Injection strategy collaborative optimization method for hydrogen direct injection internal combustion engine

Abstract

The invention discloses an injection strategy collaborative optimization method for a hydrogen direct injection engine. In a working condition domain of 1200 r / min, BMEP = 2-8 bar and lambda = 1.0-2.3, a multi-dimensional mapping table of efficiency, emission and cycle stability is established and used for online selection through injection start (SOI) scanning of single injection, checking of injection pulse width and injection end position by injection pressure and joint calibration of secondary injection end (SEOI) and secondary injection proportion (SIP) of double injection. According to the method, under the equivalent and rarefied working conditions, the optimal interval of SOI and the optimal interval of SEOI and SIP are given respectively; and a strategy elimination and rollback logic with a cyclic variation coefficient (COV) smaller than or equal to 3% as a threshold value is introduced, so that a parameter combination taking heat efficiency, NOx and combustion stability into account is obtained under different lambda and loads. The method is suitable for calibration and control of the hydrogen direct injection spark ignition engine.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of hydrogen fuel internal combustion engine combustion and control technology, and particularly relates to a jet strategy coordination optimization method for a hydrogen direct injection (HDI) internal combustion engine. BACKGROUND

[0002] Hydrogen, as a zero-carbon fuel, has the characteristics of fast combustion speed, strong diffusion and wide flammable range, and can achieve both high thermal efficiency and low emissions in lean or even ultra-lean combustion in internal combustion engines; but its combustion process is highly sensitive to injection strategy, and injection timing, injection pressure and segmented (double) injection will directly affect the in-cylinder mixture distribution and combustion phase, and then affect key indicators such as thermal efficiency and NOx. Existing research and paper reviews have pointed out that optimizing injection timing and angle and using segmented injection to construct stratified mixture can improve emissions and improve thermal efficiency, but systematic and engineering guidance is still insufficient.

[0003] In order to facilitate engineering comparison and reproduction, recent experimental research usually limits a representative operating condition domain and unifies the test criteria. For example: the engine speed is fixed at 1200r / min, the BMEP (average effective pressure) mainly covers 2-8bar (under heavy load, due to the increase of injection pulse width and the fact that combustion is already fast, the benefits and adjustable space of strategy optimization are limited), and the excess air ratio λ is divided into stages within 1.0-2.3; CA10, CA50 and CA90 are used to represent the crank angles at which the cumulative heat release reaches 10%, 50% and 90%, respectively; the combustion duration is defined as the crank angle interval from CA10 to CA90; the ignition delay is defined as the crank angle interval from the ignition time to CA10; and the data validity criterion is that the cycle variation coefficient of BMEP is ≤3%, if it exceeds this threshold, it is considered that the injection strategy is not suitable.

[0004] From the existing published results, there are contradictions between multiple objectives and multiple constraints in the injection strategy:

[0005] (1) Injection timing (SOI) trade-off. A moderate delay of SOI can reduce the compression stroke negative work, promote moderate stratification and improve thermal efficiency, but too late SOI will lead to near-wall hydrogen enrichment due to insufficient mixing diffusion time, intensified heat transfer and efficiency decline; at the same time, delaying SOI can significantly suppress NOx under equivalent conditions, but the sensitivity of NOx to SOI is weak under lean conditions. The above rules determine that SOI optimization must be processed by load and λ partitioning, and attention should be paid to the injection blockage caused by back pressure when approaching the top dead center.

[0006] (2) Injection pressure (Pinj) and "timing window". Since gaseous hydrogen has no atomization process and strong diffusion, simply increasing the injection pressure has little direct impact on the combustion rate and emissions; its engineering significance mainly lies in shortening the injection pulse width, creating a "timing window" for the delayed EOI or SEOI. For example, when the injection pressure is increased from 2 MPa to 8 MPa, the pulse width can be shortened by about 75%, which is beneficial to more delayed injection without worsening combustion stability, reducing the risk of pre-ignition or backfire.

