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

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-cm-long 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.