An ammonia single-fuel full-load high-efficiency combustion control strategy and system

Abstract

This application relates to a single-fuel, full-load, high-efficiency combustion control strategy for ammonia, comprising the following steps: acquiring operating data of a pure ammonia engine, and identifying the current operating condition based on the operating data; the current operating condition includes idling, low-load, medium-load, and high-load conditions; when identified as idling, a multi-ignition mode is adopted as the ignition strategy, and a preset idle ignition timing is used for ignition, while a first valve strategy is adopted where the intake valve closing angle advance is not greater than a preset idle crankshaft angle and the valve overlap angle is controlled within a preset idle overlap angle range; when identified as low-load conditions, a dual-ignition mode is adopted as the ignition strategy, and a preset low-load ignition timing is used for ignition. This application, through the zoned coordinated control of the ignition strategy and valve strategy, enables stable combustion of ammonia fuel across the entire operating range without the need for mixing with hydrogen, diesel, or other combustion-supporting fuels, resulting in a simpler fuel supply system and higher safety.

Description

Technical Field

[0001] This invention relates to the field of ammonia engine combustion control technology, specifically to a high-efficiency combustion control strategy and system for ammonia as a single fuel at full load. Background Technology

[0002] Ammonia, as a zero-carbon fuel, has broad application prospects in the field of internal combustion engines. However, ammonia fuel has inherent characteristics such as high ignition energy (minimum ignition energy is about 60 times that of gasoline), slow flame propagation speed (laminar flame speed is about 1 / 5 of that of gasoline), and high auto-ignition temperature, which make it difficult to achieve stable and efficient combustion in engines. How to overcome the above defects and achieve efficient and stable combustion of ammonia fuel across the entire operating range is a technical problem that urgently needs to be solved in this field.

[0003] Existing ammonia-fueled engines generally employ a dual-fuel technology approach, which involves blending ammonia fuel with highly reactive fuels such as hydrogen, natural gas, or diesel to assist ignition and combustion. For example, mixing ammonia with hydrogen (ammonia-hydrogen dual-fuel) utilizes the high reactivity of hydrogen (low ignition energy, high flame propagation speed) to compensate for the shortcomings of ammonia fuel combustion characteristics. On the other hand, in terms of valve control, existing technologies are beginning to explore the application of the Miller cycle to ammonia engines. Studies have shown that employing an early intake valve closing (EIVC) strategy can not only prevent ammonia leakage but also improve ammonia combustion conditions and enhance engine efficiency. Under a 60% ammonia energy ratio, an optimized geometric compression ratio of 21.9 combined with an EIVC strategy of 60°CA Miller degree can increase braking torque by 8%, indicated thermal efficiency by 6.9%, and reduce unburned ammonia by 39%. Other studies have proposed various load control strategies (ammonia volume fraction adjustment, quality adjustment, quantity adjustment, and intake VVT ​​adjustment) for ammonia-hydrogen dual-fuel engines. Results show that quality adjustment and intake VVT ​​adjustment can maintain a BTE above 37% under most operating conditions. However, relying on combustion-supporting fuels such as hydrogen and diesel not only increases the complexity and cost of the fuel supply system, but also brings additional carbon emissions (if blended with hydrocarbon fuels) or safety issues related to hydrogen storage / transportation. Furthermore, the control strategy has not been optimized for all operating conditions based on the characteristics of ammonia fuel. The special requirements of difficult ignition of ammonia fuel under idling conditions, the need to achieve high-pressure ratio and high-efficiency combustion under medium and low loads, and the need to control the risk of detonation under medium and high loads have not been systematically integrated into a complete control strategy by existing technologies. The ignition system and valve system also lack coordinated control. Although some studies have introduced the Miller cycle into ammonia engines to improve performance, it has not yet been coordinated with the ignition strategy for all operating conditions, which restricts the efficient and stable combustion of ammonia fuel engines across the entire operating range. Summary of the Invention

[0004] This application provides a high-efficiency combustion control strategy and system for ammonia as a single fuel under full load. By controlling the ignition strategy and valve strategy in a zoned manner, it achieves efficient and stable combustion of pure ammonia fuel across the entire operating range.

