Experimental Study on Duct-Vented Explosion of Hydrogen–Air Mixtures in a Wide Range of Equivalence Ratio

Abstract

A relief duct is often used for indoor vented enclosures to discharge unburnt and burnt gas mixtures to outdoors, but its use can significantly affect pressure relief and flame behavior. In the current paper, duct-vented explosions of hydrogen−air mixtures with equivalence ratios ranging from 0.8 to 4.0 were experimentally investigated in a small cylindrical vessel with a 50-cmlong relief duct. Different from "coherent deflagration" as previously reported, the maximum pressure rise rate in the duct is always larger than that in the vessel. Three pressure peaks can be identified on the external pressure profile, which result from the burst of the vent cover, the burn-up in the duct, and the external explosion, respectively. Whether the second or the third pressure peak is the dominant one depends on the hydrogen equivalence ratio. Compared with simple vented explosions, the use of a relief duct decreases the pressure relief efficiency and the external flame size for all equivalence ratios tested.

Duct-vented hydrogen–air deflagrations: The effect of duct length and hydrogen concentration

“…It was found that explosion overpressure increased with an increase in hydrogen concentration. Vented explosion of hydrogen air mixtures through a 0.5-m-long duct was investigated and it was found that the use of the relief duct significantly increased the explosion overpressure compared with the cases without the duct for hydrogen concentration ranging from lean to rich [25]. The experiments on explosion venting of hydrogen-air mixtures from a 1.5-m-long duct to a vented cylindrical vessel showed that maximum reduced overpressure first increased and then decreased with an increase in hydrogen concentration [26].…”

“…Apart from the previous investigations on duct-vented explosion of hydrogen-air mixtures [21,24,25], one of the most important issue has not been studied yet: how does the length of relief duct affect explosion venting? Because in the previous research [21,24,25], relief ducts with fixed length were used.…”

“…Apart from the previous investigations on duct-vented explosion of hydrogen-air mixtures [21,24,25], one of the most important issue has not been studied yet: how does the length of relief duct affect explosion venting? Because in the previous research [21,24,25], relief ducts with fixed length were used. To answer the question, relief ducts of different length were used in this study to investigate the pressure buildup and flow field within and outside the vented enclosure during explosion venting of hydrogen air mixtures with concentration ranging from 20% to 55%.…”

“…The venting enclosure consisted of a 12.3 l cylindrical vessel and relief ducts 7 × 7 cm in cross-section with different lengths. Details of the test enclosure can be found in our previous study [25]. The flame images in the vessel and duct were captured by a high-speed Schlieren system at a frequency of 30000 Hz.…”

“…4(a); therefore, unburned hydrogen air mixtures were first vented and mixed turbulently with the air in the duct to form combustible gas mixtures with high turbulence levels. The violent burn-up in the duct was triggered when the flame propagated into the duct as shown in Fig.4(b), and transient higher overpressure in the duct was reached as a result [8, 16,25]. After that, the overpressure in vessel increased continuously to its maximum value and then decreased.…”