In order to study the effect of carbon nanotubes (CNTs) on the flame retardancy of carbon fiber (CF)/epoxy resin (EP) composites, CF/EP and CNTs/CF/EP composites were prepared by solution blending. The flame retardancy and thermal stability were studied by cone calorimetry and thermogravimetric analysis. It was found that CNTs and CF had a certain synergistic effect on improving flame retardancy and thermal stability of EP. The peak heat release rate of F7N7, which represents the EP composites with 0.7 wt % CF and 0.7 wt % CNTs, was minimal. The total smoke production of F5N5 which represents the EP composites with 0.5 wt % CF and 0.5 wt % CNTs was the smallest, which was decreased by 43.04% more than the EP. The initial decomposition temperature of F7N7 was about 14 °C higher than that of F7, and the mass loss at T_max was greatly reduced. The apparent activation energy of F7N7 is 2.7 kJ·mol⁻¹ more than EP. Finally, the tensile and flexural strength of the composites were also improved, so it could be applied to a high-performance matrix of CF/EP composites, which are usually used as the advanced composites in the aerospace field.

Lithium-ion batteries experience rapid temperature increases with a high risk of combustion and explosion during thermal runaway, and water mist has been considered as one of the most effective cooling strategies. The water mist field can be impacted by the safety valve airflow, subsequently affecting the cooling characteristics. In this paper, the water mist nozzle with a fixed working pressure is located 1 m above the 100 Ah LiFePO₄ battery to suppress the thermal runaway, and the cooling characteristics under various stages have been compared and analyzed. The results show that the development of thermal runaway can be inhibited before thermal runaway is initiated, and the water mist presents a better cooling effect after the battery safety valve is opened. The critical accumulation heat density of 155 kJ/kg has been identified, which is the threshold for thermal runaway suppression. The confrontation between water mist and the flame has been analyzed, and the water mist droplets cannot fall on the battery surface, resulting in a poor cooling rate of 0.57 kW. This means the suppression effect of water mist will be affected by the airflow impact of the safety valve.

The longitudinal temperature distribution in a tunnel fire has been investigated wildly as the classical problem, while the transverse temperature distribution, especially sidewall temperature, has not received adequate attention. In this article, a 1:3.7 reduced scale horseshoe shaped model tunnel constructed by concrete was established, in which a series of comparative burning experiments were carried out to investigate the longitudinal and transverse temperature distributions. The quantitative trends of smoke longitudinal and transverse temperature including sidewall temperature were observed and analyzed. The major conclusions are summarized as follows: The temperature rise under the ceiling first decreases sharply with longitudinal distance from fire source, followed by a slight decrease, which can be well predicted by Gong’s model of a sum function of two exponential equations. The transverse temperature rise in fire zone is dominated by two different heat transfer regions: convection region (angle below 45° or dimensionless angle below 0.8) and radiation region (angle beyond 45° or dimensionless angle beyond 0.8). The inclination angle is the angle between center line of tunnel and connection line of thermocouple with fire source. The transverse temperature drops with angle in convection region and rises in radiation region, which can be well described by proposed empirical exponential functions. The non-monotonic variation trend of transverse temperature distribution in fire zone is a result of competition between convection of hot smoke and radiation of fire source. All these results are significantly important for fire safety design of tunnel and fire hazard evaluation of tunnel fire.