Structure of Combustion Wave

From considerations of combustion-wave structure, it will be indicated in Section 6.1.3 that strong deflagrations do not occur hence the physically meaningful section of the deflagration branch of the Hugoniot curve is DE. Most deflagrations are, in fact, nearly isobaric. 

Figure 3-10. Thermal structure and heat feedback process of combustion wave.

To study the detonation of liquid explosives and its spreading/transportation, nitromethane, nitroglycerine, diethyleneglycol dinitrate, and methyl nitrite are designed as the objectives of liquid explosives to study the chemical dynamics and the complex unsteady process of shock waves combustion. These phenomena determine the structure of detonation wave fronts and spreading limit of detonation waves. They help to clear the flow dynamics of wave fronts, and refer suggestions for the formula of liquid explosives, study and application of equipment features. They help to improve and perfect the detonation theory. 

R. Takai, K. Yoneda, and T. Hikita, Study of detonation wave structure. Proceedings 15th Symposium (International) on Combustion, The Combustion Institute, Pittsburg, pp. 69-78, 1974. 

Pulsation in a spray is generated by hydrodynamic instabilities and waves on liquid surfaces, even for continuous supply of liquid and air to the atomizer. Dense clusters of droplets are projected into spray chamber at frequencies very similar to those of the liquid surface waves. The clusters interact with small-scale turbulent structures of the air in the core of the spray, and with large-scale structures of the air in the shear and entrainment layers of outer regions of the spray. The phenomenon of cluster formation accounts for the observation of many flame surfaces rather than a single flame in spray combustion. Each flame surrounds a cluster of droplets, and ignition and combustion appear to occur in configurations of flames surrounding droplet clusters rather than individual droplets. 

Fig. 5.4. Schematic evolution of the internal structure of a star with 25 times the mass of the Sun. The figure shows the various combustion phases (shaded) and their main products. Between two combustion phases, the stellar core contracts and the central temperature rises. Combustion phases grow ever shorter. Before the explosion, the star has assumed a shell-like structure. The centre is occupied by iron and the outer layer by hydrogen, whilst intermediate elements are located between them. CoUapse followed by rebound from the core generates a shock wave that reignites nuclear reactions in the depths and propels the layers it traverses out into space. The collapsed core cools by neutrino emission to become a neutron star or even a black hole. Most of the gravitational energy liberated by implosion of the core (some 10 erg) is released in about 10 seconds in the form of neutrinos. (Courtesy of Marcel Amould, Universite Libre, Brussels.)...

A schematic representation of the combustion wave structure of a typical energetic material is shown in Fig. 3.9 and the heat transfer process as a function of the burning distance and temperature is shown in Fig. 3.10. In zone I (solid-phase zone or condensed-phase zone), no chemical reactions occur and the temperature increases from the initial temperature (Tq) to the decomposition temperature (T ). In zone II (condensed-phase reaction zone), in which there is a phase change from solid to liquid and/or to gas and reactive gaseous species are formed in endothermic or exothermic reactions, the temperature increases from T to the burning surface temperature (Tf In zone III (gas-phase reaction zone), in which exothermic gas-phase reactions occur, the temperature increases rapidly from Tj to the flame temperature (Tg). 

Fig. 3.10 Thermal structure of a combustion wave and heat feedback processes therein.

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