Propagation of combustion

In rocket technology the term burning rate is usually employed in the more restricted sense of the rate of propagation of combustion at constant pressure in the rocket motor... 

Refs 1)J. Manton et al, JChemPhys 20, 153-7(1952) CA 46, 6385(1952)(Nonisotropic propagation of combustion waves in explosive gas mixts and development of cellular flames) 2)G.H. Mark stein, JChemPhys 20, 1051-52 (1952) CA 46, 11688(1952)(Nonisotropic propagation of combustion waves)... 

A. P. Aldushin, T. M. Martemyanova, A. G. Merzhanov, B. I. Khaddn, K. G. Shkadinsky, Autooscillatory Propagation of Combustion Front in Heterogeneous Condensed Media, Combustion Explosion and Shock Waves 9 (1973), 531. 

G. 1. Sivashinsky, On Spinning Propagation of Combustion Waves, SIAM J. Appl. Math. 40 (1981), 432. 

The differentiation between a detonation type of combustion and deflagration is based on the velocity of combustion zone. According to NFPA Standard 69 (1986) edition the deflagration is defined as a propagation of combustion zone at a velocity that is less than the speed of sonnd in the unreacted medium. The opposite feature is characteristic for the detonation type of the velocity combustion. 

But is it always necessary to complete the reaction for the propagation of combustion wave For example, in the Ti-N2 system reaction, heat is so high that the adiabatic combustion temperature reaches 3446 K, while the reaction product TiN melts completely and dissociates partially. Thermodynamic calculations show that if only one-tenth of titanium reacts with nitrogen, the temperature in the reaction zone may exceed 1300 K, and if one-fifth of titanium reacts, the temperature... 

A graphical symbolic representation of the four factors needed for the propagation of combustion or fire. Each side of the tetrahedron is representative of a factor. The four factors include fuel, oxidizer, ignition source, and chain reaction. Removal or blockage of one of the elements prevents the combustion process from occurring or continuing. See also Combustion. 

The normal process is a rapid-but-smooth combustion of the fuel-air mixture in the engine due to the propagation of a flame front emanating from the spark created between the electrodes of the spark plug. 

Maintenance and propagation of the combustion front are problems. This has led to a near-weUbore technology in which the same well is used for air injection and oil production. The combustion front needs to be propagated for a relatively short distance (275). 

Another important concept is that of the critical ignition volume. During the propagation of the combustion wave, the flame volume cannot continually grow beyond a critical value without an additional supply of energy. The condition that controls the critical volume for ignition is reached when the rate of increase of flame volume is less than the rate of increase of volume of the combustion products. In this condition a positive exchange of heat between the flame and the fresh mixture is achieved. 

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. 

Many finely divided metal powders in suspension in air are potential e] losion hazards, and causes for ignition of such dust clouds are numerous [Hartmann and Greenwald, Min. MetalL, 26, 331 (1945)]. Concentration of the dust in air and its particle size are important fac tors that determine explosibility. Below a lower Umit of concentration, no explosion can result because the heat of combustion is insufficient to propagate it. Above a maximum limiting concentration, an explosion cannot be produced because insufficient oxygen is available. The finer the particles, the more easily is ignition accomplished and the more rapid is the rate of combustion. This is illustrated in Fig. 20-7. 

Elammability Limits The minimum and maximum concentrations of combustible material in a homogeneous mixture with gaseous oxidizer that will propagate a flame. 

Overview of Combustion and Flame Propagation Phenomena Related to DDAs... 

Fundamental, laminar, and turbulent burning velocities describe three modes of flame propagation (see the Glossary for definitions). The fundamental burning velocity, S, is as its name implies, a fundamental property of a flammable mixture, and is a measure of how fast reactants are consumed and transformed into products of combustion. Fundamental burning velocity data for selected gases and vapors are listed in Appendix C of NFPA68 (1998). 

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