A hydrogen injection strategy optimization method for a dual-fuel X-type rotor engine

Abstract

The application discloses a hydrogen injection strategy optimization method for a dual-fuel X-type rotor engine, obtains geometric parameters of the X-type rotor engine, establishes a CDF fluid simulation model of a dual-fuel X-type rotor engine with gasoline intake port premixing and hydrogen in-cylinder direct injection, determines engine ignition parameters and operating conditions of a single hydrogen injection strategy, and obtains, through simulation calculation, a hydrogen injection time point at which a hydrogen distribution area is maximum and a hydrogen injection time point at which a flame front area is maximum. Under the condition that the hydrogen injection total amount at the two hydrogen injection time points is the same as that of the single hydrogen injection strategy and the hydrogen injection mass fraction at the two hydrogen injection time points is taken as a variable, the hydrogen injection mass fraction corresponding to the hydrogen injection time point at which the hydrogen distribution area is maximum and the hydrogen injection mass fraction corresponding to the hydrogen injection time point at which the flame front area is maximum are obtained through simulation calculation, an optimal two-stage hydrogen direct injection strategy of the dual-fuel X-type rotor engine is obtained, and the thermal efficiency and emission performance of the rotor engine are improved.

Description

Technical Field

[0001] This invention belongs to the field of aviation propulsion technology, specifically to an optimization method for hydrogen injection strategy of a dual-fuel X-type rotary engine. Background Technology

[0002] The X-type rotary engine is an improved design of the traditional Wankel rotary engine. Structurally, its rotor and cylinder profiles are "inverted" from those of the traditional Wankel rotary engine, further improving the engine's compactness and power-to-weight ratio. Furthermore, the X-type rotary engine eliminates the sealing column, effectively solving the apex leakage problem and further improving combustion efficiency. In terms of the combustion process, the X-type rotary engine is similar to the traditional Wankel rotary engine, employing a four-stroke process including intake, compression, combustion, and exhaust. The X-type rotary engine can achieve a highly efficient hybrid cycle, possessing broad potential for applications in drones and vehicle range extenders. However, due to its unique structure, the combustion chamber is not truly separated, thus leakage issues still exist during operation, significantly impacting fuel combustion speed and efficiency. Therefore, the performance of the X-type rotary engine still has considerable potential for improvement.

[0003] To achieve the goal of low carbon emissions, addressing the problems of low combustion efficiency and poor emission performance in X-type rotary engines is crucial. Among these measures, employing a dual-fuel combustion strategy can significantly reduce fuel consumption. Hydrogen-infused combustion has a positive impact on fuel combustion in X-type rotary engines, contributing to improved combustion and emission performance. Current research on hydrogen injection strategies for X-type rotary engines focuses on aspects such as nozzle position, injection angle, and injection pressure. Geng et al. studied the effects of different hydrogen injection positions on the performance of X-type rotary engines. Their research found that the indicated thermal efficiency was 10.08% higher under the front injection strategy than under the right injection strategy. However, the mechanism by which the timing of hydrogen injection affects engine performance still needs further investigation. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides an optimization method for hydrogen injection strategy of a dual-fuel X-type rotary engine. By establishing a CFD model of the X-type rotary engine and using CONVERGE simulation software, the engine performance obtained under different hydrogen injection strategies can be compared. The optimal two-stage hydrogen direct injection strategy for the gasoline-hydrogen dual-fuel X-type rotary engine can be obtained, thereby improving the thermal efficiency and emission performance of the rotary engine.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for optimizing hydrogen injection strategy of a dual-fuel X-type rotary engine, the specific steps of which are as follows:

[0006] S1 Obtain the geometric parameters of the X-type rotary engine and establish a CDF fluid simulation model of the dual-fuel X-type rotary engine with gasoline intake premixing and hydrogen direct injection in the cylinder.

[0007] S2 determines the engine ignition parameters and operating conditions for a single hydrogen injection strategy. Using CONVERGE simulation calculations, it obtains the hydrogen injection time that maximizes the hydrogen distribution area and the hydrogen injection time that maximizes the flame front area.