[0007] (3) The mechanism and effect of double injection (SEOI, SIP) are as follows: when SEOI is delayed, the motion path of the secondary jet will first be guided by the cylinder wall in a clockwise motion, gradually transition to a motion without obvious guidance, and finally change to a counterclockwise motion guided by the piston; the corresponding ignition delay and combustion duration show a non-monotonic response of first decreasing, then increasing, and then decreasing. The increase of SIP has limited gain on thermal efficiency, but the inhibition of NOx is more significant under relatively rich conditions; while under ultra-lean conditions, moderate SIP helps to increase the peak heat release and shorten the combustion duration. The above phenomena show that SEOI and SIP need to be optimized in conjunction with λ and load, and cannot be fixed.

[0008] However, although there have been many studies on HDI (hydrogen direct injection) injection strategies, most of them are theoretical analysis and numerical simulation, lacking systematic experimental comparison and engineering mapping of SOI, Pinj, SEOI, and SIP under different loads (BMEP) and different dilution degrees (λ). Especially under the constraints of limited pulse width at heavy load and increased back pressure near top dead center, there is still a lack of "parameter-target-constraint" integrated collaborative optimization framework that can directly guide development.

[0009] The present application provides a kind of injection strategy collaborative optimization method for hydrogen direct injection internal combustion engine, especially about how to obtain the optimal combination of SOI, injection pressure, SEOI and SIP, form structured mapping table, and call according to λ And BMEP in operation, realize the collaborative optimization of BTE promotion, NOx inhibition and cycle stability. SUMMARY

[0010] The present application aims to solve at least one of the technical problems in the prior art. To this end, the present application provides an injection strategy collaborative optimization method for hydrogen direct injection internal combustion engine, which aims to obtain the optimal combination of SOI, injection pressure, SEOI and SIP, form structured mapping table, and call according to λ And BMEP in operation, realize the collaborative optimization of BTE promotion, NOx inhibition and cycle stability.

[0011] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: an injection strategy collaborative optimization method for hydrogen direct injection internal combustion engine, comprising the steps of:

[0012] S1, in the engine speed is 1200r / min, brake mean effective pressure BMEP is 2-8bar, excess air coefficient λ is 1.0-2.3 working condition domain, with cycle variation coefficient COV≤3% as stability criterion, with combustion phase parameters CA10, CA50, CA90 as combustion duration discriminant quantity;

[0013] S2, by experiment calibration to build injection strategy mapping table, the mapping table contains single injection injection start angle SOI, injection pressure, and double injection secondary injection end angle SEOI and secondary injection ratio SIP Optimal combination relationship;

[0014] S3, when the engine is running, the current λ and BMEP are obtained in real time, and the corresponding injection strategy is queried from the mapping table and executed.

[0015] The calibration process of the single injection includes:

[0016] Under the conditions of BMEP being 2bar, 5bar and λ being 1.0, 1.5, 2.0, scan SOI from 30-200°CA BTDC, and record brake thermal efficiency BTE and NOx emission data;

[0017] Wherein, when BMEP is 2bar, SOI is set in the interval of 120-80°CA BTDC;

[0018] When BMEP is 5bar, SOI is set in the interval of 130-80°CA BTDC, and SOI is not later than 80°CA BTDC.

[0019] The calibration process of the single injection includes:

[0020] Around the fixed SOI, compare the pulse width under the injection pressure of 2MPa, 5MPa, 8MPa and the combustion performance;

[0021] Wherein, when the injection pressure is increased from 2MPa to 8MPa, the pulse width is shortened by 75%, which provides timing margin for delayed injection.

[0022] The calibration process of the double injection includes:

[0023] Fixing the primary injection start angle PSOI at 180°CA BTDC, under the conditions of λ being 1.0, 1.5, 1.8, 2.3 and BMEP being 5bar, scanning SEOI from 100-20°CA BTDC, and cross testing SIP at 10%, 30%, 50%;

[0024] Wherein, when λ is 1.8-2.3, the later angle in the SOI range is adopted; when λ is 1.0-1.5, the middle-later angle in the SOI range is adopted.

[0025] SIP is set to 10%-30% when λ is 1.0-1.5, and SIP is set to 30% when λ is 2.3.

[0026] The generation criterion of the mapping table is:

[0027] In equivalent conditions, SOI is preferentially delayed to suppress NOx emission;

[0028] In lean conditions, SEOI is preferentially delayed and cooperated with medium SIP to promote speed combustion;

[0029] When the pulse width is affected by the injection end angle position, the injection pressure is increased to ensure the feasible window of the delayed injection.

