Effect Of Spark Plug Micro-hole Hydrogen Injection On Hydrogen/Gasoline Engine Performance

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.