[0008] S3 is performed under the same engine ignition parameters and operating conditions as S2, the total amount of hydrogen injected at two hydrogen injection moments is the same as the total amount of hydrogen injected in a single hydrogen injection strategy, and the hydrogen mass fraction at two hydrogen injection moments is used as a variable. CONVERGE simulation calculation is performed to obtain the hydrogen mass fraction corresponding to the hydrogen injection moment that maximizes the hydrogen distribution area and the hydrogen mass fraction corresponding to the hydrogen injection moment that maximizes the flame front area.

[0009] S4 obtains a two-stage hydrogen injection strategy based on the determined two hydrogen injection times and the corresponding hydrogen mass fractions at the two hydrogen injection times, thereby optimizing the hydrogen injection strategy of the dual-fuel X-type rotary engine.

[0010] Furthermore, in S1, the geometric parameters of the X-type rotary engine include eccentricity, generating radius, cylinder width, speed, displacement, ignition angle, equivalence ratio, and geometric compression ratio.

[0011] Furthermore, in S2, the engine ignition parameters include ignition advance angle, top dead center position, ignition position, ignition core radius, ignition energy, and ignition pulse width, where the engine ignition position is the center of the combustion chamber.

[0012] Furthermore, in S2, the engine operating conditions include fuel, intake pressure, hydrogen energy fraction, nozzle diameter, hydrogen injection pressure, and injection pulse width, wherein the fuel is hydrogen-blended gasoline.

[0013] Furthermore, in S2 and S3, the CONVERGE simulation calculations use the IC8H18 skeleton reaction combustion mechanism as the reaction mechanism. The physical models specifically include the turbulence model RNG k-ε model, the ignition model Spark-energy deposition model, the NOx reaction mechanism Extended Zeldovich mechanism, the combustion model SAGE model, and the wall heat transfer model Han and Reitz model.

[0014] Furthermore, in S2, the single-injection hydrogen strategy adopts a pre-injection strategy, selecting different hydrogen injection times between the end of the intake and the ignition time. Under the determined engine ignition parameters and operating conditions of the single-injection hydrogen strategy, CONVERGE simulation calculations are used to obtain the hydrogen injection time that maximizes the hydrogen distribution area and the hydrogen injection time that maximizes the flame front area, which are respectively used as the first hydrogen injection time and the second hydrogen injection time.

[0015] Furthermore, the total amount of hydrogen injected at the two hydrogen injection moments is the same as the total amount of hydrogen injected in a single hydrogen injection strategy. Using the mass fraction of hydrogen injected in the first injection as a variable, under the operating conditions of a single hydrogen injection strategy, CONVERGE simulation is used to calculate and obtain the hydrogen injection mass fraction that maximizes the working volume utilization of the engine cylinder and the fuel conversion rate as the mass fraction of hydrogen injected in the first injection.

[0016] Furthermore, the mass fraction of hydrogen injected in the second injection is 100% - the mass fraction of hydrogen injected in the first injection.

[0017] The present invention also provides a dual-fuel X-type rotary engine, wherein the X-type rotary engine is operated using the hydrogen injection strategy optimization method described above to obtain a two-stage hydrogen injection strategy.

[0018] The present invention also provides a method for improving the combustion performance of a dual-fuel X-type rotary engine, wherein the above-mentioned hydrogen injection strategy optimization method is used to obtain a two-stage hydrogen injection strategy during operation.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] This invention provides an optimization method for hydrogen injection strategy of a dual-fuel X-type rotary engine. A CDF simulation model of a gasoline intake premixed and hydrogen direct injection dual-fuel X-type rotary engine was established to explore the influence of a single hydrogen injection on the combustion performance of the rotary engine. The timing of two hydrogen injections was obtained, and hydrogen was injected at the two times before and after the injection while keeping the total amount of hydrogen injected constant, resulting in a two-injection strategy. When the X-type rotary engine is running, the two-injection strategy can improve the problem of incomplete combustion of fuel in the later combustion slit of the engine while ensuring the combustion speed in the early stage, thereby further improving the thermodynamic performance of the engine.

