Some observations of the jet initiation of detonation

A conventional shock tube was used to accelerate a preignited flame bubble from a circular pipe into a larger vessel. The diffraction of the ensuing s hock-jet flame at the abrupt area change was observed by spark and streak s chlieren photography. The results confirm previous findings that jet initia tion of detonation can occur at initial conditions where an established det onation would fail to transit into the unconfined volume. The schlieren obs ervations also show that significant unconfined flame acceleration can occu r in the larger volume. Transition to detonation was always observed to occ ur in close proximity to the surface of the diffracting turbulent flame fro nt and the results do not favor a transition mechanism involving extended v ortex roll-up and larger scale mixing of burned and unburned gas. (C) 1999 by The Combustion Institute.