Multi-frequency modelling of unsteady flow in the inlet manifold of an internal combustion engine

Pressure wave propagation in the inlet and exhaust manifolds of internal combustion engines is an important phenomenon which affects the filling and emptying of the cylinders. The objective of this paper is to present a new methodology that takes into account this phenomenon without the use of a one-dimensional resolution scheme. First, an analogy is made between the compressible air in a pipe and a mechanical ideal mass-damper-spring system. A multi-frequency model is then presented. The principle of the model is to define a link between the pressure and the flow velocity by means of the impedance. The parameters of this model can be determined using a flow bench working in unsteady conditions and called the 'dynamic flow bench'. The new model is then tested with a more complex geometry. The latter corresponds to a specific air intake system of an internal combustion engine. It is then possible to introduce the new model into an internal combustion engine simulation code and to compare the numerical results with the experimental data. Good agreement is obtained between the two, and the new multi-frequency model appears to be an alternative method for modelling the pressure waves in the intake and exhaust systems of internal combustion engines. It is therefore possible to reduce the computational times.