A method for optimizing pilot injection of a diesel / methanol dual direct injection engine

Abstract

The present application relates to a kind of diesel / methanol double direct injection engine pilot oil injection cooperative optimization method, first by gradient calibration locking the optimal reference interval of pilot oil injection pressure, combined with full working condition MAP diagram completes basic parameter pre-matching;Again, pre-injection timing, pre-injection equivalence ratio are sequentially subjected to multi-objective iterative optimization, with power output, thermal efficiency, fuel consumption rate and NO x Emission as cooperative constraint condition, filter out the optimal adaptive combination of three groups of pilot oil injection core parameters, finally complete the parameter self-adaptive calibration of full working condition domain.The present application effectively solves the problem that power emission imbalance and poor calibration adaptability easily occur when pilot oil parameters of existing DMDDI engine are optimized alone, has very strong engineering landing practicability, can directly adapt to the calibration upgrade demand of vehicle, generator set and other multi-scene DMDDI engine.

Description

Technical Field

[0001] This invention belongs to the field of combustion control technology for marine low-speed two-stroke dual-fuel engines, and particularly relates to a method for coordinating and optimizing fuel injection in a diesel / methanol dual direct injection engine. Background Technology

[0002] Under high methanol substitution rates, methanol's low reactivity, high latent heat of vaporization, and the large combustion space of large-bore, low-speed engines make methanol ignition and stable combustion highly sensitive to pilot fuel injection strategies. Existing technologies primarily optimize methanol injection pressure, injection timing, or injection duration, neglecting the synergistic effect of pilot fuel injection pressure and segmented injection strategies. If the pilot fuel injection pressure is too low, the pilot fuel spray momentum is insufficient, failing to effectively cover the main methanol combustion zone, easily leading to insufficient ignition capacity and prolonged combustion duration. Conversely, if the pilot fuel injection pressure is too high, it may cause excessive spray penetration, an increased near-wall fuel-rich zone, and increased heat transfer losses, thereby weakening combustion economy and increasing nitrogen oxide emissions.

[0003] Furthermore, existing pilot fuel injection strategies mostly employ single injection or fixed segmented injection parameters, lacking a systematic method for determining these parameters under high methanol substitution rates. The timing and mass ratio of pilot fuel injection directly affect the main injection's ignition capability, the subsequent heat release process, the distribution of high-temperature zones, and nitrogen oxide emissions. If the pilot fuel is injected too early, it tends to strongly couple with the methanol main combustion stage, which, while helping to improve local reactivity, may lead to an increase in in-cylinder peak pressure, pressure rise rate, and local high-temperature zones. If the pilot fuel is injected too late, it mainly acts on the later stages of combustion, which, while potentially reducing nitrogen oxide emissions, may also cause enhanced afterburning, combustion phase lag, and decreased combustion efficiency. Therefore, establishing a synergistic optimization method that can sequentially determine the pilot fuel injection pressure, pilot fuel injection timing, and pilot fuel injection mass ratio under high methanol substitution conditions is a technical problem that needs to be solved in the injection control and engineering calibration of diesel / methanol dual direct injection large-bore engines. Summary of the Invention

[0004] (a) Purpose of the invention To overcome the above shortcomings, the present invention aims to provide a method for coordinating and optimizing fuel injection in a diesel / methanol dual direct injection engine, so as to solve the above technical problems.

[0005] (II) Technical Solution To achieve the above objectives, the technical solution provided in this application is as follows: A method for co-optimizing pilot fuel injection in a diesel / methanol dual direct injection engine includes the following steps: S1 Engine Object and Parameter Acquisition: Acquire engine structural parameters, operating condition parameters, methanol injection parameters, and pilot fuel injection parameters; S2 Methanol Substitution Rate Calculation and Establishment and Verification of Combustion Analysis Model: Calculate the methanol substitution rate (MSR), determine whether it is under high methanol substitution rate conditions, fix the methanol direct injection strategy, and control the MSR range to 80%-95%; establish a combustion analysis model for a diesel / methanol dual direct injection engine, and perform grid independence verification and experimental data calibration. S3 Engine Performance, Combustion, and Emission Parameter Calculation: Calculation of Indicated Power Indicating thermal efficiency Equivalent indicated fuel consumption rate Combustion phase index / / and maximum pressure rise rate ; S4 Pilot fuel injection pressure PFIP optimization: Set pilot fuel injection pressure candidate values, calculate performance, combustion and emission parameters under different PFIPs, and determine target PFIP candidate values; S5 ignition fuel post-injection timing optimization: in the target Below, set candidate values ​​for the post-spray timing and calculate different... Based on parameters such as combustion phase, performance, and NOx emissions, the target is determined. Candidate values; S6 ignition fuel post-injection mass ratio optimization: Under the premise of determined injection pressure and post-injection time, the optimal post-injection mass ratio is determined by traversing the candidate set through simulation calculation and matching the scenario priority under the safety threshold constraint. S7 pilot fuel injection segmented control parameter output and application: Output the final optimized combination of control parameters: target pilot fuel injection pressure PFIPs, target pilot fuel post-injection time PPIton, target pilot fuel post-injection mass ratio PIMRe, and fixed methanol injection parameter MI.

[0006] Preferably, S1 specifically includes: S1.1: Obtain the structural parameters and operating condition parameters of the diesel / methanol dual direct injection large-bore engine, including at least the cylinder diameter, piston stroke, compression ratio, rated speed, rated power, intake valve closing time, exhaust valve opening time, number of methanol direct injection injectors, number of pilot fuel direct injection injectors, methanol injection orifice diameter, and pilot fuel injection orifice diameter; the operating condition parameters include at least the engine load, engine speed, intake pressure, intake temperature, cylinder pressure, cylinder volume, and emission data; S1.2: Based on the structural parameters obtained in step S1.1, a methanol direct injection injector and a pilot fuel direct injection injector are installed on the cylinder head. The methanol direct injection injector is used to directly inject methanol main fuel into the cylinder near or after top dead center. The pilot fuel direct injection injector is used to inject pilot fuel and form a high-temperature and high-activity ignition zone in the cylinder. The methanol direct injection injector and the pilot fuel direct injection injector are symmetrically arranged around the cylinder axis so that the high-temperature reaction zone formed by the pilot fuel spray and the methanol spray action zone have controllable spatial overlap. S1.3: Based on the engine object and injection system parameters obtained in steps S1.1 and S1.2, determine the set of injection parameters to be optimized: ; in, This represents the set of injection parameters to be optimized. Indicates the fuel injection pressure; Indicates the timing of the main fuel injection; Indicates the mass of pilot fuel injection within a single work cycle; Indicates the timing of the fuel injection after ignition; The set of injection parameters obtained in step S1 represents the post-injection mass of the pilot fuel within a single working cycle. This serves as input for subsequent steps S2 to S6 to calculate the methanol substitution rate, evaluate engine performance, and determine the target injection parameter combination.

