Comprehensive Review of Hydrogen Leakage in Relation to Fuel Cell Vehicles and Hydrogen Refueling Stations: Status, Challenges, and Future Prospects

As fuel cell vehicles (FCVs) are increasingly put on the market and hydrogen refueling stations (HRSs) are built accordingly, fatal accidents caused by explosion due to hydrogen leakage are reported and have become a critical issue. The explosion results from complicated processes associated with the so-called hydrogen jet and diffusion when the hydrogen leaks from FCVs or HRSs, demonstrating its sophisticated characteristics and presenting significant technical challenges. Recently, particularly in the past a few years, researchers have established a variety of theoretical models to reveal the relevant mechanisms and introduced a series of monitoring/diagnostic approaches to detect and control the relevant hazards. This comprehensive review summarizes the major research outcomes and particularly the state-of-the-art progresses in relation to hydrogen leakage in FCVs and HRSs, including (1) subsonic jets, (2) underexpanded jets, (3) hydrogen diffusion behavior, (4) hazard reduction methods for confined and free spaces, (5) four types of widely used hydrogen detection technologies, and (6) the application of hydrogen leakage diagnostic methods in different systems. An insight of the review is that research on hydrogen leakage related to FCVs and HRSs should be combined with the relevant realistic characteristics. The characteristics of hydrogen jets generated in real gaps are discussed, and hazard reduction methods are proposed based on the characteristics of hydrogen diffusion in different confined and free spaces. It is suggested that, in order to integrate and evaluate multiple sensor data points and more accurately determine the leakage location and the leakage level, artificial intelligence technologies could be introduced to resolve the issues encountered currently.