[0030] In the double injection, the motion form of the secondary jet presents regular changes with the delay of SEOI: the motion trajectory is gradually transitioned from the clockwise motion guided by the cylinder wall to the motion without obvious guidance, and finally changed into the counterclockwise motion guided by the piston; and the corresponding ignition lag and combustion duration present the change trend of first decreasing, then increasing, and then decreasing.

[0031] The injection strategy of the hydrogen direct injection engine is realized by the following way:

[0032] In equivalent conditions, the NOx emission is reduced by more than 80% through the delay of SOI;

[0033] In lean conditions, the peak heat release rate is increased by 14% and the combustion duration is shortened by 19% through the delay of SEOI and the setting of SIP to 30%;

[0034] The feasible window of the delayed injection is expanded by increasing the injection pressure, and the back pressure blockage and premixing deficiency near the top dead center are avoided.

[0035] The injection strategy optimization method for the hydrogen direct injection engine further comprises the following steps:

[0036] S4, when the injection strategy causes COV>3%, the last stable strategy point is returned.

[0037] The injection strategy optimization method for the hydrogen direct injection engine gives the preferred interval of SOI, SEOI and SIP under equivalent and lean conditions respectively, and introduces the strategy elimination and return logic with COV≤3% as the threshold, so that the parameter combination considering thermal efficiency, NOx and stability is obtained under different λ and loads. The method is suitable for the calibration and control of the hydrogen direct injection spark-ignition engine. BRIEF DESCRIPTION OF DRAWINGS

[0038] The specification includes the following drawings, which are depicted below:

[0039] Figure 1 Schematic diagram of engine test bench and measurement arrangement;

[0040] Figure 2a BTE variation with SOI at different λ for BMEP = 2 bar;

[0041] Figure 2b BTE variation with SOI at different λ for BMEP = 5 bar;

[0042] Figure 2c Injection pulse width versus EOI position at different injection pressures;

[0043] Figure 2d BTE variation at different injection pressures;

[0044] Figure 2e NOx variation at different injection pressures;

[0045] Figure 2f NOx variation with SOI at different λ for BMEP = 2 bar and 5 bar;

[0046] Figure 3a BTE variation with SEOI at different λ;

[0047] Figure 3b NOx variation with SEOI at different λ;

[0048] Figure 4a Ignition delay variation with SEOI at different λ;

[0049] Figure 4b Combustion duration (CA10-90) variation with SEOI at different λ;

[0050] Figure 5a Cylinder pressure and heat release rate plots at different SIP for λ = 2.3;

[0051] Figure 5b Combustion duration variation with SIP at different λ.

[0052] In the figures, the following are marked: 1. Encoder; 2. Exhaust pipe; 3. Computer; 4. Data acquisition; 5. Turbocharger; 6. Intercooler; 7. Solenoid valve; 8. Hydrogen rail; 9. Intake pipe; 10. Dynamometer; 11. Hydrogen tank group; 12. Flame arrester; 13. Hydrogen flow meter; 14. Pressure reducing valve. DETAILED DESCRIPTION

[0053] The specific embodiments of the present application are further described in detail below with the accompanying drawings, by describing the embodiments, in order to help the skilled in the art to have a more complete, accurate and in-depth understanding of the concept and technical solutions of the present application, and to help the implementation.

[0054] The embodiment of the present application provides a jet strategy cooperative optimization method for a hydrogen direct injection internal combustion engine, comprising the following steps:

[0055] S1, in the working condition domain of the engine speed of 1200r / min, the brake mean effective pressure BMEP of 2-8bar, and the excess air coefficient λ of 1.0-2.3, taking the cycle variation coefficient COV≤3% as the stability criterion, and taking the combustion phase parameters CA10, CA50 and CA90 as the combustion duration discriminant;

[0056] S2, constructing a jet strategy mapping table through experimental calibration, wherein the mapping table comprises the optimal combination relationship of the single injection start angle SOI, the injection pressure, the secondary injection end angle SEOI and the secondary injection ratio SIP of the double injection;

[0057] S3, when the engine is running, the current λ and BMEP are obtained in real time, the corresponding jet strategy is inquired from the mapping table, and the jet strategy is executed.