[0007] Preferably, S2 specifically includes: S2.1: Based on the engine object obtained in step S1, determine the methanol substitution rate, and define the methanol substitution rate as the proportion of heat released by methanol combustion to the total heat input from methanol and pilot fuel: ; in, Indicates the methanol substitution rate; This indicates the mass of methanol injected within a single work cycle; This indicates the lower heating value of methanol; Indicates the mass of pilot fuel injected within a single work cycle; This indicates the lower heating value of the pilot fuel; S2.2: When When the methanol injection rate is within a preset range of 80% to 95%, the engine is determined to be operating at a high methanol substitution rate, and a fixed methanol direct injection strategy is established. This strategy includes at least one of the following: methanol injection pressure, methanol injection timing, methanol injection duration, methanol injection quality, and the number of activated methanol injectors. When it is not within the preset range, adjust or make Enter the preset range; S2.3: Based on the engine structural parameters, operating parameters, and fuel parameters obtained in step S1, and the high methanol substitution rate operating conditions obtained in step S2.2, a combustion analysis model for a diesel / methanol dual direct injection engine is established. The combustion analysis model includes at least a cylinder, piston, cylinder head, scavenging air box, scavenging port, exhaust valve, exhaust passage, methanol direct injection injector, and pilot fuel direct injection injector. The combustion analysis model is used to simulate in-cylinder gas flow, fuel spray, droplet evaporation, fuel / air mixing, pilot fuel ignition, methanol combustion, wall heat transfer, combustion model, nitrogen oxide generation model, and diesel / methanol chemical reaction mechanism. It is used to calculate in-cylinder pressure, heat release rate, temperature distribution, indicated power, indicated thermal efficiency, equivalent indicated fuel consumption rate, and nitrogen oxide emissions under different injection parameter combinations. S2.4: Verify the mesh independence of the combustion analysis model and check the experimental data. When the changes in key combustion parameters under different basic mesh sizes or local densification schemes are less than the preset range, and the error between the simulation results and the experimental data meets the preset requirements, the combustion analysis model is confirmed to be usable for subsequent injection strategy optimization. The high methanol substitution rate operating conditions obtained in step S2 and the verified combustion analysis model serve as the calculation basis for steps S3 to S6.

[0008] Preferably, S3 specifically includes: S3.1: Based on the combustion analysis model obtained in step S2, calculate the indicated work within a single working cycle: ; in, Indicates the indicated work done within a single work cycle; Indicates the time when the intake valve closes; Indicates the opening time of the exhaust valve; Indicates the pressure inside the engine cylinder; Indicates cylinder volume; A small component representing the cylinder volume; S3.2: Based on the indicated power obtained in step S3.1 Calculate the indicated thermal efficiency: ; in, Indicates thermal efficiency; Indicates the indicated work done within a single work cycle; This indicates the mass of methanol injected within a single work cycle; This indicates the lower heating value of methanol; Indicates the mass of pilot fuel injected within a single work cycle; This indicates the lower heating value of the pilot fuel; S3.3: Based on the indicated power obtained in step S3.1 Calculate the equivalent indicated fuel consumption rate: ; in, This indicates the equivalent indicated fuel consumption rate, expressed in g / kWh. This indicates the mass of methanol injected within a single work cycle, in kg. This indicates the lower heating value of methanol; This indicates the mass of pilot fuel injected within a single work cycle, in kg. This indicates the lower heating value of the pilot fuel; Indicates the indicated work done within a single work cycle; S3.4: Extract combustion phase indicators , and ,in, , and These represent the crankshaft angles at which the accumulated heat release reaches 10%, 50%, and 90% of the total heat release, respectively. The combustion duration is expressed as: ; S3.5: Extraction of maximum pressure rise rate: ; in This represents the maximum pressure rise rate, expressed in MPa / °CA.

[0009] Preferably, S4 specifically includes: S4.1: Based on the high methanol substitution rate operating conditions and fixed methanol direct injection strategy determined in step S2, set a candidate set of pilot fuel injection pressures: ; in, Represents the candidate set of ignition fuel injection pressure; This represents the a-th candidate value for pilot fuel injection pressure; a represents the candidate value number for pilot fuel injection pressure; A represents the total number of candidate values ​​for pilot fuel injection pressure. S4.2: Will Each of them Input the combustion analysis model obtained in step S2, and calculate the corresponding in-cylinder pressure, heat release rate, temperature distribution, ITE, EISFC, IP, NOx, etc. , , And the parameters of CD; S4.3: Under the condition that the maximum in-cylinder pressure and the maximum pressure rise rate meet the preset safety threshold, determine the target pilot fuel injection pressure based on at least two parameters among the indicated thermal efficiency, equivalent indicated fuel consumption rate, in-cylinder pressure, heat release rate, combustion phase, high-temperature zone volume fraction, and nitrogen oxide emissions corresponding to each candidate pressure value. ; S4.4: When prioritizing indicated power, indicated thermal efficiency, and equivalent indicated fuel consumption rate in engineering applications, a medium pilot fuel injection pressure is selected as the target pilot fuel injection pressure. The target pilot fuel injection pressure obtained in step S4... This serves as a fixed input for optimizing the post-injection of pilot fuel in steps S5 and S6.

[0010] Preferably, S5 specifically includes: S5.1: Target pilot fuel injection pressure obtained in step S4 The total injection mass of pilot fuel is divided into the main injection mass and the post-injection mass, and the proportion of the post-injection mass is defined as follows: ; in, Indicates the mass ratio of ignition fuel injected after ignition; Indicates the mass of fuel injected after ignition within a single work cycle; Indicates the mass of pilot fuel injection within a single work cycle; S5.2: Fixed in step S5.1 Under the condition of preset values, set a candidate set for the timing of the fuel injection after the pilot fuel: ; in, This represents the candidate set of times for the fuel injection after ignition; represents the b-th candidate value for the post-injection time of the ignition fuel; b represents the candidate value number for the post-injection time of the ignition fuel; B represents the total number of candidate values ​​for the post-injection time of the ignition fuel. S5.3: Will Each of them Input the combustion analysis model obtained in step S2, and calculate the corresponding in-cylinder pressure, heat release rate, combustion phase, high-temperature zone distribution, and nitrogen oxide emission parameters; S5.4: Determine the target pilot fuel injection timing provided that the indicated thermal efficiency decrease does not exceed the preset limit and the maximum in-cylinder pressure and maximum pressure rise rate meet the preset safety threshold. ; S5.5: For operating conditions that balance engine performance and nitrogen oxide emissions, the target timing for priming fuel injection is 10°CA to 14°CA after top dead center.

[0011] Preferably, S6 specifically includes: S6.1: Target pilot fuel injection pressure obtained in step S4 The target ignition fuel injection time obtained in step S5 Set a candidate set for the mass ratio of fuel injected after ignition: in, This represents the candidate set of post-injection fuel mass ratios. This represents the c-th candidate value for the mass ratio of the ignition fuel after injection; C represents the candidate value number for the mass ratio of the ignition fuel after injection; C represents the total number of candidate values ​​for the mass ratio of the ignition fuel after injection. S6.2: Will Each of them Input the combustion analysis model obtained in step S2 and calculate the corresponding ITE, EISFC, IP, NOx, in-cylinder pressure, heat release rate, temperature distribution and combustion phase evaluation parameters; S6.3: Under the condition that the maximum in-cylinder pressure and the maximum pressure rise rate meet the preset safety threshold, determine the target pilot fuel injection mass ratio based on performance, combustion, and emission parameters. ; S6.4: When prioritizing the reduction of nitrogen oxide emissions, the target fuel injection post-injection mass ratio is preferably 10% to 30%; when prioritizing engine performance, the target fuel injection post-injection mass ratio is preferably 50% to 70%.

