Representation of Two-Stroke Engine Scavenging in 1D Models Using 3D Simulations 2018-01-0166
The paper proposes the way of using scavenging curves, i.e., dependence of residual gas fraction in exhaust port or valve on residual fraction in a cylinder, found by CFD simulations. In the general case, exhaust gas recirculation outside of a cylinder (EGR) or internal gas recirculation caused by variable values of burned gas backflow to inlet system may influence in-cylinder residual gas fraction. These deviations may take place during engine optimization, done by 1D models. The determination of scavenging curves via 3D CFD simulations is a time consuming process, which cannot be repeated for every 1D case.
The way of generalization of scavenging curves is based on reduction of cylinder burned gas contents (cylinder residual ratio) to scavenging progress variable, and reduction of burned gas contents in exhaust port gas flow (exhaust residual ratio), which makes the use of single result of 3D simulation possible for more variants of inlet timing or different pressure drop between inlet and exhaust system. The reduction is based on a stepwise integrated burned gas contents in fresh charge for every 1D simulated case. By this way, the procedure developed accelerates the optimization process substantially. The important condition is compatibility between 1D and 3D boundary conditions. The results are validated using dedicated 3D simulations.