Study on the deflagrations of NH3/H2/air in an end-open duct: Effects of ignition position and hydrogen fraction

• Published in: International journal of hydrogen energy 2024-03, Vol.60, p.55-65
• Main Authors: Huang, Shikai, Guo, Jin, Mei, Liang, Yang, Zexuan
• Format: Article
• Language: English
• Subjects: Flame; Ignition position; NH3/H2/air deflagration; Overpressure; Pressure oscillation
• ISSN: 0360-3199
• DOI: 10.1016/j.ijhydene.2024.02.115

In this study, experiments were conducted in a 1 m-long horizontal rectangular duct at an initial temperature of 285 K and an initial pressure of 100 kPa to investigate the influence of ignition position and hydrogen fraction (χ) on the vented deflagration of NH3/H2/air. A range of χ from 0.1 to 0.9, as well as three ignition positions, including FI (front ignition), CI (central ignition), and RI (rear ignition), were employed. It was indicated that the ignition position and χ remarkably influenced on the overpressure accumulation and flame evolution inside and outside the duct. With χ increasing from 0.1 to 0.9, the maximum explosion overpressure (pmax) and the maximum external overpressure increased with χ at three ignition positions. As χ increased from 0.1 to 0.9, pmax increased from 7 kPa to 22 kPa at FI, from 13 kPa to 50 kPa at CI, and from 13 kPa to 33 kPa at RI. With χ increasing from 0.1 to 0.9, the maximum external overpressure increased from 0.15 kPa to 4 kPa in the case of FI, from 0.43 kPa to 16.36 kPa in the case of CI, and from 1 kPa to 35.58 kPa in the case of RI. Left flame front deformation owing to R-T instability was found and was the most severe at FI. In rear ignition explosions, the flame always propagates toward the opening end as χ > 0.5, but when χ ≤ 0.5, the flame front may transiently move away from the opening. In the case of RI, the shape of the external combustible cloud transferred from a “mushroom” to a “dumbbell” as χ increased from 0.5 to 0.9. Two types of oscillations (Helmholtz-type and acoustic oscillations) could be found. As χ increased from 0.3 to 0.7, the Helmholtz-type oscillations could be easily distinguished in the cases of FI and CI. As χ increased from 0.3 to 0.7, the frequency of Helmholtz-type oscillations increased from 125 Hz at χ = 0.3–140 Hz at χ = 0.5–150 Hz at χ = 0.7 in the case of FI and from 135 Hz at χ = 0.3–160 Hz at χ = 0.5–170 Hz at χ = 0.7 in the case of CI. Acoustic oscillations could only be observed in tests with χ ≥ 0.7 and were the most intense when χ = 0.7. •Both pmax and maximum external overpressure increase with χ.•Acoustic oscillations can only be observed in tests with χ ≥ 0.7.•Left flame front deformation is the most severe in the case of FI.•Two fireballs form downstream of the opening at χ = 0.5 and 0.7 at RI.