Ignition temperature theory

Rapid flame spread. As we know, radiant preheating of a material can cause its surface temperature to approach its piloted ignition temperature. This causes a singularity in simple flame spread theory that physically means that a premixed mixture at its lower flammability limit occurs ahead of the surface flame. Hence, a rapid spread results in the order of 1 m/s. 

Mallard-Le Chatelier theory, Semenov assumed an ignition temperature, but by approximations eliminated it from the final equation to make the final result more useful. This approach is similar to what is now termed activation energy asymptotics. 

A problem with trying to develop logical theory using literature values of ignition temperatures is the substantial variation in observed values that can occur depending upon the experimental conditions employed to measure the ignition points. Ratio... 

Taffanel s indisputable achievement is his statement of the problem of flame velocity in a mixture characterized by a specific smooth dependence of the reaction rate on the temperature, whereas many authors, both before and after Taffanel, based their calculations on the concept of an ignition temperature at which there was supposedly a jump in the reaction rate. This achievement is a consequence of the theory of self-ignition which Taffanel developed in which the temperature of ignition depends on the interrelation between the continuously varying heat release rate and the conditions of heat transfer. 

It would seem that the concept of ignition temperature as a basic kinetic characteristic of a mixture, and a crucial one in the propagation of the flame as well, is revived in the theory developed by Semenov of branching chain... 

However, no.theory of the concentration limit has existed until recently. The opinion was expressed that the limits correspond to the composition at which the flame velocity goes to zero (Bunte, Jahn) since the combustion temperature is equal to the ignition temperature (Jouguet). 

The objective of this theory is to insulate the combustible substrate (fuel) from attaining igniting temperature. The mastic becomes the thermal barrier for conductivity of heat of fire. It can accomplish this in two ways through rapid conductivity of the heat away from the fire, as illustrated by the wire gauze over the Bunsen burner, through very slow thermal conductivity as exemplified by a fire-insulating brick. 

Later, there were improvements in the thermal theories. Probably the most significant of these is the theory proposed by Zeldovich and Frank-Kamenetskii. Because their derivation was presented in detail by Semenov [4], it is commonly called the Semenov theory. These authors included the diffusion of molecules as well as heat, but did not include the diffusion of free radicals or atoms. As a result, their approach emphasized a thermal mechanism and was widely used in correlations of experimental flame velocities. As in the Mallard-Le Chatelier theory, Semenov assumed an ignition temperature, but by approximations eliminated... 

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