ABSTRACT
The concentration of all species in the post-flame zone must approach that defined by thermodynamic equilibrium at the prevailing temperature. Flames can occur only in mixtures within a certain composition range, bounded by the flammability limits. These limits refer to the composition range within which ignition and flame propagation can be brought about by the application of an external stimulus, example a spark or pilot flame. A related phenomenon is that of flame quenching close to a solid surface. A premixed flame will propagate through a stationary gas at a characteristic velocity termed the burning velocity, or it may remain in one place if the reactant gas is forced to move towards the flame front at the same speed. In slow-burning diffusion flames the fuel rises slowly and laminar flow ensues. The character of the flame depends on the nature of the gas flow which is usually indicated by the Reynolds number.
