Hydrogen tanks are a crucial component of fuel cell electric vehicles (FCEV) that store high-pressure hydrogen. They are classified into four types, ranging from Type 1 to Type 4, depending on the materials used and reinforcement methods. The higher types are typically lightweight models, making them a popular choice for FCEV. Tank classification are specified by international standards such as ISO 11439. To ensure the mechanical stability of these hydrogen storage containers, international standards (ISO 15869) have regulated the maximum allowable temperature to 85 degrees Celsius. Excessive hydrogen temperature during charging can lead to tank durability degradation and insufficient charging capacity. In order to address these issues, FCEV's main advantage, which is short charging time, is regulated by limiting the tank temperature to 85 degrees Celsius. The United States of America and Japan have developed charging protocols to standardize charging speeds to comply with this regulation. However, the currently operating charging protocols are mainly composed of passenger cars, and only vehicles that fall within the range of the hot / cold case, where the hydrogen temperature rises the most and least, respectively, at the end of charging can be considered. Moreover, finding the table corresponding to various factors affecting charging, such as ambient temperature, tank pressure, and tank capacity is limited and excessively complicated. Particularly for commercial vehicles, which have a different number of tank depending on vehicle size, establishing a standard charging case is impossible. Therefore, this study aims to develop a predictive model of hydrogen tank charging performance for commercial FCEV and propose the optimal charging speed that meets regulations for each condition, including tank type, seasonal ambient temperature, and charging hydrogen temperature. The development of a predictive model for hydrogen tank charging performance for FCEV involved several key steps. Firstly, an appropriate equation of state was reviewed to accurately describe the behavior of hydrogen gas at high pressures. This allowed for a better understanding of the relationship between gas particles under varying pressure and temperature conditions. Second, a heat transfer model for each element of the charging system was constructed in detail. Hydrogen convection heat transfer with the inner wall of the tank in consideration of the hydrogen flow inside the tank during charging, conduction of different tank materials, and convection heat transfer between the outer wall of the tank and the surrounding air were modeled in detail. Finally, based on the above model, test consistency has been ensured, charging performance review for various situations and optimal charging conditions are suggested by reflecting charging station and weather conditions. The predictive model can suggest optimal charging condition to reduce the time required for hydrogen charging, making FCEV a more attractive option for commercial vehicles.
Mr. WOOKHYUN HAN, Senior Research Engineer, Hyundai Motor Company