A low-temperature starting segmented injection calibration method and ECU system for a methanol compression ignition engine

Abstract

This invention discloses a low-temperature start-up segmented injection calibration method and ECU system for a methanol compression ignition engine, belonging to the technical field of methanol compression ignition engines. The invention includes using the target engine as the data acquisition target, with the ECU collecting three sets of basic data in real time: the ambient temperature of the engine, the cylinder coolant temperature, and the battery terminal voltage. Based on the basic data, a low-temperature start-up temperature level is determined, and then the in-cylinder preheating plug is controlled in a closed loop based on the determination result to stabilize the in-cylinder temperature within the methanol ignition requirement range. This invention, through closed-loop control of in-cylinder preheating and segmented injection coordinated calibration, can reliably achieve a successful start-up at extreme low temperatures of -25°C on the first attempt. This eliminates the energy and fuel consumption caused by external heating, reduces system structural complexity and maintenance costs, while fully retaining the core advantages of methanol's clean and low-carbon operation, significantly increasing the methanol substitution rate and meeting energy conservation and environmental protection requirements.

Description

Technical Field

[0001] This invention relates to the field of methanol compression ignition engine technology, specifically to a low-temperature start-up segmented injection calibration method and ECU system for a methanol compression ignition engine. Background Technology

[0002] With the continuous development of society and the upgrading of national energy conservation and emission reduction, methanol, as a clean alternative fuel, has advantages such as high combustion efficiency, low carbon emissions, and wide availability, and has broad application prospects in the field of compression ignition engines. Methanol has become one of the core alternative fuels for compression ignition engines due to its advantages of low carbon, cleanliness, wide availability, and high combustion efficiency. Low-temperature start control of methanol compression ignition engines is a key technology direction for the industry.

[0003] The low-temperature start technology for methanol compression ignition engines has significant shortcomings: external heating schemes require additional electricity / fuel consumption, have low heating efficiency and poor thermal utilization, and cannot meet the requirements for starting in extreme low temperatures below -20°C, while also increasing system complexity and maintenance costs; igniter-assisted schemes require an independent fuel supply system, reducing the methanol substitution rate and weakening methanol's core advantages of being clean and low-carbon, which is inconsistent with the trend of energy conservation and environmental protection. Furthermore, existing calibration methods have poor adaptability and lack temperature-adaptive segmented injection logic, resulting in a disconnect between preheating and injection control. This can easily lead to insufficient evaporation of the in-cylinder mixture, large ignition delay, violent fluctuations in the combustion cycle, and even misfires and starting failures, severely restricting the low-temperature adaptability and industrialization of methanol compression ignition engines.

[0004] To address the aforementioned technical shortcomings, a solution is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a low-temperature start-up segmented injection calibration method and ECU system for a methanol compression ignition engine, in order to solve the problems mentioned above.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a low-temperature start-up segmented injection calibration method for a methanol compression ignition engine, comprising using the target engine as the data acquisition target, and having the ECU collect three sets of basic data in real time: the ambient temperature of the engine, the cylinder water temperature, and the battery terminal voltage.

[0007] Based on the basic data, the low-temperature start-up temperature level is determined. Then, based on the determination result, the cylinder preheating plug is controlled in a closed loop to stabilize the cylinder temperature within the methanol ignition requirement range. The throttle opening is adjusted synchronously and the EGR valve is closed to perform segmented injection operations of two methanol pre-injections, one methanol main injection, and one methanol post-injection.

[0008] Based on the cold start success rate and combustion cycle fluctuation data, the preheating and injection parameters are optimized and calibrated. No external heating device or igniter is used throughout the process, and the engine can be successfully started on the first attempt at an extreme low temperature of -25℃.

[0009] Furthermore, the preset four temperature thresholds of -25℃, -15℃, -5℃, and 0℃ are used to compare the collected ambient temperature and cylinder water temperature data one by one to match the corresponding temperature level. Each temperature level corresponds to an independent preheating target temperature, preheating cycle time, and injection quantity benchmark value. The results are summarized into a judgment result, which is directly sent to the ECU internal control unit to provide a fixed basis for subsequent preheating and injection control, and solve the problem that fixed parameters cannot be adapted to different low-temperature operating conditions.

