Interactions of flame propagation, auto-ignition and pressure wave during knocking combustion

Using one-dimensional numerical simulation, the interactions of flame propagation, auto-ignition and pressure wave during various knocking combustion scenarios are systematically investigated, for stoichiometric H2-air mixture fueled in a closed constant volume reactor. Different types of auto-ignition and pressure mutation are identified with various initial temperatures. It is found that as initial temperature increases, there is a transition for the auto-ignition (AI) position from the near-wall region to the region ahead of SI flame front, resulting in distinct pressure mutation and knocking intensity. Further analysis on sequential knocking combustion demonstrates that knocking intensity not only corresponds to the initial auto-ignition events induced by thermal inhomogeneity, but also to the subsequent interactions of flame front propagation, as well as AI spots initiation and pressure wave generation. Consequently, more intense pressure mutation could result from the developing detonations. Finally, the mechanism of AI occurrence and AI development is identified, which demonstrates the essential role of pressure wave disturbance in the formation of thermal inhomogeneity and detonations.