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. 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-m3 facility that confined the mixture within a thin plastic tent that was cut prior to initiating a deflagration. Initial homogeneous hydrogen concentrations varied from 15% to 30%. An array of large cylindrical obstacles was placed within the mixture for some experiments to explore turbulent enhancement of the combustion. 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 within the tunnel using homogeneous hydrogen mixtures. Several experiments were performed in which 0.1 kg and 2.2 kg of hydrogen were released into the tunnel with and without ventilation. 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 aluminium plates. The attenuation of a blast wave was investigated using a 4-m-tall protective blast wall. 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 seconds. The hydrogen plume spontaneously ignited early in the release.