Effect of expansion on spontaneous ignition of hydrogen jets
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2011
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Abstract
Spontaneous jet ignition, consisting of ignition during early, transient stages of gaseous fuel outflow, like hydrogen, due to a sudden rupture of a high pressure reservoir into atmosphere, was first observed by Wolanski and Wojcicki in 1973. The phenomenon clearly has an important role in hydrogen safety, increasing the risk of explosions. One potential explanation is that the combined effect of heat and mass diffusion at the contact surface, separating the expanded and cooled hydrogen from shocked hence compressed and heated air, leads to ignition. Experimental and numerical evidence shows that the size of the release opening is a crucial parameter with ignition being more likely for larger openings. The structures of the shock and contact surface are multi-dimensional which makes the numerical attempts limited to computational capabilities. However, for constant pressure and planar geometry this process was analyzed by Linan and Crespo in the limit of high activation energy for single step Arrhenius kinetics and unity Lewis number. In the current study, the analysis is extended to account for different fuel mass diffusivities and expansion due to evolution of the shock. The analysis shows that ignition can occur for fuels with higher mass diffusivity like hydrogen, with Lewis number less than unity, but that it does not occur for fuels such as hydrocarbons, with Lewis number greater than unity. In the former case, it also identifies a critical value for expansion, separating situations whereby ignition is inhibited from cases in which ignition will occur.
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Bibliography: p. 71-73
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Rezaeyan, N. (2011). Effect of expansion on spontaneous ignition of hydrogen jets (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/3970