Combustion and Autoignition Modelling in a Turbocharged SI Engine

A holistic modelling approach has been employed to predict combustion, cyclic variability and knock propensity of a turbocharged downsized SI engine fuelled with gasoline. A quasi-dimensional, thermodynamic combustion modelling approach has been coupled with chemical kinetics modelling of autoignition using reduced mechanisms for realistic gasoline surrogates. The quasi-dimensional approach allows a fast and appreciably accurate prediction of the effects of operating conditions on the burn-rate and makes it possible to evaluate engine performance. It has also provided an insight into the nature of the turbulent flame as the boost pressure and speed is varied. In order to assess the sensitivity of the end-gas chemical kinetics to cyclic variability, the in-cylinder turbulence and charge composition were perturbed according to a Gaussian distribution. Coupling cyclic variability with autoignition modelling allowed prediction of the autoignition propensity for the entire spectrum of cyclic variations in cylinder pressure. The models have been validated against engine test data from a technology demonstrator downsized, turbocharged engine. The knock-limited spark advance was predicted for a RON 95 and RON 102 gasoline within 2° of crank angle. This work demonstrates the viability of chemical kinetics for gasoline surrogates coupled with 0-dimensional thermodynamic modelling approach as a fast and reliable development tool for high performance engines