Geometrical Limitations of Flame Propagation

It should be noted that, apparently, the ignition energy increase is characteristic of any mixture. Similar ignition energy behavior has been demonstrated for a mixture diluted with carbon dioxide gas. 

Let us consider flame propagation limitations caused by aperture sizes, tube diameters, or gap dimensions through which the flame cannot propagate. These issues are important for safe engineering. 

A critical tube diameter is a characteristic parameter of flame extinction. There is also a term critical gap du, i.e. a distance between two parallel plates when flame extinction occurs. It has been found empirically that the critical tube diameter is approximately 1.5 times bigger than the critical gap du [29]. 

In practice these critical geometrical parameters are used in devices where flame breakthrough must be prevented. Besides, a mixture composition including the fuel excess factor should be taken into account. Two key parameters are velocity and initial pressure. 

It is customary to assume that tube critical diameter da is in inverse proportion to pressure P. The experimental data from [30] and [31], demonstrate this proportion 

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