The aviation industry is under increasing pressure to reduce its carbon footprint. Hydrogen is emerging as a promising alternative fuel, but its unique properties present significant engineering challenges. Now, US engineers are developing innovative solutions, including a next-generation hydrogen system that not only fuels jets but also cools them.
Why Hydrogen for Aviation?
Hydrogen offers several potential advantages over traditional jet fuel:
- Zero Carbon Emissions: When hydrogen is produced using renewable energy, its combustion emits only water vapor, eliminating carbon dioxide emissions from aircraft operations.
- High Energy Density: Hydrogen has three times the energy per kilogram compared to kerosene-based jet fuel, potentially reducing the amount of fuel needed for a given flight.
However, hydrogen also presents challenges:
- Low Volumetric Energy Density: Hydrogen occupies significantly more volume than jet fuel for the same amount of energy, requiring larger fuel tanks.
- Cryogenic Storage: To achieve a practical density, hydrogen must be stored as a liquid at extremely low temperatures (-253°C or -423°F), necessitating specialized cryogenic tanks and handling procedures.
- Infrastructure: Airports need to be revamped to supply and store hydrogen, and transportation of hydrogen is also a logistical challenge.
Integrated System Design
Researchers at the FAMU-FSU College of Engineering have designed a liquid hydrogen storage and delivery system that tackles these challenges head-on. This system is designed to:
- Efficiently store liquid hydrogen.
- Safely transfer hydrogen.
- Cool onboard systems.
- Support power demands during all flight phases.
Wei Guo, a professor in the Department of Mechanical Engineering and corresponding author of the study, stated that the goal was to create a single system that handles multiple critical tasks, including fuel storage, cooling, and delivery control, with the design laying the foundation for real-world hydrogen aviation systems.
Cooling with Hydrogen: A Key Innovation
A key feature of the new system is its use of liquid hydrogen as a cooling medium for critical power systems. Instead of installing a separate cooling system, the design routes the ultra-cold hydrogen through a series of heat exchangers to remove waste heat from components like superconducting generators, motors, cables, and power electronics.
How it Works
- Staged Heat Exchangers: The heat exchangers are arranged in a staged sequence.
- Cooling Cryogenic Components: The hydrogen first cools high-efficiency components operating at cryogenic temperatures, such as high-temperature superconducting generators and cables.
- Absorbing Heat: It then absorbs heat from higher-temperature components, including electric motors, motor drives, and power electronics.
- Preheating: Finally, before reaching the fuel cells, the hydrogen is preheated to match the optimal fuel cell inlet conditions.
This staged thermal integration allows liquid hydrogen to serve as both a coolant and a fuel, maximizing system efficiency while minimizing hardware complexity.
Implications for Aircraft Design
The integrated design has several implications for next-generation aircraft:
- Reduced Weight: By using hydrogen for cooling, the system eliminates the need for a separate cooling system, reducing overall weight.
- Improved Efficiency: The staged heat exchangers optimize the use of hydrogen’s cooling capacity, improving system efficiency.
- Compact Design: Integration of multiple functions into a single system simplifies the overall design and reduces space requirements.
Challenges and Future Directions
Despite these advancements, significant challenges remain in developing hydrogen-powered aircraft:
- Hydrogen Production: Sourcing clean hydrogen is crucial. Most hydrogen production today relies on natural gas, which emits CO2. Green hydrogen, produced using renewable energy to split water, is the most sustainable option but is currently more expensive.
- Storage and Handling: Maintaining liquid hydrogen at cryogenic temperatures requires advanced materials and insulation to prevent leaks and minimize energy losses.
- Infrastructure Development: Airports need significant investment to build refueling and storage infrastructure for hydrogen.
- Non-CO2 Impacts: Even with zero-carbon emissions, hydrogen-powered aircraft may still have a climate impact due to the formation of contrails and nitrogen oxide emissions.
Industry Efforts and Timelines
Several companies and organizations are working towards hydrogen-powered aviation. Airbus, for example, is developing hydrogen technologies and aims to have a commercially viable hydrogen aircraft in service by the mid-2030s. Their approach involves fully electric aircraft powered by hydrogen fuel cells.
The FAA is also developing a Hydrogen-Fueled Aircraft Safety and Certification Roadmap, with prototypes being tested in flight and regulatory gaps being investigated.
The Path Forward
Hydrogen-powered aviation holds significant potential for decarbonizing air travel. While challenges remain, ongoing research and development efforts are paving the way for a future where hydrogen fuels cleaner, more efficient aircraft. The integrated fuel and cooling system developed by researchers at FAMU-FSU College of Engineering represents a significant step towards that future, demonstrating the potential for innovative solutions to overcome the hurdles of hydrogen aviation.