[0012] Preferably, S7 specifically includes: S7.1: Based on the target parameters obtained in steps S4, S5, and S6, a combination of pilot fuel injection segment control parameters is formed: ; in, This indicates the combination of control parameters for segmented injection of the target pilot fuel; Indicates the target fuel injection pressure; Indicates the timing of the main fuel injection; Indicates the target ignition fuel main injection mass; Indicates the timing of the fuel injection after the target is ignited; Indicates the mass of fuel injected after the target is ignited; S7.2: Based on the definition of PIMR in step S5, calculate the target pilot fuel main injection mass and the target pilot fuel post-injection mass: ; ; in, Indicates the mass of fuel injected after the target is ignited; Indicates the mass ratio of the target ignition fuel injected afterward; Indicates the mass of pilot fuel injected within a single work cycle; Indicates the target ignition fuel main injection mass; S7.3: Write the target pilot fuel segmented injection control parameters into the engine injection control unit or calibration parameter table so that the pilot fuel direct injection injector performs segmented injection control according to the target pilot fuel injection pressure, pilot fuel main injection time, target pilot fuel post-injection time, target pilot fuel main injection mass and target pilot fuel post-injection mass; S7.4: If the engine load, speed, methanol substitution rate, intake state or emission limit changes during engine operation, steps S2 to S7 are re-executed to update the target pilot fuel segment injection control parameter combination in order to achieve adaptive calibration of the injection strategy under different operating conditions.

[0013] Beneficial effects: 1. Improve the systematicness and repeatability of pilot fuel injection strategy calibration under high methanol substitution rate conditions. This invention does not adjust a single injection parameter individually, but rather, under high methanol substitution rate conditions, it forms a complete injection strategy calibration process in the order of methanol substitution rate determination, combustion analysis model establishment, pilot fuel injection pressure optimization, pilot fuel post-injection timing optimization, and pilot fuel post-injection mass ratio optimization. This allows the pilot fuel segmented injection parameters under different operating conditions to be obtained according to clear steps.

[0014] 2. Improve the ignition stability and combustion economy of methanol as the main fuel. This invention optimizes the pilot fuel injection pressure to create an appropriate high-temperature, high-activity ignition zone within the cylinder, which helps enhance the stable ignition capability of the methanol main fuel. Simultaneously, it avoids the problems of insufficient ignition capability due to excessively low pilot fuel injection pressure, or excessively high injection pressure leading to excessive spray penetration, an increased near-wall fuel-rich zone, and increased heat loss from the wall surface.

[0015] 3. Reduce the concentration of localized high-temperature zones and the tendency for nitrogen oxide formation, and achieve a controllable trade-off between performance and emissions. This invention optimizes the timing and mass ratio of the pilot fuel injection, adjusts the coupling degree between the pilot fuel injection and the methanol main combustion stage and the later stage of combustion, improves the later heat release process and the distribution of high-temperature zones, and reduces the tendency for NOx formation; at the same time, through the fuel mass distribution between the main injection and the pilot injection, it balances the main injection ignition capability, the later combustion regulation effect, and combustion economy. Attached Figure Description

[0016] Figure 1 This is a diagram of the pilot fuel segment injection coordinated optimization method of the present invention; Figure 2 This is a schematic diagram of the injection system of a diesel / methanol dual direct injection engine; Figure 3 This is a graph verifying the irrelevance of the combustion analysis model; Figure 4 This is a typical load verification diagram for a combustion analysis model; Figure 5 This is a timing diagram of the main fuel injection and subsequent fuel injection. Figure 6 This is the logic diagram for optimizing the coordinated pressure of fuel injection; Figure 7 This is a flowchart of fuel parameter optimization for a 6G50ME application example; Figure 8 These are performance and emission curves of the DMDDI engine under different PFIP strategies; Figure 9 These are the performance and emission curves of the DMDDI engine under different PIT strategies; Figure 10 These are the performance and emission curves of the DMDDI engine under different PIMR strategies. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the following detailed embodiments are described in conjunction with the appendix. Figure 1-7 The present invention will be described in further detail below. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0018] This invention provides a method for coordinating and optimizing pilot fuel injection in a diesel / methanol dual direct injection engine, comprising the following steps: S1 Engine Object and Parameter Acquisition: Acquire engine structural parameters, operating condition parameters, methanol injection parameters, and pilot fuel injection parameters; Preferably, S1 specifically includes: S1.1: Obtain the structural parameters and operating condition parameters of the diesel / methanol dual direct injection large-bore engine, including at least the cylinder diameter, piston stroke, compression ratio, rated speed, rated power, intake valve closing time, exhaust valve opening time, number of methanol direct injection injectors, number of pilot fuel direct injection injectors, methanol injection orifice diameter, and pilot fuel injection orifice diameter; the operating condition parameters include at least the engine load, engine speed, intake pressure, intake temperature, cylinder pressure, cylinder volume, and emission data; S1.2: Based on the structural parameters obtained in step S1.1, a methanol direct injection injector and a pilot fuel direct injection injector are installed on the cylinder head. The methanol direct injection injector is used to directly inject methanol main fuel into the cylinder near or after top dead center. The pilot fuel direct injection injector is used to inject pilot fuel and form a high-temperature and high-activity ignition zone in the cylinder. The methanol direct injection injector and the pilot fuel direct injection injector are symmetrically arranged around the cylinder axis so that the high-temperature reaction zone formed by the pilot fuel spray and the methanol spray action zone have controllable spatial overlap. S1.3: Based on the engine object and injection system parameters obtained in steps S1.1 and S1.2, determine the set of injection parameters to be optimized: ; in, This represents the set of injection parameters to be optimized. Indicates the fuel injection pressure; Indicates the timing of the main fuel injection; Indicates the mass of pilot fuel injection within a single work cycle; Indicates the timing of the fuel injection after ignition; The set of injection parameters obtained in step S1 represents the post-injection mass of the pilot fuel within a single working cycle. This serves as input for subsequent steps S2 to S6 to calculate the methanol substitution rate, evaluate engine performance, and determine the target injection parameter combination.

[0019] S2 Methanol Substitution Rate Calculation and Establishment and Verification of Combustion Analysis Model: Calculate the methanol substitution rate (MSR), determine whether it is under high methanol substitution rate conditions, fix the methanol direct injection strategy, and control the MSR range to 80%-95%; establish a combustion analysis model for a diesel / methanol dual direct injection engine, and perform grid independence verification and experimental data calibration. Preferably, S2 specifically includes: S2.1: Based on the engine object obtained in step S1, determine the methanol substitution rate, and define the methanol substitution rate as the proportion of heat released by methanol combustion to the total heat input from methanol and pilot fuel: ; in, Indicates the methanol substitution rate; This indicates the mass of methanol injected within a single work cycle; This indicates the lower heating value of methanol; Indicates the mass of pilot fuel injected within a single work cycle; This indicates the lower heating value of the pilot fuel; S2.2: When When the methanol injection rate is within a preset range of 80% to 95%, the engine is determined to be operating at a high methanol substitution rate, and a fixed methanol direct injection strategy is established. This strategy includes at least one of the following: methanol injection pressure, methanol injection timing, methanol injection duration, methanol injection quality, and the number of activated methanol injectors. When it is not within the preset range, adjust or make Entering the preset range; preferably, 90% is used to highlight the dominant role of methanol as the primary fuel in the total input heat.

