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

采用数值流体动力学方法对往复式内燃机的缸内流动和燃烧进行了描述，以预测燃烧室形状、点火、喷射和气体流动等参数的影响。特别注意选择简单但适当的湍流、喷雾和化学反应子模型。由此开发的仿真程序被应用于各种问题。得到了以下结果：为了实现任意几何形状燃烧室的计算机模拟，提出了一种新的算法，该算法仅对靠近壁面边界的计算单元使用有限元概念，其余网格单元依赖于正交坐标系中的普通有限差分格式。将该方法应用于柴油机重入燃烧室的流动和燃烧分析。用激光同差法直接测量了火花点火发动机火焰锋面附近的湍流。结果表明，在温度升高的情况下，由于层压化，在火焰区只产生少量湍流。在计算机仿真的基础上，对深碗式直喷柴油机顶间隙的影响进行了评价。在较小的间隙下，未燃尽的混合气从燃烧室流出进入间隙空间，在燃烧的早期阶段受到抑制，因此未燃尽的原料燃料比在较大的间隙下少。对柴油机燃烧室壁面的热流密度进行了预测。假设表面有一层薄沉积层，预测的热流密度与由努塞尔数和雷诺数之间的经验关联得到的热流密度很好地吻合。

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.