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Gas explosions in obstructed vessels have been investigated for many years. However, the flame acceleration mechanism of enriched-hydrogen fuels with diluents in the piping system has received little systematic study in the literature. This particular study aimed to analyse the flame front mechanism of hydrogen-diluents/air explosion inside the pipe by considering the influence of tee junction distance from the ignition points. The tests were performed using H 2 /diluents-air at different concentrations and ignition positions, in two different tee junction pipe configurations. From the results, the worst case of explosion severity was found in 95% H 2 –2.5% Ar–2.5% N 2 /air for all ignition positions. In general, if ignition happened at the tee junction, the overpressure and rate of pressure rise profiles showed almost a similar trend on both configurations. Similar trend was also observed for the flame flow characteristic analysis. Overall, it was clearly demonstrated that a shorter distance between ignition point and obstacles resulted in higher explosion severity. [ABSTRACT FROM AUTHOR]

Hydrogen is a promising fuel for the future. In recent years it has been successfully utilised in industries, particularly in refineries and petrochemicals. In previous studies, the effect of inhibitors on hydrogen explosion behaviour has been investigated in different systems, yet only scarce data are available. Therefore, experimental study is carried out to investigate the effects of argon, nitrogen and carbon dioxide on hydrogen/air explosion in a branched pipe configuration. The fuel/air mixtures were ignited at three different ignition positions, A, B and D. The results show that, when ignited at the furthest distance (position A), the tee junction area is most vulnerable to the critical pressure impact of gas explosion. However, no similar trend was observed at the other ignition positions. In addition, mixtures with the compositions 95% H 2 –2.5% Ar–2.5% N 2 /air, 95% H 2 –5% N 2 /air, H 2 /air and 95% H 2 –5% Ar/air showed higher risks due to the higher diffusivity ratio and the associated rate of pressure rise. This phenomenon is highlighted in the discussion part of this paper. The results show that mixtures with CO 2 lead to lower severity than other compositions (∼50% reduction), as the average recorded maximum flame speed for this particular mixture was lower at all of the ignition points. This suggests that the effectiveness of the inhibitors should be in the order of Ar < N 2 < CO 2 . [ABSTRACT FROM AUTHOR]