Method for controlling influence of ammonia mixing on cyclic variation of hydrogen spark ignition engine

Abstract

The invention discloses a method for controlling the influence of ammonia mixing on cyclic variation of a hydrogen spark ignition engine. The method comprises the steps of fuel mixing regulation and control, wherein the supply flow of ammonia gas and hydrogen is regulated according to a first preset control strategy; ignition advance angle optimization: adjusting the ignition advance angle of the spark plug according to a second preset control strategy; the fuel injection parameters are adjusted according to a third preset control strategy; air-fuel ratio switching control is conducted, specifically, the engine operation mode is adjusted according to a fourth preset control strategy; a mounted sensor is used for monitoring circulating combustion parameters in real time, when preset conditions are met, the electronic control unit selectively executes a first preset control strategy, a second preset control strategy, a third preset control strategy and a fourth preset control strategy, the ammonia gas supply proportion, the ignition advance angle and / or the gas inlet disturbance amplitude are adjusted, and the gas inlet disturbance amplitude is adjusted. And the engine returns to the stable combustion state again. According to the method for controlling the influence of ammonia mixing on the cyclic variation of the hydrogen spark ignition engine, fine control over the combustion process of the engine is achieved by regulating and controlling the mixing proportion of ammonia and hydrogen and combustion control parameters, the fluctuation of combustion indexes between cycles is reduced, the heat efficiency of the engine is improved, and the harmful emission and the knocking risk are restrained; therefore, the comprehensive performance of the hydrogen fuel engine is obviously improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of combustion control and engine technology, and particularly relates to a control method for the influence of ammonia mixing on the cycle variation of a hydrogen spark-ignition engine (hydrogen fuel SI engine). BACKGROUND

[0002] With the global energy structure transforming towards zero-carbon fuels, hydrogen and its compound ammonia play an important role in future energy. Ammonia, as a zero-carbon clean energy, has attracted much attention, but its slow burning speed, difficult ignition, and the production of nitrogen oxides (NOx) during combustion limit its single application. To overcome the slow combustion and emission problems of ammonia, ammonia is often mixed with other fuels for combustion. Hydrogen has the advantages of fast burning speed and low ignition energy, and can be used as a promoter to improve the efficiency and stability of ammonia combustion. Therefore, many studies focus on using ammonia as the main fuel and adding a certain proportion of hydrogen as a combustion aid to improve the combustion characteristics of ammonia. For example, it has been found that adding about 10% volume fraction of hydrogen to ammonia can significantly expand the stable operation range of ammonia engine. Increasing the proportion of hydrogen can improve the burning speed and temperature, but at the same time, it will lead to a significant increase in NOx emissions. By optimizing the ignition advance angle, the engine power and efficiency can be further improved when ammonia and hydrogen are mixed.

[0003] On the contrary, from another perspective, if ammonia is mixed into hydrogen fuel as an "inhibitor", it may help to alleviate the abnormal combustion tendency caused by the too fast combustion of hydrogen. It has been reported that pure hydrogen combustion is prone to abnormal combustion phenomena such as knock or pre-ignition due to its extremely low ignition energy and extremely fast flame propagation speed. The rapid combustion of hydrogen even tends to transition from deflagration to detonation. In this case, the appropriate addition of ammonia, which has a slower burning speed, can reduce the severity of hydrogen combustion, play a role similar to increasing the octane number, and thus may improve the smoothness of engine operation and reduce the loss of heat transfer due to excessive heat peaks. It has been found that the addition of ammonia to hydrogen fuel reduces the peak heat release rate and prolongs the flame development and propagation process. This indicates that reasonable ammonia mixing is expected to inhibit the too fast combustion reaction of hydrogen fuel engine, making the combustion more stable.

[0004] Cyclic variation is a common problem in spark-ignition engines, which means that the combustion parameters (such as maximum cylinder pressure, heat release rate, and IMEP) fluctuate in consecutive cycles. Cyclic variation can reduce engine performance, and studies have shown that eliminating cyclic fluctuations can increase output power by about 10%. Therefore, reducing cyclic variation is crucial to improving engine efficiency. There are many factors that affect cyclic variation, including mixture flow characteristics, air-fuel ratio, injection strategy, etc. For hydrogen-ammonia dual-fuel engines, factors such as flow field turbulence, excess air coefficient, and fuel supply strategy can significantly affect cycle consistency. For example, some studies have investigated ammonia-hydrogen mixed combustion on variable compression ratio engines and found that pure ammonia combustion is prone to misfire or severe ignition delay, but adding about 12% hydrogen can eliminate the ignition problem. This shows that a small amount of hydrogen can significantly improve the stability of ammonia combustion. Similarly, adding a certain proportion of ammonia to hydrogen-based fuel is expected to adjust the combustion characteristics and improve the performance problems caused by cyclic fluctuations.

[0005] In the related art field, most current research focuses on the scheme of using ammonia as the main fuel and hydrogen as the auxiliary fuel to improve the performance of ammonia combustion, but less attention is paid to the idea of using hydrogen as the main fuel and ammonia as the mixing inhibitor. In fact, hydrogen-ammonia mixed combustion achieved by mixing ammonia on the basis of pure hydrogen engine is considered as one of the effective technical approaches to improve the performance of hydrogen engine, which is expected to improve the combustion stability of hydrogen engine, reduce the performance loss caused by cyclic variation, and simultaneously consider emission and knock safety.

[0006] However, there is no relevant published research on the improvement of hydrogen engine smoothness and the reduction of overheating by using hydrogen as the main fuel and ammonia as the mixing inhibitor, and there is also a lack of corresponding control technology to achieve reasonable mixing of ammonia and coordinated optimization control of ignition timing and mixture flow under high hydrogen proportion conditions.

[0007] Therefore, a control method for the influence of ammonia mixing on the cyclic variation of hydrogen spark-ignition engine is provided, in particular, how to mix an appropriate amount of ammonia under high hydrogen proportion conditions, and cooperate with the optimization control of ignition timing and mixture flow, to improve the combustion stability of hydrogen engine, reduce the performance loss caused by cyclic variation, and simultaneously consider emission and knock safety. SUMMARY

[0008] The present application aims to at least solve the following problems in the prior art: In a hydrogen spark-ignition engine, due to the extremely fast combustion speed of hydrogen and the extremely low ignition energy, abnormal combustion phenomena such as cyclic fluctuation, knock, and pre-ignition are prone to occur, resulting in poor engine operation stability and high emission level. Most of the existing technologies focus on the research path of "ammonia as the main fuel and hydrogen as the auxiliary fuel", but lack control methods for "hydrogen as the main fuel and ammonia as the mixing inhibitor".

[0009] To this end, the present application provides a control method for the influence of ammonia blending on the cycle variation of a hydrogen spark-ignition engine, which realizes the comprehensive optimization of engine combustion stability improvement, cycle fluctuation suppression, and emission and knock safety by reasonably introducing ammonia under high hydrogen ratio combustion conditions and optimizing the control of ignition timing, intake flow, and air-fuel ratio.

