Buoyancy effects on combustion products from high-pressure hydrogen jet flames

Due to the lower radiative fraction and typically higher storage pressures, gas temperatures can often result in longer safety distances compared to radiative heat transfer for hydrogen jet flames. The high temperatures, however, also lead to a low density causing the flow to rise at a certain distance from the release. Unfortunately, a model to determine this distance, similar to what is available for unignited releases, is currently not available which this paper aim to provide. An experimental study was conducted investigating the buoyancy effect on ignited horizontal hydrogen jet releases with different release diameters. The invisible hydrogen plume was visualized using a Background Oriented Schlieren technique (BOS). The transition of the initial momentum-driven jet into a fully buoyancy-driven jet was estimated by following the gradient of the centerline of the plume. A model based on the Froude number of the release similar to the model for unignited releases was developed and the distance showed a very similar dependence on the Froude number, but giving consistently approximately 39% shorter distances.