Spherical deflagration

The extent to which a detonation will propagate from one experimental configuration into another determines the dynamic parameter called critical tube diameter. It has been found that if a planar detonation wave propagating in a circular tube emerges suddenly into an unconfined volume containing the same mixture, the planar wave will transform into a spherical wave if the tube diameter d exceeds a certain critical value dc (i.e., d > dc). II d < d.. the expansion waves will decouple the reaction zone from the shock, and a spherical deflagration wave results [6],... 

Fig. 9.9 Diagram of hydrogenous mixture spherical deflagration 1 - 5.23-m high hemi-sphere 2 - 0.46-m diameter tubes (obstacles)...

Fig. 9.11 Blast wave relative amplitude (a) and scaled positive impulse (b) resulting from a spherical deflagration in a stoichiometric HAM of different volumes with obstacles (points 0) and without them (points A and t) [7]...

Peak deflagration pressure in closed equipment is approximately eight times the initial absolute pressure, whetner atmospheric, subatmo-spheric, or elevated. This maximum pressure occurs at a concentration just slightly richer in fuel than the stoichiometric concentration for combustion in air icA as shown in Table 26-14 for propane and methane ... 

To overcome this problem, they proposed a working-fluid heat-addition model. This model implies that the gas dynamics are not computed on the basis of real values for heat of combustion and specific heat ratio of the combustion products, but on the basis of effective values. Effective values for the heat addition and product specific heat ratios were determined for six different stoichiometric fuel-air mixtures. Using this numerical model, Luckritz (1977) and Strehlow et al. (1979) systematically registered the properties of blast generated by spherical, constant-velocity deflagrations over a large range of flame speeds. 

Rarefaction waves are generated circumferentially at the tube as the detonation leaves then they propagate toward the tube axis, cool the shock-heated gases, and, consequently, increase the reaction induction time. This induced delay decouples the reaction zone from the shock and a deflagration persists. The tube diameter must be large enough so that a core near the tube axis is not quenched and this core can support the development of a spherical detonation wave. 

The Dynasafe static kiln is a near-spherical, armored, dual-walled high-alloy stainless steel detonation chamber (heated retort) inside a containment structure (Ohlson et al., 2004).18 The total thickness, including a safety layer, is 15 cm. The detonation chamber can operate in a pyrolytic or oxidizing environment. Intact munitions are indirectly heated by electrical resistance elements between the inner and outer walls of the detonation chamber. The munitions are heated to a temperature of 400°C-600°C, resulting in deflagration, detonation, or burning of the munition s explosive till. The chemical agent in the munition is destroyed as a result of the... 

With representative values for A, Cp, and po> and with Vq 50 cm/s, equation (4) gives d 10" cm. Therefore 5 is large compared with a molecular mean free path (about 10 cm), and the continum equations of fluid dynamics are valid within the deflagration wave but 6 is small compared with typical dimensions of experimental equipment (for example, the diameter of the burner mouth, and hence the radius of curvature of the flame cone, for experiments with Bunsen-type burners), and laminar deflagration waves may be approximated as discontinuities in many experiments. Since equations (3) and (4) imply that b at constant temperature, experimental studies of the interiors of laminar flames are often performed at subatmo-spheric pressures. 

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