Simulation Study On Effect Of Exhaust Gas Recirculation On Performance Of Hydrogen Gasoline Dual Fuel Engine

As a promising alternative fuel of future,hydrogen can solve the problem of fossil energy shortage and reduce the burden of our living environment by using exhaust gas recirculation which is a mature machine purification method.This thesis based upon the National Natural Science Foundation of China of “Study on Energy-saving Mechanism of HEV Equipped with Lean-burn Gasoline Engine with Hydrogen Direct Injection System and Local Hydrogenous Mixture”,and applied a new generation of CFD simulation software CONVERGE,a dual fuel engine with hydrogen and gasoline simulation platform was established.The main conclusions are given as follows:Gasoline enters the cylinder along the direction of the inlet flap while the intake valve is opening and forms the tumble flow.Before hydrogen spraying time,basically,gasoline distribute evenly in the combustion chamber;hydrogen is sprayed into the cylinder in compression stroke,hydrogen form the area of enrichment hydrogen near the spark plug along with the piston’s moving up,with the guidance of piston top wall;after the ignition of the engine,the overall pressure field distribution is even and the trend is increasing first and then decreasing.The high temperature zone in the cylinder is expanded from the position of the spark plug to the entire combustion chamber in combustion process,and the temperature in the cylinder is gradually reduced with the finish of combustion process.NOX in the cylinder is generated in the high temperature region and diffuses when the piston downs to the entire combustion chamber.NOX is generated and rapidly increases during the rapid combustion period.As the temperature in the cylinder decreases,the amount of NOX reduces slightly,and then stays the same.The NOX generation process is slightly delayed in the cylinder during the heating process.With the increase of hydrogen energy ratio,the peak value of the average pressure in the cylinder,the peak value of the average temperature in the cylinder and the peak value of the instantaneous heat release rate are increased.Hydrogen is sprayed into the cylinder in the compression stroke,which speeds up the flame spread time,and shorts the ignition delay time.What’s more,at same ignition time,with the increasing of the hydrogen energy ratio,the amount of hydrogen near the spark plug before the ignition time is growing,and the combustion performance in the cylinder is getting better,but the mass and the growth rate of the NOX and the mass of the CO is lager.There is a large amount of inert gas in the cylinder can prevent the combustion reaction from proceeding with the exhaust gas’ s adding.Simultaneously,the addition of exhaust gas hinders the flame spreading speed,reduces the rate of flame propagation and the equal capacity,which results deterioration of the combustion.The deterioration of combustion leads to the decrease of peak value of the average temperature and pressure.The peak value of the exothermic rate decreases with the increasing of EGR rate,and the position corresponding the maximum pressure and temperature backwards with the increasing of EGR rate.But the introduction of EGR can effectively reduce nitrogen oxide emissions of hydrogen gasoline dual fuel engine.With the increase of the ignition advance angle,the peak value of the average pressure in the cylinder and the peak value of the average temperature in the cylinder increase slightly,the ignition delay is shortened,the release of heat is more concentrated,the maximum of the heat release rate increases,which means combustion performance in the cylinder is improving.The mass of NOX and CO in the cylinder increases with the increases of the ignition advance angle,and the growth rate of CO is small while the growth rate of NOX is obvious.ERG combined with a reasonable ignition time can reduce the emissions,at the same time,the engine is in a more ideal work state.