Structure and extinction of laminar ethanol-air spray flames

Abstract

A numerical study of structures of laminar ethanol-air spray flames in the counterflow configuration is presented. The model describes a thin spray where the gas phase is formulated in Eulerian coordinates and the spray is described through Lagrangian equations. The study presents structures and extinction conditions for atmospheric spray flames, and the focus is the fuel ethanol that has not been studied so far in the literature. Moreover, both mono- and bidisperse sprays are studied for strain rates that range from 55 s⁻¹ up to extinction. The different droplet size groups that are considered in the discrete droplet model are treated completely separately from each other so that their individual history is represented by the model. The emphasis is the possible representation of bidisperse sprays through a Sauter mean radius for the above specified conditions which has a specific significance to the consideration of laminar spray flame structures in turbulent spray flame computations where a flamelet model may be employed. The results show that ethanol-air spray flames are more stable than methanol-air spray flames and their extinction flame temperature is above that of methanol-air spray flames all the way up to extinction. The extinction conditions of the bidisperse and the monodisperse ethanol-air spray flames with a Sauter mean radius differ considerably. This is attributable to the occurrence of droplet reversal and oscillation. The study also shows the effect of the spray dispersity on the species profiles.