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To investigate the events that could arise when fighting fires in vehicles with carbon fiber reinforced plastic (CFRP) hydrogen storage cylinders, we conducted experiments to examine whether a hydrogen jet diffusion flame caused by activation of the pressure relief device (PRD) can be extinguished and how spraying water influences the cylinder and PRD. The experiments clarified that the hydrogen jet flame cannot be extinguished easily with water or dry powder extinguishers and that spraying water during activation of the PRD may result in closure of the PRD, but is useful for maintaining the strength of CFRP composite cylinders for vehicles.

The environmental temperature where vehicles are used varies significantly by region and season, so this study investigated the influence of environmental temperature on the fatigue life of compressed hydrogen tanks for vehicles (Type 3). Pressure-cycle tests with varying environmental temperature were conducted on tanks until the tank was failed. Results indicated that fatigue life decreased in low-temperature environments and improved in high-temperature environments. We investigated the cause of such results using the strains inside and outside the tank and other indexes and found that the effect of autofrettage varied as environmental temperature changed, due to the difference between the thermal expansion rate of CFRP and that of aluminum alloy. Thus, we concluded that fatigue life changed according to changes in environmental temperature.

The purpose of this study is to clarify the influence of the maximum pressure on the lifetimes of compressed hydrogen tanks during ambient temperature pressure cycling tests. We varied the maximum pressure from 100% to 200% of designed filling pressure (FP) in five levels. Type 3 (Fully wrapped composite tank with metal liner): The tank's lifetimes, i.e. the numbers of cycles up to Leak Before Break (LBB), decreased with increasing maximum pressure. We observed that the internal surface of the liners had linear flaws resulting from the manufacturing process. Cracks causing LBB seemed to initiate from these flaws. Striation marks clearly appeared at the fracture surface of LBB cracks when the maximum pressure exceeded 125% of FP. Therefore, we suggest that LBB cracks were caused by a similar process of crack propagation in this range. In spite of the maximum pressure changes (100% to 200% of FP), tank strain was proportional to pressure at all times.