Detonation Length Scales for Fuel-Air Explosives

This paper reports on a series of large-scale field experiments performed to measure the critical tube diameters and detonation cell sizes for fuel-air mixtures. The results for ethylene-air reported previously are extended to include results for acetylene-, ethane-, propane- and methane-air for tube diameters up to 1.83 m. Detonation cell sizes of about 280 mm are obtained for stoichiometric methane-air mixtures. Based on the results of this investigation and results from other investigations, proposed relations between the critical initiation energy (Ec), the critical tube diameter (dc) and the detonation cell size (S), are examined. Although, the empirical relation dc = 13S appears to provide a good correlation for much of the data, the usefulness of this relation for predicting the detonation behavior in less sensitive fuel-air mixtures is questioned. For these less sensitive mixtures, the cellular structure is highly irregular with many modes of cellular patterns, so that the identification of a dominant mode is subject to considerable interpretation. The relations of the critical tube diameter, the cell size and the critical explosion