General Properties of Explosive Processes

It is commonly observed that several main combustion regimes can occur when a combustible mixture gets into an obstructed duct or into a structure with various obstacles. They are as follows  

An approximate dimension-concentration chart of the above regions generated in tubes with methane + air and hydrogen + air mixtures are shown in Fig. 5.24 [34]. The conditional character of the chart is explained by the subjectivity of the combustion regime classification. 

One of the phenomena leading to development of explosion processes is flame acceleration (FA). If a combustion is spark initiated (a low-power initiator), initially the flame is laminar, if parameters of the mixture are considered within ignition limits. The laminar flame propagation velocity with respect to the gas ahead of the flame front is determined by the local combustion velocity. The combustion 

In real life, since a combustion process is accompanied by the expansion of the combustion products, the combustion development is not restricted to the laminar flame stage. If combustion is initiated at the closed end of a volume, then, in laboratory coordinates system, the flame propagation velocity is determined by the combustion velocity and the rate of expansion of the combustion products. The flame propagation velocity can be several times higher than the normal combustion velocity. 

When the flame velocity, with respect to the combustion products, reaches the sound speed in the products, the flame becomes locked. Such locked or sonic flames are characterized by the maximum possible velocity of turbulent combustion propagation. Typical velocity values of sonic flame propagation are 600-1,000 m/s. 

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