[0010] Furthermore, based on the temperature level determination results, a corresponding preheating target temperature is set, and the preheating plug feedback temperature is collected in real time and compared with the target temperature: if the temperature is insufficient, the preheating power is increased and the preheating time is extended; if the temperature meets the target, a stable output is maintained, while limiting the duration of a single preheating cycle and the maximum number of cycles to avoid preheating plug overheating and loss. The preheating output power is compensated according to the fluctuation range of the battery terminal voltage throughout the process to ensure stable in-cylinder preheating effect and no additional fuel consumption.

[0011] Furthermore, after the preheating signal in the cylinder is triggered, the injection is started. First, the first methanol pre-injection is performed to raise the local temperature in the cylinder to complete the cylinder warm-up. After a fixed interval, the second methanol pre-injection is performed to form a uniform combustible mixture. Then, the main methanol injection is performed to provide starting power. Finally, the methanol post-injection is performed to stabilize the combustion cycle. The pre-injection interval is automatically adjusted according to the temperature level. The lower the temperature, the shorter the pre-injection interval, matching the low-temperature vaporization characteristics of methanol.

[0012] Furthermore, a fixed allocation rule is preset: the first pre-injection accounts for 10% of the total injection volume, which is used to quickly increase the cylinder temperature; the second pre-injection accounts for 20% of the total injection volume, which is used to form a flammable mixture; the main injection accounts for 65% of the total injection volume, which is used to ensure engine starting power; and the post-injection accounts for 10% of the total injection volume, which is used to reduce combustion cycle fluctuations. For each temperature level decrease, the injection volume of each stage is adjusted upward by a fixed amount.

[0013] Furthermore, during the preheating stage, the throttle opening is reduced to decrease the intake of cold air and retain the residual heat of the cylinder. During the injection stage, the throttle opening is gradually increased to ensure the amount of air intake for combustion. During the start-up process, the throttle is opened to reduce the amount of air intake and increase the cylinder temperature. The EGR valve is opened according to the operating conditions to control the amount of methanol leakage and emissions, so that the intake, preheating and injection work together to improve combustion stability.

[0014] Furthermore, the actual value of the battery terminal voltage is collected in real time and compared with the preset safe starting voltage threshold. If the actual voltage value is lower than the preset safe starting voltage threshold, the preheating cycle time is automatically extended and the pre-injection volume is slightly increased. If the actual voltage value is within the preset safe starting voltage threshold range, the control is executed according to the standard parameters. The voltage compensation logic is integrated into the preheating and injection process to avoid insufficient battery power supply at low temperatures, which could lead to starting failure.

[0015] Furthermore, by reducing the piston top recess and thinning the cylinder head gasket, the engine compression ratio is set at 17.5-21. For every unit increase in compression ratio, the in-cylinder compression final temperature increases by 20°C. The ECU adjusts the preheating target temperature based on the actual compression ratio value, and the methanol low-temperature ignition temperature requirement can be met without additional preheating power.

[0016] Furthermore, the real-time acquisition of actual cold start success rate and actual combustion cycle fluctuation data is compared with preset thresholds: if the real-time data does not meet the threshold, the number of preheating cycles, pre-injection interval duration and injection volume at each stage are automatically fine-tuned; if the real-time data meets the threshold, the current parameters are locked and stored in the ECU storage unit to form a temperature-adaptive calibration parameter library.

[0017] A low-temperature start-up segmented injection calibration ECU system for a methanol compression ignition engine includes the following modules:

[0018] Low-temperature start-up temperature classification module: collects ambient temperature and cylinder water temperature signals, compares them with four fixed temperature thresholds to classify the low-temperature level, and outputs the corresponding preheating and injection basic control parameters to provide a basis for judging the working conditions for the whole process control.

[0019] In-cylinder preheating closed-loop control module: Set the target preheating temperature according to the temperature level, compare the preheating plug feedback temperature in real time to adjust the preheating power and duration, and combine the battery voltage to compensate the preheating output to stabilize the in-cylinder preheating temperature and prevent overheating and loss of components.