[0005] In a first aspect, embodiments of this application provide a high-efficiency combustion control strategy for ammonia as a single fuel at full load, applied to a pure ammonia engine with a geometric compression ratio greater than or equal to 18:1, comprising the following steps: The system acquires the operating data of the pure ammonia engine and identifies the current operating condition based on the operating data; the current operating condition includes idling condition, low load condition, medium load condition and high load condition. When the idling condition is identified, a multi-ignition mode is used as the ignition strategy, and ignition is performed using a preset idle ignition timing. At the same time, a first valve strategy is adopted, in which the intake valve closing angle advance is not greater than the preset idle crankshaft angle and the valve overlap angle is controlled within the preset idle overlap angle range. When the low-load condition is identified, a dual-ignition mode is adopted as the ignition strategy, and ignition is performed using a preset low-load ignition timing. At the same time, a second valve strategy is adopted with the intake valve closing angle advance not greater than the preset low-load crankshaft angle. When the condition is identified as medium load, a single ignition mode is used as the ignition strategy, and a preset low load ignition timing is used for ignition, while the second valve strategy is used at the same time. When a high-load condition is identified, a single ignition mode is used as the ignition strategy, and ignition is performed using a preset high-load ignition timing. At the same time, a third valve strategy is adopted to reduce the effective compression ratio by either closing the intake valve in advance or delaying the intake valve in advance.

[0006] In conjunction with the first aspect, in one embodiment, the preset idle crankshaft angle is 15°CA, the preset idle overlap angle range is 10°CA to 30°CA, and the preset idle ignition timing is located within the range of 45°CA before top dead center of the compression stroke to 10°CA after top dead center.

[0007] In conjunction with the first aspect, in one embodiment, the preset low-load crankshaft angle is 20°CA, and the preset low-load ignition timing is such that the combustion phase CA50 is located within the range of 8°CA to 12°CA after top dead center.

[0008] In conjunction with the first aspect, in one embodiment, the preset advance angle range is 30°CA to 60°CA, the preset retard angle range is 30°CA to 60°CA, and the preset high-load ignition timing is such that the combustion phase CA50 is located within the range of 10°CA to 20°CA after top dead center.

[0009] In conjunction with the first aspect, in one embodiment, the operating data includes engine speed and engine braking mean effective pressure.

[0010] In conjunction with the first aspect, in one implementation method, identifying the current operating condition based on the operating data specifically includes: If the engine speed is within the idle speed range and the average effective pressure of the engine braking is less than or equal to the first pressure threshold, it is identified as an idle condition. If the engine speed is within the first speed range, and the average effective pressure of engine braking is greater than the first pressure threshold and less than or equal to the second pressure threshold, it is identified as a low-load condition. If the engine speed is in the first speed range, and the average effective pressure of engine braking is greater than the second pressure threshold and less than the third pressure threshold, it is identified as a medium load condition. If the engine speed is within the first speed range and the average effective pressure of engine braking is greater than or equal to the third pressure threshold, it is identified as a high-load condition.

[0011] In conjunction with the first aspect, in one embodiment, the idle speed range is 450 rpm to 550 rpm, the first pressure threshold is 0.1 MPa, the second pressure threshold is 0.4 MPa, the third pressure threshold is 0.8 MPa, and the first speed range is 600 rpm to 1800 rpm.

[0012] In conjunction with the first aspect, in one implementation method, The multiple ignition mode includes: continuously outputting at least two high-energy sparks within a single working cycle, with a single ignition energy of not less than 80mJ and a total ignition energy of 100mJ to 500mJ; The dual ignition mode includes: continuously outputting two high-energy sparks within a single working cycle, with a single ignition energy of not less than 80mJ; The single ignition mode includes: a single ignition energy of not less than 80mJ.

[0013] In conjunction with the first aspect, in one embodiment, a zone boundary transition control step is also included: within the load change range transitioning from low load condition to high load condition, the advance or retardation of the intake valve closing angle is controlled to continuously increase with the increase of load, and the number of ignitions is controlled to smoothly transition from multiple to single ignitions.

[0014] Secondly, embodiments of this application provide a system based on ammonia-only single-fuel full-load high-efficiency combustion control strategy, including: The operating condition identification unit is used to acquire the operating data of the pure ammonia engine and identify the current operating condition based on the operating data; the current operating condition includes idling condition, low load condition, medium load condition and high load condition; The ignition control unit is used to employ a multi-ignition mode as the ignition strategy and a preset idle ignition timing during idling; a dual-ignition mode as the ignition strategy and a preset low-load ignition timing during low-load operation; a single-ignition mode as the ignition strategy and a preset low-load ignition timing during medium-load operation; and a single-ignition mode as the ignition strategy and a preset high-load ignition timing during high-load operation. The valve control unit is used to employ a first valve strategy under idling conditions, where the intake valve closing angle advance is no greater than a preset idle crankshaft angle and the valve overlap angle is controlled within a preset idle overlap angle range; a second valve strategy under low load conditions, where the intake valve closing angle advance is no greater than a preset low load crankshaft angle; the second valve strategy under medium load conditions; and a third valve strategy under high load conditions, where the effective compression ratio is reduced by advancing the intake valve by a preset advance angle range or delaying the intake valve closing by a preset delay angle range.

