Reed valve modelling in a computational fluid dynamics simulation of the two-stroke engine

Abstract

A method of modelling the crankcase induction process through the integration of computational fluid dynamics (CFD) and one-dimensional engine simulation methods is described. A study of flow in the crankcase of a typical two-stroke engine by Cunningham et al. [1] has led to the development of a method for predicting and duplicating the motion of the reed valve in the inlet system. The response of the reed valve was predicted by a one-dimensional mathematical model and the corresponding inlet flow geometry that results from the reed motion was accommodated via a mesh movement routine in the CFD. The resultant hybrid model showed good correlation with the reed lift, crankcase pressure and delivery ratio predicted by a proven one-dimensional engine simulation code. The predicted velocity fields from the CFD also provided a more detailed view of the processes that occur in and around the reed valve, including the backflow prior to reed closure and the flow reversal which characterizes the two-stage lift profile of the reed. The results from this model show that it should now be possible to create a complete CFD representation of a two-stroke engine by including these techniques in the conventional in-cylinder models.