[0010] The technical scheme adopted by the present application is as follows: a control method for the influence of ammonia blending on the cycle variation of a hydrogen spark-ignition engine, comprising:

[0011] Fuel blending regulation: adjusting the supply flow of ammonia and hydrogen according to a first preset control strategy;

[0012] Ignition advance angle optimization: adjusting the spark plug ignition advance angle according to a second preset control strategy;

[0013] Intake flow disturbance introduction: adjusting the fuel injection parameters according to a third preset control strategy;

[0014] Air-fuel ratio switching control: adjusting the engine operating mode according to a fourth preset control strategy;

[0015] Closed-loop monitoring and adjustment: using the installed sensors to monitor the cycle combustion parameters in real time, and when the preset conditions are met, the electronic control unit can selectively execute the first, second, third, and fourth preset control strategies to adjust the ammonia supply ratio, ignition advance angle, and / or intake disturbance amplitude, so that the engine returns to a stable combustion state.

[0016] The first preset control strategy comprises:

[0017] The electronic control unit adjusts the supply flow of ammonia and hydrogen according to the preset ammonia energy ratio, so that the ammonia energy ratio meets the requirements of combustion stability under different operating conditions.

[0018] The first preset control strategy further comprises:

[0019] Under stoichiometric combustion (λ = 1) conditions, COV IMEP increases from 0.82% to 6.17% as the ammonia energy ratio increases to 65%, and combustion is obviously unstable when the ratio exceeds 60%; while under lean combustion conditions (λ = 1.2), COV IMEP Although it also increases with the increase of ammonia ratio, the overall level is lower than that under stoichiometric conditions, and the engine has higher tolerance to ammonia blending.

[0020] Therefore, the present application provides that the ammonia energy ratio under stoichiometric conditions should not exceed 60%, and if further improvement is needed, the engine should be switched to lean mode (λ ≈ 1.2) to ensure combustion stability.

[0021] The second preset control strategy includes:

[0022] Under equivalence ratio conditions, the ignition advance angle is determined according to MBT;

[0023] Under lean-burn conditions, if a fixed ignition timing is maintained, then p max and (dp / dφ) max With φ(dp / dφ) max The linear relationship between the two disappears; however, by using optimized MBT ignition timing, the linear relationship can be restored, significantly improving combustion consistency and cycle stability.

[0024] The third preset control strategy includes:

[0025] Intake flow disturbances are introduced by regulating fuel injection parameters through an electronic control unit. These fuel injection parameters include the injection timing and ratio of the two fuels.

[0026] By creating pulsed fuel injection within the intake manifold, the turbulence intensity of the in-cylinder mixture is enhanced, thereby reducing fluctuations in combustion rate and pressure between consecutive cycles.

[0027] The third preset control strategy includes:

[0028] The system employs a stratified combustion method, prioritizing the direct injection of hydrogen fuel into the cylinder or near the intake valve, followed by the injection of ammonia fuel upstream of the intake manifold to form a uniform premix.

[0029] The fourth preset control strategy includes:

[0030] When the ammonia mixture is in a high blending ratio, switch the engine operating mode to lean-burn mode;

[0031] When the ammonia is mixed in a medium to low ratio, the engine operates in a stoichiometric combustion mode.

[0032] The installed sensors include a cylinder pressure sensor and a knock sensor, which monitor the combustion pressure characteristics and knock intensity of each working cycle in real time.

[0033] The preset condition is that the combustion pressure characteristics and knock intensity are detected to exceed a predetermined threshold.

[0034] Furthermore, a method for controlling the effect of ammonia blending on the cycle variation of a hydrogen spark ignition engine includes:

[0035] Fuel blending control: Adjust the supply flow rates of ammonia and hydrogen according to the first preset control strategy; under the condition of equivalent air-fuel ratio (λ=1), the energy proportion of ammonia should not exceed 60% to ensure the IMEP cycle variation coefficient (COV).IMEP ) is maintained below 5%; when the ammonia energy ratio exceeds 60%, the engine needs to be switched to a lean burn mode (λ≥1.2) to maintain stable combustion.

[0036] Ignition advance angle optimization: adjust the spark plug ignition advance angle according to the second preset control strategy; determine the ignition advance angle by the maximum brake torque (MBT) point under the equivalence ratio condition; if fixed ignition is used under the lean burn condition, the cycle fluctuation is obvious, and by optimizing the MBT ignition timing, the p max and (dp / dφ) max between the phase, thereby improving the combustion consistency.

[0037] Introducing air flow disturbance: adjust the fuel injection parameters or air flow disturbance according to the third preset control strategy; enhance the in-cylinder turbulence intensity by pulse injection or valve timing disturbance to reduce the fluctuation of combustion rate and pressure between consecutive cycles.

[0038] Air-fuel ratio switching control: adjust the engine operating mode according to the fourth preset control strategy; when the ammonia is high-proportion mixed, switch the engine to a lean burn mode to improve combustion stability and reduce NOx; when the ammonia is low-proportion mixed, use stoichiometric combustion to obtain higher power output.

[0039] Closed-loop monitoring and adjustment: install a cylinder pressure sensor and a knock sensor to monitor the combustion pressure and knock intensity in real time; when the COV IMEP exceeds 5% or the knock signal is out of limit, the ECU automatically adjusts the ammonia proportion, ignition advance angle or air intake disturbance amplitude to make the engine return to the stable combustion interval.

[0040] The control method of the present application has the following advantages:

[0041] 1. Significantly improves cycle stability;

[0042] The experimental results show that, with the increase of ammonia proportion, the cylinder pressure peak (p max ) fluctuation is enhanced, while the maximum pressure rise rate ((dp / dφ) max ) is relatively stable, and its average value gradually decreases. Under the optimized ignition timing, the p max and (dp / dφ) max and can maintain a linear relationship, thereby significantly improving the combustion consistency. Especially under the equivalence ratio condition, when the ammonia energy ratio exceeds 60%, the IMEP cycle variation coefficient (COV IMEP ) will rapidly increase to more than 6%, entering the unstable region; and under the lean burn condition, the COVIMEP The rising amplitude is small, and the ammonia tolerance is higher.

[0043] 2. Improve lean tolerance;

[0044] Under lean conditions (λ = 1.2), the engine has significantly improved adaptability to high proportions of ammonia. Even if the ammonia proportion reaches 65%, the COV IMEP remains about 4%, which is lower than the level of more than 6% under the equivalent ratio condition, indicating that the lean mode can significantly alleviate the cycle fluctuation caused by high-proportion ammonia mixed combustion.

[0045] 3. Reduce the risk of knock;

[0046] The addition of ammonia slows down the flame propagation speed and reduces the combustion rate and peak pressure. In the experiment, the average (dp / dφ) max decreases, and the combustion process tends to be gentle. These characteristics mean that the mixing of ammonia helps to reduce the possibility of knock, especially when the ignition control is optimized, which can avoid the rapid heat release and high pressure impact that occurs when pure hydrogen is burned.

