Numerical investigation on combustion and knock formation mechanism of hydrogen direct injection engine

Hydrogen is an ideal alternative fuel of internal combustion engine because of its high thermal efficiency and no carbon emissions, but knock has become one of the main obstacles restricting its application in engines. The characteristic of flame propagation and the interaction of flame and pressure wave during knocking development was studied numerically in a hydrogen fueled engine. The results showed that the knock is caused by the spontaneous combustion of the end mixture and the interaction between flame and pressure wave. HO2 and H2O2 play a significant role in the flame development by affecting the formation of OH in low-temperature reaction zone. Because the low-temperature reaction zone is preheated by reaction heat of the chain reaction, H2+OH=H2O+H, to prepare for the subsequent high-temperature reactions. Therefore, the faster pressure wave accelerates the flame propagation by promoting the generation of HO2 and H2O2 in the unburned zone at the flame front. The accelerated flame in turn further enhances the pressure wave. Like this, the pressure wave and flame promote and strengthen each other, and finally develop into detonation.