Research And Analysis On Combustion Process Of A Diesel Engine Under High Altitude Condition

There are vast territories of plateau in our country. Because of the need of engineeringconstruction and transportation etc., diesel engine is widely used as power source of variouskinds of equipment with its high thermal efficiency, large power range as well as goodmobility. For the diesel engine working in plateau area, the reduction of atmosphericpressure and poor environmental conditions etc. lead to a series of serious problemsincluding incomplete combustion, decrease of power, deterioration of emissions,turbocharger turbine speeding and the drop of efficiency. Therefore, having a research andanalysis on combustion process of diesel engine under the condition of the plateau hasimportant theoretical and practical significance in optimization of combustion and increaseof power recovery ability.With the method of multi-dimensional numerical simulation and STAR-CD, a kind ofCFD software of three-dimensional numerical simulation, the combustion processes of oneturbocharged diesel engine have been simulated and calculated under the condition ofplateau. The following several aspects have been completed mainly.Firstly, the three-dimensional geometric model of the diesel engine cylinder wasestablished by using UG. After the surface grids having been repaired and discretized by thePro-surface module of software STAR-CD, the model was imported into the ES-ICEmodule to have the dynamic grids divided and cut. And then the simulation calculationmodel of diesel engine was established after setting the initial conditions, boundaryconditions and the parameters of each model.Secondly, the combustion processes of diesel engine were simulated and calculatedunder the condition of the plain, the simulation results were in good agreement with thoseobtained with the test data, which indicated that the calculation model was accurate andreliable. And then the combustion processes of diesel engine under the condition of theplateau were simulated with this model. With the validation of plateau test data, thesimulation results were also reasonable and reliable.Thirdly, combustion processes under three different pressure ratios were simulated andcalculated at an altitude of3500m. And we got the distribution of combustible mixture incylinder, the size of the pressure and temperature and the emissions generation. Theinfluence of inlet pressure on diesel engine combustion process was discussed from the perspective of combustion mechanism.Finally, combustion processes under different fuel injection advance angles and loadswere simulated and calculated at an altitude of4550m. We got the effects of different fuelinjection advance angles and loads on the distribution of mixture and temperature, thepressure and emissions generation. And we optimized the fuel injection advance angles. Theresults show that as the angle increases, the quantity of formation of combustible mixtureincreases, the combustion process occurs much earlier, pressure and temperature in cylinderrise, NOXgeneration increases but the soot generation shows a trend of increase after thefirst reduce. Comprehensive consideration, this paper argues that17°CA is the suitable fuelinjection advance angle for this diesel engine to work under the condition of the altitude. Asthe load becomes larger, the quantity of fuel injection rises, the ignition delay periodshortens, the ratio of diffusion combustion increases, the pressure and temperature incylinder rise, and so does the NOXgeneration and soot generation.In this paper, we research and analyze the combustion process of diesel engine underthe condition of the plateau from the perspective of combustion mechanism, which providesreference on research of combustion optimization and power recovery etc.