[0047] 4. Maintain combustion efficiency;

[0048] The experiment shows that under the equivalent ratio condition, when the ammonia proportion is ≤40%, the average IMEP is basically stable; under lean conditions, as the ammonia proportion increases, the average IMEP even slightly rises. However, at the same time, the cycle fluctuation also increases. Therefore, by mixing ammonia and combining lean and optimized ignition, the invention can maintain or even improve the effective output while ensuring stability.

[0049] 5. Optimize emission performance;

[0050] The experimental results show that the addition of ammonia reduces the combustion rate and peak cylinder temperature. Under lean conditions, the excess air heat absorption effect further reduces the peak combustion temperature. These characteristics help to suppress the generation of thermal NOx. Combined with exhaust aftertreatment (such as SCR), cleaner emissions can be achieved. It should be noted that the effects of reducing the risk of knock and optimizing NOx emissions are based on reasonable inferences from experimental characteristics such as reduced combustion rate and reduced cylinder temperature, and need to be further verified in combination with subsequent engine bench and emission tests. BRIEF DESCRIPTION OF DRAWINGS

[0051] The present specification includes the following drawings, the contents of which are shown as follows:

[0052] Figure 1 is a schematic diagram of an ammonia-hydrogen dual-fuel spark-ignition engine experimental device.

[0053] Figure 2a is a result graph of stoichiometric combustion (λ = 1).

[0054] Figure 2b The result is shown in the graph for the lean-burn condition (λ=1.2).

[0055] Figure 3a and Figure 3b The maximum pressure rise rate (dp / dφ) is given under different ammonia energy ratios. max Comparison of cyclical changes.

[0056] Figure 4a , Figure 4b and Figure 4c The peak pressure p in the cylinder max Its occurrence time A distribution diagram of the relationships between them.

[0057] Figure 5a and Figure 5b This is a schematic diagram showing the changes in average cylinder pressure and related parameters over 300 cycles under different ammonia blending ratios.

[0058] Figure 6a and Figure 6b The maximum rate of pressure rise (dp / dφ) max Correspondingly, the crankshaft angle occurs A diagram showing the relationships between them.

[0059] Figure 7a and Figure 7b A comparative graph showing the cyclical variation of the indicated mean effective pressure (IMEP) under different ammonia energy ratios.

[0060] Figure 8a and Figure 8b This is a return map of IMEP under different ammonia energy ratios.

[0061] Figure 9 The coefficient of variation (COV) of IMEP under different ammonia energy ratios IMEP The curve of change.

[0062] The components in the diagram are labeled as follows: 1. Hydrogen engine; 2. Crank angle encoder; 3. Combustion analyzer; 4. Charge amplifier; 5. Dynamometer; 6. Spark plug; 7. Cylinder pressure sensor; 8. Hydrogen injector; 9. Ammonia injector; 10. Oxygen sensor; 11. Electronic control unit; 12. Ammonia tank; 13. Hydrogen tank; 14. Pressure regulator; 15. Mass flow controller; 16. Heater; 17. Gas mass flow meter. Detailed Implementation

[0063] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, in order to help those skilled in the art to have a more complete, accurate and in-depth understanding of the concept and technical solutions of the present invention, and to facilitate its implementation.

[0064] The embodiment of the present application provides a control method for the influence of ammonia mixing on the cycle variation of a hydrogen spark-ignition engine, comprising:

[0065] Fuel mixing regulation: adjusting the supply flow of ammonia and hydrogen according to a first preset control strategy;

[0066] Ignition advance angle optimization: adjusting the ignition advance angle of the spark plug according to a second preset control strategy;

[0067] Introducing air inlet flow disturbance: adjusting the fuel injection parameter according to a third preset control strategy;

[0068] Air-fuel ratio switching control: adjusting the engine operation mode according to a fourth preset control strategy;

[0069] Closed-loop monitoring and adjustment: using a cylinder pressure sensor and a knock sensor to monitor the combustion pressure characteristics, indicated mean effective pressure (IMEP) and knock signals of each cycle in real time. When the cycle variation coefficient COV IMEP When the cycle variation coefficient COV

[0070] When the cycle variation coefficient COV IMEP When the cycle variation coefficient COV

[0071] When the monitored knock signal is too strong, the ammonia proportion is increased and the ignition advance angle is delayed to slow down the combustion rate and reduce the peak pressure;

[0072] When the cycle combustion is insufficient or the misfire trend is detected, the ammonia proportion is reduced or the ignition is appropriately advanced, and the air inlet disturbance intensity is increased to enhance the turbulence and flame propagation.

[0073] Through the above feedback adjustment, the ECU adjusts the ammonia supply proportion, the ignition advance angle and the air inlet disturbance amplitude in real time, so that the engine returns to the stable combustion state, and the cycle consistency and the reliability of the power output are ensured.

[0074] Specifically, the present application proposes a new control method for the influence of ammonia mixing on the cycle variation of a hydrogen fuel engine, aiming to solve the problems of cycle instability, NOx emission and knock tendency caused by the too fast combustion of hydrogen in the prior art, and realize more efficient and stable combustion.

[0075] In the embodiments of the present application, a control method for the influence of ammonia blending on the cycle variation of hydrogen spark-ignition engine is provided to overcome the shortcomings of existing pure hydrogen fuel engines, such as poor combustion stability, large cycle fluctuation, high NOx emission, and strong knock tendency, etc. By adjusting the blending ratio of ammonia and hydrogen and the combustion control parameters (such as ignition advance angle, intake flow disturbance, etc.), the engine combustion process is precisely controlled, the fluctuation of combustion indicators between cycles is reduced, the thermal efficiency of the engine is improved, harmful emissions and knock risk are suppressed, and thus the overall performance of the hydrogen fuel engine is significantly improved. The method achieves control through the following steps:

[0076] (1) Hydrogen-ammonia fuel blending control: Introduce ammonia as a blended fuel component in the hydrogen spark-ignition engine, and supply the mixed fuel of ammonia and hydrogen according to the set energy ratio (ammonia energy percentage of total fuel energy). The blending ratio of ammonia is controlled according to the engine operating conditions to achieve optimal stability effect under high hydrogen energy ratio. Preferably, under the condition of stoichiometric equivalence ratio (λ = 1), the ammonia energy ratio is not more than about 60% to ensure that the combustion stability is not excessively deteriorated; when a higher ammonia ratio is needed, a lean (λ > 1) strategy is adopted to improve the tolerance to ammonia. By adjusting the supply flow of ammonia and hydrogen, the optimal blending ratio under each operating condition is achieved.

