【作者】 吴颖；

【导师】 庄远； 钱多德；

【作者基本信息】 合肥工业大学 ， 动力工程（专业学位）， 2021， 硕士

【摘要】 日益严苛的排放法规与愈加恶劣的市场环境,迫使发动机进一步升级。氢气具有改善火花点火双燃料发动机燃烧和排放特性的能力,稀燃能提高发动机热效率减低排放。为了降低NOx排放,消除稀燃对燃烧的不利影响,本研究对一台1.5L涡轮增压汽油直喷（GDI）发动机进行了改造;安装了一个直接氢气喷射系统,在火花塞上开小孔向发动机导入氢气。研究稀薄燃烧和火花塞微孔喷氢对发动机燃烧和排放的协同作用。利用AVL Fire对试验发动机进行三维建模,验证了模型的合理性,模拟了发动机的进气压缩过程进行,研究了不同喷氢策略对缸内混合气的影响。本文对火花塞微孔直喷发动机的工作过程进行实验研究和模拟计算。模拟选取节气门开度为35%与100%,掺氢比为5%工况下,不同喷氢时刻和喷氢压力对缸内混合气的影响。然后,根据模拟结果选取合理的喷氢策略进行实验。实验在1600r/min,节气门开度35%条件下进行,研究不同喷氢比例和过量空气系数（）对发动机燃烧和排放的影响。模拟结果表明,氢气进入气缸后受缸内气流影响,主要聚集在缸内进气门侧。加大喷氢压力会提高氢气的扩散速率,使氢气扩散更广泛,使火花塞附近湍动能更高,但会造成火花塞局部气流速度变大。增加喷氢提前角会增加氢气扩散时间,不同喷氢时刻火花塞局部都富集较高浓度的氢气。早期喷氢时,动能耗散完全,火花正式时缸内湍动能与流场与未喷氢时基本没有变化。在喷氢压力为8MPa,喷氢时刻为655°CA,节气门开度为35%时,缸内混合气分层效果达到最佳。实验结果表明,稀燃模式下,掺氢能使缸压峰值升高,峰值相位提前,掺入少量氢气可以抵消稀燃导致的燃烧恶化的影响,使得CA0-10、CA10-50、CA10-90降低明显,在各种过量充气系数下,掺氢比3.5%能使发动机IMEP协方差(COV_IMEP)降低到5%以下。火花塞微孔喷氢能显著提高稀燃工况下火焰传播速度及帮助形成优良火核,推进了发动机的稀燃极限。喷氢和稀燃协同作用使氮氧化物（NOx）、一氧化碳（CO）和碳氢化合物（HC）排放显著下降。更多还原

【Abstract】 Increasingly stringent emissions regulations and harsher market conditions are forcing further engine upgrades.Hydrogen has the ability to improve the combustion and emission characteristics of spark ignition dual-fuel engines,and rarefied combustion can improve engine thermal efficiency and reduce emissions.In order to reduce NOx emissions due to hydrogen addition and to eliminate the adverse effects of rarefied combustion on combustion,a 1.5L turbocharged gasoline direct injection（GDI）engine was modified in this study;a direct hydrogen injection system was installed with a small hole in the spark plug to introduce hydrogen into the engine.The synergistic effects of lean combustion and spark plug micro-hole hydrogen injection on engine combustion and emissions were investigated.Three-dimensional modeling of the test engine is performed using commercial software AVL Fire to verify the rationality of the model,simulate the inlet compression process of the engine,and study the effect of different hydrogen injection strategies on the in-cylinder mixture.In this paper,the working process of spark plug micro-hole direct injection engine is experimentally studied and simulated.The effect of different hydrogen injection time and pressure on the in-cylinder mixture is simulated at 35%and 100%throttle opening and 5%hydrogen doping ratio.Then,a reasonable hydrogen injection strategy is selected for the experiment according to the simulation results.The experiments were conducted at 1600r/min and 35%throttle opening to study the effects of different hydrogen injection ratios and excess air coefficients（）on engine combustion and emissions.The simulation results show that hydrogen gas entering the cylinder is influenced by the in-cylinder airflow and mainly collects in the inlet valve side of the cylinder.Increasing the hydrogen injection pressure will increase the hydrogen diffusion rate and make the hydrogen diffuse more widely and make the turbulence energy near the spark plug higher,but it will cause the local airflow velocity of the spark plug to become larger.Increasing the hydrogen injection advance angle will increase the hydrogen diffusion time,and the spark plug is locally enriched with higher concentration of hydrogen at different hydrogen injection moments.When hydrogen is injected early,the kinetic energy is completely dissipated,and the turbulent kinetic energy and flow field in the cylinder when the spark is formal are basically unchanged from that when hydrogen is not injected.The best effect of in-cylinder mixture stratification was achieved when the hydrogen injection pressure was 8MPa,the hydrogen injection moment was 655°CA,and the throttle opening was 35%.The experimental results show that hydrogen doping can increase the peak cylinder pressure and advance the peak phase in the rarefied combustion mode,and a small amount of hydrogen doping can offset the effect of combustion deterioration caused by rarefied combustion,which makes CA0-10,CA10-50 and CA10-90 decrease significantly,and the hydrogen doping ratio of 3.5%can reduce the engine COV_IMEP to less than 5%under various overfilling factors.The spark plug micro-hole hydrogen injection can significantly improve the flame propagation speed and help form a good fire nucleus under rarefied combustion conditions,which advances the rarefied combustion limit of the engine.The synergistic effect of hydrogen injection and rarefied combustion resulted in a significant reduction of nitrogen oxide（NOx）,carbon monoxide（CO）and hydrocarbon（HC）emissions.更多还原