1. Introduction
Theairintakelineofaninternalcombustionengineistheperfect applicationofunsteadyfluiddynamics.Thereciprocatingmotionof the intake valves causes pressure pulses to be generated that propagateinthepipingsystem.Inthecaseofamulti-cylinderenginefor a constant engine speed, pressure bursts from different cylinders establishesasystemofstandingwavesthataffecttheemptying,filling and scavenging processes of the engine. The volumetric efficiency and the output torque of the engine are thus influenced by this wave action, which is turn dependant on two factors: the exci
tationoftheengine(atthevalvesinterface)andthegeometryitself of the intake line. This subject have been studied and analyzed for many years. Broome [1] distinguished between inertial and wave effects,thatwhencombinedtogetherwithapropervalvetiminginducesrameffect.Ontheotherhand,thedesignoftheenginemanifolditselfrequiresbeingabletocalculatetheunsteadycompressible flowoftheairflowingthroughtheengineintakeandexhaust.Nowadays,thisispossibleusingone-dimensionalcalculationcodesthat discretize the continuous ordinary differential equations of gas dynamics in the space and time domains [2]. Winterboneand Pearson [3] give an excellent review of the current techniques and numerical schemes employed in 1D codes, these have become the benchmark for engine simulation in the automotive industry. However, experimental engine tests are a must in order to calibrate different parameters such as pressure loss coefficients. Also the dimensions of the modeled geometries in the case of a complex part often differ from their physical values