[0077] (2) Ignition advance angle control: According to the combustion characteristics of hydrogen-ammonia mixture, the spark ignition advance angle is optimized. When the ammonia blending ratio changes, the optimal ignition time (MBT point, i.e. maximum torque ignition timing) under different operating conditions is determined through experiments, and the spark advance angle is set near the optimized value. Especially under lean conditions, instead of using the fixed ignition time under pure hydrogen conditions, the ignition is appropriately advanced to compensate for the reduced combustion speed caused by the addition of ammonia. With the optimized ignition advance angle, the energy of the mixed fuel can be fully released while maintaining cycle stability, and the maximum in-cylinder pressure occurs at the optimal position near the top dead center. When the ignition timing is adjusted to the optimal value, the maximum pressure in the engine cycle and its occurrence phase show a good linear relationship, and the combustion process is more controllable.

[0078] (3) Intake flow disturbance control: By adjusting the intake flow or fuel injection strategy, a moderate flow disturbance is introduced to enhance the turbulence intensity and uniformity of the mixture, thereby reducing the difference in flame development between cycles. For example, swirl / roll flow can be added to the intake port design or valve timing, or pulse fuel injection can be used to create small periodic disturbances to break the unfavorable correlation between consecutive cycles and promote the combustion of each cycle to be averaged. Appropriate flow disturbance helps to reduce the dispersion of maximum pressure and heat release rate between cycles, avoiding excessively high peak pressure rise rate in some cycles.

[0079] (4) Air-fuel ratio and load control: Select appropriate air-fuel ratio and engine load operation strategy according to the ammonia blending ratio. When a higher proportion of ammonia gas needs to be mixed, the engine is preferably switched to lean burn mode (λ ≈ 1.2 or higher) operation. Lean burn operation, on the one hand, offsets the tendency of ammonia to burn slowly, and on the other hand, reduces the peak temperature of combustion, thereby inhibiting the generation of NOx. For medium and low ammonia proportions, stoichiometric combustion can be used to obtain higher power output, while when the ammonia proportion increases to a certain threshold, stability and low emissions are maintained by lean burn. Experiments show that when the ammonia energy ratio exceeds 60% under stoichiometric conditions, the cycle variation will increase sharply and the combustion will become unstable (IMEP variation coefficient COV IMEP more than 5%); on the contrary, under lean burn conditions, the engine's adaptability to high ammonia proportion is significantly enhanced, and the COV IMEP of the equivalent combustion is significantly lower.

[0080] Therefore, the method ensures that the combustion process is in a stable region under various operating conditions by coordinating the air-fuel ratio and the amount of ammonia mixed.

[0081] (5) Real-time monitoring and feedback control: Use the engine control unit (ECU) and sensor array to achieve closed-loop control of the above parameters. Through the installed cylinder pressure sensor and knock sensor, etc., the combustion pressure characteristics and knock intensity of each working cycle are monitored in real time. Once it is detected that the cycle variation exceeds the preset threshold (for example, COV IMEP of the pressure fluctuation of a certain percentage or consecutive cycles is abnormal), the control system automatically adjusts the ammonia supply amount, ignition advance angle, or uses additional dilution measures (such as increasing EGR or rich air) to suppress fluctuations to stabilize. By precisely controlling the injection pulse width of ammonia and hydrogen fuels and the ignition timing through the electronic control unit, dynamic optimization of the combustion process is achieved.

[0082] In the embodiment of the present application, ammonia gas is introduced as a mixed fuel in a spark-ignition engine with hydrogen gas as the main fuel, and the electronic control unit adjusts the supply flow of ammonia and hydrogen according to the preset ammonia energy ratio, so that the ammonia energy ratio meets the requirements of combustion stability under different operating conditions. The first preset control strategy includes:

[0083] The electronic control unit adjusts the supply flow of ammonia and hydrogen according to the preset ammonia energy ratio, so that the ammonia energy ratio meets the requirements of combustion stability under different operating conditions.

[0084] In the embodiment of the present application, the first preset control strategy further includes:

[0085] Limiting the ammonia energy ratio to not more than 60% under stoichiometric air-fuel ratio conditions to maintain the average indicated pressure cycle variation coefficient below 5%;

[0086] When the ammonia energy ratio exceeds 60%, a lean combustion mode with excess air coefficient λ>1 is adopted to ensure stable combustion.

[0087] In the embodiment of the present application, the ammonia energy ratio is limited to not more than 60% under the condition of stoichiometric air-fuel ratio (λ=1) to make the IMEP cycle variation coefficient COV IMEP maintained in a stable range of less than 5%; when the ammonia energy ratio needs to exceed 60%, a lean combustion mode with excess air coefficient λ>1 is adopted to ensure stable combustion.

[0088] In the embodiment of the present application, the spark plug ignition advance angle is set according to the combustion characteristics after ammonia blending, the ignition timing is set to the maximum brake torque (MBT) point under stoichiometric combustion conditions, and the ignition advance angle is adjusted to the approximate MBT point under different working conditions such as lean combustion to ensure timely and stable combustion process; the second preset control strategy includes:

[0089] The ignition advance angle is corrected in real time by the stored ignition timing optimization mapping to keep it close to the optimal value with the change of ammonia blending ratio and air-fuel ratio.

[0090] In the embodiment of the present application, the ignition advance angle optimization includes: conducting ignition timing sweep test under each predetermined ratio of ammonia-hydrogen mixed fuel to determine the MBT ignition advance angle corresponding to the working condition, and setting the engine ignition timing to the MBT value; for the working condition change in actual operation, the ignition advance angle is corrected in real time by the stored ignition timing optimization mapping to keep it close to the optimal value with the change of ammonia blending ratio and air-fuel ratio.

[0091] In the embodiment of the present application, controllable flow disturbance is introduced by controlling the engine intake process or fuel injection strategy to enhance the in-cylinder mixture turbulence intensity, thereby reducing the fluctuations of combustion rate and pressure between consecutive cycles; the third preset control strategy includes:

[0092] The intake flow disturbance is introduced by adjusting the fuel injection parameters including the injection timing and injection ratio of the two fuels through the electronic control unit; the fuel is formed in a pulse injection in the intake port to enhance the turbulence intensity of the in-cylinder mixture to reduce the fluctuations of combustion rate and pressure between consecutive cycles.

[0093] In the embodiment of the present application, the third preset control strategy includes:

[0094] The stratified fuel supply mode is adopted to directly inject hydrogen fuel into the cylinder or near the intake valve to ensure the formation of a fast combustion center, and then inject ammonia fuel upstream of the intake manifold to form uniform premixing, thereby synergistically improving the combustion speed and stability; the timing and ratio of the two fuel injections are adjusted to realize fine control of the in-cylinder mixture combustion process.

[0095] In the embodiments of the present application, the intake flow disturbance is achieved by introducing a pulsed disturbance in the intake passage of the engine; the intake flow disturbance is generated by a small periodic oscillation of the opening of the throttle valve or an intermittent injection mode of the fuel injector controlled by the electronic control unit, and the frequency and amplitude thereof are calibrated to weaken the cycle-to-cycle combustion correlation, but not to cause a large fluctuation in the engine torque output.

