Study On Combustion And Emission The Performance Of Hydrogen Direct-injection Engine

Hydrogen engine has the significant advantages of zero carbon emission,high efficiency and low cost.It has become one of the important directions of the transformation of traditional fuel engine.Direct-injection hydrogen engine can effectively improve the charge coefficient of the engine and simultaneously avoid the abnormal combustion such as back fire and pre-ignition.The research on the hydrogen internal combustion engine is becoming a hot spot at present.In this paper,the 3D numerical simulation of a turbocharged direct-injection hydrogen engine is carried out by using CONVERGE to study the effects of different parameters on the combustion and NO_x emission performance of the engine.Firstly,the effects of different equivalence ratio and ignition time on combustion and NO_x emission performance of the direct injection hydrogen engine are studied.We found that the formation time of flame center and the length of ignition delay period are closely related to the mixture concentration near the spark plug.After reducing the equivalence ratio or delaying the ignition time,the flame development speed of hydrogen engine becomes slower and the combustion duration becomes longer.Reducing the equivalence ratio or delaying the ignition angle can reduce the combustion temperature in the cylinder of hydrogen engine,and then reduce the generation of NO_x.Secondly,in order to further improve the thermal efficiency of hydrogen engine,the variation laws of combustion and NO_x emission of hydrogen engine at the best ignition time under different inlet pressure and equivalence ratio were studied.The results show that with the increase of inlet pressure,the back pressure of hydrogen injection increases,the penetration distance and diffusion area of hydrogen jet in the cylinder decrease,and the mixture distribution in the cylinder is more concentrated,so as to achieve a better stratification effect.After the intake pressure increases from 0.14MPa to 0.30 MPa,the indicated thermal efficiency of the engine increases from 39.2%to 40.5%,an increase of 1.3%is obtained.Increasing the intake pressure leads to the NO_x emission deterioration of the hydrogen engine.Appropriately reducing the equivalence ratio makes the engine achieve higher indicated thermal efficiency and improve the emission of NO_x.Finally,the effects of different compression ratios on combustion and NO_xemission performance of the direct injection hydrogen engine are studied.The results show that with the increase of compression ratio,the peak value of cylinder pressure and heat release rate increases and the peak value appears in advance.The ignition delay period and combustion duration are shortened,and CA50 is advanced accordingly.When the compression ratio increases from 9.8 to 12,the indicated thermal efficiency of the engine increases from 37.8%to 40.7%,but the optimal ignition time should be postponed to prevent detonation.With the increase of compression ratio,the generation of NO_x in the engine increases.Using direct water injection in cylinder can reduce the knock intensity and NO_x emission of hydrogen internal combustion engine under the high compression ratio.