[0020] S2.3: Based on the engine structural parameters, operating parameters, and fuel parameters obtained in step S1, and the high methanol substitution rate operating conditions obtained in step S2.2, a combustion analysis model for a diesel / methanol dual direct injection engine is established. The combustion analysis model includes at least a cylinder, piston, cylinder head, scavenging air box, scavenging port, exhaust valve, exhaust passage, methanol direct injection injector, and pilot fuel direct injection injector. The combustion analysis model is used to simulate in-cylinder gas flow, fuel spray, droplet evaporation, fuel / air mixing, pilot fuel ignition, methanol combustion, wall heat transfer, combustion model, nitrogen oxide generation model, and diesel / methanol chemical reaction mechanism. It is used to calculate in-cylinder pressure, heat release rate, temperature distribution, indicated power, indicated thermal efficiency, equivalent indicated fuel consumption rate, and nitrogen oxide emissions under different injection parameter combinations. S2.4: Verify the mesh independence of the combustion analysis model and check the experimental data. When the changes in key combustion parameters under different basic mesh sizes or local densification schemes are less than the preset range, and the error between the simulation results and the experimental data meets the preset requirements, the combustion analysis model is confirmed to be usable for subsequent injection strategy optimization. The high methanol substitution rate operating conditions obtained in step S2 and the verified combustion analysis model serve as the calculation basis for steps S3 to S6.

[0021] S3 Engine Performance, Combustion, and Emission Parameter Calculation: Calculation of Indicated Power Indicating thermal efficiency Equivalent indicated fuel consumption rate Combustion phase index / / and maximum pressure rise rate ; Preferably, S3 specifically includes: S3.1: Based on the combustion analysis model obtained in step S2, calculate the indicated work within a single working cycle: ; in, Indicates the indicated work done within a single work cycle; Indicates the time when the intake valve closes; Indicates the opening time of the exhaust valve; Indicates the pressure inside the engine cylinder; Indicates cylinder volume; A small component representing the cylinder volume; S3.2: Based on the indicated power obtained in step S3.1 Calculate the indicated thermal efficiency: ; in, Indicates thermal efficiency; Indicates the indicated work done within a single work cycle; This indicates the mass of methanol injected within a single work cycle; This indicates the lower heating value of methanol; Indicates the mass of pilot fuel injected within a single work cycle; This indicates the lower heating value of the pilot fuel; S3.3: Based on the indicated power obtained in step S3.1 Calculate the equivalent indicated fuel consumption rate: ; in, This indicates the equivalent indicated fuel consumption rate, expressed in g / kWh. This indicates the mass of methanol injected within a single work cycle, in kg. This indicates the lower heating value of methanol; This indicates the mass of pilot fuel injected within a single work cycle, in kg. This indicates the lower heating value of the pilot fuel; Indicates the indicated work done within a single work cycle; S3.4: Extract combustion phase indicators , and ,in, , and These represent the crankshaft angles at which the accumulated heat release reaches 10%, 50%, and 90% of the total heat release, respectively. The combustion duration is expressed as: ; S3.5: Extraction of maximum pressure rise rate: ; in This represents the maximum pressure rise rate, expressed in MPa / °CA.

[0022] S4 Pilot fuel injection pressure PFIP optimization: Set pilot fuel injection pressure candidate values, calculate performance, combustion and emission parameters under different PFIPs, and determine target PFIP candidate values; Preferably, S4 specifically includes: S4.1: Based on the high methanol substitution rate operating conditions and fixed methanol direct injection strategy determined in step S2, set a candidate set of pilot fuel injection pressures: ; in, Represents the candidate set of ignition fuel injection pressure; This represents the a-th candidate value for pilot fuel injection pressure; a represents the candidate value number for pilot fuel injection pressure; A represents the total number of candidate values ​​for pilot fuel injection pressure. S4.2: Will Each of them Input the combustion analysis model obtained in step S2, and calculate the corresponding in-cylinder pressure, heat release rate, temperature distribution, ITE, EISFC, IP, NOx, etc. , , And the parameters of CD; S4.3: Under the condition that the maximum in-cylinder pressure and the maximum pressure rise rate meet the preset safety threshold, determine the target pilot fuel injection pressure based on at least two parameters among the indicated thermal efficiency, equivalent indicated fuel consumption rate, in-cylinder pressure, heat release rate, combustion phase, high-temperature zone volume fraction, and nitrogen oxide emissions corresponding to each candidate pressure value. ; S4.4: When prioritizing indicated power, indicated thermal efficiency, and equivalent indicated fuel consumption rate in engineering applications, a medium pilot fuel injection pressure is selected as the target pilot fuel injection pressure. For a large-bore low-speed diesel / methanol dual direct injection engine with a rated power of approximately 6400kW, a rated speed of approximately 80.4rpm, and a compression ratio of approximately 29.6, a target pilot fuel injection pressure of 60MPa is preferred. The target pilot fuel injection pressure obtained in step S4... This serves as a fixed input for optimizing the post-injection of pilot fuel in steps S5 and S6.

[0023] S5 ignition fuel post-injection timing optimization: in the target Below, set candidate values ​​for the post-spray timing and calculate different... Based on parameters such as combustion phase, performance, and NOx emissions, the target is determined. Candidate values; Preferably, S5 specifically includes: S5.1: Target pilot fuel injection pressure obtained in step S4 The total injection mass of pilot fuel is divided into the main injection mass and the post-injection mass, and the proportion of the post-injection mass is defined as follows: ; in, Indicates the mass ratio of ignition fuel injected after ignition; Indicates the mass of fuel injected after ignition within a single work cycle; Indicates the mass of pilot fuel injection within a single work cycle; S5.2: Fixed in step S5.1 Under the condition of preset values, set a candidate set for the timing of the fuel injection after the pilot fuel: ; in, This represents the candidate set of times for the fuel injection after ignition; Let b represent the candidate value for the post-ignition fuel injection time; b represents the candidate value number for the post-ignition fuel injection time; B represents the total number of candidate values ​​for the post-ignition fuel injection time; preferably, the candidate set for the post-ignition fuel injection time includes 6°CA, 8°CA, 10°CA, 14°CA and 18°CA after the top dead center.

[0024] S5.3: Will Each of them Input the combustion analysis model obtained in step S2, and calculate the corresponding in-cylinder pressure, heat release rate, combustion phase, high-temperature zone distribution, and nitrogen oxide emission parameters; S5.4: Determine the target pilot fuel injection timing provided that the indicated thermal efficiency decrease does not exceed the preset limit and the maximum in-cylinder pressure and maximum pressure rise rate meet the preset safety threshold. ; S5.5: For operating conditions that balance engine performance and nitrogen oxide emissions, the target timing for priming fuel injection is 10°CA to 14°CA after top dead center.

