Simulation Of Variable Valve Timing On Combustion And Emission Characteristics Of Hydrogen Fueled Natural Gas HCCI Engine

In the face of the contradiction between the supply and demand of energy fuels and the pollution of the ecological environment caused by automotive exhaust emissions,scholars pay more attention to the research of clean alternative fuels and the development of new combustion modes for automotive engines.Hydrogen-doped natural gas has better combustion characteristics.Homogeneous Compression ignition(HCCI)engine has both high thermal efficiency of compression ignition diesel engine and homogeneous mixing characteristics of ignition gasoline engine.However,the addition of hydrogen into natural gas will increase the emission of NOx from HCCI engine,and the addition of variable valve timing can reduce the emission of NOx from HCCI engine.In this paper,the effect of variable valve timing on combustion and emission characteristics of hydrogen-doped natural gas homogeneous compression ignition engine is studied by simulation,which has theoretical significance for improving combustion characteristics and reducing pollutant emissions of hydrogen-doped natural gas homogeneous compression ignition engine.Firstly,a model of electronically controlled hydraulic variable valve timing phase is established in GT-Power.The zero-dimensional model of hydrogen-doped natural gas homogeneous compression ignition engine is established in CHEMKIN software,and the turbulent sub-model and Woschni heat transfer sub-model are added.The structural parameters of ZS195 non-pressurized water-cooled direct injection natural gas engine are taken as the initial parameters.The physical properties of hydrogen-doped natural gas(HCNG)blends are also calculated.The mechanism of GRI(Gas Research Institute)Mech 3.0 chemical reaction was introduced into homogeneous zero-dimensional model for pretreatment.The two software were coupled to simulate the combustion process of hydrogen-doped natural gas homogeneous compression ignition engine,which was validated with reference values.Then,different valve allocation schemes are studied.The effects of EVC and IVO on In-Cylinder temperature,in-cylinder pressure,in-cylinder pressure rise rate and heat release rate of hydrogen-doped natural gas homogeneous compression ignition engine are changed.Finally,the effects of different gas distribution schemes on NOx emission from a hydrogen-doped natural gas homogeneous compression ignition engine are studied.The results show that changing the valve timing has dual effects on improving the combustion characteristics of hydrogen-doped natural gas and reducing NOx.It can not only heat the working fluid,increase the intake temperature,increase the heat capacity of the gas in the cylinder,slow down the chemical reaction rate,prolong the combustion duration and reduce the maximum temperature in the cylinder,but also reduce the pressure rise rate in the cylinder,and help to reduce the emission of NOx.Therefore,the application of variable valve timing technology in hydrogen-doped natural gas homogeneous compression ignition engine can improve compression ignition and reduce pollution emissions,which has good research and application prospects.