Numerical study on liquid hydrogen boil-off gas release for fuel cell heavy-duty truck in tunnel

Abstract

The future of liquid hydrogen (LH₂) fuel cell vehicles promises considerable potential. However, unexpected scenarios are frequently encountered that may induce heat leakage in LH₂ storage tanks, triggering rapid vaporization of the cryogenic fluid. The associated safety risks with LH₂ boil-off gas (BOG) releases pose significant challenges to the development of LH₂ fuel cell vehicles. The dispersion process of BOG exhibits pronounced differences in spatial and velocity scales, especially in limited space. To achieve both computational efficiency and accuracy, this study divides the space into two regions: the near field for release and the far field for dispersion. In the near field, a steady-state compressible model is employed to analyze the variation characteristics of jet flow parameters. For the far field, a transient incompressible model is utilized to investigate the diffusion dynamics of the hydrogen cloud. Our study simulates the process of active venting in a LH₂ heavy-duty truck within a tunnel. The results reveal that higher pressure ratios between nozzle exits and environment result in greater peak intensities of pressure, temperature, Mach number, and density. Increased wind velocity extends the dispersion distance while limiting the cloud’s volume growth and accelerating its dissipation. At the filling level of 5 %, the maximum wind velocity decreases cloud volume by approximately 13 %, comparing to the minimum wind velocity. The risk level during release is inversely proportional to the filling level. At the wind velocity of 2 m/s and filling level of 5 %, the maximum volume and duration of hydrogen cloud are 8.3 times, 2.5 times greater than the filling level of 85 %. This study offers critical reference data to enhance the safety of LH₂ BOG releases and support the stable operation of LH₂ heavy-duty trucks.