Cooperative control method for air-fuel ratio, injection opportunity and cooling liquid temperature in hydrogen fuel engine

Abstract

The invention discloses a cooperative control method for the air-fuel ratio, the injection opportunity and the cooling liquid temperature of a hydrogen fuel engine. The cooperative control method comprises the steps that S1, operation condition parameters and combustion state parameters of the hydrogen fuel engine are monitored; s2, based on the operation condition parameters, adaptively determining a target air-fuel ratio, a fuel injection opportunity and a cooling liquid temperature through a preset control strategy; s3, the combustion state and the engine operation condition are evaluated in real time through a closed-loop feedback control system, and the following cooperative adjustment is executed: the hydrogen supply amount is adjusted to maintain the target air-fuel ratio; the hydrogen injection time is adjusted, and the combustion phase is optimized. According to the cooperative control method for the air-fuel ratio, the injection opportunity and the cooling liquid temperature in the hydrogen fuel engine, the target air-fuel ratio, the hydrogen fuel injection opportunity and the engine cooling liquid temperature are comprehensively adjusted under a closed-loop feedback control framework, optimal control over the combustion process under different working conditions is achieved, and therefore the braking heat efficiency of the engine is improved, and the service life of the engine is prolonged. And pollutant emission is reduced, knocking is restrained, and the application requirement for efficient cleaning of the engine is met.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of internal combustion engine clean combustion and control technology, and particularly relates to a synergistic control method for air-fuel ratio, injection timing and coolant temperature in a hydrogen fuel engine. BACKGROUND

[0002] Hydrogen, as an important energy carrier for carbon neutralization, is considered as one of the most promising alternative fuels for internal combustion engines due to its carbon-free combustion, which only generates water and a small amount of nitrogen oxides (NOx). The physicochemical properties of hydrogen endow it with excellent combustion performance: high diffusion coefficient and extremely low ignition energy make the formation of mixture and ignition stable, and the wide flammable concentration range (4% to 75% by volume) supports ultra-lean combustion to reduce emissions. In addition, the laminar flame speed of hydrogen is about 7.6 times that of gasoline, the self-ignition temperature is high, and the extinction distance is short, which helps to improve the thermal efficiency of the engine and enhance the anti-knock ability.

[0003] Despite the above advantages of hydrogen fuel, large-scale application of hydrogen internal combustion engines still faces many technical challenges, including pre-ignition (pre-ignition), knock, lubricating oil emulsification, and high NOx emissions. NOx (nitrogen oxides) emissions are one of the difficult problems to be solved for hydrogen internal combustion engines, especially the N2O and NO2 components, which have strong greenhouse effect and toxicity, respectively. NO accounts for most of NOx in conventional fossil fuel engines, while the generation mechanisms of NO2 and N2O are different under hydrogen combustion conditions. For example, when hydrogen fuel is mixed with ammonia fuel at a very small proportion, N2O may become the dominant product, and its greenhouse effect is 298 times that of CO2. As the proportion of hydrogen fuel increases, NO gradually becomes the main component of NOx, and high-temperature thermal NO generation dominates. Therefore, in order to effectively control the NOx emissions of hydrogen combustion, it is necessary to deeply understand the generation and conversion mechanisms of NO, NO2 and N2O under different working conditions.

[0004] To improve combustion performance and reduce emissions, researchers have proposed various control strategies. For example, by controlling the air-fuel ratio and ignition parameters to suppress the generation of NOx: when the excess air coefficient λ is between 1.1 and 1.5, the peak in-cylinder temperature may exceed 2200 K, leading to an exponential increase in NOx, which requires combustion control strategies to alleviate. Lee et al. reduced NOx emissions by more than 80% through hydrogen post-injection technology; BMW's phased load strategy uses ultra-lean combustion (λ>2.5) at low load and rich combustion (λ<1) at high load, combined with a three-way catalyst, to increase NOx conversion efficiency to 99.5%. For example, advanced ignition technology (pre-chamber, multi-spark plug, etc.) further expands the hydrogen engine's lean combustion limit, achieving low NOx emissions and high thermal efficiency operation. In addition, the injection strategy has a significant impact on hydrogen fuel combustion. Studies have shown that direct injection hydrogen engines can significantly improve combustion and emission performance by optimizing injection timing and injection strategy: delaying direct injection to 60°CA before top dead center increases the concentration gradient near the spark plug, increasing the indicated thermal efficiency to about 49.9%, but unburned hydrocarbon (UHC) emissions rise; using a "double injection" strategy (such as early premixed injection at 120°CA BTDC, followed by a second enrichment injection during compression) reduces NOx by 67% while controlling the cycle-to-cycle variation (COV) to within 3%. For example, early injection (starting at about 300°CA before top dead center) combined with high tumble intake design can achieve a mixture homogeneity of 92%, effectively suppressing knock and reducing NOx emissions. In addition to air-fuel ratio and injection control, water injection and exhaust gas recirculation (EGR) can also reduce NOx: in-cylinder direct injection of water can maintain the cylinder temperature below 1600 K, reducing NOx emissions to the order of 0.01 g / kWh, but such measures can cause oil emulsification and increase system complexity. Overall, the above studies focus on the improvement of a single parameter or a single measure, and there is a lack of systematic research and comprehensive control means for the dynamic coupling effects of engine air-fuel ratio, injection timing, coolant temperature, and other key parameters.

[0005] However, in the actual operation of hydrogen fuel engines, the performance is affected by various operating parameters, which are not isolated but show complex interdependence. Specifically, engine load, air-fuel ratio, injection timing, and coolant temperature are key parameters that determine the engine's combustion state, thermal efficiency, and emission performance.

[0006] For example, with the air-fuel ratio parameter, although the extremely lean air-fuel ratio can reduce the combustion temperature, thereby inhibiting the generation of nitrogen oxides (NOx) to some extent, meeting the requirements of clean engine operation, at the same time, the extremely lean air-fuel ratio often causes unstable combustion problems, and in severe cases, even causes engine stall, greatly affecting the stable operation of the engine. In order to compensate for the defect of reduced combustion rate caused by lean combustion, it is usually necessary to adjust the ignition or fuel injection strategy to stabilize the generation of flame kernel, which fully embodies the close relationship between the air-fuel ratio and the injection timing and other parameters.

[0007] The coolant temperature directly affects the heat dissipation of the cylinder wall and the combustion temperature gradient, which in turn affects the engine knock tendency and NOx generation. When the coolant temperature is at different levels, the combustion environment inside the engine will change, and various performance parameters will also change.

[0008] In the prior art, the control of hydrogen fuel engine mostly adopts a single parameter control method, which is difficult to take into account the synergy between various parameters. In the actual complex and variable working conditions on the road, it is often impossible to simultaneously achieve efficient, clean and stable operation of the engine, affecting the combustion stability of the engine, and greatly limiting the promotion and application of hydrogen fuel engine in practice.

[0009] The present application provides a method for coordinated control of air-fuel ratio, injection timing and coolant temperature in a hydrogen fuel engine, and in particular relates to how to improve the combustion stability of a hydrogen fuel engine. SUMMARY

[0010] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a method for coordinated control of air-fuel ratio, injection timing and coolant temperature in a hydrogen fuel engine, with the purpose of improving the combustion stability of a hydrogen fuel engine.

