The extinction behavior of small interacting droplets in cross-flow

Abstract

Experiments were conducted on monodisperse streams of small (Ͻ100 m) methanol and ethanol droplets, injected perpendicularly to the axis of an axisymmetric methane diffusion flame. After crossing the methane flame, the droplets ignited and continued to burn outside of the "domain of influence" of the gaseous flame till they eventually extinguished. The extinction behavior was studied as a function of droplet spacing, oxidizer concentration and velocity, and droplet velocity by measuring droplet size and velocity at the time of extinction using a commercial Phase Doppler Anemometer. The onset of droplet interaction effects on extinction was found at interdroplet distances well above the limits reported in the literature. The interaction is attributed to the vitiated atmosphere left behind by the leading droplet that affects the extinction conditions of the trailing one. The ratio between interdroplet time and convection time normal to the droplet direction of travel was found to be the controlling parameter. Results were correlated in terms of a critical Damköhler number that was found to scale as dY o,ϱ no /v, where d is the droplet diameter, Y o,ϱ is the oxidizer mass fraction, v is the droplet velocity, and n o is 0.5 and 0.75 for methanol and ethanol, respectively.

Structure of laminar coflow spray flames at different pressures

“…Under certain conditions, even direct droplet/flame interaction may occur in which case droplets ''punch through'' this primary diffusion flame and burn isolated on the oxidizer side. They eventually extinguish when they reach a critical diameter dependent on the dropletgas relative speed [8]. Experimental evidence of direct droplet/flame interaction was presented in Ref.…”

On the generalisation of the mixture fraction to a monotonic mixing-describing variable for the flamelet formulation of spray flames

“…While gaseous diffusion flames are characterized by the competition between scalar mixing and chemistry, spray flames require the continuous supply of gaseous fuel via evaporation and transport to the reaction zone to sustain combustion. Because of this complexity, the investigation of spray flames in canonical combustion configurations, such as mixing layers, coflow and counterflow flames, represents a viable approach to obtain physical insight into the behavior of spray flames [7][8][9][10][11].…”