Sprays deflagrations

FIGURE 11.6. Rough schematic diagram of model of spray deflagration. 

For typical hydrocarbon sprays in air, v and by using B 10 and Pilpf 10, we find that equation (115) becomes (/> > 0.7. Although there are a number of inaccuracies here, for example, associated with the use of equation (3-63), it may be concluded that stoichiometric hydrocarbon sprays in air may be expected to experience at least some cloud-burning effects. Analyses of spray deflagrations with droplet-group burning have not been pursued. 

The presentation of the subject of spray combustion in Chapter 11 is not greatly different from that in the first edition. An updated outlook on the subject has been provided, and the formulation has been generalized to admit time dependences in the conservation equations. The analysis of spray deflagration has been abbreviated, and qualitative aspects of the results therefrom have been anticipated on the basis of simplified physical reasoning. In addition, brief discussions of the topics of spray penetration and of cloud combustion have been added. 

The maximum and minimum concentrations of a gas, vapor, mist, spray, or dust in the air or other gaseous oxidant for a stable detonation to occur are the so-called upper and lower detonation limits. These limits depend on the size and geometry of the surroundings as well as other factors. Therefore, detonation limits found in the literature should be used with caution. Detonation limits are sometimes confused with deflagration limits and the term explosive limits is then used inconsiderately [40]. 

Of the approximately 12 motion pictures we made of the impact initiation process, all show that the structure of the air bubble is broken down and replaced by a turbulence area. Ignition occurs at the former site of the bubble after an induction period. The compression ratio of the air bubble appears to be the major factor determining probability of initiation by impact. The mechanism for impact initiation of nitroglycerin therefore appears to be a quasi-adiabatic compression of the gas, with heat transfer accelerated by spray formation. Hot spots formed at the former site of the bubble undergo an accelerating exothermic reaction which proceeds to a deflagration. The possibility that liquid explosives under reduced pressure may be sensitized to weak impacts must be considered. 

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