Numerical Study Of Wall-film Evaporation In The Internal Combustion Engine

The spray and combustion is the most important work process in the internal combustion engine(ICE), the quality of spray and combustion process affects the thermal efficiency and emissions of ICE directly. As an inevitable phenomenon, spray impingement and wall-film formation have a great influence on the performance and emissions of ICE. The wall-film formation has a direct impact on the gas/oil mixture formation and studies have shown that the appearance of wall-film is an important reason for unburned hydrocarbon emissions.On the basis of the bubble dynamics, the bubble dynamics and heat and mass transfer characteristics in the two-phase flow in the wall-film are studied firstly in this article. Numerical methods are used to analysis the wall-film evaporation mechanisms refer to the practice operating conditions of ICE.The Volume of Fluid method(VOF) coupled with local adaptive mesh method are used to catch the interface movement of two-phase flow. A numerical model which established by the application of User-defined Function(UDF) is used to simulate the bubble growth process in the film. Through the simulation of the process of bubble nucleation and evolution, the factors that affect the film evaporation are analyzed.Then, according to the experiment conditions and data in the references, bubble growth in a single artificial cavity is simulated by the model established.Through the data comparison such as time and bubble size of numerical and experiment referenced, the model shows a good adaptability and feasibility. The influence of the changes of physical parameters that affect by the variations of temperature and pressure are taken into account. Simulations are conducted to analysis the main influences of the wall temperature, film thickness, enviroment conditions on wall-film evaporation combined with surface tension, gravity and viscosity use the n-heptane as working fluid and reference to the cylinder actual working conditions of ICE.Finally, a micron-scale simuation is conducted by reference the actual wall-film thickness under the practice working conditions of ICE. The phenomenon and mechanisms of boiling phase change process in current scale are analyzed.