[0011] In order to achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows: a method for coordinated control of air-fuel ratio, injection timing and coolant temperature in a hydrogen fuel engine, comprising the steps of:

[0012] S1, monitoring the operating condition parameters and combustion state parameters of the hydrogen fuel engine;

[0013] S2, based on the operating condition parameters, determining the target air-fuel ratio, fuel injection timing and coolant temperature through a pre-set control strategy;

[0014] S3, real-time evaluation of the combustion state and engine operating condition through a closed-loop feedback control system, and performing the following coordinated adjustment:

[0015] Adjusting the hydrogen supply to maintain the target air-fuel ratio;

[0016] Adjusting the hydrogen injection timing optimizes the combustion phase.

[0017] The operating condition parameters include engine load and engine speed, and the combustion state parameters include in-cylinder pressure, knock intensity, air-fuel ratio, and coolant temperature.

[0018] In the low load condition of the engine, the upper limit of the target air-fuel ratio λ is set not to exceed a first preset threshold value; in the medium and high load condition, the target air-fuel ratio is increased to a second preset threshold value range;

[0019] Wherein, the first preset threshold value is λ≤2.8, and the second preset threshold value range is 2.5≤λ≤3.0.

[0020] According to the comparison result of the engine load and the preset load threshold value, the hydrogen injection strategy is selected:

[0021] (a) When the engine is in a light load condition, an early direct injection strategy is adopted, which makes the hydrogen injection end early before ignition, forming a homogeneous lean mixture;

[0022] (b) When the engine is in a high load condition, a late direct injection strategy is adopted, which makes the hydrogen injection complete near the ignition time, forming a stratified combustion;

[0023] Wherein, the early direct injection strategy reduces the formation of local high temperature area in the cylinder by increasing the mixing time of hydrogen and air; the late direct injection strategy reduces the risk of spontaneous combustion by shortening the residence time of hydrogen in the compression stroke;

[0024] The light load condition of the engine is the condition that the engine load is lower than the predetermined load threshold value, and the high load condition of the engine is the condition that the engine load is higher than the predetermined load threshold value.

[0025] The preset control strategy includes:

[0026] (1) The engine coolant temperature is set in the range of 60℃ to 90℃;

[0027] (2) When signs of knock or over-temperature state are monitored, temporarily reduce the coolant temperature or enhance the cooling intensity;

[0028] (3) After the knock is eliminated or the high temperature state is alleviated, the high temperature operation of the coolant is restored.

[0029] The closed-loop feedback control system is realized by the following ways:

[0030] Using in-cylinder pressure sensor or acceleration knock sensor to monitor knock intensity, when the knock intensity exceeds the preset threshold value, automatically delay the hydrogen injection timing and / or ignition timing, and reduce the coolant temperature;

[0031] Using exhaust oxygen sensor to monitor air-fuel ratio deviation, and adjusting the hydrogen injection pulse width in real time;

[0032] The actual temperature of the cooling liquid is monitored by a temperature sensor, and the temperature of the cooling liquid is stabilized in a target temperature range by controlling the electronic thermostat and the rotating speed of the water pump.

[0033] In step S3, the combustion stability is controlled by monitoring the cycle variation coefficient indicating the average effective pressure;

[0034] When the cycle variation coefficient is higher than a third preset threshold value, the fuel injection amount is increased or the injection timing is advanced; when the cycle variation coefficient is lower than a fourth preset threshold value and there is no risk of knocking, the fuel injection amount is reduced or the injection timing is delayed.

[0035] The third preset threshold value is greater than or equal to 3%, and the fourth preset threshold value is less than or equal to 1%.

[0036] In step S3, the advance direct injection strategy makes the end time of hydrogen injection not later than 120° crank angle before the top dead center of the compression stroke, and the lag direct injection strategy makes the end time of hydrogen injection not earlier than 30° crank angle before the top dead center of the compression stroke.

[0037] In step S3, when the engine braking average effective pressure is greater than or equal to 8 bar, the cycle variation coefficient is maintained at less than or equal to 1% by adjusting the cooling liquid temperature and the lag direct injection strategy.

[0038] The synergistic control method of hydrogen fuel engine air-fuel ratio, injection timing and cooling liquid temperature in the application, by comprehensively adjusting the target air-fuel ratio, hydrogen fuel injection timing and engine cooling liquid temperature under the closed-loop feedback control framework, realizes the optimization control of the combustion process under different working conditions, so as to improve the brake thermal efficiency of the engine, reduce the pollutant emission and inhibit the knocking, and meets the application demand of high-efficiency clean engine. BRIEF DESCRIPTION OF DRAWINGS

[0039] The present specification includes the following drawings, and the contents shown are as follows:

[0040] Figure 1 It is a hydrogen fuel engine test bench schematic diagram for researching and verifying the method of the application.

[0041] Figure 2a It is a trend chart showing that the ignition delay, combustion duration and cycle variation coefficient (COV) increase with the increase of air-fuel ratio.

[0042] Figure 2b It is a trend chart showing that the specific hydrogen consumption (SHC) gradually decreases, and the brake thermal efficiency (BTE) increases with the increase of air-fuel ratio.

[0043] Figure 3Distribution of maximum cylinder pressure Pmax and its crank angle of occurrence APmax for 200 cycles at medium load (BMEP = 8 bar) for different relative air-fuel ratios.

[0044] Figure 4a Plot of NO, NO2 and N2O concentration in exhaust gas of hydrogen fueled engine as a function of relative air-fuel ratio for BMEP = 4 bar.

[0045] Figure 4b Plot of NO, NO2 and N2O concentration in exhaust gas of hydrogen fueled engine as a function of relative air-fuel ratio for BMEP = 8 bar.

[0046] Figure 4c Plot of NO, NO2 and N2O concentration in exhaust gas of hydrogen fueled engine as a function of relative air-fuel ratio for BMEP = 10 bar.

[0047] Figure 5a Plot of specific hydrogen consumption (SHC) and brake thermal efficiency (BTE) as a function of EOI.

[0048] Figure 5b Plot of 50% burn center (CA50) and exhaust gas temperature as a function of EOI.

[0049] Figure 6 Comparison plot of energy distribution for different hydrogen injection timings.

[0050] Figure 7 Comparison of NOx emission composition for different injection timings.

[0051] Figure 8a Distribution of cycle cylinder pressure characteristics for different hydrogen injection timings at light load (BMEP = 4 bar).

[0052] Figure 8b Distribution of cycle cylinder pressure characteristics for different hydrogen injection timings at high load (BMEP = 12 bar).

[0053] Figure 9a , Figure 9b , Figure 9c , Figure 9d Comparison plot of cylinder pressure, heat release rate (HRR) and temperature variation for different injection timings at different loads (4 bar and 12 bar).

[0054] Figure 10 Plot of variation of specific hydrogen consumption (SHC) and brake thermal efficiency (BTE) for different coolant temperatures.

