Experiment on the Shock-Induced Ignition in a Converging Wedged Cavity

A new type of experimental method was proposed for the investigation of ignition behaviors by using a smoothly convergent cylindrical shock wave. The cylindrical shock wave is generated with a specially designed wall contour based on shock dynamic theory that can transform a planar shock front into a curved cylindrical one and propagates along a following wedged convergent channel. The experiments were conducted in a shock tube filled with H2 / air combustible mixture. Two kinds of ignition modes were observed under current experimental conditions. When the contraction is sufficiently large, the enhancement of the converging shock will result in a sudden occurrence of the ignition soon after the passage of the incident shock. On the other hand, if the intensity of the converging shock is not sufficiently strong, a mild ignition starts at the vicinity of the outlet, in which a combustion driven precursor shock and a following flame move towards upstream separately. When the flame overtakes the precursor shock, the overlap results in an onset of a detonation.