Abstract
This doctoral study investigates and closes several knowledge gaps in hydrogen safety engineering. The knowledge generated is particularly applicable for the safe employment of high-pressure hydrogen tanks in confined or indoor environments. A Computational Fluid Dynamics (CFD) model was developed and validated against experiments to reproduce hydrogen flame stability limits and applied to demonstrate a safer TPRD design.A hydrogen jet fire will become unstable over a certain range of pressure during tank blowdown. When a hydrogen jet fire approaches the blow-out velocity at a certain pressure depending on the nozzle diameter, it becomes unstable, and blow-out occurs. This phenomenon could lead to hydrogen accumulation in an indoor or confined space. A flammable hydrogen cloud may form increasing the risk of an explosion. This work demonstrates a method of avoiding this.
A numerical approach was applied in this study to reproduce hydrogen flame stability limits measured experimentally by Mogi and Horiguchi (2009). The hydrogen critical diameter which is the minimum diameter size through which flame would be stable at any pressures, was predicted numerically for the first time. The hydrogen critical diameter was predicted as 1 mm in line with experiments (Mogi and Horiguchi, 2009, Yamamoto et al. 2018).
A novelty of the study is the numerical prediction of the limits for attached hydrogen flames. A two-part nozzle which called a “double-diameter nozzle” was introduced and demonstrated as a safer TPRD design. The design eliminates of blow-out at any pressures. The dynamic behaviour of a hydrogen flame during tank blowdown in a real-like scenario was modelled. Finally, steps were made to extend the model making it applicable to other fuels specifically methane. Methane flame characteristics were successfully reproduced numerically, and the methane critical diameter was predicted as 42 mm, in line with experimental studies (McCaffrey and Evans, 1988).
Thesis embargoed until 30 September 2026
Date of Award | Sept 2024 |
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Original language | English |
Supervisor | Vladimir Molkov (Supervisor) & Sile Brennan (Supervisor) |
Keywords
- CFD
- hydrogen safety
- critical diameter
- lift-off
- blow-out
- flame length
- flame width
- under-expanded jets
- jet fire
- blowdown
- attached flame
- methane flame
- flame stability