[0055] In the figures, the following is marked:

[0056] 1, encoder; 2, exhaust pipe; 3, computer; 4, data collector; 5, turbocharger; 6, intercooler; 7, solenoid valve; 8, hydrogen guide rail; 9, air intake pipe; 10, dynamometer; 11, hydrogen tank group; 12, flame arrester; 13, hydrogen flowmeter; 14, pressure reducing valve. DETAILED DESCRIPTION

[0057] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings, and the purpose is to help the technical personnel in the art to have a more complete, accurate and in-depth understanding of the concept and technical solution of the present application, and to help its implementation.

[0058] The embodiment of the present application provides a synergistic control method for air-fuel ratio, injection timing and coolant temperature in a hydrogen fuel engine, comprising the following steps:

[0059] S1, monitoring the operating condition parameters and combustion state parameters of the hydrogen fuel engine;

[0060] S2, based on the operating condition parameters, the target air-fuel ratio, fuel injection timing and coolant temperature are determined adaptively through a preset control strategy;

[0061] S3, the combustion state and engine operating condition are evaluated in real time through a closed-loop feedback control system, and the following synergistic adjustment is performed:

[0062] Adjusting the hydrogen supply amount to maintain the target air-fuel ratio;

[0063] Adjusting the fuel injection timing (especially the end of injection EOI) to control the combustion center position (CA50) and optimize the combustion phase, realize homogeneous stable combustion under light load and stratified anti-knock combustion under high load;

[0064] Adjusting the coolant temperature set value, reducing heat loss and improving thermal efficiency through high temperature operation, temporarily reducing the coolant temperature under the risk of knocking or high temperature to ensure the stability of combustion.

[0065] Specifically, in the embodiment of the present application, a synergistic control method for air-fuel ratio, injection timing and coolant temperature in a hydrogen fuel engine is provided to solve the current situation of single control deficiency in the prior art for poor combustion stability, high NOx emission and high load knock of hydrogen fuel engine. By comprehensively adjusting the intake excess air coefficient (i.e. relative air-fuel ratio λ), hydrogen fuel injection timing and engine coolant temperature under the closed-loop feedback control framework, the optimization control of the combustion process under different conditions is realized, so as to improve the brake thermal efficiency of the engine, reduce the pollutant emission and suppress the occurrence of knock, and meet the application requirements of high-efficiency clean engine.

[0066] The embodiment of the present application proposes an adaptive control strategy based on closed-loop feedback, which coordinates the control of air-fuel ratio, fuel injection timing and coolant temperature on a hydrogen fuel engine. The specific scheme is as follows:

[0067] 1. Control system configuration: The closed-loop feedback control system includes an engine control unit (ECU), in which a multi-parameter coordinated control algorithm is set, and key feedback variables including engine load (such as BMEP or throttle opening), engine speed, in-cylinder pressure sensor / knock sensor signal, exhaust oxygen sensor signal, coolant temperature sensor signal, etc. are collected. The system evaluates the combustion state and engine operating condition in real time according to these feedbacks.

[0068] 2. Air-fuel ratio control: The supply amount or intake amount of hydrogen fuel is controlled by using the feedback of the exhaust oxygen sensor, and the relative air-fuel ratio λ is adjusted to the target value.

[0069] In the above step S2, the target air-fuel ratio is adaptively set according to the engine load. The preset control strategy includes:

[0070] In medium and high load conditions, lean mixture should be used as much as possible to improve brake thermal efficiency and suppress NOx generation; while in low load conditions, excessive lean burn should be avoided to ensure combustion stability and prevent misfire. Specifically, at low load (such as BMEP < 4 bar), the target air-fuel ratio should be controlled in the range of λ ≈ 2.0-2.8 to avoid too low combustion rate and aggravate cycle fluctuation; at high load (such as BMEP ≥ 8 bar), relying on the high combustion rate of hydrogen, good stability can still be maintained, and the target air-fuel ratio can be increased to λ ≈ 2.5-3.0 to realize ultra-lean burn condition, thereby significantly improving thermal efficiency and stabilizing the cycle variation coefficient (COV) within an acceptable range (such as COV < 3%, even close to 1%).

[0071] 3. Injection timing control: The combustion phase and knock intensity are monitored by using in-cylinder pressure sensor or knock sensor, and the timing of hydrogen fuel direct injection (mainly the position of EOI or SOI relative to top dead center) is closed-loop adjusted.

[0072] In the above step S2, the control strategy adaptively switches the hydrogen injection timing according to the engine load and combustion state, and the preset control strategy includes:

[0073] At low load (e.g. BMEP < 4 bar), the hydrogen injection timing is properly advanced so that the hydrogen injection is completed long before the spark advance, forming a homogeneous lean mixture. On one hand, the early injection allows sufficient time for the hydrogen to mix with air thoroughly, eliminating concentration inhomogeneity and achieving homogeneous combustion, thus improving combustion stability and reducing cycle-to-cycle variation; on the other hand, the homogeneous lean combustion reduces local high-temperature regions and wall heat loss, helping to improve thermal efficiency and reduce NOx generation. At high load (e.g. BMEP ≥ 8-10 bar), based on the feedback from the knock sensor, the hydrogen injection timing is gradually delayed (i.e. the interval between injection and spark is shortened), so that the combustion is carried out under the condition of relatively stratified mixture. The slightly late injection strategy can form an air-fuel concentration gradient in the late compression stage, maintaining a proper equivalence ratio near the spark plug while keeping a lean mixture far from the spark plug, thus suppressing the tendency of knock. If knock is detected at this time, the injection can be further delayed or the spark timing can be retarded, so that the combustion phase is shifted backward, avoiding premature high-pressure heat release. By using the late injection to achieve stratified combustion at high load, the intensity of knock can be significantly reduced and the cycle variation can be reduced.

[0074] Preferably, when the engine is in high load condition, the fuel injection timing is determined as follows: the injection advance angle is controlled to be around 70°CA (crank angle) before top dead center (slightly later than the injection advance angle at low load), to balance the mixture uniformity and the knock safety margin.

[0075] 4. Cooling liquid temperature control: Under the action of the engine thermal management system, the cooling liquid temperature set value is appropriately increased (the conventional range is 60-90°C, and it can be increased to 100°C if necessary) to reduce cylinder wall heat loss and improve thermal efficiency, while meeting the mechanical temperature stress limit. The present application uses an electronic control thermostat and an adjustable speed water pump to close-loop regulate the cooling liquid temperature: under conventional conditions, the cooling liquid temperature is maintained at a high level (about 90°C) to obtain higher combustion efficiency; when signs of knock or continuous high load cause the cylinder temperature to be too high, the controller can temporarily lower the cooling liquid temperature set point or increase the heat dissipation intensity (such as increasing the water pump or fan speed) to enhance the cooling effect and improve the knock resistance; when the risk of knock is removed, it is restored to the high temperature set interval, achieving dynamic compromise between knock prevention and high efficiency. Through the above adjustment strategy, the heat dissipation loss can be minimized while ensuring the safety of high load operation, thereby improving the overall thermal efficiency.

