Study On Two Stage Fuel Injection And EGR Coupling Control Of Diesel Low Temperature Combustion

As a new combustion method of high efficiency and low emission,low temperature combustion is highly studied worldwide in recent years.Diesel low temperature combustions faced two major problem as follows.Firstly,the mixture of diesel and air is hard to form because of the physical characteristics of diesel.Secondly,there is hardly direct method to control the combustion phase of low temperature combustion.In this thesis,a two stage injection strategy including one main injection and one trigger injection is applied.The fuel of main injection(about 85% of fuel quantity per cycle)is injected in the cylinder early in the compression stoke to form the mixture of diesel and air.The trigger injection is executed just before the top dead center.It is an ignition promoter.With the help of EGR(Exhaust Gas Recirculation),a stable diesel low temperature combustion is realized by two stage injection strategy.As a result of experiment,the trigger injection could improve the IMEP of combustion.The ratio between two injection stage and the timing of the main injection was studied by experiment.The result shows that there is a best injection timing of main injection in different engine speeds.Once the speed is higher,the injection timing need to be earlier to get the best IMEP and NOx.Based on the hotcold EGR system,the effects of EGR ratio and EGR temperature are studied.And the coupling effect of EGR ratio and temperature is studied at load boundary.The result shows that the load boundary could be expanded by controlling the EGR ratio and temperature synergistically.Based on the experimental study,the EGR control strategy under all operation conditions is provided.