Three Dimensional Transient Simulation Of Air-Fuel Mixture Formation In The Port Fuel Injected Gasoline Engine

The whole performance of the internal combustion engine should be improved because of the draining energy sources and rigorous law of conservancy of environment. New technologies as lean burn combustion, electronic control and exhaust after treatment are applied in the design of engines. Among these technologies electronic control is regarded as the core technology for its precise control on air intake system and fuel injection system.One of the essential theories of electronic control system of gasoline engine is the air fuel mixing mechanics inside the internal combustion engine. Three dimensional transient simulation can help to understand the mechanics well by simulating the thermodynamic and hydrodynamic process of the mixture process inside the engine.The thesis developed three dimensional transient numerical model of air fuel mixing process of port-fuel-injected gasoline engine. Based on the mechanics of the motion of wall film in the port and valve back of the PFI gasoline engine, wall film dynamic model and valve seat liquid expelling model are developed.The generation of the initial computational grids is also crucial for the three dimensional transient simulation. Block-structured grids of a four valve gasoline engine with a pentroof shaped combustion chamber and a flat head piston are constructed. Adjustment techniques for the moving grid are applied to make the computational grid fit the needs of calculation of a closed engine cycle calculation.In order to execute further analysis of in-cylinder air motion of tumble and swirl, calculations are taken on the in-cylinder air motion under transient pressure boundary condition from the beginning of the intake process to the ignition moment. The different influence of transient pressure boundary and steady pressure boundary on in-cylinder fluid field are analyzed.Simulations of mixture formation process are executed with closed-valve- injection mode under two kinds of working conditions, 3500r/min full load condition and 800r/min idle condition. Distributions are analyzed for both the gas phase fuel and liquid phase fuel. In order to compare the difference between open-valve-injection mode and closed-valve-injection mode, Calculations under two working conditions are taken again for the open-valve-injection mode. Comparisons are made on the distributions of the mixture under different fuel injection mode and different working conditions.Factorial experimental design is an extension to the application of simulation calculation. It provides a new way for the multi-parameter optimal design of gasoline engine with the powerful data analysis function of factorial design combined with precise prediction ability of simulation. The thesis presents the basic theories of simulation suited factorial design, and executes examples of valve timing optimization to illustrate the application of the new method.