Seoul National University Develops Safety Framework for Hydrogen UAV Systems

New Safety Framework for Liquid Hydrogen Storage in UAVs

In a groundbreaking development, researchers from Seoul National University of Science and Technology (SEOULTECH) have introduced a comprehensive safety assessment framework for liquid hydrogen storage systems utilized in unmanned aerial vehicles (UAVs). This innovative framework aims to facilitate the adoption of greener propulsion systems in the aviation industry, especially as it grapples with the environmental impact of carbon dioxide emissions, which accounts for approximately 12% of global emissions.

Hydrogen, recognized for its clean combustion properties—yielding only water vapor—has emerged as a promising alternative to traditional fossil fuels. However, its low volumetric energy density presents significant challenges when applied to UAVs, necessitating advanced storage solutions. Liquid hydrogen storage systems offer a potential path to mitigate size and weight issues associated with hydrogen fuel, but they also introduce complexities such as vessel deformation from thermal stresses and risks from fatigue failure under the unique operational conditions of UAVs.

To address these challenges, the research team led by Assistant Professor Nak-Kyun Cho, alongside Mr. Jinmyeong Heo and Professor Nam-Su Huh, developed a holistic analytical framework that evaluates multiple performance and safety parameters. The framework encompasses thermal, structural, fatigue, and impact assessments, providing a well-rounded approach tailored specifically for UAV applications. This contrasts with previous studies, which predominantly focused on isolated analyses, leaving a gap in comprehensive safety evaluations.

The research commenced with acquiring cryogenic property data for materials used in storage systems, facilitated by funding and the operational support of the Hydrogen Materials Research Center at the Korea Institute of Materials Science (KIMS). The team initially selected a standard liquid hydrogen storage tank constructed from SUS316L steel and Al6061-T6 aluminum to reduce thermal ingress. Using a 100 kN tensile-fatigue testing system, they measured temperature-dependent properties that were crucial for the following finite element analyses.

Key Findings

1. Thermal Analysis: The introduction of a vapor-cooled shield (VCS) proved effective, reducing the boil-off rate (BOR) by 30% in analyses and by 15% based on experimental data. The BOR is a critical metric indicating the rate at which stored liquid hydrogen vaporizes—lowering this rate is essential for maintaining efficient storage capacity.

2. Structural Integrity: The analysis pinpointed pipes and supports as the critical weak points within UAV-specific operational conditions, underscoring a requirement for targeted structural modifications to enhance resilience during operation.

3. Fatigue Performance: Impressively, the storage vessel surpassed the 10,000 cycle requirement outlined in the ISO 21029-1 standards, demonstrating an effectively unlimited fatigue life, crucial for operational reliability.

4. Drop Impact Testing: Utilizing a new simulation method founded on a VUSDFLD subroutine-based approach, the researchers identified connecting pipes and supports as particularly vulnerable areas during impact, paving the way for enhanced design considerations.

This new research marks a significant advancement in setting safety standards for hydrogen storage in UAVs, essential for promoting wider acceptance of hydrogen as a sustainable aviation fuel source. As the industry pushes towards greener solutions, the comprehensive framework developed by SEOULTECH is poised to influence future designs and operational strategies within UAVs, ultimately contributing to the reduction of aviation's carbon footprint.

The full findings from the study, titled Analytical framework for liquid hydrogen storage tanks in UAVs Thermal performance validation and structural integrity assessment, can be found in the International Journal of Hydrogen Energy. This research reinforces SEOULTECH's commitment to addressing pressing environmental issues while advancing innovative technologies in the aerospace sector.