Abstract
This paper describes the main features of the thermodynamic and chemical model included in the GASDYN engine simulation code to calculate the combustion process in spark-ignition engines. The aim of this model is to compute correctly the main pollutants which characterize the operating conditions of s.i. engines: nitric oxides, carbon monoxide and hydrocarbons. The behavior of a new reaction scheme, based on the extended Zeldovich scheme, for the prediction of NO formation level is investigated, while a kinetic mechanism controls the process of formation and destruction of CO in the combustion chamber. The importance of adopting a multi-zone model is outlined in order to achieve a satisfactory prediction of the temperature distribution inside the cylinder. Finally a phenomenological model calculates the hydrocarbons emissions, separating the individual processes which constitute the generating sources: ring-pack crevices, oil film, partial burn effects. An exhaustive comparison is shown between the results obtained by the simulation and the experimental data, considering the Fiat-AlfaRomeo Twin Spark 2.0L engine.