Flame propagation regimes at cryogenic temperature

In the frame of the PRESLHY project more than 100 experiments on hydrogen – air flame propagation regimes in a shock tube at cryogenic temperatures were made with the combustion tube at the KIT HYKA test site. More than half of the experiments were made at cryogenic temperatures (between approx. 90 K and 130 K). The rest experiments were conducted at ambient conditions as the reference data. It was however possible to provide experimental data at various H2 concentrations from 8 to 60 Vol. %H2 and 3 blockage ratios (BR = 0, 0.3 and 0.6). During the course of the experiments, many experimental difficulties and peculiarities specific for cryogenic temperatures were encountered. Critical conditions for flame acceleration to the speed of sound and to the detonation onset at cryo-temperatures were experimentally found. It was also found that the danger of hydrogen combustion and explosion in terms of maximum combustion pressure is much higher than at ambient temperatures because of several times higher density of the combusted substance. Then, even for sonic deflagration at cryogenic temperatures, the maximum pressure might be higher than the detonation pressure at ambient conditions. The data obtained in current work can be used for safety distance assessment for LH2 safety applications.