[0015] The beneficial effects of the technical solutions provided in this application include: 1. This application achieves full-condition zoned ignition control by identifying engine operating conditions and employing a multi-ignition mode under idling conditions, a dual-ignition mode under low-load conditions, a single-ignition mode under medium-load conditions, and a single-ignition mode under high-load conditions. Simultaneously, under low-load conditions (including idling, low-load, and medium-load), a first-valve strategy or a second-valve strategy is employed to bring the effective compression ratio close to the geometric compression ratio; under high-load conditions, a third-valve strategy is employed to reduce the effective compression ratio by advancing or delaying the intake valve closure. Through zoned coordinated control of the ignition and valve strategies, ammonia fuel can be stably combusted across the entire operating range without the need for mixing with hydrogen, diesel, or other combustion-supporting fuels, resulting in a simpler fuel supply system and higher safety.

[0016] 2. This application adopts a multiple ignition mode in the idling condition and controls the intake valve closing angle advance to be no greater than the preset idling crankshaft angle and the valve overlap angle to be controlled within the preset idling overlap angle range. Through the synergistic effect of high geometric compression ratio and multiple discharges, ammonia fuel can be stably and reliably ignited and burned in the idling condition, thus solving the technical problem of difficult ignition of ammonia fuel at idle.

[0017] 3. This application adopts a dual ignition mode under low load conditions and a single ignition mode under medium load conditions. It is combined with a second valve strategy where the intake valve closing angle advance is no greater than the preset crankshaft angle under low load conditions. By setting the number of ignitions in zones and coordinating with a high effective compression ratio, the requirements for ignition reliability under low load and the requirements for efficient combustion under medium load are met respectively, thus achieving efficient combustion of ammonia fuel under low and medium load conditions.

[0018] 4. This application adopts a single ignition mode under high load conditions and uses a third valve strategy to reduce the effective compression ratio by pre-setting the intake valve advance angle interval or delaying the pre-setting retard angle interval. While maintaining a high expansion ratio, it reduces the effective compression ratio and controls the maximum in-cylinder explosion pressure within the mechanical tolerance range of the engine. At the same time, with the optimization of the preset ignition timing under high load, it maintains high thermal efficiency while protecting the engine. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the control method of the present invention; Figure 2 This is a schematic diagram of the working condition zoning control strategy of the present invention. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0022] Example 1: Please see Figure 1 and Figure 2 , Figure 2 The horizontal axis represents engine speed (rpm), and the vertical axis represents brake mean effective pressure (BMEP) (MPa). This shows three regions: the idle speed region, the low-to-medium load region, and the high-to-medium load region, along with their corresponding control strategies. The low-to-medium load region is further subdivided into low-load and medium-load conditions, corresponding to dual-ignition mode and single-ignition mode, respectively. The high-to-medium load region corresponds to high-load conditions, and to single-ignition mode and third-valve strategy. Embodiment 1 of this application provides a high-efficiency combustion control strategy for ammonia-only fuel at full load, which is used in a pure ammonia engine and specifically includes the following steps: Before executing the control method, the engine system used in this embodiment includes the following hardware configuration: Ultra-high compression ratio piston: Use an ultra-high compression ratio piston with a geometric compression ratio greater than or equal to 18:1, preferably in the range of 18:1 to 32:1, to increase the compression end temperature, promote the pre-reaction and ignition of ammonia, and improve combustion stability; Multiple high-energy ignition system: A high-energy ignition system capable of multiple discharges is adopted, including but not limited to a multi-pulse capacitor discharge ignition system, a nanosecond pulse transient plasma ignition system, or an active pre-combustion chamber turbulent jet ignition system. This ignition system can continuously output at least two high-energy sparks in a single power stroke, with a single ignition energy of not less than 80mJ, and the total ignition energy can be adjusted within the range of 100mJ to 500mJ according to the operating conditions. Variable valve drive system: Equipped with continuously variable intake and exhaust valve timing (VVT) and variable valve lift (VVA) to achieve continuous adjustment of intake valve closing angle, continuous adjustment of intake valve opening angle (adjustment range not less than 40°CA), and continuous variable valve overlap angle within the range of 0 to 80°CA; The compression ratio piston, ignition system and variable valve drive system described above are merely exemplary implementations of this embodiment. Any device capable of performing the corresponding functions can be applied to this embodiment, and this application does not limit them.

