A hydrogen deflagration-jet flame coupled behavior in a ventilated confined space: Effects of ventilation area and leakage duration

Abstract

Non-uniform hydrogen deflagrations were experimentally conducted in a ceiling ventilated chamber considering the effects of ventilation area A_v and leakage duration t_ig. Two new coupled flame behaviors are observed. The first type of coupled flame structure involves the non-growing conical flame bubbles and jet flames, while the second type involves the growing ellipsoid flame bubbles and jet flames. A decrease in A_v or an increase in t_ig promotes the evolution of first type of coupled flame behavior into the second type. The horizontal propagation of deflagration flames can be divided into three typical stages and the horizontal flame front undergoes a gradual decrease in speed and then a slight acceleration. The overpressure transient exhibits a double peak structure in under-ventilated cases. The overpressure peak P₁ is induced by the coupled upward propagation of jet flames and initial flame bubbles. The overpressure peak P₂ is related to the coupled flame behavior involving jet flame combustion and flame bubble expansion. The maximum overpressure and maximum pressure rise rate show a sharp upward trend as the first type of coupled flame structure evolves into the second type.