[0021] In this invention, to avoid the intake and ignition processes affecting hydrogen injection, the hydrogen injection timing is set between the start of intake and the ignition timing. With a single hydrogen injection, the earlier the injection timing, the longer the hydrogen diffusion time, resulting in a more uniform distribution before ignition, and hydrogen distribution even in the slits on both sides of the combustion chamber. This contributes to more complete fuel combustion in the later stages of combustion. However, this also leads to a low hydrogen concentration near the spark plug, reducing the hydrogen's ignition capability. Conversely, the later the injection timing, the shorter the hydrogen diffusion time, with hydrogen mainly concentrated near the spark plug. This ensures the hydrogen's ignition capability but reduces the engine's combustion performance in the later stages of combustion. Therefore, a single hydrogen injection strategy struggles to simultaneously ensure good hydrogen ignition capability in the early stages of combustion and excellent combustion performance in the later stages. Combining early and late injection strategies to form a two-injection strategy further improves the engine's thermodynamic performance. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a diagram of the two-stage hydrogen direct injection strategy for the gasoline-hydrogen dual-fuel X-type rotary engine of the present invention.

[0024] Figure 2 This is the CFD simulation model of the X-type rotary engine of the present invention.

[0025] Figure 3 This is a verification of the mesh independence and model validity of the CFD simulation model of the X-type rotary engine of this invention.

[0026] Figure 4 This is a comparison of hydrogen distribution cloud maps and temperature cloud maps at different injection times according to the present invention.

[0027] Figure 5 This invention compares the engine combustion performance at different hydrogen injection times.

[0028] Figure 6 This invention relates to a different two-stage hydrogen injection strategy setting for the X-type rotary engine.

[0029] Figure 7 This invention compares flame growth under different FIMF conditions.

[0030] Figure 8 This invention compares the sum of the peak reactant mass, intermediate product mass, and instantaneous exothermic rate under different FIMF conditions.

[0031] Figure 9 This invention compares the combustion performance of engines under different FIMF conditions. Detailed Implementation

[0032] To make the objectives, technical effects, and technical solutions of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention. Based on the embodiments disclosed in the present invention, other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0033] Please see Figure 1 This invention provides a method for optimizing the hydrogen injection strategy of a dual-fuel X-type rotary engine, the specific steps of which are as follows:

[0034] First, using gasoline-hydrogen dual fuel, based on the geometric parameters of the X-type rotary engine, a CDF fluid simulation model of the gasoline intake manifold premixed and hydrogen in-cylinder direct injection dual-fuel X-type rotary engine was established to determine the engine ignition parameters and operating conditions.

[0035] Secondly, the hydrogen injection timing of the single-injection strategy is optimized to obtain the two hydrogen injection timings of the two-injection strategy, specifically:

[0036] The single-shot hydrogen injection strategy adopts a front-injection strategy. Different hydrogen injection times of the front-injection strategy are selected between the end of the intake and the ignition time. Based on the engine operating conditions, the hydrogen distribution area and flame front area corresponding to different hydrogen injection times are obtained by CONVERGE simulation calculation.

[0037] Among them, the moment when hydrogen is injected to maximize the hydrogen distribution area is taken as the first hydrogen injection moment, so that hydrogen is distributed in the narrow gaps on both sides of the engine combustion chamber, thereby enhancing the combustion performance of the engine in the later stage of combustion.

[0038] The moment when hydrogen is injected to maximize the flame front area is designated as the second hydrogen injection moment, thereby ensuring sufficient hydrogen concentration near the spark plug before ignition to enhance the ignition capability of hydrogen.

[0039] Furthermore, based on the operating conditions of the single hydrogen injection strategy, the hydrogen injection mass fraction at the two hydrogen injection moments is optimized to obtain the hydrogen injection mass fraction at the two hydrogen injection moments in the two hydrogen injection strategies.