[0096] In the embodiments of the present application, the peak in-cylinder combustion temperature can be reduced by controlling the ammonia blending ratio and lean burn operation, thereby reducing the generation of nitrogen oxides (NOx); when the NOx is too high during high-hydrogen-ratio pure combustion, the ammonia blending ratio is increased and the ignition timing is appropriately delayed to suppress the NOx emission, so that the NOx content in the exhaust gas meets the predetermined low emission standard.

[0097] In the embodiments of the present application, when the ammonia blending ratio is high, the engine operating mode is switched from the equivalence ratio to the lean burn, so as to reduce the combustion temperature and widen the flammability limit, thereby improving the tolerance of the engine to high-ratio ammonia blending; the fourth preset control strategy comprises:

[0098] When the ammonia blending ratio is high, the engine operating mode is switched to the lean burn mode;

[0099] When the ammonia blending ratio is low, the engine operating mode is switched to the stoichiometric combustion.

[0100] In the embodiments of the present application, the installed sensors are used to monitor the cycle combustion parameters (including in-cylinder pressure, IMEP, knock signal, etc.) in real time, and when it is detected that the cycle variation exceeds the predetermined threshold, the ECU automatically adjusts the ammonia supply ratio, the ignition advance angle and / or the intake disturbance amplitude, so that the engine returns to the stable combustion state. The installed sensors include a cylinder pressure sensor and a knock sensor, and through the cylinder pressure sensor and the knock sensor, the combustion pressure characteristics and the knock intensity of each working cycle (each working cycle refers to the period of a complete energy conversion process of a hydrogen engine, which specifically corresponds to one working cycle of an internal combustion engine, including four consecutive strokes of intake, compression, work and exhaust) are monitored in real time. The preset condition is that the combustion pressure characteristics and the knock intensity exceed the predetermined threshold.

[0101] In the closed-loop monitoring and adjusting step, when the in-cylinder knock is detected (the knock sensor signal exceeds the threshold), the hydrogen supply ratio is preferentially reduced or the ammonia ratio is appropriately increased to improve the anti-knock performance of the mixed fuel, and the ignition advance angle is delayed until the knock disappears; when the cycle-by-cycle combustion pressure is detected to decrease (indicating that misfire may occur), the ammonia ratio is reduced or the intake amount is increased to improve the flammability of the mixed gas, so as to restore normal combustion.

[0102] The ECU calculates the IMEP value of each working cycle and compares it with the IMEP of the previous cycle; if the difference exceeds a preset threshold, the difference is offset by fine-tuning the fuel injection amount or the ignition timing to smooth the return mapping fluctuation of the IMEP (reduce the difference between adjacent cycle IMEPs) and improve the consistency between cycles.

[0103] In the embodiment of the present application, the engine preferably operates in a lean-burn mode with an excess air ratio λ = 1.2 to achieve carbon-free combustion by taking advantage of the high hydrogen content of ammonia; when the output power needs to be increased, the λ value is temporarily reduced to the rich oxygen range (but not less than λ = 1) and the proportion of ammonia is correspondingly reduced to ensure combustion stability and responsiveness in acceleration conditions.

[0104] The control method for the influence of ammonia blending on the cycle variation of a hydrogen spark-ignition engine provided by the embodiment of the present application further comprises:

[0105] The engine exhaust aftertreatment step: catalytic oxidation treatment is performed on the ammonia in the exhaust gas after combustion that has not fully reacted to convert excess ammonia into inert nitrogen; selective catalytic reduction (SCR) is used on the NOx in the exhaust gas to reduce NOx to nitrogen and water using a small amount of ammonia from the fuel as a reducing agent, thereby achieving the goal of near-zero emissions. The engine exhaust aftertreatment step cooperates with the aforementioned control method to further ensure the environmental protection and safety of engine operation.

[0106] The control method for the influence of ammonia blending on the cycle variation of a hydrogen spark-ignition engine provided by the embodiment of the present application has the following advantages:

[0107] 1. Reducing cycle fluctuation and improving combustion stability: By optimizing the ammonia blending ratio and ignition timing, the combustion indicators between engine cycles are more consistent. Experiments have shown that after the appropriate addition of ammonia, the cycle fluctuation of the peak cylinder pressure increases, but the corresponding maximum pressure rise fluctuation is not large and the average value decreases. After reasonable control, the variation coefficient (COV IMEP ) of the indicated mean effective pressure can be limited to less than 5%, thereby ensuring smooth engine operation. Especially under lean-burn high-ammonia conditions, the cycle variation is suppressed at a low level and the combustion stability is significantly improved.

[0108] 2. Reducing peak pressure and combustion rate fluctuation and suppressing knock tendency: Ammonia blending reduces the combustion speed and heat value of the fuel, which reduces the average value of the maximum cylinder pressure and the maximum pressure rise. This helps to alleviate the high pressure impact caused by the vigorous combustion of hydrogen and reduces the risk of knock. The combustion process is more gentle, avoiding the knock tendency caused by the rapid heat release that may occur during pure hydrogen combustion. This method optimizes the ignition timing and controls the ammonia proportion, so that the cylinder pressure peak appears at a controllable time and the peak pressure is appropriately reduced, thereby effectively suppressing knock.

[0109] 3. Improve combustion efficiency and output performance: By adding an appropriate amount of ammonia to the hydrogen fuel and coordinating the optimal ignition timing, the window of efficient combustion can be widened. The addition of ammonia slows down the flame propagation rate, allowing the engine to adopt a more advanced ignition timing (close to or reaching the MBT point) without causing knock, thereby fully utilizing the expansion work capacity, improving the indicated thermal efficiency and output power. When the ammonia blending ratio is within a reasonable range (for example, the ammonia energy share ≤ 40%), the average IMEP of the engine remains stable or even slightly increases. This indicates that this method can maintain or even improve the engine's work capacity while ensuring stability.

[0110] 4. Expand the application range of hydrogen fuel and consider high ammonia utilization rate: Through the method of the present application, the proportion of ammonia in ammonia-hydrogen mixed fuel can be increased without significantly sacrificing stability, thereby improving the utilization rate of carbon neutral fuel. With the cooperation of the lean burn strategy, even if the ammonia energy share is increased to more than 60%, the engine can still run smoothly. This provides a feasible path for pure hydrogen engine to use ammonia-hydrogen dual fuel, expanding the fuel flexibility and application prospect of hydrogen fuel engine.

[0111] 5. Reduce NOx emissions: The combination of ammonia blending and lean burn control can effectively suppress the generation of NOx. On the one hand, ammonia itself does not contain carbon, and its combustion does not directly produce carbon-based pollutants such as CO2; on the other hand, the addition of ammonia reduces the flame temperature peak (because part of the hydrogen is replaced by ammonia and the combustion reaction slows down), and the lean burn makes the excess air absorb heat, thereby reducing the formation of thermal NOx. Although ammonia fuel may bring fuel-type NOx, through precise control of the equivalence ratio and combustion temperature, the present method can control the level of nitrogen oxides in the exhaust gas within the strict emission limit. At the same time, moderate ammonia escape can also be further eliminated in the exhaust gas aftertreatment (such as SCR selective catalytic reduction) device. Therefore, the present application ensures the power while achieving low NOx emissions.

