COMBUSTION MODEL FOR A HOMOGENEOUS TURBOCHARGED GASOLINE DIRECT-INJECTION ENGINE

Homogeneous charge is a preferred operation mode of gasoline direct-injection (GDI) engines. However, a limited amount of work exists in the literature for combustion models of this mode of engine operation. Current work describes a model developed and used to study combustion in a GDI engine having early intake fuel injection. The model was validated using experimental data obtained from a 1.6L Ford EcoBoost four cylinder engine, tested at the U.S. EPA. The start of combustion was determined from filtered cycle-averaged cylinder pressure measurements, based on the local maximum of third derivative with respect to crank angle. The subsequent heat release, meanwhile, was approximated using a double-Wiebe function, to account for the rapid initial pre-mixed combustion (stage 1) followed by a gradual diffusion-like state of combustion (stage 2) as observed in this GDI engine. A non-linear least-squares optimization was used to determine the tuning variables of Wiebe correlations, resulting in a semi-predictive combustion model. The effectiveness of the semi-predictive combustion model was tested by comparing the experimental in-cylinder pressures with results obtained from a model built using a one-dimensional engine simulation tool, GT-POWER (Gamma Technologies). Model comparisons were made for loads of 60, 120, and 180 N-m at speeds ranging from 1500 to 4500 rpm, in 500 rpm increments. The root-mean-square errors between predicted cylinder pressures and the experimental data were within 2.5% of in-cylinder peak pressure during combustion. The semi-predictive combustion model, verified using the GT-POWER simulation, was further studied to develop a predictive combustion model. The performance of the predictive combustion model was examined by regenerating the experimental cumulative heat release. The heat release analysis developed for the GDI engine was further applied to a dual mode, turbulent jet ignition (DM-TJI) engine. DM-TJI is an advanced combustion technology with a promising potential to extend the thermal efficiency of spark ignition engines with minimal engine-out emissions. The DM-TJI engine was observed to offer a faster burn rate and lower in-cylinder heat transfer when compared to the GDI engine under the same loads and speeds.