[0058] Specifically, in the embodiment of the present application, a jet strategy cooperative optimization method combining "experiment-mapping-online application" is proposed: in the domain that can cover the actual working condition, the optimal combination relationship of SOI, injection pressure, SEOI and SIP is obtained, a structured mapping table is formed, and the λ and BMEP are called in the running, so as to realize the cooperative optimization of BTE promotion, NOx inhibition and cycle stability, which is suitable for hydrogen direct injection spark-ignition engine (HDI).

[0059] In the above step S1, the engine operating condition domain and criterion setting are carried out: the engine speed is set to 1200r / min, the BMEP is set to 2-8bar; λ is set to 1.0-2.3 in stages, and a plurality of specific values in the interval are selected to carry out experimental calibration; COV≤3% is taken as the effective data criterion; CA10, CA50 and CA90 are defined as combustion phase and duration discriminant. CA10, CA50 and CA90 are defined as combustion phase and duration discriminant, which are key parameters for describing the combustion process, CA10 refers to the crank angle at which the combustion heat release reaches 10%, CA50 refers to the crank angle at which the combustion heat release reaches 50%, and CA90 refers to the crank angle at which the combustion heat release reaches 90%.

[0060] Single injection refers to a mode that the injector sprays hydrogen only once per working cycle of the engine (such as the intake, compression, work, and exhaust strokes of a four-stroke engine). Double injection refers to a mode that the injector sprays hydrogen twice per working cycle of the engine. The second injection end angle SEOI refers to the timing of the end of the second injection of hydrogen in the double injection, and the second injection proportion SIP refers to the proportion of the amount of hydrogen in the second injection to the total amount of hydrogen in the double injection.

[0061] In the embodiment of the present application, single injection SOI calibration is performed, and the calibration process of single injection includes:

[0062] Under the conditions that BMEP is 2 bar, 5 bar, and λ is 1.0, 1.5, and 2.0, SOI is scanned from 30 to 200°CA BTDC, the brake thermal efficiency BTE and NOx emission data are recorded, and the cylinder pressure curve is recorded;

[0063] When BMEP is 2 bar, SOI is set in the interval of 120 to 80°CA BTDC.

[0064] When BMEP is 5 bar, SOI is set in the interval of 130 to 80°CA BTDC, and SOI is not later than 80°CA BTDC.

[0065] The results show that: when BMEP is 2 bar, BTE increases first and then decreases with the delay of SOI, with a maximum increase of 2.6%; when BMEP is 5 bar, the increase is 2.0% to 2.35%, and SOI is not suitable to be later than 80°CA BTDC due to back pressure limitation. Delaying SOI can reduce NOx from about 4574 ppm to about 560 ppm (≈88%) under equivalent conditions, and the reduction is limited under lean conditions. The above data are used to form a sub-mapping relationship between SOI, BTE, NOx, λ, and BMEP.

[0066] In the above step S2, the injection pressure and pulse width are checked: near the fixed SOI, the pulse width and combustion performance when the injection pressure is taken as 2 MPa, 5 MPa, and 8 MPa in turn are compared. The results show that: the injection pressure has a slight effect on the combustion rate and emission; when the injection pressure is increased from 2 MPa to 8 MPa, the pulse width can be shortened by about 75%, which significantly expands the feasible window of late injection, for avoiding the back pressure blockage and premixing deficiency near TDC. The relationship between the injection pressure, the injection pulse width, and the EOI margin is included in the check layer of the mapping.

[0067] In the embodiment of the present application, the check process of the injection pressure includes:

[0068] Near the fixed SOI, the pulse width and combustion performance under the injection pressure of 2 MPa, 5 MPa, and 8 MPa are compared.

[0069] Wherein, when the injection pressure is raised from 2 MPa to 8 MPa, the pulse width is shortened by 75%, which provides timing margin for the delayed injection.

