Spray-Flame Dynamics in a Rich Droplet Array
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We numerically study spray-flame dynamics. The initial state of the spray is schematized by alkane droplets located at the nodes of a face-centered 2D-lattice. The droplets are surrounded by a gaseous mixture of alkane and air. The lattice spacing s reduced by the combustion length scale is large enough to consider that the chemical reaction occurs in a heterogeneous medium. The overall spray equivalence ratio is denoted by ϕ T , with ϕ T = ϕ L + ϕ G , where ϕ G corresponds to the equivalence ratio of the gaseous surrounding mixture at the initial saturated partial pressure, while ϕ L is the so-called liquid loading. To model such a heterogenous combustion, the retained chemical scheme is a global irreversible one-step reaction governed by an Arrhenius law, with a modified heat of reaction depending on the local equivalence ratio. ϕ T is chosen in the range 0.9 ≤ ϕ T ≤ 2. Three geometries (s = 3, s = 6, s = 12) and four liquid loadings, ϕ L = 0.3, ϕ L = 0.5, ϕ L = 0.7, ϕ L = 0.85 are studied. In the rich sprays, our model qualitatively retrieves the recent experimental measurements: the rich spray-flames can propagate faster than the single-phase flames with the same overall equivalence ratio. To analyse the conditions for this enhancement, we introduce the concept of “spray Peclet number”, which compares the droplet vaporization time with the combustion propagation time of the single-phase flame spreading in the fresh surrounding mixture.
KeywordsDroplet combustion Heterogeneous combustion Reduced kinetics Spray-flame Two phase-combustion
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