The Study Of The Intake And Combustion Process In Dual-injection Engine

With the global energy crisis and the increase of oil consumption in China,the hot issue of engines is to suppress knock and further improve thermal efficiency in small-scale intensified engines.A new type of fuel injection and combustion system has been proposed,the fuel characteristics of various fuels have been utilized,the detonation suppression effect has been achieved,and the purpose of improving the compression ratio and thermal efficiency of the engine has been realized in the dual injection system of the engine.On the platform of dual-injection engine,two kinds of dual-injection methods have been proposed: ethanol in-cylinder direct injection and gasoline intake port injection(EDI+GPI),gasoline in-cylinder direct injection and water intake port injection(GDI+WPI),aiming at the advantages of flexible choice of fuel types and separate control of fuel injection quantity and injection time.In this thesis,dual-injection engine platform and three-dimensional simulation software are used to research the combustion process and detonation suppression mechanism of two dual-injection modes.In the EDI + GPI dual fuel compound injection mode,the effects of EDI injection time,ignition time and intake temperature on the formation,combustion and emission of engine mixtures were studied by numerical simulation,and the contribution of ethanol fuel characteristics to knocking suppression was analyzed.The simulation results show that by changing the EDI injection time,the evaporation atomization degree of ethanol is affected,and the mixture equivalent ratio distribution of different degrees is formed in the cylinder.When the injection time is 250 °CA BTDC,the mixture in the cylinder is even and produces the best combustion phase.When the maximum detonation limit spark is advanced,the influence of ethanol vaporization latent heat is offset by intake heating,and the contribution rates of ethanol high vaporization latent heat and high flame propagation speed to knock suppression are respectively 23.5 % and 76.5 %.In GDI+WPI dual injection mode,the effects of engine spray vaporization,mixture formation,and engine performance and emissions was investigated at different speeds and at different spray rates.The results show that: the wet wall amount of water was increased because of increasing the amount of water spraying,and the mass of water vapor entering the cylinder increases but the mass proportion decreases.The deterioration of gasoline evaporation was caused by water spraying,and the formation of the in-cylinder mixture was affected.The specific fuel consumption was reduced and the thermal efficiency was increased at the injection water and ignition advance angle,but the emission was not significantly reduced.