“Abstract

Hydrogen is stored at high pressure making discharge a safety concern, including flame stability issue. Previous studies were focused on circular nozzles. However, actual incidents are more likely to involve slit-shaped openings. The experiments on hydrogen release from non-circular openings were conducted for nozzle cross-sectional areas equal to circular orifices of diameters 0.5, 0.6, 0.8 mm, with aspect ratios for rectangular orifices 1, 2, 4, 6, 8. For rectangular nozzles, expansion waves are generated from the corners in addition to those originating from the nozzle lip. These waves interfere causing an “axis-switching” phenomenon and formation of octagonal Mach disk, producing jet with wider velocity boundary, thus greater air entrainment and consequently 10–30 % shorter flame length. The lift-off length for rectangular openings, i.e. 10-15 mm was approximately half that of circular nozzles. The experimental and numerical study of non-combusting jet shed light on the flame stabilisation mechanism for rectangular nozzles identified as internal flame retention, i.e. anchoring the flame base at low-velocity region at the root of the cross-shaped velocity and hydrogen concentration distributions.”

 

Keiji Takeno, Makoto Asahara, Koichi Kajino, Ito, D., Mizuno, Y., Volodymyr Shentsov, Kazemi, M., Makarov, D. and Vladimir Molkov (2025). Hydrogen jet flame stabilisation mechanism for square and rectangular openings: Internal flame retention. International Journal of Hydrogen Energy, 202, pp.152934–152934. doi:https://doi.org/10.1016/j.ijhydene.2025.152934.

The full report is accessible via: https://doi.org/10.1016/j.ijhydene.2025.152934

 

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