A spray flame propagating in a nonadiabatic duct with varying cross-sectional area

Journal Article · Sun Jan 01 04:00:00 EST 2006 · Combustion and Flame

DOI:https://doi.org/10.1016/j.combustflame.2005.08.006· OSTI ID:20685992

Tsai, Chih-Hsin ^[1]; Hou, Shuhn-Shyurng ^[2]; Lin, Ta-Hui ^[3]

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1. Department of Mechanical Engineering, Hsiuping Institute of Technology, Taichung, Taiwan 412 (Republic of China)
2. Department of Mechanical Engineering, Kun Shan University, Tainan, Taiwan 71003 (Republic of China)
3. Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan 70101 (Republic of China)

The influence of flame stretch, preferential diffusion, internal heat transfer, and external heat loss on the extinction of dilute spray flames propagating in a nonadiabatic duct with varying cross-sectional area is analyzed using activation energy asymptotics. A completely prevaporized mode and a partially prevaporized mode of flame propagation are identified. Internal heat transfer, resulting from droplets gasifying, varies with the liquid-fuel loading and the initial droplet size in the spray and also provides internal heat loss for rich sprays but heat gain for lean sprays. A spray flame propagating in a divergent (convergent) duct experiences positive (negative) stretch. The results show that the burning intensity of a lean (or rich) spray is enhanced (or reduced) with an increased liquid-fuel loading or smaller initial droplets. The positive stretch coupled with the effects of the Lewis number (Le) weakens a lean methanol-spray flame (Le>1), but intensifies a rich methanol-spray flame (Le<1). For a positively stretched flame with Le<1 or a negatively stretched flame with Le>1, without external heat loss, no extinction occurs by increasing the stretch. However, irrespective of heat loss, a flame with Le>1 experiencing positive stretch or a flame with Le<1 enduring negative stretch can be extinguished by increasing the stretch. Flame extinction characterized by a C-shaped curve is dominated by stretch or external heat loss. Note that for a methanol-rich spray flame (Le<1) experiencing positive stretch and enduring a partially prevaporized spray composed of a large enough liquid loading and sufficiently large droplets, an S-shaped extinction curve can be obtained. The S-shaped curve, which differs from the C-shaped one, indicates that flame extinction is governed by internal heat loss.

• OSTI ID: 20685992
• Journal Information: Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 1-2 Vol. 144; ISSN CBFMAO; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
DIFFUSION
DROPLETS
DUCTS
FLAME PROPAGATION
HEAT LOSSES
HEAT TRANSFER
METHANOL
SIZE
SPRAYS