Flame propagation in a transparent pipe with a single obstruction

Abstract

This report treats the problem of hydrogen explosions. The background for this thesis was based upon earlier work done by Bjerketvedt D., Vågsæther K. and Knudsen V. They investigated hydrogen explosions in a steel pipe with a single obstacle. Literature research of flame acceleration and detonation has been done, and later related to the experiments and simulations. The literature study investi- gates laminar flames and instability mechanisms. Turbulent flames are studied and described with the Borghi diagram. The literature study ends with deto- nation deflagration transition (DDT). Experiments with hydrogen explosions in a 1 m. long and 97 mm. inner diameter transparent pipe with one open end and ignition at the closed end where conducted at Telemark University College. The pipe had one obstacle. The transparent pipe allowed high speed filming of the experiments and revealed inversion of the flame before it hit the obstacle, which confirmed earlier work. There was also a clear linkage between pressure waves reflecting of the obstacle and a halted propagation and inversion of the flame. An initiation mechanism of flame inversion caused by pressure waves prop- agating at di¤erent velocity in products and reactants is proposed. It is also proposed that pressure waves interacting with inverted flames collapse the in- version. CFD simulation, using an in house code, of the process of flame inversion was done and they reproduced the proposed mechanism. The simulations revealed that pressure waves propagating from reactants to products both inverted a convex flame and collapsed an inverted flame. A draft of a scientific paper is written on the topic of flame inversion and included in the appendix. The paper focus on the proposed mechanism and the simulations. Further work regarding hydrogen explosions in a pipe with a single obstacle is also proposed in the conclusion.