| The challenges of emission reduction and energy conservation motivate studies for understanding of processes involved in engine operation. This work is focused on the modeling of multicomponent fuel vaporization processes, and a preliminary study on the modeling of micro-explosion and flash boiling is also presented.; A comprehensive model for droplet vaporization suitable for multidimensional computations was first developed. The novel aspect of this model is the ability to reproduce the effects of preferential vaporization and finite diffusion without resolving spatial governing equations within the droplet. The effects of internal circulation, surface regression, and high pressure are also considered. The model was validated through comparing with experimental data and detailed models, and good performance of the present model in computational accuracy and cost was demonstrated.; A vaporization model for films was then developed, which consists of a gas-phase submodel determining the vaporization rate and a liquid-phase submodel tracing the unsteady transport process within the film. This model brings a tremendous decrease in computational cost, while maintain a good accuracy. The model was verified through comparison with detailed numerical solutions and experimental data.; The two developed models were both used to study the air/fuel preparation process in port-injected and direct-injected spark-ignition engines. The importance of the vaporization model and fuel representation was demonstrated. For the port-injected spark-ignition engine, the effects of various engine-operating parameters on mixture preparation were analyzed.; Finally, a preliminary study on modeling micro-explosions and flash boiling was performed. These two phenomena were modeled using a bubble-droplet system. A description was formulated to predict bubble growth and was verified using experiment data. Both the breakup due to aerodynamical force and the breakup due to bubble expansion are considered. The formulated method combined with a bubble generation model was used to study effects of various parameters on the onset of micro-explosion for multicomponent droplets. The conclusions of this work agree with those in literature. A blob model was added to simulate the atomization of the spray under flash boiling conditions with a bubbly-flow in the injector nozzle, and the effect of superheat degree on spray atomization was captured. |
