Nagle and Strickland-Constable

Unfortunately, OH and O concentrations in flames are determined by detailed chemical kinetics and cannot be accurately predicted from simple equilibrium at the local temperature and stoichiometry. This is particularly true when active soot oxidation is occurring and the local temperature is decreasing with flame residence time [59], As a consequence, most attempts to model soot oxidation in flames have by necessity used a relation based on oxidation by 02 and then applied a correction factor to augment the rate to approximate the effect of oxidation by radicals. The two most commonly applied rate equations for soot oxidation by 02 are those developed by Lee el al. [61] and Nagle and Strickland-Constable [62],... 

Inherent in the developments given is the assumption that all adsorption sites will yield a product oxide. In considering the heterogeneous oxidation of coal char or soot particles, however, it is most apparent not all sites are reactive, nor do they all have the same reactivity. In an effort to obtain a more detailed analysis of the burning rates of such materials as a function of temperature, Radcliffe and Appleton [31] proposed a mechanism that leads to the development of the semiempirical correlation of Nagle and Strickland-Constable [32]. Indeed, on the basis of structural similarities, these investigators have suggested that the rate of oxidation of soot and char-like materials should be equivalent. In their mechanism of surface oxidation, they posited two types of reaction sites in the exposed area... 

Nagle and Strickland-Constable [32] chose the following values for the rate constants ... 

Using the values chosen by Nagle and Strickland-Constable, it is possible to explain the trends given in Fig. 21. One observes that at low temperatures kj 0 and xa 1, and for low O2 partial pressure. 

The oxidation model used is the one by Nagle and Strickland-Constable [34], as presented in Chan et al. [10]. In this model, the oxidation of carbon takes place by two mechanisms whose rates are dependent on the surface chemistry involving the more reactive form of carbon, Ca, and the less reactive form of carbon, Cb- This mechanism is expressed by the chemical reactions... 

J. Nagle and R. F. Strickland-Constable, Proc. Fifth Conf. on Carbon, vol 1,... 

---