Under-expansion jet flame propagation characteristics of premixed H2/air in explosion venting

• Published in: International journal of hydrogen energy 2021-11, Vol.46 (78), p.38913-38922
• Main Authors: Cao, Weiguo, Zhou, Zhuanghong, Li, Wenjuan, Zhao, Yiming, Yang, Zhenxin, Zhang, Yun, Ouyang, Shin-Mei, Shu, Chi-Min, Tan, Yingxin
• Format: Article
• Language: English
• Subjects: Duct length; Hydrogen fraction; Hydrogen safety; Under-expansion structures; Venting diameter
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2021.09.109

In premixed H2/air explosion venting, an under-expansion jet may be caused by the pressure difference between the inside and outside of the explosion vent. Based upon the under-expansion jet, studying the structure of the under-expansion jet flame and the factors influencing its formation is essential to hydrogen safety in explosion venting. This study explored the basic characteristics of the under-expansion jet flame in premixed H2/air explosion venting, and discussed the formation of two under-expansion structures (Mach disk and diamond shock wave) of such jet flames by conducting a premixed H2/air explosion venting experiment. The influences of hydrogen fraction, explosion venting diameter, and duct length on the structure of under-expansion jet flames were evaluated. The results showed that after successful explosion venting, the under-expansion jet flame would be generated when the hydrogen fractions were 30–60 vol.%, and as the hydrogen fractions were 30–50 vol.%, the lengths of the venting duct were 30 and 50 cm. The duration of under-expansion jet flame was the longest when the hydrogen fraction was 40 vol.%. With the explosion venting diameter and hydrogen fraction increased, the spacing between under-expansion jet flame structures (S) increased. However, an increase in duct length led to the attenuation of the S. During the explosion venting, the under-expansion jet caused a pressure imbalance near the explosion vent and high-intensity convection forms on both sides of a jet, which can generate two or more explosions. Therefore, understanding the basic characteristics of under-expansion jet flame can aid the effective development of measures to prevent, mitigate, and protect against premixed H2/air explosions. [Display omitted] •Under-expansion jet flame structure was discussed in the explosion venting of H2/air.•The duration of under-expansion jet flame was the longest at 40 vol% hydrogen.•Spacing of the flame structure was reduced with the increase of the duct length.•Spacing of the flame structure raised as H2 fraction and venting diameter were added.