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. The so-called super-extended Zeldovich mechanism has been introduced to perform a more detailed description of the NO_x production process. Separate modules describe CO and HC formation, considering individually the crevices, the oil film layer and the partial burn contributions. The comparison between predictions and experimental measurements carried out on a new configuration of a Fiat-Alfa Romeo four-cylinder, 2.0 L automotive s.i. engine, has pointed out a satisfactory agreement in terms of pressure trends inside the cylinder and gas composition at different locations in the exhaust system.