[0023] The control method in this embodiment includes the following steps: S1. Obtain the operating data of the pure ammonia engine; In this embodiment, the operating data of the pure ammonia engine includes engine speed and engine braking average effective pressure; In one specific implementation provided in this embodiment, the ECU obtains the current speed through the engine speed sensor and the current load through the load sensor (in this embodiment, the brake mean effective pressure BMEP is used to represent the load).

[0024] S2. Identify the current operating conditions based on operating data.

[0025] The ECU determines which of the following conditions the current operating condition is: idling, low load, medium load, or high load, based on the preset operating condition classification rules. The specific identification rules are as follows: ① If the engine speed is in the idle speed range (preferably 450rpm~550rpm in this embodiment), and the engine braking average effective pressure is less than or equal to the first pressure threshold, preferably BMEP≤0.1MPa in this embodiment, then it is identified as an idle condition; ② If the engine speed is within the first speed range (preferably 600rpm to 1800rpm in this embodiment), and the brake mean effective pressure of the engine is greater than the first pressure threshold and less than or equal to the second pressure threshold (preferably 0.1MPa < BMEP ≤ 0.4MPa in this embodiment), it is identified as a low-load working condition; ③ If the engine speed is within the first speed range (preferably 600rpm to 1800rpm in this embodiment), and the brake mean effective pressure of the engine is greater than the second pressure threshold and less than the third pressure threshold (preferably 0.4MPa < BMEP < 0.8MPa in this embodiment), it is identified as a medium-load working condition; ④ If the engine speed is within the first speed range (600rpm to 1800rpm), and the brake mean effective pressure of the engine is greater than or equal to the third pressure threshold, that is, BMEP ≥ 0.8MPa, it is identified as a high-load working condition; It should be noted that the above speed ranges and engine brake mean effective pressure thresholds are exemplary values in this embodiment. Those skilled in the art can appropriately adjust the above thresholds according to the actual displacement, design parameters and application scenarios of the engine, and these adjustments still fall within the protection scope of the present application.

[0026] S3, executing corresponding ignition strategies and valve strategies according to the identification results.

[0027] In this embodiment, executing corresponding ignition strategies and valve strategies according to the identification results is specifically as follows: When identified as an idling working condition, a multiple ignition mode is adopted as the ignition strategy, ignition is performed with a preset idling ignition timing, and meanwhile a first valve strategy is adopted, wherein the advance amount of the intake valve closing angle is not greater than a preset idling crank angle, and the valve overlap angle is controlled within a preset idling overlap angle range; When identified as a low-load working condition, a double ignition mode is adopted as the ignition strategy, ignition is performed with a preset low-load ignition timing, and meanwhile a second valve strategy is adopted, wherein the advance amount of the intake valve closing angle is not greater than a preset low-load crank angle; When identified as a medium-load working condition, a single ignition mode is adopted as the ignition strategy, ignition is performed with a preset low-load ignition timing, and meanwhile the second valve strategy is adopted; When identified as a high-load working condition, a single ignition mode is adopted as the ignition strategy, ignition is performed with a preset high-load ignition timing, and meanwhile a third valve strategy is adopted, wherein the intake valve is closed in advance within a preset advance angle range or retarded to close within a preset retard angle range to reduce the effective compression ratio.

[0028] S301, idling working condition Specifically, when the engine speed is close to idle, the load is extremely low, the throttle opening is small, the intake air volume in the cylinder is small, and the compression end temperature is low. Ammonia's minimum ignition energy is more than 60 times that of gasoline, and its laminar flame velocity is about 1 / 5 that of gasoline. The extremely low compression end temperature under idle conditions further exacerbates the ignition difficulty. Conventional single-spark ignition methods are unable to reliably ignite the lean ammonia / air mixture. Therefore: When the system is identified as idling, the control method is as follows: Ignition strategy: A multi-ignition mode is adopted, that is, 2 to 5 high-energy sparks are continuously output in a single working cycle, with a single ignition energy of not less than 80mJ and a total ignition energy controlled within the range of 100mJ to 500mJ; the ion wind effect generated by multi-pulse discharge enhances local turbulence and mixing, which can effectively increase the flame core surface area, thereby overcoming the high ignition energy requirement of ammonia fuel; in this embodiment, the ignition timing is set near the top dead center of the compression stroke, preferably within the range of 45°CA before top dead center to 10°CA after top dead center; Valve strategy: In this embodiment, the Miller cycle is preferred: the first valve strategy is adopted, in which the intake valve closing angle advance is not greater than the preset idle crankshaft angle and the valve overlap angle is controlled within the preset idle overlap angle range. In this embodiment, the preset idle crankshaft angle is 15°CA and the preset idle overlap angle range is 10°CA~30°CA, so as to reduce the dilution of fresh charge by exhaust gas, maintain the in-cylinder charge density and compression end temperature, thereby making the effective compression ratio close to the geometric compression ratio, and creating the highest compression end temperature conditions for idle ignition.

