Comparison Studies on the Method of Characteristics and Finite Difference Methods for One-Dimensional Gas Flow through IC Engine Manifold

A comparison study on the commonly used solution schemes of one-dimensional gas flow in IC engine manifolds, i.e. the method of characteristics and the finite difference schemes, was conducted in this paper. The study was based on computer simulations of the flow in a typical pipe-volume configuration under both steady and unsteady boundary conditions. The simulation results indicate that all the solution schemes offered fairly good accuracy in parallel pipes under steady flow conditions. However, under unsteady flow conditions, especially in tapered pipes commonly used in IC engine manifolds, all the existing solution schemes encountered difficulties. These included such aspects as the mass and energy conservation, non-physical overshoot, solution stability and physical process distortion. The solution schemes were compared based on the case calculations and the related problems are specified. Based on the two-step Lax-Wendroff difference scheme with flux correction technique, an improved calculation method was developed and the best compromise was achieved among the above aspects.