LEAN FLAME DYNAMICS THROUGH A 2D LATTICE OF ALKANE DROPLETS IN AIR

摘要

Flame propagation along a 1-D array or through a 2D-lattice of fuel droplets has long been suggested to schematize spray-flames spreading in a two-phase premixture. The present numerical work considers the fresh aerosol as a system of individual alkane droplets initially located at the nodes of a face-centered 2D-lattice, surrounded by a variable mixture of alkane and air, in which the droplets can move. The main parameters of the study are s, the lattice path, and φ_L, the liquid loading, which are both varied, whereas φ_T, the overall equivalence ratio, is maintained lean (φ_T = 0.85). Main results are as follows: (a) For a large lattice path (or when the droplets are large enough), spreading occurs in two stages: a short time of combustion followed by a long time lag of vaporization and a classical triple flame (with a very short rich wing) spreads around the droplets; (b) spray-flame speed decreases as liquid loading increases; (c) an elementary model invoking both propagation stages allows us to interpret flame speed as a function of the sole parameter s × φ_L; (d) when the lattice path shortens, the spray-flame exhibits a pattern that continuously goes from this situation to the plane flame front.