[0025] S6 ignition fuel post-injection mass ratio optimization: Under the premise of determined injection pressure and post-injection time, the optimal post-injection mass ratio is determined by traversing the candidate set through simulation calculation and matching the scenario priority under the safety threshold constraint. Preferably, S6 specifically includes: S6.1: Target pilot fuel injection pressure obtained in step S4 The target ignition fuel injection time obtained in step S5 Set a candidate set for the mass ratio of fuel injected after ignition: in, This represents the candidate set of post-injection fuel mass ratios. This represents the c-th candidate value for the post-injection mass ratio of the ignition fuel; C represents the candidate value number for the post-injection mass ratio of the ignition fuel; C represents the total number of candidate values ​​for the post-injection mass ratio of the ignition fuel; preferably, Including 10%, 30%, 50%, 70%, and 90%.

[0026] S6.2: Will Each of them Input the combustion analysis model obtained in step S2 and calculate the corresponding ITE, EISFC, IP, NOx, in-cylinder pressure, heat release rate, temperature distribution and combustion phase evaluation parameters; S6.3: Under the condition that the maximum in-cylinder pressure and the maximum pressure rise rate meet the preset safety threshold, determine the target pilot fuel injection mass ratio based on performance, combustion, and emission parameters. ; S6.4: When prioritizing the reduction of nitrogen oxide emissions, the target fuel injection post-injection mass ratio is preferably 10% to 30%; when prioritizing engine performance, the target fuel injection post-injection mass ratio is preferably 50% to 70%.

[0027] S7 pilot fuel injection segmented control parameter output and application: Output the final optimized combination of control parameters: target pilot fuel injection pressure PFIPs, target pilot fuel post-injection time PPIton, target pilot fuel post-injection mass ratio PIMRe, and fixed methanol injection parameter MI.

[0028] Preferably, S7 specifically includes: S7.1: Based on the target parameters obtained in steps S4, S5, and S6, a combination of pilot fuel injection segment control parameters is formed: ; in, This indicates the combination of control parameters for segmented injection of the target pilot fuel; Indicates the target fuel injection pressure; Indicates the timing of the main fuel injection; Indicates the target ignition fuel main injection mass; Indicates the timing of the fuel injection after the target is ignited; Indicates the mass of fuel injected after the target is ignited; S7.2: Based on the definition of PIMR in step S5, calculate the target pilot fuel main injection mass and the target pilot fuel post-injection mass: ; ; in, Indicates the mass of fuel injected after the target is ignited; Indicates the mass ratio of the target ignition fuel injected afterward; Indicates the mass of pilot fuel injected within a single work cycle; Indicates the target ignition fuel main injection mass; S7.3: Write the target pilot fuel segmented injection control parameters into the engine injection control unit or calibration parameter table so that the pilot fuel direct injection injector performs segmented injection control according to the target pilot fuel injection pressure, pilot fuel main injection time, target pilot fuel post-injection time, target pilot fuel main injection mass and target pilot fuel post-injection mass; S7.4: If the engine load, speed, methanol substitution rate, intake state or emission limit changes during engine operation, steps S2 to S7 are re-executed to update the target pilot fuel segment injection control parameter combination in order to achieve adaptive calibration of the injection strategy under different operating conditions.

[0029] The following are relevant application examples: The 6G50ME low-speed two-stroke diesel / methanol dual direct injection large-bore engine is used as the application example. This engine adopts methanol direct injection and pilot fuel direct injection, with methanol as the main fuel and pilot fuel as the ignition fuel. Some engine parameters are shown in Table 1. The methanol direct injection injector and the pilot fuel direct injection injector are arranged on the cylinder head to realize the injection of methanol as the main fuel and the formation of the high-activity ignition zone of the pilot fuel.

[0030] Table 1. Parameters of the 6G50ME diesel / methanol dual direct injection large-bore engine In this application example, the engine operates under high methanol substitution rate conditions, with a methanol substitution rate of approximately 90%. A fixed methanol direct injection strategy is adopted, including methanol injection mass, methanol injection pressure, methanol injection timing, and methanol injection duration. Based on this, the pilot fuel injection pressure, pilot fuel post-injection timing, and pilot fuel post-injection mass ratio are optimized sequentially.

[0031] First, a combustion analysis model for a 6G50ME diesel / methanol dual direct injection large-bore engine was established, with some sub-models shown in Table 2. The model's computational domain includes the cylinder, piston, cylinder head, combustion chamber, methanol direct injection injector, and pilot fuel direct injection injector. The model is used to simulate in-cylinder flow, methanol spray, pilot fuel spray, fuel evaporation, mixing, ignition and combustion, wall heat transfer, and NOx formation processes. After verification through mesh independence and experimental data validation, the model was used to optimize the pilot fuel segmented injection strategy.

[0032] Table 2. Combustion analysis model using sub-models In the pilot fuel injection pressure optimization stage, 20 MPa, 40 MPa, 60 MPa, 80 MPa, and 100 MPa were set as candidate pressure values. In-cylinder pressure, heat release rate, indicated power, indicated thermal efficiency, equivalent indicated fuel consumption rate, combustion phase, and nitrogen oxide emissions were calculated under different pilot fuel injection pressures. The results show that at lower pilot fuel injection pressures, pilot fuel atomization and ignition capabilities are insufficient, and the combustion process is relatively delayed; at higher pilot fuel injection pressures, spray penetration and localized high-temperature zones may be enhanced. Considering power performance, economy, and emission characteristics, the target pilot fuel injection pressure is preferably 60 MPa.

[0033] In the optimization stage of pilot fuel post-injection timing, the target pilot fuel injection pressure was fixed at 60 MPa, and the total injection mass of pilot fuel was divided into main injection mass and post-injection mass. Candidate post-injection times were set at 6°CA, 8°CA, 10°CA, 14°CA, and 18°CA after top dead center. In-cylinder pressure, heat release rate, combustion phase, performance parameters, and NOx emissions were calculated at different post-injection times. The results show that appropriately delaying the pilot fuel post-injection time can regulate the later heat release process, suppress the concentration of local high-temperature zones, and reduce the tendency for NOx formation; however, excessive delay may lead to enhanced afterburning and decreased combustion efficiency. Therefore, the target pilot fuel post-injection time is preferably 10°CA to 14°CA after top dead center, and more preferably 14°CA after top dead center.

[0034] In the optimization stage of the pilot fuel post-injection mass ratio, the target pilot fuel injection pressure was fixed at 60 MPa, and the target pilot fuel post-injection time was fixed at 14°CA after top dead center. 10%, 30%, 50%, 70%, and 90% were set as candidate post-injection mass ratios. The indicated thermal efficiency, equivalent indicated fuel consumption rate, indicated power, NOx emissions, in-cylinder pressure, heat release rate, and combustion phase were calculated for different post-injection mass ratios. The results show that a lower post-injection mass ratio is beneficial for maintaining the main injection ignition capability and reducing NOx emissions, while a higher post-injection mass ratio helps enhance the later heat release regulation effect, but may lead to an increase in the local high-temperature zone or combustion tailing. Therefore, under NOx emission priority conditions, the target pilot fuel post-injection mass ratio is preferably 10% to 30%; under performance priority conditions, the target pilot fuel post-injection mass ratio is preferably 50% to 70%.

