Deflagration, defined

Pre-Volume Vessel A process vessel or piping system (length to diameter ratio of less than 5) in which a confined deflagration occurs (as defined in CEN Standard EN 12874). 

A considerable amount of research has been conducted on the decomposition and deflagration of ammonium perchlorate with and without additives. The normal thermal decomposition of pure ammonium perchlorate involves, simultaneously, an endothermic dissociative sublimation of the mosaic crystals to gaseous perchloric acid and ammonia and an exothermic solid-phase decomposition of the intermosaic material. Although not much is presently known about the nature of the solid-phase reactions, investigations at subatmospheric and atmospheric pressures have provided some information on possible mechanisms. When ammonium perchlorate is heated, there are three competing reactions which can be defined (1) the low-temperature reaction, (2) the high-temperature reaction, and (3) sublimation (B9). 

In accordance with the usual convention, we define a detonation as a reaction traveUing faster than the local speed of sound in the unreacted medium, and a deflagration as being a reaction travelling at or slower than the local speed of sound in the unreacted medium. An example of each type of event is given below ... 

Kistiakowsky (Ref 1) suggested that for the success of detonation by impact two sets of conditions must be met a) A hot spot, as defined by Bowden, must be first produced and b) The initial deflagration must be given the opportunity to develop and to produce a shock wave within the minute charge and the short time defined by the usual conditions of explns by impact (See also Ref 3) Refs 1) G.B. Kistiakowsky, p 565 in the 6thSympCombstn (1957) 2) Cook (1958),... 

The eq in this form is valid for a detonation and a deflagration, as well as for shock wave, if e and h.are defined in the usual sense To apply this eq to explosions, however, some authors add a term Q to represent chemical energy per unit mass, and write ... 

Until now we have studiously avoided defining what constitutes an explosion or go result in an impact test, except mentioning that go s are judged on the basis of sound, flash, gas volume etc. What physical events produce these observed manifestations Based primarily on the studies of Bowden (Ref 2) it is clear that in an impact test explosion frequently starts as a relatively mild deflagration which can propagate as slowly as lOm/sec, which turns into a much more violent deflagration, (lOO-lOOOm/sec), in the confined (by striker anvil) explosive. For many insensitive explo-... 

Fuses may be defined as tube- or cordlike containers filled with deflagrating or de tonating materials. Both the outer sheathing material and the weigh and type of expls contd will depend upon the required usage... 

Cybulski s [48] extensive investigations in coal and rock have also solved the problem of the double detonation. It is now known that the deflagration of an explosive in the shothole may pass into detonation after a certain time. This occurs with particular ease in nitroglycerine explosives. The results of Cybulski s studies [48] are now taken into consideration in Poland in defining which explosives may be used in mining. 

Muraour et al(Ref 5,p 273) define "potentiel apparent" as the heat of explosion or deflagration, as detd in a calorimetric bomb at const vol either, in vacuum or in inert atmosphere. This differs from chaieur de combustion" (heat of combustion) which is detd in the bomb in the presence or an excess of compressed oxygen. In the opinion of Muraour et al, it is much simpler, less time consuming, and more precise to aet ana use the values of heat of combustion in lieu of calorimetric values... 

The deflagration point is defined as the temperature at which a small sample of the explosive, placed in a test tube and externally heated, bursts into flame, decomposes rapidly or detonates violently. 

In Chapter 1.3 we defined a detonation as the propagation of a chemical reaction through an energetic material under the influence of a shock-wave at speeds faster than the speed of sound in the material. The velocity at which the energetic material decomposes is therefore only dependent on the velocity of the shock-wave. It is not determined by a heat-transfer process as it is the case for deflagration or combustion. 

This chapter concerns the structures and propagation velocities of the deflagration waves defined in Chapter 2. Deflagrations, or laminar flames, constitute the central problem of combustion theory in at least two respects. First, the earliest combustion problem to require the simultaneous consideration of transport phenomena and of chemical kinetics was the deflagration problem. Second, knowledge of the concepts developed and results obtained in laminar-flame theory is essential for many other studies in combustion. Attention here is restricted to the steadily propagating, planar laminar flame. Time-dependent and multidimensional effects are considered in Chapter 9. 

Since detonations propagate at supersonic velocities, while deflagrations propagate at low subsonic velocities, the mass flow rate m is much larger for detonations than for deflagrations. Consequently, the dimensionless reaction-rate function F,(z, [Pg.191]

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