Analysis of Completely Prevaporized Spray Flames with Water/Octane Core/Shell Structured Droplets

Abstract

A series of studies on laminar flame propagation in off-stoichiometric dilute sprays of monodispersed inert or fuel drops had been investigated by large activation energy asymptotics. The present study extends previous theoretical model to consider water/octane core/shell structured drops instead of single-phase drops. The core/shell structured drops are composed of core fluid (water) encased by a layer of shell fluid (n-octane). In this study, we only deal with the case that core/shell structured drops are vaporized completely just at flame location. Namely, the discussions of this paper are restricted to the completely prevaporized mode. By varying parameters of core water radius, core-to-shell ratio, the amount of liquid loading, and the stoichiometric ratio (lean or rich burning), we examine the gasification of core water and shell fuel of core/shell structured drops upstream of the bulk flame and its relation to the internal heat transfer. The effects of drop radius, core-to-shell ratio, liquid loading, and overall heat loss or gain on flame propagation flux are reported and discussed.

Micro-explosion effects in a laminar water-in fuel spray diffusion flame

“…In recent work [10][11][12][13][14][15], water-in-fuel (WIFE) emulsion spray flames were considered theoretically. The droplets themselves were taken to be comprised of an outer layer of liquid fuel immiscible with an inner sphere of water.…”

“…This provides a sufficiently significant heat sink for temperature reduction which, if correctly controlled, lowers the onset of cracking of liquid phase hydrocarbons within the droplet and thereby reduces the formation of particulate matter [17,18]. The latent heat discrepancy also has a strong effect on the laminar flame speed [10][11][12][13] and flame stability [14,15], depending on the relative amount of water in the droplets and the location of onset of pure water evaporation.…”

“…In previous theoretical research [10][11][12][13][14][15] the type of water-in-flame spray flames considered was taken to be premixed, due to their applicability in realistic combustion systems. However, non-premixed spray flames are also of practical relevance in modern aircraft jet engines which are designed with lean-burn combustion (see, for example, [31] and references therein).…”

Investigation of the Influence of Microexplosions on a Laminar Premixed Water-in-Fuel Emulsion Spray Flame

“…Due to the complexity involved in modeling WIFE spray combustion under conditions in which micro-explosions take place, all theoretical studies we are aware of have only been concerned with the sequential evaporation of the fuel outer "shell" followed by the evaporation of the water inner "core". Thus, in a series of papers Hsuan et al [14], Hsuan and Lin [15,16] and Hou et al [17] considered WIFE spray flames. The mathematical analysis presented by these authors related to both fuel rich and fuel lean flames and took account of the fact that the major effect of the water evaporation was as a heat sink due to the heat loss incurred as the water absorbed heat for evaporation.…”