Numerical study on detonation initiation by multiple hot spots

Detonation initiation is important not only for the development of advanced detonation engines and but also for the control of accidental explosion. There are mainly two types of detonation initiation, i.e., direct initiation and indirect initiation. This work focuses on direct detonation initiation which has a short initiation distance but requires large amount of energy deposition. Specially, we investigate the reduction in the critical initiation energy through replacing the single hot spot by multiple hot spots. The transient detonation initiation process in a stoichiometric H₂/O₂/Ar mixture is examined through two-dimensional simulations considering detailed chemistry. It is found that under the same initiation energy, detonation initiation fails for a single large hot spot while successful detonation initiation can be achieved by employing six small hot spots. The collisions among adjacent transverse detonation waves induce new local explosions, which play a pivotal role in detonation initiation. To further assess the impact of wave collision, we change the hot spot energy used in the multiple hot spot configuration. For relatively low initiation energy, the blast wave quickly decays and decouples with the reaction zone. Consequently, the collision among transverse shock waves cannot induce new local explosion and detonation initiation fails. Increasing the initiation energy can enhance the blast wave and is favorable to the formation of local explosion, facilitating the rapid detonation initiation. Furthermore, the influence of hot spot number on detonation initiation is assessed. Interestingly the hot spot number is found to have non-monotonic effect on detonation initiation. Splitting a single hot spot into multiple hot spots enhances detonation initiation since the wave collision helps to induce local explosion. However, as the hot spot number increases, the energy of each hot spot is decreased and becomes excessively dispersed, which results in relatively weak blast wave and thereby weak wave interaction. Consequently, local explosion cannot be triggered and detonation initiation fails for relatively large hot spot numbers. This study provides insights on promoting detonation initiation through multiple hot spots.