Detonation wave, description

Argous et al (Ref 7, p 135) give the following comprehensive description of the formation of Mach detonation waves ... 

A brief description is given at the beginning of this section under DETONATION (AND EXPLOSION) WAVES, where Fig 2 is shown and under Detonation Wave, Steady-State, One-Dimensional, Plane ... 

Taylor (Ref 26, pp 65ff), under the heading "Elementary Theory of the Steady Plane Detonation Wave gives a comprehensive description which we follow here in a slightly abbreviated form... 

Note The above discussion on "Steady-State, Plane Detonation Wave taken from the book of Taylor contains some equations which are listed under DETONATION (AND EX. PLOSION) THEORIES and also at the beginning of this Section entitled DETONATION (AND EXPLOSION) WAVES. Although it is realized that these equations are repetitions, they are not eliminated but just referred in order to preserve the cohesion of the description... 

The question considered is a description of the conditions which must be met by a localized initiator if a spherical detonation wave is to be formed. The first problem is a determination of the possibility of the existence of such a wave. Taylor analyzed the dynamics of spherical deton from a point, assuming a wave of zero-reaction zone thickness at which the Chapman-Jouguet condition applies. He inquired into the hydrodynamic conditions which permit the existence of a flow for which u2 +c2 = U at a sphere which expands with radial velocity U (Here U = vel of wave with respect to observer u2 = material velocity in X direction and c -= sound vel subscript 2 signifies state where fraction of reaction completed e = 1). Taylor demonstrated theoretically the existence of a spherical deton wave with constant U and pressure p2equal to the values for the plane wave, but with radial distribution of material velocity and pressure behind the wave different from plane wave... 

A molecular description of detonation, particularly initiation, has been pursued for decades, with little success. One difficulty has been obtaining high-quality data at the appropriate length and time scales and with molecular specificity. What are the appropriate time and space scales Detonation waves have tjqjical velocities of 6-8 km/s, or equivalently 6-8 nm/ps. Recent molecular dynamics studies suggest that reactions in shocked energetic materials can occur in times as short as a few ps [1-6]. Energy transfer studies on molecular systems also reveal similar fast time scales [7-11]. Therefore, appropriate spectroscopic probes should have ps or better time resolution. Also, shock rise time measurements with sub-ps resolution require samples with surface uniformity better than 6-8 nm over the probed area. 

Detonations are extremely complex phenomena and involve many competing physical and chemical processes. Complete theoretical models of the initiation, stability, and structure of detonation waves require an accurate description of the chemical kinetics of the induction phase. The primary goal of the present work is to demonstrate that kinetic mechanisms are now available which are able to predict the induction delay period for a variety of practical fuels. 

Interesting is the Multidimensional Reactive Flow model developed by Tarver et al. [5,103,104) it is based on the Non-Equilibrium Zeldovich-von Neuman-Dhring theory. This model starts from the primary chemical changes occurring in the adiabaticaUy compressed thin layer of molecules of the given EM and multiphonon up-pumping due to shock, but in the mathematical description it works with experimental data of thermal explosion of EM [5,103,104) it considers the induction period of initiation of detonation. However, the induction period of the EM decomposition in front of the detonation wave makes the front kinetically unstable and pulsating [101 ]. 

Although phenomena such as forest fires and flashovers are sometimes described as explosive, this description is technically incorrect. However, under certain conditions, flammable mixtures can explode or, more accurately, detonate. Recall the discussion of a flame front as a propagating wave, illustrated in Figure 9.22. Detonation occurs when the speed of this flame front exceeds the speed of sound. The example shown in that figure is a combustion initiated in a closed tube. If the tube is long enough, the compression wave created by combustion can accelerate sufficiently to become a detonation wave. As shown in Figure 9.26, compression waves can catch up with earlier waves, surpass the speed of soimd, and establish a detonation wave. 

