Classification and Mechanism Analysis of Knock Modes in Hydrogen Engines

Abstract

This study uses numerical simulation methods to explore the knock mechanism of hydrogen engines and proposes a knocking classification basis based on pressure wave characteristics and the flame propagation state. Based on the location of the pressure wave, whether the flame propagation speed reaches the theoretical Chapman–Jouguet (CJ) detonation velocity, and whether the pressure wavefront is coupled with the flame front, hydrogen engine knock is divided into three categories: deflagration-knock, detonation-knock, and superknock. Analysis shows that deflagration-knock is caused by the interaction between flames and pressure waves, and its intensity is relatively weak. Both detonation-knock and superknock are caused by the coupling of the flame front and pressure wavefront to form detonation waves. The core difference between the two is that the pressure waves appear in different positions. The pressure wave of detonation-knock appears near the cylinder wall, while the pressure wave of superknock appears at the flame front, and the latter has significantly higher knock intensity than the former. Additionally, this study simulated preignition events by setting up dual ignition sources to explore the knock mechanism induced by preignition.