Numerical Investigation on the Influence of Length–Width Ratio of Fire Source on the Smoke Movement and Temperature Distribution in Tunnel Fires

  • Jie JiEmail author
  • Tiantian Tan
  • Zihe Gao
  • Huaxian Wan
  • Jiping Zhu
  • Long Ding


The behaviors hot and toxic smoke in tunnel fires is important to the engineering applications of fire protection systems. The shapes of fire source may affect the characteristics of smoke movement in tunnels. In the current study, a numerical investigation is conducted to explore the effect of fire source shape on the smoke movement and temperature distribution in a full scale road tunnel. The area of fire was fixed with the length–width ratio (n) varying from 1 to 11 and the heat release rate (HRR) of the fire source varying from 5 MW to 15 MW. Results show that with increasing HRR and decreasing n, the impinging flow on the tunnel ceiling transits from buoyancy plume to continuous flame and the smoke becomes more difficultly to be uniform along the longitudinal direction, resulting in further starting position of one-dimensional spread stage (L). Due to the change of entrainment behavior, for a certain HRR, the smoke mass flow rate decreases with decreasing n, which is proportional to the perimeter of the fire source. As n decreases from 11 to 1, the smoke mass flow rate decreases for 23%. Moreover, a correlation of the longitudinal smoke temperature distribution under the tunnel ceiling is developed, with the temperature at the initial position of the one-dimension spread stage as the reference value. This study obtains the variation laws of smoke mass flow and temperature distribution under the effects of fire source shape. It can provide a reference for the smoke control and safe evacuation in straight tunnel without forced flow.


Length–width ratio Smoke spread Mass flow rate Smoke temperature Fire 

List of Symbols


The ceiling clearance from the top of the fuel

\( l_{b} \)

One-half of the corridor width

\( \Delta T_{p} \)

The excess temperature on the plume centerline at the level of the ceiling


The distance along the corridor from the plume impingement point

\( \rho_{\infty } \)

Ambient air density

\( c_{P} \)

The constant pressure specific heat capacity


Convection heat transfer system


Fluid velocity


The Stanton number

\( \dot{Q} \)

The heat release rate of fire source


Ambient temperature


Gravity acceleration


The long side length of fire source


The area of fire source. According to the dimensional analysis

\( \dot{m}_{ent} \)

Mass flow of air entrainment

\( \rho_{fl} \)

The gas density of flame

\( W_{f} \)

The fire source perimeter


The elevation above the point source of buoyancy

\( x_{st} \)

The location of the beginning of one-dimensional stage



This work is supported by the National Key Research and Development Plan under Grant No. 2017YFC0803300 and National Natural Science Foundation of China (NSFC) under Grant No. 51706219. Jie Ji was supported by the National Program for Support of Top-notch Young Professionals and the Young Innovation Promotion Association of CAS (2015386).


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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  • Jie Ji
    • 1
    Email author
  • Tiantian Tan
    • 1
  • Zihe Gao
    • 1
  • Huaxian Wan
    • 1
  • Jiping Zhu
    • 1
  • Long Ding
    • 1
  1. 1.State Key Laboratory of Fire ScienceUniversity of Science and Technology of ChinaHefeiChina

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