In this work, experimental results are presented for the first time on the shock-initiated combustion of a spherical density inhomogeneity. A converging lens geometry, in which a heavy bubble free-falls in a lighter fluid, is used to focus a planar shock wave resulting in the ignition of a mixture of H-2, O-2 and Xe (55%, 30% and 15%, respectively) in N-2. The experiments are performed at the Wisconsin Shock Tube Laboratory in a 9 m vertical shock tube with a 25.4 cm square cross-section. A pneumatic injector is used to generate a 4 cm diameter soap film bubble filled with the combustible mixture. The injector retracts flush into the side of the tube releasing the bubble into a state of free-fall. The initial conditions are captured with two high speed CMOS cameras orientated perpendicular to one another. Simultaneous Mie scattering and chemiluminescence diagnostics are used to image the post-shock bubble morphology and combustion, respectively. The ignition delay times are measured for several incident shock strengths (1.3

Keywords:Shock bubble;Autoignition;Converging shock;Shock implosion;Shock initiated combustion;Compressible flow