Rosas Martinez, Camilo Andres (2016-05). Deflagration-to-Detonation Transition (DDT) Studies: Effect of Non-Uniform Obstacle Distribution on DDT. Doctoral Dissertation.
Most of the previous work has been guided towards the understanding of this phenomenon under a uniform obstacle distribution, i.e., same obstacle shape, blockage ratio, and gap between obstacles. However, industrial facilities lack this uniform obstruction arrangement. This research aimed to gain a better understanding of which non-uniform obstacle distribution enhances or weakens the flame acceleration. For this research, a 2.77 m long detonation tube with an internal diameter of 0.04 m was utilized. For the purpose of this investigation, a rig characterization was first performed to determine if a series of explosions under the same conditions was repeatable; the obtained responses showed similar behavior. Then, a Taguchi design of experiments was used. In this matrix, the parameters that were modified were: fuel type, obstacle shape, blockage ratio, and obstacle distribution. In general, each experiment consisted of nine obstacles inserted into the first meter of the detonation tube. The obstruction in each experiment had the same shape, but different blockage ratio and spacing between the obstacles. It was found that block-shaped obstacles with a decreasing blockage ratio and a "staggered" obstacle distribution had the highest tendency to promote the flame acceleration and, consequently, minimize the run-up distance to obtain a detonation. In contrast, experiments that had ring-shaped obstacles with an increasing blockage ratio and a "variation" obstacle distribution have an adverse effect on the flame acceleration and, consequently, maximize the distance at which DDT is observed. Finally, the responses obtained from a Computational Fluid Dynamics (CFD) model were compared against data available in the literature and the experimental data obtained in this research. Even though this CFD model does not predict precisely the onset of DDT, it estimates the likelihood for having the onset of a detonation. In general, the CFD code predicts that the scenario that promotes a faster flame acceleration uses block-shaped obstacles with an equal blockage ratio and a "staggered" obstacle distribution. While the scenario that slows down the flame acceleration is given by ring-shaped obstacles with an increasing blockage ratio and a "variation" obstacle distribution. These trends agree with those from the experiment.