The kinetic parameters of ignition of a solid fuel may change with various combustion gas environments. Some reported the activation energy is independent on [O2], whilst some others argued that both the activation energy Ea and the pre-exponential factor A compensatorily increase with increasing [O2]. In my opinion, both the reactants: fuel and O2 are not changed, thus Ea is supposed to be remained. As [O2] increases, the O2 molecules increase as a sequence, resulting in a higher ratio collision factor (i.e., pre-exponential factor A). Which proposal is correct in you opinion? Thanks.
For combustion of carbonaceous solid fuels and some liquid fuels in a continuous flow system, the rate equation is often written in the generic form r = A * Tb * exp(-Ea/RT) * Sm * [O2]n. When such rate equation is used, Ea and A are supposed to be insensitive to [O2] and diluent gas concentrations in the bulk gas flow. Note that the term "diluent gases" implies that these gases only have no other effects than diluting effect, which may or may not be true depending on what gases we're talking about. However, the reaction order w.r.t. [O2] is very likely to decrease with increasing [O2], i.e. it becomes less sensitive at high O2 concentrations.
Thanks, Xuantian. Indeed, it makes sense to add a term [O2] with reaction order n. qualitatively, it is correct that n decrease with increasing [O2], e.g., n=0 means reaction rate is oxygen independent . I guess you probably give a modification type of Arrhenius equation since with the term of Tb for the pre-exponential factor A, and obviously the reaction rate you mentioned above is taking [O2] as the "leading component" because there is no density or concentration term of solid fuel. What does Sm represent? Now the question is how do you determine or derive the kinetic parameters on [O2] basis? Do you have some experiences on this topic? As far as I know, both the approaches of the F-K model combining with basket test with various basket volumes and TGA test with various heating rates are on the solid fuel basis.
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