| The growth of vehicle ownership brings our country a series of problems to be solved,so researchers have been unremitting efforts to seek the clean alternative fuel of internal combustion engine.Hydrogen combustion theoretically produces only water.So hydrogen is an ideal clean energy.Besides hydrogen gas with high concentration of low calorific value,burning range,low ignition energy needed for comparison,flame propagation speed and characteristics of diffusion is faster in the air,very suitable for as the alternative fuel cars.Under low load,the thin mixture in the cylinder of hydrogen internal combustion engine makes the combustion insufficient,and the temperature and pressure in the cylinder are low,resulting in low thermal efficiency,poor dynamic performance and other problems.When the load is very low,hydrogen internal combustion engine will have large cycle changes.Hydrogen internal combustion will generate a large amount of NO_X emission under medium and high load,which becomes the main technical obstacle of practical application of internal combustion engine.Improving the working state of hydrogen internal combustion engine under low load,improving the efficiency of internal combustion engine,and ensuring the dynamic performance of the internal combustion engine at medium and high load to reduce emissions play an important role in the practical application of hydrogen internal combustion engine.Therefore,the research on the in-cylinder combustion performance of hydrogen internal combustion engine is of great significance to the application and development of hydrogen internal combustion engine.In this paper,the effects of different combustion modes on the combustion performance of hydrogen internal combustion engines are studied by using the simulation method of three-dimensional grid-coupled chemical reaction mechanism.The H-O-N chemical reaction mechanism,which has been verified,including the 19-step reversible elemental reaction and the 67-step reversible elemental reaction,was selected.To establish 3-D entity model hydrogen internal combustion engine,the selection CONVERGE to generate 3-D computing grid,select a reasonable mathematical model and turbulent model,ignition and combustion model and determine the model parameters according to the results of the calibration.The model is verified and calibrated based on the experimental data so as to ensure the accuracy and reliability of the simulation calculation.Based on the calibrated simulation model,the effects of lean combustion,equivalent combustion(with medium-cooled EGR dilution)and enriched combustion(with medium-cooled EGR dilution)modes on the combustion characteristics of low,medium and high-load hydrogen internal combustion engines in cylinders were studied,and the emission characteristics of hydrogen internal combustion engines in different modes were analyzed.The results show that under low load,equivalent combustion and enriched combustion can accelerate the combustion in the cylinder,shorten the combustion delay period and combustion duration,accelerate the heat release rate,improve the temperature and pressure in the cylinder,and contribute to the improvement of the power performance,and its NO_X emission is at a very low level.In the middle load,equivalent combustion reduces combustion characteristics of hydrogen internal combustion engine,but significantly reduces NO_X emission.The pressure and temperature of excessive hydrogen combustion cylinder increase gradually with the increase of excess hydrogen,and the combustion is accelerated.When the load is high,the temperature and pressure in the equivalent combustion cylinder are lower than the lean combustion,and the dynamic performance is reduced,but the NO_X emission is greatly reduced.Compared with equivalent combustion,small enriched combustion has little influence on in-cylinder combustion,with small changes in temperature and pressure,and further reduces NO_X emission,leaving NO_X at a very low level. |
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