Theory of vaporization and combustion of fuel sprays in strained laminar mixing layers

The vaporization and combustion of a monodisperse fuel spray in a laminar counterflow mixing layer is investigated under conditions such that the droplet Stokes number is smaller than 1/4, so that the droplets do not cross the stagnation plane, but instead tend to accumulate there because of their inertial slip motion. Vaporization is confined to the thin strained mixing layer separating the spray from the hot stream, which can be described with an Eulerian description for the liquid phase. The numerical integration of the resulting boundary-value problem provides the structure of the reactive mixing layer, including the standoff distance from the stagnation plane where droplets disappear and the flame location. Limiting asymptotic solutions for extreme values of the controlling parameters are also determined, and a generalized vaporization law for droplets in the presence of thermal gradients is derived. The results provide increased understanding of laminar spray flamelets.