Computation of Inviscid Vortical Flows in Piston Engines

Summary

Two and three-dimensional vortical flow in a cylinder of a piston engine is investigated by means of finite-difference solutions of the Euler equations. Since both, the physical understanding of piston flows is far from complete and adequate computational methods for such complex processes are missing, the restriction to inviscid flow is considered as a first step to achieve basic insight into the large-scale vortical motion of the flow.The discretization of the conservation equations is carried out in a time-dependent, node-centred grid. Central differences are used to approximate the spatial derivations. For the integration in time two methods are applied, an implicit factorization scheme for plane and axisymmetric flows and an explicit Runge-Kutta time-stepping scheme for the three-dimensional flow.The numerical results for plane flow are compared with experiments using Mach-Zehnder-interferometry. The comparison confirms that the results obtained with the Euler equations reflect essential features of the flow in the cylinder of piston engines. For three-dimensional flow two examples are chosen to discuss the influence of off-centred valves and of the shape of the piston crown on the onset of the swirling flow during the intake stroke and its subsequent development during the compression stroke.