[0020] Segmented injection timing control module: Receives preheating completion signal to start injection process, triggers two pre-injection, main injection and post-injection in sequence according to cylinder warm-up, ignition, main combustion and stable combustion logic, and adjusts injection interval according to low temperature level to adapt to the low temperature vaporization and ignition rhythm of methanol.

[0021] Segmented injection quantity distribution module: Distributes methanol injection quantity at each stage according to a fixed ratio, and dynamically adjusts the injection quantity according to the low temperature level to ensure that the in-cylinder mixture concentration meets the ignition and combustion requirements under different low temperature conditions.

[0022] Intake and valve coordination control module: During startup, the throttle valve is opened to reduce the intake air volume and increase the cylinder temperature. Methanol is an oxygen-containing fuel. The throttle valve opening is controlled in conjunction with the preheating and injection stages. The EGR valve opens according to the operating conditions to control the amount of methanol leakage and emissions, reduce the loss of cold air waste heat, and optimize the cylinder environment to improve combustion stability.

[0023] Battery voltage compensation module: Collects battery terminal voltage and compares it with safety threshold. When the voltage is insufficient, it corrects the preheating time and injection volume, eliminates the impact of low temperature power supply fluctuations on start-up control, and ensures reliable execution.

[0024] Compression ratio adaptation control module: Combining the high compression ratio structural parameters of the engine, the preheating target temperature is corrected according to the quantitative relationship between compression ratio and cylinder temperature rise, and the final cylinder temperature is increased by utilizing the structure to reduce the preheating control load;

[0025] Parameter closed-loop optimization and calibration module: Collects start-up success rate and combustion fluctuation data, fine-tunes preheating and injection parameters according to the target threshold, and stores the target parameters in the storage unit to form a temperature-adaptive calibration parameter library.

[0026] The beneficial effects of this invention are:

[0027] 1. This invention eliminates the reliance on external heating devices and igniters. Through closed-loop control of in-cylinder preheating and coordinated calibration of segmented injection, it can stably achieve a successful start-up at an extreme low temperature of -25℃. This not only eliminates the energy and fuel consumption caused by external heating and reduces the complexity of the system structure and maintenance costs, but also fully retains the core advantages of methanol as a clean and low-carbon product, significantly improving the methanol substitution rate and meeting the requirements of energy conservation and environmental protection.

[0028] 2. This invention effectively solves problems such as insufficient methanol evaporation at low temperatures, large ignition delay, and severe combustion cycle fluctuations by relying on temperature-grade adaptive control and multi-module collaborative logic, resulting in faster start-up and more stable combustion. The matching ECU closed-loop calibration system can automatically complete parameter optimization and storage, adapting to the entire low-temperature range without the need for repeated manual calibration, significantly improving the engine's low-temperature adaptability and control accuracy, and powerfully promoting the industrialization and large-scale promotion of methanol compression ignition engines. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a flowchart of the modules of the present invention;

[0031] Figure 2 This is a schematic diagram of the analysis process of the present invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1: Please refer to Figure 1 - Figure 2 As shown, this embodiment is a low-temperature start-up segmented injection calibration method and ECU system for a methanol compression ignition engine, which is used to solve the problems of low-temperature start-up of methanol compression ignition engines relying on external heating and igniter, poor calibration adaptation, and low start-up reliability. Only three sets of basic data are collected: the actual ambient temperature of the engine, the actual coolant temperature of the engine block, and the actual terminal voltage of the battery. These are summarized and labeled as ambient temperature, engine block coolant temperature, and battery terminal voltage.

[0034] The ECU first integrates and processes three sets of basic data to determine the low-temperature start-up temperature level. Then, based on the determination result, it outputs a control signal to the in-cylinder preheating plug, and stabilizes the in-cylinder temperature within the range required for methanol low-temperature ignition through closed-loop regulation. Simultaneously, it outputs control signals to the throttle body and EGR valve to optimize the intake and in-cylinder environment. Subsequently, it executes segmented injections of two pre-injections, one main injection, and one post-injection according to preset logic. Finally, it collects cold start success rate and combustion cycle fluctuation data to complete parameter optimization and calibration. It should be noted that no external heating device is used throughout the process, and no igniters such as diesel or dimethyl ether are added. It relies solely on the coordinated control of in-cylinder preheating and segmented injection to achieve a successful start at an extreme low temperature of -25℃, fundamentally solving the defects of high energy consumption of external heating and reduced methanol substitution rate of igniters.