[0076] 5. Closed-loop feedback and adaptive control: The above-mentioned control of air-fuel ratio, hydrogen injection timing and coolant temperature are all adjusted in real time by closed-loop algorithms within the ECU. Specifically, the ECU performs fuel supply closed-loop control according to the exhaust gas oxygen sensor signal to achieve the target air-fuel ratio; calculates the heat release center of combustion (such as CA50) and the cycle variation COV according to the cylinder pressure signal, and adjusts the hydrogen injection timing or air-fuel ratio when it detects that the combustion is slow (CA50 lags) or the fluctuation increases; according to the knock sensor signal, when the knock intensity approaches the preset threshold, the measures such as delaying the injection timing and / or temporarily reducing the coolant temperature are immediately executed to suppress the knock;

[0077] In the above step S3, when the operating condition (such as engine load or speed) changes, the ECU adaptively adjusts the target air-fuel ratio λ and the hydrogen injection timing according to the preset control mapping or algorithm rules to adapt to different operating states. In the whole control process, the adjustment of each parameter follows the principle of coordinated optimization: first, ensure the stability of combustion and the safety of operation (avoid knock and misfire); on this basis, further improve the dilution degree and maintain a high coolant temperature to reduce heat loss and improve thermal efficiency; at the same time, rely on real-time feedback correction to continuously approach the optimal state of engine performance.

[0078] In the embodiments of the present application, the operating condition parameters include engine load and engine speed, and the combustion state parameters include in-cylinder pressure, knock intensity, air-fuel ratio and coolant temperature.

[0079] In the embodiments of the present application, in the low load operating condition of the engine, the upper limit of the target air-fuel ratio λ is set to be not more than a first preset threshold; in the medium and high load operating condition, the target air-fuel ratio is increased to a second preset threshold range; wherein the first preset threshold is λ≤2.8, and the second preset threshold range is 2.5≤λ≤3.0.

[0080] The upper limit of the target air-fuel ratio λ is set to be not more than about 2.8 in the low load operating condition of the engine to prevent excessive dilution from causing unstable combustion and efficiency decline; the target air-fuel ratio is increased to the range of 2.5-3.0 in the medium and high load operating condition to utilize the wide dilution capability of hydrogen to improve thermal efficiency, while ensuring stable combustion, and maintaining the cycle variation coefficient COV within about 1% when BMEP≥8 bar.

[0081] In the embodiments of the present application, according to the comparison result of the engine load and the preset load threshold, the hydrogen injection strategy is selected:

[0082] (a) When the engine is in a light load operating condition (the engine load is lower than the predetermined load threshold), the early direct injection strategy is adopted, so that the hydrogen injection ends earlier before ignition, the hydrogen and air form a homogeneous lean mixture, and the combustion stability is enhanced;

[0083] (b) When the engine is in a high load condition (engine load is higher than a predetermined load threshold), a late direct injection strategy is adopted to make the hydrogen injection complete close to the ignition timing, forming stratified combustion, thereby relieving the knock tendency at high load;

[0084] Wherein, the early direct injection strategy reduces the formation of local high temperature area in the cylinder by increasing the mixing time of hydrogen and air, significantly reducing the total amount of NOx emissions, mainly reflected in the significant reduction of NO generation; At the same time, due to the decrease of combustion temperature peak, the generation of NO2 and N2O also remains at a low level. The late direct injection strategy reduces the risk of premature self-ignition by shortening the residence time of hydrogen in the compression stroke, which can effectively suppress engine knock and reduce cycle-to-cycle combustion instability; When stratified combustion is achieved by late injection, the local rich combustion area increases the combustion rate, ensuring stable power output and more concentrated and complete combustion at high load.

[0085] In the embodiment of the present application, the engine light load condition is a condition in which the engine load is lower than the predetermined load threshold, and the engine high load condition is a condition in which the engine load is higher than the predetermined load threshold.

[0086] In the embodiment of the present application, the preset control strategy includes:

[0087] (1) The engine coolant temperature is set in the range of 60-90℃;

[0088] (2) When the knock sign or over-load high temperature state is monitored, temporarily reduce the target temperature of the coolant or enhance the cooling intensity;

[0089] (3) After the knock is eliminated or the high temperature state is relieved, the high temperature operation of the coolant is restored.

[0090] Setting the target temperature of the engine coolant to run in a range higher than the conventional value (60-90℃) can reduce the heat loss of the cylinder wall, improve the effective heat utilization rate, and thus improve the brake thermal efficiency of the engine; When the engine shows signs of knock or over-load high temperature state is monitored, temporarily reduce the target temperature of the coolant or enhance the cooling intensity to increase the cooling effect on the combustion chamber to suppress knock, and then restore the high temperature operation of the coolant to continue to improve the efficiency.

[0091] In the embodiment of the present application, the closed-loop feedback control system realizes adaptive control by using multiple sensor signals, and the closed-loop feedback control system is realized by the following ways:

[0092] The in-cylinder pressure sensor or acceleration knock sensor is used to monitor the knock intensity, and when the knock intensity exceeds the preset threshold, the hydrogen injection timing and / or the ignition timing are automatically delayed, and the coolant temperature setting value is reduced to eliminate the knock in time;

[0093] The exhaust oxygen sensor is used to monitor the air-fuel ratio deviation, and the hydrogen supply injection pulse width is adjusted in real time to maintain the target air-fuel ratio.

[0094] The temperature sensor is used to monitor the actual temperature of the coolant, and the coolant temperature is stabilized in the target temperature range by controlling the electronic thermostat and the water pump speed.

[0095] In the embodiment of the present application, in the step S3, the hydrogen supply amount is adjusted by a closed-loop feedback control system to maintain the target air-fuel ratio, the hydrogen fuel injection timing is adjusted to optimize the combustion phase, and the coolant temperature is adjusted to control the heat transfer loss and the combustion temperature, so as to synergistically optimize the combustion stability, thermal efficiency and emission performance of the engine under different load and speed conditions. The combustion stability is controlled by monitoring the cycle variation coefficient of the indicated mean effective pressure;

[0096] When the cycle variation coefficient is higher than a third preset threshold, the fuel injection amount is increased or the injection timing is advanced; when the cycle variation coefficient is lower than a fourth preset threshold and there is no risk of knock, the fuel injection amount is reduced or the injection timing is delayed. The third preset threshold is ≥3%, and the fourth preset threshold is ≤1%.

[0097] In the step S3, the advance direct injection strategy makes the hydrogen injection end time not later than 120° crank angle before the top dead center of the compression stroke, and the late direct injection strategy makes the hydrogen injection end time not earlier than 30° crank angle before the top dead center of the compression stroke.

[0098] In the step S3, when the engine brake mean effective pressure is ≥8 bar, the cycle variation coefficient is maintained at ≤1% by the synergistic effect of adjusting the coolant temperature and the late direct injection strategy.

[0099] In the embodiment of the present application, the combustion stability control is realized by monitoring the indicated pressure cycle variation: when the calculated IMEP cycle variation coefficient COV is higher than a predetermined threshold (for example, 3%), the control unit increases the fuel injection amount (equivalent to reducing λ) or appropriately advances the injection to enhance the combustion rate, so as to adjust the COV to an acceptable range; when the COV is at a very low level and there is no risk of knock, the control unit tends to reduce the fuel injection amount (increase λ) or delay the injection to pursue higher thermal efficiency, thereby achieving a dynamic balance between stability and efficiency.