[0040] To ensure that the total amount of hydrogen injected at two hydrogen injection moments is the same as the total amount of hydrogen injected in a single hydrogen injection strategy, and using the mass fraction of the first hydrogen injection as a variable, CONVERGE simulation was used to calculate the working volume utilization rate and fuel conversion rate of the engine cylinder under different mass fractions of the first hydrogen injection under the working conditions of a single hydrogen injection strategy.

[0041] The first hydrogen injection mass fraction, which maximizes the utilization of the engine cylinder working volume and the fuel conversion rate, is taken as the final first hydrogen injection mass fraction. The final second hydrogen injection mass fraction is 100% minus the final first hydrogen injection mass fraction.

[0042] Finally, a two-stage hydrogen injection strategy was obtained, which determined the timing and mass fraction of the two hydrogen injections, thus optimizing the hydrogen injection strategy of the dual-fuel X-type rotary engine. Applying the two-stage hydrogen injection strategy to the X-type rotary engine improves its combustion performance.

[0043] Example 1

[0044] Taking the XMv3 rotary engine as an example, the present invention provides a detailed description of a hydrogen injection strategy optimization method for a dual-fuel X-type rotary engine, as follows:

[0045] First, a CFD simulation model was established based on the geometric parameters of the XMv3 rotary engine. The geometric parameters of the XMv3 rotary engine are shown in Table 1. The CFD simulation model of the X-type rotary engine is also available in [reference]. Figure 2 .

[0046] Table 1 Geometric parameters of XMv3 rotary engine

[0047] parameter symbol value Eccentricity / mm e 6 Creation radius / mm R 41 Cylinder block width / mm B 18.5 engine speed / rpm n 10000 Displacement / cm3 Vd 70 Ignition angle / °CA / 345 Equivalent ratio φ 1.2 Geometric compression ratio ε 11：1

[0048] The ignition parameters and operating conditions of the X-type rotary engine are shown in Table 2. The ignition location is the center of the combustion chamber. (See also...) Figure 2 .

[0049] Table 2 Ignition parameters and operating conditions of X-type rotary engine

[0050] parameter value fuel Hydrogen-blended gasoline Intake pressure / bar 1.03 Ignition advance angle / °CA 30 Top dead center position / °CA 360 Ignition position Combustion chamber center Fire core radius / mm 0.5 Ignition energy / mJ 20 Ignition pulse width / °CA 0.5 Hydrogen energy fraction / % 3 Nozzle diameter / mm 1 Hydrogen injection pressure / MPa 0.5 Injection pulse width / °CA 3.5

[0051] In this case, the reaction mechanism adopts the isooctane IC8H18 skeleton reaction combustion mechanism proposed by Liu et al., which is composed of 48 components and 152 free radicals.

[0052] To better simulate the combustion process, the SAGE model was used in the simulation calculation, and the specific physical parameters are shown in Table 3.

[0053] Table 3 Physical Model of X-type Rotary Engine

[0054] parameter value Turbulence model RNG k-ε model Ignition Model Spark-energy deposition model NOx reaction mechanism Extended Zeldovich mechanism Combustion Model SAGE model Wall heat transfer model Han and Reitz model

[0055] The hydrogen energy fraction is calculated using formula (1), and in this invention, the hydrogen energy fraction is 3%. The injection angle is 90°, which reduces the resistance of hydrogen entering the combustion chamber. The nozzle diameter is 1 mm, and the injection pulse width is 3.5°CA.

[0056] (1)

[0057] In the formula: and These represent the mass of hydrogen injected into the combustion chamber and the mass of IC8H18 entering the combustion chamber through the intake port, respectively. This represents the low calorific value of hydrogen (120 MJ / kg); This represents the low calorific value (44 MJ / kg) of IC8H18.

[0058] The results of the grid independence and model validity verification are as follows: Figure 3 As shown. For mesh independence verification, this invention used five standard mesh sizes—3, 3.5, 4, 4.5, and 5 mm—for comparison. Simulation calculations were performed on the engine under the operating conditions described in Table 2, without hydrogen doping.

