An experimental investigation of the initiation, transition and quasi-steady propagation of blast initiated cylindrical detonations in Methyl Acetylene, Propane, Prodadiene (MAPP)-air mixtures is described. A sectored shock tube was employed which was originally designed to allow study of cylindrical shock, and homogeneous and heterogeneous detonation waves. Cylindrical blast waves were generated by firing of controlled amounts of a condensed explosive at the apex of the sector. Experimental data served to suggest the existence of three wave propagation regimes: subcritical energy regime, where decoupling of shock and reaction zone results in a reacting blast wave-type decay; the critical energy regime, where decoupling occurs but is followed by the re-establishment of a sub-Chapman-Jouguet condition, with an asymptotic strengthening to the C J state; and supercritical energy regime, where the initially overdriven detonation decays asymptotically to its CJ state. Threshold energy levels delineating the subcritical to critical energy regimes were established for a wide range of MAPP-air mixtures. Lean and rich limits for steady propagating detonation waves were also established. Comparisons made with the work of others reveal that these limits do not suffer from scale effects. The detonation velocity, when attained, displayed a definite dependence on blast wave energy with the higher energy runs giving reasonable agreement with theory. The measured transition distances from blast to detonation wave, nondimensionalized by the blast wave explosion length, compared satisfactorily with theoretical predictions.

A simplified theory of blast initiation of detonations in clouds of fuel in gaseous or droplet form is developed and agrees with the experiments described below. The flow is at first dominated by the strong blast wave but transition from blast to detonation behavior occurs near a critical radius r. where the blast energy and the heat of combustion contained in r < r. are equal. The complex flow in this transition region cannot be determined analytically. In the simplified theory the details of the transition region are ignored but the flow is represented by the self-similar solution for a strong blast wave for r < r. and by the self-similar detonation solution for r > r.. The development of a sectored shock tube to study cylindrical shock waves and two-phase detonations is described. Data are presented for shock waves as well as for blast initiated detonations of a monodisperse spray of 400/t kerosene droplets in air at standard conditions. Two regimes of propagation were established experimentally: (1) the subcritical energy regime, where decoupling of shock and reaction zone results in a strong blast wave type decay and, (2) the supercritical energy regime, where the initially overdriven cylindrical detonation decays, at some critical radius, to its Chapman-Jouguet state. Experimentally determined critical radii and steady-state detonation velocity agree very well with theoretical predictions. Detonation velocity was found to be constant at the plane C-J value for radius greater than the critical radius.

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problem, mainly because of the increased size of these spills. Further, there has been interest in deliberate fuel-air explosions wherein a liquid or gaseous fuel is dispersed throughout a volume of