Prediction of S.I. Engine Emissions During an ECE Driving Cycle via Integrated Thermo-Fluid Dynamic Simulation

The paper describes the research work carried out on the thermo-fluid dynamic modeling of an S.I. engine coupled to the vehicle in order to predict the engine and tailpipe emissions during the ECE European driving cycle. The numerical code GASDYN has been extended to simulate the engine + vehicle operation during the first 90 seconds of the NEDC driving cycle, taking account of the engine and exhaust system warm-up after the cold start. The chemical composition of the engine exhaust gas is calculated by means of a thermodynamic multi-zone combustion model, augmented by kinetic emission sub-models for the prediction of pollutant emissions.

A simple procedure has been implemented to model the vehicle dynamic behavior (one degree of freedom model). A closed-loop control strategy (proportional-derivative) has been introduced to determine the throttle opening angle, corresponding to the engine operating point when the vehicle is following the ECE cycle. The calculation of about a thousand thermodynamic cycles, each with a different load and speed condition, is required to cover the first 90 seconds of the driving cycle, in order to predict the catalyst light-off and the engine and tailpipe instantaneous and cumulative emissions.

A Fiat Fire 1.4L four-cylinder S.I. engine mounted on a “Punto” vehicle (complying with Euro IV regulations) has been used to validate the integrated simulation model. The large set of experimental data enabled a comprehensive comparison between predictions and measurements, with encouraging results.