Research On GDI In-cylinder Mixture Formation Using Planar Laser-induced Fluorescence

Optical diagnostics such as Laser-induced Fluorescence (PLIF) is now an important role in vehicle engine research. At present, the backwardness of domestic engine optical diagnostics researches compared to foreign advanced level is obvious. It is necessary to build advanced optical diagnostics systems and carry on researches in this field. As the development of gasoline direct injection (GDI) engine goes on, greater attention has been paid to in-cylinder mixture formation, especially to those researches basing on multi-component fuel. Improving the ability of PLIF method and taking a deeper step into the research of GDI in-cylinder mixture formation will be significant. This research worked in the field of GDI in-cylinder PLIF diagnostics.In this work, an internal-combustion-engine based laser diagnostic system, including an optical engine which can works in GDI mode, a combustion vessel, laser sheet optics, synchronization modules and fueling systems, has been built to realize PLIF researches on spray and in-cylinder mixture distribution. Calibration and correction methods were developed basing on the system, with some improvements in the calculation.A method of designing a multi-component fuel for planar laser-induced fluorescence (PLIF) experiments was developed based on thermal gravity (TG) analysis and vapor-liquid equilibrium (VLE) calculation. The goal is to create a fuel whose volatility is similar to real gasoline and that has good coevaporation ratios (near 1.0) with tracers. Acetone, toluene, and trimethylbenzene were chosen as the tracers for light, medium, and heavy fractions, and a five-component test fuel was developed. This test fuel was used to study the influence of components and temperature on coevaporation ratios. The saturate vapor pressure and the activity coefficient of the tracer and components in a fraction group affect the coevaporation optimization substantially, indicating that these values should be a primary consideration in tracer selection.PLIF was used to study different strategies and cycle-to-cycle variation in GDI in-cylinder mixture distribution. The five-component fuel was applied to an in-cylinder gasoline direct injection fuel mixture distribution measurement using PLIF. The differences between the light, medium, and heavy fraction groups were studied under different strategies. Cycle-to-cycle variation analysis was also applied.Finally, simulation works on mixture distribution were carried out basing on KIVA-3V. The best ignition timing and available ignition ranges under different rotation speeds, air-fuel ratios, injection times and fueling percentages of second injection are analyzed.