Comparison of algorithms for unsteady flow calculations in inlet and exhaust systems of IC engines

A comparison of different numerical algorithms used in commercial codes for the calculation of the one-dimensional unsteady flow in the pipes of the i nfer and exhaust systems of internal combustion engines is presented in thi s work. The comparison is made between the Method Of Characteristics (MOC), different Lax-Wendroff schemes, first order upwind schemes and the newest TVD (Total Variation Diminishing) schemes. These algorithms are representat ive for the complete evolution noticed in the computer codes from the begin ning of their use to the present state of the art. Tw models of realistic p roblems in engine simulation tasks are considered: the shock tube calculati on (so called Sod's problem) and the calculation in a tapered pipe. The fir st test case simulates the exhaust valve opening and releasing a pressure ( shock)wave in the exhaust manifold while the other rest case covers any gra dual variation in the cross section of the manifold pipes. For both test ca ses computed results are compared with an exact solution and computer time and accuracy are evaluated. None of the examined schemes is completely sati sfactory. They either Show 100 much overshoots (for the first test case), o r they have local discretization errors (at the section changes of the seco nd test case). A new TVD scheme is proposed that does nor introduce any of the foregoing inaccuracies. With this scheme overshoots and dips are elimin ated and mass balances are fulfilled, while maintaining high accuracy.