| Faced with environmental pollution and depletion of energy,more and more people study the alternative fuels in the engine.Hydrogen has many advantages such as large reserves,clean burning and high thermal efficiency.Hydrogen has a widely used on fuel cells and internal combustion engines,which is known as the final energy of the 21 st century.But it always has abnormal combustion such as pre-ignition and tempering when hydrogen used in the engine.The causes of abnormal combustion always occurs during the formation of the mixture.So how to improve the quality of the mixture is very important.This study is based on a PFI engine to establish a complete three-dimensional model,and simulate three kinds of conditions used AVL-fire when idle speed(1000r/min)and the maximum torque speed(4500r/min)and the maximum power speed(6000r/min).This paper studies the effect of injection area and injection pressure on mixture and combustion characteristics.The study gets the variation of mixture velocity field and concentration field and turbulent kinetic energy by simulating.And on this basis,the study sum up the impact of these two parameters on the pre-ignition and tempering.The results showed that:3mm orifice diameter is too small on high speed,and the intake ratio is too small at the end of the cylinder.5mm orifice diameter can significantly improve the mixture ratio.Greater injection pressure favors the formation of a uniform mixture which make the burn more quickly.0.2MPa injection pressure need more than 5mm in diameter to match,but greater injection area causes emissions of NO increased.Reducing the injection area and ejection pressure increase the amount of hydrogen such as gas at the inlet and flowing back from the cylinder,which would cause the pre-ignition and tempering.Account,choosing the 5mm ejection orifice and 0.3MPa hydrogen pressure can be made in a smaller probability of abnormal combustion,and meet the requirements of power,economy and emissions. |
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