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Technical Paper

Modeling the Pollutant Emissions from a S.I. Engine

Nowadays 1D fluid dynamic models are widely used by engine designers, since they can give sufficiently accurate predictions in short times, allowing to support the optimization and development work of any prototype. According to the last requirements in terms of pollutant emission control, some enhancements have been introduced in the 1D code GASDYN, to improve its ability in predicting the composition of the exhaust gas discharged by the cylinders and the transport of the chemical species along the exhaust system. The main aspects of the methods adopted to model the combustion process and the related formation of pollutants are described in the paper. To account for the burnt gas stratification, two different approaches have been proposed, depending on the expected turbulence levels inside the combustion chamber. The reliability of the simulation of the pollutant formation process has been enhanced by the integration of the thermodynamic module with the Chemkin code.
Technical Paper

The Prediction of 1D Unsteady Flows in the Exhaust System of a S.I. Engine Including Chemical Reactions in the Gas and Solid Phase

The paper describes the research work concerning the simulation of 1D unsteady reacting flows in s.i. engine pipe-systems, including pre-catalysts and main catalysts. The numerical model GASDYN has been developed to enable the concurrent prediction of the wave motion in the intake and exhaust ducts, the chemical composition of the gas discharged by the cylinder of a s.i. engine, the chemical and thermal behavior of catalytic converters. The effect of considering the transport of chemical species with reactions in gas phase (post-oxidation of unburned HC in the exhaust manifold) and in solid phase (conversion of pollutants in the catalyst) on the predicted wave motion is reported.
Technical Paper

An Integrated Simulation Model for the Prediction of S.I. Engine Cylinder Emissions and Exhaust After-Treatment System Performance

The calculation of the main pollutant emissions discharged into the atmosphere by means of numerical codes requires the development of integrated models, including either an accurate thermodynamic in-cylinder analysis and the simulation of reacting unsteady flows in the duct system. This paper describes the main features of the numerical model GASDYN developed by the authors, which in the last years has been enhanced in order to achieve this kind of objectives. A multi-zone approach has been adopted to predict the combustion process in s.i. engines, whereas the so called super-extended Zeldovich mechanism has been introduced to perform a more detailed description of all the chemical reactions involved in the NOx production process. The simulation of the reacting flows in the exhaust manifold has been completed by the introduction of further enhancements to predict the chemical behavior of gases inside the catalytic converters.
Technical Paper

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.
Technical Paper

1D Fluid Dynamic Modeling of Unsteady Reacting Flows in the Exhaust System with Catalytic Converter for S.I. Engines

This paper deals with some recent advances in the field of 1D fluid dynamic modeling of unsteady reacting flows in complex s.i. engine pipe-systems, involving a catalytic converter. In particular, a numerical simulation code has been developed to allow the simulation of chemical reactions occurring in the catalyst, in order to predict the chemical specie concentration in the exhaust gas from the cylinder to the tailpipe outlet, passing through the catalytic converter. The composition of the exhaust gas, discharged by the cylinder and then flowing towards the converter, is calculated by means of a thermodynamic two-zone combustion model, including emission sub-models. The catalytic converter can be simulated by means of a 1D fluid dynamic and chemical approach, considering the laminar flow in each tiny channel of the substrate.
Technical Paper

Fluid Dynamic Modeling of the Gas Flow with Chemical Specie Transport through the Exhaust Manifold of a Four Cylinder SI Engine

The paper describes the 1-D fluid dynamic modeling of unsteady flows with chemical specie tracking in the ducts of a four-cylinder s.i. automotive engine, to predict the composition of the exhaust gas reaching the catalyst inlet. A comprehensive simulation model, based on classical and innovative numerical techniques for the solution of the governing equations, has been developed. The non-traditional shock-capturing CE-SE (Conservation Element-Solution Element) method has been extended to deal with the propagation of chemical species. A comparison of the MacCormack method plus FCT or TVD algorithms with the CE-SE method has pointed out the superiority of the latter scheme in the propagation of contact discontinuities. A realistic composition of the exhaust products in the cylinder, evaluated by a two-zone combustion model including emission sub-models, has been imposed at the opening of the exhaust valve, considering the effect of short-circuit of air during valve overlap.
Technical Paper

Modeling of 1-D Unsteady Flows in I.C. Engine Pipe Systems: Numerical Methods and Transport of Chemical Species

The paper describes recent advances in the research work concerning the 1-d fluid dynamic modeling of unsteady flows in i.c. engine pipe systems. A comprehensive simulation model has been developed, which is based on different numerical techniques for the solution of the fundamental conservation equations. Classical (MacCormack method plus TVD algorithm) and innovative (the CE-SE method, the discontinuous Galerkin FEM) shock-capturing schemes have been compared, considering the shock-tube problem and the shock-turbulence interaction problem. Moreover, the tracking of the chemical species along the intake and exhaust duct systems has been investigated, introducing the species continuity equations in the numerical model. The engine test case reported in the paper points out the predicted transport of chemical species in the ducts.