[0070] In the step S2, double injection combined calibration is performed: fixing the primary injection PSOI ≈ 180°CA BTDC, scanning SEOI from 100 to 20°CA BTDC, SIP taking 10%, 30%, 50%, and λ taking 1.0, 1.5, 1.8, 2.3 in turn, cross test is performed under the condition of BMEP = 5 bar. The results show that: the delayed SEOI makes the BTE increase by about 1.5% and 0.6% respectively under the lean working condition (λ = 1.8-2.3) and the relatively rich working condition (λ = 1.0-1.5), and makes the NOx emission decrease by more than 47% under the relatively rich working condition; the ignition delay and the combustion duration decrease first, then increase, and then decrease again with SEOI, the secondary injection jet path is guided by the cylinder wall and then clockwise, and finally guided by the piston and then counterclockwise. Increasing SIP does not increase the BTE by more than 1%, but can make NOx decrease by more than 43% under the relatively rich working condition; when λ = 2.3, increasing SIP from 0% to 30% can increase the peak heat release rate (HRR) by about 14% and shorten the combustion duration by about 19%, and when SIP continues to increase to 50%, the benefit is slow.

[0071] In the embodiment of the application, the calibration process of double injection includes:

[0072] Fixing the primary injection start angle PSOI as 180°CA BTDC, scanning SEOI from 100 to 20°CA BTDC under the condition of λ being 1.0, 1.5, 1.8, 2.3 and BMEP being 5 bar, and cross testing SIP as 10%, 30%, 50%;

[0073] Wherein, when λ is 1.8-2.3, the later angle in the SEOI range is adopted, and when λ is 1.0-1.5, the middle-later angle in the SEOI range is adopted.

[0074] In the embodiment of the application, SIP is set to 10%-30% when λ is 1.0-1.5, and SIP is set to 30% when λ is 2.3.

[0075] In the embodiment of the application, the generation criterion of the mapping table is:

[0076] Under the equivalent working condition, SOI is preferentially delayed to suppress NOx emission;

[0077] Under the lean working condition, SEOI is preferentially delayed and cooperated with moderate SIP to speed up the combustion;

[0078] When the pulse width is limited to affect the position of the end of injection (single injection end of injection EOI or secondary injection end of injection SEOI), the feasible window of delayed injection is ensured by increasing the injection pressure.

[0079] In the above step S3, the online application and switching logic: running real-time estimation of lambda and BMEP, querying the strategy from the mapping table: equivalent working condition priority delay SOI to suppress NOx; lean working condition priority delay SEOI and cooperate with medium SIP (about 30%) to accelerate combustion; when the injection pulse width is limited to cause the position of EOI or SEOI to meet the requirements, compensation is made by increasing the injection pressure.

[0080] In the embodiment of the application, the motion form of the secondary jet in the double injection presents regular changes with the delay of SEOI: clockwise motion guided by the cylinder wall, gradually transition to unguided motion, and finally change to counterclockwise motion guided by the piston; the corresponding ignition lag and combustion duration show the change trend of first decreasing, then increasing, and then decreasing.

[0081] In the embodiment of the application, the injection strategy of the hydrogen direct injection engine is synergistically optimized in the following ways:

[0082] In the equivalent working condition, the NOx emission is reduced by more than 80% by delaying SOI;

[0083] In the lean working condition, the peak heat release rate is increased by 14% and the combustion duration is shortened by 19% by delaying SEOI and setting SIP to 30%;

[0084] The feasible window of delayed injection is expanded by increasing the injection pressure to avoid back pressure blockage and premixing deficiency near the top dead center.

[0085] The injection strategy synergistic optimization method for the hydrogen direct injection internal combustion engine in the embodiment of the application further includes the following steps:

[0086] S4, when the COV is greater than 3% due to the execution of the injection strategy, the last stable strategy point is returned to.

[0087] The injection strategy synergistic optimization method for the hydrogen direct injection internal combustion engine in the embodiment of the application gives the engineering optimal combination rule of SOI, injection pressure, SEOI and SIP under the unified working condition domain and criterion: significant NOx suppression and combustion acceleration are respectively realized in the equivalent working condition and the lean working condition, and the feasible window of delayed injection is expanded through the synergistic effect of injection pressure and injection pulse width, thereby improving the robustness to pre-ignition and backfire.

[0088] Embodiment 1: Single injection SOI optimization

[0089] The results show that the BTE increases first and then decreases with the SOI delay, increasing by 1.8% to 2.6% at 2 bar and by 2.0% to 2.35% at 5 bar. To avoid back pressure obstruction near the top dead center, the SOI should not be delayed beyond 80°CA BTDC, as shown in FIG. 1. Figure 2a , Figure 2b The mechanism is that a moderate delay of the SOI can reduce the compression stroke negative work and decrease the near-wall heat loss, but a too late SOI can lead to a decrease in efficiency due to insufficient diffusion.

