Study On Effect Of Secondary Hydrogen Injection On Combustion And Emission Of Ethanol Ignition Engine

In recent years,the energy crisis and environmental pollution caused by the continuous increase in car ownership need to be solved urgently.As a clean and renewable energy,ethanol has become one of the most research-worthy alternative fuels for automobiles due to its high oxygen content and similar physical and chemical properties to gasoline.Aiming at the engine’s need for optimizing combustion and emission performance,this paper uses the ethanol port injection/hydrogen in-cylinder direct injection compound injection technology to explore the method of optimizing the stratified state of the in-cylinder mixture.In turn,a larger proportion of hydrogen can be blended to help formulate richer hydrogen injection strategies to further improve the combustion and emission performance of the engine.To this end,this article uses a compound injection mode engine,where ethanol is injected into the intake port,and hydrogen is directly injected into the cylinder.By changing parameters such as excess air ratio,hydrogen mixing ratio,hydrogen injection times,hydrogen injection ratio and hydrogen injection pressure,the performance changes of ethanol ignition engines under different hydrogen injection strategies are analyzed.The main research work and conclusions of this paper are summarized as follows:(1)The effect of hydrogen mixing on the combustion and emission characteristics of ethanol ignition engines is explored.The addition of hydrogen effectively compensates for problems such as the long combustion cycle of ethanol ignition engines,thereby improving the power of the engine.This improvement effect is more obvious under lean burn conditions.When the hydrogen mixing ratio is 20%and the excess air coefficient is 0.9,1.0,1.1,1.2,1.3,the peak cylinder pressure increases are 11.83%,13.96%,15.28%,20.88%,32.49%,respectively.Under a variety of excess space factors,hydrogen doping can reduce HC and CO emissions.However,due to the improvement effect of hydrogen on combustion,the maximum temperature in the cylinder rises,and the time of the temperature peak appears earlier,so NO_Xemissions have increased.(2)The influence of the secondary injection of hydrogen on the combustion state in the compound injection cylinder is explored.The secondary injection of hydrogen can achieve the ideal mixture stratification state where the mixture is evenly distributed in the cylinder,and hydrogen is enriched near the spark plug.While helping to form a stable flame core,the isovolume of the combustion process is improved,thereby improving engine power.Compared with a single injection of hydrogen,the emissions of HC and CO are significantly reduced.(3)The influence of the ratio of secondary injection of hydrogen and time on engine combustion and emission performance was explored.With the increase in the proportion of the second injection of hydrogen,the peak cylinder pressure and the average indicated pressure showed a trend of first increasing and then decreasing,and the cyclic variation showed a trend of first decreasing and then increasing.Each secondary injection ratio corresponds to an optimal secondary injection timing to maximize engine power,and as the secondary injection ratio increases,the optimal secondary injection timing is advanced.The reasonable coordination of the ratio of secondary hydrogen injection and the timing of secondary hydrogen injection can effectively reduce CO and HC emissions.However,due to the improvement of sufficient combustion,NO_Xemissions will increase to a certain extent.(4)The influence of hydrogen injection pressure on combustion and emissions under lean burn conditions is explored.Too large or too small hydrogen injection pressure will lead to a decrease in the degree of hydrogen enrichment near the spark plug.There is an optimal hydrogen injection pressure to form an ideal mixed gas stratification state in the cylinder.At various times or proportions of secondary hydrogen injection,proper hydrogen injection pressure can also significantly reduce HC emissions.However,due to the high oxygen concentration under lean burn conditions,the impact on CO is not obvious.The ideal distribution of hydrogen significantly improves combustion,resulting in an increase in NO_X emissions.