Flame acceleration in stoichiometric H 2 /O 2 at 12 and 25 kPa initial pressure in an obstacle-laden square cross-section channel was studied experimentally using planar laser-induced fluorescence imaging of hydroxyl radicals (OH-PLIF) and simultaneous high-speed schlieren imaging. Results were obtained resolving the explosion front structure as it develops immediately after ignition as a slow-flame to the eventual formation of a shock-flame complex in the fast-flame regime. The images provide a novel level of detail and allow for the determination of the effects of turbulence-flame and shockflame interaction. In the slow-flame regime, vortex shedding off obstacle edges occurs over long time-scales, vortices are convected downstream and turbulent combustion takes place in the obstacle wakes. The fast-flame regime is marked by the presence of compression waves (and shock waves) which interact with the flame and cause macroscopic deformation of the flame and small-scale wrinkling due to Richtmyer-Meshkov instability. A quasi-steady fast-flame is characterized by the close proximity of the precursor shock and the turbulent flame. The flow-field that governs the flame shape is established by the precursor shock. Shock-flame interactions lead to flame front perturbations on both small and large scales. The OH-PLIF technique makes it possible to discern the flame front from other density interfaces that appear in the complex fast-flame structure observed in schlieren images and also eliminates the line-of-sight integration limitation.

This study used self-luminous high-speed photography to visualize quasi-detonation propagation and deflagration-to-detonation transition (DDT) in a transparent round tube equipped with repeating orifice plates. Experiments were conducted in a combustion channel consisting of a 3.16 m square channel with a 7.6 cm by 7.6 cm cross-section connected to a 1.55 m cylindrical channel filled with orifice plates. Rectangular 'fence-type' obstacles were installed on the top and bottom of the square channel with a 3.8 cm opening between them. Two sets of orifice plates with different diameters, d, representing different blockage ratios (BR) were tested (d=5.33 cm for 50% BR and 3.81 cm for 75% BR orifice plates). Stoichiometric hydrogen-oxygen mixtures at initial pressures of 4-60 kPa were ignited at one end of the combustion channel. Average propagation velocities were derived from shock-time-of-arrival measurements using pressure transducers in the square channel and high-speed video filmed through the round tube. First and foremost, I'd like to thank my supervisor, Dr. Gaby Ciccarelli, for his guidance, support and teaching over the past two years. This degree has been a wonderful opportunity and it has been a real pleasure to work on this project with him.