Development and Application of S.I. Combustion Models for Emissions Prediction 2006-01-1108

The s.i. combustion process and its corresponding pollutant formation are investigated by means of a quasiD approach and a CFD model. This work has been motivated by the need to better understand the reliability of such models and to assess their accuracies with respect to the prediction of engine performances and emissions. An extended dissertation about the fundamental mechanisms governing the pollutant formation in the turbulent premixed combustion which characterizes the s.i. engines is given. The conclusion of such analysis is the definition of a new reduced chemical scheme, based on the application of partial-equilibrium and steady-state assumptions for the radicals and the solution of a transport equation for each specie which is kinetically controlled.

For this purpose the CFD code OpenFOAM [1, 2, 3] and the thermo-fluid dynamic code GASDYN [4, 5] have been applied and enhanced. The proposed multi-D combustion model has then been adapted to the quasi-dimensional approach, embedded into a 1D fluid-dynamic code for the simulation of the whole engine system. Computed results are compared with the available experimental data of in-cylinder pressure histories and engine emissions for two different engine configurations. The availability of identical engine conditions simulated by the two different approaches allows a deeper understanding of the reliability of the simplifications made in the quasi-dimensional model. A comprehensive investigation of several physical variables (whose experimental measure is not usually available), such as the burnt gas temperature stratification and the corresponding chemical specie concentrations, was performed.