Theoretical and experimental studies on smoke temperature decay in train fires in railway tunnels

In tunnels, the spread of the smoke along the ceiling can be seen as one-dimensional. In this study, a theoretical formula was derived to predict the smoke temperature when the fire source was set at the center of the train in a tunnel with uphill slope θ by establishing a simplified model, considering the heat loss to the wall of the tunnel and the train. It appears that the reduction in temperature down the tunnel of train fires can be fitted by exponential function on the distance, but there are some differences between the decay law above the train and that behind the train. Besides, on the basis of the first extra-long underwater railway tunnel in China, three train fire tests were carried out in a 1:9 reduced-scale model tunnel to study the distribution of smoke temperature along the tunnel, and through the fire tests the unknown parameters of the theoretical equation such as the smoke layer velocity and smoke layer thickness were determined, contributing to the prediction of the smoke temperature decay down the tunnel. Finally, the predictions of the theoretical model were compared with the measured data on smoke temperature in two train fire tests, and the dimensionless excess smoke temperature distributions along the ceiling were compared in tunnels with or without a train. Results show that the temperature curve of the theoretical model agreed well with experimental data of the train fire tests, the model reasonably represents the decay of smoke temperature down the tunnel, and the smoke temperature decays faster in tunnel with a train than that without a train.