection stage and the second injection stage. The injection amount in the first injection stage accounts for 60%-70% of the total injection amount and is used to establish the basic combustion; the injection amount in the second injection stage accounts for 40%-30% of the total injection amount and is used to maintain the combustion stability.

[0083] In step 1:

[0084] The hydrogen injection amount is dynamically adjusted according to the engine load. When the engine is in the low load condition, hydrogen is injected with an equivalence ratio of 0.8 to 1.0; when the engine is in the high load condition, hydrogen is injected with an equivalence ratio of 1.0 to 1.2.

[0085] In this embodiment, when the engine is in the low load condition, hydrogen is injected with an equivalence ratio of 0.8; when the engine is in the high load condition, hydrogen is injected with an equivalence ratio of 1.0.

[0086] As an embodiment,

[0087] The engine speed is set to 2000 rpm, the initial in-cylinder pressure is 2.31 bar, the piston temperature is 630 K, the cylinder head temperature is 530 K, the cylinder wall temperature is 540 K, and the pre-chamber boundary temperature is 450 K

[0088] Table 1 Sets the calculated boundary conditions

[0089]

[0090] Take the ignition energy Q of the pure hydrogen pre-chamber ign = 10 mj, the lower heating value LHV of hydrogen H = 120 MJ / kg, ρ H = 0.09 kg

[0091]

[0092] The stepped pre-chamber increases the volume to 1.5 cm through stratified combustion 3 , and the energy release is more sufficient, corresponding to an increase in the thermal efficiency.

[0093] In order to verify the combustion kinetic characteristics of the stepped pre-chamber, four comparative models of the stepped pre-chamber, the single-stage pure hydrogen pre-chamber, the diesel engine without a pre-chamber, and the pure hydrogen without a pre-chamber are constructed through simulation.

[0094] The stepped pre-chamber adopts a dual-jet collaborative design (hydrogen premixing + diesel ignition) to optimize the flame propagation path and energy release efficiency; the single-stage pure hydrogen pre-chamber strengthens the stability of the jet flame and reduces the quenching risk of the main combustion chamber through high-pressure direct injection (ΔP = 12 MPa) and hydrogen-rich equivalence ratio design. The pure hydrogen without pre-chamber and the diesel engine without pre-chamber are used as the reference group, adopting the traditional diffusion combustion mode and using a spark plug for ignition to quantify the improvement of the pre-chamber technology on thermal efficiency and emissions.

[0095] The experimental simulation model is created as Figure 2 shown. The simulation model integrates the RNG k-ε turbulence model, the SAGE combustion model, and the n-heptane-methane coupled chemical reaction mechanism, and captures transient processes such as jet collision and turbulent dissipation through adaptive mesh refinement (AMR). The boundary conditions are set to ensure that the initial pressure and temperature are consistent with the experimental conditions (2000 rpm).

[0096] The calculation conditions and parameters under the four working conditions are shown in Tables 2 and 3. Based on the above boundary conditions and model establishment, the cylinder pressure, heat release rate, average temperature, and turbulent kinetic energy data are extracted using the Converge data post-processing module and imported into the Origin software to draw two-dimensional curve graphs. Finally, the three-dimensional temperature cloud map and flame propagation map are drawn using the Tecplot software.

[0097] Table 2 Calculation conditions and parameters for the four working conditions

[0098]

[0099] Table 3 Continued calculation conditions and parameters for the four working conditions

[0100]

[0101] Working principle setting and performance analysis

[0102] Taking 0°CA as the top dead center of compression, hydrogen is injected in the section from -20 to -10°CA, and then the hydrogen is ignited by the spark plug at -6°CA to make the hydrogen burn. The combustion of hydrogen increases the internal temperature and turbulent effect of the pre-chamber. After an interval of 1°CA, diesel is continuously injected at -5°CA. After the diesel is atomized, it is ignited. The combustion of diesel is fast and stable, which increases the turbulent effect and the temperature of the pre-chamber again. Subsequently, the flame of the mixed gas jets into the cylinder through the jet nozzle to complete an ignition process.

[0103] The turbulent kinetic energy in the cylinder is as Figure 3 shown. The comparison of the indicated thermal efficiency is as Figure 4As shown, it can be seen that before and after ignition, the turbulent kinetic energy of the multi-stage pre-combustion is much greater than that of the single-stage pre-combustion chamber and the hydrogen-diesel without a pre-combustion chamber. After consulting the data, this relatively appropriate increase in turbulent energy improves the flame propagation efficiency. Combining the pre-mixing of hydrogen and diesel, the indicated thermal efficiency of the multi-stage pre-combustion chamber is increased by 10.9% compared with the single-stage pre-combustion hydrogen, and the thermal efficiency is increased by 4.57% compared with the spark-ignition diesel engine without a pre-combustion chamber.

