Experimental study of carriage fire in a tunnel: Evolution of flame geometry characteristics under relative strong crosswinds

Abstract The present study investigated experimentally the effects of relative strong crosswinds on the flame geometry characteristics (flame height and flame horizontal length) from carriage fires in a tunnel, which have not been quantified previously. Overall 144 test conditions were involved for various heat release rates, crosswind speeds and opening sizes. It was found that, with increase in crosswind speed till relative strong conditions, the flame height first decreased then remained nearly unchanged, while the flame horizontal length first increased then decreased. Finally, the flame is blown-off at strong crosswind conditions. A physical model is proposed to interpret and characterize the evolution behavior of these flame geometry characteristics with crosswind till relative strong condition. Two non-dimensional parameters, the wind Froude number and the dimensionless excess heat release rate, were found based on the analysis of the controlling mechanisms including the flame tilt and air combustion with excess fuel outside the carriage. The experimental results were shown to be well represented by the proposed parameters. This study provides quantitative data and basic understanding of the flame geometry characteristics under relative strong crosswinds from carriage fires in a tunnel.