[0029] It should be noted that the above-mentioned ignition frequency, ignition energy and valve angle range are exemplary values ​​in this embodiment. Those skilled in the art can perform calibration and optimization according to the specific design parameters of the engine and the requirements for idle speed stability. Under the premise of meeting stable combustion, appropriate adjustments are still within the protection scope of this application. By combining a high geometric compression ratio with a Miller valve-less strategy, a high compression end temperature and pressure are generated; coupled with 2 to 5 consecutive high-energy ignitions, the two work synergistically to enable stable and reliable ignition and combustion of ammonia fuel under idling conditions.

[0030] S302, Low-load operating condition: When the condition is identified as low load (BMEP greater than 0.1 MPa and less than or equal to 0.4 MPa), the control method is as follows: Ignition Strategy: A dual ignition mode is adopted as the ignition strategy, and a preset low-load ignition timing is used for ignition. In this embodiment, the preset low-load ignition timing is such that the combustion phase CA50 is located within the range of 8°CA to 12°CA after top dead center; the dual ignition mode outputs two high-energy sparks continuously within a single working cycle, with a single ignition energy of not less than 80mJ, to enhance ignition reliability; Valve strategy: A second valve strategy is adopted, where the intake valve closing angle advance is no greater than the preset low-load crankshaft angle. In this embodiment, the preset low-load crankshaft angle is 20°CA, maintaining the effective compression ratio close to the geometric compression ratio. Simultaneously, the throttle opening and / or intake VVT ​​are adjusted according to the load to achieve a load control mode that primarily uses quality regulation (changing the charge density) and secondarily uses quantity regulation, in order to maintain a high partial load thermal efficiency. Specifically, the ECU has a pre-stored calibration MAP of throttle opening, intake VVT ​​angle, and load (BMEP). By reading the current load signal in real time, the corresponding target control parameters are obtained by looking up the table, and the control signal is output to the throttle actuator and variable valve drive system for execution.

[0031] Under low-load conditions, dual ignition enhances ignition reliability, and combined with a high effective compression ratio, it ensures stable combustion at low loads, creating conditions for a smooth transition to medium-load conditions.

[0032] It should be noted that the CA50 range, ignition energy, and valve angle range mentioned above are exemplary values ​​for this embodiment. Those skilled in the art can perform calibration and optimization based on the specific design parameters of the engine. Appropriate adjustments, while ensuring stable combustion and thermal efficiency, still fall within the scope of protection of this application. S303, medium load condition: When the condition is identified as medium load (BMEP greater than 0.4 MPa and less than 0.8 MPa), the control method is as follows: Ignition strategy: A single ignition mode is adopted as the ignition strategy, and a preset low-load ignition timing is used for ignition. In this embodiment, the preset low-load ignition timing is such that the combustion phase CA50 is located within the range of 8°CA to 12°CA after top dead center; the single ignition mode is such that the single ignition energy is not less than 80mJ, and the combustion is in the optimal position by optimizing the ignition timing; Valve strategy: A second valve strategy is adopted, that is, the intake valve closing angle advance is not greater than the preset low-load crankshaft angle (20°CA in this embodiment), that is, there is no Miller cycle or a shallow Miller cycle, and the effective compression ratio is kept close to the geometric compression ratio. At the same time, the throttle opening and / or intake VVT ​​are adjusted according to the load to achieve a load control mode with quality regulation (changing the charge density) as the main method and quantity regulation as the auxiliary method, so as to maintain a high partial load thermal efficiency. Specifically, the ECU has a pre-stored calibration MAP of throttle opening, intake VVT ​​angle and load (BMEP). By reading the current load signal in real time, the corresponding target control parameters are obtained by looking up the table, and the control signal is output to the throttle actuator and variable valve drive system for execution.

[0033] Under medium load conditions, the high effective compression ratio provides excellent compression termination conditions, which, combined with optimized ignition timing, enables efficient combustion of ammonia fuel.

