Sustained Hydrogen Leak Concentration in Enclosure with One Vent

Abstract

The phenomenon of hydrogen jet flame self-extinction in an enclosure with one vent is simulated numerically for the first time. The eddy dissipation concept model of combustion with a full chemistry scheme is applied along with the renormalization group theory for turbulence modelling within RANS approach. The analysis of temporary profiles of temperature and species (hydrogen, oxygen, hydroxyl, water) concentrations in the numerical experiment, as well as velocity through the vent, shed a light on the dynamics of under-ventilated hydrogen fire the self-extinction process in the enclosure with one horizontal vent located under the ceiling. The self-extinction is a process rather than an instance. The analysis of under-ventilated fire based on parameters averaged throughout the enclosure can give a good indication of the moment when combustion essentially reduces due to lack of oxygen, yet it can mislead in interpretation of the moment when combustion is fully ceased. It is shown that the pressure peaking phenomenon is more pronounced for jet fire compared to unignited release from the same source (by factor 100 in this particular experiment, i.e. about 300 Pa and 3 Pa respectively). The separation distances from the enclosure are estimated for this indoor fire scenario. The maximum length of hot gases jet escaping the enclosure was about twice of the enclosure size. The simulations demonstrated a complex flow dynamics through the vent in both directions during the self-extinction process. This is thought due to the interaction between processes of sustained hydrogen leak, combustion, and heat transfer to the enclosure walls. The separation distances from the enclosure are estimated for indoor fire scenario.