Deflagrations steady

Pipeline deflagrations and detonations can be initiated by varions ignition sonrces. The flame proceeds from a slow flame throngh a faster accelerating tnrbnlent flame to a point where a shock wave forms and a detonation transition occnrs, resnlting in an overdriven detonation (see Fignre 4-3). A stable (steady state) detonation follows after the peak overdriven detonation pressnre snbsides. 

Fast deflagration—the flame position is much closer to the precursor shock wave. Overdriven detonation—a transition to detonation that has just occurred and the detonation is significantly overdriven with the peak pressure, well in excess (2-3 times) of the value usually associated with a steady Chapman-Jouget (CJ) detonation. This peak pressure generated during the transition process is a particular point of concern in the industry. 

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. 

A deflagration wave formed by a reactive gas under one-dimensional steady-state flow conditions is illustrated in Fig. 3.7. In the combustion wave, the temperature increases from the initial temperature of the unburned gas to the ignition temperature and then reaches the flame temperature. The heat generated in the reaction zone is transferred back to the unbumed gas zone. 

Nachbar, "Deflagration Limits in the Steady Linear Burning of a Monopropellant With Application of Ammonium Perchlorate ,... 

The velocity of advance of the front is super sonic in a detonation and subsonic in a deflagration. In view of the importance of a shock process in initiating detonation, it has seemed difficult to explain how the transition to it could occur from the smooth combustion wave in laminar burning. Actually the one-dimensional steady-state combustion or deflagration wave, while convenient for discussion, is not easily achieved in practice. The familiar model in which the flame-front advances at uniform subsonic velocity (v) into the unburnt mixture, has Po> Po> an[Pg.249]

Initiation is followed by the 2nd stage, deflagration, known also as the steady-state surface combustion (Ref 13, p 49) ... 

The 3rd stage, transition from deflagration to detonation (DDT), is the stage during which the reaction accelerates from the slow transport-determined steady state to supersonic speeds. In condensed explosives the velocity of propagation during transition must increase by a factor of about a million... 

In Section IV, B (Ref 66, pp l47ff) it was postulated that a steady zone exists which consist of two parts which can be t reated separately, the first a shock, the-second a deflagration wave with the shock pressure and density as initial conditions. 

Detonation Wave Transient, One-Dimensional. In the discussion entitled One-Dimensional Transient Reaction Waves by Evans Ablow (Ref 66, Section VI, pp 167-68), a model is assumed according to which a detonation wave is a shock followed by a deflagration wave. In a steady wave the reaction at a given layer of unreacted material is initiated by the leading shock. 

IV. Characteristics of Steady Detonation V, Initiation Behavior VI. Deflagration-to-Detonation Transition (DDT) and Combustion VII. Decomposition and Kinetics VIII. Analytical Methods IX. Waste Disposal X. Toxicity XI. RDX Detonators XII. Military Specifications and XIII. References. Major emphasis will be placed on Sections IV, V, and VI... 

Magnesium oxide exerts quite a different effect than do the above catalysts. Thus, less of it, 2%, is required to promote steady deflagration, but it is not capable of producing as spectacular a rate as copper chromite or potassium dichromate even in amounts as great as 10%. 

A General Description of the Hydrazine Perchlorate Deflagration Process. Let us first describe the deflagration process for hydrazine perchlorate from the above results. It is a process characterized by the formation of a molten zone which is quite turbulent and foamy it is a very erratic process, particularly for the pure material, and it is subject to very potent catalysis by copper chromite and potassium dichromate and to moderate catalysis by magnesium oxide. The process is comparatively reproducible in the presence of small amounts of fuel, and the rate obtained apparently does not depend on the nature of the fuel but only on the ambient pressure. It can be expressed by r — 0.22P where f is in cm./sec. and P in atmospheres. This corresponds to a rate, at 1 atm., some 15 times greater than that calculated by extrapolation for ammonium perchlorate (16). However the process is unstable at pressures above about 7 atm. and steady deflagration cannot be attained above this pressure. 

In this chapter we shall classify the various types of infinite, plane, steady-state, one-dimensional flows involving exothermic chemical reactions, in which the properties become uniform as x oo. Such a classification provides a framework within which plane deflagration and detonation waves may be investigated. The experimental conditions under which these waves appear are described in Chapters 5 and 6, where detailed analyses of each type of wave are presented. 

For purposes of further analyses of detonation structure, the shock wave may be treated as a discontinuity. Both the viscous interaction between the shock and the reaction region and the molecular transport within the reaction region are small perturbations that do not appear to exert qualitatively significant influences on the wave structure. This conclusion appears to apply not only to steady, planar waves but also to unsteady, three-dimensional structures it affords one helpful simplification in the complicated analyses of transverse wave structures. It also alters the interpretation of a detonation as a deflagration-supported shock the support provided by the chemical reactions is of a nonplanar compressible gasdynamic character with negligible molecular transport. 

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