Large-scale hydrogen deflagrations and detonations

Large-scale deflagration and detonation experiments of hydrogen and air mixtures provide fundamental data needed to address accident scenarios and to help in the evaluation and validation of numerical models such as the AutoReaGas code (used by Mitsubishi Heavy Industries, Ltd). Several different experiments of this type were performed. Measurements included flame-front time of arrival (TOA) using ionization probes, blast pressure, heat flux, high-speed video, standard video, and infrared video. The large-scale open-space tests used a hemispherical 300-m(3) facility that confined the mixture within a thin plastic tent that was cut prior to initiation of a deflagration. Initial homogeneous hydrogen concentrations varied from 15% (similar to 3.7 kg) to 30% (similar to 7.3 kg). An array of large cylindrical obstacles was placed within the mixture for some experiments to explore turbulent enhancement of the combustion using objects similar in scale to what might be found at a refuelling station. All tests were ignited at the bottom center of the facility using either a spark or, in one case, a small quantity of high explosive to generate a detonation. Spark-initiated deflagration tests were performed in a 1/5-scale tunnel using homogeneous hydrogen mixtures to compare against similar tests performed in the open space. Several experiments performed in the 1/5-scale tunnel released 0.1 and 2.2 kg of hydrogen into the tunnel with and without ventilation to represent, respectively, a release from a fuel cell vehicle or the storage cylinder on a hydrogen transport. For some tunnel tests, obstacles representing vehicles were used to investigate turbulent enhancement. A test was performed to investigate any enhancement of the deflagration due to partial confinement produced by a narrow gap between aluminum plates, similar to gaps that might be found between equipment in a hydrogen processing facility or refuelling station. The attenuation of a blast wave was investigated using a 4-m-tall protective blast wall, such as that which might be placed around a hydrogen production facility, storage yard, or refuelling station to protect surrounding structures. Finally, a large-scale hydrogen jet experiment was performed in which 27 kg of hydrogen was released vertically into the open atmosphere in a period of about 30 s to simulate the bursting of interconnecting piping between large high-pressure storage tanks. The hydrogen plume spontaneously ignited early in the release. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.