[0059] from Figure 3 As shown in (a), comparing the results with 3mm and 3.5mm mesh sizes, the peak pressure difference between the two groups is 1.59%, a difference sufficient to meet the requirements of analytical accuracy. To obtain more accurate calculation results, a basic mesh size of 3mm was used in all subsequent cases. Figure 3 As can be seen in (b), the peak pressure difference between the simulation results and the experimental results is less than 1%, and the difference in crankshaft angle corresponding to the peak pressure is less than 2%; while the maximum error between the simulation results and the experimental results for the heat release rate is less than 3%, and the simulated trends of cylinder pressure change and heat release rate change are in good agreement with the experimental data, thus verifying the rationality of the model.

[0060] Secondly, using CONVERGE simulation software, the influence of different single hydrogen injection times on the X-type rotary engine was studied.

[0061] Under the single-shot hydrogen injection strategy, the hydrogen injection timing is set between the end of the intake (225°CA) and the ignition timing (330°CA), specifically 230°CA, 250°CA, 270°CA, and 290°CA. The specific operating conditions are shown in Table 4.

[0062] Table 4. Hydrogen injection timing settings for a single hydrogen injection cycle of the X-type rotary engine.

[0063]

[0064] Using CONVERGE simulation software, calculations were performed to obtain comparative data on hydrogen gas distribution cloud maps and OH group concentration distribution cloud maps at different injection times. Figure 4As shown in Figure (a), the hydrogen distribution before ignition is affected by the diffusion time and cylinder pressure. The later the hydrogen injection time, the longer the hydrogen diffusion time, and the cylinder pressure increases with the crankshaft angle, limiting the hydrogen diffusion rate. Overall, when the hydrogen injection time is 230°CA, the hydrogen diffusion time is the longest, the resistance from cylinder pressure is the smallest, and thus the hydrogen distribution area before ignition is the largest. As can be seen from the figure, under the condition of hydrogen injection time of 230°CA, the hydrogen distribution area is the largest, mainly distributed in the combustion chamber and the right slit of the combustion chamber. The hydrogen in the slit ensures the continuous combustion of fuel in the slit during the later stages of combustion. Conversely, under the condition of 290°CA hydrogen, the hydrogen diffusion time is the shortest, and the resistance from cylinder pressure is the greatest. Before ignition, the hydrogen is concentrated in the combustion chamber, and the hydrogen concentration is the highest near the spark plug. Therefore, under this condition, the hydrogen ignition effect is the best, and the fuel combustion speed is the fastest. However, there is almost no hydrogen distribution in the narrow slits on both sides, leaving room for improvement in the later combustion performance of the engine. As can be seen from Figure (b), delaying the hydrogen injection timing results in a more concentrated hydrogen distribution and higher hydrogen concentration near the spark plug before ignition. This ensures the ignition capability of hydrogen at ignition and accelerates flame growth. In the early stage of combustion (0°CABTDC), the spread range of the flame front increases with the delay of the hydrogen injection timing. When the hydrogen injection timing is 290°CA, the flame front area is the largest. This indicates that the fuel burns fastest and releases the most heat under this condition. In summary, delaying the hydrogen injection timing accelerates the fuel combustion rate in the early stage of combustion, but deteriorates the combustion performance in the later stage. Furthermore, when the hydrogen injection timing is 290°CA, the flame front area is the largest and the combustion speed is the fastest.