[0104] Temperature contour and flame propagation comparison Figure 5 , it can be analyzed that the timing control and multi-stage coupled ignition of the multi-stage pre-combustion chamber make the flame propagation speed faster, and the combustion in the contour is more sufficient and uniform. The effect of the single-stage pre-combustion is the second, while the combustion diffusion speed of the ordinary hydrogen-diesel is relatively slow, resulting in its thermal efficiency being lower than that of the hydrogen-diesel engine with a multi-stage pre-combustion chamber.

[0105] Introduce the formula for thermal efficiency and fuel consumption rate

[0106]

[0107] This formula comprehensively considers the combustion work (W ind ), heat loss (Q loss ), and mechanical efficiency (η mech = 0.88), Fuel mass flow rate, LHV H Lower heating value of fuel, Air mass flow rate, LHV d Lower heating value of air, Q fuel Total energy released by fuel combustion, calculate thermal efficiency;

[0108] Q loss = h g AΔTt com

[0109] η ith = 46.1%, BSFC = 190.7 g / KWh

[0110] Among them, Q loss is the heat loss, h g is the convective heat transfer coefficient, A is the heat transfer area, ΔT is the temperature difference, and t com represents the combustion duration

[0111] Based on the Woschni model, the heat transfer coefficient hg = 480 W / (mK) is calculated. It is estimated that the shortening of the high-temperature period of the multi-stage pre-combustion chamber reduces the proportion of heat loss from 18% to 12%. This can be further judged in combination with the simulation experiment.

[0112] On this basis, combined with fluid mechanics, introduce the turbulent kinetic energy equation:

[0113]

[0114] In the formula: represents the rate of change of turbulent kinetic energy with time, and P k is the shear production term, ∈ is the turbulent dissipation rate, and T k is the turbulent transport term

[0115] This equation describes the dynamic balance of the generation, dissipation, and jet input of turbulent kinetic energy: Introducing

[0116]

[0117] In the formula: P k is the shear production term, v t is the turbulent viscosity, is the velocity gradient tensor.

[0118] The shear production term is related to the velocity gradient. When the turbulent kinetic energy increases moderately, the velocity gradient of the multi-stage pre-chamber jet increases, and accurate results can be obtained by auxiliary measurement

[0119]

[0120] In the formula: k is the turbulent kinetic energy, and u′ represents the pulsating velocity.

[0121] It is calculated that k = 196m 2 / s 2 ;

[0122] The simulation values are compared with the calculated values. The simulation data are shown in Table 4 below. The theoretical turbulent kinetic energy k = 196m / s, the simulated turbulent kinetic energy is 182, and the difference of 7.7% is due to the unmodeled local dissipation of jet collision. The theoretical thermal efficiency η ith = 46.1% (45.72% in the simulation experiment), and the difference of 0.8% is due to the fine optimization of the parameter grid. The theoretical value of BSFC is 190.7g / kWh (189.6g / kWh in the simulation experiment, with an error of 0.6%). The difference comes from the incomplete parameterization of the dynamic response of the injection timing. By comparison, it is found that the simulation effect of the calculated results is basically close within the error range, so the theoretical feasibility of the device can be proved.

[0123] The indicated thermal efficiency of the gas-diesel pre-mixed multi-stage pre-chamber is increased by 10.9% compared with the single-stage pre-chamber, and the thermal efficiency is increased by 4.57% compared with the spark plug diesel engine without a pre-chamber. The indicated fuel consumption of the hydrogen-diesel pre-mixed multi-stage pre-chamber is decreased by 8.44% compared with the single-stage pre-chamber, and is decreased by 4.61% compared with the spark plug diesel engine without a pre-chamber.

[0124] Table 4 Analysis of simulation data in four cases

[0125]

[0126] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the various embodiments, reference can be made to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple. For the relevant parts, reference can be made to the description in the method section.

[0127] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multi-stage pre-chamber coupling system for a hydrogen-diesel dual-fuel engine, characterized in that: It includes a stepped pre-chamber (1) connected to the top of the main combustion chamber of the engine. The stepped pre-chamber (1) is connected to the main combustion chamber through a tapered flow channel jet nozzle (2) opened at the lower end. The top of the stepped pre-chamber (1) is connected with a hydrogen injector (3), a diesel injector (4) and a spark plug (5); The stepped pre-chamber (1) is composed of three cylindrical cavities with decreasing diameters. The diameter gradient of each stage is 10%-15%, the height difference is 5 mm, the ratio of the total length of the cavity to the diameter of the main combustion chamber is 1:3 - 1:5, and the volume of the stepped pre-chamber (1) is 3% of the volume of the main combustion chamber; The ratio of the inlet diameter to the outlet diameter of the tapered flow channel jet nozzle (2) is 2:1, the number of spray holes is 6 - 8, spiral guide grooves are opened on the inner surface, and a tungsten carbide coating is provided, and the groove depth is 0.2 - 0.3 mm.

