Flame Spread Over Ultra-thin Solids: Effect of Area Density and Concurrent-Opposed Spread Reversal Phenomenon

  • Anthony Vetturini
  • Wohan Cui
  • Ya-Ting LiaoEmail author
  • Sandra Olson
  • Paul Ferkul


There are no existing experimental studies of flame spread rate trends for ultra-thin solid samples. Previous theory has predicted that for concurrent flame in kinetic regime, the flame spread rate decreases as the sample thickness decreases and there is a critical thickness below which burning is not possible. To test this hypothesis, a series of microgravity experiments of concurrent-flow flame spread over samples of ultra-low area densities are conducted using NASA Glenn Research Center’s Zero Gravity Research Facility (the 5.18 s drop tower). The tested samples are cellulose-based materials of various area densities, ranging from 0.2 mg/cm2 to 13 mg/cm2, as low as one order of magnitude less than those ever tested before. Each sample is 30 cm long by 5 cm wide and is burned in a low-speed concurrent air flow (5 to 30 cm/s). The results show that the concurrent flame spread rate is proportional to the flow velocity relative to the flame and is inversely proportional to the sample area density. A theoretical formulation, provided in this work, suggests that the flame length has a linear relationship with the relative flow speed and has no direct dependency on the sample area density. The experimental data supports this conclusion. From the images recorded in the experiments, a unique flame base tubular structure directed upstream away from the burnout zone is observed for thin samples. This structure is suspected to be due to flame stretching and localized blowoff caused by the oxidative pyrolysis Stefan flows at the sample burnout. This can be an indication that the chemical time becomes comparable to the flow time of the Stefan flow and the tested samples are approaching the kinetically-limited thickness. For the thinnest tested sample (0.2 mg/cm2), flames with concurrent and opposed dual natures are observed when the air flow rate is low (< 20 cm/s). At the lowest tested flow rate (5 cm/s), the flame spread rate exceeds the air flow rate and the flame transits to an opposed flame in the concurrent flow. The dual nature and flame transition are presented and discussed. This study provides detailed examination through high-resolution images of the transition between the concurrent to opposed flame spread modes.


Flame spread Material flammability Quenching limit Concurrent-opposed reversal Ultra-thin solid fuel 

List of Symbols


Species diffusivity

\( k_{g} \)

Gas-phase thermal conductivity


Latent heat of a solid fuel

\( L_{f} \)

Flame length

\( L_{p} \)

Pyrolysis length

\( \dot{m}' \)

Total burning rate of a sample per unit width \( ( = \rho \tau V_{f} ) \)

\( \overline{{\dot{m}''}} \)

Average burning rate of a sample \( \left( { = \frac{{\rho \tau V_{f} }}{{L_{f} }}} \right) \)

\( \overline{{\dot{q}_{c} ''}} \)

Average conductive heat flux


Reynolds number


Local Reynolds number


Time after drop

\( T_{f} \)

Flame temperature

\( T_{p} \)

Pyrolysis temperature

\( V_{f} \)

Flame spread rate

\( V_{rel} \)

Relative flow velocity (concurrent, dual nature, and concurrent-reversed: \( V_{rel} = \left| {V_{\infty } - V_{f} } \right| \); opposed: \( V_{rel} = V_{\infty } + V_{f} \))

\( V_{\infty } \)

Forced flow velocity


Distance away from the upstream leading edge of a sample

\( y_{f} \)

Cross-stream location (away from sample surface) of a flame

\( \alpha \)

Gas-phase thermal diffusivity

\( \rho \tau \)

Sample area density

\( \nu \)

Kinematic viscosity



This work is supported by National Science Foundation under Award #1740478 (Division of Chemical, Bioengineering, Environmental, and Transport Systems) and NASA Glenn Research Center under Award #NNX16AL61A. We would also like to thank the crew members of the Zero Gravity Research Facility, Eric Neumann, Luke Ogorzaly, Mingo Rolince, Moses Brown, and Vittorio Valletta, for their tremendous help during the experiment operation.


