Burning characteristic and ceiling temperature of moving fires in a tunnel: A comparative study

Abstract

Moving fire is a very important fire scenario in highway tunnel and subway tunnel. Compared to fixed fire sources, there is still limited research on moving fires in tunnels. In order to reveal the burning characteristics and evolutionary mechanisms of moving fires in tunnels, this study conducted reduced scale tunnel fire experiments on moving fires under natural ventilation conditions (Movefire) at travelling speeds ranging from 0.5 m/s to 2.0 m/s, as well as fixed fires under longitudinal ventilation (Ventfire) velocities ranging from 0.5 m/s to 2.0 m/s. The results demonstrate that it is unreasonable to solely use Ventfire experiments as a substitute for Movefire experiments to study fire development and ceiling smoke temperature distributions. When the travelling speed of fire and the ventilation velocity were equal, the HRRs of Movefires were less than those of Ventfires. At the same relative moving velocity of 0.5 m/s, Ventfire received more fresh air to increase burning intensity, while Movefire experienced decreases in thermal feedback and burning intensity. The Movefire smoke temperature rise was small and short in duration, while the Ventfire smoke temperature rise was large and long in duration. Furthermore, the dimensionless maximum ceiling temperature rise of the Movefire experiment was lower than that of the Ventfire experiment. And then a modified ceiling temperature model applicable to the Movefire experiment was proposed by introducing a speed correction factor.