【作者】 王晓瑜；

【导师】 陈国华；

【作者基本信息】 华中科技大学 ， 动力机械及工程， 2007， 博士

【摘要】 随着不可再生资源的日益枯竭以及环保法规的日益严格,对汽油机的综合性能提出了更高的要求。新技术如稀薄分层燃烧、电控技术、排放后处理技术等都先后得到运用。其中,电控技术因为涉及对进气系统、燃油喷射系统两大系统在内的精准控制,对燃烧质量和排放特性产生极为关键的影响,所以一直被看作是世界汽车领域难度最大、水平最高的核心技术。深透地理解汽油机气体流动机理、燃油喷射机理以及油气混合机理是掌握汽油机电控技术的重要保证,而数值模拟是实现这一过程最有效的工具。本文运用三维瞬态数值模拟方法模拟了进气道喷油式汽油机气道及缸内油气混合的气液两相热力学运动过程,分析了油气混合过程中气相运动特性以及液相燃油运动特性,为进一步深入探究油气混合机理提供了理论依据。本文针对进气道喷油式汽油机工作状态下存在附壁油膜的特点,发展了附壁油膜动力学运动模型,完善了包括燃油液滴、附壁油膜在内的液相燃油动力学运动模型,使气道-缸内油气混合过程的三维瞬态数值模型能够更为真实地反映出进气道喷油式汽油机的实际工作状况。网格处理是三维瞬态数值模拟的关键技术之一。文中以CV20汽油机为例,建立了包括气道、气门和气缸在内的具有屋脊型燃烧室、平顶活塞的4气门汽油机初始计算网格,并在计算过程中对缸内的计算网格实施了有效的动态调整,使得计算网格能够完成整个发动机三维工作过程计算的需要。汽油机的油气混合过程是包含气液两相的热力学流动过程,其中气相流动占主导地位,对油气混合质量起到关键的影响作用。本文计算了从进气初始时刻到点火时刻气道-缸内的气体流动过程。分析了缸内流场特性以及缸内气流涡旋运动的运动特点。在气体流动分析的基础上,进行了油气混合过程的三维瞬态数值模拟,分析比较了不同工况以及不同燃油喷射模式下液相燃油分布以及燃油蒸气浓度分布的特点。在数值模拟的基础上,对模拟的应用进行了推广,把析因试验设计强大的数据分析功能与数值模拟能够反映工作过程、预测工作性能的特点结合起来,针对CV20汽油机进气门接近关闭时刻存在气体从气缸向气道回流的现象,分析了配气相位对容积效率的影响,为参数优化设计提供了一条新思路。更多还原

【Abstract】 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.更多还原