  1. 1.
    Olson SL, Miller FJ (2009) Experimental comparison of opposed and concurrent flame spread in a forced convective microgravity environment. Proc Combust Inst 32(2):2445–2452CrossRefGoogle Scholar
  2. 2.
    Markstein GH, de Ris J (1973) Upward fire spread over textiles. Proc Combust Inst 14(1):1085–1097CrossRefGoogle Scholar
  3. 3.
    Fernandez-Pello AC (1979) Flame spread in a forward forced flow. Combust Flame 36:63–78CrossRefGoogle Scholar
  4. 4.
    Loh HT, Fernandez-Pello AC (1986) Flow assisted flame spread over thermally thin fuels. Fire Saf Sci 1:65–74CrossRefGoogle Scholar
  5. 5.
    Saito K, Quintiere JG, Williams FA (1986) Upward turbulent flame spread. Fire Saf Sci 1:75–86CrossRefGoogle Scholar
  6. 6.
    Tseng Y-T, T’ien JS (2010) Limiting length, steady spread, and nongrowing flames in concurrent flow over solids. J Heat Transf 132(9):091201-1–091201-9CrossRefGoogle Scholar
  7. 7.
    Urban DL, Ferkul P, Olson S, Ruff GA, Easton J, T’ien JS, Liao Y-TT, Li C, Fernandez-Pello C, Torero JL, Legros G, Eigenbrod C, Smirnov N, Fujita O, Rouvreau S, Toth B, Jomaas G (2019) Flame spread: effects of microgravity and scale. Combust Flame 199:168–182CrossRefGoogle Scholar
  8. 8.
    Li C, Liao Y-TT, T’ien JS, Urban DL, Ferkul DL, Olson S, Ruff GA, Easton J (2019) Transient flame growth and spread processes over a large solid fabric in concurrent low-speed flows in microgravity—model versus experiment. Proc Combust Inst 37(3):4163–4171CrossRefGoogle Scholar
  9. 9.
    Zhao X, Liao Y-TT, Johnston MC, T’ien JS, Ferkul PV, Olson SL (2017) Concurrent flame growth, spread, and quenching over composite fabric samples in low speed purely forced flow in microgravity. Proc Combust Inst 36(2):2971–2978CrossRefGoogle Scholar
  10. 10.
    Gollner MJ, Huang X, Cobian J, Rangwala AS, Williams FA (2013) Experimental study of upward flame spread of an inclined fuel surface. Proc Combust Inst 34(2):2531–2538CrossRefGoogle Scholar
  11. 11.
    Olson SL, Ferkul PV, T’ien JS (1989) Near-limit flame spread over a thin solid fuel in microgravity. Symp (Int) Combust 22(1):1213–1222CrossRefGoogle Scholar
  12. 12.
    Olson SL (1991) Mechanisms of microgravity flame spread over a thin solid fuel: oxygen and opposed flow effects. Combust Sci Technol 76:233–249CrossRefGoogle Scholar
  13. 13.
    Sacksteder KR, T’ien JS (1994) Buoyant downward diffusion flame spread and extinction in partial-gravity accelerations. Symp (Int) Combust 25(1):1685–1692CrossRefGoogle Scholar
  14. 14.
    Olson SL, Miller FJ, Jahangirian S, Wichman I (2009) Flame spread over thin fuels in actual and simulated microgravity conditions. Combust Flame 156(6):1214–1226CrossRefGoogle Scholar
  15. 15.
    Jiang C-B (1995) A model of flame spread over a thin solid in concurrent flow with flame radiation. Ph.D. Dissertation, Case Western Reserve University, Cleveland, OHGoogle Scholar
  16. 16.
    Di Blasi C (1995) Influences of sample thickness on the early transient stages of concurrent flame spread and solid burning. Fire Saf J 25(4):287–304CrossRefGoogle Scholar
  17. 17.
    Quintiere JG (2006) Fundamental of fire phenomena. Wiley, West SussexCrossRefGoogle Scholar
  18. 18.
  19. 19.
    White FM (2003) Fluid mechanics. McGraw-Hill, New YorkGoogle Scholar
  20. 20.
    Olson SL, T’ien JS (2000) Buoyant low-stretch diffusion flames beneath cylindrical PMMA samples. Combust Flame 121(3):439–452CrossRefGoogle Scholar
  21. 21.
    Ferkul PV, T’ien JS (1994) A model of low-speed concurrent flow flame spread over a thin fuel. Combust Sci Technol 99:345–370CrossRefGoogle Scholar
  22. 22.
    Kundu PK, Cohen IM (2004) Fluid mechanics, 3rd edn. Elsevier Academic Press, San DiegoGoogle Scholar
  23. 23.
    de Ris JN (1969) Spread of a laminar diffusion flame. Symp (Int) Combust 12(1):241–252CrossRefGoogle Scholar
  24. 24.
    Prasad K, Nakamura Y, Olson SL, Fujita O, Nishizawa K, Ito K, Kashiwagi T (2002) Effect of wind velocity on flame spread in microgravity. Proc Combust Inst 29:2553–2560CrossRefGoogle Scholar

Copyright information

© This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2019

Authors and Affiliations

  1. 1.Department of Mechanical and Aerospace EngineeringCase Western Reserve UniversityClevelandUSA
  2. 2.NASA Glenn Research CenterClevelandUSA

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