DNS of spark ignition and edge flame propagation in turbulent droplet-laden mixing layers

Journal Article · Tue Jun 15 00:00:00 EDT 2010 · Combustion and Flame

DOI:https://doi.org/10.1016/J.COMBUSTFLAME.2010.01.019· OSTI ID:21318358

Neophytou, A; Mastorakos, E; Cant, R S ^[1]

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1. Hopkinson Laboratory, Department of Engineering, University of Cambridge (United Kingdom)

A parametric study of forced ignition at the mixing layer between air and air carrying fine monosized fuel droplets is done through one-step chemistry direct numerical simulations to determine the influence of the size and volatility of the droplets, the spark location, the droplet-air mixing layer initial thickness and the turbulence intensity on the ignition success and the subsequent flame propagation. The propagation is analyzed in terms of edge flame displacement speed, which has not been studied before for turbulent edge spray flames. Spark ignition successfully resulted in a tribrachial flame if enough fuel vapour was available at the spark location, which occurred when the local droplet number density was high. Ignition was achieved even when the spark was offset from the spray, on the air side, due to the diffusion of heat from the spark, provided droplets evaporated rapidly. Large kernels were obtained by sparking close to the spray, since fuel was more readily available. At long times after the spark, for all flames studied, the probability density function of the displacement speed was wide, with a mean value in the range 0.55-0.75S{sub L}, with S{sub L} the laminar burning velocity of a stoichiometric gaseous premixed flame. This value is close to the mean displacement speed in turbulent edge flames with gaseous fuel. The displacement speed was negatively correlated with curvature. The detrimental effect of curvature was attenuated with a large initial kernel and by increasing the thickness of the mixing layer. The mixing layer was thicker when evaporation was slow and the turbulence intensity higher. However, high turbulence intensity also distorted the kernel which could lead to high values of curvature. The edge flame reaction component increased when the maximum temperature coincided with the stoichiometric contour. The results are consistent with the limited available experimental evidence and provide insights into the processes associated with ignition of practical spray flames. (author)

• OSTI ID: 21318358
• Journal Information: Combustion and Flame, Vol. 157, Issue 6; Other Information: Elsevier Ltd. All rights reserved; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
VAPORS
DROPLETS
AIR
FLAMES
IGNITION
LAYERS
MIXING
VELOCITY
FLAME PROPAGATION
SPRAYS
FUELS
THICKNESS
SIZE
PROBABILITY DENSITY FUNCTIONS
TURBULENCE
COMPUTERIZED SIMULATION
EVAPORATION
HEAT
CORRELATIONS
COMBUSTION KINETICS
PARAMETRIC ANALYSIS
ELECTRIC SPARKS
DIFFUSION
VOLATILITY
Turbulent edge flames
Displacement speed