[0065] The effect of different hydrogen injection times on engine combustion performance, for example Figure 5 As shown. From Figure 5 As shown in (a) and 5(b), after the crank angle reaches 350°CA, different hydrogen injection timings cause inconsistent hydrogen distribution, further leading to differences in the post-combustion heat release rate and combustion rate. The peak pressure and temperature inside the cylinder increase with the delay in hydrogen injection timing. When the hydrogen injection timing is 290°CA, the peak pressure and temperature inside the cylinder reach their maximum values ​​of 4.04 MPa and 1828.07 K, respectively. However, delaying the hydrogen injection timing negatively impacts the combustion performance in the later stages of engine combustion, with a faster temperature drop after reaching the peak. When the hydrogen injection timing is 230°CA, the temperature drops slowly after reaching the peak, indicating better combustion performance in the later stages of engine combustion under this condition. Figure 5 (c) It can be seen that the closed curve encloses the largest area at the hydrogen injection time of 290°CA, combined with... Figure 5(d) shows that the indicated work is the highest under this condition, at 13.21 J, further indicating that the fuel combustion rate is fastest and the efficiency of fuel conversion to kinetic energy is highest under this condition. Under the condition of hydrogen injection at 230°C CA, although the combustion rate is slower in the initial stage, the temperature in the later stage of combustion is significantly higher than in other conditions. Therefore, the indicated work under this condition is second only to the indicated work at 290°C CA, at 13 J. From... Figure 5 (e) It can be seen that the best performance parameters are achieved under the condition of hydrogen injection at 290°CA, with an average effective pressure (IMEP) of 0.574 MPa and an thermal efficiency (ITE) of 31.54%. Under this condition, the efficiency of converting internal energy into kinetic energy during gasoline combustion is the highest. Compared with the condition of hydrogen injection at 270°CA, the indicated thermal efficiency is improved by 6.09%.

[0066] In summary, the impact of a single hydrogen injection timing on engine combustion performance is as follows: the hydrogen distribution before ignition is jointly determined by the injection timing and in-cylinder pressure, and further affects engine combustion performance. With a delayed hydrogen injection timing, the hydrogen distribution in the combustion chamber is wider, but this results in a lower hydrogen concentration in the ignition zone, affecting the hydrogen's ignition capability. The hydrogen distribution through the slits on both sides helps improve combustion performance in the later stages of combustion. The optimal combustion performance is achieved at a hydrogen injection timing of 290°CA, with a peak in-cylinder pressure of 4.04 MPa and an indicated thermal efficiency 6.09% higher than at 270°CA. While combustion performance is poor in the initial stages at a hydrogen injection timing of 230°CA, fuel combustion is more complete in the later stages.

[0067] The two-stage hydrogen injection strategy aims to ensure sufficient hydrogen concentration near the spark plug before ignition, thereby improving the ignition capability of hydrogen; and to ensure hydrogen distribution in the slits on both sides, further enhancing the combustion performance in the later stages of engine combustion. The strategy is implemented as follows: keeping the total injection pulse width constant at 3.5°CA, the first hydrogen injection mass fraction (FIMF) is the variable, and hydrogen is injected at two times, 230°CA and 290°CA. The variable is controlled by changing the FIMF, which are 100%, 80%, 60%, 40%, 20%, and 0%, corresponding to A1, B1, B2, B3, B4, and A4, respectively. A1 and A4 are reference conditions at 230°CA and 290°CA for a single hydrogen injection. The two-stage hydrogen injection strategy for the X-type rotary engine is as follows. Figure 6 As shown.

[0068] Comparison of flame growth under different FIMF conditions Figure 7As shown, with the increase of the crankshaft angle, the flame gradually grows outward and towards the right side of the combustion chamber along with the rotor's rotation direction. In the middle of the obvious combustion period, the flame area is largest under the condition of 60% FIMF, with the flame mainly distributed in the combustion chamber and the right-side slit. This indicates that combustion is most intense under this condition, and that the flame distribution area under this condition is significantly larger than that under condition A4 in the later stage of the obvious combustion period. The results show that the two-stage hydrogen injection strategy significantly improves the combustion performance of the X-type rotary engine in the later stages of combustion.