[0100] In the embodiment of the present application, the above-mentioned synergistic control can significantly improve the comprehensive performance of the engine: under the action of the control strategy, the specific hydrogen consumption of the engine is significantly reduced, the brake thermal efficiency is improved, especially under the traditional control of the medium and high load lean burn conditions, the NOx emission is effectively inhibited, the total amount is significantly reduced and mainly composed of NO, and the proportion of harmful components such as NO2 and N2O is reduced; the engine runs without knock under high compression ratio and high load, and the combustion pressure curve is smooth without abnormal fluctuation.

[0101] In the embodiments of the present application, the synergistic control method is applicable to various hydrogen fuel internal combustion engines and can be further optimized in combination with other control measures, for example, can be used in combination with an exhaust gas recirculation (EGR) system to reduce the oxygen content of intake air under ultra-lean combustion conditions to alleviate NOx emissions, or in combination with a multi-spark plug and pre-chamber ignition technology to expand the lean combustion limit, so as to further improve the performance of a hydrogen fuel engine without deviating from the principles of the present application.

[0102] By using the synergistic control method of the present application, the performance and emission performance of a hydrogen fuel engine in the entire operating range can be significantly improved. The beneficial effects are specifically embodied in:

[0103] 1. Improved combustion stability: By closed-loop control of air-fuel ratio and injection timing, the present application can control the cycle variation coefficient COV to be less than 3%, achieving smooth combustion. Even under high load, the combustion remains highly stable even if ultra-lean mixture is used, and the measured COV can be maintained below 1%; under low load, excessive dilution is avoided and early injection is used, so that the combustion rate and flame propagation are improved, and there is no misfire or severe cycle fluctuation. Therefore, the present method widens the stable operating range of the hydrogen engine under lean combustion, and improves the smoothness of engine operation under various operating conditions.

[0104] 2. Significant improvement in thermal efficiency: The synergistic control strategy effectively reduces the energy loss in the combustion process. First, appropriately increasing the air-fuel ratio (lean combustion) can improve the thermal efficiency, and experiments show that when the relative air-fuel ratio is increased from 2.0 to 3.0, the engine brake thermal efficiency BTE gradually increases. At the same time, early injection for homogeneous combustion reduces the heat loss in the high-temperature zone of the cylinder wall and the loss of unburned hydrogen. Second, increasing the coolant temperature effectively reduces the heat carried away by the cooling system. According to experiments, increasing the coolant temperature from 30°C to 90°C under high load can significantly reduce the heat transfer loss and increase the proportion of exhaust energy, thereby significantly improving the brake thermal efficiency. Under the combined action, the present application can push the engine thermal efficiency to a higher level, achieving lower specific hydrogen consumption, i.e. releasing the same power with less hydrogen consumption.

[0105] 3. Reduction of NOx emissions and optimization of composition: The present invention significantly reduces the total amount of NOx generated by means of lean-burn and optimized injection, while adjusting the composition ratio of NOx to make the exhaust aftertreatment easier. On one hand, as the air-fuel ratio increases, the combustion temperature decreases to inhibit the generation of thermal NOx, and the measured concentrations of NO and NO2 emissions decrease significantly with the increase of λ. Although the proportion of N2O increases under lean-burn conditions, its absolute concentration is still very low (not more than 2 ppm). On the other hand, the realization of homogeneous combustion by early injection significantly reduces the generation of NO (in the present invention, the proportion of NO in total NOx decreases from about 80.5% to 75.8%), while NO2 and N2O are less affected due to the limitation of chemical kinetics, and basically remain unchanged. This means that the total NOx emissions decrease with the realization of homogeneous combustion, especially the most important component of NO decreases more significantly. In addition, increasing the coolant temperature can further optimize the composition of NOx: when the coolant temperature increases from 30°C to 90°C, the proportions of N2O and NO2 in the exhaust gas decrease, while the proportion of NO increases. Under light load conditions, the volume concentration of N2O decreases by about 7%, while NO2 is significantly reduced due to high temperature inhibition, and NO becomes the dominant product. Since N2O has high greenhouse effect, NO2 is highly toxic and contributes to the generation of photochemical smog in the atmosphere, while NO is relatively easier to be reduced to nitrogen in catalytic reduction devices, the present invention reduces the environmental hazards of NOx emissions. In addition, under high load knock-prone conditions, the use of stratified combustion (retarded injection) slightly increases NOx due to local temperature rise, but with the regulation of lean-burn and coolant temperature, the overall NOx emissions remain low and there is no abnormal surge.

[0106] 4. Significant knock suppression effect: Through the synergistic control of the present invention, knock can be suppressed while maintaining high thermal efficiency. On one hand, delaying the injection timing at high load reduces the residence time of hydrogen during the compression stroke, avoiding excessive premixing time that leads to premature auto-ignition, and fundamentally reducing the possibility of knock. Experiments show that at high load BMEP = 12 bar, adjusting the injection from 160°CA to a later time, the cycle dispersion of cylinder pressure peak Pmax and occurrence angle APmax significantly decreases, indicating that knock and abnormal combustion are effectively suppressed. On the other hand, increasing the coolant flow rate or reducing the temperature setting can intervene in time when knock is detected, reducing the cylinder wall temperature and the amount of heat retained in the cylinder, which can increase the knock margin. The present invention can achieve knock-free stable combustion even under conditions close to the knock limit, providing a feasible guarantee for the application of hydrogen fuel under higher load and compression ratio conditions.

[0107] The attached figures show the schematic and characteristic curves of the tests and control methods on which the present invention is based, wherein:

[0108] Figure 1A schematic diagram of the test bench for hydrogen-fueled engine. The test bench contains hydrogen supply system, constant temperature cooling control system, electric dynamometer and data acquisition and analysis system, etc., which is used for experimental verification of engine control strategy.

[0109] Figure 2a and Figure 2b The variation curves of engine combustion characteristics under different relative air-fuel ratio conditions. Among them Figure 2a The subgraph shows the trend of increasing ignition delay, combustion duration and cycle variation coefficient (COV) with the increase of air-fuel ratio; Figure 2b The subgraph shows the trend of gradually decreasing specific hydrogen consumption (SHC) and increasing brake thermal efficiency (BTE) with the increase of air-fuel ratio. When the load is low (BMEP=4 bar), SHC rises after air-fuel ratio exceeds 2.8, indicating that over-dilution causes combustion deterioration, resulting in efficiency decrease.

