Abstract
Multiple energy sources in a tunnel might lead to merge of flames with small enough spacings, releasing more heat and pollutant emissions than a single energy release source in tunnel and thus posing a great threat to tunnel structure, facilities and trapped people. As the heat detection, controlling and cooling systems are originally designed for the single energy release source, while the spacing between energy sources in tunnel is changeable and unpredictable. Then it is important and helpful to research on the much different characteristics of multiple energy sources with interacting ceiling flames for effective control the high risk scenarios. This paper aims to study the ceiling gas temperature profile and flame properties induced by two interacting energy sources in tunnel so as to improve the understanding of the arrangement of heat detectors and water sprinklers in tunnel. Two identical propane burners were used as energy sources located in a longitudinal array in tunnel. The total energy release rate and burner spacing were varied. The flame merging probability, ceiling gas temperature, vertical flame height and longitudinal flame extension were measured. The criteria of beginning merging and fully merging of flames are respectively proposed for two energy sources in tunnel. Results showed that the area of ceiling flame region increases with higher energy release rate. Models for predicting the ceiling gas temperature profiles induced by two energy sources in tunnel are established respectively for weak and strong plumes impinging on the ceiling. A modified model for predicting the combined vertical and longitudinal flame lengths from two burners in tunnel is proposed involving the normalized energy release rate, burner size and spacing. Finally, the comparison between models proposed for ceiling gas temperatures and flame lengths in tunnel and other configurations identifies the high risk of multiple energy sources in tunnel.
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