[0034] S304, High-load operating conditions: Under high load conditions, the combustion pressure inside the cylinder increases significantly. If a high geometric compression ratio is used without any measures to reduce the compression ratio, the maximum combustion pressure in the cylinder may exceed the limits of the engine's mechanical structure, causing engine damage. Therefore: When the condition is identified as a high-load condition (engine speed between 600 rpm and 1800 rpm, and BMEP ≥ 0.8 MPa), the control method is as follows: Ignition Strategy: A single ignition mode is adopted as the ignition strategy, and a preset high-load ignition timing is used for ignition. In this embodiment, the preset high-load ignition timing is to ensure that the combustion phase CA50 is within the range of 10°CA to 20°CA after top dead center. The single ignition mode is to ensure that the single ignition energy is not less than 80mJ, so as to reduce the peak combustion pressure and avoid incomplete combustion and excessive exhaust temperature caused by excessively late ignition timing. Valve strategy: A third valve strategy is adopted to reduce the effective compression ratio by either closing the intake valve in advance within a preset advance angle range or closing the intake valve in a preset retard angle range. This embodiment preferably uses a Miller cycle with early intake valve closing, where the preset advance angle range is 30°CA to 60°CA, to prevent unburned ammonia leakage into the intake manifold, reduce the effective compression ratio, thereby reducing the peak in-cylinder pressure while maintaining a large expansion ratio and high thermal efficiency. Alternatively, a Miller cycle with delayed intake valve closing can also be used, where the preset retard angle range is 30°CA to 60°CA, which also achieves the purpose of reducing the effective compression ratio to control knock pressure. It should be noted that the above angle range and ignition energy values ​​are exemplary values ​​in this embodiment. Those skilled in the art can calibrate and optimize them according to the specific design parameters of the engine. Under the premise of meeting the requirements of explosion pressure control and thermal efficiency, appropriate adjustments are still within the protection scope of this application. The intake valve early closing angle is dynamically adjusted according to the load size—the higher the load, the larger the intake valve early closing angle, and the greater the reduction in effective compression ratio, so as to achieve precise control of burst pressure. Specifically, the ECU has a pre-stored calibration MAP of intake valve early closing angle and load (BMEP). By reading the current load signal in real time, the corresponding target intake valve early closing angle is obtained by looking up the table, and the control signal is output to the variable valve drive system for execution. By reducing the effective compression ratio through the third valve strategy, the peak pressure in the cylinder is controlled within the mechanical tolerance range of the engine; at the same time, the expansion ratio is still kept at a high level (the expansion ratio is equal to the geometric compression ratio), ensuring that the cycle thermal efficiency does not decrease significantly. Combined with the preset high-load ignition timing, the engine is protected while maintaining high thermal efficiency, effectively solving the technical problem of excessive explosion pressure under high-load conditions.

[0035] In addition, this method also includes a partition boundary transition control step, specifically: S305, Partition Boundary Transition Control: During the load change range from low load to high load (e.g., when BMEP approaches 0.8 MPa), to avoid combustion instability caused by sudden changes in control parameters, this embodiment adopts a smooth transition control strategy: Valve strategy: The intake valve closing angle increases continuously with the increase of load (non-step change); in this embodiment, the transition zone uses linear interpolation or a load-based mapping table to make the advance of the intake valve closing angle increase continuously with the increase of load.

[0036] Ignition strategy: The number of ignitions smoothly transitions from multiple (double) to single ignition. The ignition timing is appropriately advanced as the intake valve closing angle increases to compensate for the decrease in combustion rate caused by the reduction in effective compression ratio.

[0037] The above-mentioned smooth transition control ensures stable combustion during the switching of operating conditions and avoids torque fluctuations or misfires caused by sudden changes in parameters.

[0038] This embodiment also includes a closed-loop feedback step, specifically: S306, Closed-loop feedback control: The ECU monitors the combustion status in real time through the knock sensor and cylinder pressure sensor. If the knock pressure exceeds the limit or the combustion is unstable, the control parameters are fine-tuned until the combustion status returns to normal. In this embodiment, the control parameters are fine-tuned, including but not limited to ignition timing and intake valve early closing angle. For example, if the explosion pressure is detected to be close to the limit under high load conditions, the intake valve early closing angle can be further increased to reduce the effective compression ratio, or the ignition timing can be delayed.

[0039] Example 2: This embodiment provides an ammonia-based single-fuel full-load high-efficiency combustion control system for executing the control method of Embodiment 1. Specifically, the system includes: The operating condition identification unit is used to acquire the operating data of the pure ammonia engine (including engine speed and engine braking mean effective pressure) and identify the current operating condition based on the operating data. Specifically, the operating condition identification unit identifies conditions according to the following rules: If the engine speed is in the idle speed range (450rpm~550rpm) and the engine braking average effective pressure is less than or equal to the first pressure threshold (BMEP≤0.1MPa in this embodiment), it is identified as an idle condition. If the engine speed is within the first speed range (600rpm~1800rpm), and the brake mean effective pressure of the engine is greater than the first pressure threshold and less than or equal to the second pressure threshold (in this embodiment, 0.1MPa < BMEP ≤ 0.4MPa), it is identified as a low-load operating condition; If the engine speed is within the first speed range (600rpm~1800rpm), and the brake mean effective pressure of the engine is greater than the second pressure threshold and less than the third pressure threshold (in this embodiment, 0.4MPa < BMEP < 0.8MPa), it is identified as a medium-load operating condition; If the engine speed is within the first speed range (600rpm~1800rpm), and the brake mean effective pressure of the engine is greater than or equal to the third pressure threshold (in this embodiment, BMEP ≥ 0.8MPa), it is identified as a high-load operating condition.

