The authors investigated the thermal explosion of polydisperse fuel spray with a complete description of the chemistry via a single-step 2-reactant model of general order. A detailed mathematical analysis has been carried out of this new physical model that encompasses oxidizer effects on the thermal explosion of a hot combustible mixture of gases and evaporating fuel droplets. The polydisperse spray is modeled by using a probability density function (PDF). The dynamics of the explosion is presented in terms of the dynamics of a multiscale system, which enabled the authors to apply the method of integral manifolds (MIM). An explicit expression of the critical condition for thermal explosion limit was derived analytically. Numerical simulations demonstrated an essential dependence of this critical parameter on the PDF type and represent a generalization (for polydisperse sprays) of the critical parameter of the classical Semenov theory.