An Integrated Simulation Model for the Prediction of GDI Engine Cylinder Emissions and Exhaust After-Treatment System Performance 2004-01-0043

The paper describes the development and validation of a quasi-dimensional multi-zone combustion model for Gasoline Direct Injection engines. The model has been embedded in the 1D thermo-fluid-dynamic code for the simulation of the whole engine system named GASDYN and developed by the authors [1, 2 and 3].

The GDI engine combustion model solves mass, energy and species equations using a 4^th order Runge-Kutta integration method; the fuel spray is initially divided into a number of zones fixed regardless of the injected amount and the time step, considering the following break-up, droplet evaporation and air entrainment in each single zone. Experimental correlations have been used for the spray penetration and spatial information. Once the ignition begins it is assumed that the flame propagates spherically, evaluating its velocity by means of a fractal combustion approach and considering the local air-fuel ratio, which is the result of the spray evolution within the combustion chamber. The burnt gas is finally divided into zones of equal mass to account for its temperature stratification, while its composition is evaluated assuming the main species at equilibrium and solving a kinetically controlled equation for NO.

A Fiat-GM Powertrain GDI, four-cylinder 2.0L automotive S.I. engine coupled to its complete intake and exhaust systems has been modeled, in order to predict not only in-cylinder phenomena (pressure, composition) but also the wave motion along the duct system and the consequent mutual interaction. An initial set of experimental data has enabled a preliminary comparison between predictions and measurements, with encouraging results.