[0040] An ignition control unit, configured to execute a corresponding ignition strategy according to the operating condition identification result, which is specifically as follows: Under idling operating condition, a multiple ignition mode is adopted as the ignition strategy, and ignition is performed with a preset idling ignition timing; the multiple ignition mode means that 2 to 5 high-energy sparks are continuously output within a single working cycle, the single ignition energy is not less than 80mJ, and the total ignition energy is 100mJ to 500mJ; the preset idling ignition timing is within the range from 45°CA before top dead center to 10°CA after top dead center of the compression stroke; Under low-load operating condition, a double ignition mode is adopted as the ignition strategy, and ignition is performed with a preset low-load ignition timing; the double ignition mode means that two high-energy sparks are continuously output within a single working cycle, and the single ignition energy is not less than 80mJ; the preset low-load ignition timing enables the combustion phase CA50 to be within the range of 8°CA to 12°CA after top dead center; Under medium-load operating condition, a single ignition mode is adopted as the ignition strategy, and ignition is performed with a preset low-load ignition timing; the single ignition mode means that the single ignition energy is not less than 80mJ; Under high-load operating condition, a single ignition mode is adopted as the ignition strategy, and ignition is performed with a preset high-load ignition timing; the preset high-load ignition timing enables the combustion phase CA50 to be within the range of 10°CA to 20°CA after top dead center.

[0041] A valve control unit, configured to execute a corresponding valve strategy according to the operating condition identification result, which is specifically as follows: Under idling operating condition, a first valve strategy is adopted, in which the advance amount of the intake valve closing angle is not greater than a preset idling crankshaft angle, and the valve overlap angle is controlled within a preset idling overlap angle range; in this embodiment, the preset idling crankshaft angle is 15°CA, and the preset idling overlap angle range is 10°CA~30°CA; Under low load conditions, a second valve strategy is adopted, in which the intake valve closing angle advance is no greater than the preset low load crankshaft angle; in this embodiment, the preset low load crankshaft angle is 20°CA. Under medium load conditions, a second valve strategy is adopted; Under high-load conditions, a third valve strategy is adopted to reduce the effective compression ratio by closing the intake valve in advance within a preset advance angle range or closing the intake valve in a preset retard angle range. In this embodiment, the Miller cycle with early intake valve closure is preferred, with a preset advance angle range of 30°CA to 60°CA. As an alternative, a Miller cycle with delayed intake valve closure can also be used, with a preset retard angle range of 30°CA to 60°CA.

[0042] The operating condition identification unit, ignition control unit, and valve control unit are connected to each other. The ignition control unit and valve control unit execute corresponding ignition strategies and valve strategies in response to the identification results of the operating condition identification unit. Preferably, the operating condition identification unit, ignition control unit, and valve control unit are integrated into the engine's electronic control unit (ECU).

[0043] The system in this embodiment can implement all the control methods of Embodiment 1 and achieve the corresponding technical effects. For details, please refer to the description of Embodiment 1, which will not be repeated here.

[0044] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0045] It should be noted that in this application, relational terms such as "first" and "second" are used merely 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.

[0046] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A high-efficiency combustion control strategy for ammonia as a single fuel at full load, characterized in that, For pure ammonia engines with a geometric compression ratio greater than or equal to 18:1, the following steps are included: The system acquires the operating data of the pure ammonia engine and identifies the current operating condition based on the operating data; the current operating condition includes idling condition, low load condition, medium load condition and high load condition. When the idling condition is identified, a multi-ignition mode is used as the ignition strategy, and ignition is performed using a preset idle ignition timing. At the same time, a first valve strategy is adopted, in which the intake valve closing angle advance is not greater than the preset idle crankshaft angle and the valve overlap angle is controlled within the preset idle overlap angle range. When the low-load condition is identified, a dual-ignition mode is adopted as the ignition strategy, and ignition is performed using a preset low-load ignition timing. At the same time, a second valve strategy is adopted with the intake valve closing angle advance not greater than the preset low-load crankshaft angle. When the condition is identified as medium load, a single ignition mode is used as the ignition strategy, and a preset low load ignition timing is used for ignition, while the second valve strategy is used at the same time. When a high-load condition is identified, a single ignition mode is used as the ignition strategy, and ignition is performed using a preset high-load ignition timing. At the same time, a third valve strategy is adopted to reduce the effective compression ratio by either closing the intake valve in advance or delaying the intake valve in advance.