[0035] Ultimately, a set of pilot fuel segmented injection control parameters suitable for the 6G50ME diesel / methanol dual direct injection large-bore engine was formed, including target pilot fuel injection pressure, pilot fuel main injection timing, target pilot fuel post-injection timing, target pilot fuel main injection mass, and target pilot fuel post-injection mass.

[0036] like Figure 8 As shown, the power, energy efficiency, and emissions performance of this DMDDI engine under different PFIP strategies exhibit regular variation characteristics. For details, please refer to the corresponding performance curves. Power output performance: The engine indicated power (IP) gradually increases as PFIP increases from 20% to 60%, reaching a peak of about 4820kW at PFIP60. After further increasing PFIP from 60% to 100%, the indicated power shows a gradual downward trend. Overall, the power output remains at a relatively high level of over 4750kW throughout the entire range, demonstrating excellent power stability.

[0037] Thermal efficiency performance: The trend of the indicated thermal efficiency (ITE) is highly matched with the indicated power, reaching a peak efficiency of approximately 49.4% under PFIP60 conditions. The thermal efficiency remains above 48.5% throughout the entire PFIP adjustment range, achieving high-efficiency operation across the entire strategy range.

[0038] Fuel consumption performance: The indicated fuel economy (EISFC) first decreases and then increases with the increase of PFIP, and reaches the lowest value of about 162g / kWh under PFIP60 condition. Compared with the fuel consumption levels of PFIP20 and PFIP100 conditions, the fuel economy can be significantly optimized under the optimal condition.

[0039] Nitrogen oxide emissions performance: NO x Emissions increase monotonically with the increase of PFIP (Power-Integrated Product Protection) ratio, reaching the lowest level under PFIP20 condition. When PFIP is adjusted to 100%, emissions gradually increase to nearly 11.5 g / kWh. Emissions can be improved in terms of power, fuel efficiency, and NOx by adjusting PFIP parameters. x The emissions are matched to find the optimal balance range to suit different usage needs.

[0040] like Figure 9 As shown, this DMDDI engine underwent multi-condition parameter calibration tests for pre-injection timing (PIT), using the performance indicators of the basic operating condition (BASE) as a reference benchmark. The test results fully validated the feasibility and comprehensive benefits of this parameter optimization scheme: The engine's power and thermal efficiency performance is superior to the benchmark: Throughout the full PIT test range, the engine's indicated power IP (IP) remained above 4730kW, only slightly lower than the benchmark power value of 4820kW, demonstrating excellent power output stability. At the same time, the indicated thermal efficiency (ITE) remained above 48.5% throughout the range, with thermal efficiency approaching 49.2% in PIT6 and PIT8 conditions, only slightly lower than the benchmark thermal efficiency peak of 49.46%, maintaining an extremely high level of energy utilization throughout the entire test.

[0041] Fuel economy is positively optimized: the indicated specific fuel consumption (EISFC) under all PIT conditions is controlled within 165g / kWh, and reaches a low value of about 163.8g / kWh under PIT8 conditions. The deviation from the fuel consumption level of 162.04g / kWh under the benchmark condition is minimal. Stable control of fuel consumption is achieved within an acceptable engineering error range, and there is no problem of significant deterioration in fuel consumption.

[0042] NO x Significant improvements in emissions: compared to the baseline NO of 10.32 g / kWh. x Emission levels, except for PIT8 which is close to the baseline emission value, all other tested PIT conditions showed NO levels... xEmissions were all below baseline levels, with NO2 decreasing as PIT was further delayed from 10° to 18°. x Emissions can be gradually reduced to around 8g / kWh, achieving a significant reduction in nitrogen oxide emissions with almost no loss of power and thermal efficiency.

[0043] This PIT parameter adjustment scheme requires no modification to the engine hardware. Through calibration and optimization alone, it can significantly reduce NO while maintaining essentially the same power and fuel economy as the baseline operating conditions. x The emissions are fully compatible with the requirements for project implementation, and it has extremely high practical value and feasibility.

[0044] This invention calculates the methanol substitution rate (MSR) by considering the methanol injection mass, the pilot fuel injection mass, and their lower heating values. When the MSR is within a preset high methanol substitution rate range, a fixed methanol direct injection strategy is employed. Based on a combustion analysis model, the target pilot fuel injection pressure, the target pilot fuel post-injection timing, and the target pilot fuel post-injection mass ratio are determined sequentially. This avoids the lack of systematicity in traditional empirical or single-parameter calibration methods, thus improving the systematicness and repeatability of pilot fuel injection strategy calibration under high methanol substitution rate conditions.

[0045] like Figure 10 As shown, the performance and emission curves of the DMDDI engine under different PIMR strategies are presented. This DMDDI engine underwent full-gradient parameter calibration verification for the pre-injection equivalence ratio (PIMR), using the original manufacturer's baseline performance as a reference. The measured data fully demonstrates that this calibration optimization scheme can achieve synergistic optimization of performance and emissions without modifying the hardware structure, possessing extremely high engineering application value. High-level performance: The engine indicated power (IP) remained stable above 4720kW throughout the entire PIMR test range, reaching a peak of approximately 4790kW under PIMR70 conditions. It deviated only slightly from the benchmark power value of 4820kW, with no drastic fluctuations in power output throughout the test, fully covering the power requirements of normal operating conditions.

[0046] Thermal efficiency performance is close to the baseline optimal level: the indicated thermal efficiency (ITE) is maintained above 48.5% across the entire parameter adjustment range, and the thermal efficiency under PIMR10 and PIMR70 conditions is close to 49.2%, only slightly lower than the baseline thermal efficiency peak of 49.46%, maintaining extremely high energy utilization efficiency throughout the process.

[0047] Excellent fuel economy controllability: The indicated fuel consumption (EISFC) under all operating conditions is controlled within 165.5g / kWh, and the fuel consumption under PIMR10 and PIMR70 conditions is as low as about 163g / kWh. The deviation from the fuel consumption level of 162.04g / kWh under the benchmark operating condition is within the acceptable error range for engineering applications, and there is no problem of significant deterioration in fuel consumption.

[0048] NO x Ample room for emission optimization: Within the commonly used adjustment range of PIMR10 to PIMR50, NO x Emissions are far below the baseline level of 10.32 g / kWh, and can be controlled to a minimum of around 8 g / kWh. Emissions only slightly exceed the baseline value in the range above PIMR70. By combining with the previously verified PIT and PFIP for collaborative calibration, the system can flexibly adapt to the needs of different application scenarios in terms of power, thermal efficiency, fuel consumption and emissions, and quickly match the optimal operating range.

[0049] This invention sets multiple candidate values ​​for pilot fuel injection pressure under a fixed methanol direct injection strategy and determines the target pilot fuel injection pressure by combining combustion, performance, and emission parameters. Through a combustion analysis model, in-cylinder pressure, heat release rate, combustion phase, indicated thermal efficiency, equivalent indicated fuel consumption rate, maximum pressure rise rate, and nitrogen oxide emissions under different PFIP (Power Factor Injection) conditions are calculated. While meeting the constraints of maximum in-cylinder pressure and maximum pressure rise rate, a target pilot fuel injection pressure that balances ignition capability and combustion economy is determined, effectively improving the ignition stability and combustion economy of methanol as the primary fuel.