[0035] The low-temperature start-up temperature grading determination module relies on basic data: ambient temperature and cylinder water temperature. The methanol vaporization rate and cylinder heat dissipation rate are different under different low-temperature environments. Fixed parameters cannot be adapted to all operating conditions, so basic parameters need to be set in stages. The ECU has four preset fixed temperature thresholds: -25℃, -15℃, -5℃, and 0℃.

[0036] The average of the ambient temperature and the tank water temperature is compared with the preset four fixed temperature thresholds:

[0037] If the average temperature is below -25°C, it is classified as an extreme low temperature.

[0038] If the average value is between -25℃ and -15℃, it is classified as a severe low temperature level.

[0039] If the average temperature is between -15℃ and -5℃, it is classified as a moderate low temperature level.

[0040] If the average temperature is between -5℃ and 0℃, it is classified as a mild low temperature level.

[0041] Each level corresponds to an independent preheating target temperature, preheating cycle time, and injection quantity benchmark value. The judgment result is directly transmitted to the internal control unit of the ECU, providing accurate basis for subsequent control and solving the problem of poor parameter adaptability.

[0042] The in-cylinder preheating closed-loop control module relies on basic data: temperature level determination results, actual feedback temperature of the glow plug, and battery terminal voltage. If the preheating temperature is too high, it will damage the glow plug; if it is too low, it will not meet the ignition requirements. Therefore, a closed-loop temperature stabilization is required. At low temperatures, battery voltage fluctuations will affect the preheating power, and compensation is required to ensure the effect.

[0043] Based on the temperature level determination results, the preheating target temperature is set as follows: 85 degrees Celsius for extreme low temperature level, 75 degrees Celsius for severe low temperature level, 65 degrees Celsius for moderate low temperature level, and 55 degrees Celsius for mild low temperature level.

[0044] The ECU collects the glow plug feedback temperature in real time and compares it with the target temperature.

[0045] If the actual temperature is five degrees Celsius or more lower than the target temperature, increase the preheating power.

[0046] If the difference between the actual temperature and the target temperature is less than five degrees Celsius, maintain the current power.

[0047] If the actual temperature reaches the target temperature, maintain a stable output;

[0048] Meanwhile, the duration of a single preheating cycle is limited to three seconds, and the maximum number of cycles is five, to prevent the preheating plug from overheating; the battery terminal voltage is collected, and for every 0.1 volt decrease in voltage, the preheating output power is increased by 5% to ensure stable preheating effect and no additional fuel consumption.

[0049] The segmented injection timing control module relies on basic data: preheating completion signal and temperature level determination result; methanol has a high latent heat of vaporization, and single injection is prone to insufficient evaporation, while segmented injection can achieve cylinder warm-up, ignition and stable combustion in stages.

[0050] After the preheating completion signal is triggered, the first methanol pre-injection is immediately executed to increase the local temperature inside the cylinder; the second methanol pre-injection is executed after a fixed interval to form a uniform combustible mixture; the main methanol injection is executed after a one-second interval; after the main injection is completed, the methanol post-injection is executed after a 0.5-second interval; the pre-injection interval is 0.5 seconds for extreme low temperature level, 1 second for severe low temperature level, 1.5 seconds for moderate low temperature level, and 2 seconds for mild low temperature level. The lower the temperature, the shorter the interval, to ensure rapid vaporization of methanol and solve the problems of ignition delay and insufficient vaporization of the mixture.

[0051] The segmented injection quantity allocation module relies on basic data: the total injection quantity required for engine start-up and the temperature level determination result; the injection quantity ratio of each stage directly affects the cylinder warm-up effect, ignition success rate and combustion stability, and a fixed allocation rule needs to be set.