The numerical model used to interpret cylinder wall expansion experiments must include a realistic description of build-up of detonation, Forest Fire burn and resulting detonation wave curvature. A problem in numerical simulation of long cylinders of explosive confined by thin metal walls is to obtain sufficient numerical resolution to describe the explosive burn properly and also to follow the simulation of long cylinders. The NOBEL code includes the necessary physics and will numerically model cylinder tests as described in Chapter 6. 

In the 1950s, the more descriptive schlieren records of the interactions between pressure waves and deflagration fronts were obtained [16-18], and Oppenheim [9] introduced the hypothesis of the "explosion in the explosion" (of the detonating mixture) occurring in the regime of accelerating flame to explain the sudden change in the velocity of the combustion wave observed in the experiments. 

Detonation (and Explosion), Effects of Blast and Shock Wave on Structures. As this subject was not discussed in Vol 2 of Encycl, under "BLAST EFFECTS IN AIR, EARTH AND WATER , pp B180-L to B184-R, there is given here a brief description as taken from the book of Robinson (1944), where it is described in detail on pp 45-53... 

For more detailed description of particle-velocity measurements, see "Detonation, Particle Velocity in and Its Determination Andreev Belyaev (Ref 44, pp 247-49) describe a method of experimental determination of pressure of detonation, using the arrangement shown in Fig B, Here 1 is charge of an explosive enclosed in a metallic container, and 2 is a metallic (usually aluminum) plate, 1-2mm thick, firmly inserted as a cover at the end of cartridge opposite detonator, 3. On initiation of charge, a shock wave will spread to plate 2 and, when the wave reaches the outer surface of the plate, it will start to move with initial velocity VH (here H is nachaT-naya, which means initial). After determining this velocity experimentally, the... 

Kistiakowsky Kydd (Ref 2) investigated rarefaction waves in gaseous detonations. Cook (Ref 4, pp 91 105 gave a fairly comprehensive description of rarefaction waves, including "lateral rarefaction waves , called "release waves by E.M. Pugh... 

Equation (6) is used to calibrate the apparatus and determine the detonation temperature Baum et al (Ref 44, p 97) described the spectroscope method developed in Russia in 1945 by Alentsev, Belyaev, Sobolev Stepanov, which was applicable only to transparent liquid expls, such as NG, NGc, etc. In order to elimi-. nate luminosity caused by shock wave in the atmosphere, the authors immersed the test tube with. sample in water. For a more detailed description of the method, see Ref 16 and pp 98-100 of Ref 44. The values obtd by this method are considerably lower than the calcd values. For example, for NG the exptl value was only 3150CK vs 4520°K obtd by calcn and for NGc. 3160 vs 4700... 

C. Fauquignon et al, 4thONRSymp Deton (1965), p 39 (Listed as "Water or plexiglas induced shock wave velocity , without giving its description)... 

Output tests for detonator type components are generally based on an attempt to measure the brisance or the peak pressure of the shock wave. The common tests for detonators are practically all applicable to each of the three main varieties, namely stab, electric and flash detonators. Following are brief descriptions of output test for detonators and primers ... 

Tiffany, "Physical Testing of Explosives, USBurMines Bull 346 (1931), 60-2 (Detailed description of Mettegang Chronograph) 18)W. Friederich, SS 26, 221-22(1931) (Rotating Drum Chronograph for detg deton vels of expls) 18a)Marshall 3, (1932) 143 46 (Detn of deton vels of expls by Condenser Sound Wave and Photographic methods) 19)T. 

For a more complete discussion of combustion waves, detonations, and flame stability the reader is referred to the very detailed exposition in the text by Lewis and Von Elbe, loc. dt., and also the text by Frank-Kamenetskii, loc. cii. An excellent qualitative description of the initiation of detonations in gases will be found in an article by G. B. Kistiakowsky, Ind. Kng. Cheni., 43, 2794 (1951). 

Detonation is universally defined as a chemically supported shock wave. It is a cooperative process in which the shock wave activates an exothermic chem reaction and the chem reaction, in turn, supports the shock. The products generated in such detonation reactions are the subject of this article. A very, cursory description of detonation products was given in Vol 4, D494-R. Below we will consider the main equilibria that control the compn of detonation products, and... 

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