Radical recombination in fuel-rich systems. Partial equilibration concepts

1 Radical recombination in fuel-rich systems. Partial equilibration concepts 

A number of flame-photometric methods have been developed by Sugden and co-workers [131—134] to measure hydrogen atom concentrations in the burnt gas from hydrogen—oxygen flames. When small quantities of a sodium (or similar) salt are added to a flame, and if the flame temperature is high enough, thermal sodium D-line emission occurs. At low concentrations this emission is proportional to the concentration of the metal atoms. However, if lithium salts are added to the flame, some hydroxide is formed [135] by the process 

This reaction is sufficiently rapid for the maintenance of equilibrium. Thus the total amount of lithium added to the flame, [Li] o, is equal to [Li] + [LiOH], and if the amount of free lithium [Li] at a position in the flame is measured spectroscopically the concentration of lithium hydroxide can be deduced. Since the water vapour concentration in the burnt gas is known, it is then possible to deduce the concentrations of H atoms from the equilibrium expression. In sufficiently hot flames the concentration of free lithium may be estimated, after calibration of the 

In flames with lower final flame temperatures where the thermal emission from added metal atoms is less, a chemiluminescent effect [134] may occur. Here, there is a rapid rise of intensity in the reaction zone followed by a steady decay towards the thermal level. The chemiluminescence is due to excitation of the metal (in this case sodium) by the reactions 

In the burnt gas recombination region of fast, fuel-rich hydrogen-nitrogen—oxygen flames the observed intensities of chemiluminescence for sodium and other metal additives were found [134] to obey the relation 

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