Simulation study on the knock mechanism of a hydrogen direct injection internal combustion engine

Hydrogen fuel is a more suitable option for traditional internal combustion engines to achieve carbon neutrality. However, pre-ignition and knock seriously hinder the operation and adoptions of hydrogen internal combustion engines. To explore the characteristics and the mechanism of different knock modes, an improved combustion model coefficient is used to simulate the transition from normal combustion to normal knock and super knock by adjusting end of hydrogen injection timing. The results indicate that the accuracy of predicting the knock onset in different knock modes using H 2 O 2 is higher than that of HO 2 . In the case of normal knock, the end mixture only undergoes auto-ignition, and there is no coupling between pressure waves and the auto-ignition flame front. When super knock occurs, the pressure wave and auto-ignition flame front become coupled, and they reinforce each other, leading to a significant increase in knock intensity and pressure fluctuations that are much greater than those in normal knock. Before knock occurs, the higher pressure of the unburned end mixture results in a lower equivalence ratio being required for end mixture auto-ignition to occur. A higher mass fraction of unburned end mixture results in greater knock intensity.