Stable detonation

Overdriven detonation is the condition that exists during a DDT before a state of stable detonation is reached. Transition occurs over the length of a few pipe diameters and propagation velocities np to 2000 m/s have been measnred for hydrocarbons in air. This is greater than the speed of sonnd as measnred at the flame front. Overdriven detonations are typically accompanied by side-on pressnre ratios (at the pipe wall) in the range of 50-100. A severe test for detonation flame arresters is to adjust the mn-np distance so that DDT occurs at the arrester, subjecting it to the overdriven detonation impulse. 

Overdriven detonations, not long-pipe stable detonations, provide a greater potential for mechanical damage to detonation flame arresters. 

The detonation flame arrester mnst be able to arrest ten deflagrations with and withont a pipe restriction downstream of the flame arrester and five nnrestricted stable and overdriven detonations. The UL standard states, after tests determine the maximnm nnsta-ble (overdriven) detonation, the arrester is to be snbjected to fonr additional nnstable detonations with the length of pipe that resnlted in the maximnm nnstable (overdriven) detonation. The arrester is also to be snbjected to five stable detonations. ... 

Stable Detonation A detonation that progresses through a confined system without significant variadon of velocity and pressure character-isdcs. Eor atmospheric condidons, typical velocides range between 1600 and 2200 m/s for standard test mixtures and test procedures. 

Stable detonation—a steady detonation wave with velocity and pressure close to CJ values. 

Nonel fuse, invented by Nitro Nobel AB in Sweden, consists of a thick plastic tube of bore about 1 mm, the inside surface of which is dusted with a small amount of powdered high explosive. If a shock wave is formed at one end of the tube the explosive powder is raised to a dust and a stable detonation at velocity 2000 m s 1 proceeds indefinitely along the fuse. The plastic itself is unaffected and the only outside effect is a flash of light seen through the tube walls. This therefore is an extremely safe method of propagating a detonation from one place to another. 

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]. 

Thermodynamic cycles are a useful way to understand energy release mechanisms. Detonation can be thought of as a cycle that transforms the unreacted explosive into stable product molecules at the Chapman-Jouguet (C-J) state,15 which is simply described as the slowest steady-state shock state that conserves mass, momentum, and energy (see Figure 1). Similarly, the deflagration of a propellant converts the unreacted material into product molecules at constant enthalpy and pressure. The nature of the C-J state and other special thermodynamic states important to energetic materials is determined by the equation of state of the stable detonation products. 

Dr Price mentions on p 694 that the work on relationship betw density and diameter was done in Russia (mostly on AN explosives) as early as 1945 (Ref 1). It was stated that "some pure explosives possess the capacity for a stable detonation only under the condition that their density does not exceed a certain limiting value". In later Rus works, such as of Blinov, Bobolev, etc, not only behavior of AN expls but also of DNT DNPhenol were briefly described in the book of Andreev Belyaev (Ref 4). Among the expls described, the 50/50 Amatol draws particular attention because its behavior seems to differ from those of group 1 or 2 (Ref 17, p 696)... 

Curvature of Wave Fronts. In many discussions of stable detonation waves plane wave fronts are assumed to exist. Actually stable, plane wave fronts do not exist, at least in condensed expls as shown by Cook et ai (Ref 1)... 

An exothermic chemical reaction that propagates with such rapidity that the rate of advance of the reaction zone into the unreacted material exceeds the velocity of sound in the unreacted material, that is the advancing reaction zone is preceded by a shock wave. The rate of advance of the reaction zone is termed detonation rate or detonation velocity. When this rate of advance attains such a value that it will continue without diminution thru the unreacted material, it is termed a stable detonation velocity. The exact value of this term is dependent upon a number of factors, principally the chemical and physical properties of the material. When the detonation rate is equal to or greater than the stable detona-... 

The reaction zone length "a (See Fig 1) is the important parameter when considering boostering of main explosive charges. It largely determines how easily and how rapidly stable deton may be established in the main chge. The shorter the reaction zone length, the more rapidly and the more easily stable conditions are reached in the initiated expl. 

It is also stated by Kistiakowsky, that the theoretical justification of the minimal value for the stable detonation velocity... 

Under the heading "Wave Front , Cook (Ref 52, p 99), reported that in many discussions of stable detonation waves, plane wave ftonts ate assumed to exist. 

Table 3.3. Distance of Tow-Velocity Regime from Point of Initiation ( 6 Cap) to Stable Detonation...

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