Work package five of the PRESLHY project focusses on the combustion phenomena of liquid hydrogen (LH 2 ). The experimental programme was designed to provide insight into a number of credible and poorly understood LH 2 combustion scenarios. One such scenario is the effect of congestion or confinement on an ignited hydrogen cloud stemming from a release of LH 2 , potentially leading to deflagration to detonation transition (DDT). This report summarises the large-scale experiments carried out at the HSE Science and Research Centre in Buxton investigating the effect of differing levels of congestion and confinement on the combustion properties of a hydrogen cloud developing from a release of LH2. Various combustion parameters were measured, including; the overpressure, heat flux, and noise. Monitoring of ambient and release conditions were also made to allow for a thorough analysis of the results. A total of 23 ignited trials were completed and involved releasing LH2 using the same initial conditions as in the rainout experiments of work package 3, meaning that the dispersion patterns should remain similar. The congestion and confinement was created by a configurable steel structure placed directly in the path of the release. Two congestion levels, confinement and pool experiments were planned, however due to the safe noise level being reached, only the congestion experiments were completed. To compensate for this, multiple repeats and experiments with a wide variety of source conditions were conducted. From the results, it is clear that higher levels of volumetric congestion increases the measured overpressures in releases with the same initial conditions. The results also show that an increasing hydrogen inventory, either through an increased release pressure or larger nozzle, can result in a larger event upon ignition. However, the mixing of the jet also plays a part; some releases through the largest release orifice diameter showed lower overpressures potentially due to the hydrogen cloud being too rich. It was observed that the ambient conditions, in particular the wind speed and direction, were a significant factor in the outcome of each ignition. This was particularly prominent in trials 21 to 23.

file consists of data from following sensors, obtained during experiments: • blast pressure sensor • noise sensor • heat flux sensor • pipework thermocouples • pressure sensor • mass flow sensor • near-field weather station • far-field wind sensor • far-field humidity sensor and videos getted during experiments