Effect of distance between ignition location and window on indoor gas explosion development

Introduction. It has been previously known that for gas explosions in an unconfined chamber the following rule applies: the larger the distance between gas ignition location and relief opening (window), the higher the explosion pressure. This statement is based on results obtained by a number of researchers, including ourselves. However, as demonstrated by recent physical experiments, it is valid only for window sizes comparable to those recommended by guidelines to ensure certain safety conditions. For smaller window sizes, this relationship is leveled out or even changes its sign.

Research objective is to determine the cause of inversed relationship between distance from the window to ignition location and explosion pressure. Tackling this objective is of scientific and practical importance.

Research methods and tools. Two mathematical model variants for gas explosion development in an unconfined chamber were employed to study the revealed phenomenon, i. e. simplified model and numerical model. The first one, i. e. simplified model, is based on chamber representation as lumped volume, and using the Clapeyron equation in differential form. It was obtained that besides known factors, such as window size, properties of outflowing gases, etc., explosion development is influenced by the area of flame front and the time when it approaches the window. Unfortunately, this model does not take into account the dynamics of last factors development altogether. This task can be handled by the other model, numerical, implemented in Vulkan-M software. It is based on solving the gas dynamics equation system using large-particle method in Eulerian representation with added flame propagation conditions. Besides, Vulkan-M can visualize the physical process evolution, as well as record how its parameters and indicators develop.

Research results. It was found that if the window size is comparable to regulatory values, such a strong influence of window position on pressure is due not only to the difference of out flowing gas properties (initial mixture and combustion products), but also dueto the factthatin the initial period of explosion development the flame front area is much larger for a further removed window than in case of a small distance between the window and ignition location. For a smaller window, the pressure increase rate in the initial period is high and almost identical for both explosion scenarios. Therefore, combustion time becomes decisive for the maximum pressure value. If the window is located far from the ignition, combustion time is shorter than in case of a smaller distance. As a result, maximum pressure in the second case is higher than in the first case. This explains the revealed phenomenon.

Conclusion. The larger the window size, the stronger it affects the explosion pressure. This influence is determined not only by gas outflow, but it intensifies, sometimes significantly, due to the influence on flame front development. If the window size is decreased, its influence on flame front development is weakened and becomes negligible. In this case, the explosion pressure is affected by combustion time, besides window size.

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