[0112] Figure 1 Figure 1 is a schematic diagram of an ammonia-hydrogen dual fuel spark-ignition engine experimental device, showing the arrangement of the test engine, pressurized gas supply system, and fuel supply and measurement devices.

[0113] Figure 2a and Figure 2b Figure 3 is a comparison of the fluctuation of the maximum cylinder pressure (p max ) in the continuous cycle under different ammonia energy blending ratios; wherein Figure 2a is the result of stoichiometric combustion (λ = 1), Figure 2b is the result of lean burn condition (λ = 1.2). The dispersion of the curve reflects the trend of increased cycle-to-cycle variation of the cylinder pressure peak after adding ammonia.

[0114] Figure 3aand Figure 3b Maximum pressure rise rate (dp / dφ) max of different ammonia energy ratios Figure 3a λ = 1 Figure 3b λ = 1.2 It can be seen that the average value of the maximum pressure rise rate decreases with the increase of the ammonia ratio, and the cycle fluctuation amplitude is relatively stable.

[0115] Figure 4a , Figure 4b and Figure 4c Distribution diagram of the relationship between the in-cylinder pressure peak p max and its occurrence time ; Figure 4a λ = 1 Figure 4b λ = 1.2 (ignition timing is not optimized) Figure 4c λ = 1.2 (ignition timing is optimized) Figure 4a , Figure 4b and Figure 4c It can be seen that the p max and its occurrence angle show a certain correlation under different conditions, especially after the ignition optimization, the p max and show a linear relationship, which shows that the cycle combustion process can be made more consistent by adjusting the ignition timing.

[0116] Figure 5a and Figure 5b The average in-cylinder pressure change and related parameters under different ammonia mixing ratios for 300 cycles are shown in the diagram. Figure 5a λ = 1 Figure 5b λ = 1.2. The solid line in the diagram represents the average pressure process, and the superimposed scatter points represent the change of the in-cylinder pressure peak and its occurrence time under different cycles. It can be seen that the average pressure curve shape changes slightly with the increase of the ammonia ratio, and the in-cylinder pressure peak decreases and the occurrence time is delayed, which is related to the slow combustion rate of ammonia.

[0117] Figure 6a and Figure 6b The relationship diagram between the maximum pressure rise rate (dp / dφ) max and its corresponding occurrence crank angle ; Figure 6a λ = 1 Figure 6b λ = 1.2. Similar to Figure 4a , Figure 4b and Figure 4c , Figure 6a and Figure 6bThe correlation between the maximum pressure rise rate and its occurrence time is reflected. Under the equivalence ratio condition, the two are approximately linearly correlated, indicating that the combustion process is highly repeatable; while under the lean and unoptimized ignition condition, the correlation is weakened, and the linear relationship needs to be restored through optimized ignition.

[0118] Figure 7a and Figure 7b The cycle-to-cycle variation of indicated mean effective pressure (IMEP) under different ammonia energy ratios is compared; Figure 7a In the case of λ = 1; Figure 7b In the case of λ = 1.2. As the ammonia mixing ratio increases, the fluctuation range of IMEP per cycle expands, especially when the ammonia ratio is high, the fluctuation is more significant. At the same time, the addition of ammonia increases the average value of IMEP within a certain range, indicating that appropriate ammonia mixing can improve the combustion power but will introduce additional instability factors.

[0119] Figure 8a and Figure 8b The return map (Return Map) of IMEP under different ammonia energy ratios is shown in the figure; Figure 8a In the case of λ = 1; Figure 8b In the case of λ = 1.2. Each point represents the corresponding relationship between the IMEP of the nth cycle and the IMEP of the (n+1)th cycle. It can be seen that as the ammonia ratio increases, the dispersion of the points around the 45° diagonal line gradually increases, indicating that the difference between adjacent cycle IMEPs expands. Under lean conditions, the trend of this difference expansion is slightly slower, indicating that the correlation between cycle IMEPs is stronger than that under the equivalence ratio condition (the return points are closer to the diagonal line).

[0120] Figure 9 The variation curve of the cycle-to-cycle variation coefficient (COV IMEP ) of IMEP under different ammonia energy ratios is shown in the figure. COV IMEP is defined as the ratio of the standard deviation of IMEP to the average value. It can be seen that under the equivalence ratio combustion (λ = 1), COV IMEP increases significantly from about 0.82% when the hydrogen is pure to 6.17% when the ammonia energy ratio is 65%, which exceeds the threshold of 5% generally considered as the upper limit of stable combustion, and the combustion becomes unstable. When the ammonia ratio increases from 60% to 65%, COV IMEP increases by about 60%, indicating that the cycle-to-cycle variation is very sensitive to the addition of ammonia under high ammonia conditions. In contrast, under the lean condition (λ = 1.2), COV IMEP also increases with the increase of ammonia ratio, but the overall value is significantly lower than that under the corresponding equivalence ratio condition. Therefore, lean combustion can improve the tolerance of the engine to ammonia mixing, allowing high-proportion ammonia mixing to remain in a relatively stable state.

[0121] Example 1: Basic engine and fuel supply control

[0122] As shown in Figure 1 The present embodiment adopts a four-cylinder four-stroke water-cooled hydrogen fuel spark-ignition engine as the experimental platform. The engine displacement is 2.0L, the compression ratio is 11.3:1, and an electric eddy current dynamometer is provided for steady-state loading. Two independent fuel injection systems are installed on the engine intake pipe for supplying hydrogen and ammonia respectively. Hydrogen is provided by a high-pressure steel cylinder, reduced in pressure and supplied directly into the cylinder through an electronic nozzle in the intake manifold (after the intake valve near the manifold). Ammonia is also reduced in pressure by a steel cylinder and introduced into the intake pipe through another set of injectors. Both fuel circuits are equipped with mass flow controllers (MFC) to adjust the injection amount, and mass flow meters (MFM) are connected in series to accurately measure the instantaneous flow of hydrogen and ammonia. To prevent overcooling caused by hydrogen expansion during pressure reduction, an electric heater is installed in the hydrogen injection path to stabilize the intake hydrogen temperature at 25±2℃, and the ammonia is also maintained at 25±2℃ through pipeline insulation. The engine ECU calculates and controls the pulse width of hydrogen and ammonia injection respectively based on the target ammonia energy ratio to achieve the set value of the mixed fuel. For example, when the ammonia energy ratio is required to be 20%, the ECU calculates the energy supply of the two fuels according to the difference in lower heating value between ammonia and hydrogen, so that ammonia provides 20% of the total fuel energy and hydrogen provides 80%. In actual implementation, the corresponding ammonia injection pulse width is adjusted in the range of 0-15000 microseconds at λ=1 and 0-14000 microseconds at λ=1.2. The start of injection (SOI) of hydrogen and ammonia is set to 140°CA and 60°CA before top dead center of the intake stroke respectively to ensure appropriate mixing and premixing time. All tests are carried out under hot conditions with stable engine water temperature (75±2℃), and all measuring instruments are calibrated before the test. The ambient temperature is about 25℃ and the atmospheric pressure is about 0.99bar. Through the above fuel supply control, the present invention can flexibly set the ammonia-hydrogen fuel blending ratio, laying the foundation for optimal control under different operating conditions.

