The Research Of Dynamic Characteristics Of Mixture In Cylinder And Its Impact On The Process Of Combustion Of DI Diesel Engine

With the improvement of the living standards, the car has become an indispensableproduct in people’s life. While with the convenience the car bringing to us, the exhaustemissions of the car have also caused a great threat to our environment. The engine is thesource of the exhaust emissions. Even though diesel engine has been widely used in cars inrecent years because of its power, economy, durability and low emissions of greenhouse gasCO2, when facing the increasingly serious global energy crisis and environmental pollution,the world has developed many restrictive regulations on its development. All world dieselengine researchers proposed many remedies in order to match the regulations and ultimatelythese methods are to improve the combustion of the engine, improve the thermal efficiencyand reduce harmful emissions. The quality of the combustion of the engine is essentiallydetermined by the dynamic characteristic of the mixture in cylinder. So it is necessary toresearch the dynamic characteristic of the mixture in cylinder and its impact on the process ofcombustion of DI diesel engine. In this paper, with the numerical simulation, the dynamiccharacteristic of the mixture in cylinder and its impact on the process of combustion of ahigh-pressure common-rail, turbocharged and inter-cool DI diesel engine has been studiedqualitatively and quantitatively.First of all, the geometric model and mesh model of the diesel combustion flow fieldregions have been established respectively by using Pro/E and FIRE. Then for the originalmachine maximum torque speed1300r/min with full-load, the initial boundary conditions andmathematical models have been set and selected. After the comparison of the calculation andexperimental pressure curve, the selecting of the model has been proved exactly.Secondly, the study of the dynamic characteristic of the mixture in cylinder and itsimpact on the process of combustion has been done by changing the structural parameters ofthe combustion chamber such as central boss and D/H. The study has found that, for differentcombustion chamber(central boss), the combustion efficiency of combustion chamberⅠishigher than combustion chamber Ⅱ and the combustion effect of combustion chamberA(=3.09) is better than combustion chamber B(=2.878).Thirdly, the study of the dynamic characteristic of the mixture in cylinder and its impacton the process of combustion has been done by changing the injection position, the spray railpressure and injection time. The study has found that the combustion of the injection positionof2.7mm is best. With higher spray rail pressure, the mixture in cylinder becomes moreuniform and combustion efficiency is higher, but the amount of NOxwill increase. Theselection of injection time should be reasonable, while with too early injection time, thepressure in cylinder will exceed the maximum explosion pressure of the simulated conditionsand the amount of NOxis high, with too late injection time, the power of the engine will be low and the temperature of the exhaust gas is high. Furthermore, with the decrease of thepercent of oxygen in intake air, the pressure and temperature in cylinder at TDC ofcompression stroke are lower and the ignition is delayed and the rate of combustion is slowerand the amount of NOxand Soot is decreased simultaneously.Finally, the skill of virtual sampling points in cylinder has been used in order to study theequivalence ratio distribution in cylinder quantitatively. The study has found that the mixturein cylinder has both squish and swirl characteristics and the mixture concentration of thecombustion chamber wall is thicker and the fuel injected in the combustion chamber willdeflection in the circumferential direction and some NOxoccurs due to the mechanism ofprompt NO.