Deflagration wave

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. 

The thermal balance of the heat flux transferred back from the reaction zone to the unburned gas zone and the heat supplied to the unbumed gas to increase its temperature from the initial temperature Tq to the ignition temperature Tj, is represented by 

---

A radial force on the pipe wall ahead of the deflagration wave. There is a varying pressnre between the aconstic wave and the flame front where the pressnre bnilds from near atmospheric pressnre, Pi (step change at the wave front) to eight times Pi (or higher) at the flame front. The pressnre ratios depend on the flame acceleration. There is no snch effect with a detonation. 

Buckmaster ]., The quenching of deflagration waves. Combust. Flame, 26 151-162,1976. 

The extent to which a detonation will propagate from one experimental configuration into another determines the dynamic parameter called critical tube diameter. It has been found that if a planar detonation wave propagating in a circular tube emerges suddenly into an unconfined volume containing the same mixture, the planar wave will transform into a spherical wave if the tube diameter d exceeds a certain critical value dc (i.e., d > dc). II d < d.. the expansion waves will decouple the reaction zone from the shock, and a spherical deflagration wave results [6],... 

Since pj < p2 for a detonation and pj > p2 for a deflagration, the flow field becomes 0 < Up < Ui for detonation, and Up < 0 for deflagration. In the case of detonation, the velocity of the combustion products is less than the detonation wave velocity. In the case of deflagration, the combustion products are expelled in the opposite direction to the deflagration wave. 

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]

Let us consider (as in Fig 1) a standing detonation or deflagration wave where subscript (1) denotes conditions before the front (unburned gases) and subscript (2) conditions after the front (burned gases)... 

Chapman-J ouguet (C-J) Condition and Postulate. C-J condition is the condition that exists for a detonation or deflagration wave when the gases in the burned portion of the wave move at a velocity relative to the wave just equal to the local sonic velocity in the burned portion of the gas (Ref 58, p 4)... 

IV,A. Existence, Uniqueness, and Mechanism of Propagation of. Deflagration Waves. It is... 

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. 

The accuracy of any of the above-mentioned methods of analytically determining the rate of propagation of a deflagration wave depends finally on the validity of the rate laws used, and on the values of the physical constants of the gases under consideration. In particular, the activation energy, and steric factor for any combustible are very important parameters. Much work is being done on the kinetics of chemical reactions, so that more accurate data on reaction rates will be available. It is hoped that this work will lead to better agreement between theoretical and experimental results. 

Figure 3. Tracing of thermocouple record of hydrazine perchlorate deflagration wave. Strand composition 94.5% hydrazine perchlorate, 5% Delrin, 0.5% magnesium oxide density 1.85 grams/cc. pressure 0.5 atm. deflagration rate 0.09 cm./sec.

---