[0110] Figure 3 The distribution diagram of maximum cylinder pressure Pmax and its occurrence crank angle APmax of 200 cycles under different relative air-fuel ratio conditions at medium load (BMEP=8 bar). The results show that when λ=2.0, Pmax and APmax are concentrated, and when λ increases to 2.5 and 3.0, the distribution ellipse is significantly lengthened and widened, indicating that the cycle-to-cycle variation is intensified, which is consistent with the observed increase in combustion instability. Figure 2a

[0111] Figure 4a , Figure 4b , Figure 4c The curves of NO, NO2 and N2O concentrations in the exhaust gas of hydrogen-fueled engine under different engine loads and relative air-fuel ratios. Figure 4a , Figure 4b , Figure 4c Corresponding to BMEP=4 bar, 8 bar and 10 bar conditions respectively. It can be seen that with the dilution of the mixture, the concentrations of NO and NO2 decrease almost linearly, while the concentration of N2O rises rapidly, but its absolute value is always lower than 2 ppm. Increasing engine load will increase combustion temperature, resulting in increased NO and NO2 emissions but suppressed N2O generation. Overall, the NOx produced by hydrogen combustion is mainly NO, accounting for more than 70% of total NOx and more than 90% under certain conditions.

[0112] Figure 5a , Figure 5b The variation of engine performance parameters under different hydrogen injection end times (EOI). Among them Figure 5a The subgraph is the curve of specific hydrogen consumption (SHC) and brake thermal efficiency (BTE) with EOI, showing that advancing the hydrogen injection timing (increasing EOI angle means injecting earlier) will increase hydrogen consumption and reduce thermal efficiency; Figure 5b ​The sub-plot of 50% combustion center (CA50) and exhaust temperature versus EOI shows that early injection delays the combustion center (from 6.8° ATDC to 8.0° ATDC) and causes the exhaust temperature to rise. This is mainly due to the fact that early injection increases the in-cylinder hydrogen residence time, which, under the influence of compression heating, leads to a slight knock tendency, necessitating a slight delay in ignition, thus delaying the combustion phase.

[0113] Figure 6 The energy distribution under different hydrogen injection timings is compared. As the injection timing is advanced, the energy carried away by the exhaust gas increases from 27.3% to 28.3%, while the heat loss through the cylinder wall decreases slightly. This is because early injection makes the mixture more homogeneous, with the high-temperature combustion zone more evenly distributed in the cylinder center, reducing the local high-temperature heat transfer near the wall. At the same time, homogeneous combustion is more complete, and the unburned hydrogen loss also decreases.

[0114] Figure 7 The composition of NOx emissions under different injection timings is compared. Under test condition 1 (medium load), as the hydrogen injection is gradually advanced, the total NOx emission decreases, corresponding to the transition from stratified combustion to homogeneous combustion. The proportion of NO in NOx decreases from 80.5% to 75.8% as the injection is advanced, indicating that early injection reduces the peak combustion temperature, reducing NO generation. The oxidation reaction of NO2 is mainly limited by chemical kinetics, and N2O is mainly generated in the temperature window of 900-1300 K, so the content of both is basically unchanged.

[0115] Figure 8a 、 Figure 8b The cyclic cylinder pressure characteristic distribution diagram under different hydrogen injection timings at different loads is shown. Among them Figure 8a for light load conditions (BMEP = 4 bar), Figure 8b for high load conditions (BMEP = 12 bar). In Figure 8a , early injection (EOI = 160°C ABTDC) forms homogeneous lean mixture, stable combustion, and the maximum cylinder pressure Pmax and the corresponding occurrence angle APmax of 200 cycles are highly concentrated; as the injection is gradually delayed, the stratification of the mixture is uneven, and the distribution of Pmax and APmax gradually spreads out. Conversely, Figure 8b for high load conditions, early injection prolongs the residence time of hydrogen at high temperature and high pressure, close to the self-ignition limit, causing the combustion phase to fluctuate, resulting in a significant widening of the Pmax and APmax distribution area; appropriate delay of injection suppresses knock and reduces cycle variation.

[0116] Figure 9a 、 Figure 9b 、 Figure 9c 、 Figure 9dThe cylinder pressure, heat release rate (HRR) and temperature variation curves for different injection timings at different loads (4 bar and 12 bar). For low load 4 bar: Figure 9a The subplots show the cylinder pressure and HRR curves for different injection timings are almost coincident with little difference; Figure 9b The subplots show the corresponding in-cylinder temperature curves, early injection slightly increases the compression work and requires higher peak pressure to maintain the same output. For high load 12 bar: Figure 9c The subplots show that the early injection case needs to retard the combustion phase due to knock tendency, and the peak pressure slightly decreases, while the stratified combustion formed by late injection has a faster combustion rate, which makes the instantaneous HRR peak increase and produces higher combustion temperature; Figure 9d The subplots show the cylinder temperature curves at high load, late injection (stratified combustion) produces higher local temperature peak compared to early injection (homogeneous combustion), but the knock does not occur by properly retarding the ignition.

[0117] Figure 10 The variation trend graphs of specific hydrogen consumption (SHC) and brake thermal efficiency (BTE) of the engine at different coolant temperatures. Figure 10 Corresponding to light load BMEP = 2 bar, medium load 6 bar and high load 10 bar conditions respectively. It can be seen that increasing the coolant temperature can reduce SHC and improve BTE at each load, which shows that as the coolant temperature rises from 30°C to 90°C, more energy released by combustion is effectively utilized rather than dissipated. Energy distribution analysis shows that increasing the coolant temperature significantly reduces heat transfer loss, increases the energy share taken away by exhaust gas, and at the same time, other losses (unburned loss, friction loss, etc.) also decrease, which together contributes to the improvement of thermal efficiency.

[0118] Example 1: Control strategy verification test platform

[0119] As Figure 1An experimental bench is built on a four-cylinder hydrogen direct injection engine with a displacement of 1.99 L to verify the control strategy proposed by the synergistic control method of the application. The engine is modified to be supplied with high-pressure hydrogen direct injection, with a compression ratio of 11.9:1 and equipped with an eddy current dynamometer for loading. Hydrogen is supplied by a 20 MPa high-pressure cylinder, stabilized to 1.6-2.5 MPa through two-stage pressure reduction, and then measured by a Coriolis mass flowmeter to accurately control the fuel supply. The coolant temperature is maintained at 30-90°C by a constant temperature control system to simulate different thermal boundary conditions. The in-cylinder pressure is obtained by a piezoelectric pressure sensor installed in one cylinder and sent to a combustion analyzer along with the crank encoder signal to calculate the combustion parameters (ignition delay, combustion duration, heat release rate, etc.). The exhaust composition is measured in real time by an infrared spectrum exhaust analyzer, including the concentrations of NO, NO2, N2O, etc. The above platform provides experimental support for the implementation of the control method of the application.

