Production of trace species

Oxides of nitrogen and soot-related species are examples of chemical components present in very low concentrations in turbulent diffusion flames they are trace species. Trace species that maintain chemical equilibrium pose no special problems in that they may be handled directly by the methods of the preceding subsection. However, the trace species of interest often are far from equilibrium, as soot-related species always are and oxides of nitrogen almost always are. The fact that the concentrations of these species are low means that they affect the thermochemistry to a negligible extent and that finite-rate effects for them can therefore be analyzed more easily than those for major species. Methods of analysis have been developed in the literature [15], [27], [28], [82], [83]. Here we shall indicate how calculations of interest may be performed. 

Let there be T trace species out of equilibrium, identified by subscript i = 1. T, and assume (quite reasonably) that their chemistry involves at 

First consider production of NO by the Zel dovich mechanism given at the end of Section B.2.5 [15], [83]. The molar rate of production of NO is where kf is the specific reaction-rate constant for the 

Since N2 and O2 are major species, the first of which is practically inert and the second of which usually nearly maintains chemical equilibrium, the equilibrium chemistry for the diffusion flame gives jo q(Z) from equation (41). Then, as in equation (40), 

Equation (42) provides an estimate of the average rate of production of NO. 

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