Experimental And Simulation Study On Soot Emissionof Direct & Port Injection Engine

GDI engine has manyadvantages,such as less HC emission at cold start,high fuel economy,fast transient response and strong anti knock ability,so it’s one of the important development directions of vehicle engines.Because GDI engine inject fuel into cylinder in the charging stage,the formation time of the mixture is shorten,and the fuel impinged into the wall,resulting in oil dilution,fuel economy degradation and particle emissions.To reduce the particulate emissions in GDI engine,the spray characteristics and soot emission characteristics of dual injection engine were studied by experiments and simulations,and the influences of injection strategy on the mixture in cylinder and the wall film and the formation of soot were studied.Oncombined injectionstrategy ofgasoline direct injection(GDI)and gasoline port injection(GPI)combustion mode,the spray proportion has little influence on the average temperature and the mean pressure,but its influences on final soot mass fraction and particle number concentration is obvious.The particle number concentration and soot mass fraction decreased with the decrease of GDI injection proportion.Compared with the 100%GDI injection proportion,the wall film mass of85%GDI injection proportion decreased by 18.5%,and 65%GDI injection proportion is reduced by 38.9%.And the uniformity of the gas mixture in the cylinder at the ignition time increasedwith the reducing of GDI proportion.At 85%GDI injection proportion,the particle number concentration and soot mass fraction is reduced at first and then increased with GDI injection timing delay.In most cases,ethanol and gasoline dual fuel injection mode can reduce particulate emissions.But under the condition of early injection timing,the particle emissions increased.Simulation results show that,when the injection time is earlier,the injection strategy of dual fuel dual injection mode has a great influence on the soot mass fraction.The peak soot mass fraction of dual fuel injection mode is higher than pure gasoline injection mode,and the peak of soot mass fraction on EDI+GPI injection strategy is highest.That is because the low heat value(LHV)of ethanol is lower,the fuel it need is more,longer duration of injection process,fuel more likely against the wall,fuel wall film is thicker,moreover,the evaporatationrate of ethanol is slower,and the inhomogeneity of the mixture in the cylinder increases,resulting in the increase of soot mass fraction.Due to the tumble in the cylinder,there is a concentrated gas mixture in the intake side,which makes the soot concentrate on the side of the inlet valve.