[0090] At the same time, the experiment shows that, under equivalent conditions (λ = 1.0), delaying the SOI can reduce NOx from about 4574 ppm to about 560 ppm (a decrease of about 88%), and under lean conditions, the decrease in NOx is limited, as shown in FIG. 2. Figure 2f The results show that delaying the SOI can not only improve the thermal efficiency but also significantly reduce NOx under equivalent conditions, but the effect on NOx under lean conditions is weak.

[0091] Example 2: Injection pressure as a regulator of pulse width and timing window

[0092] Near the optimal SOI of Example 1, the effects of injection pressure of 2 MPa, 5 MPa and 8 MPa on the injection pulse width, EOI position and combustion performance are compared. The experimental results show that hydrogen is gaseous and has strong diffusion, and increasing the injection pressure has a slight direct effect on the combustion rate and emissions, as shown in FIG. 3 and FIG. 4, and the BTE and NOx remain basically unchanged under different λ. Figure 2d , Figure 2e However, when the injection pressure is increased from 2 MPa to 8 MPa, the injection pulse width is significantly shortened (about 75%), the EOI position is advanced, and the feasible window of delayed injection is significantly expanded, avoiding the risk of injection obstruction and insufficient mixing near the top dead center due to back pressure, as shown in FIG. 5. The test bench and measurement arrangement are shown in FIG. 6. Figure 2c Figure 1 Therefore, the engineering significance of injection pressure in strategy optimization mainly lies in its role as a regulator of "pulse width-EOI window", rather than directly improving efficiency or emissions.

[0093] Example 3: Synergistic optimization of double injection (SEOI, SIP)

[0094] ​The combined calibration was conducted with fixed or grouped SIP (10% / 30% / 50%) and delayed SEOI from 100°CA BTDC to 20°CA BTDC at BMEP=5 bar, PSOI≈180°CA BTDC. The results show that the delay of SEOI can increase BTE by about 1.5% in lean region (λ=1.8, 2.3) and about 0.6% in rich region (λ=1.5, 1.0), as shown in Figure 3a . The NOx reduction in rich region is more than 47%, as shown in Figure 3b .

[0095] Meanwhile, the ignition delay and combustion duration (CA10-90) are shortened first, then lengthened, and shortened again with SEOI, corresponding to the secondary jet path transition from cylinder wall guided clockwise to no obvious guidance, and finally to piston guided counterclockwise, as shown in Figure 4a , Figure 4b .

[0096] Increasing SIP can increase BTE by no more than 1%, but can reduce NOx in rich region by more than 43%; when λ=2.3, increasing SIP from 0% to 30% can significantly increase cylinder pressure and HRR peak value and shorten combustion duration by about 19%, and when increasing to 50%, the marginal benefit is slow, as shown in Figure 5a , Figure 5b .

[0097] Example 4: Mapping online call and stability fallback

[0098] During operation, the control unit estimates λ and BMEP in real time and calls the combination of SOI, injection pressure, SEOI, and SIP from the mapping table. When the pulse width is limited and EOI / SEOI cannot be implemented according to the mapping, the injection pressure is first increased to shorten the pulse width and then moved backward; if COV>3% is monitored, the last stable strategy point is returned in time sequence and the disturbance amplitude is limited until stability is restored. The related strategy is shown in the trend and threshold relationship of Figures 3a-5b .

[0099] The above has been described by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present application is not limited to the above-mentioned manner. As long as various non-essential improvements are made using the method concept and technical solution of the present application; or without improvement, the above-mentioned concept and technical solution of the present application is directly applied to other occasions, all within the protection scope of the present application.

