Development of a methodology for the numerical simulation of a high-performance 2-stroke engine by the use of 1D-3D coupling

The 2 stroke engines have wide variety of applications, especially in the field of recreational vehicles, handled products and small two wheelers. This is due to the 3 advantages that characterize these kind of engines: the high power density, the low weight and the low production costs. The main research activities in this field are focused on the optimization of these advantages while minimizing the well known disadvantages: high emissions and fuel consumption. The aim of this work is the development of a simulation methodology able to predict the performance of the engine under development with special attention to the scavenging process, mixture preparation and combustion. Up to now, in the field of simulation, two state of art approaches exist. The first one characterized by the detailed description of the gas exchange and thermodynamic processes by means of 3D-CFD software tools able to model and analyse complex geometries. But unfortunately this kind of approach requires reliable initial conditions and, in addition, the model build-up and computational times are very high. So, during the development process of a two stroke engine, the 3D simulation results are not achieved before the prototype phase begins. The second approach, on the other hand, is performed by means of 1D-CFD software tools. It is less time consuming compared to the 3D approach and requires a lower demand on initial conditions since an higher number of iterations can be calculated to get a converged solution. But on the negative side it has to be considered that it cannot provide predictive models for what concern crucial aspects of two stroke engines, such as the scavenging and the mixture preparation. Since a detailed understandings of the thermodynamic processes and a predictive simulation strategy performed in a reasonable amount of time is needed, the combination of the two approaches is necessary. The focus of this thesis is the evaluation of the feasibility of the 1D-3D methodology and the accuracy of the results for the simulation of a real world high performance two stroke engine.