2. The ammonia single-fuel full-load high-efficiency combustion control strategy according to claim 1, characterized in that, The preset idle crankshaft angle is 15°CA, the preset idle overlap angle range is 10°CA~30°CA, and the preset idle ignition timing is located within the range of 45°CA before top dead center of the compression stroke to 10°CA after top dead center.

3. The ammonia single-fuel full-load high-efficiency combustion control strategy according to claim 1, characterized in that, The preset low-load crankshaft angle is 20°CA, and the preset low-load ignition timing is such that the combustion phase CA50 is located within the range of 8°CA to 12°CA after top dead center.

4. The ammonia single-fuel full-load high-efficiency combustion control strategy according to claim 1, characterized in that, The preset advance angle range is 30°CA to 60°CA, the preset retard angle range is 30°CA to 60°CA, and the preset high-load ignition timing is such that the combustion phase CA50 is located within the range of 10°CA to 20°CA after top dead center.

5. The ammonia single-fuel full-load high-efficiency combustion control strategy according to claim 1, characterized in that, The operating data includes engine speed and engine braking mean effective pressure.

6. The ammonia single-fuel full-load high-efficiency combustion control strategy according to claim 1, characterized in that, Identifying the current operating condition based on the aforementioned operating data specifically includes: If the engine speed is within the idle speed range and the average effective pressure of the engine braking is less than or equal to the first pressure threshold, it is identified as an idle condition. If the engine speed is within the first speed range, and the average effective pressure of engine braking is greater than the first pressure threshold and less than or equal to the second pressure threshold, it is identified as a low-load condition. If the engine speed is in the first speed range, and the average effective pressure of engine braking is greater than the second pressure threshold and less than the third pressure threshold, it is identified as a medium load condition. If the engine speed is within the first speed range and the average effective pressure of engine braking is greater than or equal to the third pressure threshold, it is identified as a high-load condition.

7. The ammonia single-fuel full-load high-efficiency combustion control strategy according to claim 6, characterized in that, The idle speed range is 450 rpm to 550 rpm, the first pressure threshold is 0.1 MPa, the second pressure threshold is 0.4 MPa, the third pressure threshold is 0.8 MPa, and the first speed range is 600 rpm to 1800 rpm.

8. The ammonia single-fuel full-load high-efficiency combustion control strategy according to claim 1, characterized in that: The multiple ignition mode includes: continuously outputting at least two high-energy sparks within a single working cycle, with a single ignition energy of not less than 80mJ and a total ignition energy of 100mJ to 500mJ; The dual ignition mode includes: continuously outputting two high-energy sparks within a single working cycle, with a single ignition energy of not less than 80mJ; The single ignition mode includes: a single ignition energy of not less than 80mJ.

9. The ammonia single-fuel full-load high-efficiency combustion control strategy according to claim 1, characterized in that, It also includes a zone boundary transition control step: in the load change range from low load condition to high load condition, the advance or retardation of the intake valve closing angle is controlled to increase continuously with the increase of load, and the number of ignitions is controlled to smoothly transition from multiple to single.

10. A system based on the ammonia single-fuel full-load high-efficiency combustion control strategy of claim 1, characterized in that, include: The operating condition identification unit is used to acquire the operating data of the pure ammonia engine and identify the current operating condition based on the operating data; The current operating conditions include idling, low load, medium load, and high load. The ignition control unit is used to employ a multi-ignition mode as the ignition strategy and a preset idle ignition timing during idling; a dual-ignition mode as the ignition strategy and a preset low-load ignition timing during low-load conditions; a single-ignition mode as the ignition strategy and a preset low-load ignition timing during medium-load conditions; and a single-ignition mode as the ignition strategy and a preset high-load ignition timing during high-load conditions. The valve control unit is used to employ a first valve strategy when idling, where the intake valve closing angle advance is no greater than a preset idle crankshaft angle and the valve overlap angle is controlled within a preset idle overlap angle range; a second valve strategy when low load, where the intake valve closing angle advance is no greater than a preset low load crankshaft angle; and a second valve strategy when medium load. In addition, under high load conditions, a third valve strategy is adopted to reduce the effective compression ratio by pre-setting the intake valve advance angle range or delaying the intake valve retard angle range.

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