2.2.1. Option *i*: C2H5–Air Mixture

The expression for Ψ is

$$\mathbf{Y} = \begin{cases} \mathbf{W\_{C\_2H\_5}} \frac{d\boldsymbol{n\_{C\_2H\_5}}}{dt} \text{ for } \mathbf{C\_2H\_5} \\ \text{ 0 for other species} \end{cases} \tag{20}$$

Here, *W*C2H<sup>5</sup> is the molecular mass of C2H5; *dn*C2H5 *dt* is the rate of change in the concentration (mol/cm3/s) of C2H<sup>5</sup> radicals in the heterogeneous reaction (6), which, in accordance with reaction (6) and Equation (13), satisfies the equation

$$\frac{d\mathfrak{u}\_{\rm C\_2H\_5}}{dt} = \frac{\lambda}{4} \mathfrak{u}\_{\rm O\_2} \text{SN}\mathfrak{n}\_{\rm O\_2} \exp\left(-\frac{\varepsilon}{RT}\right) \tag{21}$$
