1D Unsteady Flows with Chemical Reactions in the Exhaust Duct-System of S.I. Engines: Predictions and Experiments

This paper describes some recent advances of the research work concerning the 1D fluid dynamic modeling of unsteady reacting flows in s.i. engine pipe-systems, including pre-catalysts and main catalysts. The numerical model GASDYN developed in previous work has been further enhanced to enable the simulation of the catalyst. The main chemical reactions occurring in the wash-coat have been accounted in the model, considering the mass transfer between gas and solid phase. The oxidation of CO, C₃H₆, C₃H₈, H₂ and reduction of NO, the steam-reforming reactions of C₃H₆, C₃H₈, the water-gas shift reaction of CO have been considered. Moreover, an oxygen-storage sub-model has been introduced, to account for the behavior of Cerium oxides. A detailed thermal model of the converter takes into account the heat released by the exothermic reactions as a source term in the heat transfer equations. The influence of the insulating mat is accounted. The 1D fluid dynamic model developed has been applied to the simulation of the unsteady flows with transport of reacting chemical species in the exhaust manifold of a Fiat-AlfaRomeo four-cylinder, 2.0L automotive s.i. engine, which adopts two close-coupled metallic pre-catalysts and a main ceramic catalyst. A satisfactory agreement between predicted results and measured data has been achieved.