[0069] Comparison of the sum of peak reactant mass, intermediate mass, and instantaneous exothermic rate under different FIMF conditions. Figure 8 As shown, under different FIMF (Fuel Intake Maturity Factor), the mass decay rate of IC8H18 exhibits a trend of initially rapid then slowing down. Under the condition of 60% FIMF, after 360°CA (Complete Calorific Value), the consumption rate of IC8H18 increases rapidly, and the decay rate is the largest, indicating that under this condition, IC8H18 is consumed most quickly, and fuel combustion is most complete. From... Figure 8 (b) It can be seen that when FIMF is 60%, Figure 3 The peaks for O and H groups reached their maximum value of 2.33166 × 10⁻⁶. -2 mg. Compared to operating conditions A1 and A4 under a single hydrogen injection strategy, this represents an improvement of 9.24% and 5.45%, respectively. From Figure 8 (c) It can be seen that the peak instantaneous heat release rate under the condition of 60% FIMF is 2.42 J / °CA, which is significantly higher than that under other conditions. It is also 28.13% and 17.10% higher than that under conditions A1 and A4 under the single hydrogen injection strategy, respectively. In addition, when the crank angle reaches 375°CA, the transient heat release rate under this condition is still very high.

[0070] Comparison of engine combustion performance under different FIMF conditions, as follows Figure 9 As shown. From Figure 9 As shown in (a), the cylinder pressure curves are basically the same before the crankshaft angle reaches 340°CA. At a crankshaft angle of 360°CA, a significant combustion phase is reached, fuel consumption accelerates, and cylinder pressure rises sharply. Hydrogen distribution is also affected by different FIMF levels, which further affects the fuel combustion rate and thus the peak cylinder pressure. Under the condition of 60% FIMF, the cylinder pressure reaches its peak first, at 4.10 MPa. Combined with... Figure 9 (b) Under this operating condition, the reactant consumption rate is the highest, the heat generated is the greatest, and the peak temperature is the highest, reaching 1844.08 K. Furthermore, the fuel combustion efficiency is highest under this condition, reaching 87.57%. Figure 9 As can be seen in (c), under the condition of FIMF of 60%, the area enclosed by the closed curve is the largest, and combined with... Figure 9 (d) shows that under this operating condition, the indicated work reaches a maximum value of 13.56 J, which is 4.31% higher than that under condition A1 with a single hydrogen injection. Figure 9 (e) It can be seen that under the condition of 60% FIMF, the mean effective pressure (IMEP) and indicated thermal efficiency (ITE) are the highest, at 0.59 MPa and 31.82%, respectively. The results indicate that this condition has the optimal performance parameters. In summary, under the condition of 60% FIMF, the engine cylinder working volume utilization rate and fuel conversion rate are the highest. The two-stage hydrogen injection strategy can improve the combustion performance in the later stages of engine combustion and has good potential for improving engine performance. Therefore, the optimal two-stage hydrogen injection strategy is obtained; in this embodiment, the optimal two-stage hydrogen injection strategy is 60% FIMF.

[0071] A two-stage hydrogen direct injection strategy for a gasoline-hydrogen dual-fuel X-type rotary engine. The gasoline-hydrogen dual-fuel system employs gasoline premixing in the intake manifold and hydrogen direct injection into the cylinder. The two-stage hydrogen direct injection strategy of the X-type rotary engine maintains a constant total hydrogen injection volume while altering the initial hydrogen mass fraction (FIMF), injecting hydrogen at two separate times before and after the initial injection.

[0072] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still make modifications or equivalent substitutions to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the claims of the present invention pending approval.

