Development of a Model for the Simulation of a Reed Valve Based Secondary Air Injection System for SI Engines 2005-01-0224

This paper describes a research activity, carried out at the University of Perugia, focused on the modelling of an automatic reed valve in a coupled fluid-structure approach. The application here concerned is a reed device used to control a Secondary Air Injection (SAI) system which allows ambient air to enter the exhaust pipe upstream of the catalyst (useful for the reduction of emissions in rich mixture engine operating conditions).

Since currently no commercial codes are still available for simulating in a comprehensive way the non-linear dynamics of a reed valve device with position constraints, the main objective of the work is the calculation of the air mass flow rate admitted to the exhaust system through the reed, by means of a slim and easy software tool. The task is accomplished by integrating two different codes, developed by the authors. For the gasdynamics phenomena a one-dimensional unsteady approach is used, while the dynamic behaviour of the reed valve is modelled by means of the finite element method. Moreover the present paper describes the methodology used for coupling the fluid and structure codes. To this end, experimental measurements were performed for the evaluation of the discharge coefficient, while various 3D-CFD steady state simulations were also carried out to analyse the pressure field on the actual reed geometry.

The results of the 1D simulations are then compared with experimental measurements of mass flow rate and pressure histories, carried out on a Piaggio 150 cc engine, focusing the attention on the air injection subsystem. The comparison between the numerical and the experimental results shows a satisfactory agreement. As future work, the model seems suitable to be integrated in a comprehensive 1D code for engine cycle simulation.