A Study on Combustion in Reciprocating Internal Combustion Engines by Computational Fluid Dynamic Approach

用数值流体动力学方法描述了往复式内燃机的缸内流动和燃烧，以预测燃烧室形状、点火、喷射和气体流动等各种参数的影响。特别注意为湍流、喷雾和化学反应选择简单但适当的子模型。所开发的模拟程序被应用于各种问题。取得了以下研究成果：1.为了实现对任意几何形状燃烧室的计算机模拟，提出了一种新的算法，该算法只对邻近壁面边界的计算单元使用有限元概念，其余的网格单元依赖于正交坐标系中的普通有限差分格式。将所提出的方法应用于柴油机缩口燃烧室内的流动和燃烧研究。用激光零差法直接测量了火花点火发动机火焰前锋区附近的湍流。计算结果表明，由于高温下的层化作用，火焰区只有少量的湍流产生。在计算机模拟的基础上，对深碗式直喷式柴油机顶隙的影响进行了评估。在较小的间隙，在燃烧的早期阶段，未燃烧的混合物从碗中流出到间隙空间被抑制，因此，未燃烧的原始燃料比在较大的间隙下要少。预测了柴油机燃烧室壁面的热流密度。假设表面存在薄层沉积层，预测的热流密度与Nusselt数和Reynolds数之间的经验关联式吻合较好。

The in-cylinder flows and combustion in reciprocating internal combustion engines were described by a numerical fluid dynamic method, to enable prediction of effects of various parameters such as combustion-chamber shape, ignition, injection, and gas flows. A special caution was paid to select simple but adequate submodels for turbulence, spray, and chemical reactions. The simulation programs thus developed was applied to various problems. The following results were obtained.1. To allow the computer simulation at combustion chambers with arbitrary geometries, a new algorithm was proposed such that used finite element concept only for computational cells adjacent to wall boundaries, the remaining grid cells relying on an ordinary finite difference scheme in an orthogonal coordinate system. The proposed method was applied to elucidate flows and combustion in a reentrant chamber of a diesel engine.2. Turbulence near the region of flame front in a spark-ignition engine was directly measured by a laser homodyne method. The obtained results show that there is only a little production of turbulence in the flame zone, because of the laminarization at increased temperature.3. The effect of the top clearance in a deep-bowl direct-injection diesel engine was assessed based on the computer simulation. At a smaller clearance, unburnt outflow of the mixture from the bowl into the clearance space is suppressed in earlier stages of burning, and as a result unburnt raw fuel is less than at bigger clearance.4. Heat flux through the combustion-chamber walls of diesel engines was predicted. The predicted heat flux was in good agreement with that by the empirical correlations between the Nusselt and Reynolds numbers, once a thin deposit layer on the surface was assumed.