Claims

1. A method for optimizing hydrogen injection strategy in a dual-fuel X-type rotary engine, characterized in that, The specific steps are as follows: S1 acquires the geometric parameters of the X-type rotary engine and establishes a CDF fluid simulation model of the dual-fuel X-type rotary engine with gasoline intake premixing and hydrogen direct injection in the cylinder. S2 determines the engine ignition parameters and operating conditions for a single hydrogen injection strategy. Using CONVERGE simulation calculations, it obtains the hydrogen injection time that maximizes the hydrogen distribution area and the hydrogen injection time that maximizes the flame front area. S3 is performed under the same engine ignition parameters and operating conditions as S2, the total amount of hydrogen injected at two hydrogen injection moments is the same as the total amount of hydrogen injected in a single hydrogen injection strategy, and the hydrogen mass fraction at two hydrogen injection moments is used as a variable. CONVERGE simulation calculation is performed to obtain the hydrogen mass fraction corresponding to the hydrogen injection moment that maximizes the hydrogen distribution area and the hydrogen mass fraction corresponding to the hydrogen injection moment that maximizes the flame front area. S4 obtains a two-stage hydrogen injection strategy based on the determined two hydrogen injection times and the corresponding hydrogen mass fractions at the two hydrogen injection times, thereby optimizing the hydrogen injection strategy of the dual-fuel X-type rotary engine.

2. The method for optimizing hydrogen injection strategy of a dual-fuel X-type rotary engine according to claim 1, characterized in that, In S1, the geometric parameters of the X-type rotary engine include eccentricity, generation radius, cylinder width, speed, displacement, ignition angle, equivalence ratio, and geometric compression ratio.

3. The method for optimizing hydrogen injection strategy of a dual-fuel X-type rotary engine according to claim 1, characterized in that, In S2, the engine ignition parameters include ignition advance angle, top dead center position, ignition position, ignition core radius, ignition energy, and ignition pulse width. The engine ignition position is the center of the combustion chamber.

4. The method for optimizing hydrogen injection strategy of a dual-fuel X-type rotary engine according to claim 1, characterized in that, In S2, the engine operating conditions include fuel, intake pressure, hydrogen energy fraction, nozzle diameter, hydrogen injection pressure, and injection pulse width, with the fuel being hydrogen-blended gasoline.

5. The method for optimizing hydrogen injection strategy of a dual-fuel X-type rotary engine according to claim 1, characterized in that, In S2 and S3, the reaction mechanism in the CONVERGE simulation calculation adopts the IC8H18 skeleton reaction combustion mechanism. The physical models specifically include the turbulence model RNG k-ε model, the ignition model Spark-energy deposition model, the NOx reaction mechanism Extended Zeldovich mechanism, the combustion model SAGE model, and the wall heat transfer model Han and Reitz model.

6. The method for optimizing hydrogen injection strategy of a dual-fuel X-type rotary engine according to claim 1, characterized in that, In S2, the single-injection hydrogen strategy adopts a front-injection strategy. Different hydrogen injection times are selected between the end of the intake and the ignition time. Under the determined engine ignition parameters and operating conditions of the single-injection hydrogen strategy, CONVERGE simulation calculations are used to obtain the hydrogen injection time that maximizes the hydrogen distribution area and the hydrogen injection time that maximizes the flame front area, which are respectively used as the first hydrogen injection time and the second hydrogen injection time.

7. The method for optimizing hydrogen injection strategy of a dual-fuel X-type rotary engine according to claim 6, characterized in that, The total amount of hydrogen injected at the two hydrogen injection moments is the same as the total amount of hydrogen injected in a single hydrogen injection strategy. Using the mass fraction of hydrogen injected in the first injection as a variable, under the operating conditions of a single hydrogen injection strategy, CONVERGE simulation is used to calculate and obtain the mass fraction of hydrogen injected in the first injection that maximizes the utilization rate of the engine cylinder working volume and the fuel conversion rate.

8. The method for optimizing hydrogen injection strategy of a dual-fuel X-type rotary engine according to claim 7, characterized in that, The mass fraction of hydrogen injected in the second injection is 100% - the mass fraction of hydrogen injected in the first injection.

9. A dual-fuel X-type rotary engine, characterized in that, The X-type rotary engine is operated using the hydrogen injection strategy optimization method described in any one of claims 1-8 to obtain a two-stage hydrogen injection strategy.

10. A method for improving the combustion performance of a dual-fuel X-type rotary engine, characterized in that, During operation, the hydrogen injection strategy optimization method described in any one of claims 1-8 is used to obtain a two-stage hydrogen injection strategy for hydrogen injection.

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