Experimental study of the perturbation of the cavity on the deflagration to detonation transition

The perturbation in the deflagration to detonation transition process is investigated experimentally by utilizing one cavity and three successive cavities to induce weak and strong turbulences, respectively. The cavity serves as a "hot spot" in propagating deflagration, generating a pulse of shock waves locally and accelerating its velocity. The results suggest three modes of cavity perturbation on deflagration acceleration: direct transition to detonation, secondary acceleration to detonation after a long distance of steady propagation or mild decline in velocity, and failure to transition to detonation. This variation can primarily be attributed to various strengths of the precursor shock resulting from the acceleration of the flame by the cavity disturbance. The cavity perturbation must satisfy specific critical conditions to directly assist in the deflagration-to-detonation transition. Firstly, the escalated flame velocity due to the cavity perturbation must exceed the sound speed in combustion products. Secondly, the acceleration of the velocity rise must surpass specific critical values for the transition to detonation to be smoothly completed without a secondary acceleration.