Implementation of a Single Zone k-ε Turbulence Model in a Multi Zone Combustion Model

Research into internal combustion engines requires the development of engine simulation models which should ensure acceptable results of engine performances over a wide range of engine speeds and loads. Due to high costs of experiments and a rapid increase in the computer power, researches all over the world devote great effort to the development and improvement of simulation models. Well-known multi-dimensional simulation models (CFD models) of the engine cycle are the most demanding models in terms of computational resources. On the other hand, there are multi-zone models that are very robust and that are able to capture a certain in-cylinder property during the engine operating cycle. It is known that turbulence effects inside engine cylinder play an important role in the combustion process. In order to properly predict combustion process, characteristics of the turbulent flow field should also be accurately defined. The single-zone k-ε turbulence model for 0D applications proposed in the literature is based on a simplified approach. A complete derivation of 0D differential equations from multi-dimensional equations is presented. The defined single-zone k-ε turbulence model was implemented in the cycle-simulation software. The purpose of this implementation is to obtain results of the turbulent kinetic energy in the 0D model that correlate with the results of the 3D-CFD simulations. This turbulence analysis was concentrated only on the high pressure cycle (compression and expansion). By means of a specific modification of the differential equations the implemented single-zone turbulence model is able to capture the evolution of the turbulent kinetic energy very close to the 3D-CFD results. The calculation of the combustion process was carried out by a fractal combustion model which is available in the cycle-simulation software. The implementation of the single zone k-ε turbulence model shows significant improvements, both in terms of the prediction of the turbulent kinetic energy and the combustion process as one of the main parts of the engine cycle.