Claims

1. A method for coordinated optimization of injection strategies for a hydrogen direct injection internal combustion engine, characterized in that, The method comprises the steps of: S1, in the working condition domain of engine speed 1200 r / min, brake mean effective pressure BMEP 2-8 bar and excess air coefficient λ 1.0-2.3, taking cycle variation coefficient COV ≤ 3% as the stability criterion and taking combustion phase parameters CA10, CA50 and CA90 as the combustion duration discriminant; S2, constructing a fuel injection strategy mapping table through experimental calibration, the mapping table comprising the optimal combination relationship of single injection injection start angle SOI, injection pressure and double injection secondary injection end angle SEOI and secondary injection ratio SIP; S3, during engine operation, real-time acquisition of current λ and BMEP, query of the corresponding fuel injection strategy from the mapping table and execution.

2. The injection strategy co-optimization method for a hydrogen direct injection internal combustion engine according to claim 1, characterized in that, The calibration process of the single injection comprises: Under the working conditions of BMEP 2 bar, 5 bar and λ 1.0, 1.5 and 2.0, scanning SOI 30-200°CA BTDC (before top dead center), recording brake thermal efficiency BTE and NOx emission data; Wherein, when BMEP is 2 bar, SOI is set in the interval of 120-80°CA BTDC; When BMEP is 5 bar, SOI is set in the interval of 130-80°CA BTDC, and SOI is not later than 80°CA BTDC.

3. The injection strategy co-optimization method for a hydrogen direct injection internal combustion engine according to claim 1, characterized in that, The checking process of the injection pressure comprises: Comparing pulse width and combustion performance under injection pressures 2 MPa, 5 MPa and 8 MPa near fixed SOI; Wherein, when the injection pressure is increased from 2 MPa to 8 MPa, the pulse width is shortened by 75%, which provides timing allowance for delayed injection.

4. The method for the injection strategy co-optimization of a hydrogen direct injection internal combustion engine according to any one of claims 1 to 3, characterized in that, The calibration process of the double injection comprises: Fixing primary injection start angle PSOI 180°CA BTDC, scanning SEOI 100-20°CA BTDC under the working conditions of λ 1.0, 1.5, 1.8 and 2.3 and BMEP 5 bar, and cross-testing SIP 10%, 30% and 50%; Wherein, when λ is 1.8-2.3, the later angle in the SEOI range is adopted, and when λ is 1.0-1.5, the middle-later angle in the SEOI range is adopted.

5. A method for the synergistic optimization of injection strategies for a hydrogen direct injection internal combustion engine according to claim 4, characterized in that, SIP is set to 10%-30% when λ is 1.0-1.5, and SIP is set to 30% when λ is 2.

3.

6. The method for synergetic optimization of injection strategy for a hydrogen direct injection internal combustion engine according to any one of claims 1 to 3, characterized in that, The generation criteria of the mapping table are: Under equivalent working conditions, SOI is preferentially delayed to reduce NOx emission; Under lean working conditions, SEOI is preferentially delayed and combined with moderate SIP to speed up combustion; When injection pulse width is limited, the injection end angle (EOI or SEOI) position is insufficient, the pulse width is shortened by increasing the injection pressure, so as to ensure the feasible window of delayed injection and reduce the risk of back pressure blockage and insufficient mixture near the top dead center.

7. The method for synergetic optimization of injection strategy for a hydrogen direct injection internal combustion engine according to any one of claims 1 to 3, characterized in that, The motion form of the secondary jet in the double injection presents regular changes with the delay of SEOI: clockwise motion guided by the cylinder wall, gradual transition to unguided motion, and finally change to counterclockwise motion guided by the piston; the corresponding ignition lag and combustion duration show the change trend of first decreasing, then increasing, and then decreasing.

8. The method for synergetic optimization of injection strategy for a hydrogen direct injection internal combustion engine according to any one of claims 1 to 3, characterized in that, The injection strategy of the hydrogen direct injection engine is synergistically optimized by the following ways: Under equivalent conditions, the NOx emission is reduced by more than 80% by delaying SOI; Under lean conditions, the peak heat release rate is increased by about 14% and the combustion duration is shortened by about 19% by delaying SOI and setting SIP at about 30%. By increasing the injection pressure, the feasible window of delayed injection is expanded, thereby avoiding back pressure blockage and premixing deficiency near the top dead center, and improving combustion stability.

9. The method for the synergic optimization of the injection strategy for a hydrogen direct injection internal combustion engine according to any of claims 1 to 8, characterized in that, Further comprising steps: S4, when the injection strategy causes COV> 3%, fallback to the last stable strategy point.

Images