抄録
The numerical simulation of Internal Combustion Engine (ICE) flows is a powerful tool which is widely applied for the engine design process. In particular, CFD simulation is useful at a preliminary stage in order to better understand how geometrical and operating engine variables can affect mixture flow features and, in turn, the combustion process. In a previous work, a comparison was carried out among three different versions of the k-e turbulence model (Standard and RNG two-equation models, Two-Scale four-equation model) through their application to the turbulence and mean-flow field prediction within the open chamber of a model engine in the absence of swirl. The RNG model, including a modified approach with respect to the Logarithmic Wall-Function boundary conditions, was shown to yield, on the average, a better agreement with experimental results than the other two models. The present paper is concerned with mean-flow and turbulence simulation in a motored model engine having an axisymmetric combustion chamber, one centrally located valve and each of a flat piston and cylindrical bowl-in-piston arrangements. Numerical results obtained with the RNG k-e model are first compared with available experimental data obtained in the presence of swirl. Subsequently, the main flow features predicted for the swirling flow configuration are compared to those obtained in the absence of swirl. Finally, the turbulence model capabilities in capturing in-cylinder flow features is assessed, by analyzing its prediction of the flow parameter variation when geometrical and operating engine variables are modified. The calculations are performed using a non-commercial CFD code that was originally developed in and updated for the present investigation. A finite-volume conservative implicit method is employed for the discretization of the partial differential equations modeling the in-cylinder turbulent flow. The resultant algebraic equations are linearized first and then sequentially solved by an iterative procedure based on a pressure equation, derived from the continuity equation, and on under-relaxation practices in order to improve stability.
