Mechanism of transition to detonation in unconfined volumes

The paper is aimed at numerical study of one of the most hazardous events at a launch place: open space explosion of fuel air mixtures due to accidental loss of containments. A mechanism of transition to detonation in the process of unconfined flame propagation is proposed. It is shown that the detonation onset takes place as a result of local exponential growth of unstable short-wavelength perturbations. Exactly the same mechanism is known to be responsible for the self-similar flame acceleration, however the detonation can arise only in the case of extremely high reaction rate. High reaction rate defines a coupling of the accelerating flamelets with diverging shock waves that leads to the detonation onset.