The assumption of one-dimensional unsteady flows in the inlet and exhaust systems of turbocharged diesel engines is widely used although multi-dimensional simulations using fluid dynamics are also possible. However, difficulties persist concerning the boundary conditions, particularly at the pipe ends (inflow or outflow) and at the intra-pipe boundary conditions (sudden or gradual area changes, bends, junctions, etc.). This paper focuses on the two first steps leading to a 1D flow simulation code: the selection of a numerical scheme and the study of an open end boundary condition. The first section compares several numerical algorithms, including Lax-Wendoff, Flux-Corrected-Transport methods (FCT), and Harten-Lax-Leer (Riemann solver), extended to the second order. The selection criterion is the best compromise between numerical instabilities and computational time. A numerical study using the Fluent CFD code is then presented on a constant area duct in order to determine some characteristics at the pipe end, specifically the dead zone length and the throat area. Finally, a model parameterized by the pressure ratio between inlet and outlet is proposed.

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