Fast Deflagration and Quasi-Detonation in a Confined Volume

1 Fast Deflagration and Quasi-Detonation in a Confined Volume 

In an effort to explain the dependence of the combustion feedback effect on the conditions of its response to external impacts, let us consider the known sequence of combustion regimes in a smooth non-obstructed tube. 

For this purpose, a simplified scheme [2] presented in Fig. 5.1 is used. The smooth tube 1 with the igniter 2 at its closed end is illustrated in Fig. 5.1a. The primarily smooth combustion front 3 propagates through the tube, where the initial combustible mixture 4 is transformed into combustion products 5. The expanding combustion products push the unburned gas 6 with a velocity profile distributed across the tube cross-section. The flame front 7 starts distorting during propagation and the fresh mixture stream 8 becomes unstable (Fig. 5.1b). After that, the 

Gelfand et al., Thermo-Gas Dynamics of Hydrogen Combustion and Explosion, Shock Wave and High Pressure Phenomena, 

The instability of boundaries between gases of various densities is considerable in confined vessels, tubes and ducts. Flame acceleration due to Rayleigh -Taylor instability is explained by the fact that when the pressure wave crosses the flame front from the side of the combustion products (their density is less than that in the fresh mixture), the amplitude of all the flame front irregularities grows rapidly and the flame surface area increases. The extreme H2 + air mixture flame acceleration resulting from turbulence was mentioned earlier. In confined vessels, flame acceleration up to the detonation velocity is often caused by flame front instabilities when it interacts with compression waves. 

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