[0120] Example 2: Synergistic control of air-fuel ratio and load

[0121] This example verifies the influence of adjusting the air-fuel ratio on combustion and emissions under different engine loads to guide the setting of the control strategy. According to the working condition combinations shown in Table 1, at an engine speed of 2500 rpm, BMEP=4, 8, and 10 bar are selected to represent low, medium, and high loads, respectively, and the relative air-fuel ratio λ is gradually increased from 2.0 to 3.0 to test the combustion performance and NOx emissions at each point. The results are shown in Figures 2a to 4c : As the mixture becomes lean, the ignition delay and combustion duration increase significantly, especially at low load 4 bar, where COV increases significantly with λ, and the combustion becomes unstable; in contrast, the COV at medium and high loads (8 and 10 bar) is not very sensitive to λ and remains at a low level. This indicates that the high combustion rate of hydrogen at high load can compensate for the slow flame propagation caused by lean burn, keeping the cycle stability good, which can be seen from Figure 3 Pmax and APmax distributions at λ=2.0 to 3.0 change from compact to slightly diffuse. On the other hand, the increase of air-fuel ratio significantly improves the fuel economy, Figure 2b showing that the SHC gradually decreases while the BTE steadily increases, indicating that lean mixture improves the efficiency of the thermodynamic process. However, when λ exceeds about 2.8, the efficiency decreases at low load (SHC rises), indicating that excessive lean burn leads to incomplete combustion and increased unburned loss. Therefore, the control needs to set an upper limit for λ at low load to avoid entering the unfavorable region. This example also observes the influence of different λ on NOx components ( Figure 4a , Figure 4b , Figure 4c): NO and NO2emission concentrations decreased significantly while N2O concentration increased as lambda increased from 2.0 to 3.0. At lambda = 3.0, NO2was almost eliminated, NO dominated NOx, and N2O increased in proportion but only to about 1-2 ppm in absolute value. Increasing engine load tended to increase NO and NO2emissions (because higher temperatures promoted their formation) while suppressing N2O formation by higher temperatures and faster reactions. These test results verified that dilution control was effective in reducing NOx, while pointing out the difference in dilution effects on stability at different loads, which needed to be considered in control strategies.

[0122] Example 3: Synergistic control of injection timing and load

[0123] This example investigated the effects of fuel injection timing on combustion and emission characteristics and their interaction with engine load. Three typical operating conditions were set (see Table 1): Case 1 was a medium load (BMEP = 8 bar, lambda = 2.6) to study the effects of injection timing by varying the end of injection (EOI = 70°-160° BTDC); Case 2 was a light load (BMEP = 4 bar, lambda = 3.0); and Case 3 was a high load (BMEP = 12 bar, lambda = 2.0), with the same EOI range. The ignition timing was adjusted to the optimum combustion position (close to MBT) for all operating conditions.

[0124] Table 1 Test operating conditions

[0125]

[0126] In Case 1 (see Figures 5a to 7 ), as the EOI was advanced from 70° to 160° BTDC, i.e. the injection timing was gradually moved from close to ignition to the intake stroke, the results showed that the hydrogen consumption increased and the brake thermal efficiency decreased; the combustion center (CA50) moved backward and the heat release process was delayed, resulting in an increase in exhaust gas temperature. This was because early injection caused the hydrogen to stay in the cylinder for too long and be easily induced to self-ignite by compression heating. In the test, to avoid knocking, the ignition angle needed to be delayed, so that the combustion phase lagged further behind the top dead center, the constant volume combustion ratio decreased, and the thermal efficiency decreased.

[0127] The energy distribution results ( Figure 6 ) showed that early injection improved the mixture uniformity, slightly reduced the heat loss through the cylinder wall, but released more energy in the exhaust. The emission results ( Figure 7The results show that as the EOI (exposure initiation) is earlier (earlier injection), the total NOx emissions decrease, especially NO, indicating that homogeneous combustion effectively suppresses the formation of high-temperature regions. Conversely, when the EOI is delayed (injection close to ignition), NOx emissions increase, and the proportion of NO increases significantly. Notably, regardless of the EOI, the ratio of NO2 to N2O remains relatively stable, indicating that their formation is limited by chemical kinetic processes.

[0128] In Case 2 (low load 4 bar), we focused on the promoting effect of advance injection on lean and stable combustion. Experimental results showed that when EOI = 160°BTDC (the earliest possible EOI), the combustion pressure cycle fluctuation was minimal, Pmax and APmax were highly repetitive between cycles, and COV was only about 1%. However, as EOI was gradually delayed to 70°BTDC, the mixture gradually changed from homogeneous to stratified, leading to poorer combustion repeatability, a wider distribution range of Pmax and APmax, and an increase in COV to nearly 3%. This demonstrates that advance injection under light load conditions to form homogeneous combustion is very effective in improving combustion stability. Based on this, this invention employs an advance injection strategy at low loads to fully utilize the advantages of hydrogen's easy ignition and fast burning rate to achieve stable ultra-lean combustion.

[0129] In Case 3 (high load 12 bar), premature injection exhibited negative effects. During the process of advancing the EOI from 70° to 160° BTDC, increased peak cylinder pressure fluctuations occurred. Particularly with the earliest injection, the prolonged exposure of hydrogen to a high-temperature, high-pressure environment, approaching the limits of knocking and auto-ignition, led to significant fluctuations in the combustion phase between cycles (see...). Figure 8b The Pmax / APmax distribution is shown in the figure. By delaying the EOI back to 70°BTDC (or even later), knocking signs disappeared, and cyclic combustion became smooth. Simultaneously, it was observed that delayed injection, due to the generation of a certain degree of stratification, can locally enrich the combustion rate, making the heat release under high loads faster and more concentrated, manifested as an increase in the peak value of the HRR curve. Figure 9c This also leads to an increase in peak cylinder temperature (Figure 9(d)). Therefore, under high load conditions, a slightly richer stratified combustion can actually help to fully release the energy of hydrogen, provided that excessive knocking is not caused. This suggests that the control at high loads should strike a balance between delaying injection to suppress knocking and moderate stratification to promote combustion rate. Based on the above experimental results, this invention sets a lower limit for EOI in the high load control strategy to ensure that the combustion phase is not too early, and dynamically adjusts the injection timing by monitoring knocking in a closed loop, thereby taking into account both knock prevention and combustion rate optimization.

[0130] Example 4: The effect of coolant temperature on performance and emissions

[0131] This example verifies the influence of coolant temperature as a controllable parameter on engine efficiency and NOx emission composition. The experiment is conducted at engine speed 2500 rpm, medium air-fuel ratio λ = 2.5, and three load points BMEP = 2, 6, 10 bar, respectively, with coolant temperature controlled at 30℃, 60℃ and 90℃, to test combustion performance and emissions. The results are shown in Figure 10 As shown in the table, at all loads, increasing coolant temperature brings about obvious changes in SHC decrease and BTE increase. Taking high load 10 bar as an example, coolant temperature rising from 30℃ to 90℃ makes BTE increase by about several percentage points, and the efficiency improvement is more significant at light load 2 bar. This is mainly due to the reduction of heat loss in the combustion process at higher coolant temperature. As the temperature rises, the temperature difference between the cylinder wall and the coolant decreases, and the heat transfer per unit time decreases, so more energy released by combustion is used for work or enters the exhaust. At the same time, we also notice the influence of coolant temperature on different losses: at light load, unburned loss and friction loss also decrease slightly with temperature rise, which further promotes efficiency improvement.

