Detonation front

Detonation. In a detonation, the flame front travels as a shock wave, followed closely by a combustion wave, which releases the energy to sustain the shock wave. The detonation front travels with a velocity greater than the speed of sound in the unreacted medium. 

The other detonability length scale is the detonation cell width, X (also called cell size) which is the transverse dimension of diamond shaped cells generated by the transverse wave stmctnre at a detonation front. It has a fish scale pattern (see Figure 4-4). Detonation cell widths are nsnally measured by the traces (soot) deposited on smoke foils inserted in test vessels or piping surfaces. The more reactive the gas-air mixture, the smaller is the cell size. The same is tme for chemical indnction length as a qualitative measure of detonability. The cell width, X, is a parameter that is of practical importance. The transition from dehagration to detonation, propagation, and transmission of a detonation, can to some extent be eval-... 

Analytical A proc is described for the quant titrimetric analysis of TeNMe in nitric acid (Ref 35)s and a spectrophotometric method is described in Ref 41 for the detn of small amts of TeNMe in air and w Critical Diameter. The crit diam for deton propagation of TeNMe thickened with poly-(methyl acrylate) and loaded with up to 75% inert solids was detd and found to decrease with increasing solids loading. It was postulated that the solids acted as reaction foci ahead of the deton front (Ref 45)... 

The instability and nonplanar character of the detonation front was first exhibited by Manson [1] and Fay [2] in certain particular cases of detonation propagation, such as fhe "spinning detonations." The multidimensional nature of the detonation front has been established by Voitsekhovskii [3], Denisov and Troshin [4],... 

Numerical simulation of a spirming detonation in Hj/air mixture in a circular tube at various times. Gray and green space isosurfaces in pressure are the detonation front and the pressure of 6 MPa. White arrow propagating direction of the detonation front, pink arrow rotating direction of the transverse detonation. TD—transverse detonation, and LT—long pressure trail. (Reprinted from Tsuboi, N., Eto, K., and Hayashi, A.K., Combust. Flame, 149,144,2007. With permission.)... 

K.I. Schchelkin and Ya.K. Troshin, Non stationary phenomena in the gaseous detonation front. Combust. Flame, 7, 143-151, 1963. 

The major difficulty in applying this hydrodynamic theory of detonation to practical cases lies in the calculation of E2, the specific internal energy of the explosion products immediately behind the detonation front, without which the Rankine-Hugoniot curve cannot be drawn. The calculations require a knowledge of the equation of state of the detonation products and also a full knowledge of the chemical equilibria involved, both at very high temperatures and pressures. The first equation of state used was the Abel equation... 

The reaction zone in a detonation wave is no different from that in other flames, in that it supplies the sustaining energy. A difference does exist in that the detonation front initiates chemical reaction by compression, by diffusion of both heat and species, and thus inherently maintains itself. A further, but not essential, difference worth noting is that the reaction takes place with extreme rapidity in highly compressed and preheated gases. 

F. THE STRUCTURE OF THE CELLULAR DETONATION FRONT AND OTHER DETONATION PHENOMENA PARAMETERS... 

An excellent description of the cellular detonation front, its relation to chemical rates and their effect on the dynamic parameters, has been given by Lee [6], With permission, from the Annual Review of Fluid Mechanics, Volume 16, 1984 by Annual Reviews Inc., this description is reproduced almost verbatim here. 

We thus see that the motion of a real detonation front is far from the steady and one-dimensional motion given by the ZND model. Instead, it proceeds in a cyclic manner in which the shock velocity fluctuates within a cell about the equilibrium C-J value. Chemical reactions are essentially complete within a cycle or a cell length. However, the gas dynamic flow structure is highly three-dimensional and full equilibration of the transverse shocks, so that the flow becomes essentially one-dimensional, will probably take an additional distance of the order of a few more cell lengths. 

Many of the unsolved problems of physics and chemistry were concerned with combustion and detonation. A really well-developed scheme of normal combustion is seldom realized in nature. The most common form of gaseous combustion - turbulent combustion - was found to be the result of the hydrodynamic instability of the combustion process in a flow. Even in the simplest system, the physical scheme of turbulent combustion is very far from being perfectly understood. Just as in the analysis of detonative combustion, it is still possible to speak only of the universal instability of the hydrodynamic process accompanying the chemical transformation of matter. Actually, "turbulence is hardly the term for the result of the manifestation of this instability - the appearance of a multifront shockwave in the detonation front. However, the derivation of a complete physical scheme of detonation (especially in relation to condensed expls) will eventually follow from further research in this field... 

Measurement of the Detonation-Front Structure in Condensed-Phase Explosives , Ibid, 863-67 11) W.E. Gordon, "Detonation Limits in Condensed Explosives , 4thONRSympDeton(1965), 179-97 12) M.C. Chick, "The Effect of... 

This results in a successive diminishing of the detonation front. A process of this kind may stop detonation, provided no new detonation front develops within the compressed explosive behind the shock wave left by the terminated reaction. The new detonation wave would travel over the com-... 

This would occur in the event the old detonation front succeeded in disappearing and the rarefied waves from the charge periphery rarefied the compressed explosive before a new detonation wave is initiated... 

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