Development of quasi-dimensional combustion model of SI engines equipped with variable valve actuation

Abstract

Variable valve actuation technology has great potential of improving both fuel economy and performance of SI engines. However, due to numerous valve profiles and excessive calculation time, optimization of valve actuation under various engine operation conditions can hardly be achieved by experimental method or 3D engine simulation tools. Therefore, in this work, a quasi-dimensional combustion model for fast simulation of SI engines equipped with VVA was developed. MIT quasi-dimensional combustion model was used as the base code. It was modified to reflect the effect of VVA on burning rate prediction which is mainly affected by turbulent intensity and residual gas fraction. STAR-CD and GT-POWER were used to obtain base data of turbulent intensity and residual gas fraction under various valve lift, duration and timing. Using these base data, the turbulent flow energy model and boundary conditions of gas exchange process were modified to improve the accuracy of turbulent intensity and residual gas fraction prediction. Model calibration based on experimental data was carried out. Simulation results showed that the modified model can predict burning rate with acceptable degree of accuracy under various valve lift, duration and timing. Finally, using the modified quasi-dimensional combustion model, the effect of VVA on fuel economy improvements was verified.