[0050] This invention establishes a stepwise optimization method for the timing and mass ratio of pilot fuel injection. Under a target pilot fuel injection pressure, multiple candidate values ​​for the injection timing are first set, and the target injection timing is determined based on combustion phase, engine performance indicators, in-cylinder pressure, and NOx emissions. Subsequently, under the target injection pressure and target injection timing, multiple candidate values ​​for the injection mass ratio are set, and the target injection mass ratio is determined based on parameters such as indicated thermal efficiency, equivalent indicated fuel consumption rate, NOx emissions, maximum in-cylinder pressure, and maximum pressure rise rate. This achieves synergistic optimization between combustion economy and emission control, reduces the concentration of local high-temperature zones and the tendency for NOx formation, and achieves a controllable trade-off between performance and emissions.

[0051] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for coordinating and optimizing fuel injection in a diesel / methanol dual direct injection engine, characterized in that, Includes the following steps: S1 Engine Object and Parameter Acquisition: Acquire engine structural parameters, operating condition parameters, methanol injection parameters, and pilot fuel injection parameters; S2 Methanol Substitution Rate Calculation and Establishment and Verification of Combustion Analysis Model: Calculate the methanol substitution rate (MSR), determine whether it is under high methanol substitution rate conditions, fix the methanol direct injection strategy, and control the MSR range to 80%-95%; establish a combustion analysis model for a diesel / methanol dual direct injection engine, and perform grid independence verification and experimental data calibration. S3 Engine Performance, Combustion, and Emission Parameter Calculation: Calculation of Indicated Power Indicating thermal efficiency Equivalent indicated fuel consumption rate Combustion phase index / / and maximum pressure rise rate ; S4 Pilot fuel injection pressure PFIP optimization: Set pilot fuel injection pressure candidate values, calculate performance, combustion and emission parameters under different PFIPs, and determine target PFIP candidate values; S5 ignition fuel post-injection timing optimization: in the target Below, set candidate values ​​for the post-spray timing and calculate different... Based on parameters such as combustion phase, performance, and NOx emissions, the target is determined. Candidate values; S6 ignition fuel post-injection mass ratio optimization: Under the premise of determined injection pressure and post-injection time, the optimal post-injection mass ratio is determined by traversing the candidate set through simulation calculation and matching the scenario priority under the safety threshold constraint. S7 pilot fuel injection segmented control parameter output and application: Output the final optimized combination of control parameters: target pilot fuel injection pressure PFIPs, target pilot fuel post-injection time PPIton, target pilot fuel post-injection mass ratio PIMRe, and fixed methanol injection parameter MI.

2. The method for coordinating and optimizing fuel injection in a diesel / methanol dual direct injection engine according to claim 1, characterized in that, S1 specifically includes: S1.1: Obtain the structural parameters and operating condition parameters of the diesel / methanol dual direct injection large-bore engine, including at least the cylinder diameter, piston stroke, compression ratio, rated speed, rated power, intake valve closing time, exhaust valve opening time, number of methanol direct injection injectors, number of pilot fuel direct injection injectors, methanol injection orifice diameter, and pilot fuel injection orifice diameter; the operating condition parameters include at least the engine load, engine speed, intake pressure, intake temperature, cylinder pressure, cylinder volume, and emission data; S1.2: Based on the structural parameters obtained in step S1.1, a methanol direct injection injector and a pilot fuel direct injection injector are installed on the cylinder head. The methanol direct injection injector is used to directly inject methanol main fuel into the cylinder near or after top dead center. The pilot fuel direct injection injector is used to inject pilot fuel and form a high-temperature and high-activity ignition zone in the cylinder. The methanol direct injection injector and the pilot fuel direct injection injector are symmetrically arranged around the cylinder axis so that the high-temperature reaction zone formed by the pilot fuel spray and the methanol spray action zone have controllable spatial overlap. S1.3: Based on the engine object and injection system parameters obtained in steps S1.1 and S1.2, determine the set of injection parameters to be optimized: ； in, This represents the set of injection parameters to be optimized. Indicates the fuel injection pressure; Indicates the timing of the main fuel injection; Indicates the mass of pilot fuel injection within a single work cycle; Indicates the timing of the fuel injection after ignition; The set of injection parameters obtained in step S1 represents the post-injection mass of the pilot fuel within a single working cycle. This serves as input for subsequent steps S2 to S6 to calculate the methanol substitution rate, evaluate engine performance, and determine the target injection parameter combination.

3. The method for coordinating and optimizing fuel injection in a diesel / methanol dual direct injection engine according to claim 1, characterized in that, S2 specifically includes: S2.1: Based on the engine object obtained in step S1, determine the methanol substitution rate, and define the methanol substitution rate as the proportion of heat released by methanol combustion to the total heat input from methanol and pilot fuel: ； in, Indicates the methanol substitution rate; This indicates the mass of methanol injected within a single work cycle; This indicates the lower heating value of methanol; Indicates the mass of pilot fuel injected within a single work cycle; This indicates the lower heating value of the pilot fuel; S2.2: When When the methanol injection rate is within a preset range of 80% to 95%, the engine is determined to be operating at a high methanol substitution rate, and a fixed methanol direct injection strategy is established. This strategy includes at least one of the following: methanol injection pressure, methanol injection timing, methanol injection duration, methanol injection quality, and the number of activated methanol injectors. When it is not within the preset range, adjust or make Enter the preset range; S2.3: Based on the engine structural parameters, operating parameters, and fuel parameters obtained in step S1, and the high methanol substitution rate operating conditions obtained in step S2.2, a combustion analysis model for a diesel / methanol dual direct injection engine is established. The combustion analysis model includes at least a cylinder, piston, cylinder head, scavenging air box, scavenging port, exhaust valve, exhaust passage, methanol direct injection injector, and pilot fuel direct injection injector. The combustion analysis model is used to simulate in-cylinder gas flow, fuel spray, droplet evaporation, fuel / air mixing, pilot fuel ignition, methanol combustion, wall heat transfer, combustion model, nitrogen oxide generation model, and diesel / methanol chemical reaction mechanism. It is used to calculate in-cylinder pressure, heat release rate, temperature distribution, indicated power, indicated thermal efficiency, equivalent indicated fuel consumption rate, and nitrogen oxide emissions under different injection parameter combinations. S2.4: Verify the mesh independence of the combustion analysis model and check the experimental data. When the changes in key combustion parameters under different basic mesh sizes or local densification schemes are less than the preset range, and the error between the simulation results and the experimental data meets the preset requirements, the combustion analysis model is confirmed to be usable for subsequent injection strategy optimization. The high methanol substitution rate operating conditions obtained in step S2 and the verified combustion analysis model serve as the calculation basis for steps S3 to S6.

