Analysis of onset and severity of knock in SI engine based on in-cylinder pressure oscillations

Abstract

This paper, based on pressure wave equation coupled with KIVA-3V combustion codes with reduced kinetics mechanism, analyzed and discussed the onset and severity of knock identified by different knock metrics in SI engine running at different speeds. The calculated results demonstrated that the knock onset defined by pressure oscillations characteristics here was approximately consistent with that defined by heat release. Meanwhile, the knock onset shifted backwards in high-speed region where relatively high flame propagation speed prevented the occurrence of auto-ignition, and thus knock intensity, characterized by knock metrics, MAPO and KI20, decreased observably. Visualized 3D calculation results were presented to show the flame propagation and pressure oscillation characteristics. Finally, the correlation between engine speed and the onset and severity of knock indicated that knock onset was highly correlated to engine speed, the knock intensity judged by MAPO and KI20 was accurate basically, and KI20 knock metric was better due to more pressure oscillations characteristics information contained. The comparison between experimental and calculated results indicated that the onset and intensity of knock can be characterized and quantified accurately with high-frequency pressure oscillations characteristics calculated with pressure wave equation.