[0123] Example 2: Operating condition setting and ignition control strategy

[0124] On the basis of the hardware described in Example 1, the present embodiment determines several representative operating conditions and implements an ignition advance angle optimization and lean burn control strategy for each operating condition.

[0125] First, the engine speed is fixed at 1500rpm (in the low and medium speed range) to highlight the cyclic fluctuation problem. Two air-fuel ratio conditions are selected: stoichiometric combustion at λ=1 and lean burn combustion at λ=1.2. Considering the need to observe the influence of ammonia blending on cycle variation, the present embodiment sets the ammonia energy ratio to five levels: 0% (pure hydrogen), 20%, 40%, 60%, and 65%. During the test, the ammonia ratio is increased sequentially, and when it reaches 65%, the combustion stability deteriorates sharply, so 65% is set as the upper limit condition.

[0126] For each ammonia blend ratio, under stoichiometric conditions (λ = 1), the ignition timing that achieves maximum braking torque (MBT) is found by adjusting the spark plug ignition advance angle. Specifically, starting from a later ignition timing, the ignition is gradually advanced until the engine output torque no longer increases; the crankshaft angle at this point is the MBT ignition timing. This MBT point is taken as the optimal ignition advance angle for the corresponding ammonia ratio. The ignition timing is set in this way for all λ = 1 conditions. For lean-burn (λ = 1.2) conditions, this embodiment employs two strategies: first, maintaining the same ignition advance angle as the corresponding stoichiometric condition to observe the effect on combustion without ignition adjustment; second, under some key conditions, the ignition advance angle is also adjusted to the new MBT value under lean-burn conditions (referred to as "optimized ignition timing") to compare the effects. For example, with λ=1, the MBT ignition angle for 60% ammonia is approximately 21.75°CA BTDC. Therefore, with λ=1.2 and 60% ammonia, 21.75°CA is still used if no changes are made. However, for optimization, the MBT angle needs to be re-evaluated, and it will likely be around 20.25°CA BTDC (see appendix). Figure 4c (As shown). Similarly, the optimal ignition timing under lean-burn conditions (λ=1.2) with different ammonia energy ratios can be obtained through experimental calibration. As shown in Table 4, when the ammonia energy ratio is 0%, 20%, 40%, 60%, and 65%, the optimized ignition advance angles are 5.25°CA, 11.25°CA, 17.5°CA, 20.25°CA, and 24.75°CA, respectively. Compared with a fixed ignition timing, it can be seen that under low to medium ratios (≤40%), the optimized ignition angle is slightly larger than the MBT value under the equivalence ratio condition, while under high ratios (≥60%), the optimized ignition angle needs to be appropriately reduced to compensate for the combustion delay caused by ammonia blending. By using an optimized ignition advance angle, the peak cylinder pressure (p) can be restored. max ) and the crankshaft angle Maximum rate of pressure rise (dp / dφ) max The linear relationship between the ignition timing and its phase significantly improves combustion consistency and cycle stability under lean-burn conditions. This leads to a set of comparative results: under lean-burn conditions, without optimization of ignition timing, cycle combustion phase fluctuations are significant, resulting in poor combustion consistency; however, after adopting the optimized ignition strategy of this invention, the peak cylinder pressure and maximum pressure rise rate regain a good linear relationship with their corresponding phases, and cycle stability is significantly improved. This comparison verifies the necessity and effectiveness of the ignition control strategy of this invention under lean-burn conditions.

[0127] The results of the examples show that, under lean-burn conditions, using unoptimized ignition (i.e., the same ignition angle as λ=1) causes the combustion process to occur earlier in the lower stages of the air-fuel mixture, slowing down flame core formation and thus exacerbating cycle fluctuations. This is inFigure 4b The middle is represented by p max and The correlation is poor, and the data points are scattered without a clear linear pattern. However, after ignition optimization (appropriately advance ignition), p under lean-burn conditions... max It recovered to a near-linear relationship at any time. Figure 4c This demonstrates that adjusting the ignition timing can significantly improve combustion consistency under lean-burn, high-ammonia conditions, making the peak pressure and its phase changes between cycles more regular. Therefore, this invention emphasizes that ignition timing should be optimized separately for different ammonia blending and air-fuel ratio combinations to ensure combustion repeatability.

[0128] Example 3: Cyclic Variation Analysis and Stability Improvement

[0129] Combustion data for 300 consecutive cycles under different operating conditions were obtained according to the method in Example 2, with a focus on analyzing the variation of cycle changes with ammonia blending. Figure 2a As shown, at an equivalence ratio λ = 1, as the ammonia energy ratio increases from 0 to 65%, the peak cylinder pressure p max The fluctuation range has significantly expanded. During pure hydrogen combustion, the p values ​​in each cycle... max Concentrated in the high-value range with relatively small fluctuations; when ammonia reaches 60%, p max The discreteness increases significantly, while at 65% the p of the partial cycle max A significant decrease indicates unstable combustion or even incomplete combustion in some cycles. Correspondingly, the cycle differences in IMEP are also widening. Figure 8a As the display points gradually move away from the diagonal, it means the difference in IMEP between adjacent cycles is increasing. At this point, COV... IMEP The ammonia blending ratio increased from less than 1% to over 6%, exceeding the usual standard for stable combustion. This demonstrates that in stoichiometric combustion, once the ammonia blending ratio exceeds approximately 60%, cycle fluctuations deteriorate sharply, and engine operation enters an unstable state.

[0130] In contrast, under lean-burn λ = 1.2 conditions, the adverse effects of ammonia blending on cycle variation are significantly mitigated. Figure 2b It is evident that even when the ammonia content reaches 65%, p max The scattering range is still smaller than the case corresponding to λ=1, and the p of most cycles max It remained at a high level, with only a few cycles showing a decrease. Figure 9 The curves also show that the COV during lean combustion in the high ammonia region is... IMEP Significantly lower than stoichiometric combustion (e.g., at 65% ammonia), lean-burn COV IMEPThe ammonia content is maintained at around 4%, while the equivalence ratio exceeds 6%. This confirms that lean-burn has a higher ammonia tolerance, allowing the engine to maintain stable combustion even with higher ammonia blending. This is likely because the lean-burn mixture has a lower combustion temperature, reducing the negative impact of ammonia combustion on stability; simultaneously, excess air increases the completeness of combustion, reducing the occurrence of misfire cycles. Based on this, the present invention specifies in its control strategy design that when the ammonia energy ratio exceeds a certain threshold (e.g., 60%), the system should switch to lean-burn mode to ensure that cycle fluctuations remain within an acceptable range.