[0052] Total injection quantity is determined by engine displacement and starting conditions, and is derived from the basic data:

[0053] The first pre-spray consists of 10% of the total spray volume and is used only for localized heating.

[0054] The second pre-spray injection accounts for 20% of the total injection volume and is used to form a combustible mixture.

[0055] The main injection volume accounts for 65% of the total injection volume, ensuring starting power; the rear injection volume accounts for 10% of the total injection volume, stabilizing the combustion cycle; for each temperature level decrease, the injection volume of each stage is increased by 10% to ensure that the air-fuel mixture concentration reaches the ignition critical value at low temperatures, avoiding misfire due to insufficient concentration.

[0056] Example 2: The intake and valve coordination control module relies on basic data: preheating stage signal, injection stage signal; EGR is the exhaust gas valve, throttle is the fresh air valve, the throttle opens during startup to reduce the intake volume and increase the cylinder temperature, and methanol is an oxygenated fuel.

[0057] When the preheating signal is triggered, the ECU controls the throttle to open to 90% to reduce the intake of cold air and retain residual heat in the cylinder; when the first pre-injection signal is triggered, the throttle opens to 80%; when the main injection signal is triggered, the throttle opens to 70% to ensure the amount of air intake for combustion; during the start-up process, the throttle opens to reduce the amount of air intake and increase the cylinder temperature; EGR is activated as needed to control methanol leakage and emissions.

[0058] The battery voltage compensation module relies on basic data: battery terminal voltage and preset safe starting voltage threshold. At low temperatures, the battery discharge capacity decreases, and insufficient voltage will lead to insufficient preheating power and injection execution deviation, so compensation and correction parameters are required.

[0059] The preset safe starting voltage threshold is 12 volts, which is a common industry safe voltage value. The battery terminal voltage is compared and analyzed with the preset safe starting voltage threshold.

[0060] If the battery terminal voltage is lower than 12 volts, it is determined to be a voltage deficiency state, and the number of preheating cycles will be increased by one and the pre-spray volume will be increased by 10%.

[0061] If the actual terminal voltage of the battery is greater than or equal to 12 volts, preheating and injection control shall be performed according to the standard parameters.

[0062] The voltage compensation logic is integrated into the preheating closed loop and injection control process, eliminating the need for additional power supply equipment, simplifying the system structure, and improving startup reliability under extreme low temperatures.

[0063] The compression ratio adaptation control module relies on basic data: the engine's actual compression ratio and compression ratio temperature rise coefficient; the methanol has a low cetane number, so the compression ratio needs to be increased to increase the final cylinder temperature and assist in low-temperature ignition, and the quantitative relationship needs to be clearly defined.

[0064] By reducing the piston crown recess and thinning the cylinder head gasket, the engine compression ratio is set between 17.5 and 21, providing a basis for optimizing the engine's structural parameters. The internal preset compression ratio temperature rise coefficient is 20°C per unit compression ratio, meaning that for every unit increase in compression ratio, the in-cylinder compression final temperature increases by 20°C. The ECU calculates the increase in in-cylinder compression final temperature based on the actual compression ratio value and simultaneously corrects the preheating target temperature. For every unit increase in compression ratio, the preheating target temperature is lowered by 20°C, thus meeting the methanol low-temperature ignition temperature requirement without additional preheating power.

[0065] The parameter closed-loop optimization and calibration module relies on basic data: real-time cold start success rate, real-time combustion cycle fluctuation amplitude, and preset compliance threshold. A single calibration parameter cannot adapt to all operating conditions and needs to be optimized in real time to form an adaptive parameter library.

[0066] The preset threshold for cold start success rate is 95%, and the threshold for combustion cycle fluctuation is 100%. The real-time cold start success rate is compared and analyzed with the preset cold start success rate threshold.

[0067] The ECU collects real-time data after startup. If the cold start success rate is less than 95% or the combustion cycle fluctuation is greater than 10%, it automatically fine-tunes the number of preheating cycles, the pre-injection interval, and the injection quantity at each stage. If the cold start success rate is greater than or equal to 95% and the combustion cycle fluctuation is less than or equal to 10%, the parameters are deemed to meet the standards. The current parameters are then stored in the ECU storage unit to form a temperature adaptive calibration system, solving the problem of disconnect between preheating and injection control.