2. The hydrogen-diesel dual-fuel engine multi-stage pre-chamber coupling system according to claim 1, wherein: The hydrogen injector (3) selects a multi-hole electromagnetic injection valve. The injection holes of the multi-hole electromagnetic injection valve are set to at least 6 spray holes and are symmetrically arranged. The hole diameter is set to 0.2 mm, and the injection axis forms an angle of 60° with the center line of the stepped pre-chamber (1).

3. The hydrogen-diesel dual-fuel engine multi-stage pre-chamber coupling system according to claim 1, wherein: The diesel injector (4) is configured with a piezoelectric high-pressure common rail injector. The injection holes of the configured piezoelectric high-pressure common rail injector are set to at least 6 spray holes and are evenly distributed. The hole diameter is set to 0.15 mm, and the injection cone angle is set to 90°.

4. The control method of the multi-stage pre-chamber coupling system of the hydrogen-diesel dual-fuel engine according to any one of claims 1 to 3, characterized in that, It includes the following steps: Step 1, hydrogen injection stage, -20°CA to -10°CA; Inject hydrogen with an equivalence ratio of 0.8 - 1.2 into the pre-chamber through the hydrogen injector (3); Step 2, hydrogen combustion stage, -6°CA; The spark plug (5) ignites the hydrogen to make the temperature in the pre-chamber reach 800 - 1000 °C, and the turbulent flame intensity is increased to 5 - 8 m / s; Step 3, diesel injection stage, -5°CA to 0°CA; The diesel injector (4) injects diesel with a pulse width of 2 - 3 ms, and uses the high-temperature environment in the pre-chamber to achieve atomization ignition; Step 4, jet ignition stage, 0°CA to +15°CA; The high-temperature gas forms a flame jet through the tapered flow channel jet, and the jet velocity is 200 - 250 m / s, which ignites the lean mixture in the main combustion chamber.

5. The control method of the multi-stage pre-chamber coupling system for a hydrogen-diesel dual-fuel engine according to claim 4, characterized in that The specific content of Step 1 is as follows: The injection pressure is set to 8 Mpa to 12 MPa, corresponding to the injection pressures under low-load conditions and high-load conditions. The hydrogen flow rate is adjusted to 0.3 g / cycle to 0.8 g / cycle through PID closed-loop control; The injection pulse width is set to 10°CA, corresponding to an injection duration of 1.67 ms @ 3000 rpm. The equivalence ratio Φ is taken as 0.9 to 1.1 to ensure that a uniform hydrogen mixture layer is formed in the pre-chamber; Introduce the calculation formula for the hydrogen injection timing matching Based on the law of mass conservation in fluid mechanics, calculate the hydrogen mass flow rate corresponding to the injection pulse width, C d is the flow coefficient obtained through CFD (Computational Fluid Dynamics), is the hydrogen mass flow rate, determined by the engine speed and the cyclic hydrogen injection amount, and ΔP is the pressure change value, which can be measured through simulation experiments.

6. The control method of the multi-stage pre-chamber coupling system for a hydrogen-diesel dual-fuel engine according to claim 5, characterized in that The specific content of Step 2 is as follows: The ignition energy is set to 80 mJ, and a dual-pulse ignition strategy is adopted. The first discharge energy is 50 mJ, and the second discharge is 30 mJ after an interval of 0.5 ms. The spark duration is 2.5 ms to ensure stable ignition of hydrogen in the turbulent flow field; Combustion monitoring is carried out during ignition, and the combustion state is fed back in real time through the ion current sensor integrated in the spark plug (5). If misfire is detected, that is, the ion current < 0.1 mA, the ECU is triggered to perform supplementary ignition at -4°CA; The calculation method of the turbulent flame intensity is as follows: Where, S T is the turbulent flame speed, which determines the combustion duration. S L is the laminar flame speed, which is affected by temperature after hydrogen addition. α is the turbulence intensification coefficient, k is the turbulent kinetic energy, is the turbulent fluctuation velocity.

7. The control method of the multi-stage pre-chamber coupling system of a hydrogen-diesel dual-fuel engine according to claim 6, characterized in that The specific content of step 3 is as follows: The injection pressure is set to 25 MPa to 30 MPa, corresponding to the first injection stage and the second injection stage. The injection quantity in the first injection stage accounts for 60%-70% of the total injection quantity and is used to establish the basic combustion; The injection quantity in the second injection stage accounts for 40%-30% of the total injection quantity and is used to maintain the combustion stability.

8. The control method of the multi-stage pre-chamber coupling system for a hydrogen-diesel dual-fuel engine according to claim 5, characterized in that In step 1: The hydrogen injection quantity is dynamically adjusted according to the engine load. Hydrogen injection with an equivalence ratio of 0.8 to 1.0 is adopted under low load conditions; hydrogen injection with an equivalence ratio of 1.0 to 1.2 is adopted under high load conditions.

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