Effect of opposed flow on flame spread over a finite-length pmma slab in a two-dimensional wind tunnel

Wen Kuei Chang, Chiun-Hsun Chen*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The ignition delay and subsequent downward flame spread over a finite-length PMMA slab with the effect of radiation included in a two-dimensional wind tunnel are investigated using the opposed flow velocity as a parameter. The gas and solid phase temperatures, preheat length and heat flux are considered in order to examine the flame ignition and spread characteristics. The numerical results reveal that the ignition delay time increases with the opposed flow velocity. However, the flame spread rate varies with the opposed flow velocity in a non-monotonic manner that can be identified as two distinct regimes with a peak value in between. The flame spread rate reaches a maximum at Vg=32cm/s, and then falls, regardless of whether the flow velocity is increasing or decreasing. For Vg32cm/s, the flame behaviors are dominated by oxygen transport. For Vg32cm/s, the flame stretch effect controls the flame behavior. Additionally, this work demonstrates that the effect of radiation delays the flame ignition and reduces both the flame strength and the corresponding spread rate. The effects of the opposed flow temperature and thickness of the solid fuel are also investigated. The predicted results indicate that a higher opposed flow temperature or a thinner solid fuel facilitates the ignition and accelerates flame spread. The effect of opposed flow velocity eventually overcomes that of opposed flow temperature as the flow speed is further increased.

Original languageEnglish
Pages (from-to)2489-2510
Number of pages22
JournalCombustion science and technology
Volume179
Issue number12
DOIs
StatePublished - 1 Dec 2007

Keywords

  • Downward flame spread
  • Ignition delay
  • Opposed flow velocity
  • Radiation effect

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