An experimental study on the intermittent flame ejecting behavior and critical excess heat release rate of carriage fires in tunnels with longitudinal ventilation

Abstract

This paper describes the quantitative study on the effects of tunnel longitudinal ventilation velocities on the critical excess heat release rate and intermittent flame ejecting behaviors of carriage fires. Experiments were carried out in a 1/8 model tunnel with the dimensions of 22 m × 1.2 m × 0.8 m (length × width × height). 442 repeatable test conditions contained gas fuel (propane) and solid fuel (corrugated paperboard), including variations on fuel supply rates, tunnel opening sizes, and longitudinal ventilation velocities. The intermittent flame ejecting behaviors were expressed as the flame ejection probability in carriage fires, which was characterized by image statistical processing. The results showed that the flame ejection probability was positively correlated with the fire heat release rate, but it was negatively correlated with the ventilation factors of carriage opening and longitudinal ventilation velocities. New non-dimensional correlations between the critical excess heat release rate and the longitudinal ventilation velocities are proposed. Moreover, a piecewise equation is proposed to describe flame ejection probability that is affected by longitudinal ventilation velocities for the first time. All the proposed correlations are found to fit well with the experimental data, which established an essential foundation to quantify the critical heat release rate and intermittent flame ejecting behaviors of carriage fire in various longitudinal ventilation velocities. Finally, the some limitations of propane gas fuel are analyzed. Moreover, this paper depicted the flame ejecting behaviors induced by gas fuel and solid fuel, and reveal the difference and relationship between them.