Experimental study of the coupling effects of ignition position and nitrogen inerting on vented hydrogen-air deflagrations
Kai Zhang, Jingui Wang, Jin Guo, Saifeng Du, Hao Chen, Hongyan Wang, Yiming Li, Rui Liu, Yezhe Yan, Shulei Gao
Abstract
In this paper, the flame evolution and pressure dynamics of hydrogen-nitrogen-air explosions with nitrogen addition ratio (χ) ranging from 0 to 40 %, ignited at three different positions (“central”, “back” or “front” with respect to the vent) in a vented cylindrical vessel , were experimentally studied. Experimental results reveal that the coupling effects of χ and ignition position significantly affect the pressure curves and flame behavior within and outside the vessel. The higher the χ, the smoother the internal flame captured by a high-speed schlieren system. When χ<30 %, the maximum reduced overpressure ( P max ) at different ignitions decreases with increasing χ, and the central explosion yields the best suppression of P max : when χ is increased from 0 to 30 %, P max monotonically decreases from 232 kPa to 38 kPa. However, the differences in P max among the three ignition positions become negligible when χ ≥ 30 %. The structure of the pressure peaks and the types of oscillations measured near the vent depend on the combinations of ignition location and χ. The formation of a shock wave generated by the external explosion and its effect on the internal pressure-time histories are described. In general, for a given ignition, the maximum external overpressure ( P e-max ) decreases with χ is increased. The most pronounced decreasing trend of P e-max is consistently observed in back explosions when χ ranging from 0 to 40 %. Furthermore, compared to other ignition positions, the highest P max is always attained in central-ignition with χ<30 %; while the highest P e-max is always attained in back-ignition with χ ≤ 30 %; as χ ≥ 10 %, both P max and P e-max recorded at front-ignitions are almost insensitive to χ.