[0068] The ECU system is additionally equipped with a low-temperature start-up performance evaluation module, which summarizes the actual start-up time, actual combustion fluctuation value, and actual number of successful starts. The start-up performance needs to be quantified to provide the final judgment basis for parameter optimization. At an extreme low temperature of -25℃, if the actual start-up time is less than or equal to three seconds, the actual start-up success rate is 100%, and the actual combustion cycle fluctuation amplitude is less than or equal to the preset fluctuation threshold, all three indicators are met simultaneously to determine that the start-up is satisfactory. If any one of them is not met, it is determined that optimization is required. The evaluation results are fed back to the parameter closed-loop optimization and calibration module in real time. The module readjusts the control parameters based on the evaluation results, forming a complete closed-loop calibration process of control, data acquisition, optimization, and re-control, ensuring that the engine maintains stable start-up performance at extreme low temperatures and completely solving all the defects of existing technologies.

[0069] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

[0070] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0071] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to any specific implementation. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for calibrating a methanol compression ignition engine for low-temperature start-up segmented injection, characterized in that, This includes using the target engine as the data acquisition target, with the ECU collecting three sets of basic data in real time: the ambient temperature of the engine, the cylinder water temperature, and the battery terminal voltage. Based on the basic data, the low-temperature start-up temperature level is determined. Then, based on the determination result, the cylinder preheating plug is controlled in a closed loop to stabilize the cylinder temperature within the methanol ignition requirement range. The throttle opening is adjusted synchronously and the EGR valve is closed to perform segmented injection operations of two methanol pre-injections, one methanol main injection, and one methanol post-injection. Based on the cold start success rate and combustion cycle fluctuation data, the preheating and injection parameters are optimized and calibrated. No external heating device or igniter is used throughout the process, and the engine can be successfully started on the first attempt at an extreme low temperature of -25℃.

2. The method for low-temperature start-up segmented injection calibration of a methanol compression ignition engine according to claim 1, characterized in that, The preset temperature thresholds of -25℃, -15℃, -5℃, and 0℃ are used to compare the collected ambient temperature and cylinder water temperature data one by one to match the corresponding temperature level. Each temperature level corresponds to an independent preheating target temperature, preheating cycle time, and injection quantity benchmark value. The results are summarized into a judgment result, which is then sent directly to the ECU internal control unit.

3. The method for low-temperature start-up segmented injection calibration of a methanol compression ignition engine according to claim 2, characterized in that, Based on the temperature level determination result, the corresponding preheating target temperature is set, and the preheating plug feedback temperature is collected in real time and compared with the target temperature: if the temperature is insufficient, the preheating power is increased and the preheating time is extended; if the temperature meets the target, the output is kept stable.

4. The method for low-temperature start-up segmented injection calibration of a methanol compression ignition engine according to claim 1, characterized in that, After the preheating in the cylinder is completed and the signal is triggered, the injection is started. First, the first methanol pre-injection is performed to increase the local temperature in the cylinder to complete the cylinder warm-up. After a fixed interval, the second methanol pre-injection is performed to form a uniform combustible mixture. Then, the main methanol injection is performed to provide starting power. Finally, the methanol post-injection is performed to stabilize the combustion cycle.

5. The method for low-temperature start-up segmented injection calibration of a methanol compression ignition engine according to claim 4, characterized in that, The system has a fixed pre-spraying rule: the first pre-spray accounts for 10% of the total injection volume and is used to quickly increase the cylinder temperature; the second pre-spray accounts for 20% of the total injection volume and is used to form a flammable mixture; the main injection accounts for 65% of the total injection volume and is used to ensure engine starting power; and the post-spray accounts for 10% of the total injection volume and is used to reduce combustion cycle fluctuations. For each temperature level decrease, the injection volume of each stage is adjusted upward by a fixed amount.

