Experimental Investigation of the Reactive Shock-bubble Interaction

A series of experiments have been carried out to study shock-initiated combustion in a converging lens geometry. For heavy gas bubbles, the acoustic impedance mismatch results in a focusing of the transmitted shock wave known as the shock focusing phenomenon. The increase in temperature and pressure that result from this phenomenon are used to ignite a combustible gas mixture near the downstream pole of the bubble. The characteristics of the ignition and propagation of the reaction front are studied experimentally in conjunction with the hydrodynamic bubble morphology. The experiments cover a range of incident shock wave Mach numbers (1.35 < Mi < 2.85) while the densities of the bubble and ambient gases are held constant. Both chemically reactive (55% Xe, 30% H2, 15% O2) and inert (50% Xe, 50% O2) bubbles are studied after the shock-acceleration by a planar shock wave in N2.;For low incident Mach numbers (Mi < 2.07), the combustion does not have a measurable effect on the measured length scales of the post-shock bubble morphology. For high incident Mach numbers ( Mi = 2.85), combustion time scales become much shorter than the hydrodynamic time scales associated with the vortex ring formation. The rapid combustion causes a volumetric expansion of the bubble that is measurable in the post-shock length scales extracted from the experiments. Through a combination of 1D gas dynamics and an induction time model for the combustion of the H2-O2 system, a technique is developed to provide a better understanding of the shock-focusing phenomenon. From this analysis, it is estimated that the effect of shock-focusing can increase the temperature and pressure within the bubble gas by factors of 3 and 11, respectively, over the temperature and pressure that would be achieved in the absence of shock-focusing.