Kinetics, flame propagation

The balanced equation for turbulent kinetic energy in a reacting turbulent flow contains the terms that represent production as a result of mean flow shear, which can be influenced by combustion, and the terms that represent mean flow dilations, which can remove turbulent energy as a result of combustion. Some of the discrepancies between turbulent flame propagation speeds might be explained in terms of the balance between these competing effects. 

The work of Mayer and Cams (44) gives a theoretical analysis of flame propagation in a laminar flame model based on simplified reaction kinetics. 

Two very distinguishing features of flames are the emission of visible radiation and the presence of an abnormal number of ions in the reaction zone (Cl, Gl). Both of these features appear to be kinetic by-products, which are completely unnecessary for flame propagation.5 The radical CH is responsible for much radiation and now also appears to be the precursor of many of the ions observed in flames (C2). Enhancement of CH or other radical or ion concentration in flames could result in any number of applications if an understanding of their formation made such control possible. 

Moreover, the phenomena of combustion themselves prove to be more complicated. For a long period the study of combustion broke away from chemical kinetics and set itself its own specific tasks. These included especially studies of the influence of instrumental parameters on ignition, flame propagation and limits, i.e., the influence of the diameter and length of tubes, the form of vessels, the direction of propagation, etc. 

From the technology of combustion we move to the molecular mechanism of flame propagation. We shall give a molecular-kinetic expression for the heat release rate by calculating the frequency v of collisions of fuel molecules with other molecules (v is proportional to the molecular velocity and inversely proportional to the mean free path), further taking into account that only a small (1/j/) part of all collisions are effective. The quantity 1/v—the probability of reaction taken with respect to a single collision— depends on the activation heat of an elementary reaction event, as well as on the fraction of all molecules comprised of those radicals or atoms by means of which the reaction occurs. The molecular-kinetic expression for the coefficient of thermal conductivity follows from formulas (1.2.4) and (1.2.3). 

The mechanism of the reaction of hydrogen with bromide is known today in complete detail all the individual stages of the reaction, their probabilities, and activation heats are known. Because of this, it was possible to calculate the flame propagation velocity from kinetic data after the combustion temperature had been found by thermochemical computations, and with... 

The calculation gave a combustion rate which differed by 15% from the experimental one. Thus, for the first time, the combustion rate was calculated from independent data, and for the first time in this example the practical possibility was demonstrated of reducing the laws of flame propagation to the laws of phenomena which lie at the basis of the process, i.e., to the laws of chemical kinetics and of heat conductivity and diffusion. 

However, we know that the kinetic characteristics on which the flame velocity depends differ from the factors which determine the conditions of self-ignition in particular, self-ignition is relatively hindered, while flame propagation is eased in the case of an autocatalytic reaction or a reaction with branching chains. 

Thus, the study of chemical kinetics in a jet in the MCD sector of the curve in Fig. 4 will be extremely significant for the theory of flame propagation. 

Works published on this subject include Semenov s fundamental theory of thermal explosion [1], Todes analysis of the kinetics of thermal explosion [2], Frank-Kamenetskii s calculation of the absolute values of the limit of thermal explosion [3], the theory of ignition [4], and finally, most closely related to the first part of this paper, the theory of flame propagation by Frank-Kamenetskii and the author [5]. 

Studying anew the differential equations of heat conduction, diffusion, gas motion and chemical kinetics under the conditions of a chemical reaction (flame) propagating in a tube, through a narrow slit or under similar conditions, using the methods of the theory of similarity we find the following dimensionless governing criteria ... 

CA 50, 12482 (1956) (Flame propagation in ozone) 29)Sax (1957), 161-61 (Destruction of expls) 30)F.C.Ikle, "The Social Impact of Bomb Destruction , Univ of Oklahoma Press, Norman, Okla (1958) 3l)Anon, Ordnance Service in the Field , US Army Field Manual FM 9-1 (1959) (Destruction of ammo) 32)Anon, Ordnance Ammunition Service , FM 9 5 (1959) (Destruction of ammo) 33)A.B.Amster, "Relationship Between Decomposition Kinetics and Sensitivity (U), Stanford Research Institute, Menlo Park, California,Repts (1962), Contract No Nonr 3760(00) (Conf, not used as a source of info) 34)P.W.M.Jacobs A.R.T.Kureishy, Kinetics of Thermal and Photochemical Decomposition of Some Alkali Metal Azides , Imperial College, London, England, Final Tech Rept (1964) Contract DA-91-591-EUC-2059 34a)Anon, Care, Handling, Preservation and Destruction of Ammunition , TM 9-1300-206 (1961) 35)-Anon, Investigations of the Mech-... 

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