*2.2. Self-Ignition Delays for C2H5–Air and C2H5O–Air Mixtures*

The mathematical statement of the problem is the statement of the standard problem of the self-ignition of a gas mixture [25] with a given detailed kinetics [26], which is supplemented by a heterogeneous mechanism for the formation of C2H<sup>5</sup> or C2H5O radicals. The equations for the conservation of the energy and mass of the components have the form

$$
\sigma\_p \rho \frac{dT}{dt} = \Phi \tag{18}
$$

$$
\rho \frac{dY\_j}{dt} = w\_j + \Psi\_\prime \; j = 1, 2, \dots, M \tag{19}
$$

where *t* is time; *M* is the number of components in the gas mixture; *Y<sup>j</sup>* is the mass fraction of the *j*th component; *c<sup>p</sup>* is the heat capacity of the gas mixture at constant pressure; *ρ* is the density of the mixture; Φ is the heat release in chemical reactions; *w<sup>j</sup>* is the component consumption in chemical reactions; and Ψ is the formation of C2H<sup>5</sup> or C2H5O in reaction (6) or (5), respectively. The system of Equations (18) and (19) is supplemented by the ideal gas equation of state, expressions for Φ and *w<sup>j</sup>* [27], and by the polynomial relationship for the heat capacity, while the polynomial coefficients are taken from [28].

Compared to the standard problem formulation for gas mixture self-ignition, the expression for Ψ and all other considerations associated with this circumstance are new. It is assumed that the mixture is initially represented by pure air, and radicals C2H<sup>5</sup> or C2H5O appear in the gas due to the heterogeneous reaction (6) or (5), respectively. Self-ignition delays depend on the rates of formation of C2H<sup>5</sup> and C2H5O radicals in heterogeneous reactions (6) and (5) and on the rates of their interaction with oxygen in the gas phase. As both reactions, (6) and (5), are possible, for determining the effect of these radicals on the self-ignition delay, the problem must be solved for two options: (*i*) for a C2H5–air mixture and (*ii*) for a C2H5O–air mixture.
