Detonation physical kinetics

In 1998 one of WoUcer s most recent papers [97] argues for his theory of physical kinetics of detonation. The theory is described as a non-equilibrium, non-thermal process ehcited by the exceedingly high kinetic energy of shock and/or in the detonation front. This process leads to massive mechanical fracture of covalent bonds at and near to the detonation front. According to this theory, the reaction rate is determined by the medium vibrational energy of free electron pairs (radicals) formed by the fracture of a molecule within a time period of 10 to 10 s [40]. This theory can be considered as an example of views of some physicists on chemical reactions, but in its time it was a considerable contribution to development of detonation theory. 

In 1999 Zeman [98] summarized the pubhshed significant views on initiation of detonation (except for the model of physical kinetics) as follows the influence of shock on energetic materials results in adiabatic compression of the moleciflar layer struck. According to Klimenko s and Dremin s accmmflation mechanism [99-101], the kinetic energy of the shock in this compression is accumulated through translational-vibrational relaxation processes by trans-... 

The quantitative requirements as in the onedimensional case, are determined by the reaction kinetics, the physical state, and the equations of stat e of the material or of its components if the chge is heterogeneous. The shock- terminating rarefaction is here provided by the three- dimensional geometry and does not need a pressure-relieving rear boundary condition as in the one-dimensional case. If the shock wave is inadequate for detonation initiation, a deflagration frequently occurs instead. In Section VI,B of Ref 66, it was shown that for the correct boundary conditions a deflgrn can create a shock wave which can initiate a deton... 

A special place among kinetic studies in combustion is occupied by work on nitrogen oxidation. Begun at the AS USSR Institute of Chemical Physics in the mid-thirties on the initiative of N. N. Semenov, research to determine the feasibility of fixation of atmospheric nitrogen for the production of mineral fertilizers has today found application in the development of environmental protection measures for toxic components of combustion products, including nitrogen oxide. In December, 1939, Ya.B. defended his doctoral dissertation on The Oxidation of Nitrogen in Combustion and Explosions. It was precisely these studies, in which D. A. Frank-Kamenetskii, P. Ya. Sadovnikov, A. A. Rudoy, A. A. Kovalskii, and others actively participated, that led Ya.B. to the problems of combustion and detonation. 

Quite a few different approaches have been tried. One popular approach (CJ and ZND theories. Section 2.3) explicitly states that in a detonation, the chemical reaction kinetics and pathways do not matter at all. All that matters are physical and mechanical properties such as the Hugoniot of the unreacted... 

We summarize a number of simulations aimed at deciphering some of the basic effects which arise from the interaction of chemical kinetics and fluid dynamics in the ignition and propagation of detonations in gas phase materials. The studies presented have used one- and two-dimensional numerical models which couple a description of the fluid dynamics to descriptions of the detailed chemical kinetics and physical diffusion processes. We briefly describe, in order of complexity, a) chemical-acoustic coupling, b) hot spot formation, ignition and the shock-to-detonation transition, c) kinetic factors in detonation cell sizes, and d) flame acceleration and the transition to turbulence. 

Detonations are extremely complex phenomena and involve many competing physical and chemical processes. Complete theoretical models of the initiation, stability, and structure of detonation waves require an accurate description of the chemical kinetics of the induction phase. The primary goal of the present work is to demonstrate that kinetic mechanisms are now available which are able to predict the induction delay period for a variety of practical fuels. 

How to solve the problem of combining the chemical reaction equations and the three equations of gas kinetic theory It s extremely difiicult because of the complexity of chemical reaction inside detonation area. There must be a simplified approach, which stipulates that chemical compositions react stoichiometrically according to some way, and the proceeding variable (1,) of stoichiometric reactions represents the complex changes of chemical compositions. This makes a chemical problem into a physical one. The simplest stoichiometric reaction is Eq. 2.24. 

One integral of the differential equations, Eqs. (160), (162), (163), and (164), may be obtained in simple form in the special case in which = 1 and P = 3/4. Since these are physically reasonable values of the dimensionless groups, we restrict the present discussion to this special case. As a result of this choice of unity for the Lewis number and of three-fourths for the Prandtl number, it follows that the enthalpy of the gas (relative to the detonation wave) remains constant throughout the wave. The specific enthalpy including kinetic energy is... 

---