6. The method for low-temperature start-up segmented injection calibration of a methanol compression ignition engine according to claim 5, characterized in that, During the preheating stage, the throttle opening is reduced to minimize the entry of cold air and retain residual heat in the cylinder. During the injection stage, the throttle opening is gradually increased to ensure the amount of air intake for combustion. Throughout the entire process, the EGR valve is kept closed to prevent exhaust gas from entering the cylinder and interfering with the formation of the air-fuel mixture. This allows the intake, preheating, and injection processes to work together to improve combustion stability.

7. The method for low-temperature start-up segmented injection calibration of a methanol compression ignition engine according to claim 3, characterized in that, The actual voltage value of the battery terminal is collected in real time and compared with the preset safe starting voltage threshold. If the actual voltage value is lower than the preset safe starting voltage threshold, the preheating cycle time is automatically extended and the pre-injection volume is slightly increased. If the actual voltage value is within the preset safe starting voltage threshold range, the control is executed according to the standard parameters. The voltage compensation logic is integrated into the preheating and injection process throughout.

8. The method for low-temperature start-up segmented injection calibration of a methanol compression ignition engine according to claim 1, characterized in that, By reducing the piston crown recess and thinning the cylinder head gasket, the engine compression ratio is set between 17.5 and 21. For every unit increase in the compression ratio, the in-cylinder compression final temperature increases by 20°C. The ECU adjusts the preheating target temperature based on the actual compression ratio value.

9. The method for low-temperature start-up segmented injection calibration of a methanol compression ignition engine according to claim 1, characterized in that, The system collects real-time data on the actual success rate of cold starts and the actual fluctuation range of combustion cycles, and compares the real-time data with preset thresholds. If the real-time data does not meet the thresholds, it automatically fine-tunes the number of preheating cycles, the pre-injection interval, and the injection volume at each stage. If the real-time data meets the thresholds, it locks the current parameters and stores them in the ECU storage unit to form a temperature-adaptive calibration parameter library.

10. A low-temperature start-up segmented injection calibration ECU system for a methanol compression ignition engine, used in the low-temperature start-up segmented injection calibration method for the methanol compression ignition engine according to any one of claims 1-9, characterized in that, Includes the following modules: Low-temperature start-up temperature classification module: collects ambient temperature and cylinder water temperature signals, compares them with four fixed temperature thresholds to classify the low-temperature level, and outputs the corresponding preheating and injection basic control parameters to provide a basis for judging the working conditions for the whole process control. In-cylinder preheating closed-loop control module: Set the target preheating temperature according to the temperature level, compare the preheating plug feedback temperature in real time to adjust the preheating power and duration, and combine the battery voltage to compensate the preheating output to stabilize the in-cylinder preheating temperature and prevent overheating and loss of components. Segmented injection timing control module: Receives preheating completion signal to start injection process, triggers two pre-injection, main injection and post-injection in sequence according to cylinder warm-up, ignition, main combustion and stable combustion logic, and adjusts injection interval according to low temperature level to adapt to the low temperature vaporization and ignition rhythm of methanol. Segmented injection quantity distribution module: Distributes methanol injection quantity at each stage according to a fixed ratio, and dynamically adjusts the injection quantity according to the low temperature level to ensure that the in-cylinder mixture concentration meets the ignition and combustion requirements under different low temperature conditions. Intake and valve coordination control module: controls throttle opening during the preheating and injection phases, and opens the throttle during startup to reduce intake air volume and increase cylinder temperature; Battery voltage compensation module: Collects battery terminal voltage and compares it with safety threshold. When the voltage is insufficient, it corrects the preheating time and injection volume, eliminates the impact of low temperature power supply fluctuations on start-up control, and ensures reliable execution. Compression ratio adaptation control module: Combining the high compression ratio structural parameters of the engine, the preheating target temperature is corrected according to the quantitative relationship between compression ratio and cylinder temperature rise, and the final cylinder temperature is increased by utilizing the structure to reduce the preheating control load; Parameter closed-loop optimization and calibration module: Collects start-up success rate and combustion fluctuation data, fine-tunes preheating and injection parameters according to the target threshold, and stores the target parameters in the storage unit to form a temperature-adaptive calibration parameter library.

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