PRESLHY_D5_5_Combustion-Tube_210319_DM_MK_SJ_JW_reviewed

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 conducted with the
combustion tube at the KIT HYKA test site. More than half of the experiments were carried out
at cryogenic temperatures (between approx. 80 K and 130 K). The rest of the tests 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 were experimentally identified for
hydrogen-air mixtures at cryo-temperatures. The critical expansion ratio and detonation cell sizes
as function of temperature were experimentally measured for hydrogen-air mixtures. It was also
found that the danger of hydrogen combustion and explosion in terms of maximum combustion
pressure is 2-3 times 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.