Deflagration-to-detonation transition in an unconfined space: II. Expanding hydrogen-oxygen flames

The problem of deflagration-to-detonation transition in an unconfined environment is revisited. With a freely expanding self-accelerating hydrogen-oxygen flame as an example, it is shown that deflagration-to-detonation transition is indeed possible provided the flame is large enough. The transition occurs prior to merging of the flame with the flame-supported precursor shock. The pre-transition flame does not reach the threshold of CJ-deflagration. Numerical simulations employed are based on the recently developed pseudo-spectral method with time and space adaptation.