Supersonic Combustion Wave Propagation in an Obstructed Volume of Hydrogen

Abstract

As the use of hydrogen as an energy carrier becomes more prevalent, deep knowledge of its combustion characteristics are required to protect personnel and property in the vicinity of its use. This knowledge is also important for new and novel applications of this carbon-free fuel in the transportation, home energy, grid storage, and gas generation markets. An atmospheric release of gas, even in small quantities due to its wide flammability range, can be ignited by a low energy source. Acceleration of the flame in the presence of obstructions can lead to supersonic combustion and transition to detonation. This work, consisting of six related studies presented in manuscript format, focuses on the combustion wave propagation characteristics of hydrogen in obstructed environments, such as those typically encountered in accidental release scenarios. Specific focus is directed to four areas linked to supersonic combustion: the role of shock reflections, the development of an unobtrusive low-cost diagnostic for detonations, leveraging simultaneous and multi-axis diagnostic techniques, and the role of three-dimensional behaviour. The cyclic nature of quasi-detonation propagation in an obstructed channel, consisting of gas transition from deflagration to detonation and back, is investigated using high-speed schlieren photography and a simultaneous soot-foil technique to couple the physical record of the combustion wave with the temporal record. This allows for the identification of key shock reflection processes, and how they couple to each other in the propagation mechanism. The impact of channel width on wave behaviour revealed a new continuous detonation mechanism supported by obstructions but not involving more common shock ignition. Numerical investigation of the prevalent shock reflection ignition at an obstacle was used to determine the critical incident condition required for direct detonation (strong) ignition at typical quasi-detonation conditions.