Experimental study of self-extinguishing behavior of hydrogen jet fires in the confined space with a ceiling vent

Abstract

With the widespread utilization of hydrogen energy, the hydrogen safety issues, especially hydrogen jet fires, should be much paid attention to, since the latter present high temperature and radiation in confined space. Hydrogen jet fire experiments were conducted with various release rates and vent sizes in a confined space with ceiling vent to investigate the hydrogen jet flame height, oxygen concentration, and self-extinguishing time. The results show that, the large vent sizes with low hydrogen release rates result in well-ventilated hydrogen jet fires. As the vent size decreases or the hydrogen release rate increases, the hydrogen jet flame evolves from a well-ventilated one to one having self-extinguishing behavior with under-ventilation. The combustion process can be divided into four stages: the growth stage, the quasi-steady stage, the stretch stage and the self-extinguishing stage. The flame height increases with the hydrogen release rate at the quasi-steady stage, and the vent size has almost no effect. However, in the case of under-ventilation, the flame height at the stretch stage is determined by the joint actions of vent size and hydrogen release rate, and the flame height is positively connected with the size of the ceiling vent. The oxygen concentration and self-extinguishing time decrease dramatically as the vent size and hydrogen release rate increase. The parameter Q˙VA1/3 is proposed to reflect the coupling effects of hydrogen release rate and vent size, and the correlations of oxygen concentration and self-extinguishing time are determined with Q˙VA1/3.