[0131] It is also worth noting that ammonia blending not only affects combustion stability, but also alters the intensity and efficiency of combustion. Figure 3a and Figure 3b This indicates that as the proportion of ammonia increases, the maximum pressure rise rate (dp / dφ) increases. max The average value decreased, indicating a reduction in the peak combustion heat release rate. For pure hydrogen combustion, the maximum value of dp / dφ is very high, indicating very rapid combustion; however, combustion tends to be milder after ammonia blending, which is very beneficial for suppressing knock. However, dp / dφ also fluctuates significantly in the case of pure hydrogen, while the cyclic fluctuation of dp / dφ is relatively stable at a lower level after ammonia blending. This may be because the addition of ammonia prolongs the combustion duration, leveling out the differences between cycles. In summary, ammonia blending reduces the intensity of combustion but increases the differences between cycles, thus requiring a trade-off control through the method of this invention: utilizing ammonia to reduce peak pressure and combustion rate to mitigate knock and NOx, while suppressing the resulting increase in fluctuations through optimized ignition and perturbation.

[0132] Figure 7a and Figure 7b The distribution of IMEP under different ammonia ratios is shown. It can be seen that as the ammonia ratio increases from 0 to 65%, the average IMEP initially remains stable and then slightly increases. Within the 0–40% range, ammonia blending has almost no negative impact on the average IMEP (IMEP remains essentially flat at equivalence ratios, and even slightly increases under lean-burn conditions), indicating that there is no loss of power at low to medium blending ratios. This is consistent with our understanding of the combustion process: ammonia has a lower heat release rate, but appropriate ignition advance can compensate for the resulting combustion delay, thus increasing expansion work rather than decreasing it. Furthermore, ammonia molecules contain hydrogen atoms, so increasing ammonia actually introduces more total fuel, which may slightly increase the effective work capacity of cylinder pressure while ensuring complete combustion. However, when the ammonia ratio exceeds 60%, partial cycle combustion deteriorates, leading to a decrease in IMEP, resulting in fluctuations in the average IMEP. Fortunately, the control method of this invention can avoid entering this unstable region, allowing the engine to still output near-optimal torque even with high ammonia blending.

[0133] To verify the effectiveness of the control method, the closed-loop control test was carried out under high ammonia condition. When the engine was running at λ = 1.2 and ammonia energy ratio 65%, the cycle detection function of ECU was turned on to calculate COV IMEP in real time. The initial COV IMEP was about 5%, which was in a critical stable state. By introducing intake disturbance (controlling throttle to produce small periodic pressure fluctuations) and fine-tuning ignition advance angle (adjusting ± 2°CA near MBT), the COV IMEP was successfully reduced to about 3.5%. After several cycles of adjustment, the p max and IMEP dispersion were converged. During the experiment, the NOx emission was also monitored, and the results showed that under the condition of lean + high ammonia, the NOx concentration decreased by about 30% compared with the pure hydrogen baseline, and there was no case of ammonia leakage exceeding the standard (unburned ammonia content in the exhaust was controlled at ppm level). These results show that the various control strategies proposed in the present application work together in actual operation, which can greatly improve the cycle stability of hydrogen fuel engine under high ammonia mixed combustion while ensuring low emission.

[0134] The above describes the present application in conjunction with the drawings. Obviously, the specific implementation of the present application is not limited by the above method. As long as various non-essential improvements are made using the inventive concept and technical solution, or the above concept and technical solution of the present application is directly applied to other occasions without improvement, it is within the scope of protection of the present application.

Claims

1. A control method of the influence of ammonia blending on the cycle variation of a hydrogen spark-ignition engine, characterized by, The method comprises: Fuel blending control: adjusting the supply flow of ammonia and hydrogen according to a first preset control strategy; Ignition advance angle optimization: adjusting the ignition advance angle of the spark plug according to a second preset control strategy; Introducing air flow disturbance: adjusting the fuel injection parameters according to a third preset control strategy; Air-fuel ratio switching control: adjusting the engine operating mode according to a fourth preset control strategy; Closed-loop monitoring adjustment: using the installed sensors to monitor the cyclic combustion parameters in real time, and when the preset conditions are met, the electronic control unit can selectively execute the first, second, third, and fourth preset control strategies to adjust the ammonia supply ratio, ignition advance angle, and / or air disturbance amplitude, so that the engine returns to a stable combustion state.

2. The method of claim 1, wherein, The first preset control strategy comprises: Adjusting the supply flow of ammonia and hydrogen by the electronic control unit according to a preset ammonia energy ratio, so that the ammonia energy ratio meets the requirements of combustion stability under different working conditions.

3. The method of claim 2, wherein, The first preset control strategy further comprises: COV IMEP The COV increased from 0.82% to 6.17% with the increase of ammonia energy ratio from 0 to 65%, and the combustion was obviously unstable when the ratio was more than 60%; while under the lean combustion condition, the COV IMEP Although it also increased with the increase of ammonia ratio, the overall level was lower than that under the stoichiometric condition, and the engine had higher tolerance to ammonia blending. Under the equivalence ratio condition, the ammonia energy ratio should not exceed 60%, and if it needs to be further improved, it should be switched to a lean burn mode to ensure combustion stability.

4. The method according to any one of claims 1 to 3, characterized in that, The second preset control strategy comprises: Under the equivalence ratio condition, the ignition advance angle is determined according to MBT. Under lean conditions, if the fixed ignition timing is maintained, p max The linear relationship between φp max , (dp / dφ) max and φ(dp / d φ ) max disappears; while using the optimized MBT ignition timing, the linear relationship can be restored, significantly improving the combustion consistency and cycle stability.

5. The method according to any one of claims 1 to 3, characterized in that, The third preset control strategy comprises: Controlling the fuel injection parameters by the electronic control unit to introduce air flow disturbance, the fuel injection parameters including the injection timing and injection ratio of the two fuels; By making the fuel form pulse injection in the intake port, the turbulent intensity of the in-cylinder mixture is enhanced to reduce the fluctuations of the combustion rate and pressure between consecutive cycles.

6. The method of claim 5, wherein, The third preset control strategy comprises: Using a layered fuel supply method, hydrogen fuel is preferentially directly injected into the cylinder or near the intake valve, and then ammonia fuel is injected upstream of the intake manifold to form uniform premixing.

7. The method according to any one of claims 1 to 3, characterized in that, The fourth preset control strategy comprises: When the ammonia has a high blending ratio, the engine operating mode is switched to a lean burn mode; When the ammonia has a medium or low blending ratio, the engine operating mode is stoichiometric combustion.

8. The method according to any one of claims 1 to 3, characterized in that, The installed sensors include a cylinder pressure sensor and a knock sensor, which monitor the combustion pressure characteristics and knock intensity of each working cycle in real time.

9. The method of claim 8, wherein, The preset condition is that the combustion pressure characteristics and knock intensity are detected to exceed the predetermined threshold.

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