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缸内流动和燃烧过程，预测了燃烧室形状、点火、喷射和气体流动等参数对缸内流动和燃烧的影响。特别注意选择简单但足够的湍流，喷雾和化学反应的子模型。因此，开发的模拟程序被应用到各种问题。得到以下结果.为了对任意几何形状的燃烧室进行计算机模拟，提出了一种新的算法，该算法只对壁面边界附近的计算单元采用有限元概念，其余的网格单元采用正交坐标系中的有限差分格式。将该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缘附近的湍流度。计算结果表明，由于温度升高，火焰区产生的湍流很小，这是由于火焰层化的结果.在计算机模拟的基础上，对深凹缸内直喷柴油机顶部间隙的影响进行了评价。在较小的间隙处，在燃烧的早期阶段抑制了混合物从碗状物到间隙空间中的未燃烧的流出，并且因此未燃烧的原燃料比在较大间隙处少。预测了柴油机燃烧室壁面的热流密度。在假定表面有薄存款层的情况下，预测的热流密度与Nusselt数和Reynolds数之间的经验关联式吻合得很好。

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.