4. The method for coordinating and optimizing fuel injection in a diesel / methanol dual direct injection engine according to claim 1, characterized in that, S3 specifically includes: S3.1: Based on the combustion analysis model obtained in step S2, calculate the indicated work within a single working cycle: ； in, Indicates the indicated work done within a single work cycle; Indicates the time when the intake valve closes; Indicates the opening time of the exhaust valve; Indicates the pressure inside the engine cylinder; Indicates cylinder volume; A small component representing the cylinder volume; S3.2: Based on the indicated power obtained in step S3.1 Calculate the indicated thermal efficiency: ； in, Indicates thermal efficiency; Indicates the indicated work done within a single work cycle; This indicates the mass of methanol injected within a single work cycle; This indicates the lower heating value of methanol; Indicates the mass of pilot fuel injected within a single work cycle; This indicates the lower heating value of the pilot fuel; S3.3: Based on the indicated power obtained in step S3.1 Calculate the equivalent indicated fuel consumption rate: ； in, This indicates the equivalent indicated fuel consumption rate, expressed in g / kWh. This indicates the mass of methanol injected within a single work cycle, in kg. This indicates the lower heating value of methanol; This indicates the mass of pilot fuel injected within a single work cycle, in kg. This indicates the lower heating value of the pilot fuel; Indicates the indicated work done within a single work cycle; S3.4: Extract combustion phase indicators , and ,in, , and These represent the crankshaft angles at which the accumulated heat release reaches 10%, 50%, and 90% of the total heat release, respectively. The combustion duration is expressed as: ； S3.5: Extraction of maximum pressure rise rate: ； in This represents the maximum pressure rise rate, expressed in MPa / °CA.

5. The method for coordinating and optimizing fuel injection in a diesel / methanol dual direct injection engine according to claim 1, characterized in that, S4 specifically includes: S4.1: Based on the high methanol substitution rate operating conditions and fixed methanol direct injection strategy determined in step S2, set a candidate set of pilot fuel injection pressures: ； in, Represents the candidate set of ignition fuel injection pressure; This represents the a-th candidate value for pilot fuel injection pressure; a represents the candidate value number for pilot fuel injection pressure; A represents the total number of candidate values ​​for pilot fuel injection pressure. S4.2: Will Each of them Input the combustion analysis model obtained in step S2, and calculate the corresponding in-cylinder pressure, heat release rate, temperature distribution, ITE, EISFC, IP, NOx, etc. , , And the parameters of CD; S4.3: Under the condition that the maximum in-cylinder pressure and the maximum pressure rise rate meet the preset safety threshold, determine the target pilot fuel injection pressure based on at least two parameters among the indicated thermal efficiency, equivalent indicated fuel consumption rate, in-cylinder pressure, heat release rate, combustion phase, high-temperature zone volume fraction, and nitrogen oxide emissions corresponding to each candidate pressure value. ; S4.4: When prioritizing indicated power, indicated thermal efficiency, and equivalent indicated fuel consumption rate in engineering applications, a medium pilot fuel injection pressure is selected as the target pilot fuel injection pressure. The target pilot fuel injection pressure obtained in step S4... This serves as a fixed input for optimizing the post-injection of pilot fuel in steps S5 and S6.

6. The method for coordinated optimization of pilot fuel injection in a diesel / methanol dual direct injection engine according to claim 1, characterized in that, S5 specifically includes: S5.1: Target pilot fuel injection pressure obtained in step S4 The total injection mass of pilot fuel is divided into the main injection mass and the post-injection mass, and the proportion of the post-injection mass is defined as follows: ； in, Indicates the mass ratio of ignition fuel injected after ignition; Indicates the mass of fuel injected after ignition within a single work cycle; Indicates the mass of pilot fuel injection within a single work cycle; S5.2: Fixed in step S5.1 Under the condition of preset values, set a candidate set for the timing of the fuel injection after the pilot fuel: ； in, This represents the candidate set of times for the fuel injection after ignition; represents the b-th candidate value for the post-injection time of the ignition fuel; b represents the candidate value number for the post-injection time of the ignition fuel; B represents the total number of candidate values ​​for the post-injection time of the ignition fuel. S5.3: Will Each of them Input the combustion analysis model obtained in step S2, and calculate the corresponding in-cylinder pressure, heat release rate, combustion phase, high-temperature zone distribution, and nitrogen oxide emission parameters; S5.4: Determine the target pilot fuel injection timing provided that the indicated thermal efficiency decrease does not exceed the preset limit and the maximum in-cylinder pressure and maximum pressure rise rate meet the preset safety threshold. ; S5.5: For operating conditions that balance engine performance and nitrogen oxide emissions, the target timing for priming fuel injection is 10°CA to 14°CA after top dead center.

7. The method for co-optimization of pilot fuel injection in a diesel / methanol dual direct injection engine according to claim 1, characterized in that, S6 specifically includes: S6.1: Target pilot fuel injection pressure obtained in step S4 The target ignition fuel injection time obtained in step S5 Set a candidate set for the mass ratio of fuel injected after ignition: in, This represents the candidate set of post-injection fuel mass ratios. This represents the c-th candidate value for the mass ratio of the ignition fuel after injection; C represents the candidate value number for the mass ratio of the ignition fuel after injection; C represents the total number of candidate values ​​for the mass ratio of the ignition fuel after injection. S6.2: Will Each of them Input the combustion analysis model obtained in step S2 and calculate the corresponding ITE, EISFC, IP, NOx, in-cylinder pressure, heat release rate, temperature distribution and combustion phase evaluation parameters; S6.3: Under the condition that the maximum in-cylinder pressure and the maximum pressure rise rate meet the preset safety threshold, determine the target pilot fuel injection mass ratio based on performance, combustion, and emission parameters. ; S6.4: When prioritizing the reduction of nitrogen oxide emissions, the target fuel injection post-injection mass ratio is preferably 10% to 30%; when prioritizing engine performance, the target fuel injection post-injection mass ratio is preferably 50% to 70%.

8. The method for co-optimizing fuel injection in a diesel / methanol dual direct injection engine according to claim 1, characterized in that, Specifically, S7 includes: S7.1: Based on the target parameters obtained in steps S4, S5, and S6, a combination of pilot fuel injection segment control parameters is formed: ； in, This indicates the combination of control parameters for segmented injection of the target pilot fuel; Indicates the target fuel injection pressure; Indicates the timing of the main fuel injection; Indicates the target ignition fuel main injection mass; Indicates the timing of the fuel injection after the target is ignited; Indicates the mass of fuel injected after the target is ignited; S7.2: Based on the definition of PIMR in step S5, calculate the target pilot fuel main injection mass and the target pilot fuel post-injection mass: ； ； in, Indicates the mass of fuel injected after the target is ignited; Indicates the mass ratio of the target ignition fuel injected afterward; Indicates the mass of pilot fuel injected within a single work cycle; Indicates the target ignition fuel main injection mass; S7.3: Write the target pilot fuel segmented injection control parameters into the engine injection control unit or calibration parameter table so that the pilot fuel direct injection injector performs segmented injection control according to the target pilot fuel injection pressure, pilot fuel main injection time, target pilot fuel post-injection time, target pilot fuel main injection mass and target pilot fuel post-injection mass; S7.4: If the engine load, speed, methanol substitution rate, intake state or emission limit changes during engine operation, steps S2 to S7 are re-executed to update the target pilot fuel segment injection control parameter combination in order to achieve adaptive calibration of the injection strategy under different operating conditions.

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