Flame properties and maximum ceiling smoke temperature in tunnel fires with two asymmetric fire sources under natural ventilation

Multiple fire source fires in a tunnel may cause serious fire consequences. In the present study, the flame properties and maximum ceiling smoke temperature for two asymmetric fire sources in the tunnel with natural ventilation are studied in detail. A large number of model-scale fire experiments are performed, considering energy release rate ratio ratio and fire source spacing. The results show that the smaller fire has a larger flame inclination angle and the flame inclination angle of the smaller fire increases with energy release rate ratio. In contrast, the flame tilt angle of the larger fire becomes slightly smaller with the energy release rate ratio. When mean flames merge vertically, the flame height becomes higher when the energy release rate ratio increases. A revised model based on the air entrainment perimeter is proposed to calculate the height of the merged flame. When mean flames cannot merge vertically, a non-dimensional correlation is also developed. With a longer fire source spacing, the maximum ceiling smoke temperature decreases first and then remains unchanged. According to the relative position of the flame tip and tunnel ceiling height, a model is developed to calculate the maximum ceiling smoke temperature. The results of this paper are significant to the fire detection and structure protection for the possibility of two asymmetric fire sources in a tunnel with natural ventilation.