Reaction zone length

Eyring et al (Refs 1 3) first investigated the effect of curvature of the wave front on the detonation velocity. They obtd a relation betw the ratio of the actual to the ideal wave velocities (D/Dq) on the one hand and the ratio of the reaction zone length to the radius of curvature of the front (X/r) on the other. The reaction zone was defined as the zone betw the Cj (Chapman-Jouguet)-layer. If the wave front is assumed to maintain its... 

Reaction-zone lengths calcd from this theory are somewhat smaller than those calcd from the "Nozzle Theory of Jones ... 

In the Langweiler concept no influence on velocity would be felt by any finite reaction zone of length less than 3Dt/8. Moreover, for any reaction zone length acs would the detonation become nonideal... 

The influence of the reaction-zone length aG in this model is simply the following ... 

The effective "Chapman-Jouguet (CJ) point" on the cylindrical charge axis always coincides with the beginning of the sharp rarefaction region outlined by the heavy line in Fig 5.2 (Ref 8, p 94). If aQ is less than or equal to the distance from the wave front to this point on the charge axis, detonation will be ideal. But if it is greater than the distance h, detonation will be nonideal In this model nonideal detonation is restricted to effective reaction-zone length of a =3/8(Dt) for L [Pg.364]

HMTeA, AN/TNT AN/Comp B) show that chge density, per se, has the strongest influence on critical pressure. Another important factor is reaction zone length. Chem differences betwn expls have a minor effect dynamites contg NG are a notable exception The problem of sensitivity testing is also examined because deton limit data show that the critical shock pressure decreases with increasing particle size. This seems to run counter to the results of minimum booster-type sensitivity tests. The discrepancy is resolved when shock wave initiation is viewed as a combination effect of both pressure duration... 

E. Houston, Measurement of the Chapman-Jouguet Pressure and Reaction Zone Length in a Detonating High Explosive , p 225 in the 2ndONRSympDeton (1955) and in JChemPhys 23, 1268-73(55) 32) H.D. 

Detonation reaction zone in nonideal gases) 77-79 (Reaction zone in condensed expls) 138-40 [Measured reaction zones in Dithekite 13 (MNB/HN03/H20-24.2/62.6/13.2) and Nitromethane] 147, Table 7.3 (Comparison of reaction-zone lengths of current... 

This equation makes possible the detn of C-J pressure p2 by extrapolation to zero-plate thickuess in cases where reaction-zone length aD is negligible. Deal assumed, furthermore, that this extrapolation should give p2 even where a0 is appreciable by an e xtrapolation which ignores the spike (Ref 3, pp 111-14)... 

Fig, 6.2 (Influence of reaction zone length on transient and steady-state velocities) 140-41 (Transient and anomalous wave propagation) ... 

Detonation, Water Plexiglos Induced Shock Wove Velocity in. Cook et al (Ref 2) applied the "aquarium technique in the exptl detn of the equation of state for water Lucire. The results for water are compared with similar results by other methods. Measurements of the peak pressures in the deton wave are presented for RDX, RDX/salt, TNT HBX-1. Peak pressures were found to be the CJ or deton pressures of the thermohydro-dynamic theory. There was no evidence whatever for the "spike of the Zel dovich-von Neumann model even though conditions were such that this spike would have been detected by the method employed if it were present, at lease in the large diam, nonideal expls of max reaction zone length Refs.T) C. Fauquignon, CR 251, 38 (I960) 2) M, A. Cook et al, JAppl... 

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. 

In the abstract of the paper (Ref 36a, p 1920) it is stated The limiting slope of he detonation velociry-wave front curvature locus for small- velocity deficits is obtained under an assumption concerning the "reaction zone length as related to the charge diameter and the radius of curvature of the wave front. The model is an extension to two dimensions of von Neumann s classical theory of the plane wave detonation... 

The quenching distance detonation limit comes about if the induction period or reaction zone length increases greatly as one proceeds away from the stoichiometric mixture ratio. Then the variation of or / will be so great that, no matter how lai e the containing distance, the quenching condition will be achieved for the given mixture ratio. This mixture is the detonation limit. 

As mentioned in Sec. 3.1.1, the chemical reactions driving the detonation depicted in Fig. 4, obtained with Model I, are largely complete between 2 nm and 5 nm behind the detonation front. When coupled with continuum theory, this extremely short reaction zone length implies that the model should exhibit a critical width for detonation that is small enough to be directly accessible in a molecular dynamics simulation of a two-dimensional strip. The results of this section show that this is the case. The results further establish the connection between our simulations and continuum theory and suggest the possibility of observing nanoscaJe detonations in highly reactive ribbons. 

High purity explosives are known to be very insensitive to the method of initiation. However, the very short reaction zone lengths and the... 

Reaction-zone lengths cannot conveniently be measured directly. Their dimensions are deduced from their effects on other parameters, such as initial free-surface velocity of very thin foil flyers. Lengths vary from as little as a hundredth of a millimeter for some high-density high explosives and some liquids, up to several centimeters for some blasting agents. Table 21.1 lists some reaction-zone length data. 

Figure 21.2 Detonation reaction zone length for TNT as a function of loading density (Ref 5).

We are interested in reaction-zone length because it appears to be the major parameter controlling detonation velocity in the nonideal detonation region. It appears that explosives with thick reaction zones have a larger effect on detonation-velocity/diameter and failure diameters than explosives with thin reaction zones. 

The term a, the slope of the linear portion, a constant, is different for different explosives and is different for the same explosive at different initial conditions, which include density, temperature, and particle size. Although there are few data, the constant a appears to be proportional to reaction-zone length. Table 21.3 gives data for several different explosives as well as for several densities of one explosive, cyclotol (60/40). 

Table IV. Reaction-Zone Length in Lead Azide...

In contrast with the AB system described above, RDX and most other energetic materials have long reaction times—fractions of a microsecond—and extended reaction zone lengths, on the order of a millimeter. Due to the size of the reaction zone and the complexity of the interatomic potentials necessary to describe real nitramines, steady-state NEMD simulations of detonation are beyond current and near-fixture capabilities, both in computation time and computer memory requirements. Keeping these limitations in mind, we use NEMD to study the initial chemical events in RDX under shock loading. In Section 5 we will describe equilibrium MD simulations to study phenomena at longer time-scales. 

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