Flame propagation, theory

A theory, termed as the back-pressure drive flame propagation theory, has been proposed to account for the measured flame speeds [12]. This theory gives the momentum flux conservation on the axis of rotation in the form of... 

The back-pressure drive flame propagation theory has been extended to a general case of variable burning... 

The line 9 is given by the steady-state, back-pressure drive flame propagation theory [29], which assumes the momentum flux balance between the upstream and downstream positions on the center streamline and the angular momentum conservation on each streamline. 

Before leaving this account of this two-stage gas-phase flame propagation theory and its predictions we must concede that solid-phase interfacial reactions and heterogeneous reaction between the HCIO4 vapor or products and the solid fuel cannot be ruled out on the basis of the experimental evidence at hand. However, there is no evidence that includes them as major contributory heat sources. The gas-phase driving source seems to account for all the known facts. 

The description of laminar flame structure shows that the burning velocity will be a complex function of both the rate of the initiation process in the preheat zone and the rate of the chemical process in the reaction zone. In the literature, burning velocity is sometimes discussed as if it were purely a chemical phenomenon, but this cannot be the case to date, the only way to get information on the chemical process alone is with the aid of one of the flame-propagation theories that makes assumptions about events in the preheat zone. 

A direct, however approximative, scale-up of the experimental results obtained to real structures on the basis of turbulent flame propagation theory seems not possible at the moment, due to the highly complex interactions in real cases. Nevertheless, the experiments... 

Further development of the thermal flame propagation theory either completely disregarded the ignition temperature or used it as an auxiliary value omitted in the final equations. Moreover, in all subsequent theories the thermal conductivity equation was solved together with that (or those) of diffusion. Consequently, these theories are referred to as thermal only conditionally. 

An important advance was the introduction of chemical kinetics into the flame propagation theory as illustrated by the explosive ozone decomposition (Lewis and Elbe [272]). Formulating the mechanism... 

The Lewis and von Elbe theory was only the first attempt to replace the formal concepts of earlier thermal flame propagation theories by physical concepts based on chemical kinetics. Further development of the flame propagation theory revealed the high effec-tivity and fruitfulness of this kinetic trend in the combustion theory. 

One of the first theories of flame propagation based on the notion of the dominant role of heat losses is that proposed by Zel dovich [530]. In terms of the thermal flame propagation theory Zel dovich derived the relation (see also [145], Chapter VI)... 

Coating Theory. This theory includes fire retardants which form an impervious skin on the fiber surface. This coating may be formed during normal chemical finishing, or subsequently when the fire retardant and substrate are heated. It excludes the air necessary for flame propagation and traps any tarry volatiles produced during pyrolysis of the substrate. Examples of this type of agent include the easily fusible salts such as carbonates or borates. 

This chapter presents fundamental concepts of comhnstion theory relating hoth to flame propagation and DDA technology. 

The chronology of the most remarkable contributions to combustion in the early stages of its development is as follows. In 1815, Sir Humphry Davy developed the miner s safety lamp. In 1826, Michael Faraday gave a series of lectures and wrote The Chemical History of Candle. In 1855, Robert Bunsen developed his premixed gas burner and measured flame temperatures and flame speed. Francois-Ernest Mallard and Emile Le Chatelier studied flame propagation and proposed the first flame structure theory in 1883. At the same time, the first evidence of detonation was discovered in 1879-1881 by Marcellin Berthelot and Paul Vieille this was immediately confirmed in 1881 by Mallard and Le Chatelier. In 1899-1905, David Chapman and Emile Jouguet developed the theory of deflagration and detonation and calculated the speed of detonation. In 1900, Paul Vieille provided the physical explanation of detonation... 

Lovachev L.A., The theory of limits on flame propagation in gases. Combust. Flame, 17 275-278,1971. 

To date, many theories and models have been proposed by various researchers, such as Atobiloye and Britter [14], Ashurust [15], Asato et al. [16], and Umemura [17,18]. Numerical simulations have also been conducted by Hasegawa and coworkers [19,20]. Recently, the phenomenon of rapid flame propagation has received keen interest from a practical viewpoint, to realize a new engine operated at increased compression ratios, far from the knock limit [21]. 

P. Clavin and F.A. Williams. Theory of premixed-flame propagation in large-scale turbulence. Journal of Fluid Mechanics, 90(pt 3) 589-604, 1979. 

Ya.B. Zel dovich and D.A Frank-Kamenetskii. A theory of thermal flame propagation. Acta Physicochimica URSS, IX 341-350, 1938. 

P. Clavin and J. Sun. Theory of acoustic instabilities of planar flames propagating in sprays or particle-laden gases. Combustion Science and Technology, 78 265-288, 1991. 

Mayer, E., A theory of flame propagation limits due to heat loss. Combust. Flame, 1 438,1957. 

The function of halogen-containing compounds as flame retardants has been explained by the radical trap theory. Liberated halogen acid (HX) competes in the above reactions for those radical species that are critical for flame propagation. 

Hirschfelder et al. [7] reasoned that no dissociation occurs in the cyanogen-oxygen flame. In this reaction the products are solely CO and N2, no intermediate species form, and the C=0 and N=N bonds are difficult to break. It is apparent that the concentration of radicals is not important for flame propagation in this system, so one must conclude that thermal effects predominate. Hirschfelder et al. [7] essentially concluded that one should follow the thermal theory concept while including the diffusion of all particles, both into and out of the flame zone. 

A review with 42 refs) l8)Ibid, 12, 198-214 (1945) (Initiation of expln in solid expla. A review with 37 refs) l9)Ya.B.ZeI dovich, ZhFizKhim 22, 27-49 (1948) (Theory of flame propagation) 20)J.A.Nicholls et al, " De-tonative Combustion UnivMichigan Research Inst, Final Rept, Project M898 (1953) 21)... 

C. Franze H.Gg. Wagner, Theorie der Fiammenausbreitung(Theory of flame propagation), p 562—4... 

The first attempts to understand quantitatively the high-temperature chemical processes were related to combustion. They took place in the first part of the last century, partly with the development of thermal theories and theories for chain reactions and partly with work on high-temperature oxidation of hydrocarbons (to understand flame propagation) and low-temperature oxidation (to understand autoignition and knock in internal combustion engines). 

The so-called diffusion theories of flame propagation, as exemplified by the work of Tanford and Pease 38), emphasize the transport of mass, in that concentration of an active radical is assumed to be the rate-controlling property. Its use seems to be fairly limited in that only a few specific reactions have been successfully studied with this theory. What is more interesting, however, is that this theory forms the counterpart to the thermal theory. These two extreme views bracket the actual case, and their study allows a consideration of each of two of the basic flame mechanisms, unencumbered by the other. Actual deflagration depends on both the transport of heat and the transport of mass, and a successful theory should contain both phenomena. 

---