Numerical simulation of the effects of the EGR ratio and ignition timing on a supercharged and high compression ratio hybrid gasoline engine

Abstract

This paper explores the potential effects of the exhaust gas recirculation (EGR) ratio and ignition timing on knock suppression in a supercharged and high compression ratio (CR) hybrid gasoline engine, whereas previous knock studies have focused on conventional CRs and equivalence ratios. According to the simulation results, EGR can significantly reduce the knock intensity (KI). The high CR and EGR enable the realization of an indicated thermal efficiency of 47.46 %. Chemical modeling and solvers make free radical detection convenient. Therefore, this paper investigates the relationships between chemical kinetics and low-temperature reactions, preignition (PI) and spontaneous combustion of end mixtures (SCEM). The numerical results demonstrate that IC4H7 is an important indicator of low-temperature reactions. In the cases where SCEM and PI occur, H2O2 and CH2O substantially decompose and the masses of CH3, HCO, and CO start to decrease before the peak heat release rate (HRR) is attained. High CH2O concentration is an important indicator for high-temperature reactions, while high concentrations of CH3 and HCO can characterize the onset of SCEM or PI. The peak masses of IC4H7, HCO, and CH3 positively correlate with the KI value.