Development of a Simplified CFD Model for In-Cylinder Flow in Two-Stroke Engines

Abstract

With ever stricter emission laws, a main focus in the development of new chainsaws is not only to optimize the performance but also to lessen the environmental impact from the operation of the two-stroke engine. A big part of this is to optimize the geometry to reduce the leakage of unburned fuel. Long simulation times makes this process slow and tedious. This thesis investigates different ways of reducing the simulation time to enable a faster design iteration process in the future. This is done by removing non-vital geometry to reduce the size and complexity of the domain. The mesh is also examined to assess which areas can be coarsened and thereby reduce the number of cells. Furthermore the physics setup and time discretization of the simulation is studied. These are modified by increasing the time step and changing a gas model. Finally, the successful changes from the three different approaches are combined into one single model. To verify that the changes made does not impact the results of the simulations significantly, several measurements are set up in the model with extra focus towards quantities like the pressures that later can be measured easily in a physical prototype. The study results in a simplified model which runs more than three times faster compared to the original, without significantly reducing the accuracy of the results.