PIV Measurement And Numerical Simulation Of Fuel High Pressure Injection Process Of Diesel Engine

In recent years, to reduce emissions of particles and NOx in diesel engines, the fuel injection pressure was generally becoming higher and higher and the process of fuel high- pressure injection became one of focuses in engine researches around the world. Through experiments, people have had a basic understanding of the fuel injection process, but most experiments were under middle or low injection pressures. Empirical equations and models available currently are all based on assumptions and hypotheses and the research of spray-wall impingement is just in its initial phase. So the objective of this thesis is to study the fuel high-pressure injection process of diesel engines with analytical, experimental and computational methods.Firstly, with advanced particle image velocimetry (PIV) and high resolution CCD digital camera, we observed the detailed structures of sprays. The spray experiments were carried out in many conditions, including different hole diameters, hole numbers, injection angles, atmosphere pressures and injection pressures. Also, the spray-wall impingement experiments were carried out with different impingement angles. We obtained and analyzed a large amount of valuable test data to validate the theoretical and computational results.Secondly, we employed the advanced 3D CFD software for engines, FIRE to simulate the spray process under different conditions, creating computational grids, setting boundary and initial conditions, coupling basic flowing equations with spray submodels. The computational results are close to the experimental ones.At last, comparing the experimental and computational results, we drew a conclusion that increasing injection pressure, smaller hole diameters, multi holes injection and reasonable spray-wall impingement are in favor of expediting the fuel-air mixture speed and enhancing the mixture quality to improve combustion processes and decrease waste emissions.