Explosion and flame characteristics of methane/air mixtures in a large‐scale vessel

Abstract

In this study, experiments of explosions and flame characteristics in methane/air mixtures are performed in a 10-m 3 vessel. Pressure gauges and a high-speed camera are utilized to record the pressure trajectories and the flame propagation process of ignition growth. The experimental results show that the maximum value of overpressure and the maximum rate of the explosion pressure rise are 0.596 MPa and 1.82 MPa/s for the methane (9.5% in volume)/air mixture at atmospheric conditions, respectively. Both values are higher than for other mixtures with different compositions. The results also indicate that the overpressure from the large-scale vessel in this study is lower than that of a smaller apparatus (e.g., 5-L closed cylindrical vessel). This difference occurs due to the cooling effect and because the reflected sonic disturbances by the vessel wall affect the explosion process and weaken the energy during the pressure attenuation stage, thus rendering the value of overpressure in the large-scale apparatus lower than in the tiny cylindrical vessels. The maximum overpressure is observed at 0.75 m for C 5 7% ("C" means the methane concentration) and 9.5% but at 1.3 m for C 5 5%, 6.5%, 11.2%, and 13%. These results indicate that methane/air is an easier means to generate overpressure and that the overpressure is higher near the stoichiometric condition. Based on the analysis of the flame propagation process, the mean value of the flame speed of methane (C 5 9.5%)/air is calculated to be approximately 2.43 m/s because the nonuniformity of the chemical reaction at the flame front results in a maximum fluctuation of flame speed of approximately 28.5%. The flame thickness (u) of methane (C 5 9.5%)/air fluctuates between 9.84 and 10.95 mm, with a mean value of 10.53 mm.

Explosion behavior of methane–dimethyl ether/air mixtures

“…It is noteworthy that the flammability limits for the CH 4 -air mixture obtained in this study agree well with the result published in a previous study (4.9% and 15.9%) [42]. For the DME-air mixture, Mogi et al [43] reported that the flammability limits were 4% and 13% obtained using an explosion vessel with an internal volume of 180 L. A noticeable discrepancy is thus found on the rich limit, and the size of the chamber appears to be an influencing factor on the flammability limits, as argued by Zhang et al [44]. This difference may be explained by the fact that in the small-scale apparatus, acoustic disturbance reflected from the chamber wall may generate turbulent fluctuations facilitating the flame propagation, hence prolonging the explosion limit.…”

The effect of an obstacle on methane-air explosions in a spherical vessel connected to a pipeline

“…When the gas mixture enters the relatively narrow pipeline, pressure waves develop causing a pressure increase (as seen from the solid lines in Figures and ). A wide, low velocity pressure wave will change into a narrow, fast pressure wave when it encounters a constriction, along with some energy loss . During the explosion process, the pressure wave in both the vessel and in the pipeline encounter the reflected wave from the other side, causing the waves to oscillate back and forth.…”

Effects of argon/nitrogen dilution on explosion and combustion characteristics of dimethyl ether–air mixtures

“…High-voltage electric spark was used to supply ignition energy as in previous studies [39][40][41][42][43][44][45][46]. The igniter was mounted at the center of the spherical bomb and a spark energy of 10 J, estimated from 1/2 CU 2 (''C'' and ''U'' refer the capacitance and voltage, respectively.…”