[0132] In terms of emissions, coolant temperature mainly affects the generation balance of NOx. Analyzing the exhaust composition: as the coolant temperature rises, the volume fraction of NO2 and N2O in the exhaust gradually decreases, while the proportion of NO increases. At light load 2 bar, N2O decreases from about 0.7 ppm at 30℃ to about 0.65 ppm at 90℃, a decrease of about 7%; the proportion of NO2 also decreases significantly. This is because higher coolant temperature increases the cylinder wall temperature, and after reducing heat loss, the actual combustion temperature is higher, which promotes the decomposition of N2O and inhibits the generation of NO2. NO2 is mainly formed through the exothermic reversible reaction 2NO + O2 ↔ 2NO2, and at lower temperatures the equilibrium is more biased towards NO2, while at high temperatures the reaction equilibrium is inhibited, so NO2 decreases and NO relatively increases. Therefore, high coolant temperature operation increases the proportion of NO in emissions, but the total amount of NOx does not increase significantly, and it is beneficial to reduce the emission of N2O, a greenhouse gas. This shows that by increasing the coolant temperature, the composition of NOx can be optimized and the efficiency can be improved without worsening the total amount of NOx. Therefore, the present invention takes coolant temperature as one of the control parameters, and in the closed-loop strategy, it is preferred to maintain high coolant temperature operation to optimize the overall efficiency and emissions; in special cases, it can also be combined with temperature reduction to avoid knocking or overheating of devices, etc.

[0133] Based on the test results of the above embodiments, the synergistic control method proposed by the application is feasible and effective in actual engine operation. By adaptively adjusting the air-fuel ratio, injection timing and coolant temperature for different operating conditions, multiple objectives are achieved: improving efficiency (lean burn + high cooling temperature), reducing emissions (lean burn + homogeneous combustion reduces NOx, and high cooling temperature reduces N2O / NO2), and preventing knock (injection delay + moderate cooling at high load). Compared with the traditional single-parameter control method, the application can more effectively utilize the characteristics of hydrogen fuel, and solve the long-standing contradiction between high-efficiency combustion and knock control, and NOx emission reduction of hydrogen engine.

[0134] The application has been described above with reference to the drawings. Obviously, the specific implementation of the application is not limited by the above manner. As long as various non-essential improvements are made using the method concept and technical solution of the application; or without improvement, the above concept and technical solution of the application are directly applied to other occasions, which are within the protection scope of the application.

Claims

1. A method of synergic control of air-fuel ratio, injection timing and coolant temperature in a hydrogen-fueled engine, characterized by, The method comprises the steps of: S1, monitoring the operating condition parameters and combustion state parameters of the hydrogen fuel engine; S2, based on the operating condition parameters, the target air-fuel ratio, fuel injection timing and coolant temperature are determined adaptively through a preset control strategy; S3, the combustion state and engine operating condition are evaluated in real time through a closed-loop feedback control system, and the following coordinated adjustments are performed: Adjusting the hydrogen supply to maintain the target air-fuel ratio; Adjusting the hydrogen injection timing to optimize the combustion phase.

2. The method of synergic control of air-fuel ratio, injection timing and coolant temperature in a hydrogen-fueled engine according to claim 1, characterized by, The operating condition parameters include engine load and engine speed, and the combustion state parameters include in-cylinder pressure, knock intensity, air-fuel ratio and coolant temperature.

3. The method of synergic control of air-fuel ratio, injection timing and coolant temperature in a hydrogen-fueled engine according to claim 1, characterized by, In the low load operating condition of the engine, the upper limit of the target air-fuel ratio λ is set to be not more than a first preset threshold value; in the medium and high load operating condition, the target air-fuel ratio is increased to a second preset threshold value range; Wherein, the first preset threshold value is λ≤2.8, and the second preset threshold value range is 2.5≤λ≤3.

0.

4. The method of synergic control of air-fuel ratio, injection timing and coolant temperature in a hydrogen-fueled engine according to any one of claims 1 to 3, characterized by, According to the comparison result of the engine load and the preset load threshold value, the hydrogen injection strategy is selected: (a) When the engine is in light load condition, the advance direct injection strategy is adopted, so that the hydrogen injection is completed earlier before ignition, forming homogeneous lean mixture; (b) When the engine is in high load condition, the lag direct injection strategy is adopted, so that the hydrogen injection is completed near the ignition time, forming stratified combustion; Wherein, the advance direct injection strategy reduces the formation of local high temperature area in the cylinder by increasing the mixing time of hydrogen and air; the lag direct injection strategy reduces the risk of spontaneous combustion by shortening the residence time of hydrogen in the compression stroke; The light load condition of the engine is the condition that the engine load is lower than the predetermined load threshold value, and the high load condition of the engine is the condition that the engine load is higher than the predetermined load threshold value.

5. The method of synergic control of air-fuel ratio, injection timing and coolant temperature in a hydrogen-fueled engine according to any one of claims 1 to 3, characterized by, The preset control strategy includes: (1) The engine coolant temperature is set in the range of 60℃ to 90℃; (2) When the signs of knock or overloading high temperature state are monitored, the coolant temperature is temporarily lowered or the cooling intensity is increased; (3) After the knock is eliminated or the high temperature state is alleviated, the high temperature operation of the coolant is restored.

6. The method of synergic control of air-fuel ratio, injection timing and coolant temperature in a hydrogen-fueled engine according to any one of claims 1 to 3, characterized by, The closed-loop feedback control system is realized by the following ways: Using in-cylinder pressure sensor or acceleration knock sensor to monitor the knock intensity, when the knock intensity exceeds the preset threshold value, the hydrogen injection timing and / or ignition timing are automatically delayed, and the coolant temperature is lowered; Using exhaust oxygen sensor to monitor the air-fuel ratio deviation, and adjusting the hydrogen injection pulse width in real time; Using temperature sensor to monitor the actual temperature of the coolant, and stabilizing the coolant temperature in the target temperature range by controlling the electronic thermostat and the water pump speed.

7. The method of synergic control of air-fuel ratio, injection timing and coolant temperature in a hydrogen-fueled engine according to any one of claims 1 to 3, characterized by, In step S3, the combustion stability is controlled by monitoring the cycle variation coefficient of the indicated mean effective pressure; When the cycle variation coefficient is higher than the third preset threshold value, the fuel injection amount is increased or the injection timing is advanced; When the cycle variation coefficient is lower than the fourth preset threshold value and there is no risk of knock, the fuel injection amount is reduced or the injection timing is delayed.

8. The method of synergic control of the air-fuel ratio, injection timing and coolant temperature in a hydrogen-fueled engine according to claim 7, characterized by, The third preset threshold value is ≥3%, and the fourth preset threshold value is ≤1%.

9. The method of synergic control of air-fuel ratio, injection timing and coolant temperature in a hydrogen-fueled engine according to claim 4, characterized by, In step S3, the advance direct injection strategy makes the end time of hydrogen injection not later than 120° crank angle before the top dead center of compression stroke; the lag direct injection strategy makes the end time of hydrogen injection not earlier than 30° crank angle before the top dead center of compression stroke.

10. The method for coordinated control of air-fuel ratio, injection timing, and coolant temperature in a hydrogen fuel cell engine according to claim 9, characterized in that, In step S3, when the engine braking average effective pressure ≥ 8 bar, the cycle variation coefficient is maintained at ≤ 1% by the synergistic effect of adjusting the coolant temperature and the late direct injection strategy.

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